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Ethernet Reference Guide Your everyday Ethernet testing reference tool Cover Ethernet.1AN: Cover Ethernet.1AN 5/7/07 10:13 AM Page 4

This guide provides a detailed overview of Ethernet technology. It presents common Ethernet implementations in service- provider networks, the testing requirements to ensure reliable service, as well as installation and maintenance techniques.

Following its introduction in the early 1970s, the Ethernet protocol for data networking has been characterized by ever-increasing popularity and adaptation. In recent years, Ethernet has become the predominant network access protocol, now used in over 95% of all local-area networks.

With the advent of and , this technology has matured and made its way from local-area networks to metropolitan-area networks, and now wide-area networks, challenging traditional transport protocols such as SONET/SDH and ATM.

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...... 3 2.7 Tag ...... 23 2.8 VLAN Tagging...... 23 1. Introduction...... 5 2.9 Traffic Priority ...... 25 1.1 What is Ethernet? ...... 5 2.10 Frame Bursting ...... 26 1.2TableSome of History...... 6 Contents 2.11 Jumbo Frames...... 26 1.3 Ethernet in Carrier Networks...... 7 2.12 Ethernet Media Access Control...... 26 1.4SymbolsEthernet NamingUsed and in StandardsIllustrations ...... 8 2.12.1 Half-Duplex Ethernet and CSMA/CD ...... 26 1.4.1 802.3 Naming Convention ...... 8 2.12.2 Carrier Sense...... 27 1.4.2 Evolution of Ethernet Standards ...... 9 2.12.3 Multiple Access ...... 27 2.12.4 Collision Detection ...... 27 2.13 CSMA/CD Transmission Flow ...... 28 2.13.1 Full-Duplex Ethernet ...... 28 2. Ethernet Nuts and Bolts...... 13 2.13.2 Flow Control...... 28 2.1 Ethernet Logical Specifications ...... 13 2.13.3 Pause Frame Format ...... 29 2.2 Basic Ethernet 2 Frame ...... 14 2.13.4 Auto-Negotiation ...... 29 2.2.1 Ethernet vs. 802.3 Frame Format ...... 15 2.13.5 ...... 30 2.2.2 Preamble and Start-of-Frame...... 15 2.14 10 Gigabit Ethernet...... 31 2.2.3 Destination and Source Addresses ...... 16 2.14.1 Physical-Layer Specifications...... 31 2.2.4 Type/Length ...... 18 2.2.5 802.3 Logical Link Control Header ...... 19 2.2.6 Snap Header ...... 20 2.3 Data Field...... 21 3. Ethernet Applications...... 36 2.3.1 Ethernet ...... 21 3.1 Ethernet in Local-Area Networks (LANs)...... 36 2.3.2 IEEE 802.3...... 21 3.2 Ethernet in Access Networks ...... 39 2.4 Frame Check Sequence ...... 22 3.3 Ethernet in Metro Networks ...... 41 2.5 Interframe Gap ...... 22 3.4 Ethernet in Wide-Area or Long-Haul Networks ...... 41 2.6 Ethernet Frame Format Extensions ...... 22 3.5 Ethernet Service Types...... 41 3.5.1 E-Line Variants...... 44 3.5.2 E-LAN Variants...... 45

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3.6 Ethernet Infrastructures ...... 456. Monitoring Ethernet Networks...... 71 3.6.1 Native Ethernet ...... 466.1 Ethernet Quality-of-Service Assurance...... 71 3.6.2 SONET/SDH...... 466.1.1 Performances and Traffic Monitoring ...... 71 3.6.3 Native Ethernet vs. SONET/SDH: Pros and6.2 Cons Remote...... 46 Testing for Ethernet in the First Mile Deployments ...... 72 3.6.4 (RPR) ...... 476.2.1 Access Line Management 3.6.5 ATM ...... 48 Using the 802.3ah Standard ...... 73 3.6.6 IP/MPLS ...... 486.2.2 Demarcation Devices ...... 74 6.2.3 Ethernet Test-Heads ...... 74 6.2.4 Management Software...... 76 4. Introduction to

Installation and Provisioning...... 52 4.1 Quality and Performance ...... 52 7. Glossary...... 78 4.2 Ethernet Performance Verification ...... 52 ...... 92 4.2.1 Test Configurations...... 53 8. Acronyms Index 4.2.2 RFC 2544 tests ...... 55 4.3 Fiber Characterization...... 61 4.4 BERT over Ethernet ...... 62 4.4.1 GigE and 10 GigE BERT over Dark Fiber and PONs ...... 63 4.4.2 GigE and 10 GigE BERT over a DWDM Network ...... 63 4.5 Ethernet Service Acceptance Testing ...... 64

5. Commissioning Ethernet for Voice-over-IP

and Video-over-IP Deployment...... 66 5.1 Essential Testing Techniques ...... 66 5.2 Simulating the Customer’s Network ...... 66 5.3 Simulating Real-World Traffic Patterns...... 67 5.4 Performing Unidirectional Testing ...... 68

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Symbols Used in Illustrations

Router DWDM Filter

ATM or Ethernet Switch Multilayer Switch

Workgroup Switch Metro DWDM Add/Drop Multiplexer

SONET/SDH Add-Drop Multiplexer (ADM) DWDM Ring or Multiservice Provisioning Platform (MSPP)

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Introduction Guide Ethernet.1-ang: Guide Ethernet.1AN 5/7/07 10:06 AM Page 5

Central Office Home Point of Presence (POP) 1.1 What is Ethernet? Since its invention in the 1970s, Ethernet has gradually become the world’s most widely used network technology. In local-area networks (LANs), Ethernet has largely replaced all other LAN standards such as , Business ARCNET (Attached1. Introduction Resource ), and FDDI (Fiber LAN Distributed Data Interface). More recently, Ethernet has moved into WAN MAN Access metropolitan and wide-area networks (MANs and WANs) as well. Hundreds or Ten or Several km thousands of km hundreds of km Ethernet is a frame 1-based computer networking technology that has been Figure 1.1 – LAN, Access, MAN and WAN networks standardized by the Institute of Electrical and Electronics Engineers (IEEE, pronounced “I-triple-E”). The Ethernet standards define cabling and signaling standards for the physical layer of the Open Systems Interconnection 2 (OSI) model, as well as frame formats and protocols for the data-link layer. Although Ethernet has become closely associated with Protocol (IP), it can carry almost any other networking protocol used within LANs. In a LAN, Ethernet carries frames of data between desktop computers, servers, printers and other devices located within a small area, usually inside a single building. Devices on a LAN are interconnected using coaxial cable, special categories of twisted-pair wiring, fiber-optic cable or wireless (radio or infrared) connections. The most popular Ethernet LAN standard (10Base-T) supports a data transmission rate of 10 Mb/s. Newer versions called and Gigabit Ethernet support data rates of 100 Mb/s and 1 Gb/s, respectively. In a MAN or WAN, fiber-optic cables carry Ethernet frames over greater distances and at speeds up to 10 Gb/s. Virtual LANs (VLANs) are used to provide a secure virtual network to each customer, allowing geographically dispersed users to communicate as if they were in the same building (see Figure 1.2). Initially, the VLAN was created to segregate a single LAN domain into multiple virtual LANs. It was intended to limit the spread of broadcasts between VLANs.

1 A frame is a unit of data that is transmitted between network points; it includes a data payload as well as addressing and protocol control information. 2 The Open Systems Interconnection (OSI) Reference Model is a seven-layered description of how messages should be transmitted between any two points in a telecommunication network.

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1.2 Some History Ethernet was invented at the Xerox Palo Alto Customer C Research Center in the 1970s by Dr. Robert M. Customer A Customer B Store Customer B Customer A Metcalfe. Originally known as experimental CustoEthernet,mer B it was designed to support Store research on the “office of the future,” which OC-48 OC-48 DWDM included one of the world's first personal Customer C Customer C workstations, the Xerox Alto. Ethernet then ran at approximately 3 Mb/s over tapped, half-inch-thick coaxial cable. Figure 1.2 Custoshowsmer A a drawing used by Dr. Metcalfe to CustoOC-3 mer C Customer C present Ethernet to the National Computer Customer B Customer A CustoConferencemer B in June 1976. Customer A Ether refers to luminiferous ether, postulated in the nineteenth century as an all-pervading, infinitely elastic, massless medium of propagation of electromagnetic waves. Figure 1.2 — Ethernet VLANs provide secure virtualEthernet networks was to individualso-named customers to describe across a MAN the way that cabling could similarly carry data throughout the network. The first formal specification for Ethernet was published in 1980 by DEC-Intel-Xerox (DIX). A second version of the DIX standard was published two years later, and became known as Ethernet 2. In 1983, the IEEE published its version of the LAN standard entitled IEEE 802.3 Carrier-Sense Multiple-Access with Collision Detection (CSMA/CD) Access Method and Physical-Layer Specifications. Standard 802.3 was based on Ethernet 2, the most significant difference being an altered frame format, and was designed to provide interoperability between the two frame types on a single LAN.

Figure 1.3 — Drawing used by Dr. Metcalfe to present Ethernet

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IEEE 802.3 was also known as thicknet, since it specified 10 mm coaxial cable to connect devices in a bus topology. In 1985, the IEEE published the 802.3a (thinnet) standard, which made it possible to use less expensive 5 mm coaxial cable, resulting in an immediate increase in popularity. Since 1985, all Ethernet LAN equipment is built according to the IEEE 802.3 standard, although the vast majority of Ethernet frames sent still use the DIX Ethernet 2 format. The differences between Ethernet 2 and IEEE 802.3 are subtle and are transparently managed by network equipment; the frame type is not a concern during practical use or testing.

1.3 Ethernet in Carrier Networks Ethernet is now the most widely deployed access technology in carrier networks. In new installations, Ethernet access lines are outselling all other forms of access combined. Ethernet is also carried throughout MANs and WANs, either in its pure (native) form or combined with other technologies. Gigabit Ethernet Metro Network What makes Ethernet so attractive? Why is it either replacing, or being used in combination with, other 10/100Base-T transport protocols and infrastructures such as ATM, frame relay, SONET/SDH, and CWDM/DWDM?

Gigabit Ethernet One reason is that the recent Ethernet standards, such Metro Network as Gigabit Ethernet (GigE), 10 Gigabit Ethernet Access Network (10 GigE) and the new IEEE 802.3ah standard for 10/100Base-T Ethernet in the first mile, as well as emerging technologies such as the multiprotocol label switching (MPLS) and resilient packet ring (RPR), are helping to make Ethernet a reliable and economically viable

Figure 1.4 — Ethernet is used throughout carrier networks carrier-class transport technology.

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Due to economies of scale, Ethernet equipment has historically been more cost-effective than competing technologies. Manufacturers are now offering economic solutions for Ethernet switching and routing, virtual LAN (VLAN) services, MPLS, and IP forwarding, as well as traffic- management features that allow service providers to fulfill various service agreements. Ethernet services require less time for commissioning and provisioning than legacy services, and can even be provisioned remotely, resulting in additional savings for service providers. Since almost all LANs use Ethernet, they can easily be integrated with Ethernet-based carrier networks since Ethernet equipment performs bit-rate conversion and statistical multiplexing. Ethernet is flexible in that it can be used with many different infrastructures and protocols. Ethernet services can be offered over existing ATM architectures. In next-generation SONET/SDH networks, Ethernet frames can be encapsulated into Generic Framing Procedure (GFP) frames and transported through SONET/SDH channels. Ethernet can also be transmitted in its native format over dark fiber or on a DWDM wavelength, or using free-space optics (FSO). Other advantages of Ethernet include dynamic bandwidth commissioning (ability to increment bandwidth to subscribers on an as-needed basis) and a wide range of services based on Ethernet standards for wide-area networking (virtual private LAN, E-Line services, etc.). Ethernet services will be described in detail in Chapter 3.

1.4 Ethernet Naming and Standards Base = Baseband 1.4.1 802.3 Naming Convention

LAN Speed, in Mb/s Physical Media Type Different physical implementations of Ethernet (rate, medium, etc.) follow a standard naming convention developed within IEEE 802.3. Figure 1.5 illustrates the name format using 10 Base 10Base-T as an example. The first section refers to the speed of the transmission, the second T refers to type of transmission, and the third refers to the type of medium used (T designates an electrical medium, whereas X designates an optical medium). Figure 1.5 — 802.3 naming convention Baseband signaling simply means that transmitted signals use the whole available bandwidth and are not modulated onto other carrier frequencies or time-lotted to share the bandwidth; i.e., one-at-a-time transmission. Baseband is the only standard used in Ethernet today.

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1.4.2 Evolution of Ethernet Standards Since the initial Ethernet standards were defined, newer IEEE 802.3x standards have evolved that have enhanced Ethernet’s performance and versatility. These are summarized in Table 1.1. The 10Base-T standard represented a major advance as it allowed the use of inexpensive Category 3 unshielded twisted-pair (UTP) cable instead of coaxial cable. It also allowed the devices to be connected in the shape of a star, rather than a bus topology making it much easier to install, manage, and troubleshoot the network. Some of these early rates and cabling standards are no longer in common use. The 100Base-T standard increased data rates by a factor of 10 and was hence known as Fast Ethernet. Performance was again improved by a factor of 10 with the release of the 1000Base-T Gigabit Ethernet standard. Originally only available when using or short-haul shielded twisted-pair (STP) cable, Gigabit Ethernet can now be carried over inexpensive Category 5/Category 5e UTP cable. With the recent introduction of 10 Gigabit Ethernet, integration of LAN and WAN applications is greatly simplified. 10 GigE supports two physical interfaces at different rates: one for LANs at 10 times the rate of GigE (LAN PHY), and one at 9.585 Gb/s (WAN PHY); these are the same rates as SONET/SDH-based transmission systems. The WAN rate, and its related frame enhancements, allow Ethernet traffic to be transparently carried over OC-192 SONET or STM-64 SDH networks. In 2004, the IEEE approved the 802.3ah specification for Ethernet in the first mile. This new standard has the largest scope of any IEEE 802.3 standard and will give service providers a variety of flexible and cost-effective solutions for delivering Ethernet services in access networks.

