White Paper

Gigabit Ethernet and ATM A Technology Perspective

Bursty, high-bandwidth applications are driving

the need for similarly high-bandwidth campus

backbone infrastructures. Today, there are two choices

for the high-speed campus backbone: ATM or Gigabit

Ethernet. For many reasons, business and technical,

Gigabit Ethernet is selected as the technology of choice.

This paper briefly presents, from a technical perspective,

why Gigabit Ethernet is favored for most enterprise LANs. In the past, most campuses use shared-media backbones — such as 16/32 Mbps Token-Ring and 100 Mbps FDDI — that are only slightly higher in speed than the LANs and end stations they interconnect. This has caused severe congestion in the campus backbones when these backbones interconnect a number of access LANs.

A high capacity, high performance, and highly resilient backbone is needed-one that can be scaled as end stations grow in number or demand more bandwidth. Also needed is the ability to support differentiated service levels (Quality of Service or QoS), so that high priority, time-sensitive, and mission-critical applications can share the same network infrastructure as those that require only best-effort service.

2 Gigabit Ethernet and ATM: A Technology Perspective White Paper Until recently, Asynchronous Transfer Interface, and Multiprotocol over ATM). Which is a “better” technology is no Mode (ATM) was the only switching This additional complexity is required in longer a subject of heated industry debate technology able to deliver high capacity order to adapt ATM to the connectionless, — Gigabit Ethernet is an appropriate and scalable bandwidth, with the promise frame-based world of the campus LAN. choice for most campus backbones. of end-to-end Quality of Service. ATM Meanwhile, the very successful Fast Many business users have chosen Gigabit offered seamless integration from the Ethernet experience spurred the development Ethernet as the backbone technology desktop, across the campus, and over the of Gigabit Ethernet standards. Within for their campus networks. An Infonetics metropolitan/wide area network. It was two years of their conception (June Research survey (March 1999) records thought that users would massively 1996), Gigabit Ethernet over fiber that 91 percent of respondents believe deploy connection-oriented, cell-based (1000BASE-X) and copper (1000BASE-T) that Gigabit Ethernet is suitable for LAN ATM to the desktop to enable new native standards were approved, developed, and backbone connection, compared with 66 ATM applications to leverage ATM’s rich in operation. Gigabit Ethernet not only percent for ATM. ATM continues to be a functionality (such as QoS). However, provides a massive scaling of bandwidth good option where its unique, rich, and this did not come to pass. The Internet to 1000 Mbps (1 Gbps), but also shares a complex functionality can be exploited Protocol (IP), aided and abetted by the natural affinity with the vast installed base by its deployment, most commonly in exploding growth of the Internet, rode of Ethernet and Fast Ethernet campus metropolitan and wide area networks. roughshod over ATM deployment and LANs running IP applications. Whether Gigabit Ethernet or ATM marched relentlessly to world dominance. Enhanced by additional protocols already is deployed as the campus backbone When no other gigabit technology existed, common to Ethernet (such as IEEE technology of choice, the ultimate ATM provided much needed relief as a 802.1Q Virtual LAN tagging, IEEE decision is one of economics and sound high bandwidth backbone to interconnect 802.1p prioritization, IETF business sense, rather than pure technical numerous connectionless, frame-based Differentiated Services, and Common considerations. campus LANs. But with the massive Open Policy Services), Gigabit Ethernet is The next two sections provide a brief proliferation of IP applications, new now able to provide the differential qualities description of each technology. native ATM applications did not appear. of service that previously only ATM could Even 25 Mbps and 155 Mbps ATM provide. One key difference with Gigabit Asynchronous Transfer to the desktop did not appeal to the Ethernet is that additional functionality Mode (ATM) vast majority of users, because of their can be incrementally added in a Asynchronous Transfer Mode (ATM) complexity, small bandwidth increase, non-disruptive way as required, compared has been used as a campus backbone and high costs when compared with the with the rather revolutionary approach of technology since its introduction in the very simple and inexpensive 100 Mbps ATM. Further developments in bandwidth early 1990s. ATM is specifically designed Fast Ethernet. and distance scalability will see 10 Gbps to transport multiple traffic types — On the other hand, Fast Ethernet, with its Ethernet over local (10G-BASE-T) and data, voice and video, real-time or auto-sensing, auto-negotiation capabilities, wide area (10G-BASE-WX) networks. non-real-time — with inherent QoS integrated seamlessly with the millions Thus, the promise of end-to-end seamless for each traffic category. of installed 10 Mbps Ethernet clients integration, once only the province of To enable this and other capabilities, and servers. Although relatively simple ATM, will be possible with Ethernet additional functions and protocols are and elegant in concept, the actual and all its derivations. added to the basic ATM technology. implementation of ATM is complicated Today, there are two technology choices Private Network Node Interface (PNNI) by a multitude of protocol standards for the high-speed campus backbone: provides OSPF-like functions to signal and specifications (for instance, LAN ATM and Gigabit Ethernet. While both and route QoS requests through a Emulation, Private Network Node seek to provide high bandwidth and hierarchical ATM network. Multiprotocol differentiated QoS within enterprise LANs, these are very different technologies.

Gigabit Ethernet and ATM: A Technology Perspective White Paper 3 The main reason for this success is that Gigabit Ethernet provides the functionality that meets today’s immediate needs at an Interface, LAN Emulation Network- affordable price, without undue complexity Network Interface, and a multitude of and cost. Gigabit Ethernet is complemented additional protocols, signaling controls, by a superset of functions and capabilities and connections (point-to-point, point- that can be added as needed, with the to-multipoint, multipoint-to-point, and promise of further functional enhancements multipoint-to-multipoint). and bandwidth scalability (for example, over ATM (MPOA) allows the establish- IEEE 802.3ad Link Aggregation, and 10 Until recently, ATM was the only ment of short-cut routes between Gbps Ethernet) in the near future. Thus, technology able to promise the benefits communicating end systems on different Gigabit Ethernet provides a simple of QoS from the desktop, across the LAN subnets, bypassing the performance scaling-up in bandwidth from the 10/100 and campus, and right across the world. bottlenecks of intervening routers. There Mbps Ethernet and Fast Ethernet LANs However, the deployment of ATM to the have been and continue to be enhancements that are already massively deployed. in the areas of physical connectivity, desktop, or even in the campus backbone Simply put, Gigabit Ethernet is Ethernet, bandwidth scalability, signaling, routing LANs, has not been as widespread as but 100 times faster! and addressing, security, and management. predicted. Nor have there been many native applications available or able to Since Gigabit Ethernet uses the same While rich in features, this functionality benefit from the inherent QoS capabilities frame format as today’s legacy installed has come with a fairly heavy price tag in provided by an end-to-end ATM solution. LANs, it does not need the segmentation complexity and cost. To provide backbone Thus, the benefits of end-to-end QoS and reassembly function that ATM connectivity for today’s legacy access have been more imagined than realized. requires to provide cell-to-frame and networks, ATM — a connection-oriented frame-to-cell transitions. As a connection- technology — has to emulate capabilities Gigabit Ethernet as the campus backbone less technology, Gigabit Ethernet does not inherently available in the predominantly technology of choice is now surpassing require the added complexity of signaling connectionless Ethernet LANs, including ATM. This is due to the complexity and control protocols and connections broadcast, multicast, and unicast and the much higher pricing of ATM that ATM requires. Finally, because QoS- transmissions. ATM must also manipulate components such as network interface capable desktops are not readily available, the predominantly frame-based traffic on cards, switches, system software, Gigabit Ethernet is no less deficient in these LANs, segmenting all frames into cells management software, troubleshooting providing QoS. New methods have been prior to transport, and then reassembling tools, and staff skill sets. There are also developed to incrementally deliver QoS cells into frames prior to final delivery. interoperability issues, and a lack of and other needed capabilities that lend Many of the complexity and interoperability suitable exploiters of ATM technology. themselves to much more pragmatic and issues are the result of this LAN cost-effective adoption and deployment. Emulation, as well as the need to provide Gigabit Ethernet resiliency in these emulated LANs. There Today, Gigabit Ethernet is a very viable To complement the high-bandwidth are many components required to make and attractive solution as a campus capacity of Gigabit Ethernet as a campus this workable; these include the LAN backbone LAN infrastructure. Although backbone technology, higher-layer functions Emulation Configuration Server(s), relatively new, Gigabit Ethernet is derived and protocols are available, or are being LAN Emulation Servers, Broadcast and from a simple technology, and a large and defined by standards bodies such as the Unknown Servers, Selective Multicast well-tested Ethernet and Fast Ethernet Institute of Electrical and Electronics Servers, Server Cache Synchronization installed base. Since its introduction, Engineers (IEEE) and the Internet Protocol, LAN Emulation User Network Gigabit Ethernet has been vigorously adopted as a campus backbone technology, with possible use as a high-capacity connection for high-performance servers and workstations to the backbone switches.

