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Ethernet LAN Technologies

Ethernet LAN Technologies. Ethernet LAN Technologies. John A.Clark. Agenda. Early History Ethernet Vs Token Ring Structured Cabling Fast Ethernet Gigabit Ethernet GigE Vs ATM. Early History. ALOHAnet - Norman Abrahamson, University of Hawaii First packet radio network, circa 1970

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Ethernet LAN Technologies

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  1. Ethernet LAN Technologies Ethernet LAN Technologies John A.Clark

  2. Agenda • Early History • Ethernet Vs Token Ring • Structured Cabling • Fast Ethernet • Gigabit Ethernet • GigE Vs ATM

  3. Early History • ALOHAnet - Norman Abrahamson, University of Hawaii • First packet radio network, circa 1970 • Several island transmitters communicated reliably to a central station • Had to deal with contention on the radio channel • Multiple stations attempting to transmit at once i.e. “a collision” • Packet transmissions repeated where collisions occurred • Remains in use today for "many to one" telecommunication applications e.g. GSM digital cellular standards … became the basis for Ethernet • Name coined 1972 - Luminiferous “Ether” • … Was though to be the passive medium, through which electromagnetic • waves could propagate, like water ripples, before the work of 20th • century physics

  4. Early History Robert Metcalfe - Inventor of Ethernet Also famous for founding a network/palm-top vendor! • Bob Metcalfe's Harvard PhD Thesis outlines idea for Ethernet • Experimental version at Xerox PARC - Paulo Alto Research Centre in 1972, focussed on coaxial cable shared transmission medium • Metcalfe, Boggs et al patent 1975 • DEC, Intel & Xerox - Ethernet Version 1.0 (1980) & 2.0 (1982) • IEEE 802.3 standard 1983

  5. Experimental Version 1.0 Data Rate 2.94 Mbps 10 Mbps Max Network Span 1 Km 2.5 Km Max Segment Length 1 Km 500 m Encoding Type Manchester Manchester Coax Cable Impedance 75 ohms 50 ohms Signalling Levels 0 to +3 volts 0 to -2 volts Preamble Length 1 bit 64 bits CRC Length 16 bits 32 bits Address Length 8 bits 48 bits Early History Experimental Ethernet - “Ironing out the bugs”! Changes in the Version 1.0 specification and were based upon the experiences with the 1st generation Ethernet First generation successfully proved concept … ran between two computers called Michelson and Morley, who proved “Ether” did not exist!

  6. Early History CSMA/CD - Carrier Sense Multiple Access/ Collision Detect • Carrier sensing & collision detection added to ALOHAnet scheme • Accumulation of -0.9 volt D.C. “carrier” voltage on coax • All collisions must be detected within propagation time of min size packet, 64 bytes (512 bits) = 51.2 usec at 10 Mbps … the Slot Time • Minimum inter-packet gap of 9.6 usec • 32 bit jam - collision consensus enforcement … to flood entire segment

  7. Early History Truncated Binary Exponential Back-off Algorithm Random retransmission delay before retrying after collision • A maximum of 16 retries are allowed • Delay on the nth attempt is a random number of slot times (51.2 usec) between 0 and 2n • Holds until the 11th retry (n=10), when the random delay is truncated to a value between 0 and 210 (1024) slot times • Fairly resolves contention amongst up to 1024 stations • 32 Bit CRC (Cyclic Redundancy Check) Error detection • G(x)=x32+x26+x23+x22+ x16+x12+x11+x10+ x8+x7+x5+x4+ x2 +x+1 • The binary number from the Destination,Source, Length(Type) and Data fields is divided by the result of cycling the last CRC through the polynomial G(x) • The remainder is placed in the CRC field, following the data. • During checking a recalculated CRC is XOR’d to check for a 0 remainder

  8. Ethernet Vs Token Ring • IEEE 802.5 Token Ring • Signals travel around the network from one station to the next, the cabling forming a logical ring • Networks originally operated at 4Mbps, increasing to 16Mbps • Access method on token ring networks is by token passing • Ensures only one station can transmit at a time

  9. Ethernet Vs Token Ring IEEE 802.3 Ethernet • 10 Mbps • CSMA/CD - statistical access • Approx 40% bandwidth efficiency • 1518 Max frame size • No inherent resilience at Physical level • Cost effective to deploy • Rapid advances in technology IEEE 802.5 Token Ring • 4/16 Mbps • Token passing - deterministic access • Up to 90% efficiency - little drop in response time • 15K+ MTU size • Self-healing beaconing process • Higher equipment costs • Slower development of standards & products