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Year Name EEE Speed Description Used? 1983 10Base-5 (Thick Ethernet or Thicknet) 802.3 10 Mb/sΩ; 10 mm 50 coaxial cable; bus topology Not common 1985 10Base-2 (Thin Ethernet or Thinnet) 802.3a 10 Mb/sΩ; 5 mm 50coaxial RG58 cable; bus topology Not common

1990 10Base-T 802.3i 10 Mb/s 100 ΩCategory 3 UTP; two-pair cable; Yes star topology; 100 m link (switch to host) 1993 10Base-F (FL, FB, and FP) 802.3j 10 Mb/s 850 nm light over two multimode fibers Yes (Ethernet over Fiber) 1995 100Base-T (Fast Ethernet) • 100Base-T4 802.3u 100 Mb/s 100 Ω; Category 3 UTP, four-pair cable No

• 100Base-TX 802.3u 100 Mb/s 100 Ω; Category 5 UTP, two-pair cable; Most common 100 m link length (switch to host)

• 100Base-FX 802.3u 100 Mb/s 1300 nm light over two multimode fibers Yes 1997 Full-Duplex Ethernet 802.3x 10 and All applications (FDX) 100 Mb/s

1997 100Base-T2 802.3y 100 Mb/sΩ; Category 100 3 UTP; two-pair cable No 1998 Virtual LANs (VLANs) 802.3ac Extensions to support VLAN tagging Yes

Table 1.1 — Main Ethernet standards

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Year Name EEE Speed Description Used? 1998 1000Base-X (Gigabit Ethernet or GigE) • 1000Base-SX 802.3z 1 Gb/s 850 nm light over multimode fiber Yes • 1000Base-LX/HX 802.3z 1 Gb/s 1300 nm light over multimode or singlemode fiber Yes • 1000Base-CX 802.3z 1 Gb/s Short-haul copper STP cable; 100 m link Yes

length (switch to host) 1999 1000Base-T 802.3ab 1 Gb/s 100Ω ; Category 5/5e UTP; four-pair cable Yes (Gigabit Ethernet or GigE) 2002 10 Gigabit Ethernet 802.3ae 10 Gb/s 850 nm over multimode fiber; 1310 nm and Yes (10 GigE) 1550 nm over singlemode fiber. Full-duplex mode only. Includes a WAN physical interface (PHY) to simplify interfacing to a SONET/SDH

or G.709 OTN network. 2004 Ethernet in the First Mile 802.3ah 1 Gb/s Support for various access technologies: Yes • Point-to-point copper • Point-to-point fiber • Point-to-multipoint fiber (EPON) Support for operation, administration, and maintenance (OAM) in access networks including: • Remote failure indication • Remote loopback indication • Link monitoring

Table 1.1 — Main Ethernet standards (continued)

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Ethernet Nuts and Bolts Guide Ethernet.1-ang: Guide Ethernet.1AN 5/7/07 10:06 AM Page 13

2. Ethernet Nuts and Bolts Ethernet is a packet-based technology; i.e., fixed amounts of data are encapsulated into Ethernet frames. In addition to the data payload, each frame also contains information about the source of the packet, its destination address, the type of data in the payload, and other useful information required for transmission. The focus of this chapter will be the basic frame structure of Ethernet, as well as the applications some special frame extensions provide. As introduced in Chapter 1, there are two frame formats used in Ethernet networks: the original and more common Ethernet 2 format, and the IEEE 802.3 variation. Both frame types will be described, as these can be used in combination on any given network. Except for some specific applications, network equipment is typically transparent to the type of frame transmitted.

2.1 Ethernet Logical Specifications The most commonly deployed Ethernet connections today run at 10, 100, and 1000 Mb/s. The logical specifications are similar with the exception of the connectors and cable category requirements shown in the table in the previous chapter: Media Access: CSMA/CD (HDX/Shared) Frame Format: 802.3/Ethernet MAC Address: 6 bytes Min. Frame Size: 64 bytes Max. Frame Size: 1518 bytes

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2.2 Basic Ethernet 2 Frame The original Ethernet frame as developed by Xerox was updated to the Ethernet 2 frame, now in common use.

Ethernet Encapsulation (RFC 894) Frame Format Source PreambleDestination Type DATA Unit FCS Address Address Bytes 8 6 6 2 46-1500 4

Frame Check 10101... Sequence CRC-32

Ethernet Protocol Types Destination/Source addresses Value Description I/G U/L 46 bits (hexadecimal) 0800 IPv4 6-byte address 0801 X.75 Internet 0802 NBS Internet I/G = Individual/Group Address 0803 ECMA Internet 0 = Individual Address 0805 X.25 Level 3 1 = Group Adress 0806 Arp (for IP and for CHAOS) 0BAD Banyan Systems Inc. U/L = Universal/Local Address 6001 DEC MOP Dump/Load Assistance 0 = Universally Administered 6002 DEC MOP Remote Console 1 = Locally Administered 6003 DEC DECnet Phase IV 6004 DEC LAT 6005 DEC DECnet Diagnostics Transmission Parameters 6010-6014 3Com Corporation 7000-7002 Ungermann-Bass download Parameters Values 7034 Cabletron Inter Frame Gap (10Base-T) 9.6 ms 8035 Reverse ARP Inter Frame Gap (100Base-TX) 0.96 ms 8046-8047 AT&T Max Frame Size 1518 bytes8088-808A Xyplex Min Frame Size 64 bytes 809B Kinetics Ethertalk - Appletalk over Ethern Address Size 48 bits 80C0-80C3 Digital Communication Associates 80D5 IBM SNA Services over Ethern

et 80F3-80F5 Kinetics 80F7 Apollo Computer 80FF-8103 Wellfleet Communications 8137-8138 Novell 86DD IPv6

Figure 2.1 — Ethernet frame format and common parameters

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2.2.1 Ethernet vs. 802.3 Frame Format Ethernet S Source PreambleDestinationO Type DATA FCS As shown in the figures below, Ethernet frames differ slightly from IEEE 802.3 AddressF Address 716 6 2 46-1500frames. 4

IEEE 802.3 S DestinationSource 802.2 PreambleO HeaderLength DATA FCS F Address6Address 6 2 46-1500 4 71 The field lengths are in bytes

Figure 2.2 — Ethernet and 802.3 frame format

2.2.2 Preamble and Start-of-Frame: Because there is no synchronous clocking mechanism between Ethernet devices, components in the network require time to detect the presence of a signal: a transmitted frame carries leading preamble bits (or bytes) to enable synchronization to take place before the actual frame begins; two consecutive 1s mark the start-of-frame. The preamble takes the form of alternate 1s and 0s: 7 bytes of 10101010, while the start-of-frame (SOF) is indicated by one preamble-like byte with two 1s at the end —10101011.

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2.2.3 Destination and Source Addresses Known as MAC addresses (short for media access control), these are hardware addresses that uniquely identify each node on a network. Ethernet S Source PreambleDestinationO Type DATA FCS AddressF Address 716 6 2 46-1500 4 Source Address: The source address is always a unicast (single-node) address. IEEE 802.3 S DestinationSource 802.2 PreambleO Header Length DATA FCS Destination Address: The destination address can be unicast, F Address6Address 6 2 46-1500 4 71 multicast (group of nodes), or broadcast The field lengths are in bytes (all nodes).

Figure 2.3 — Destination and source address location Each address is associated with a user (host) device, more specifically with an interface on that device. It consists of a 6-byte (48-bit) field, which must contain a globally unique number. The address is divided into two sections—the first (sometimes known as the organizationally unique identifier or OUI) is allocated to network interface card (NIC) manufacturers by the IEEE; the other section is like a serial number allocated to each NIC by the manufacturer himself. Shown below is a typical MAC address in its various formats.

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0000 1000 0000 0000 0000 1100 1001 1110 0001 0111 1000 1010 Binary 08000c9e 1 7 8aHex

08 — 00 — 0c — 9e — 17 — 8a Sometimes 08 : 00 : 0c : 9e : 17 : 8a Written 08 . 00 . 0c . 9e . 17 . 8a

IEEE Assigned0800 Manufacturer . 00c9e .Assigned 178a

Figure 2.4 — Sample MAC address in three common formats

The IEEE manufacturer number allocation forms the most significant part of the MAC address; and this, combined with the serial number, provides a globally unique address for every manufactured NIC. Various formats exist to represent MAC addresses, but they all break down into a binary number. Although the IEEE OUI is assumed to be 24 bits long, the two most significant bits have another purpose: bit 47 — when set to 0, indicates an individual address; when set to 1, indicates a group (multicast) address. bit 46 — when set to 0, indicates the universally administered global addressing IEEE scheme; when set to 1, indicates a locally administered addressing scheme.

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A MAC address of FF-FF-FF-FF-FF-FF (all ones) is reserved for use as a broadcast address. Unfortunately, the MAC system is based on what is known as a flat addressing scheme, as Destination Source opposed to a hierarchical scheme. For example, a flat scheme would be the equivalent of a street Address Address full of houses with names instead of numbered addresses; the only way of locating a specific house would be to inspect them all individually. With a hierarchical scheme, on the other hand, the

66 sequential numbered addresses make it much easier and quicker to locate the position of a specific destination. This is why MAC addressing is only used in confined (local) areas. 00-80-0c-9e-17-8a Here is the address shown above in context of the destination address. Both Ethernet and 802.3 use a similar address format. AB

A: Address specified by IEEE B: Address specified by manufacturer 2.2.4 Type/Length This is the major difference between the two Ethernet standards. Where Ethernet 2 uses a TYPE field, 802.3 specifies a LENGTH field, followed EthernetFigure 2.5 — IEEE and manufacturer MAC address division by a special data header known as the 802.2 logical link control layer (LLC). Source PreambleDestination Type DATA FCS AddressAddress These fields are used to identify the Layer 3 protocol that the data payload is 8 6 6 2 46-1500 4 encoded with. This allows routers to correctly forward the traffic to the related Layer 3 device. The following diagram shows the values these fields contain IEEE 802.3 when indicating the Ethernet payload is encoded with Internet Protocol (IP) at S DestinationSource 802.2 Layer 3. PreambleO Header Length DATA FCS F AddressAddress 7 1 6 6 2 46-1500 4

The field lengths are in bytes

Figure 2.6 — Type/length fields

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Ethernet TYPE field — identifies the protocol type of the data field for IP forwarding to the appropriate higher-layer protocol.

Network Layer 802.3 LENGTH field — indicates the length of data (minus padding) in the 08-00 06 data field.

Type Snap 2.2.5 802.3 Logical Link Control Header (LLC)

Ethernet 802.3/802.2 Data-Linkr LayeThe IEEE, having written their 802.3 specification according to a LENGTH field, were faced with finding another way to represent the function of the 00-03-01-xx-xx-xx Or FF:FF:FF:FF:FF:FF TYPE field. They did this by creating another protocol (LLC) that ‘sits’ directly above the MAC layer (but still within the Layer 2 data-link layer). Coax, UTP/STP, Fiber Optics Physical Layer At the LLC level, Ethernet functionality is not evident, so this protocol, defined in the 802.2 specification, can function on other LAN types as well (e.g., token Figure 2.7 — Type and snap fields defining IP Layer 3 payload ring, FDDI, etc.), forming a common layer between them. This 802.2 specification is known as the logical link control (LLC) layer.

LLC (802.2) DSAP SSAP Control

1 1 1-2 IEEE 802.3 S DestinationSource 802.2 PreambleO Header Length DATA FCS 7 1F 6AddressAddress 6 2 46-1500 4

Figure 2.8 — Logical link layer header location

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LLC consists of the following: Destination or Source Service Access Points (DSAP/SSAP) is the equivalent of the Ethernet 2 TYPE field – A range of numbers, specified by the IEEE 802.2 sub-committee, to identify the higher-layer protocols requiring the data field contents. Only seven bits are used for protocol identification, which means there are a total of 128 numbers. Of these 128, 64 are allocated to ISO protocols and 64 to proprietary protocols. The most significant DSAP bit is used to indicate individual or group addressing, while the most significant SSAP bit indicates whether the PDU is a command or a response. The Control Field consists of 1 byte (optionally 2 bytes) and could carry 802.2 control information such as type of service (connectionless/connection-oriented) etc. Currently it is unused and set to 03hex. Padding is used to ensure minimum frame length.

2.2.6 SNAP Header The TYPE field of Ethernet 2 can contain more than 1500 unique data type values, whereas the SSAP fields in the LLC header can only contain 128. To enable compatibility between Ethernet 2 and the 802.3 frame, the SNAP header variant was added to the 802.2 LLC standard. LLC (802.2) OUI Type In a SNAP frame, the 802.2 header has both DSAP and SSAP set to 0xAA,

3 2 and the first 5 bytes of the data field are used to give the protocol ID – out of IEEE 802.3 the 5 bytes, the last two specify the value of the TYPE field, using the Ethernet 2 standard; the first three bytes specify an OUI (like in MAC addressing) but S DestinationSource 802.2 PreambleO Header Length DATA FCS 7 1F 6AddressAddress 6 2 46-1500 4 are typically set to zero.

Figure 2.9 — Snap header location

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2.3 Data Field Ethernet S Source PreambleDestinationO Type DATA FCS 2.3.1 Ethernet AddressF Address 716 6 2 46-1500Once 4 physical-layer and link-layer processing is complete, the data contained in the frame is sent to an upper-layer protocol, which is identified in the Type IEEE 802.3 field. Although Ethernet Version 2 does not specify any padding (in contrast S DestinationSource 802.2 PreambleO Header Length DATAto FCS IEEE 802.3), Ethernet expects at least 46 bytes of data. Any padding has F Address6Address 6 2 46-1500 4 71 to be removed by the higher-layer protocol and this contravenes the principles The field lengths are in bytes of the OSI model.

2.3.2 IEEE Figure802.3 2.10 — Data field location In comparison, according to the IEEE 802.3 standard, once physical-layer and link-layer processing is complete, the data is also sent to an upper-layer protocol, but it is defined within the data portion of the frame, if at all. If data in the frame is insufficient to fill the frame to its minimum 64-byte size, padding bytes are inserted to ensure at least a 64-byte frame. This padding is removed before the data is presented to the higher- layer protocol, thus meeting the OSI model requirements.

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2.4 Frame Check Sequence (FCS) This sequence contains a four-byte cyclic redundancy check (CRC) value, Ethernet S Source PreambleDestinationO Type DATA FCS which is created by the sending device and is recalculated by the receiving AddressF Address device to check for damaged frames. If the CRC values do not match, an error 716 6 2 46-1500is 4detected and the frame is discarded.

IEEE 802.3 There is no error correction in Ethernet — higher-layer protocols are S DestinationSource 802.2 responsible for detecting the loss of frames and initiating retransmission. PreambleO Header Length DATA FCS F Address6Address 6 2 46-1500 4 71 The field lengths are in bytes

Figure 2.11 — Frame check sequence location

2.5 Interframe Gap Ethernet devices must allow a minimum idle period between transmission of frames known as the interframe gap (IFG) or interpacket gap (IPG). It provides a brief recovery time between frames to allow devices to prepare for reception of the next frame. The minimum interframe gap is specified according to the time it takes to transmit 96 bits (12 bytes), which is 9.6 µs for 10 Mb/s Ethernet, 960 ns for 100 Mb/s Ethernet, and 96 ns for 1 Gb/s Ethernet.

2.6 Ethernet Frame Format Extensions The original Ethernet standards defined the minimum frame size as 64 bytes and the maximum as 1518 bytes. These numbers include all bytes from the Destination MAC Address field through the Frame Check Sequence field. The Preamble and Start Frame Delimiter fields are not included when quoting the size of a frame. In 1998, the IEEE 802.3Q standard extended the allowable frame sizes to permit traffic to be segregated into different broadcast domains within LANs. The minimum frame size was brought down to 68 bytes, while the maximum was increased to 1522 bytes, allowing VLAN frame tags to be inserted into the standard frame format and thus accommodating emerging needs.This change was adopted to allow traffic to be segregated into different broadcast domains within LANs. In wide-area networks VLANs are used by service providers to separate and prioritize customer traffic.

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2.7 Ethernet Frame Tag

Ethernet Frame Tag The Tag Protocol Identifier (TPID) – 2 bytes – Destination Tag Frame Control Length/ MAC Client Pad Preamble MAC Type Check indicates that a tag header comes next. Start Address Destination Length/TypeInformation Data Sequence = 802.1 Q Frame MAC Tag Control Field (TCI) – 2 bytes – 71Delimiter 66Address Tag Type 2 22004The is further subdivided into a 3-bit User Priority field that is ETHERNET FRAME TAG TCI defined in 802.1Q, a 1-bit canonical format Tag Protocol ID User Priority CFI VLAN ID indicator (CFI) that is used in Ethernet to show that there is a routing information field after the length field, and the 12-bit VLAN identifier (VID).