4 Gigabit Ethernet and ATM: A Technology Perspective White Paper Engineering Task Force (IETF). Many of these capabilities recognize the desire for convergence upon the ubiquitous Internet Protocol (IP). IP applications and transport Technological Aspects protocols are being enhanced or developed Aspects of a technology are important to address the needs of high speed, multi- because they must meet some minimum media networking that benefit Gigabit requirements to be acceptable to users. Ethernet. The Differentiated Services Value-added capabilities will be used (DiffServ) standard provides differential where desirable or affordable. If these QoS that can be deployed from the additional capabilities are not used, Quality of Service Ethernet and Fast Ethernet desktops whether for reasons of complexity or lack Until recently, Quality of Service (QoS) across the Gigabit Ethernet campus of “exploiters” of those capabilities, then was a key differentiator between ATM backbones. The use of IEEE 802.1Q users are paying for them for no reason and Gigabit Ethernet. ATM was the only VLAN Tagging and 802.1p User Priority (a common example is that many of the technology that promised QoS for voice, settings allow different traffic types to advanced features of a VCR are rarely video, and data traffic. The Internet be accorded the appropriate forwarding exploited by most users). If features are Engineering Task Force (IETF) and priority and service. too expensive, relative to the benefits that various vendors have since developed When combined with policy-enabled can be derived, then the technology is protocol specifications and standards that networks, DiffServ provides powerful, not likely to find widespread acceptance. enhance the frame-switched world with secure, and flexible QoS capabilities for Technology choices are ultimately QoS and QoS-like capabilities. These Gigabit Ethernet campus LANs by using business decisions. efforts are accelerating and, in certain cases, have evolved for use in both the protocols such as Common Open Policy The fundamental requirements for LAN ATM and frame-based worlds. Services (COPS), Lightweight Directory campus networks are very much different Access Protocol (LDAP), Dynamic Host from those of the WAN. It is thus The difference between ATM and Gigabit Configuration Protocol (DHCP), and necessary to identify the minimum Ethernet in the delivery of QoS is that Domain Name System (DNS). Further requirements of a network, as well as ATM is connection-oriented, whereas developments, such as Resource the value-added capabilities that are Ethernet is connectionless. With ATM, Reservation Protocol, multicasting, “nice to have”. QoS is requested via signaling before real-time multimedia, audio and video communication can begin. The connection In the sections that follow, various terms transport, and IP telephony, will add is only accepted if it is without detriment are used with the following meanings: functionality to a Gigabit Ethernet campus, to existing connections (especially for using a gradual and manageable approach • “Ethernet” is used to refer to all current reserved bandwidth applications). when users need these functions. variations of the Ethernet technology: Network resources are then reserved as traditional 10 Mbps Ethernet, 100 There are major technical differences required, and the accepted QoS service is Mbps Fast Ethernet, and 1000 Mbps between Gigabit Ethernet and ATM. A guaranteed to be delivered “end-to-end.” Gigabit Ethernet. companion white paper, Gigabit Ethernet By contrast, QoS for Ethernet is mainly and ATM: A Business Perspective, provides a • “Frame” and “packet” are used delivered hop-by-hop, with standards comparative view of the two technologies interchangeably, although this is not in progress for signaling, connection from a managerial perspective. absolutely correct from a technical admission control, and resource reservation. purist point of view.

Gigabit Ethernet and ATM: A Technology Perspective White Paper 5 services to already established connections. Once established, traffic from the end systems are policed and shaped for

• nrt-VBR: Non-real-time Variable Bit conformance with the agreed traffic Rate, for applications with similar contract. Flow and congestion are needs as rt-VBR, requiring low cell loss, managed in order to ensure the proper varying amounts of bandwidth, and QoS delivery. with no critical delay and delay variation requirements. Example Gigabit Ethernet QoS ATM QoS applications include non-real-time One simple strategy for solving the From its inception, ATM has been voice and video. backbone congestion problem is to over- designed with QoS for voice, video provision bandwidth in the backbone. • ABR: Available Bit Rate, for applications and data applications. Each of these This is especially attractive if the initial requiring low cell loss, guaranteed has different timing bounds, delay, investment is relatively inexpensive and minimum and maximum bandwidths, delay variation sensitivities (jitter), the ongoing maintenance is virtually and with no critical delay or delay and bandwidth requirements. ‘costless’ during its operational life. variation requirements. The minimum In ATM, QoS has very specific meanings and maximum bandwidths are Gigabit Ethernet is an enabler of just such that are the subject of ATM Forum and characterized by the Minimum Cell a strategy in the LAN. Gigabit Ethernet, other standards specifications. Defined at Rate and Peak Cell Rate respectively. and soon 10-Gigabit Ethernet, will the ATM layer (OSI Layer 2), the service provide all the bandwidth that is ever • UBR: Unspecified Bit Rate, for architecture provides five categories of needed for many application types, applications that can use the network services that relate traffic characteristics eliminating the need for complex QoS on a best-effort basis, with no service and QoS requirements to network behavior: schemes in many environments. However, guarantees for cell loss, delay and delay some applications are bursty in nature • CBR: Constant Bit Rate, for applications variations. Example applications are and will consume all available bandwidth, that are sensitive to delay and delay e-mail and file transfer. variations, and need a fixed but to the detriment of other applications that Depending on the QoS requested, ATM continuously available amount of may have time-critical requirements. The provides a specific level of service. At bandwidth for the duration of a solution is to provide a priority mechanism one extreme, ATM provides a best-effort connection. The amount of bandwidth that ensures bandwidth, buffer space, service for the lowest QoS (UBR), with required is characterized by the and processor power are allocated to the no bandwidth reserved for the traffic. Peak Cell Rate. An example of this different types of traffic. At the other extreme, ATM provides a is circuit emulation. With Gigabit Ethernet, QoS has a broader guaranteed level of service for the higher interpretation than with ATM. But it • rt-VBR: Real-time Variable Bit Rate, for QoS (that is, CBR and VBR) traffic. is just as able — albeit with different applications that need varying amounts Between these extremes, ABR is able to mechanisms — to meet the requirements of bandwidth with tightly regulated use whatever bandwidth is available with of voice, video and data applications. delay and delay variation, and whose proper traffic management and controls. traffic is bursty in nature. The amount In general, Ethernet QoS is delivered Because ATM is connection-oriented, of bandwidth is characterized by the at a high layer of the OSI model. Frames requests for a particular QoS, admission Peak Cell Rate and Sustainable Cell are typically classified individually by a control, and resource allocation are an Rate; burstiness is defined by the filtering scheme. Different priorities are integral part of the call signaling and Maximum Burst Size. Example assigned to each class of traffic, either connection setup process. The call is applications include real-time voice explicitly by means of priority bit settings admitted and the connection established and video conferencing. in the frame header, or implicitly in the between communicating end systems only if the resources exist to meet a requested QoS, without jeopardizing

6 Gigabit Ethernet and ATM: A Technology Perspective White Paper priority level of the queue or VLAN to which they are assigned. Resources are then provided in a preferentially prioritized (unequal or unfair) way to service the These definitions are required in order queues. In this manner, QoS is delivered to guarantee the consistency of expected by providing differential services to service when a packet crosses from one the differentiated traffic through this network’s administrative domain to mechanism of classification, priority another, or for multi-vendor interoperability. setting, prioritized queue assignment, The Working Group also standardized the and prioritized queue servicing. (For following specific per-hop behaviors and restricted, medium precedence frames further information on QoS in Frame- recommended bit patterns (also known as are discarded next, and low precedence Switched Networks, see WP3510-A/5-99, code points or DSCPs) of the DS Field frames are dropped only in the most a Nortel Networks white paper available for each PHB: extreme lack of resource conditions. on the Web at www.nortelnetworks.com.) • Expedited Forwarding (EF-PHB), • A recommended Default PHB with sometimes described as Premium a DSCP of b’000000’ (six zeros) that Differentiated Services Service, uses a DSCP of b’101110’. equates to today’s best-effort service Chief among the mechanisms available when no explicit DS marking exists. for Ethernet QoS is Differentiated The EF-PHB provides the equivalent Services (DiffServ). The IETF DiffServ service of a low loss, low latency, low In essence, DiffServ operates as follows: Working Group proposed DiffServ jitter, assured bandwidth point-to- • Each frame entering a network is as a simple means to provide scalable point connection (a virtual leased line). analyzed and classified to determine differentiated services in an IP network. EF-PHB frames are assigned to a high the appropriate service desired by the DiffServ redefines the IP Precedence/Type priority queue where the arrival rate of application. frames at a node is shaped to be always of Service field in the IPv4 header and • Once classified, the frame is marked in the Traffic Class field in the IPv6 header less than the configured departure rate at that node. the DS field with the assigned DSCP as the new DS Field (see Figure 1). An IP value to indicate the appropriate PHB. packet’s DS Field is then marked with a • Assured Forwarding (AF-PHB) uses Within the core of the network, frames specific bit pattern, so the packet will 12 DSCPs to identify four forwarding are forwarded according to the PHB receive the desired differentiated service classes, each with three levels of drop indicated. (that is, the desired forwarding priority), precedence (12 PHBs). Frames are • Analysis, classification, marking, also known as per-hop behavior (PHB), assigned by the user to the different policing, and shaping operations need at each network node along the path classes and drop precedence depending only be carried out at the host or from source to destination. on the desired degree of assured — but not guaranteed — delivery. When network boundary node. Intervening To provide a common use and interpreta- nodes need only examine the short tion of the possible DSCP bit patterns, allocated resources (buffers and band- width) are insufficient to meet demand, fixed length DS Field to determine the RFC 2474 and RFC 2475 define the appropriate PHB to be given to the architecture, format, and general use frames with the high drop precedence are discarded first. If resources are still frame. This architecture is the key to of these bits within the DSCP Field. DiffServ scalability. In contrast, other models such as RSVP/Integrated Services are severely limited by signaling, Figure 1: Differentiated Services Field (RFC 2474). application flow, and forwarding state Byte Bit 1 2 3 4 5 6 7 8 maintenance at each and every node 1 IP Version IP Header Length along the path. 2 Differentiated Services Code Point (DSCP) Currently Unused 3-20 (Remainder of IP Header)

Gigabit Ethernet and ATM: A Technology Perspective White Paper 7 Figure 2: Passport Campus Solution and Optivity Policy Services.

