Unit 13: IEEE 802.3 (Ethernet) a Bit of History…

EECS 122: Introduction to Communication Networks

Unit 13: IEEE 802.3 (Ethernet) A bit of history…

• 1970 ALOHAnet radio network deployed in Hawaiian islands • 1973 Metcalf and Boggs invent Ethernet, random access in wired net • 1979 DIX Ethernet II Standard • 1985 IEEE 802.3 LAN Standard (10 Mbps) • 1995 Fast Ethernet (100 Mbps) • 1998 Gigabit Ethernet • 2002 10 Gigabit Ethernet • Ethernet is today the dominant LAN standard

Metcalf’s Sketch

AW: Unit 13 2 EE 122 Spring 2015 IEEE 802.3 – The „classical Ethernet“

AW: Unit 13 3 EE 122 Spring 2015 IEEE 802.3 MAC: Ethernet

• MAC Protocol: CSMA/CD. • Slot Time is the critical system parameter - upper bound on time to detect collision - upper bound on time to acquire channel - upper bound on length of frame segment generated by collision - quantum for retransmission scheduling - max{round-trip propagation, MAC jam time}

• Truncated binary exponential backoff - for retransmission n: 0 < r < 2k, where k=min(n,10) - Give up after 16 retransmissions

AW: Unit 13 4 EE 122 Spring 2015 IEEE 802.3 Original Parameters

• BASIC ASSUMPTION: all collisions can always be detected by the participating parties (transmitters!) • Transmission Rate: 10 Mbps • Min Frame: 512 bits = 64 bytes • Slot time: 512 bits/10 Mbps = 51.2 µsec - 51.2 µsec x 2x105 km/sec =10.24 km, 1 way - 5.12 km round trip distance • Max Length: 2500 meters + 4 repeaters

• Each x10 increase in bit rate, must be accompanied by x10 decrease in distance

AW: Unit 13 5 EE 122 Spring 2015 LAN Standard Relationship to the ISO/OSI Model

n AUI – Attachment Unit Interface

n MAU – Medium Attachment Unit

n MDI – Medium Dependent Interface

n PMA – Physical Medium Attachment

AW: Unit 13 6 EE 122 Spring 2015 IEEE 802.3 MAC Frame

802.3 MAC Frame 7 1 6 6 2 4 Destination Source Preamble SD Length Information Pad FCS address address Synch Start 64 - 1518 bytes frame l Every frame transmission begins “from scratch” l Preamble helps receivers synchronize their clocks to transmitter clock l 7 bytes of 10101010 generate a square wave l Start frame byte changes to 10101011 l Receivers look for change in 10 pattern

AW: Unit 13 7 EE 122 Spring 2015 IEEE 802.3 MAC Frame

802.3 MAC Frame 7 1 6 6 2 4 Destination Source Preamble SD Length Information Pad FCS address address Synch Start 64 - 1518 bytes frame

0 Single address • Destination address • single address • group address 1 Group address • broadcast = 111...111 Addresses 0 Local address • local or global • Global addresses • first 24 bits assigned to manufacturer; 1 Global address • next 24 bits assigned by manufacturer • Cisco 00-00-0C AW: Unit 13 8• 3COM 02-60-8C EE 122 Spring 2015 IEEE 802.3 MAC Frame

802.3 MAC Frame 7 1 6 6 2 4 Destination Source Preamble SD Length Information Pad FCS address address Synch Start 64 - 1518 bytes frame l Length: # bytes in information field l Max frame 1518 bytes, excluding preamble & SD l Max information 1500 bytes: 05DC l Pad: ensures min frame of 64 bytes l FCS: CCITT-32 CRC, covers addresses, length, information, pad fields l NIC discards frames with improper lengths or failed CRC

AW: Unit 13 9 EE 122 Spring 2015 MAC Frame Format (summary) • Preamble – synchronization of circuitry - 7 bytes made of: 10101010 • SFD – Start Frame Delimiter - Fixed sequence: 10101011 • Length – determine number of data octets • Data – sequence of octets - min/max size is determined by physical layer specification • PAD – padding - If length field is below a certain threshold, a PAD field will be added at the end of the data field - Max(0, minFrameSize - (8n + 2addressSize + 48)), where n is the number of LLC data field octets • FCS – Frame Check Sequence - Check includes all fields between SFD and FCS, CRC polynom G(x)=x32+x26+x23+x22+x16+x12+x11+x10+x8 +x7 +x5 +x4 +x2 +x+1