Figure 2.12 — Ethernet frame tag location and VLAN ID

2.8 VLAN Tagging VLAN tagging, detailed in 802.1Q, permits various virtual LANs to be created — segregating customer traffic over common Ethernet network links. Virtual LANs (VLANs) allow a network administrator to group devices together into broadcast domains that are logical rather than physical. This requires an additional identification (tag header) for the VLAN at the data-link layer. As a 12-bit field, the VLAN ID allows 4096 possible VLANs. ID=0 is reserved to identify priority frames (no VLAN specified), and ID=FFF is simply reserved (not to be used). In the diagram above, two switches are connected to each other; as they are both aware of 802.1Q, the VLANs can understand the tag header. This link between them is called a trunk link and uses explicit tagging; i.e., packets sent on this link have the tag header added. Connecting devices that do not need to be VLAN are connected via access links. As these devices do not understand the tag header, it is not sent; this is called implicit tagging. It is possible to have a device that is VLAN-aware and can be connected directly to a trunk link. It is also possible to have both “aware” and “not aware” devices on the same link; this is called a hybrid link.

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In 802.1Q, devices in the network can be assigned to a VLAN either through the port they are connected to, VLAN Aware their MAC address or the protocol type they are using. In all cases, the bridge/switch needs to have a filter Trunk Link database that identifies who is on which VLAN.

Switch Switch The MAC address option is the most administration- intensive, as the allocations have to be done manually for every device. The entries in the database can be static or dynamic. Generic Attribute Registration Protocol (GVRP) is used to dynamically update port-to-VLAN Host Host assignment and to communicate between VLAN-aware bridges or switches.

Workstation Workstation Group Multicast Registration Protocol (GMRP) is used to send multicasts on a single VLAN without affecting other VLANs. For each VLAN, Virtual LAN 1 Virtual LAN 2 Virtual LAN 3 a spanning tree algorithm must be calculated.

Figure 2.13 — Example of virtual LAN

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2.9 Traffic Priority In addition to specifying a method to delineate virtual LANs, the frame tag also allows traffic priority to be specified. This is outlined in the 802.1p standard, which defines a way for MAC devices (such as switches) to interoperate. The 802.1p standard primarily relies on traffic buffering to assist priority data flow. 802.1p allows the device doing the buffering to determine which packet to transmit first. It is commonly used in applications where two traffic streams use the same port, or if two connected LANs are running at different speeds. Potentially, depending on the protocol used on the WAN and the extent to which 802.1p-compliant devices have been deployed, a consistent level of service can be ensured over a WAN from one Ethernet LAN to another Ethernet LAN. The User Priority value is a 3-bit field that provides eight priority levels (0 through 7), with 0 representing the lowest priority (best effort) and 7 representing the highest priority (reserved). These eight priority levels map to the prioritization schemes used by many protocols (such as ATM) that operate at Layer 2 (the data-link layer) of the OSI model. The priorities that are available are shown in Figure 2.14 (left). Using these priority levels, it is possible, in a VLAN-aware device, to assign a traffic class on the basis of protocol type, source or destination MAC address or port number. There are also suggestions for providing the same choice for higher layers such as applications, but this is not currently ETHERNET FRAME TAG TCI implemented in the standard. With this system, it is possible to make prioritizing policy Tag Protocol ID User Priority CFI VLAN ID decisions across the network and implement them in VLAN-aware networking devices.

Priority Binary Traffic Types 7 111 Network Control 6 110 Interactive Voice 5 101 Interactive Multimedia 4 100 Controlled Load Applications (Streaming Multimedia) 3 011 Excellent Effort 2 010 Spare 1 001 Background 0 000 Best Effort (Default)

Figure 2.14 — Traffic priority and related types

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2.10 Frame Bursting The 802.3z (1 Gigabit Ethernet) standard introduced burst mode operation. This optionally allows a station to transmit a series of frames (up to 65,536 bit times or 8192 byte times) without relinquishing control of the transmission medium. Burst mode is only specified for Gigabit and higher Ethernet speeds and applies to half-duplex mode only. It is designed to improve short frame transmission. The first frame of a burst is transmitted normally and may have an extension field. Following frames in the burst do not require the extension field because if a collision occurs, only the first frame in the burst is affected.

2.11 Jumbo Frames In 1998, Alteon Networks, Inc. proposed that the maximum size of the MAC Client Data field be increased from 1500 bytes to 9000 bytes. This way, larger frames could use network bandwidth more efficiently while reducing the number of frames that have to be processed. Although this initiative was not adopted by the IEEE 802.3 Working Group, it was adopted by a number of network element manufacturers who continue to support this functionality. The specification restricts the use of jumbo frames to full-duplex Ethernet links, and defines a link-negotiation protocol that allows a station to determine whether or not the station at the other end of the segment is capable of supporting jumbo frames.

2.12 Ethernet Media Access Control There are two media access control protocols defined for Ethernet: half-duplex, and full-duplex. 2.12.1 Half-Duplex Ethernet and Carrier-Sense Multiple-Access/Collision Detection (CSMA/CD) In half-duplex Ethernet, devices both transmit and receive, but the cabling structure in the device is common to both the transmitter and the receiver, so it cannot transmit its own data and receive incoming data at the same time; i.e., it cannot talk and listen at the same time. This means that only one device can successfully send output onto the media at any given moment. The technique used to control traffic flow on a half-duplex network is called Carrier-Sense Multiple-Access/Collision Detection (CSMA/CD). The basic components of this method are the following:

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2.12.2 Carrier Sense (CS) Since only one device at a time can successfully send output, the Carrier Sense component refers to the “sensing” operation that occurs when a device listens for a signal. It must ascertain that no other device is transmitting before it starts sending its own transmission. The device does this by detecting or sensing a carrier signal, hence the term Carrier Sense (CS). 2.12.3 Multiple Access (MA) This component refers to how many devices have access to the medium. Since there is no organized access system — no hierarchy or preference in terms of order of transmission — multiple devices have equal-opportunity access, hence Multiple Access (MA). ? Listen (Carrier Sense) 2.12.4 Collision Detection (CD) CS Transmit (Access) This component refers to the signal collision that occurs when two devices try to access the medium simultaneously (at times, this is inevitable). In such case, the collision can be recognized by the receiving function of the NICs and, as each individual transmission will now be corrupted, the devices stop transmitting. They have detected a collision, hence Collision Detection (CD). Any Device Listen — Transmit ??(Multiple Access) MA

Device Listen — Transmit at same ??time (Collision Detect) CD

Figure 2.15 — Illustration of CSMA/CD

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Devices detecting a collision will generate a predetermined jamming signal to tell all other devices that a collision has occurred and will then withdraw for a while (referred to as a Backoff Strategy, in which the specific withdrawal time period is governed by a randomly generated number), before going back to the Carrier Sense phase and trying again.

2.13 CSMA/CD Transmission Flow Data Station Ready to Send 2.13.1 Full-Duplex Ethernet New AttemptWait According to Backoff Strategy In full-duplex Ethernet, devices at each end of a link can send and receive data simultaneously. One advantage of this approach is that the full-duplex link can theoretically provide twice the bandwidth Sense Channel Busy Channel of normal (half-duplex) Ethernet. The full-duplex mode of operation requires that each end of the link Channel Free connect only to a single device, such as a workstation or a switched hub port. A device at the end of a full-duplex Ethernet link does not have to listen for other transmissions or for Collision Transmit Data Detected Transmit collisions when sending data. Therefore, there is no need to adhere to the original Ethernet medium SenseNo Channel collision Detected Jam Signal access control system (CSMA/CD); The 10Base-T, 100Base-TX, and 100Base-FX and 1000Base-T/X signaling systems support full-duplex Transmission operation; they have transmission and reception signal paths that can be simultaneously active. Complete

2.13.2 Figure Flow 2.16 Control — CSMA/CD (802.3x) algorythm Flow control is a mechanism created by the IEEE to define a standard to manage the flow of data between two Ethernet devices operating in full- duplex mode. Flow control is supported on 10, 100, GigE and 10 GigE links. Using flow control, a device that can no longer process frames as they arrive sends a pause message to its link partner to temporarily reduce the amount of data transmitted. Otherwise, buffer overflow occurs, data is lost and retransmission is required.

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Flow control is defined for neighboring devices on a point-to-point link; i.e., flow control is not implemented end to end. If a receiving station becomes congested, it sends a pause frame to the transmitting station specifying the amount of time for which the transmitting station should stop sending packets. The transmitting station waits for the specified time before sending additional packets. This effectively reduces throughput between the two devices and results in much less retransmission, as the packet loss that occurs from lack of flow control is no longer an issue. A second form of flow control, called XON/XOFF, toggles traffic flow by sending one pause frame to stop traffic flow and a second to request a resumption of traffic (typically when the receiving buffer has emptied). 2.13.3 Pause Frame Format The pause frame is a standard Ethernet frame that is sent where the type field is specified as 8808. The pause time is specified in the data payload as S Source PreamblePreambleO Destination 8808 DATA FCS shown below. F AddressAddress 2.13.4 Auto-Negotiation

0100 0-0xFFFF PAD (0x0000) There is an optional part of Ethernet allowing two devices to negotiate the best possible connection between them. Auto-negotiation devices exchange 802.3x Pause OpCode Time information about their range of link speeds, possible modes of operation (full-duplex or half-duplex), and whether they support flow control. For 1000Base-T links, auto-negotiation also includes master clock support. Flow control can be implemented symmetrically or asymmetrically (if one device has manually configured and/or fixed transmission settings). Figure 2.17 — Pause frame format and location On copper connections, the auto-negotiation process takes place using a modified version of the normal link pulse (NLP) signals used to verify link integrity, called the fast link pulse (FLP) signals. It should be noted that NLPs and FLPs are specified only for twisted-pair media using eight-pin connectors, such as 100Base-TX over unshielded twisted-pair wire. Optical links use a special order-set control symbol instead of FLPs to carry auto-negotiation information.

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Devices on a network that are capable of auto-negotiation find their highest-performance mode of operation based on a set of negotiation rules, shown in the table below. Auto-Negotiation Priority Rules A 1000Base-T B 100Base-TX full-duplex C 100Base-T4 D 100Base-TX E 10Base-T full-duplex F 10Base-T

The negotiation process works its way from F to A until the highest value match is achieved. Switches and hosts can override auto-negotiation with manual settings. 10 GigE does not support auto-negotiation. 2.13.5 Link Aggregation Link aggregation (or trunking) is another Ethernet feature only applicable to the full-duplex operation. It provides increased link availability and bandwidth between two Ethernet stations by allowing multiple physical links to be combined as a single "logical" link. The link-aggregation specification is specified in 802.3ad. Prior to link aggregation, it was difficult if not impossible to have multiple links between two Ethernet stations; the (STP) algorithm used in Ethernet bridging (802.1D) disables parallel paths to prevent loops in the network.

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Link aggregation allows multiple links between any two Ethernet stations if they consist of two switches, a switch and a server, or a switch and an end-user station. The following advantages are provided: • Bandwidth can be increased by combining available lines (for example, two 10 Mb/s links can result in a 20 Mb/s link) • Load balancing can be performed by distributing traffic across the multiple links. One line can be dedicated to high-priority traffic, if required. • Redundancy is provided by the multiple links Link aggregation operates by adding a new layer of function between the Ethernet MACs and the higher-layer protocols above. The link-aggregation function is completely transparent to all higher-layer protocols and functions, including the spanning tree algorithm, VLANs, SNMP and routers. Aggregation can only be performed if: • Links are point-to-point (no multipoint permitted) • Links must operate in full-duplex mode • Links being aggregated run at the same data rate (e.g. 10 Mb/s, 100 Mb/s, or 1 Gb/s)

2.14 10 Gigabit Ethernet (10 GigE) 10 Gigabit Ethernet is a departure from standard 10/100/1000 Mb/s Ethernet in that it is optimized for both LAN and WAN applications. Since most 10 Gb/s WAN links today are SONET/SDH-based, the 10 GigE specification has a second physical-layer specification allowing it to easily interact with existing SONET/SDH network elements. 10 GigE maintains the standard 802.3 Ethernet frame size and format, so that Layer 3 and higher protocols are preserved. It operates over point-to-point links in full-duplex mode only. 2.14.1 Physical-Layer Specifications LAN PHY runs at 10.000 Gb/s and is designed to directly aggregate and carry GigE traffic. This interface comes in two different versions: a serial version using 64B/66B encoding, operating at a line rate of 10.313 Gb/s (data rate of 10.000 Gb/s), and a wide wave-division multiplexing (WWDM) version, 10Base-LX4, using 8B/10B encoding on four channels, each running at 3.125 Gb/s, which results in a line rate of 12.500 Gb/s (again at a data rate of 10.000 Gb/s).

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WAN PHY runs at a data rate compatible with SONET OC-192c/SDH STM-64c (9.5846 Gb/s). The WAN PHY is designed to support connections with SONET/SDH circuit-switched networks. It adds a WAN interface sublayer (WIS) to the LAN PHY. The WIS takes the data payload and encapsulates it with its embedded SONET/SDH frame into a simplified SONET OC-192c/SDH STM-64c (concatenated) frame. Because of the SONET/SDH overhead and the 64B/66B encoding, the actual data rate supported is lower than the LAN PHY, so the WIS has a mechanism to pad and buffer data to the 10 Gb/s MAC data rate. WAN PHY is designed to bridge asynchronous data media and synchronous TDM transport networks, which allows 10 GigE to be transparently carried across today’s TDM infrastructure. It is 100% compatible with current DWDM networks carrying OC-192/STM-64 and 100% compatible with OTN (DigiWrapper) networks carrying OC-192/STM-64. However, it should be understood that this WAN interface is not true SONET. The "S" in SONET (or SDH) stands for synchronous; that is, all points on the network are synchronized to an accurate central master clock. Ethernet is an asynchronous system in which each receiving device derives clock and data from the incoming stream and re-times the outgoing characters with a local clock. The 10 Gigabit Ethernet output from a device with a WAN PHY does not connect directly to a SONET/SDH ring as it requires an access device. WAN PHY has some SONET/SDH features, but does not support the full SONET/SDH standard: • Supports only the SONET/SDH overhead features required for fault isolation • Ignores line and section DCC • Ignores local and express orderwire • Supports pointer processing to allow carriage over future OC-768/STM-256 backbones Telco-like features supported on 10 GigE WAN PHY: • WAN PHY has facility-loopback capabilities • WAN PHY has threshold for severely errored seconds • WAN PHY has embedded test pattern generation/detection capabilities (PRBS-31)

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Location A Data Routing Center Switch 10 GE Routing WAN PHY Switch Transponder 10 GE WAN PHY

Transponder DWDM Location B Optical Network

Routing 10 GE Transponder Switch WAN PHY

Remote Servers

Location C

Figure 2.18 — 10 GigE WAN PHY applications: ITU-T grid compatibility

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OC-766 Mux OC-766 Mux Location A National Backbone

10 GE Routing WAN PHY OC-766 Mux Switch 10 GE WAN PHY

DWDM Optical Network

Figure 2.19 — 10 GigE WAN PHY applications: OTN and OC-768 compatibility

10-100 M Ethernet link Access Routers GigE link Access Routers Edge Routers OC-48

DWDM Edge Routers 10 GigE WAN link

OC-4810 GigE LAN link Access Routers Access Routers

Figure 2.20 — Typical 10 GigE WAN and LAN PHY applications

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Ethernet Applications Guide Ethernet.1-ang: Guide Ethernet.1AN 5/7/07 10:06 AM Page 36

3. Ethernet Applications Ethernet is widely used in local-area networks (LANs) as well as in different types of carrier networks — access networks, metropolitan-area networks (MANs) and long-haul or wide-area networks (WANs).