Server Farm Optivity Policy Services Passport 8000 and Management Routing Switch Connection-oriented

Policy Server communicates vs. Connectionless filter and queuing rules using ATM is a connection-oriented protocol. Common Open Policy Services Server Switch ensures most appropriate server used, Most enterprise LAN networks are Routing Switch policies, depending on loads and End Station can set shapes and forwards response times 802.1p or DSCP field connectionless Ethernet networks, classified frames whether Ethernet, Fast Ethernet and Gigabit Ethernet. Data Passport 700 Server Switch Note: Because of Ethernet’s predominance, Routing Switch validates using policy server and sets/resets it greatly simplifies the discussion to not DSCP using Express Classification refer to the comparatively sparse Token- Ring technology; this avoids complicating the comparison with qualifications for Passport 1000 Routing Switch Token-Ring LANs and ELANs, Route Descriptors instead of MAC addresses • Policies govern how frames are marked With Gigabit Ethernet, the switches at the as LAN destinations, and so forth. and traffic conditioned upon entry network ingress may act as COPS clients. An ATM network may be used as a to the network; they also govern the COPS clients examine frames as they high-speed backbone to connect Ethernet allocation of network resources to the enter the network, communicate with a LAN switches and end stations together. traffic streams, and how the traffic is central COPS server to decide if the traffic However, a connection-oriented ATM forwarded within that network. should be admitted to the network, and backbone requires ATM Forum LAN DiffServ allows nodes that are not DS- enforce the policies. These policies include Emulation (LANE) protocols to emulate capable, or even DS-aware, to continue any QoS forwarding treatment to be the operation of connectionless legacy to use the network in the same way as applied during transport. Once this is LANs. In contrast with simple Gigabit they have previously by simply using determined, the DiffServ-capable Gigabit Ethernet backbones, much of the the Default PHB, which is best-effort Ethernet switches can mark the frames complexity of ATM backbones arises forwarding. Thus, without requiring using the selected DSCP bit pattern, from the need for LANE. end-to-end deployment, DiffServ provides apply the appropriate PHB, and forward Gigabit Ethernet with a powerful, yet the frames to the next node. The next ATM LAN Emulation v1 simple and scalable, means to provide node need only examine the DiffServ LANE version 1 was approved in January differential QoS services to support markings to apply the appropriate PHB. 1995. Whereas a Gigabit Ethernet various types of application traffic. Thus, frames are forwarded hop-by-hop backbone is very simple to implement, through a Gigabit Ethernet campus with each ATM emulated LAN (ELAN) needs the desired QoS. Common Open Policy Services several logical components and protocols To enable a Policy Based Networking In Nortel Networks’ Passport* Campus that add to ATM’s complexity. These capability, the Common Open Policy Solution, COPS will be used by Optivity* components are: Services (COPS) protocol can be used Policy Services (COPS server) and the • LAN Emulation Configuration to complement DiffServ-capable devices. Passport Enterprise and Routing Switches Server(s) (LECS) to, among other COPS provides an architecture and (COPS clients) to communicate QoS duties, provide configuration data to an a request-response protocol for policies defined at the policy server to the end system, and assign it to an ELAN communicating admission control switches for enforcement (see Figure 2). (although the same LECS may serve requests, policy-based decisions, and more than one ELAN). policy information between a network • Only one LAN Emulation Server policy server and the set of clients it serves. (LES) per ELAN to resolve 6-byte LAN MAC addresses to 20-byte ATM addresses and vice versa.

8 Gigabit Ethernet and ATM: A Technology Perspective White Paper Figure 3: LAN Emulation v1 Connections and Functions.

Point-to-point or Connection Name Uni- or Bi-directional Point-to-multipoint Used for communication

Configuration Direct VCC Bi-directional Point-to-point Between an LECS and an LEC Control Direct VCC Bi-directional Point-to-point Between an LES and its LECs** Control Distribute VCC Uni-directional Point-to-multipoint From an LES to its LECs Multicast Send VCC Bi-directional Point-to-point Between a BUS and an LEC Multicast Forward VCC Uni-directional Point-to-multipoint From a BUS to its LECs Data Direct VCC Bi-directional Point-to-point Between an LEC and another LEC

**Note: There is a difference between LECS with an uppercase “S” (meaning LAN Emulation Configuration Server) and LECs with a lowercase “s” meaning LAN Emulation Clients, or more than one LEC) at the end of the acronym.

• Only one Broadcast and Unknown after. Unintended release of a required LUNI, among other enhancements, Server (BUS) per ELAN to forward VCC may trigger the setup process. In added the Selective Multicast Server broadcast frames, multicast frames, and certain circumstances, this can lead to (SMS), to provide a more efficient means frames for destinations whose LAN or instability in the network. of forwarding multicast traffic, which ATM address is as yet unknown. The most critical components of the was previously performed by the BUS. • One or more LAN Emulation Clients LAN Emulation Service are the LES and SMS thus offloads much of the multicast (LEC) to represent the end systems. BUS, without which an ELAN cannot processing from the BUS, allowing the This is further complicated by whether function. Because each ELAN can only BUS to focus more on the forwarding the end system is a LAN switch to be served by a single LES and BUS, these of broadcast traffic and traffic with which other Ethernet end stations are components need to be backed up yet-to-be-resolved LAN destinations. attached, or whether it is an ATM- by other LESs and BUSs to prevent LNNI provides for the exchange of directly attached end station. A LAN any single point of failure stopping configuration, status, control coordination, switch requires a proxy LEC, whereas communication between the possibly and database synchronization between an ATM-attached end station requires hundreds or even thousands of end stations redundant and distributed components a non-proxy LEC. attached to an ELAN. In addition, the of the LAN Emulation Service. Collectively, the LECS, LES, and BUS single LES or BUS represents a potential However, each improvement adds new are known as the LAN Emulation performance bottleneck. complexity. Additional protocols are Services. Each LEC (proxy or non-proxy) Thus, it became necessary for the LAN required and additional VCCs need to be communicates with the LAN Emulation Emulation Service components to be established, maintained, and monitored Services using different virtual channel replicated for redundancy and elimination for communication between the new connections (VCCs) and LAN Emulation of single points of failures, and distributed LAN Emulation Service components and User Network Interface (LUNI) protocols. for performance. LECs. For example, all LESs serving an Figure 3 shows the VCCs used in ELAN communicate control messages to LANE v1. ATM LAN Emulation v2 each other through a full mesh of Control Some VCCs are mandatory — once To enable communication between Coordinate VCCs. These LESs must also established, they must be maintained if the redundant and distributed LAN synchronize their LAN-ATM address the LEC is to participate in the ELAN. Emulation Service components, as well as databases, using the Server Cache Other VCCs are optional — they may or other functional enhancements, LANE v1 Synchronization Protocol (SCSP — RFC may not be established and, if established, was re-specified as LANE v2; it now 2334), across the Cache Synchronization they may or may not be released there- comprises two separate protocols: VCC. Similarly, all BUSs serving an ELAN must be fully connected by a • LUNI: LAN Emulation User Network Interface (approved July 1997) mesh of Multicast Forward VCCs used to forward data. • LNNI: LAN Emulation Network-Network Interface (approved February 1999).

Gigabit Ethernet and ATM: A Technology Perspective White Paper 9 Figure 4: LAN Emulation v2 Additional Connections and/or Functions.

Point-to-point or Connection Name Uni- or Bi-directional Point-to-multipoint Used for communication

LECS Synchronization VCC Bi-directional Point-to-point Between LECSs Configuration Direct VCC Bi-directional Point-to-point Between an LECS and an LEC, LES or BUS Control Coordinate VCC Bi-directional Point-to-point Between LESs Cache Synchronization VCC Bi-directional Point-to-point Between an LES and its SMSs Default Multicast Send VCC Bi-directional Point-to-point Between a BUS and an LEC (as in v1) Default Multicast Forward VCC Uni-directional Point-to-multipoint From a BUS to its LECs and other BUSs Selective Multicast Send VCC Bi-directional Point-to-point Between an SMS and an LEC Selective Multicast Forward VCC Uni-directional Point-to-multipoint From an SMS to its LECs

Unicast traffic from a sending LEC is • If an SMS is available, the LEC can address database with its LES using initially forwarded to a receiving LEC via establish, in addition to the Default SCSP across Cache Synchronization the BUS. When a Data Direct VCC has Multicast Send VCC to the BUS, a VCCs. been established between the two LECs, Selective Multicast Send VCC to the Figure 4 shows the additional connections the unicast traffic is then forwarded via SMS. In this case, the BUS will add the required by LANE v2. the direct path. During the switchover LEC as a leaf to its Default Multicast from the initial to the direct path, it is Forward VCC and the SMS will add This multitude of control and coordina- possible for frames to be delivered out of the LEC as a leaf to its Selective tion connections, as well as the exchange order. To prevent this possibility, LANE Multicast Forward VCC. The BUS is of control frames, consumes memory, requires an LEC to either implement the then used initially to forward multicast processing power, and bandwidth, just Flush protocol, or for the sending LEC to traffic until the multicast destination is so that a Data Direct VCC can finally be delay transmission at some latency cost. resolved to an ATM address, at which established for persistent communication time the SMS is used. The SMS also between two end systems. The complexity The forwarding of multicast traffic can be seen in Figure 5. from an LEC depends on the availability synchronizes its LAN-ATM multicast of an SMS: • If an SMS is not available, the LEC Figure 5: Complexity of ATM LAN Emulation. establishes the Default Multicast Send 11 1 LECS LECS 1 VCC to the BUS that, in turn, will 1 1 1 1 add the LEC as a leaf to its Default 1 1 10** Multicast Forward VCC. The BUS LES LES 9** is then used for the forwarding of BUS BUS multicast traffic. 22 99 99 22 3 5 3 5 4 4 SMS SMS SMS SMS 4 4 8 8 7 7 7 7

LEC LEC LEC LEC LEC LEC 6 666 66

1 Configuration Direct VCC 7 Selective Multicast VCC 2 Control Direct VCC 8 Selective Multicast Forward VCC 3 Control Distribute VCC 9 Cache Sync-only VCC 4 Default Multicast Send VCC 10 Control Coordinate-only VCC 5 Default Multicast Forward VCC 11 LECS Sync VCC 6 Data Direct VCC ** may be combined into one dual function VCC between two neighbor LESs

10 Gigabit Ethernet and ATM: A Technology Perspective White Paper AAL-5 Encapsulation In addition to the complexity of connections and protocols, the data carried over LANE uses ATM Adaptation Layer-5 Frame Format (Full-Duplex) (AAL-5) encapsulation, which adds Full-duplex Gigabit Ethernet uses the overhead to the Ethernet frame. The same frame format as Ethernet and Fast Ethernet frame is stripped of its Frame Ethernet, with a minimum frame length Check Sequence (FCS); the remaining of 64 bytes and a maximum of 1518 bytes fields are copied to the payload portion (including the FCS but excluding the of the CPCS-PDU, and a 2-byte LANE Preamble/SFD). If the data portion is less header (LEH) is added to the front, with than 46 bytes, pad bytes are added to an 8-byte trailer at the end. Up to 47 produce a minimum frame size of 64 bytes. pad bytes may be added, to produce a CPCS-PDU that is a multiple of 48, Figure 7 shows the same frame format for the size of an ATM cell payload. Ethernet, Fast Ethernet and full-duplex Gigabit Ethernet that enables the seamless The CPCS-PDU also has to be segmented integration of Gigabit Ethernet campus into 53-byte ATM cells before being backbones with the Ethernet and transmitted onto the network. At the Fast Ethernet desktops and servers receiving end, the 53-byte ATM cells have they interconnect. to be decapsulated and reassembled into the original Ethernet frame. Figure 6: AAL-5 CPCS-PDU.