AW: Unit 13 10 EE 122 Spring 2015 MAC Frame Format (Summary – cont. )

n I/G = 0 → individual address n I/G = 1 → group address n U/L = 0 → globally administered address n U/L = 1 → locally administered address • Individual address - associated with a particular station on the network • Group address - Associated with one or more stations on the network, two types, multicast and broadcast • Locally/globally administered address - Beyond the scope of the standard

AW: Unit 13 11 EE 122 Spring 2015 Collision Handling • Access Interference and recovery

Ø Collsion avoidance by deferring Ø In case of collision: Collision detect signal turns on: Ø Transmission continues: a certain bit sequence is sent ( jam signal – can be generated by any station ) Ø Upon detection of the jam signal, transmission is stopped and retransmission is initiated after a certain deference time. Ø Deference time is selected from a certain interval that is increased after each collision and decreased in case of success. • How are collisions detected? Ø Signals are current-driven on the medium Ø In case of a collision the voltage on the medium is twice the voltage generated by a single station

AW: Unit 13 12 EE 122 Spring 2015 Retransmission and Back-off upon Collision

Ø Collisions will be followed by retransmission until either success or a maximum number of attempts (being set to 16 by the standard)

Ø Scheduling of retransmission: truncated binary exponential back-off Ø Transmission is delayed in terms of slot times Ø Number of slot times for the nth retransmission is chosen as a uniformly distributed integer r in the range: Ø 0

n Note: Introduction of more delay in a special implementation is allowed, this algorithm represents a lower bound nQUESTION: why does this schema work without acknowledgment (in contrast to ALOHA).

AW: Unit 13 13 EE 122 Spring 2015 Retransmission and Backoff upon Collision

AW: Unit 13 14 EE 122 Spring 2015 Media Access Control - Basic Functions

• Data encapsulation/decapsulation - Framing (frame boundary delimination/ synchronization) - Addressing - Error detection • Media Access management - Medium allocation (collision avoidance) - Contention resolution (collision handling)

AW: Unit 13 15 EE 122 Spring 2015 Receive Control Flow

AW: Unit 13 16 EE 122 Spring 2015 Transmit Frame Control Flow

AW: Unit 13 17 EE 122 Spring 2015 IEEE 802.3 Physical Layer

Table 6.2 IEEE 802.3 10 Mbps medium alternatives

10baseFX 10base5 10base2 10baseT (forget it!)

Medium Thick coax Thin coax Twisted pair Optical fiber

Max. Segment Length 500 m 200 m 100 m 2 km

Point-to-point Topology Bus Bus Star link

Hubs & Switches! (a) transceivers (b)

Thick Coax: Stiff, hard to work with T connectors flaky AW: Unit 13 18 EE 122 Spring 2015 Support for Different Media

Ø Coaxial cable. Baseband ! Ø Twisted pair ! - Baseband Ø 10Base5 („Yellow cable“, 10 Mbit/s) Ø 10BaseT (10 Mbit/s) Ø 10Base2 (Cheapernet, 10 Mbit/s) Ø 100BaseTX (100 Mbit/s) Ø 100BaseVG (100 Mbit/s) ØFiber 100BaseXL (100 Mbit/s) ØBroadband On Cable 10 Bas Broad 36 Note: Both the later: HISTORICAL ONLY

10Base5 10Base2 10BaseT 10Broad36 10BaseFP Transmission Coaxial Cable Coaxial Cable Unshielded Coaxial Cable 850 nm – medium (50 Ω) (50 Ω) Twisted Pair (75 Ω) optical fiber pair Signaling Baseband Baseband Baseband Broadband Manchester technique (Manchester) (Manchester) (Manchester) (DPSK) (On-Off) Topology Bus Bus Star Bus/Tree Star Maximum 500 m 185 m 100 m 1800 m 500 m segment length Nodes per 100 30 - - 33 segment Cable diameter 10 mm 5 mm 0.4 – 0.6 mm 0.4 – 1.0 mm 62.5/125 µm

AW: Unit 13 19 EE 122 Spring 2015 Twisted Pair Ethernet (10BaseT) (1)

Example for twisted pair Ethernet connection:

Ø Why Twisted Pair? Ø coax cable drawbacks: Ø 10Base5: complicated and expensive cabling Ø 10Base2: 200m per segment with 30 stations Ø both: cable breaks, bad taps, and loose connectors are major problems with repercussios on a whole segment