3.1 Ethernet in Local-Area Networks (LANs) A LAN is a network of computers and associated devices within a small geographical area, usually within a building or group of buildings. Devices on the LAN can be connected using coaxial cables, twisted pairs of copper wiring or fiber-optic cables, or even wireless radio or infrared connections. Ethernet is by far the most popular LAN technology. Common Ethernet standards are 10Base-T (10 Mb/s Corporate LAN over twisted pairs), 100Base-T or Fast Ethernet Backup WAN WAN (100 Mb/s over twisted pairs), and 1000Base-T (Gigabit Ethernet using four pairs of Category 5 or Category 5e balanced copper wiring).

Firewall File/Print Server E-mail Server Figure 3.1 shows a typical corporate LAN with a client/server architecture. Some small networks, such as home-office networks, do not include a Switch Hub server but use a peer-to-peer architecture instead. Application Server Workstations Several common network components are required Shared Laser Printer to build a corporate LAN; these include repeaters, hubs, switches, and routers: Workstations HubHub (48 port) HubHub Shared Laser Printer Workstations

Shared Laser Printer

Figure 3.1 — A typical office LAN topology

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Hub A Repeater joins two network segments together to overcome cable-length limitations. The role of this element is to simply regenerate signals. A maximum of four repeaters are allowed between

Host any two terminating clients (computers). A Hub is a multiport repeater that joins devices to a common backplane. Within the hub, the data goes through a repeater process. Workstation

Figure 3.2 — A typical office LAN topology using a 10Base-T hub Hubs can have different interfaces for different cable Host types; they can offer rate

Hub Host Hub conversion and, if software is added to them, they can become managed devices. If hubs are Shared backplane in each hub connected to each other to Hub Uplink increase the number of available ports, they must also follow the Workstation Host four-consecutive-repeater limit.

Hub Hub Host

Workstation

Workstation

Figure 3.3 — LAN using multiple hubs to add users to a common network

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All devices connected to a hub (or via interconnected hubs) are capable of colliding with each other so they are in the same collision domain (CD), allowing only one device to transmit at a time. CSMA/CD is a very efficient media access scheme under light to moderate traffic loads. As the traffic volume gets heavier, however, a significant amount of network transmission time becomes consumed by collisions, and networks need to be segmented (using a switch) to restore traffic efficiency. The use of hubs is declining because switches are now just as inexpensive and they offer a much more efficient way of constructing the LAN. Host High Speed, High Switches and Bridges Bandwidth Backplane A bridge divides a network into two segments. It restricts traffic to a single segment unless the device needs to access a device on the other segment (known as bridging). A hub cannot segment a network since segmenting is performed using MAC addresses, which are not understood by hubs; they are simply Layer 1 (repeater) devices. A strategically placed bridge can significantly reduce collisions by Switch segmenting workgroup traffic flow. Host A switch is a multisegment bridge. Each segment is connected to a port, which can be bridged to any other segment (port). Switches have a large bandwidth backplane, allowing devices on two segments to be temporarily connected at what is called wire-speed, while simultaneously Host enabling similar bridging between other device pairs. Workstation If every client on a network is interconnected through a switch, collisions do not occur and maximum possible throughput is enjoyed by all clients. Switches allow multiple hosts to transmit at the same time, without Figure 3.4 — A typical office LAN topology using a Layer 2 switch contention for bandwidth. Switches can be VLAN tag-aware, permitting

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the formation of virtual LANs.

There are various types of switching techniques: • Cut-Through – The frame is forwarded on-the-fly. This is fast, but no FCS check is possible and the communicating devices must use the same LAN format. • Modified Cut-Through – Stores the frame for 64 bytes before forwarding. Same drawbacks as the cut-through technique and slightly slower, but eliminates short frames (runts). • Store and Forward – Slowest of the three types because it stores the complete frame before forwarding it. This allows for a full check and also permits the removal of

Long-Haul Networks (WANs) the data field for insertion into a different LAN frame type; e.g., Ethernet to token ring. A Router is a multilayer switch used to direct Layer 3 (commonly Internet

Optical WDM cross- Multiple regional Protocol, or IP) traffic. By examining the IP address, a switch determines connect mesh and backbone providers the corresponding MAC address so that the Layer 3 traffic can be correctly forwarded through a Layer 2 Ethernet network. Address

Metropolitan Networks Long-Haul/ resolution protocol (ARP) is the standard mechanism used to correlate (MANs) metro MAC and IP addresses in routers. Inter-metro Intra-metro connectonIntra-metro connection connection

IP Router Frame SONET Realy ESCON ATM Ethernet Fiber Switch Gigabit LAN Channel Ethernet

Residential x-DSL or PSTN/cellular Regional ISP Corporate3.2 Ethernet in Access Networks networks enterprise clients Personal computers and LANs are usually connected to the outside world via Figure 3.5 — Interconnection of access networks, MANs and WANs

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an access network (see figure below). An access network, commonly referred to as the first mile or the last mile depending on the context, covers a relatively small geographic area and connects subscribers, such as corporations, government offices, educational institutions and residential customers, to a metropolitan-area network (MAN). MANs in close proximity may be directly interconnected. Long-distance connections between MANs are provided by long-haul telecom networks to create wide-area networks (WANs). Access networks use a variety of media such as twisted pairs of copper wire, hybrid fiber coax (HFC) or, optical fiber in FTTx and passive optical networks (PONs). Access rates range from sub-rate channels such as DS1, DS3, OC-3, OC-12, Fast Ethernet and Gigabit Ethernet, to full-wavelength capacities such as OC-48 and OC-192. Access networks use a variety of protocols including ATM, frame relay, SONET/SDH, Ethernet and MPLS. Ethernet services can be delivered over any of these access technologies, but the most cost-effective and simple method is to deploy Ethernet services directly over Ethernet access lines. Ethernet access networks typically run at 1000 Mb/s (Gigabit Ethernet, or GigE). Traffic is delivered to the customer from the tributary side of an access router or Layer 2 switch. Rate limiting is commonly used to limit the bandwidth to the Customer C customer, which can be provided in increments as Customer A Customer B Store Customer B Customer A small as 1 Mb/s. Using identifiers in Ethernet data Customer B frames called virtual private LAN (VLAN) tags (see Store Customer C Chapter 2), service providers can separate traffic OC-48 OC-48 to offer a secure virtual network to each customer DWDM over a common backbone. Customer C

Customer A

CustoOC-3 mer C Customer C Customer B Customer A Customer B Customer A

Figure 3.6 — VLANs provide secure virtual networks to individual customers across a MAN

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3.3 Ethernet in Metro Networks MANs cover geographic areas up to several hundred kilometers and typically serve concentrated metropolitan areas. They interconnect many access networks and provide connection points to WANs. Many current and emerging MAN technologies support Ethernet services. These networks use a wide variety of networking protocols and channel speeds. SONET/SDH is presently the most common technology with point-to-point or add/drop multiplexer (ADM) ring topologies. In some new MAN installations, 10 Gigabit Ethernet (10 GigE) is challenging SONET/SDH with its lower cost and simpler maintenance requirements.

3.4 Ethernet in Wide-Area or Long-Haul Networks A WAN is a network that covers a large geographical area using long-haul networks that can extend over thousands of kilometers to connect many different MANs. Most WAN links are SONET/SDH-based and many use DWDM. With the introduction of 10 Gigabit Ethernet, carriers can now use one wavelength on a long-haul DWDM system to transmit Ethernet in its native format, further simplifying the deployment of Ethernet services (see Chapter 2).

3.5 Ethernet Service Types The two basic Ethernet service types defined by the Forum (MEF) are: Ethernet Line (E-Line) for point-to-point connectivity. E-Line services are used to create Ethernet private line services, Ethernet-based Internet access services, and point-to-point Ethernet VPNs. Ethernet LAN (E-LAN) for multipoint-to-multipoint (any-to-any) connectivity. E-LAN services are designed for multipoint Ethernet VPNs and native Ethernet transparent LAN services.

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Service type Connectivity Use Ethernet Line (E-Line) Point-to-point (one-to-one) • Ethernet private line (EPL) services • Ethernet-based Internet access services

• Point-to-point Ethernet virtual private networks (VPNs) Ethernet LAN (E-LAN) Multipoint-to-multipoint (any to any) • Multipoint Ethernet VPNs • Native Ethernet transparent LAN services

Table 3.1 — Basic Ethernet service types Figure 3.7 and Figure 3.8 illustrate the two basic service types and how they are used to IP Video interconnect geographically separated LANs by interfacing customer edge (CE) equipment to the MAN. Note that each customer requires only one CE, regardless of the number of Ethernet Point-to-Point virtual connections (EVCs) involved. It would even IP Voice Ethernet Virtual ConnectionsServers (EVCs) be possible to make a multipoint-to-multipoint Data connection and several point-to-point connections to the same CE. In all cases, the Ethernet service ensures CE IP Video that frames are delivered to the correct destination. IP PBX

MAN CE

Data

IP Voice CE

Figure 3.7 — Ethernet line (E-Line) service

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Both of the basic Ethernet service types allow connectivity services that are either private or virtual. In Multipoint-to-Multipoint Ethernet Virtual Connection a private service, a specific amount of bandwidth is (EVC) Servers dedicated to the subscriber whether they are using it or not. A private service does not use dedicated physical connections (such as a TDM circuit), but is

IP Voice instead a dedicated-bandwidth service implemented over a public network infrastructure. Customer CE X Data CE separation is ensured through packet encapsulation MAN IP PB and logical connections. In contrast, a virtual service allows bandwidth to be shared among different subscribers with connections CE to the network. Virtual services are less costly than DataIP Voice CE private services because they allow the service provider to accept more traffic by dynamically IP Voice reassigning idle capacity. To maximize the use of Data infrastructure, the service provider can oversubscribe, since it is unlikely that all subscribers will require maximum capacity at the same time. Figure 3.8 — Ethernet LAN (E-LAN) service The combination of private and virtual E-Line and E-LAN service types results in the four basic Ethernet services described below:

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3.5.1 E-Line Variants Ethernet Private Lines This service consists of a point-to-point connection that uses dedicated bandwidth, be it virtually concatenated SONET/SDH channels or reserved packet bandwidth in a packet-switched network. The customer’s Ethernet frames stay strictly separated from others’ at the Ethernet layer, and the customer will always have the contracted bandwidth rate available (also known as CIR, the committed information rate). In this regard, the Ethernet private line is much like legacy TDM-based private lines, yet offers the benefit of a native Ethernet interface to the customer and to the network operator’s edge equipment. Like typical TDM private lines, the Ethernet private line can be deployed to support a number of different carrier services such as Ethernet Internet, network services access or LAN-to-LAN interconnect, in which the customer owns one or both (in the case of LAN-to-LAN) ends of the connection. The Ethernet private line is the simplest E-Line service to deploy. Carriers typically provide these services from a multiservice provisioning platform (MSPP), which acts as the demarcation between the customer’s network and the carrier’s SONET/SDH transport network. Ethernet Virtual Private Line For the Ethernet virtual private line, the rules are slightly different. In this service, the customer still gets point-to-point connectivity, but over shared bandwidth instead of dedicated. The shared bandwidth can be a TDM channel in the transport network or the switched-fabric bandwidth of switches and routers in the packet network. The service can either be offered as best-effort or with service-level agreements specifying committed information rates (CIR) and other critical network parameters such as latency. This service is quite similar to frame relay and its model of creating networks using permanent virtual circuits (PVCs). The MEF defines Ethernet virtual private line service as a point-to-point Ethernet virtual connection (EVC) between two subscribers. Multiple EVCs can be combined to provide hub-and-spoke architectures in which multiple remote offices all require access to a head office, or multiple customers all require access to managed services from an operator’s point of presence (POP).

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3.5.2 E-LAN Variants Ethernet Private LAN The Ethernet Private LAN (EPLan) service provides multipoint connectivity over dedicated bandwidth; i.e., it may connect two or more subscribers. Subscriber data sent from one customer site can be received at one or more of the other customer sites. Each site is connected to a multipoint-to-multipoint EVC and uses dedicated resources so different customers’ Ethernet frames are not multiplexed together. As new sites are added, they are connected to the same multipoint EVC, thus simplifying provisioning and service activation. From a subscriber standpoint, an EPLan makes multiple LAN sites look like a single, really big LAN. Ethernet Virtual Private LAN The Ethernet Virtual Private LAN (EVPLan) has gone by many names over the past two years, from Virtual Private LAN Service (VPLS) to Transparent LAN Service (TLS), to Virtual Private Switched Network (VPSN). Regardless of how it is termed, the EVPLan is a network service providing Layer 2 multipoint connectivity between Ethernet edge devices. Customer separation is accomplished via encapsulation using VLAN tags or other encapsulation technologies such as MPLS. The EVPLan is a cost-effective service for the carrier, as it can leverage shared transmission bandwidth in the network. However, because it is a multipoint service, it can be complex to administer. The operator must implement protection, bandwidth profiles, congestion management, buffering, etc.; these are much more complex to implement in EVPLans when compared to point-to-point services.

3.6 Ethernet Infrastructures Many means are available to carry Ethernet in carrier networks, each with their own advantages and disadvantages. The method used depends on many factors, including the reliability and manageability of legacy services and the risks involved in implementing new technologies that may not be entirely proven and standardized. Some carriers incorporate Ethernet services into existing optical WDM/SONET/SDH infrastructures while others opt for emerging packet-based technologies such as IP/MPLS.

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3.6.1 Native Ethernet The most straightforward way of carrying Ethernet is to use native Ethernet over dark fiber or on a DWDM wavelength. In a MAN, Ethernet switches are used to direct traffic over the network. This solution is particularly suitable to Ethernet virtual private line and virtual private LAN services. However, it is not easy to provide the dedicated bandwidth necessary for Ethernet private line or private LAN services. Since native Ethernet systems cannot guarantee sub-50 ms protection to redirect traffic around an outage, and since a native Ethernet network does not provide operations, administration and maintenance (OAM), the services are offered as “best-effort”; that is, there is no guarantee of QoS. 3.6.2 SONET/SDH In past years, many carriers overbuilt their SONET-based infrastructure, and much of this capacity is still underutilized. For this reason, many of the service providers in North America are seeking to capitalize on it by deploying Ethernet and other data services over their existing SONET networks. In next-generation SONET/SDH networks, Ethernet frames are encapsulated one at a time into GFP frames, which are then mapped into a SONET channel using virtual concatenation (VCAT). SONET/SDH networks are most often used for Ethernet private lines today, but will be evolving to support Ethernet virtual private lines and Ethernet virtual private LANs through integrated Ethernet switching or RPR technology. 3.6.3 Native Ethernet vs. SONET/SDH: Pros and Cons SONET and SDH were created to transmit TDM circuits carrying mostly voice. Ethernet, on the other hand, was created to transmit frames of data. Because of this difference, the type of traffic being transported influences the choice of technology. Table 3.2 summarizes these differences according to five important criteria.