Figure 6 shows the CPCS-PDU that is CPCS-PDU Trailer used to transport Ethernet frames over Bytes 1-65535 0-47 1 1 2 4 LANE. LEH CPCS-PDU Payload Pad CPCS-UU CPI Length CRC

CPCS-PDU Gigabit Ethernet LAN In contrast, a Gigabit Ethernet LAN backbone does not have the complexity Figure 7: Full-Duplex Gigabit Ethernet Frame Format and overhead of control functions, (no Carrier Extension). data encapsulation and decapsulation, Bytes 8 6 6 2 46 to 1500 4 segmentation and reassembly, and control Preamble/ Destination Source Length/ Data Pad FCS and data connections required by an SFD Address Address Type ATM backbone. 64 min to 1518 bytes max As originally intended, at least for initial deployment in the LAN environment, Gigabit Ethernet uses full-duplex transmission between switches, or between a switch and a server in a server farm — in other words, in the LAN backbone. Full-duplex Gigabit Ethernet is much simpler, and does not suffer from the complexities and deficiencies of half-duplex Gigabit Ethernet, which uses the CSMA/CD protocol, Carrier Extension, and frame bursting.

Gigabit Ethernet and ATM: A Technology Perspective White Paper 11 Figure 8: Half-Duplex Gigabit Ethernet Frame Format (with Carrier Extension).

512 bytes min transmission Bytes 8 6 6 2 46 to 493 4 448 to 1 Preamble/ Destination Source Length/ Carrier However, this calculation is only applicable Data Pad FCS SFD Address Address Type Extension to half-duplex (as opposed to full-duplex) 64 bytes min (non-extended) Gigabit Ethernet. In the backbone and server-farm connections, the vast majority “Goodput” Efficiency (if not all) of the Gigabit Ethernet With full-duplex Gigabit Ethernet, deployed will be full-duplex. the good throughput (“goodput”) in a predominantly 64-byte frame size Mapping Ethernet Frames environment, where no Carrier Extension into ATM LANE Cells is needed, is calculated as follows (where As mentioned previously, using ATM SFD=start frame delimiter, and Frame Format (Half-Duplex) LAN Emulation as the campus backbone IFG=interframe gap): Because of the greatly increased speed of for Ethernet desktops require AAL-5 propagation and the need to support encapsulation and subsequent segmentation 64 bytes (frame) practical network distances, half-duplex and reassembly. Gigabit Ethernet requires the use of the [64 bytes (frame) + 8 bytes (SFD) + 12 bytes (IFG)] Figure 9 shows a maximum-sized Carrier Extension. The Carrier Extension = 1518-byte Ethernet frame mapped into provides a minimum transmission length a CPCS-PDU and segmented into 32 of 512 bytes. This allows collisions to be 76 % approx. 53-byte ATM cells, using AAL-5; this detected without increasing the minimum This goodput translates to a forwarding translates into a goodput efficiency of: frame length of 64 bytes; thus, no changes rate of 1.488 million packets per second are required to higher layer software, such (Mpps), known as the wirespeed rate. 1514 bytes (frame without FCS) as network interface card (NIC) drivers With Carrier Extension, the resulting and protocol stacks. goodput is very much reduced: [32 ATM cells x 53 bytes per ATM cell] With half-duplex transmission, if the data = portion is less than 46 bytes, pad bytes 64 bytes (frame) 89 % approx. are added in the Pad field to increase For a minimum size 64-byte Ethernet [512 bytes (frame with CE) + 8 bytes (SFD) the minimum (non-extended) frame to frame, two ATM cells will be required; + 12 bytes (IFG)] 64 bytes. In addition, bytes are added this translates into a goodput efficiency of: in the Carrier Extension field so that a = minimum of 512 bytes for transmission is 12 % approx. 60 bytes (frame without FCS) generated. For example, with 46 bytes of In ATM and Gigabit Ethernet comparisons, data, no bytes are needed in the Pad field, [2 ATM cells x 53 bytes per ATM cell] this 12 percent figure is sometimes quoted and 448 bytes are added to the Carrier = as evidence of Gigabit Ethernet’s inefficiency. Extension field. On the other hand, with 57 % approx. 494 or more (up to 1500) bytes of data, no pad or Carrier Extension is needed. Figure 9: Mapping Ethernet Frame into ATM Cells.

Bytes 8 6 6 2 1500 4 Preamble/ Destination Source Length/ Data Pad FCS SFD Address Address Type 1514 bytes

CPCS-PDU Payload CPCS-PDU Trailer

Bytes 2 1514 12 1 1 2 4 CPCS-PDU LEH Ethernet Frame Pad CPCS-UU CPI Length CRC

ATM Cells 1 2 3 4 29 30 31 32 1696 bytes

12 Gigabit Ethernet and ATM: A Technology Perspective White Paper Figure 10: Frame Bursting.

Bytes 8 52-1518 12 8 64-1518 12 8 64-1518 12 Preamble/ MAC Extension Preamble/ MAC Preamble/ MAC IFG IFG IFG SFD Frame-1 (if needed) SFD Frame-2 SFD Frame-n 1 Frame Burst

Frame Bursting Flow Control and • Traffic Policing: monitoring and The Carrier Extension is an overhead, controlling the stream of cells entering Congestion Management the network for connections accepted, especially if short frames are the predominant In both ATM or Gigabit Ethernet, flow and marking out-of-profile traffic for traffic size. To enhance goodput, half- control and congestion management possible discard using Usage Parameter duplex Gigabit Ethernet allows frame are necessary to ensure that the network Control (UPC) and the Generic Cell bursting. Frame bursting allows an end elements, individually and collectively, Rate Algorithm (GCRA). station to send multiple frames in one are able to meet QoS objectives required access (that is, without contending for by applications using that network. • Backpressure: exerting on the source channel access for each frame) up to Sustained congestion in a switch, whether to decrease cell transmission rate when the burstLength parameter. If a frame is ATM or Gigabit Ethernet, will eventually congestion appears likely or imminent. being transmitted when the burst Length result in frames being discarded. Various • notifying the threshold is exceeded, the sender is Congestion Notification: techniques are employed to minimize source and intervening nodes of current allowed to complete the transmission. or prevent buffer overflows, especially or impending congestion by setting the Thus, the maximum duration of a frame under transient overload conditions. The Explicit Forward Congestion burst is 9710 bytes; this is the burst difference between ATM and Gigabit Indication (EFCI) bit in the cell header Length (8192 bytes) plus the max Frame Ethernet is in the availability, reach, and (Payload Type Indicator) or using Size (1518 bytes). Only the first frame is complexity (functionality and granularity) Relative Rate (RR) or Explicit Rate extended if required. Each frame is spaced of these techniques. (ER) bits in Resource Management from the previous by a 96-bit interframe (RM) cells to provide feedback both in gap. Both sender and receiver must be ATM Traffic and the forward and backward directions, able to process frame bursting. Congestion Management so that remedial action can be taken. In an ATM network, the means employed • Cell Discard: employing various discard CSMA/CD Protocol to manage traffic flow and congestion are Full-duplex Gigabit Ethernet does not strategies to avoid or relieve congestion: based on the traffic contract: the ATM use or need the CSMA/CD protocol. Service Category and the traffic descriptor • Selective Cell Discard: dropping cells Because of the dedicated, simultaneous, parameters agreed upon for a connection. that are non-compliant with traffic and separate send and receive channels, it These means may include: contracts or have their Cell Loss is very much simplified without the need Priority (CLP) bit marked for • for carrier sensing, collision detection, Connection Admission Control (CAC): possible discard if necessary backoff and retry, carrier extension, and accepting or rejecting connections frame bursting. being requested at the call setup stage, depending upon availability of network resources (this is the first point of control and takes into account connections already established).

Gigabit Ethernet and ATM: A Technology Perspective White Paper 13 Using this simple start-stop mechanism, Gigabit Ethernet prevents frame discards when input buffers are temporarily Gigabit Ethernet Flow Control depleted by transient overloads. It is only For half-duplex operation, Gigabit effective when used on a single full-duplex Ethernet uses the CSMA/CD protocol link between two switches, or between a to provide implicit flow control by switch and an end station (server). “backpressuring” the sender from Because of its simplicity, the PAUSE transmitting in two simple ways: function does not provide flow control • Early Packet Discard (EPD): dropping across multiple links, or from end-to-end • Forcing collisions with the incoming all the cells belonging to a frame that across (or through) intervening switches. traffic, which forces the sender to back is queued, but for which transmission It also requires both ends of a link (the off and retry as a result of the collision, has not been started sending and receiving partners) to be in conformance with the CSMA/CD MAC Control-capable. • Partial Packet Discard (PPD): dropping protocol. all the cells belonging to a frame that • Asserting carrier sense to provide a is being transmitted (a more drastic Bandwidth Scalability “channel busy” signal, which prevents action than EPD) Advances in computing technology have the sender from accessing the medium fueled the explosion of visually and aural- • Random Early Detection (RED): to transmit, again in conformance with ly exciting applications for e-commerce, dropping all the cells of randomly the protocol. whether Internet, intranet or extranet. selected frames (from different sources) With full-duplex operation, Gigabit These applications require exponential when traffic arrival algorithms indicate Ethernet uses explicit flow control to increases in bandwidth. As a business impending congestion (thus avoiding throttle the sender. The IEEE 802.3x grows, increases in bandwidth are also congestion), and preventing waves Task Force defined a MAC Control required to meet the greater number of of synchronized re-transmission architecture, which adds an optional users without degrading performance. precipitating congestion collapse. MAC Control sub-layer above the MAC Therefore, bandwidth scalability in A further refinement is offered using sub-layer, and uses MAC Control frames the network infrastructure is critical to Weighted RED (WRED). to control the flow. To date, only one supporting incremental or quantum • Traffic Shaping: modifying the stream MAC Control frame has been defined; increases in bandwidth capacity, which is of cells leaving a switch (to enter or this is for the PAUSE operation. frequently required by many businesses. transit a network) so as to ensure A switch or an end station can send ATM and Gigabit Ethernet both provide conformance with contracted profiles a PAUSE frame to stop a sender from bandwidth scalability. Whereas ATM’s and services. Shaping may include transmitting data frames for a specified bandwidth scalability is more granular reducing the Peak Cell Rate, limiting length of time. Upon expiration of the and extends from the desktop and over the duration of bursting traffic, and period indicated, the sender may resume the MAN/WAN, Gigabit Ethernet has spacing cells more uniformly to reduce transmission. The sender may also resume focused on scalability in campus networking the Cell Delay Variation. transmission when it receives a PAUSE from the desktop to the MAN/WAN frame with a zero time specified, indicating edge. Therefore, Gigabit Ethernet provides the waiting period has been cancelled. quantum leaps in bandwidth from On the other hand, the waiting period 10 Mbps, through 100 Mbps, 1000 may be extended if the sender receives a Mbps (1 Gbps), and even 10,000 Mbps PAUSE frame with a longer period than (10 Gbps) without a corresponding previously received. quantum leap in costs.