AW: Unit 13 20 EE 122 Spring 2015 Twisted Pair Ethernet (10BaseT) Hub

AW: Unit 13 21 EE 122 Spring 2015 Twisted Pair Ethernet (10BaseT) (2)

Ø Twisted Pair advantages: Ø easy maintenance (finding cable breaks) Ø using existing cabling (telephone, structured cabling) Ø easy adding / removing of stations

Ø 10BaseT wiring scheme Ø every station is connected directly to a central hub Ø the function of a hub is to receive and retransmit (repeat with amplification) electrical signals

Ø collision detection and handling is done by every station (DTE) as with coax Ø thus a hub forms a segment (collision domain) Ø a cable from station to hub can be 100 m to 150 m long (cable cat 3 to 5)

AW: Unit 13 22 EE 122 Spring 2015 Example Configuration - System with maximum signal path

AW: Unit 13 23 EE 122 Spring 2015 Round-trip Delays – values in bit timesa Segment Max Left End Midsegment Right End RT Delay type Len. Base Base Base Max. Max. Max. 10Base5 500 m 11.75 46.5 169.5 212.8 0.0866 55.05 89.8 10Base2 185 m 11.75 30.731 46.5 65.48 169.5 188.48 0.1026

FOIRL 1000 m 7.75 107.75 29 152 252 0.1 129 10BaseT 100 mb 15.25 26.55 42 165 176.3 0.113 53.3 10BaseFP 1000 m 11.25 111.25 61 183.5 284 0.1 161 10BaseFB 2000 m N/Ac N/A 24 N/A N/A 0.1 224 10BaseFL 2000 m 12.25 212.25 33.5 233.5 156.5 356.5 0.1

Excess AUI 48 m 0 0 0 4.88 0.1026 4.88 4.88

a. N/A = Not Applicable: 10BaseFB does not support end-connections

AW: Unit 13 24 EE 122 Spring 2015 Ethernet Hubs & Switches

High-Speed backplane Single collision domain (b) or interconnection fabric

(a) l l l l l l l l l l

-Twisted Pair Cheap - Twisted Pair Cheap - Easy to work with - Multi- port switches available - Reliable - Separate collision domains - Passive star - CSMA-CD - Full duplex operation possible SINGLE COLLOSION DOMAIN (no collisions at all !) - Also signal splitter do not scale - Different bit. Rates possible! 8will be used later!!)

AW: Unit 13 25 EE 122 Spring 2015 Hub vs. Switch Collision Domain

Hub Hub

AW: Unit 13 26 EE 122 Spring 2015 Mixed 802.3 with mixed PHY s

AW: Unit 13 27 EE 122 Spring 2015 Switched 802.3

AW: Unit 13 28 EE 122 Spring 2015 Patching the cables for phone and Ethernet

• The individual ports of a switch can be managed separately - E.g. Allowing only a specific MAC address on a given port

AW: Unit 13 29 EE 122 Spring 2015 Switched Approach vs. Shared Medium

• On a shared medium the sender is aware of losses (by detecting collisions) and starts retransmissions • For a shared medium this means no losses (up to maximum retransmission number!) - but variable delays (because of retransmissions) • In a switched topology, there is a need for buffering and forwarding thus there can be losses (buffer overflow etc.) without detection by the original sender of the packet • Higher level protocols have to cope with this problem!! • But this does not scale arbitrarily!!! /broadcasts!)

AW: Unit 13 30 EE 122 Spring 2015 Ethernet Scalability – per collision domain!

CSMA-CD a = .1 a = .01 a = .2 30 25 20 15 10 5 Avg. Transfer Delay 0 0 0.3 0.6 0.9 0.06 0.12 0.18 0.24 0.36 0.42 0.48 0.54 0.66 0.72 0.78 0.84 0.96 Load

• CSMA-CD maximum throughput depends on normalized delay-

bandwidth product a=tprop/X • x10 increase in bit rate = x10 decrease in X

• To keep a constant need to either: decrease tprop (distance) by x10; or increase frame length x10

AW: Unit 13 31 EE 122 Spring 2015 Physical Propagation Limits • In the 10 Mbits/s case, the max end-to-end delay is not achievable on a single piece of cable... The limits because of signal shape.. So we use repeaters ... • The total delay – (propagation + delay on all repeaters) on the longest path must NOT exceed the limiting value... • Higher bit-rate must be compensated by - Either shorter distances (100 Mbits/s Ethernet), or - Longer data packets (1 Gbit/s Ethernet) • In well engineered system errors NOT resulting from collisions are very rare... • This does NOT hold in case of complex topologies: numerous bus- segments interconnected via repeaters… èThe star topology is the winner!!