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Criteria SONET Native Ethernet Redundancy Provided by automatic protection switching Provided by spanning tree algorithm (minute range). (APS) capability (50 ms). A fast-spanning tree algorithm has brought this time down to

< 1 minute, now averaging in the 30-second range. Intervendor If both vendors are GR-253-compliant, both vendors If both vendors are IEEE 802.3-compliant, both vendors Operability can interoperate. OAM&P issues are created. can interoperate. OAM&P issues are created. Maintenance Loopback capability for out-of-service tests. No loopback in Ethernet. Switch and router information can Challenges be obtained through remote monitoring (RMON) statistics. Provisioning Provisioning of SONET network elements is done through Provisioning of Ethernet switches and routers is done Challenges line interface commands or an element management through line interface commands or an element management

system (EMS). system (EMS). Fault Detection B1, B2, B3 detection. Frame check sequence (FCS) errors and link status. Will provide threshold crossing as per GR-253 PM. Programmable SNMP traps can be sent upon threshold crossing. Sectionalization in terms of section, line and path. Sectionalization in terms of inter-switch link span.

Table 3.2 — Comparison of SONET/SDH and native Ethernet

3.6.4 Resilient Packet Ring (RPR) Resilient packet ring (RPR) is a technology that combines packet-switched networks with dual rings and supports sub-50 ms ring-based recovery on packet-switched networks. RPR can run over SONET/SDH or native Ethernet transport networks and supports a significant degree of bandwidth efficiency on rings through the implementation of bandwidth sharing, spatial reuse, and statistical multiplexing.

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3.6.5 ATM Ethernet can be carried over existing ATM networks by using the information in each Ethernet frame to map the frame to an appropriate ATM virtual circuit and service class. Ethernet services can thus be provided over ATM with the same QoS and resiliency as ATM. This method allows considerable flexibility in service topology, including point-to-point and multipoint-to-multipoint services and optimal levels of oversubscription. Greenfield deployments, however, are more likely to use IP/MPLS, rather than ATM, due to advantages in cost and scalability. 3.6.6 IP/MPLS The first Ethernet-based carrier services were less expensive and more flexible than leased lines or frame relay services, and they also offered full support for VLANs. However, they were not carrier class and lacked the reliability, scalability and security of traditional TDM and ATM services. In addition, the IP routers used to provide Ethernet IP services could not perform longest prefix match lookups at wire speed, resulting in lower performance. Multiprotocol label switching (MPLS) is a control-plane packet-forwarding technology that is rapidly being adopted to overcome these drawbacks and make Ethernet “carrier class” – allowing Ethernet to transmit voice and other delay-sensitive applications. MPLS also makes the entire network easier to provision and engineer. As the name implies, MPLS technologies are applicable to multiple network layer protocol including IP, ATM and frame relay. MPLS helps move traffic faster by building virtual circuits, or tunnels, called label-switched paths (LSPs) across the network (see Figure 3.9) and by using simple labels to make data-forwarding decisions. The ingress-edge label-switching router (LSR) analyzes the Layer 3 header of each packet to determine the destination address and assigns a label to the packet. The LSRs in the core only inspect the label in order to forward the packet to the next hop in the LSP. At each hop, the LSR strips off the existing label and applies a new label, which tells the next hop how to forward the packet. The LSR at the egress edge removes the label and forwards the packet normally. Label-switched paths (LSPs) can be established for virtual private networks to guarantee a certain level of performance or to route around network congestion. LSPs are similar to circuit-switched paths in ATM or frame relay networks, except that they are not dependent on a particular Layer 2 technology.

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MPLS also provides other benefits, such as virtual private networking (VPN) to create IP tunnels through the network; traffic engineering (TE) to provide traffic prioritization for different classes of traffic; quality of service (QoS); and bandwidth management. Another feature is fast rerouting, which allows traffic to be quickly transferred to a pre-established backup tunnel. This is similar to SONET’s protection switching.

Pseudo-wires, which emulate a native service over a packet-switched network (PSN) are specified in the MPLS standards as a technique to carry TDM traffic and legacy access protocols such as ATM and frame relay over MPLS networks Label-switched alongside Ethernet traffic. MPLS can be used with path (LSP) Ingress-edge native Ethernet over xWDM (dark fiber), over label-switched router Egress-edge LSR next-generation SONET/SDH networks using (LSR) labels removes the the packets labels and GFP/LCAS/VCAT, or directly over SONET delivers the packets using 10 GigE WAN technology to connect to SONET/SDH ADMs, over RPR and ATM. MPLS provides the assurance that carriers need to migrate all their transport services to a converged IP/MPLS core network (see Figure 3.10). This would eliminate the need Core LSR for separate networks for each type of switches the packet using label-swapping Layer 2 protocol.

Figure 3.9 — MPLS network connecting two premises

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Frame Relay

ATM Cirtual Circuits IP/MPLS MPLS-Based Universal Port Core Ethernet Packetized MAN

OC-n OC-n OC-n Optical OC-n Port SONET

Access MetroCore

Figure 3.10 — Convergence of services to an IP/MPLS core network

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Introduction to Installation and Provisioning Guide Ethernet.1-ang: Guide Ethernet.1AN 5/7/07 10:06 AM Page 52

4. Introduction to Installation and Provisioning

4.1 Quality and Performance Legacy transport technologies used in carrier networks, such as ATM, were designed to be able to guarantee measurable quality of service. This allowed service providers to establish service-level agreements with their customers. A service-level agreement (SLA) is a legal contract between a service provider and a customer that specifies a required level of service. SLAs help service providers attract and retain customers, but there are also penalties associated with sub-standard service: poor customer satisfaction, increased spending on maintenance and, often, direct financial payouts. SLAs typically specify maximum downtime, mean-time-to-repair (MTTR) when outages occur, and minimum performance criteria. Unfortunately, Ethernet was not designed with quality of service (QoS) in mind and, originally, offered no means to differentiate between low- and high-priority data. This made it difficult to combine different types of services, such as e-mail and voice communication over the same link, while ensuring that transfer rates met pre-established criteria. Service class extensions, such as type of service (ToS) and differentiated services (Diff Serv), have been added to IP, but these are still based on best-effort delivery and simply help to prioritize traffic flow without any SLA-type assurances. Ethernet class of service (CoS) can be supported only through VLANs (802.1p). Regardless of which technique is used, various factors such as network congestion can affect the actual rate at which the data is transferred. For this reason, specific tests are required to verify Ethernet performance in order to ensure that the SLA requirements are met.

4.2 Ethernet Performance Verification The Internet Engineering Task Force (IETF) has put together a test methodology to address the issues of performance verification at the Layer 2 and 3 levels. RFC 2544, Benchmarking Methodology for Network-Interconnect Devices, specifies the requirements and procedures for testing throughput (performance availability), latency (transmission delay), back-to-back frames (link burstability), and frame loss (service integrity).

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When these measurements are performed, they provide a baseline for service providers to define SLAs with their customers. They enable service providers to validate the quality of the service delivered and can provide them with a tool to create value-added services that can be measured and demonstrated to customers. For example, these tests provide performance statistics and commissioning verification for virtual LAN (VLAN), virtual private networks (VPNs) and transparent LAN services (TLS), all of which use Ethernet as an access technology. The SLA criteria defined in RFC 2544 can be precisely measured using specialized test instruments. The performance verification is usually done once the installation is complete. The measurements are taken when the network is out of service to make sure that all parameters are controlled. 4.2.1 Test Configurations Different configurations are possible for performing the tests. These are explained below. Dual-test-set configuration Two test sets are required for local/remote testing, also known as head-to-head testing (see Figure 4.1). This test configuration, also known as ”master-slave”, is ideal for: • End-to-end testing • Going through a routed network

This configuration, the user operates one test set, which controls the other by designating one as the local test set and the other as the remote test set. This makes it easy to determine in which direction the traffic is flowing. The remote test set is controlled via the connection under test. During the test, results from both directions are visible on the local test set.

Network under test

Figure 4.1 — Dual-test-set configuration (arrows show direction of traffic)

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Dual-port configuration In some cases, testing can be performed using one test set with two ports (see Figure 4.2). This is ideal for: • Testing a switch locally • Lab environment • End-to-end testing with high port density Single-port loopback configuration The single-port loopback configuration is similar to the dual-port configuration in Port 1 that it requires only one test set. The difference is that the traffic does not go from

Customer one port to another but simply loops from the transmit connection of one port to Network the receive connection of the same port (see Figure 4.3). It is ideal for:

Port 2 • DWDM systems • End-to-end testing with end devices that can loop back to the same port, Port 1 either with a cable or a software loopback Note: Many systems (mainly Ethernet switches or routers) will not allow a simple loopback to the same port. This is because switches forward frames 10/100 Mb/s Port 2 Layer 2 Switch according to a destination MAC address. Routers work the same way, but use a destination IP address. If such a device is looped back to the same port, it will 1000 Mb/s not know where to forward the frames and will drop them. A special loopback Port 1 device that can correctly address the originating test set is required for these configurations.

Port 2

Switch ACustomer Switch B Network

Figure 4.2 — Dual-port configuration

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4.2.2 RFC 2544 tests Port 1 TX The following sections describe each of the RFC 2544 tests. The test equipment Customer used should be able to generate and analyze traffic for 10/100/1000Base-T, Network 1000Base-SX, 1000Base-LX and 1000Base-ZX full-duplex networks at all frame Port 2 sizes in order to test transparent connectivity for LAN-to-LAN services delivered via TX ATM, frame relay, next-generation SONET/SDH, SONET/SDH hybrid multiplexers, switched Ethernet, VLANs, dark fiber, WDM or other means. The instruments should be capable of transmitting at full line rate, in order to allow the provider to Port 1 certify that the circuit is efficient and error-free at 100% utilization. TX Loopback Some test instruments enable automated testing, which helps to ensure repeatable Customer Network results. Automation also provides ease of use for technicians in the field by On the same enabling accurate, efficient measurements and providing reports they can give to Port 1 Port TX customers for future reference related to their specific SLAs. Testing can be performed end-to-end or end-to-core, depending on the SLA λ (see Figure 4.4). Remote testing is also possible. 1

Customer Network

Figure 4.3 — Single-port loopback configuration

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Throughput Remote Testing Throughput is the maximum rate at which none of the offered frames are dropped by the device under test (DUT) or network under test (NUT). Internet For example, the throughput test can be used to measure the rate-limiting capability of a switch. The throughput is essentially equivalent to the bandwidth and can be measured bidirectionally using a dual-port loopback configuration or unidirectionally using two test sets (see Figure 4.5). The throughput test allows vendors to report a Gigabit Ethernet single value, which has proven to be useful in the Metro Network marketplace. Since even the loss of one frame in Gigabit Ethernet a data stream can cause significant delays while waiting for the higher-level protocols to time out, 10/100Base-T 10/100Base-T it is useful to know the actual maximum data rate that the device can support. Measurements should be taken over an assortment of frame sizes. Separate measurements should be performed for routed and bridged data in those devices that can support both. If there is a Figure 4.4 — End-to-end, end-to-core, and remote testing checksum in the received frame, full checksum processing should be done.

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The following issues will affect throughput test results: • Single path vs. aggregate – If data always takes the same path through a network, then short-term test results will be consistent. However, if the route is dynamically OC-3 changed by MPLS fast reroute or by another traffic control protocol, then the traffic STM-1 will continually experience different environments and short-term test results will vary over time. In this case, a longer-term test is required to assess the worst case.

Dual-Port Configuration • Load – The amount of traffic on the network, on the access line, or generated by the Ethernet tester will determine how traffic reaches the other end. Congestion can result in dropped or lost frames, high latency, etc. • Unidirectional vs. bidirectional testing – Bidirectional testing means testing as data flows from A to B and back to A. As access link bandwidths tend to be OC-3 asymmetrical (download bandwidth may exceed upload bandwidth, or vice versa), STM-1 bidirectional testing provides only an overall indication of throughput. Unidirectional testing, first from A to B and then from B to A, allows for the Dual-Test-Set Configuration measurement of upload and download throughput separately. • Checksum processing required on some protocols – Checksum processing slows data transmission and affects throughput, frame loss, etc. It is preferable to use a tester that can test with or without checksum processing. Figure 4.5 — Measuring throughput • Packet size – Smaller packets can transmit quicker, but testing with smaller packets increases the likeliness of losing packets. Larger packets hold a greater percentage of payload vs. header. A compromise needs to be reached between allowing room for other traffic (smaller packets) and the greater efficiency of larger packets.

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Throughput test procedure3: 1. Send a specific number of frames at a specific rate through the DUT/NUT and then count the frames that are transmitted by the DUT/NUT. 2. If the count of offered frames is equal to the count of received frames, the rate of the offered stream is raised and the test is rerun. 3. If fewer frames are received than were transmitted, the rate of the offered stream is reduced and the test is rerun. 4. The throughput is the fastest rate at which the count of test frames transmitted by the DUT/NUT is equal to the number of test frames sent to it by the test equipment. Burst (Back-to-Back) In this test, fixed-length frames are presented at a rate such that there is the minimum legal separation for a given medium between frames over a short to medium period of time, starting from an idle state. The back-to-back value is the number of frames in the longest burst that the DUT/NUT will handle without the loss of any frames. Burst test procedure: 1. Send a burst of frames with minimum inter-frame gaps to the DUT/NUT and count the number of frames forwarded by the DUT/NUT. # of Bytes 2. If the count of transmitted frames is equal to the number of frames forwarded, the length of the burst is increased and the test is rerun.

STM-1 3. If the number of forwarded frames is less than the number X transmitted, the length of the burst is reduced and the test is rerun.

Burst 4. The back-to-back value is the number of frames in the longest burst # of Bytes that the DUT/NUT will handle without the loss of any frames. 5. The trial length must be at least two seconds and should be repeated at least 50 times, with the average of the recorded values being reported. STM-1

Burst

Figure 4.6 — Back-to-back test

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Frame Loss 86 % frames lost at 1000 Mb/s Frame loss is the percentage of frames that should have been forwarded by a network device under steady state (constant) loads that were not forwarded due to lack of

STM-1 resources. This measurement can be used in reporting the performance of a network device in an overloaded state. It can be a useful indication of how a device would perform under pathological network conditions such as broadcast storms.

Frame loss test procedure: 74 % frames lost at 900 Mb/s

STM-1 ...... 1. Send a specific number of frames at a specific rate through the DUT/NUT to be ...... tested and count the frames that are transmitted by the DUT/NUT...... 2. The frame loss at a particular line rate is calculated using the following equation:

Figure 4.7 — Frame loss test ...... Frame loss =Transmitted frames – Received frames x 100% Transmitted frames

...... 3. Separate measurements should be taken for different frame sizes.

3 All test procedures are from RFC 2544 (http://www.faqs.org/rfcs/rfc2544.html).

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Latency For store-and-forward devices, latency is the time interval between frames (input and output); it starts when the last bit of the input frame reaches the input port, and ends when the first bit of the output frame is seen at the output port. Round-trip latency is the time it takes a frame to come back to its starting point. Variability of latency can be a problem. With protocols like VoIP, a variable or long latency can cause degradation in voice quality.