14 Gigabit Ethernet and ATM: A Technology Perspective White Paper ATM Bandwidth ATM is scalable from 1.544 Mbps through to 2.4 Gbps and even higher speeds. Approved ATM Forum multiplexed. The original cell stream is specifications for the physical layer recovered in correct sequence from the include the following bandwidths: multiple physical links at the receiving • 1.544 Mbps DS1 end. Loss and recovery of individual links in an IMA group are transparent to the • 2.048 Mbps E1 users. This capability allows users to: • 25.6 Mbps over shielded and unshielded together to provide greater bandwidth • Interconnect ATM campus networks twisted pair copper cabling (the bandwidth and resiliency. Work in this area of over the WAN, where ATM WAN that was originally envisioned for ATM standardization is proceeding through facilities are not available by using to the desktop) the IEEE 802.3ad Link Aggregation Task existing DS1/E1 facilities • 34.368 Mbps E3 Force (see the Trunking and Link • Incrementally subscribe to more Aggregation section of this paper). • 44.736 Mbps DS3 DS1/E1 physical links as needed • 100 Mbps over multimode fiber cabling • Protect against single link failures Distance Scalability • 155.52 Mbps SONET/SDH over UTP when interconnecting ATM campus Distance scalability is important because and single and multimode fiber cabling networks across the WAN of the need to extend the network across widely dispersed campuses, and within • 622.08 Mbps SONET/SDH over single • Use multiple DS1/E1 links that are large multi-storied buildings, while making and multimode fiber cabling typically lower cost than a single DS3/E3 (or higher speed) ATM use of existing UTP-5 copper cabling • 622.08 Mbps and 2.4 Gbps cell- WAN link for normal operation or and common single and multimode based physical layer (without any frame as backup links. fiber cabling, and without the need for structure). additional devices such as repeaters, Work is also in progress (as of October extenders, and amplifiers. Gigabit Ethernet Bandwidth 1999) on 1 Gbps cell-based physical layer, Ethernet is scalable from the traditional Both ATM and Gigabit Ethernet (IEEE 2.4 Gbps SONET/SDH, and 10 Gbps 10 Mbps Ethernet, through 100 Mbps 802.3ab) can operate easily within the SONET/SDH interfaces. Fast Ethernet, and 1000 Mbps Gigabit limit of 100 meters from a wiring closet Ethernet. Now that the Gigabit Ethernet switch to the desktop using UTP-5 Inverse Multiplexing standards have been completed, the next copper cabling. Longer distances are over ATM evolutionary step is 10 Gbps Ethernet. typically achieved using multimode In addition, the ATM Forum’s Inverse The IEEE P802.3 Higher Speed Study (50/125 or 62.5/125 µm) or single mode Multiplexing over ATM (IMA) standard Group has been created to work on 10 (9-10/125 µm) fiber cabling. allows several lower-speed DS1/E1 physical Gbps Ethernet, with Project links to be grouped together as a single Authorization Request and formation of higher speed logical link, over which cells a Task Force targeted for November 1999 from an ATM cell stream are individually and a standard expected by 2002. Bandwidth scalability is also possible through link aggregation ( that is, grouping multiple Gigabit Ethernet links

Gigabit Ethernet and ATM: A Technology Perspective White Paper 15 Figure 11: Ethernet and Fast Ethernet Supported Distances.

Ethernet Ethernet Ethernet Ethernet 10BASE-T 10BASE-FL 100BASE-TX 100BASE-FX

IEEE Standard 802.3 802.3 802.3u 802.3u Data Rate 10 Mbps 10 Mbps 100 Mbps 100 Mbps Multimode Fiber distance N/A 2 km N/A 412 m (half duplex) 2 km (full duplex)

Singlemode Fiber distance N/A 25 km N/A 20 km Cat 5 UTP distance 100 m N/A 100 m N/A STP/Coax distance 500 m N/A 100 m N/A

Gigabit Ethernet Distances single computer room or wiring closet. The IEEE 802.3ab standard specifies the Figure 11 shows the maximum distances Collectively, the three designations — operation of Gigabit Ethernet over distances supported by Ethernet and Fast Ethernet, 1000BASE-SX, 1000BASE-LX and up to 100m using 4-pair 100 ohm using various media. 1000BASE-CX — are referred to as Category 5 balanced unshielded twisted 1000BASE-X. pair copper cabling. This standard is also IEEE 802.3z Gigabit Ethernet Figure 12 shows the maximum distances known as the 1000BASE-T specification; – Fiber Cabling supported by Gigabit Ethernet, using it allows deployment of Gigabit Ethernet IEEE 802.3u-1995 (Fast Ethernet) various media. in the wiring closets, and even to the extended the operating speed of desktops if needed, without change to the 1000BASE-X Gigabit Ethernet is capable CSMA/CD networks to 100 Mbps over UTP-5 copper cabling that is installed in of auto-negotiation for half- and full-duplex both UTP-5 copper and fiber cabling. many buildings today. operation. For full-duplex operation, The IEEE P802.3z Gigabit Ethernet Task auto-negotiation of flow control includes Force was formed in July 1996 to develop both the direction and symmetry Trunking and a Gigabit Ethernet standard. This work of operation — symmetrical and Link Aggregation Trunking provides switch-to-switch was completed in July 1998 when the asymmetrical. IEEE Standards Board approved the connectivity for ATM and Gigabit Ethernet. Link Aggregation allows IEEE 802.3z-1998 standard. IEEE 802.3ab Gigabit Ethernet multiple parallel links between switches, The IEEE 802.3z standard specifies the — Copper Cabling or between a switch and a server, to operation of Gigabit Ethernet over existing For Gigabit Ethernet over copper cabling, provide greater resiliency and bandwidth. single and multimode fiber cabling. It an IEEE Task Force started developing a While switch-to-switch connectivity also supports short (up to 25m) copper specification in 1997. A very stable draft for ATM is well-defined through the jumper cables for interconnecting switches, specification, with no significant technical NNI and PNNI specifications, several routers, or other devices (servers) in a changes, had been available since July vendor-specific 1998. This specification, known as IEEE 802.3ab, is now approved (as of June 1999) as an IEEE standard by the IEEE Standards Board.

16 Gigabit Ethernet and ATM: A Technology Perspective White Paper Figure 12: Gigabit Ethernet Supported Distances.

1000BASE-SX 1000BASE-LX 1000BASE-CX 1000BASE-T

IEEE Standard 802.3z 802.3z 802.3z 802.3ab Data Rate 1000 Mbps 1000 Mbps 1000 Mbps 1000 Mbps Optical Wavelength (nominal) 850 nm (shortwave) 1300 nm (longwave) N/A N/A Multimode Fiber (50 (m) distance 525 m 550 m N/A N/A Multimode Fiber (62.5 (m) distance 260 m 550 m N/A N/A Singlemode Fiber (10 (m) distance N/A 3 km N/A N/A UTP-5 100 ohm distance N/A N/A N/A 100m STP 150 ohm distance N/A N/A 25 m N/A Number of Wire Pairs/Fiber 2 fiber 2 fiber 2 pairs 4 pairs Connector Type Duplex SC Duplex SC Fibre Channel-2 RJ-45 or DB-9

Note: distances are for full duplex, the expected mode of operation in most cases.

protocols are used for Gigabit Ethernet, procedures as a single logical aggregated the list back to the ingress switch for with standards-based connectivity to be link. The individual links within a set of recomputation of a new path. An ATM provided once the IEEE 802.3ad Link paralleled links may be any combination switch may perform path computation as Aggregation standard is complete. of the supported ATM speeds. As more a background task before calls are received Nortel Networks is actively involved in bandwidth is needed, more PNNI links (to reduce latency during call setups), this standards effort, while providing may be added between switches as necessary or when a call request is received (for highly resilient and higher bandwidth without concern for the possibility of real-time optimized path at the cost of Multi-Link Trunking (MLT) and Gigabit loops in the traffic path. some setup delay), or both (for certain LinkSafe technology in the interim. By using source routing to establish a path QoS categories), depending on user (VCC) between any source and destination configuration. ATM PNNI end systems, PNNI automatically eliminates PNNI also provides performance scalability ATM trunking is provided through NNI the forming of loops. The end-to-end when routing traffic through an ATM (Network Node Interface or Network-to- path, computed at the ingress ATM network, using the hierarchical structure Network Interface) using the Private NNI switch using Generic Connection of ATM addresses. An individual ATM (PNNI) v1.0 protocols, an ATM Forum Admission Control (GCAC) procedures, end system in a PNNI peer group can specification approved in March 1996. is specified by a list of ATM nodes known be reached using the summary address To provide resiliency, load distribution as a Designated Transit List (DTL). for that peer group, similar to using the and balancing, and scalability in Computation based on default parameters network and subnet ID portions of an bandwidth, multiple PNNI links may be will result in the shortest path meeting the IP address. A node whose address does installed between a pair of ATM switches. requirements, although preference may be not match the summary address (the Depending on the implementation, given to certain paths by assigning lower non-matching address is known as a these parallel links may be treated for Administrative Weight to preferred links. foreign address) can be explicitly set Connection Admission Control (CAC) This DTL is then validated by local CAC to be reachable and advertised. procedures at each ATM node in the list. If an intervening node finds the path is invalid, maybe as a result of topology or link state changes in the meantime, that node is able to automatically “crank”