AW: Unit 13 32 EE 122 Spring 2015 Twisted Pair Cabling

• Category 1: Unshielded twisted-pair (UTP) cable that is suited for voice but not data. Most telephone cable installed before 1983 is Category 1 cable. Not widely used anymore.

• Category 2: UTP cable certified for data transmissions up to 4 Mbits/second. This cable has four twisted pairs.

• Category 3: UTP that supports 10-Mbits/sec transmission rates. The cable must have four pairs and three twists per foot.

• Category 4: UTP certified for 16 Mbits/sec transmission rates The cable has four pairs.

• Category 5: Defines 100-ohm, four-wire twisted-pair UTP copper cable that can transmit data at 100 Mbits/sec The cable is low-capacitance and exhibits low crosstalk.

• Category 5e: similar to above, with decreased cross- talk

• Category 6: Supporting speeds up to 250 Mbits/s, in the version 6A up to 500 mibits/s

AW: Unit 13 33 EE 122 Spring 2015 Twisted Pair Ethernet Connector

Ø The RJ 45 connector Standard wirings (one other option possible)

U + + +

Ø Pin use for 10BaseT +

U- the two paris used for 100 Base TX (one paru per direction!)

AW: Unit 13 34 EE 122 Spring 2015 Fast Ethernet

Table 6.4 IEEE 802.3 100 Mbps Ethernet medium alternatives 100baseT4 100baseT 100baseFX Twisted pair Twisted pair Optical fiber Medium category 3 category 5 multimode UTP 4 pairs UTP two pairs Two strands Max. Segment 100 m 100 m 2 km Length Topology Star Star Star

To preserve compatibility with 10 Mbps Ethernet: • Same frame format, same interfaces, same protocols • Hub topology only with twisted pair & fiber • Bus topology & coaxial cable abandoned • Category 3 twisted pair (ordinary telephone grade) requires 4 pairs • Category 5 twisted pair requires 2 pairs (one per direction). POPULAR • Most prevalent LAN today • NOTE: Auto-negotiations to allow for 100/10 Mbits/s end- systems! AW: Unit 13 35 EE 122 Spring 2015 Gigabit Ethernet

Table 6.3 IEEE 802.3 1 Gbps Fast Ethernet medium alternatives

1000baseSX 1000baseLX 1000baseCX 1000baseT Optical fiber Optical fiber Twisted pair Shielded Medium multimode single mode category 5 copper cable Two strands Two strands UTP Max. Segment 550 m 5 km 25 m 100 m Length

Topology Star Star Star Star

• Slot time increased to 512 bytes • Small frames need to be extended to 512 B • Frame bursting to allow stations to transmit burst of short frames • Frame structure preserved but CSMA-CD essentially abandoned • Extensive deployment in backbone of enterprise data networks and in server farms

AW: Unit 13 36 EE 122 Spring 2015 What Remains from the Ethernet MAC...

Further Improvement: Go duplex! • For 100B – TX one pair of wires in each direction might be used • For 1000 Base T-TX all four pairs are used for each direction in duplex modus! (remember the principle of hybrids in telephony!?) • Auto-negotiation needed to set the speed and the modus

AW: Unit 13 37 EE 122 Spring 2015 10 Gigabit Ethernet

Table 6.5 IEEE 802.3 10 Gbps Ethernet medium alternatives

10GbaseS 10GBaseLR 10GbaseER R Two optical Two optical Two optical fibers fibers fibers Multimode Medium at 850 nm Single-mode Single-mode at at 1310 nm 1550 nm 64B66B SONET Max. code 64B66B compatibility Segment 300 m 10 km 40 km Length

• Frame structure preserved • CSMA-CD protocol officially abandoned • LAN PHY for local network applications • WAN PHY for wide area interconnection using SONET OC-192c

AW: Unit 13 38 EE 122 Spring 2015 Typical Ethernet Deployment

Switches allow coupling Server farm Of segments with different Server Server Server Bit- rates!!!