Latency test procedure: 1. Determine the throughput of the DUT/NUT for each frame size. Start Time: 2. Send a stream of frames at a particular frame size through the DUT/NUT at the determined throughput rate to a specific destination. 3. Send a tagged frame after 60 seconds and store timestamp A. Capture tag frame on STM-1 reception side and store timestamp B. 4. The latency is timestamp B minus timestamp A.

Return Time: 5. The test must be repeated at least 20 times with the reported value being the average of the recorded values.

Figure 4.8 — Round-trip latency test

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4.3 Fiber Characterization As GigE and 10 GigE are now considered alternatives to SONET/SDH in the MAN, fiber characterization is crucial for ensuring optimal performance. Chromatic dispersion (CD) and polarization mode dispersion (PMD) are forms of optical dispersion that broaden pulses and limit the transmission speed over long distances. These must be measured in order to ensure high-speed transmission. Specialized PMD and CD optical measurement instruments perform these tests quickly and with minimal setup (see Figure 4.9 and Figure 4.10).

Figure 4.9 — Chromatic Dispersion Analyzer Figure 4.10 — PMD Analyzer

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4.4 BERT over Ethernet Because transparent transport of Ethernet over physical media is becoming a common service, Ethernet is increasingly carried across a variety of Layer 1 media (e.g., 10Base-FL, 100Base-FX, 1000Base-LX) over longer distances. There is therefore a growing need to certify Ethernet carriage on a bit-per-bit basis. This can be done using bit-error-rate testing (BERT). BERT uses a pseudo-random binary sequence (PRBS) encapsulated into an Ethernet frame, making it possible to go from a frame-based error measurement to a BER measurement. This provides the bit-per-bit error-count accuracy required for the acceptance testing of physical-medium transport systems. BERT over Ethernet should be used when Ethernet is carried transparently over the following Layer 1 media: • Ethernet over DWDM • Ethernet over CWDM • Ethernet over dark fiber • Ethernet over free-space optics • Ethernet over wireless LANs

Figure 4.11 — Test set providing BERT over Ethernet. This instrument enables testing of transparent Gigabit Ethernet circuits running over an xWDM network as if they were SONET/SDH circuits.

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4.4.1 GigE and 10 GigE BERT over Dark Fiber and PONs Carriers are increasingly using dark fiber and passive optical networks (PONs) to provide point-to-point and point-to-multipoint access links, respectively, using physical-layer fiber . When Ethernet services are provided over these links, short light budgets and partial GigE fiber faults will reduce GigE throughput. BERT over Ethernet testing POP allows providers to verify the ability to fully load the GigE bandwidth 5-10 Km without any bit errors (see Figure 4.12).

CPE

OC-3 4.4.2 GigE andFigure 10 4.12 GigE — Testing BERT a GigE over fiber a DWDMpoint-to-point Network access link OC-12 Gigabit Ethernet When GigE is transported transparently across DWDM networks, wavelength crosstalk and ESCON transponder fade-out reduce GigE throughput. Ethernet BERT is required to validate error- OPTera DWDM Ring free GigE transmission across the DWDM ring (see Figure 4.13). Extension Rings

DWDM Ring

Loop CLEC Office

Figure 4.13 — Testing GigE transmission over a DWDM network

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4.5 Ethernet Service Acceptance Testing The type of testing required for Ethernet service acceptance testing depends on how the Is the Ethernet Service delivered via Switched service is carried on the network. Figure 4.14 shows how to test for switched transport Transport or via Transparent Physical Transport? or transparent physical transport using either RFC 2544 tests or BERT over Ethernet. All of the tests that are part of the service-level agreement can be performed on either Switch Transport Transparent Physical Transport part of the network (end-to-core) or on all of it (end-to-end). For both switched transport and transparent physical transport, end-to-end measurements can be performed by RFC 2544 BERT using two portable units and testing from one end to the other. Another way of doing this is to send a technician to one site, and setting up a second test device in the Are SLA performance In media 100% error free? network (e.g., in a central office) to test the other site. This type of testing is useful when parameters met? two technicians cannot be sent at the same time or when the service provider is providing access to the Internet. Yes No Yes No

Service Accepted Service Rejected

Figure 4.14 — Flow chart of Ethernet service acceptance testing

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Commissioning Ethernet for Voice-over-IP and Video-over-IP Deployment Guide Ethernet.1-ang: Guide Ethernet.1AN 5/7/07 10:06 AM Page 66

5. Commissioning Ethernet for Voice-over-IP and Video-over-IP Deployment As Ethernet services grow in popularity with enterprises, the rapid deployment of voice and video conferencing over Internet protocol is a top priority for many service providers. Customers who switch from traditional voice and video-conference services to IP-based solutions, expect both toll-quality voice and high-quality video running over their Ethernet access lines. As a result, SLAs for VoIP and video conferencing outline detailed performance criteria related to quality of service (QoS). Service providers can confidently commit to these SLAs if the link is thoroughly tested when commissioned. A simple test plan that only validates the basic functionality of an Ethernet link (using ping, connectivity verification, etc.) leaves an operator exposed to poor network performance once live customer traffic begins. Knowing this problem but lacking test capabilities, some providers over-commission bandwidth to ensure SLAs will be met. This expensive practice can be avoided by diligently confirming a link’s performance before activating a service. Delay-sensitive applications such as VoIP and IP video are sensitive to performance parameters such as inter-packet delay (packet jitter) and packet sequencing (out-of-order packets). Because multimedia traffic coexists with other types of data traffic, bandwidth-demanding applications such as remote backup or FTP can degrade the quality of VoIP and video-conferencing services. This type of problem can be avoided by simulating real traffic patterns during commissioning and adjusting network parameters to provide priority for time-sensitive multimedia packets.

5.1 Essential Testing Techniques When performing these tests, the following techniques must be used to ensure accurate results.

5.2 Simulating the Customer’s Network To realistically simulate and analyze the interaction of multiple services being transported over a single link, the test instruments used must be able to re-create the client’s network environment, both on a LAN and WAN level. To emulate customer premises equipment, parameters such as flow and throughput need to be controlled. To ensure that generated test traffic is carried with the same priority and routing scheme as the customer’s data, VLAN tagging of test traffic is required.

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5.3 Simulating Real-World Traffic Patterns In order to qualify an Ethernet link carrying various services, multistream test-traffic analysis is required. This functionality allows a deployment team to simulate normal link traffic by generating unique test streams for each of the multiple services typically sharing an access line. For example, a high-priority stream with variable bandwidth and frequent bursts of data replicates VoIP traffic, while a low-priority, continuous throughput stream simulates off-site backup applications. As representative client traffic is fundamental to an accurate test plan, the Ethernet tester used must be able to support a reasonable number of independently configurable streams. Normally, a maximum of ten streams is sufficient for commissioning applications. Streams should contain frames that replicate the types of data the customer would typically use over the link. The following tables specify various Ethernet frame/payload qualities that should be used to replicate various media streams.

Predefined type-P packet Description Values VoIP G.711 No compression algorithm on the voice channel IP packet size = 140 B - Voice rate = 64 kb/s Data rate = 64 kb/s

- VoIP payload = 100 B Line rate = 80 f/s VoIP G.723.1 Compression on voice channel to: IP packet size = 64 B - Voice rate = 6.4 kb/s Data rate = 6.4 kb/s

- VoIP payload = 24 B Line rate = 33.3 f/s VoIP G.729 Compression on voice channel to: IP packet size = 50 B - Voice rate = 8 kb/s Data rate = 4 kb/s - VoIP payload = 10 B Line rate = 50 f/s

Table 5.1 — Common VoIP packet definitions as specified by the ITU

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Video streaming Video payload size (bytes) Video bandwidth (f/s) Ethernet frame size (bytes)

Business Quality Videoconferencing 915 107 973 NetMeeting Video LAN (videoconf) 779 77 837 NetMeeting Video DSL (videoconf) 363 65 421 NetMeeting Video 28K (videoconf) 288 5 346 PictureTel StarCast (stream) 1343 155 1401 RealAudio Radio (stream) 681 30 739 Media Player 80K (stream) 697 15 755 Media Player 20K (stream) 476 7 533 Real Video 28K (stream) 384 8 442

Table 5.1 — Common packet characteristics for multimedia applications including video When commissioning VoIP or video services, the test set used should be able to configure streams with these parameters. When stressing a network with multiple streams, detailed measurements are performed on one stream while controlling the priority, bandwidth and characteristics of the others. This technique enables realistic network traffic simulation over a wide variety of typical boundary conditions.

5.4 Performing Unidirectional Testing A final key consideration in VoIP pre-deployment testing is the effect of traffic direction. As traffic or bandwidth over an access link tends to be asymmetrical (downloads exceed uploads, or vice versa), quality problems often occur predominantly in one direction. It is for this reason that one-way effects are often experienced in telephone conversations using VoIP — one caller hears echo, dropouts and delay, while the other hears a perfectly clear conversation.

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To ensure that unidirectional effects are accounted for, it is important to use a test setup that permits parameter measurement in each direction Loopback testing independently. Most Ethernet testers can only perform measurements in Upload direction loopback configuration (see Figure 5.1). This results in upload and download test scores being combined into a single, averaged measurement, making it Download direction impossible to separate upload and download issues. It should be noted that one parameter — latency — cannot be measured Remote (slave) Local (munidirectionallyaster) without sophisticated clock synchronization schemes (involving GPS signals, for example). Latency is typically tested with a loopback configuration. All other performance metrics including throughput, burst, Unidirectional Ethernet network testing frame loss, and packet jitter should be measured unidirectionally to obtain Upload direction accurate test results.

Download direction

Remote (slave) Local (master)

Figure 5.1 — Loopback and unidirectional testing

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6. Monitoring Ethernet Networks

6.1 Ethernet Quality-of-Service Assurance Because SLAs specify minimum performance criteria for Ethernet services, it is important that service providers be able to continually monitor performance and live traffic on the network. This monitoring helps maintain good quality of service (QoS) for clients of the network. 6.1.1 Performance and Traffic Monitoring Performance monitoring can be achieved by polling network elements or probes across the network for their performance statistics. Simple network management protocol (SNMP) and remote monitoring (RMON) are the standard protocols used to

Probe Probe gather performance data from measurement probes or network elements. In Ethernet monitoring applications, probes may consist Gigabit Ethernet Metro Network of specialized hardware or may simply be software agents running on a network element or a standard PC. Gigabit Ethernet Probes analyze different protocol layers in order to provide a 10/100Base-T 10/100Base-T performance evaluation of the Ethernet network. In active Agent Agent monitoring applications, probes send synthetic data across the network to provide a basis for performance evaluation. In passive probe installations, live traffic is examined without generating Figure 6.1 — Ethernet performance monitoring using external probes and software agents synthetic test traffic.

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Statistics and alarms provide a high-level view of the network in order to detect problems. By using probes or protocol analyzers on the problem segment, the service provider will usually be able to identify, troubleshoot and resolve most problems before a customer experiences degraded performance. By gathering traffic statistics in a database, trending patterns can be provided to network management staff. With this data, the service provider can architect new network installations or proactively groom traffic through optimal routes to provide bandwidth to trouble areas. This approach generates additional revenues through customer retention and a reduction in SLA performance-penalty payouts.

6.2 Remote Testing for Ethernet in the First Mile Deployments Until recently, Ethernet deployment and maintenance were expensive endeavors compared with traditional alternatives; lack of sufficient remote network management solutions meant frequent on-location troubleshooting and maintenance. Probe Probe The recent ratification of the IEEE 802.3ah testing standard on Gigabit Ethernet Ethernet in the first mile offers significant opportunities for Metro Network service provider OPEX reduction and quicker deployment of RMONGigabit Ethernet Ethernet RMON services. This new standard created the operation, administration and maintenance (OAM) sub-layer within the 10/100Base-T 10/100Base-T Ethernet/data-link layer of the Open Systems Interconnection Agent Agent (OSI) Reference Model (see Figure 6.3).

Figure 6.2 — Ethernet traffic monitoring using RMON-compliant network elements and external probes

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Test solutions based on the 802.3ah guidelines address all of the key challenges Application commonly encountered with Ethernet service deployment: reliability, performance, QoS Presentation assurance and network troubleshooting. Session LLC — Logical Link Control Key to the standard are specifications for remote loopback testing to customer Transport OAM — 802.3ah Standard for Ethernet premises. This single-ended testing technique permits proactive network management Network MPMC — Multipoint MAC Control and speeds up restoration of failed services. In addition to loopback testing, 802.3ah Data Link MAC — Media Access Control also provides guidelines for remote failure and event notification, link-monitoring Physical statistics, diagnostics, as well as the ability to collect historical performance parameters from 802.3ah-compliant elements. Because this standard emulates Figure 6.3 — Open Systems Interconnection (OSI) Referencecommon Model, DS1/3 access maintenance practices, 802.3ah management solutions are showing 802.3ah OAM sub-layer in data-link layer easily integrated into existing operations. As the 802.3ah standard is increasingly adopted by system, switch and equipment suppliers, remote testing and monitoring deployment is becoming straightforward and cost-effective. 6.2.1 Access Line Management Using the 802.3ah Standard Remote testing with 802.3ah involves three key elements: • A demarcation device located between the provider and customer networks • A remote test-head capable of advanced performance evaluation and commissioning functions • Management software capable of identifying and cataloging demarcation devices and their location to simplify test access

Figure 6.4 — An Ethernet NIU made by ADC (customer and provider side)

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6.2.2 Demarcation Devices The most common demarcation device is a network interface unit (NIU), which marks the hand-off between client and provider.

Ethernet Layer 2 switches with 802.3ah compatibility may also be used as demarcation devices in some installations, but this is

10/100/1000 Mb/s 10/100/1000 Mb/s impractical if a single switch serves multiple clients (as in an office Metro Link Ethernet LinkCustomer Provided Provider Enterprise tower) or if the switch is owned by the customer. As low-cost Network NIU Switch X-Based-TXSwitch X-Based-SX or LX devices, NIUs are most often the service providers’ best choice for UTP Copper Fiber demarcation. A typical NIU installation is shown in Figure 6.5.