Gigabit Ethernet and ATM: A Technology Perspective White Paper 17 Gigabit Ethernet Link Aggregation With Gigabit Ethernet, multiple physical ATM UNI Uplinks links may be installed between two versus NNI Risers switches, or between a switch and a server, PNNI provides many benefits with to provide greater bandwidth and resiliency. regard to resiliency and scalability when Typically, the IEEE 802.1d Spanning Tree connecting ATM switches in the campus Protocol (STP) is used to prevent loops backbone. However, these advantages are forming between these parallel links, by A Peer Group Leader (PGL) may represent not available in most ATM installations blocking certain ports and forwarding on the nodes in the peer group at a higher where the LAN switches in the wiring others so that there is only one path level. These PGLs are logical group nodes closets are connected to the backbone between any pair of source-destination (LGNs) that form higher-level peer switches using ATM UNI uplinks. In end stations. In doing so, STP incurs groups, which allow even shorter summary such connections, the end stations some performance penalty when addresses. These higher-level peer groups attached to the LAN switch are associated, converging to a new spanning tree structure can be represented in even higher peer directly or indirectly (through VLANs), after a network topology change. groups, thus forming a hierarchy. By with specific proxy LECs located in the Although most switches are plug-and-play, using this multi-level hierarchical routing, uplinks. An end station cannot be associated with default STP parameters, erroneous less address, topology, and link state with more than one proxy LEC active in configuration of these parameters can lead information needs to be advertised across separate uplinks at any one time. Hence, to looping, which is difficult to resolve. In an ATM network, allowing scalability as no redundant path is available if the proxy addition, by blocking certain ports, STP the number of nodes grow. LEC (meaning uplink or uplink path) will allow only one link of several parallel However, this rich functionality comes representing the end stations should fail. links between a pair of switches to carry with a price. PNNI requires memory, While it is possible to have one uplink traffic. Hence, scalability of bandwidth processing power, and bandwidth from active and another on standby, connected between switches cannot be increased by the ATM switches for maintaining state to the backbone via a different path and adding more parallel links as required, information, topology and link state ready to take over in case of failure, very although resiliency is thus improved. update exchanges, and path computation. few ATM installations have implemented To overcome the deficiencies of STP, PNNI also results in greater complexity this design for reasons of cost, complexity, various vendor-specific capabilities are in hardware design, software algorithms, and lack of this capability from the offered to increase the resiliency, load switch configuration, deployment, and switch vendor. distribution and balancing, and scalability operational support, and ultimately much in bandwidth, for parallel links between higher costs. One solution is provided by the Nortel Networks Centillion* 50/100 and System Gigabit Ethernet switches. 5000BH/BHC LAN-ATM Switches. For example, the Nortel Networks These switches provide Token-Ring and Passport Campus Solution offers Multi- Ethernet end station connectivity on the Link Trunking and Gigabit Ethernet one (desktop) side and “NNI riser LinkSafe: uplinks” to the core ATM switches on Multi-Link Trunking (MLT) that allows the other (backbone) side. Because these up to four physical connections between “NNI risers” are PNNI uplinks, the two Passport 1000 Routing Switches, or LAN-to-ATM connectivity enjoys all the benefits of PNNI.

18 Gigabit Ethernet and ATM: A Technology Perspective White Paper a BayStack* 450 Ethernet Switch and an Passport 1000 Routing Switch, to be grouped together as a single logical link with much greater resiliency and With MLT and Gigabit Ethernet bandwidth than is possible with several LinkSafe redundant trunking and link individual connections. aggregation, the BayStack 450 Ethernet Each MLT group may be made up Switch and Passport 1000 Routing Switch of Ethernet, Fast Ethernet or Gigabit provide a solution that is comparable Ethernet physical interfaces; all links to ATM PNNI in its resilience and within a group must be of the same media incremental scalability, and is superior • Greater resiliency and fault-tolerance, type (copper or fiber), have the same in its simplicity. where traffic is automatically reassigned speed and half- or full-duplex settings, to remaining operative links, thus and belong to the same Spanning Tree IEEE P802.3ad maintaining communication if individual group, although they need not be from links between two switches, or a switch Link Aggregation the same interface module within a In recognition of the need for open and a server, fail. switch. Loads are automatically balanced standards and interoperability, Nortel • Flexible and simple migration vehicle, across the MLT links, based on source Networks actively leads in the IEEE where Ethernet and Fast Ethernet and destination MAC addresses (bridged P802.3ad Link Aggregation Task Force, switches at the LAN edges can have traffic), or source and destination IP authorized by the IEEE 802.3 Trunking multiple lower-speed links aggregated addresses (routed traffic). Up to eight Study Group in June 1998, to define to provide higher-bandwidth transport MLT groups may be configured in an a link aggregation standard for use on into the Gigabit Ethernet core. Passport 1000 Routing Switch. switch-to-switch and switch-to-server A brief description of the IEEE P802.3ad that provides Gigabit Ethernet LinkSafe parallel connections. This standard is Link Aggregation standard (which may two Gigabit Ethernet ports on an Passport currently targeted for availability in change as it is still fairly early in the 1000 Routing Switch interface module early 2000. standards process) follows. to connect to another similar module on The IEEE P802.3ad Link Aggregation is another switch, with one port active and A physical connection between two an important full-duplex, point-to-point the other on standby, ready to take over switches, or a switch and a server, is technology for the core LAN infrastructure automatically should the active port or known as a link segment. Individual link and provides several benefits: link fails. LinkSafe is used for riser and segments of the same medium type and backbone connections, with each link • Greater bandwidth capacity, allowing speed may make up a Link Aggregation routed through separate physical paths parallel links between two switches, or Group (LAG), with a link segment to provide a high degree of resiliency a switch and a server, to be aggregated belonging to only one LAG at any one protection against a port or link failure. together as a single logical pipe with time. Each LAG is associated with a single multi-Gigabit capacity (if necessary); MAC address. An important capability is that virtual traffic is automatically distributed LANs (VLANs) distributed across multiple and balanced over this pipe for high switches can be interconnected, with or performance. without IEEE 802.1Q VLAN Tagging, using MLT and Gigabit Ethernet trunks. • Incremental bandwidth scalability, allowing more links to be added between two switches, or a switch and a server, only when needed for greater performance, from a minimal initial hardware investment, and with minimal disruption to the network.

Gigabit Ethernet and ATM: A Technology Perspective White Paper 19 Integration of Layer 3 and Above Functions Both ATM and Gigabit Ethernet provide Technology the underlying internetwork over which Complexity and Cost IP packets are transported. Although initially a Layer 2 technology, ATM Two of the most critical criteria in the functionality is creeping upwards in the technology decision are the complexity OSI Reference Model. ATM Private and cost of that technology. In both Network Node Interface (PNNI) provides aspects, simple and inexpensive Gigabit Frames that belong logically together signaling and OSPF-like best route Ethernet wins hands down over complex (for example, to an application being used determination when setting up the path and expensive ATM — at least in at a given instance, flowing in sequence from a source to a destination end system. enterprise networks. between a pair of end stations) are treated Multiprotocol Over ATM (MPOA) as a conversation (similar to the concept ATM is fairly complex because it is a allows short-cut routes to be established of a “flow”). Individual conversations are connection-oriented technology that has between two communicating ATM end aggregated together to form an to emulate the operation of connection- systems located in different IP subnets, Aggregated Conversation, according to less LANs. As a result, additional physical completely bypassing intervening routers user-specified Conversation Aggregation and logical components, connections, along the path. Rules, which may specify aggregation, for and protocols have to be added, with In contrast, Gigabit Ethernet is strictly example, on the basis of source/destination the attendant need for understanding, a Layer 2 technology, with much of the address pairs, VLAN ID, IP subnet, or configuration, and operational support. other needed functionality added above protocol type. Frames that are part of a Unlike Gigabit Ethernet (which is largely it. To a large extent, this separation of given conversation are transmitted on plug-and-play), there is a steep learning functions is an advantage because changes a single link segment within a LAG to curve associated with ATM, in product to one function do not disrupt another ensure in-sequence delivery. development as well as product usage. if there is clear modularity of functions. ATM also suffers from a greater number A Link Aggregation Control Protocol This decoupling was a key motivation in of interoperability and compatibility is used to exchange link configuration, the original development of the 7-layer issues than does Gigabit Ethernet, because capability, and state information between OSI Reference Model. In fact, the of the different options vendors implement adjacent switches, with the objective complexity of ATM may be due to the in their ATM products. Although of forming LAGs dynamically. A Flush rich functionality all provided “in one interoperability testing does improve the protocol, similar to that in ATM LAN hit,” unlike the relative simplicity of situation, it also adds time and cost to Emulation, is used to flush frames in Gigabit Ethernet, where higher layer ATM product development. transit when links are added or removed functionality is kept separate from, from a LAG. Because of the greater complexity, and added “one at a time” to, the basic Among the objectives of the IEEE the result is also greater costs in: Physical and Data Link functions. P802.3ad standard are automatic • Education and training configuration, low protocol overheads, • Implementation and deployment rapid and deterministic convergence when link states change, and accommodation of • Problem determination and resolution aggregation-unaware links. • Ongoing operational support • Test and analysis equipment, and other management tools.