Gigabit Ethernet links Switch/router Switch/router Gigabit Ethernet links

Server Ethernet Server Ethernet Server Ethernet switch switch switch 100 Mbps links 100 Mbps links 100 Mbps links

Hub Hub Hub

10 Mbps links 10 Mbps links 10 Mbps links

Department A Department B Department C

AW: Unit 13 39 EE 122 Spring 2015 The IEEE 802.11 LOCAL AREA NETWORKS STANDARD FAMILY

AW: Unit 13 40 EE 122 Spring 2015 IEEE 802.x Architecture

• Data Link Layer partitioned in two sublayers:

- LLC (Logical Link Control) LLC - MAC Service - MAC layers: Interface LLC n IEEE 802.3 (CSMA/CD) Data Link Layer n IEEE 802.4 (Token-Passing Bus) MAC n IEEE 802.5 (Token-Ring) Physical n IEEE 802.6 (DQDB) PHY Layer

n IEEE 802.9 (ISLAN) Medium n IEEE 802.11 (Wireless LAN) - MAC general service

n connectionless data transfer service between peer LLC entities

n means to exchange MAC service data units (m_sdu)

AW: Unit 13 41 EE 122 Spring 2015 802.x Standards (first generation…of MAC!)

In between many, many more: Notably WLAN; Sensor Body Area Networks, …

AW: Unit 13 42 EE 122 Spring 2015 Supplementary slides: MAC Service Primitives • MA_DATA.request

MAC/Parameter f_c s_a d_a pr m_sdu s_c d_q 802.3 x x x 802.4 x x x 802.5 x x x x 802.6 x x x x x

- f_c frame control - s_a source_address - d_a destination_address - pr priority - m_sdu MAC service data unit - s_cservice_class (mapped to a single class in 802.3) - d_q desired quality (7 priorities + respond, with_respond & without respond flag) - Uni- or multicast data transfer

AW: Unit 13 43 EE 122 Spring 2015 MAC Service Primitives (2) • MA_DATA.confirm

MAC/Parameter transmission_status quality provided_service_class 802.3 x 802.4 x x 802.5 x x 802.6 - Parameter - response to MA_DATA.request - indication of success/failure with local significance for 802.3/4/5 - significance is point-to-point for 802.4 depending on response flags - (if with_response was set in ma_data.request, it will be passed upon delivery of the requested response frame, upon allowed retries number has occured or local failure) • MA_DATA.status - Parameter: status (pass information about network, MAC or node operation) - indicate change in status - only 802.6 AW: Unit 13 44 EE 122 Spring 2015 MAC Service Primitives (3)

• MA_DATA.indication

MAC/Parameter f_c s_a d_a pr m_sdu r_s q 802.3 x x x x 802.4 x x x x 802.5 x x x x x 802.6 x x x x

• Parameter - see above - r_s pass status information from MAC->LLC - q quality (if (q==with respond) then receiver should respond with a ma_data.request (d_q:=respond)) - indication of data reception

AW: Unit 13 45 EE 122 Spring 2015 Logical Link Control (LLC) Sublayer

• the LLC layer operates on a peer basis; between LLC sub-layer on the two communicating end-systems • the LLC supports connectionless and connection- oriented service • for further details see chapter HDLC

AW: Unit 13 46 EE 122 Spring 2015 LLC Frame Structure

AW: Unit 13 47 EE 122 Spring 2015 Variations of HDLC – LLC (2)

• LLC supports the following service types : - Type 1: Connectionless service (mostly used ! ) - Type 2: Connection-oriented service (very rare usage!) - Type 3: Acknowledged connectionless service (rare!)

n Acknowledged datagrams

n Data collection service (obtain reply service)

AW: Unit 13 48 EE 122 Spring 2015 Variations of HDLC – LLC (3)

Aspects of LLC protocol: a) frame format b) control field bit definitions c) data link control function (type 2)

AW: Unit 13 49 EE 122 Spring 2015 Variations of HDLC – LLC (4)

• LLC-Frames denote SAPs • LLC does not include FCS, this is provided by MAC sub-layer. • The datagram service includes additional commands: - UI (Unnumbered Information): Information Frame without number - XID (eXchange IDentification): If the FRAME uses a group address (at the MAC level) than each group member is requested to answer using the XID-Response; if the FRAME uses a broadcast address (at the MAC Level) this frame has a meaning of announcing the presence of the sending station (to everybody!). - TEST: Loopback-Test option

AW: Unit 13 50 EE 122 Spring 2015 Variations of HDLC – LLC (5)

LLC user service primitives: a) connectionless b) connection oriented

AW: Unit 13 51 EE 122 Spring 2015