Provider Customer Several NIUs can be connected to a single, carrier-supplied switch Network Network to provide separate demarcations when there are multiple customers connected to a single access link. Demarcation NIUs are often combined with media converters for optical-to-electrical Point conversion between the fiber access line and the copper-based Ethernet commonly used in enterprise environments. Advanced NIUs Figure 6.5 — Typical NIU installation on an Ethernet access line can also perform rate conversion with bandwidth provisioning, allowing providers to remotely alter customer bandwidth on demand. 802.3ah-compliant units can be remotely queried for usage 10 Mb/s Customer NIU information and link-performance statistics, and they will broadcast 1 link failures and events to network management systems. GigE Carrier 100 Mb/s 6.2.3 Ethernet Test-Heads Access Link Customer Provided NIU Switch 2 An Ethernet tester is required for remote 802.3ah link testing. 200 Mb/s Compliant test sets can activate the loopback mode in the NIU, Customer allowing advanced performance and troubleshooting tests to be NIU 3

Demarcation Point

Figure 6.6 — Typical NIU installation with multiple customers on a single access link

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conducted from a central office or other remote location. Two common examples are illustrated in Figure 6.7 and Figure 6.8. Tests commonly performed NOC Ethernet Tester Remote include RFC 2544-compliant performance analysis (throughput, latency, frame Management loss, burst tolerance), BERT and application-specific tests such as packet jitter for VoIP and other delay-sensitive applications. When customers report a problem with an Ethernet service, the cause is Metro Network often related to events or constraints within the customer’s network. Ethernet SONET/SDH/DWDM Remote testing with an NIU allows service providers to quickly segment the Switch network up to the customer premises and subsequently determine if a network issue is within the access line (service provider’s responsibility) NIU Customer or related to customer-side problems (no further support required). Premises This technique significantly reduces truck-rolls to customer premises, decreases troubleshooting time and results in faster service restoration. Figure 6.7 — Remote troubleshooting of performance on a link from a central office with customer-site NIU in loopback mode Remote testing can also be used for commissioning, monitoring and SLA management. Remote bandwidth provisioning is a typical example of the advantages of an 802.3ah-based Ethernet access network. When a customer requests additional bandwidth on their access link, the related NIU Customer is remotely accessed by the provider and a message is sent to immediately Premises 2 increase the throughput available to the customer. The NIU is then put into Ethernet Tester loopback mode and remote Ethernet performance tests are conducted to ensure that the expected bandwidth is available. A series of tests are then performed to ensure that revised SLA parameters will be met under various Metro Network network conditions. With the new bandwidth assured and commissioned, the Ethernet SONET/SDH/DWDM Switch NIU is returned to pass-through mode and the customer’s traffic passes over the upgraded link.

NIU Customer Premises 1 (under test)

Figure 6.8 — In a virtual private LAN a portable Ethernet tester can be used to test from one customer location to a second site where an NIU is installed

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6.2.4 Management Software Database Customer NIU If a large number of NIUs are deployed in a provider’s network, NOC A 1 management software that can actively catalog their location and Remote B 3 C 2 status in order to facilitate remote testing operations. Automated Management Central Office Ethernet tester discovery schemes identify active NIUs in real time and retrieve With NIU discoverycustomer-related information stored in the units. Interoperability between this database and the Ethernet test set allows for quick Customer loopback activation to any customer on the network. B

NIU 2 Metro Network SONET/SDH/DWDM

NIU 1 NIU 3

Customer Customer A B

Figure 6.9 — Automatic NIU discovery facilitates remote testing operations

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7. Glossary A B

Adapter: Also known as a network interface card (NIC). An Backbone:adapter is Part of the network that joins several local-area networks, a circuit board installed in a computing device to connecteither it toinside a a building or across a city or country. This is achieved network. The adapter or NIC performs the hardware functionsthrough that are a cable connection between telecommunication or wiring required to provide a computing device with physical communicationclosets, floor distribution terminals or entrance facilities. In star networks, capabilities. the backbone cable interconnects hubs and similar devices, as opposed to cables running between hub and station. The backbone is the part of Address Resolution Protocol (ARP): A network-layer protocolthe usedcommunications in network that carries the heaviest traffic. TCP/IP transmission. ARP is used by end stations to determine the physical address of other stations on the same LAN. Backoff Delay: In Ethernet transmission, the backoff delay is the length of time that a station waits before retransmitting a frame, after a data Asynchronous: Said of transmission in which sending andcollision receiving is detected. This operation applies to carrier-sense multiple- devices are not synchronized. Data division is indicated by accessdata itself, networks with collision detect (CSMA/CD; see separate entry). which carries these signals. Baseband: A transmission method in which one single digital signal Asynchronous Transfer Mode (ATM): A data networkinguses protocol an entire bandwidth. The unmodulated signal is sent directly over used for high-bandwidth, low-delay, connection-oriented, packet-likethe transmission medium. Baseband is simpler, cheaper and less switching and multiplexing. sophisticated than broadband. All Ethernet media types are baseband Auto-Negotiation: Algorithm allowing two devices (at each endexcept of a link)for 10Broad36, which is broadband. to negotiate common data service functions (i.e., transmission rate, half vs. full duplex, etc.)

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Bandwidth: The range of frequencies required for proper transmission Broadband: A transmission medium whose bandwidth capacity is of a signal. Bandwidth represents the amount of data that can be sufficient to carry multiple voice, video or data channels simultaneously. transmitted through a communications channel in a fixed amount of Each channel is modulated to a different frequency bandwidth and time. For digital devices, it is usually expressed in bits (or bytes) per occupies a different place on the transmission medium; the signals are second, whereas for analog devices, it is expressed in cycles per then demodulated to their original frequency at the receiving end. second, or in hertz (Hz). The greater the bandwidth, the greater the 10Broad36 is the only broadband Ethernet media type. All other information-carrying capacity and the faster the speed. A continuous Ethernet media types are considered baseband. frequency range starting from zero is said to be baseband, while a Broadcast: The act of sending a frame to all network stations. Also range starting substantially above zero is considered broadband. describes the class of media (designed especially for CSMA/CD Bit: One binary digit Ethernet) in which all stations are capable of receiving a signal transmitted by any other station. Bit Error Rate (BER): A measure of data integrity referring to the number of digital highs that are interpreted as lows (and vice versa), Broadcast Address: A multicast address that identifies all the stations divided by the total number of bits received. The BER ratio is often on a network. expressed as a negative power of ten. Broadcast Domain: A restricted area that allows all connected Bridge: Specified in IEEE 802.1D standard, a bridge is a device that devices to transmit and receive information from each other. The connects two or more networks at the data-link layer (Layer 2). Bridges devices are interconnected through bridges, allowing them to share the are not part of the collision domain; i.e., they may be used to split a transmission medium and, consequently, the data. network into multiple collision domains. Byte: A group of 8 bits. Also known as an octet.

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C Collision: A meeting of two or more data signals. A collision occurs when more than one station transmits signals concurrently over a Carrier Sense: A method of detecting the presence of signal activity CSMA/CD (Ethernet) transmission medium. on a common channel. With Ethernet, a method of detecting whether another station is transmitting. Collision Detect (CD): A method to detects two or more simultaneous transmissions on a common signal channel. Carrier-Sense Multiple-Access with Collision Detection (CSMA/CD): A network access method used by Ethernet in which a station listens Collision Domain: A single CSMA/CD network, consisting of an area for traffic before transmitting. If two stations transmit simultaneously, a in a network where data packets can collide. Collisions occur when collision is detected and both stations wait a brief time before two or more Ethernet stations are within the same collision domain and attempting to transmit again. So called because it a) allows multiple both transmit at the same time. Ethernet stations separated by a stations to access the broadcast channel at will, b) avoids contention repeater are in the same collision domain, while stations separated by via carrier sense and deference, and c) resolves contention via collision a bridge are in different collision domains. The concept of collision detection and retransmission. domain applies only to half-duplex Ethernet. Collisions do not occur in full-duplex Ethernet configurations. Channel: A logical medium in a communication system over which data is transmitted. Concentrator: LAN device allowing multiple network devices to be connected to the LAN cabling system through a central point. Chromatic Dispersion (CD): Phenomenon caused by the wavelength Sometimes called a hub. dependence of group velocity in an optical fiber. Since any practical light source has a certain spectral width, CD results in pulse Contention: Interference between colliding transmissions (see broadening. collisions). Normal part of Ethernet CSMA/CD protocol. Coarse Wavelength-Division Multiplexing (CWDM): Method of Crossover Cable: A twisted-pair patch cable, wired to route the combining multiple signals on laser beams at various wavelengths for transmitted signals from one element to the received signals of another transmission along fiber-optic cables. CWDM uses fewer channels element, and vice versa. than DWDM, but more than standard WDM.

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Cyclic Redundancy Check (CRC): Error-checking technique used to ensure the accuracy digital-code transmission over a communications channel. The transmitted signals are divided into predetermined lengths which, used as dividends, are divided by a Destination MAC Address: Address identifying the station or stations fixed divisor. The remainder of the calculation is appended onto and on a LAN to which a frame is being sent. sent with the message. At the receiving end, the computer recalculates the remainder. If it does not match the transmitted DIX: Acronym identifying the three companies that released the original remainder, an error is detected. Ethernet specification in 1980: Digital, Intel, and Xerox.

Duplex: Circuit used to transmit signals simultaneously in both directions.

D E

Data-Link Layer: Layer 2 of the OSI reference model. This layerElectronic takes Industry Association (EIA): An association of data from the network layer and passes it on to the physical layermanufacturers (layer and users that establishes standards and publishes test 1). The data-link layer is responsible for transmission and receptionmethodologies. of Formerly known as RMA or RETMA. Ethernet frames, 48-bit addressing, etc. It includes both the media access control (MAC) and logical link control (LLC) layers. Ethernet Version 2: The original Ethernet specification produced by Digital, Intel, and Xerox (DIX) that served as the basis for the IEEE Dense Wavelength-Division Multiplexing (DWDM): A technology802.3 Ethernet standard. that enables a single optical fiber to carry multiple data channels (or wavelengths). Commercial DWDM systems can have as manyExcessive as 160 Collision Error: Error that causes frame loss. This type of separate channels. error occurs when a station receives 16 consecutive collisions while attempting to transmit a single frame; then the frame is dropped due to the excessive collisions.

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F Forwarding: The process of moving frames from one port to another in a bridge or switch. Fast Ethernet: Ethernet standard supporting 100 Mb/s operation. Forwarding Rate: The maximum number of frames per second that can Fast Link Pulse (FLP): A link pulse that encodes information used in be forwarded by a bridge or switch, assuming no congestion at the the Auto-Negotiation protocol. Fast link pulses consist of bursts of the output port. normal link pulses originally used in 10Base-T. Frame: The sequence of bits that form the unit of data transmission at Fiber-to-the-x (FTTx): The x in fiber-to-the-x is a variable indicating the LAN data-link layer or medium access-control layer. In Ethernet, a the point at which the fiber in a network stops and copper frame consists of the sequence of bits transmitted by a station from the (coaxial or twisted-pair) cabling takes over; e.g., fiber-to-the-home, preamble through the frame check sequence. Also known as a packet. fiber-to-the-curb, etc. The further the fiber goes, the wider the bandwidth, the quicker the speed, and the more applications and Frame Bursting: A technique permitted only in half-duplex Gigabit services can be offered. Ethernet networks. Frame bursting optionally allows a station to transmit a series of frames without relinquishing control of the Filtering: Process that uses bridges and switches to help reduce the transmission medium. It improves the performance of Gigabit Ethernet level of congestion on a LAN. A filtering bridge or switch forwards a when transmitting short frames. packet from one LAN segment to another only as required. Packets that are not forwarded by a bridge or switch are said to be filtered. Frame Check Sequence (FCS): An encoded value appended to each frame by a transmitting station to allow transmission errors to be Filtering Rate: The maximum number of frames per second that detected by the receiving station. Implemented as a 32-bit cyclic a bridge or switch can continuously receive, parse, and make redundancy check (CRC) code. a forwarding decision on. Full-Duplex: Data transmission over a circuit capable of transmitting in Flow Control: The process of controlling data transmission at the both directions simultaneously. For Ethernet, full-duplex operation was sender to avoid overfilling buffers and loss of data at the receiver. defined in the IEEE 802.3x standard.

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G H

Gb/s or Gbps: Gigabits per second. One Gb/s equals one Half-Duplex:billion bits Data transmission over a circuit capable of transmitting per second. in either direction, but not simultaneously. For Ethernet, the CSMA/CD method is a half-duplex protocol. Generic Framing Procedure (GFP): Traffic adaptation protocol providing convergence between packet-switched and transmissionHeadend: The equipment in a cable system which receives the various networks. GFP elegantly maps packet-based protocolsprogram such as source signals, processes them, and retransmits them to Ethernet, Fibre Channel, FICON, ESCON, and various formssubscribers. of digital video into SONET/SDH, typically using virtual concatenation to Hub: provide right-sized pipes for data services. A device at the center of a star topology network. Hubs can be active (where they repeat signals set to them) or passive (where they Giants: Giants are frames that are longer than the maximumdo Ethernet not repeat but merely split signals sent through them). Hub may size (giant frames > 1518/1522 bytes with bad FCS, whereasrefer oversize to a repeater, bridge, switch, router, or any combination of these. frames > 1518/1522 bytes with good FCS). Giant packets usually occur when you have a jabbering node on your network; i.e., a node that is continuously transmitting, or transmitting improperly for short bursts – probably due to a bad transmitter on the NIC. Giants can also be caused by packets being corrupted as they are transmitted, either by the addition of garbage signals, or by the corruption of theI bits that indicate frame size. Gigabit Ethernet (GigE): A version of Ethernet that operatesIEEE: at 1 Gb/s Institute of Electrical and Electronics Engineers. A professional (1000 Mb/s). organization and standards body. The IEEE Project 802 is the group within IEEE responsible for LAN technology standards. Group Address: An address specifying a group of logically related stations on a network. Also called a multicast address. IEEE 802.1: The IEEE standards committee defining high-level interfaces, network management, internetworking, and other issues common across LAN technologies.

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IEEE 802.2: The IEEE standards committee defining logicalJ link control (LLC). IEEE 802.3: The IEEE standards committee defining EthernetJabber: networks. Term used with Ethernet to describe the act of continuously sending data. A jabbering station is one whose circuitry or logic has failed, Individual Address: A MAC address that identifies a singleand station. which has locked up a network channel with its incessant transmission. The low-order bit of the first byte (first bit transmitted) of an individual Jitter: The slight movement of a transmission signal in time or phase address is always 0. that can introduce errors and loss of synchronization. More jitter will be Intelligent Hubs: Wiring concentrators that can be monitoredencountered and with longer cables, cables with higher attenuation, and managed by network operators. signals at higher data rates. Also, called phase jitter, timing distortion, or intersymbol interference. Inter-Frame Gap (IFG): The delay or time gap between frames. Also called inter-packet gap. Internet Protocol (IP): Method or protocol by which data is sent from one computer to another on the Internet. Each computer on the Internet has at least one IP address that uniquely identifies it fromL all other computers on the Internet. Because of these standardized IP addresses, the gateway receiving the data can keep track of,LAN recognize Adapter: see Local-Area Network and Network Interface Card and route messages appropriately. Link: A transmission path between two points. The link does not include Inter-Packet Gap (IPG): The delay or time gap between packets.any of Alsothe terminal equipment, work-area cables, or equipment cables. called inter-frame gap. Link Aggregation: Link Aggregation provides for increased link availability and bandwidth between two Ethernet stations by allowing multiple physical links to be combined to operate as a single logical link. Defined by the 802.3ad Working Group. Also called trunking.

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Link Segment: In Ethernet, a point-to-point segment that connects two and only two transceivers at its endpoints. Local-Area Network (LAN): A term used to refer to a form of networking technology that implements a high-speed, relatively short Mb/s or Mbps: Megabits per second. One Mb/s equals one million distance form of computer communications. Ethernet is one type of LAN. bits per second. Logical Link Control (LLC): A protocol defined in the IEEE 802.2 Media: Wire, cable, or conductors used for transmission of signals. standard for data-link-level transmission control. It is the upper sublayer of the IEEE Layer 2 (OSI) protocol that complements the MAC Medium Access Control (MAC): A mechanism operating at the data protocol. LLC is independent of any specific LAN technology. link layer of local-area networks which manages access to the communications channel (medium). It forms the lower layer of the IEEE data link layer (OSI layer 2) which complements the Logical Link Control (LLC). MAC is a media-specific protocol within the IEEE 802 specifications.