20 Gigabit Ethernet and ATM: A Technology Perspective White Paper MPOA and NHRP A traditional router provides two basic Layer 3 functions: determining the best possible path to a destination using routing control protocols such as RIP DDVCC between a destination end and OSPF (this is known as the routing station and its gateways router, and function), and then forwarding the frames several DDVCCs between intervening over that path (this is known as the routers along the path. With MPOA, forwarding function). only one DDVCC is needed between the source and destination end stations. Multi-Protocol Over ATM (MPOA) Virtual Router enhances Layer 3 functionality over ATM Gigabit Ethernet can also leverage a similar capability for IP traffic using the Redundancy Protocol in three ways: For Gigabit Ethernet, an IETF RFC 2338 Next Hop Resolution Protocol (NHRP). Virtual Router Redundancy Protocol • MPOA uses a Virtual Router model to In fact, MPOA uses NHRP as part of the (VRRP) is available for deploying provide greater performance scalability process to resolve MPOA destination interoperable and highly resilient default by allowing the typically centralized addresses. MPOA Resolution Requests gateway routers. VRRP allows a group of routing control function to be divorced are converted to NHRP Resolution routers to provide redundant and distributed from the data frame forwarding function, Requests by the ingress MPOA server gateway functions to end stations through and distributing the data forwarding before forwarding the requests towards the mechanism of a virtual IP address — function to access switches on the the intended destination. NHRP the address that is configured in end periphery of the network. This Resolution Responses received by the stations as the default gateway router. “separation of powers” allows routing ingress MPOA server are converted to capability and forwarding capability to MPOA Resolution Responses before At any one time, the virtual IP address be distributed to where each is most being forwarded to the requesting source. is mapped to a physical router, known effective, and allows each to be scaled Just as MPOA shortcuts can be established as the Master. Should the Master fail, when needed without interference for ATM networks, NHRP shortcuts another router within the group is elected from the other. can also be established to provide the as the new Master with the same virtual • MPOA enables paths (known as short- performance enhancement in a frame IP address. The new Master automatically cut VCCs) to be directly established switched network. takes over as the new default gateway, between a source and its destination, without requiring configuration without the hop-by-hop, frame-by- Gateway Redundancy changes in the end stations. In addition, frame processing and forwarding that is For routing between subnets in an ATM each router may be Master for a set necessary in traditional router networks. or Gigabit Ethernet network, end stations of end stations in one subnet while Intervening routers, which are potentially typically are configured with the static IP providing backup functions for another, performance bottlenecks, are completely address of a Layer 3 default gateway thus distributing the load across bypassed, thereby enhancing forwarding router. Being a single point of failure, multiple routers. performance. sometimes with catastrophic consequences, • MPOA uses fewer resources in the form various techniques have been deployed to of VCCs. When traditional routers are ensure that an alternate backs this default used in an ATM network, one Data gateway when it fails. Direct VCC (DDVCC) must be With ATM, redundant and distributed established between a source end Layer 3 gateways are currently vendor- station and its gateway router, one specific. Even if a standard should emerge, it is likely that more logical components, protocols, and connections will need to be implemented to provide redundant and/or distributed gateway functionality.

Gigabit Ethernet and ATM: A Technology Perspective White Paper 21 Broadcast and Multicast Broadcasts and multicasts are very natural means to send traffic from one source to throughout. Deployment and on-going multiple recipients in a connectionless operational support are much easier LAN. Gigabit Ethernet is designed for because of the opportunity to “learn once, just such an environment. The higher- do many.” One important assumption in layer IP multicast address is easily mapped this scenario is that ATM would be widely to a hardware MAC address. Using deployed at the desktops. This assumption Internet Group Management Protocol LAN Integration does not meet with reality. (IGMP), receiving end stations report The requirements of the LAN are very ATM deployment at the desktop is group membership to (and respond to different from those of the WAN. In the almost negligible, while Ethernet and queries from) a multicast router, so as to LAN, bandwidth is practically “free” once Fast Ethernet are very widely installed receive multicast traffic from networks installed, as there are no ongoing usage in millions of desktop workstations and beyond the local attachment. Source end costs. As long as sufficient bandwidth servers. In fact, many PC vendors include stations need not belong to a multicast capacity is provisioned (or even over- Ethernet, Fast Ethernet, and (increasingly) group in order to send to members of provisioned) to meet the demand, there Gigabit Ethernet NIC cards on the that group. may not be a need for complex techniques motherboards of their workstation or to control bandwidth usage. If sufficient By contrast, broadcasts and multicasts in server offerings. Given this huge installed bandwidth exists to meet all demand, an ATM LAN present a few challenges base and the common technology that it then complex traffic management and because of the connection-oriented nature evolved from, Gigabit Ethernet provides congestion control schemes may not be of ATM. seamless integration from the desktops needed at all. For the user, other issues In each emulated LAN (ELAN), ATM to the campus and enterprise backbone assume greater importance; these include needs the services of a LAN Emulation networks. ease of integration, manageability, flexibility Server (LES) and a Broadcast and (moves, adds and changes), simplicity, If ATM were to be deployed as the Unknown Server (BUS) to translate from scalability, and performance. campus backbone for all the Ethernet MAC addresses to ATM addresses. These desktops, then there would be a need for additional components require additional Seamless Integration frame-to-cell and cell-to-frame conversion resources and complexity needed to signal, ATM has often been touted as the — the Segmentation and Reassembly set up, maintain, and tear down Control technology that provides seamless (SAR) overhead. Direct, Control Distribute, Multicast integration from the desktop, over the With Gigabit Ethernet in the campus Send, and Multicast Forward VCCs. campus and enterprise, right through backbone and Ethernet to the desktops, Complexity is further increased because to the WAN and across the world. The no cell-to-frame or frame-to-cell conversion an ELAN can only have a single same technology and protocols are used is needed. Not even frame-to-frame LES/BUS, which must be backed up by conversion is required from one form another LES/BUS to eliminate any single of Ethernet to another! Hence, Gigabit points of failure. Communication Ethernet provides a more seamless integration in the LAN environment.

22 Gigabit Ethernet and ATM: A Technology Perspective White Paper between active and backup LES/BUS nodes requires more virtual connections and protocols for synchronization, failure detection, and takeover (SCSP and LNNI). the common uplink technology and with translational bridging functionality, With all broadcast traffic going through the Ethernet and Token-Ring LANs can the BUS, the BUS poses a potential interoperate relatively easily. bottleneck. With Gigabit Ethernet, interoperation For IP multicasting in a LANE network, between Ethernet and Token-Ring LANs ATM needs the services of the BUS and, SONET OC-3c/SDH STM-1, SONET requires translational bridges that transform if available (with LUNI v2), an SMS. OC-12c/SDH STM-4, and Packet- the frame format of one type to the other. For IP multicasting in a Classical IP ATM over-SONET/SDH in their Gigabit network, ATM needs the services of a Ethernet switches. Multicast Address Resolution Server MAN/WAN Integration While an ATM LAN does offer seamless It is relatively easy to interconnect ATM (MARS), a Multicast Connection Server integration with the ATM MAN or campus backbones across the MAN or (MCS), and the Cluster Control VCCs. WAN through direct connectivity, WAN. Most ATM switches are offered These components require additional the MAN/WAN for the most part will with DS1/E1, DS3/E3, SONET OC-3c/ resources and complexity for connection continue to be heterogeneous, and not SDH STM-1 and SONET OC-12c/ signaling, setting up, maintenance and homogeneous ATM. This is due to the SDH STM-4 ATM interfaces that tearing down. installed non-ATM equipment, geographical connect directly to the ATM MAN or coverage, and time needed to change. With UNI 3.0/3.1, the source must first WAN facilities. Some switches are offered This situation will persist more so than in resolve the target multicast address to the with DS1/E1 Circuit Emulation, DS1/E1 the LAN where there is a greater control ATM addresses of the group members, Inverse Multiplexing over ATM, and by the enterprise and, therefore, greater and then construct a point-to-multipoint Frame Relay Network and Service ease of convergence. Even in the LAN, tree, with the source itself as the root to Interworking capabilities that connect the convergence is towards Ethernet and the multiple destinations before multicast to the existing non-ATM MAN or WAN not ATM as the underlying technology. traffic may be distributed. With UNI 4.0, facilities. All these interfaces allow ATM Technologies other than ATM will be end stations may join as leaves to a point- campus switches direct connections to needed for interconnecting between to-multipoint distribution tree, with or the MAN or WAN, without the need for locations, and even over entire regions, without intervention from the root. Issues additional devices at the LAN-WAN edge. of interoperability between the different because of difficult geographical terrain At this time, many Gigabit Ethernet UNI versions are raised in either case. or uneconomic reach. Thus, there will switches do not offer MAN/WAN continue to be a need for technology interfaces. Connecting Gigabit Ethernet conversion from the LAN to the Multi-LAN Integration campus networks across the MAN As a backbone technology, ATM can WAN, except where ATM has been or WAN typically requires the use of interconnect physical LAN segments implemented. additional devices to access MAN/WAN using Ethernet, Fast Ethernet, Gigabit facilities, such as Frame Relay, leased Ethernet, and Token Ring. These are lines, and even ATM networks. These the main MAC layer protocols in use on interconnect devices are typically routers campus networks today. Using ATM as or other multiservice switches that add to the total complexity and cost. With the rapid acceptance of Gigabit Ethernet as the campus backbone of choice, however, many vendors are now offering MAN/WAN interfaces such as ATM

Gigabit Ethernet and ATM: A Technology Perspective White Paper 23 While all these technologies are evolving, businesses seek to minimize risks by investing in the lower-cost Gigabit also known as IP over SONET/SDH). Ethernet, rather than the higher-cost ATM. SONET is emerging as a competitive service to ATM over the MAN/WAN. Management Aspects With POS, IP packets are directly Because businesses need to be increasingly encapsulated into SONET frames, dynamic to respond to opportunities thereby eliminating the additional and challenges, the campus networking Another development — the widespread overhead of the ATM layer (see column environment is constantly in a state of deployment of fiber optic technology — “C” in Figure 13). flux. There are continual moves, adds, may enable the LAN to be extended over and changes; users and workstations form To extend this a step further, IP packets the WAN using the seemingly boundless and re-form workgroups; road warriors can be transported over raw fiber without optical bandwidth for LAN traffic. This take the battle to the streets, and highly the overhead of SONET/SDH framing; means that Gigabit Ethernet campuses mobile users work from homes and hotels this is called IP over Optical (see column can be extended across the WAN just as to increase productivity. easily, perhaps even more easily and with “D” in Figure 13). Optical Networking With all these constant changes, less cost, than ATM over the WAN. can transport very high volumes of data, manageability of the campus network Among the possibilities are access to Dark voice and video traffic over different light is a very important selection criterion. Fiber with long-haul extended distance wavelengths. The more homogeneous and simpler Gigabit Ethernet (50 km or more), The pattern of traffic has also been rapidly the network elements are, the easier they Packet-over-SONET/SDH and IP changing, with more than 80 percent of are to manage. Given the ubiquity of over Optical Dense Wave Division the network traffic expected to traverse Ethernet and Fast Ethernet, Gigabit Multiplexing. the MAN/WAN, versus only 20 percent Ethernet presents a more seamless remaining on the local campus. Given One simple yet powerful way for extending integration with existing network the changing pattern of traffic, and the high performance Gigabit Ethernet elements than ATM. Therefore, Gigabit emergence of IP as the dominant network campus networks across the WAN, Ethernet is easier to manage. Gigabit protocol, the total elimination of layers especially in the metropolitan area, is the Ethernet is also easier to manage because of communication for IP over the use of Packet-over-SONET/SDH (POS, of its innate simplicity and the wealth of MAN/WAN means reduced bandwidth experience and tools available with its usage costs and greater application predecessor technologies. performance for the users.