M Medium-Dependent Interface (MDI): The connector used to make the mechanical and electrical interface between a and a media segment. An 8-pin RJ-45 connector is the MDI for the 10Base-T, MAC Address: The 48-bit address used in Ethernet to identify a 100Base-TX, 100Base-T2, 100Base-T4, and 1000Base-T media systems. station. Generally a unique number that is programmed into a device at time of manufacture. Media-Independent Interface (MII): Used with 100 Mb/s Ethernet systems to attach MAC level hardware to a variety of physical media MAC Frame: Name for the data unit exchanged between peer Medium systems. Similar to the AUI interface used with 10 Mb/s Ethernet Access Control sublayer entities. Also called simply a "frame". systems. An MII provides a 40-pin connection to outboard transceivers Manageable Hubs: Another definition for intelligent hubs. Each of the (also called PHY devices). ports on the managed hub can be configured, monitored, and enabled or disabled by a network operator from a hub management console.

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Metropolitan-Area Network (MAN): A network, often Oringed in structure, that covers an entire city and its suburbs. Also known as a metro network. Octet: Eight bits (also called "byte") Multicast: An addressing mode in which a given frame is targetedOptical to aTime-Domain Reflectometry (OTDR): A method for group of logically related stations. evaluating optical fiber based on detecting and measuring Multicast Address: An address specifying a group of logicallybackscattered related (reflected) light. Used to measure fiber length and stations on a network. Also called a group address. attenuation, evaluate splice and connector joints, locate faults, and certify cabling systems. Open Systems Interconnection (OSI): A communications reference model developed by the International Standards Organization (ISO) to define all of the services a LAN should provide. This model defines N seven layers, each of which provides a subset of all of the LAN services. This layered approach allows small groups of related services Network Interface Card (NIC): Also known as an adapter. toAn be NIC implemented is in a modular fashion that makes designing network circuit board installed in a computing device to connect it to softwarea network. much more flexible. The NIC or adapter performs the hardware functions that are required to provide a computing device with physical communication capabilities. Node: End point of a network connection. Nodes include any device connected to a network such as file servers, printers, or workstations. N-Way: Name originally used for the Ethernet Auto-Negotiation algorithm.

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P Pause Frames: An optional flow-control technique for full-duplex Ethernet networks. One end station may temporarily stop all traffic from Packet: Bits grouped serially in a defined format, containing the other end station by sending a pause frame. a command or data message sent over a network. Same as a frame. Physical Address: The unique address value associated with a given Packet Jitter: Also known as IP packet delay variation (IPDV). This station on the network. An Ethernet physical address is defined to be variation is defined for a selected pair of packets within the continuous distinct from all other physical addresses on the network. stream of packets going from measurement point 1 (MP1) to Physical Layer: Measurement point 2 (MP2). The IPDV is the difference between the Layer one of the seven-layer ISO Reference Model for one-way delay of the selected packets. Open Systems Interconnection. This layer is responsible for the transmission of signals – electrical, optical, or radio – between Parallel Detection: An auto-negotiation device's means to establish computing machines. links with non-negotiation, fixed-speed devices. Polarization Mode Dispersion: Dispersion of light causing a delay (PON): Network in which fiber-optic cabling between the two principal states of polarization propagating along (instead of copper) brings signals all or most of the way to the end- a fiber or through a device due to the birefringence properties user. It is described as passive because no active equipment of the material. (electrically powered) is required between the central office (or hub) Preamble: A sequence of 62 encoded bits transmitted (by a station) and the customer premises. Depending on where the PON terminates, before each frame to allow for the synchronization of clocks and other the system can be described as an FTTx network, which typically allows physical-layer circuitry at other stations on the channel. a point-to-point or point-to-multipoint connection from the central office to the subscriber’s premises; in a point-to-multipoint architecture, Propagation Delay: The signal transit time through a cable, network a number of subscribers (for example, up to 32) can be connected to segment, or device. just one of the various feeder fibers located in a fiber distribution hub, Protocol: A formal set of rules governing the format, timing, dramatically reducing network installation, management and sequencing and error control of data exchange across a network. maintenance costs. Many protocols may be required and used on a single network.

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R good FCS). In a half-duplex Ethernet environment, runt frames are almost always caused by collisions. If runt frames occur when collisions are not Registered Jack (RJ): A term from the telephone industry, used for high or in a full-duplex Ethernet environment, then they are probably the jacks (connectors) that were registered for use with particular types of result of underruns or bad software on a network interface card. telephone services. Repeater: A device that receives, amplifies (and sometimes reshapes), and retransmits a signal. It is used to boost signal levels and extend the distance a signal can be transmitted. It can connect two or Smore LAN segments and physically extend the distance of a LAN. It immediately copies all bits arriving on each segment to all other segments,Segment: whether On Ethernet, a media segment may be made up of one or or not they are part of a valid frame. more cable sections joined together to produce a continuous cable for carrying Ethernet signals. RJ-45: A USOC code identifying an 8-pin modular plug or jack used with unshielded twisted pair cable. Officially, an RJ-45 connectorShared is Ethernet: a Same as half-duplex (CSMA/CD) Ethernet. telephone connector designed for voice grade circuits only. RJ-45 type Simplex Transmission: Data transmission over a circuit capable of connectors with better signal handling characteristics are called 8-pin transmitting in one preassigned direction only. connectors in most standards documents, though most people continue to use the RJ-45 name for all 8-pin connectors. Slot Time: A key parameter for half-duplex Ethernet network operation. Defined as 512 bit times for Ethernet networks operating below Routers: These are more complex internetworking devices that are 1 Gb/s, and 4096 bit times for Gigabit Ethernet. In order for each also typically more expensive than bridges. They use Network Layer transmitter to reliably detect collisions, the minimum transmission time for Protocol Information within each packet to route it from one LAN to a complete frame must be at least one slot time, whereas the round-trip another. propagation delay (including both logic delays in all electronic Runt Frame: An Ethernet frame that is less than the minimumcomponents length of and the propagation delay in all segments) must be less 64 bytes with bad FCS (whereas undersize frames < 64 thanbytes a withslot time. SNMP: Simple Network Management Protocol

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Spanning Tree: A structure that includes all the bridges and stations Synchronous Optical NETwork (SONET): Standardized by the on an extended LAN in which there is never more than one active path American National Standards Institute (ANSI). A protocol for backbone connecting any two stations. networks, capable of transmitting at extremely high speeds and accommodating gigabit-level bandwidth. Star Topology: A network configuration in which there is a central point to which a group of systems are directly connected. All Time-Domain Reflectometry (TDR): A technique for measuring cable transmissions from one system to another pass through this central lengths by timing the period between a test pulse and the reflection of point. Ethernet 10Base-T is one example of a media system that uses the pulse from an impedance discontinuity on the cable. The returned a star topology. All stations are connected through a central device waveform reveals many undesired cable conditions, including shorts, called a hub. opens, and transmission anomalies due to excessive bends or crushing. The length to any anomaly, including the unterminated cable Station: A unique, addressable device on a network. A station is end, may be computed from the relative time of the wave return and identified by a destination address (DA). nominal velocity of propagation of the pulse through the cable. See Station Address: see MAC Address also Optical Time-Domain Reflectometry. STP: Shielded Twisted Pair Switch: A switch is a multi-port bridge. Each port on the switch is in its own collision domain. Synchronous: Transmission in which the data character and bits are transmitted at a fixed rate with the transmitter and receiver being synchronized. Synchronous Digital Hierarchy (SDH): StandardizedU by the International Telecommunication Union (ITU-TSS). A protocol for transmitting information over optical fiber. Unicast Address: An address that is assigned to uniquely identify a single station on a network. Unshielded Twisted Pair (UTP): Twisted pair cabling that includes no shielding. UTP most often refers to the 100 Ω Category 3, 4, and 5 cables specified in the TIA/EIA 568-A standard.

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V W

Virtual Concatenation (VCAT): Process enabling transport pipesWavelength-Division to be Multiplexing (WDM): Optical transmission "right-sized" for various data payloads by allowing SONET/SDHtechnique that uses different light wavelengths to send data. channels to be multiplexed in arbitrary arrangements. VCATCombination breaks of two or more optical signals for transmission over a down data packets and maps them into the base units of TDMcommon frames. optical path. This data is then grouped in multiple data flows of varying sizeWide-Area to create Network (WAN): A network that links data processing and larger, aggregate payloads optimally sized to match telecomavailable equipment over a larger area than a single work site or SONET/SDH pipe capacity. VCAT is applied at the end-pointsmetropolitan of the area. A WAN usually links cities and is based on X.25 connections, which permits each channel used to be independentlypacket switching. transmitted through a legacy transport network. Virtual LAN: A method in which a port or set of ports in a bridge or switch are grouped together and function as a single "virtual" LAN. (VPN): One or more wide-area network0-9 links over a shared public network, typically over the Internet or an IP backbone from a network service provider (NSP), that simulates10 GigE: the 10 Gigabit Ethernet behavior of dedicated WAN links over leased lines. 4B/5B Code: Scheme used to encode data for transmission in which Voice-over-Internet-Protocol (VoIP): Refers to communications4-bit binary data values are encoded into 5-bit symbols for transmission services—voice, facsimile and/or voice-messaging applications—thatacross the network media. 4B/5B is used with Ethernet 100Base-TX are transported via the Internet,rather than the public switchedand telephone 100-Base-FX media systems. network. In an Internet-based telephone call, the voice signals8B6T: Signalare encoding method used with the 100Base-T4 Ethernet converted to digital format and compressed/translated intoInternetmedia system. protocol (IP) packets for transmission over the Internet; the process is reversed at the receiving end. 8B/10B Code: Scheme used to encode data for transmission in which 8-bit binary data values are encoded into 10-bit symbols for transmission across the network media. 8B/10B is used with 1000Base-X Gigabit Ethernet media systems and 10G Base-LX4.

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LLC Logical Link Control (see entry in glossary) Acronyms Index

LSP

Label-Switched Path

LSR

Label-Switching Router

M

MAC

Medium Access Control (see entry in glossary)

MAN

Metropolitan-Area Network (see entry in glossary)

Mb/s

Megabits per second. One Mb/s equals one million bits per second. MDI

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A CoS Class of Service

ADM Add/Drop Multiplexer CRC Cyclic Redundancy Check (see entry in glossary) CSMA/CD Carrier-Sense Multiple-Access with Collision Detect APS Automatic Protection Switching 9. Acronyms Index (see entry in glossary) ARCNET Attached Resource Computer Network CRC Cyclic Redundancy Check (see entry in glossary) ARP Address Resolution Protocol (see entry in glossary) CWDM Coarse Wavelength-Division Multiplexing ATM Asynchronous Transfer Mode (see entry in glossary) (see entry in glossary) B D BER Bit Error Rate (see entry in glossary) DIX Digital, Intel, and Xerox (the three companies that BERT Bit-Error-Rate Testing released the original Ethernet specification in 1980)

b Bit (one binary digit) DUT Device Under Test DWDM Dense Wavelength-Division Multiplexing B Byte (group of 8 bits) (see entry in glossary) C E CD 1. Chromatic Dispersion (see entry in glossary) 2. Collision Detect (see entry in glossary) EIA 1. Electronic Industry Association (formerly RMA or RETMA). CE Customer Edge 2. Ethernet Internet Access CIR Committed Information Rate E-LAN Ethernet LAN

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E-Line Ethernet Line G EMS Element Managing System Gb/s or Gigabits per second. One Gb/s equals one billion bits Gbps per second. EPL Ethernet Private Line

EPLan Ethernet Private LAN GFP Generic Framing Procedure (see entry in glossary)

ESCON Enterprise System Connectivity GigE Gigabit Ethernet (operates at 1 Gb/s; i.e., 1000 Mb/s).

EVC Ethernet Virtual Connection H

EVPL Ethernet Virtual Private Line HFC Hybrid Fiber Coax EVPLan Ethernet Virtual Private LAN I F IEEE Institute of Electrical and Electronics Engineers

FCS Frame Check Sequence (see entry in glossary)IFG Inter-Frame Gap (see entry in glossary) IP Internet Protocol (see entry in glossary) FDDI Fiber-Distributed Data Interface IPG Inter-Packet Gap (see entry in glossary) FDX Full-Duplex Ethernet L FSO Free-Space Optics LAN Local-Area Network (see entry in glossary) FTTx Fiber-to-the-Building, Fiber-to-the-Home, LLC Logical Link Control (see entry in glossary) Fiber-to-the-Curb, etc. LSP Label-Switched Path LSR Label-Switching Router

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M O MAC Medium Access Control (see entry in glossary)OAM&P Operation, Administration, Maintenance and Provisioning MAN Metropolitan-Area Network (see entry in glossary)OTDR 1. Optical Time-Domain Reflectometry (see entry in glossary) Mb/s or Megabits per second. One Mb/s equals one million bits 2. Optical Time-Domain Reflectometer Mbps per second.

MDI Medium-Dependent Interface (see entry in glossary)OSI Open Systems Interconnection (see entry in glossary) P MII Media-Independent Interface (see entry in glossary) PHB Per-Hop Behaviour MEF Metro Ethernet Forum PMD Polarization Mode Dispersion (see entry in glossary) MEN Metropolitan Ethernet Network PON Passive Optical Network (see entry in glossary) MON Metropolitan Optical Network POTS Plain Old Telephone System

MPLS Multiprotocol Label Switching PRBS Pseudo-Random Binary Sequence

MSPP Multiservice Provisioning Platform PVC Permanent Virtual Circuit

MTTR Mean Time to Repair Q N QoS Quality of Service NIC Network Interface Card (see entry in glossary)

NIU Network Interface Unit

NUT Network Under Test

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R U RJ Registered Jack (see entry in glossary) UTP Unshielded Twisted Pair (see entry in glossary) RMON Remote Monitoring V

RPR Resilient Packet Ring VCAT Virtual Concatenation

S VLAN Virtual LAN (see entry in glossary)

SDH Synchronous Digital Hierarchy (see entry in glossary)VoIP Voice-over-Internet-Protocol (see entry in glossary)

SLA Service-Level Agreement VPLS Virtual Private LAN Service

SNMP Simple Network Management Protocol VPN Virtual Private Network (see entry in glossary)

SONET Synchronous Optical NETwork (see entry in glossary)VPSN Virtual Private Switched Network STP Shielded Twisted Pair W T WAN Wide-Area Network (see entry in glossary) TDR Time-Domain Reflectometry (see entry in glossary)WDM Wavelength-Division Multiplexing (see entry in glossary)

TE Traffic Engineering

TLS Transparent LAN Service

ToS Type of Service

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Notes

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Acknowledgements

This guide would not have been possible without the collaboration and teamwork of EXFO staff; particularly, the technical expertise of Mr. Bruno Giguère, B.Eng., Ethernet Product Manager; Mr. Matthew Demyttenaere, B.Eng., Application Engineer; Mr. Andre Leroux, M.Eng., Systems Engineer; and Mr. Scott Sumner, M.Eng., Strategic Marketing Manager.

No part of this guide may be reproduced in any form or by any means without the prior written permission of EXFO.

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