Figure 13: Interconnection Technologies over the MAN/WAN.

B-ISDN IP IP over ATM IP over SONET/SDH ATM IP IP IP over Optical SONET/SDH ATM SONET/SDH IP Optical Optical Optical Optical (A) (B) (C) (D)

24 Gigabit Ethernet and ATM: A Technology Perspective White Paper By contrast, ATM is significantly different from the predominant Ethernet desktops it interconnects. Because of this difference and its relative newness, there are few Because of the fast pace of development tools and skills available to manage ATM efforts during this period, a stable network elements. ATM is also more environment was felt to be needed for difficult to manage because of the consolidation, implementation and inter- complexity of logical components and operability. In April 1996, the Anchorage connections, and the multitude of protocols Accord agreed on a collection of some 60 needed to make ATM workable. On top and interoperability of Gigabit Ethernet ATM Forum specifications that provided of the physical network topology lie a standards. Since its formation in 1996, a basis for stable implementation. Besides number of logical layers, such as PNNI, the Alliance has been very successful in designating a set of foundational and LUNI, LNNI, MPOA, QoS, signaling, helping to introduce the IEEE 802.3z expanded feature specifications, the SVCs, PVCs, and soft PVCs. Logical 1000BASE-X, and the IEEE 802.3ab Accord also established criteria to ensure components are more difficult to 1000BASE-T Gigabit Ethernet standards. interoperability of ATM products and troubleshoot than physical elements services between current and future Similar to the ATM Consortium, the when problems do occur. specifications. This Accord provided the Gigabit Ethernet Consortium was formed assurance needed for the adoption of in April 1997 at the University of New Standards and ATM and a checkpoint for further standards Hampshire InterOperability Lab as a Interoperability development. As of July 1999, there are cooperative effort among Gigabit Like all technologies, ATM and Gigabit more than 40 ATM Forum specifications Ethernet product vendors. The objective Ethernet standards and functions mature in various stages of development. of the Gigabit Ethernet Consortium and stabilize over time. Evolved from a is the ongoing testing of Gigabit Ethernet To promote interoperability, the ATM common technology, frame-based Gigabit products and software from both an inter- Consortium was formed in October Ethernet backbones interoperate seamlessly operability and conformance perspective. 1993, one of several consortiums at the with the millions of connectionless, University of New Hampshire frame-based Ethernet and Fast Ethernet InterOperability Lab (IOL). The ATM desktops and servers in today’s enterprise Consortium is a grouping of ATM product campus networks. By contrast, connection- vendors interested in testing interoperability oriented, cell-based ATM backbones need and conformance of their ATM products additional functions and capabilities that in a cooperative atmosphere, without require standardization, and can easily adverse competitive publicity. lead to interoperability issues. Gigabit Ethernet Standards ATM Standards By contrast, Gigabit Ethernet has evolved Although relatively new, ATM standards from the tried and trusted Ethernet and have been in development since 1984 as Fast Ethernet technologies, which have part of B-ISDN, designed to support been in use for more than 20 years. Being private and public networks. Since the relatively simple compared to ATM, formation of the ATM Forum in 1991, much of the development was completed many ATM specifications were completed, within a relatively short time. The Gigabit especially between 1993 and 1996. Ethernet Alliance, a group of networking vendors including Nortel Networks, promotes the development, demonstration,

Gigabit Ethernet and ATM: A Technology Perspective White Paper 25 • Up to 160 Fast Ethernet 100BASE-FX ports • Up to 64 Gigabit Ethernet family, and BayStack 450 Stackable 1000BASE-SX or -LX ports Switch, complemented by Optivity Policy • Wirespeed switching for Ethernet, Services for policy-enabled networking. Fast Ethernet and Gigabit Ethernet The following highlights key features of • High resiliency through Gigabit the Passport 8000 Enterprise Switch, the LinkSafe and Multi-Link Trunking Passport winner of the Best Network Hardware award from the 1999 Annual SI Impact • High availability through fully Campus Solution distributed switching and management In response to the market requirements Awards, sponsored by IDG’s Solutions architectures, redundant and load-sharing and demand for Ethernet, Fast Ethernet, Integrator magazine: power supplies and cooling fans, and and Gigabit Ethernet, Nortel Networks • High port density, scalability ability to hot-swap all modules offers the Passport Campus Solution as and performance the best-of-breed technology for campus • Rich functionality through support of: • Switch capacity of 50 Gbps, access and backbone LANs. The Passport scalable to 256 Gbps • Port- and protocol-based VLANs Campus Solution (see Figure 14) for broadcast containment, logical • Aggregate throughput of 3 million comprises the Passport 8000 Enterprise workgroups, and easy moves, adds packets per second Switch, with its edge switching and routing and changes capabilities, the Passport 1000 Routing • Less than 9 microseconds of latency • IEEE 802.1Q VLAN Tagging for Switch family, Passport 700 Server Switch • Up to 372 Ethernet 10/100BASE-T carrying traffic from multiple VLANs auto-sensing, auto-negotiating ports over a single trunk • IEEE 802.1p traffic prioritization Figure 14: Passport Campus Solution and Optivity Policy Services. for key business applications • IGMP, broadcast and multicast Server Farm Optivity Policy Services Passport 8000 & Management 10/100 Ethernet rate limiting for efficient broadcast Voice Enterprise Switch MLT resiliency containment • Spanning Tree Protocol FastStart for Data Centillion 100 Common Open Policy Services faster network convergence and recovery Multi-LAN Switch Differentiated Services Gigabit Ethernet IP Precedence/Type of Service LinkSafe resiliency IEEE 802.1Q VLAN Tag • Remote Network Monitoring IEEE 802.1p User Priority Data Express Classification (RMON), port mirroring, and Remote Traffic Monitoring (RTM) for network

Passport 1000 10/100/Gigabit Ethernet Passport 700 Server Switch management and problem determination. Data Routing Switch MLT resiliency server redundancy OSPF & load balancing EMP WAN

Data BN Router redundant gateways System 5000BH Voice Multi-LAN Switch System 390 Mainframe Server

BayStack 450 Video Ethernet Switch Voice Data

26 Gigabit Ethernet and ATM: A Technology Perspective White Paper For users with investments in Centillion 50/100 and System 5000BH LAN-ATM Switches, evolution to a Gigabit Ethernet environment will be possible once Gigabit Ethernet switch modules are offered in available today, before the next paradigm the future. shift, and before new solutions introduce another set of completely new challenges. Information on the other award-winning members of the Passport Campus Gigabit Ethernet provides a pragmatic, Solution is available on Nortel Networks viable, and relatively inexpensive (and For these reasons, Nortel Networks website: http://www.nortelnetworks.com therefore, lower risk) campus backbone solution that meets today’s needs and recommends Gigabit Ethernet as the technology of choice for most campus Conclusion and integrates seamlessly with the omnipresence of connectionless, frame-based Ethernet backbone LANs. ATM was, and continues Recommendation and Fast Ethernet LANs. Enhanced by to be, a good option where its unique and In enterprise networks, either ATM or routing switch technology such as the complex functionality can be exploited, Gigabit Ethernet may be deployed in the Nortel Networks Passport 8000 in deployment, for example, in the campus backbone. The key difference is Enterprise Switches, and policy-enabled metropolitan and wide area network. in the complexity and much higher cost networking capabilities in the Nortel This recommendation is supported by of ATM, versus the simplicity and much Networks Optivity Policy Services, many market research surveys that show lower cost of Gigabit Ethernet. While it Gigabit Ethernet provides enterprise busi- users overwhelmingly favor Gigabit may be argued that ATM is richer in nesses with the bandwidth, functionality, Ethernet over ATM, including surveys functionality, pure technical consideration scalability, and performance they need, at such as User Plans for High Performance is only one of the decision criteria, albeit a much lower cost than ATM. LANs by Infonetics Research Inc. a very important one. (March 1999), and Hub and Switch By contrast, ATM provides a campus Of utmost importance is functionality 5-Year Forecast by the Dell’Oro Group backbone solution that has the disadvantages that meets today’s immediate needs at (July 1999). of undue complexity, unused functionality, a price that is realistic. There is no point and much higher cost of ownership in the in paying for more functionality and enterprise LAN. Much of the complexity complexity than is necessary, that may results from the multitude of additional or may not be needed, and may even components, protocols, control, and be obsolete in the future. The rate of data connections required by connection- technology change and competitive oriented, cell-based ATM to emulate pressures demand that the solution be broadcast-centric, connectionless, frame- based LANs. While Quality of Service (QoS) is an increasingly important requirement in enterprise networks, there are other solutions to the problem that are simpler, incremental, and less expensive.

Gigabit Ethernet and ATM: A Technology Perspective White Paper 27 For more sales and product information, please call 1-800-822-9638. Author: Tony Tan, Portfolio Marketing, Commercial Marketing

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*Nortel Networks, the Nortel Networks logo, the Globemark, How the World Shares Ideas, Unified Networks, BayStack, Centillion, Optivity, and Passport are trademarks of Nortel Networks. All other trademarks are the property of their owners. © 2000 Nortel Networks. All rights reserved. Information in this document is subject to change without notice. Nortel Networks assumes no responsibility for any errors that may appear in this document. Printed in USA. WP3740-B / 04-00