  10. Ethernet Vs Token Ring Market Trends do not always follow technoloy (VHS Vs Betamax!) • Industry analysis has shown that Ethernet continued to win the battle of the desktop technologies • Token Ring really only significant in vertical markets

  11. Structured Cabling • Ethernet over twisted pair “telephone cable” !! • Thicknet 10Base5, Thinnet 10base2, optic fibre 10BaseF • AT&T Systimax PDS (Premisis Distribution System) • Flood wiring of new buildings, grid pattern outlets per sq metre • Ronald Schmidt, technical director of SynOptics, creator of the Ethernet 10baseT standard • 10 megabits of baseband data over twisted pair Network Type Max Nodes Per Segment Max Distance Per Segment 10BASE5 100 500 m 10BASE2 30 185 m 10BASE-FL 2 2000 m 10BASE-T 2 100 m

  12. Fast Ethernet Same Ethernet but 10 times faster !! IEEE802.3u 100BaseT Standard approved in 1995 Employs original Ethernet CSMA/CD access method 100BaseT supports 3 physical layers: 100BaseTx: two pair system for Category 5 cabling 100BaseT4: four pair system for Category 3, 4 and 5 cable 100BaseFx: A two strand optic fibre

  13. Gigabit Ethernet 1000 Mbps Ethernet !! • 1996 Gigabit Ethernet developed IEEE 802.3z approved 1997 Leonard Kleinrock of UCLA helped define the mathematical limits of Ethernet, and for naming CSMA/CD).

  14. Gigabit Ethernet Standards Modifications • CSMA/CD method enhanced to maintain 200m collision diameters • Carrier time and Ethernet Slot Time extended from 64 bytes (512 bits) to 512 bytes (4096 bits) = 4.096 usec • Without this change, minimum sized frames could be transmitted before CSMA/CD could detect a collision • Packets smaller than 512 bytes (min still 64 bytes) have a carrier extension to 512 bytes • Adversely affects small packet performance - new facility in CSMA/CD called packet bursting to allow switches/server to send multiple small packets • Switches operating in full-duplex mode do not need carrier/slot time extension or packet bursting • Differential Mode Delay (DMD) problems with laser launch on 62.5 micron optic fibre

  15. GigE Vs ATM Network Speed/Distance Gigabit-Ethernet • 1000BaseCX: 25m • 1000BaseSX: 500m on 50 micron MM fibre, 160m on 62.5 micron (DMD) • 1000BaseLX: 550m all MM fibre , 3km SM fibre • 1Gbps limit • Network Diameter Restrictions when Shared ATM • 25Mbps • 155Mbps - OC3c • 622Mbps - OC12c800m MM/15km SM • 2.4Gbps - OC48c … no theoretical limit • No Network Diameter Restrictions

  16. GigE Vs ATM Network Resilience Gigabit-Ethernet • Spanning Tree Protocol blocks parallel links - stability issues? • No standards based load-sharing - Mostly proprietary • Use of OSPF / RIP with Layer 3 switching ATM • Build-in Redundancy • Parallel Load-sharing links for resilience & aggregate bandwidth • Full Meshed Topologies

  17. GigE Vs ATM Standards Required Gigabit-Ethernet • 802.3z (1000BaseLX/SX/CX) • 802.3ab (1000BaseTX) • 802.3x (Flow Control), Standard since 3/97 • 802.1P (Prioritisation) • 802.1Q (Vlan Queuing) • RSVP (Resource reSerVation Protocol), RFC 2205 ATM • LANE 1.0 • IISP (PNNI Ph 0) • PNNI • LANE 2.0 • MPOA 1.0 • NHRP

  18. GigE Vs ATM Routing/Layer3 Switching Gigabit-Ethernet • Routing via high 100/1000 Mbps links • VLAN trunks with IEEE 802.1Q coming • Layer 3 hardware routing switches with n Mbps throughout/ n usec latency ATM • Routing via high 100 Mbps links (1000Mbps to follow) • VLAN trunks with ATM VNR proven • Layer 3 switching via ATM Forum MPOA (Nortel/Bay) rolling out during Q199

  19. Conclusions Ethernet has evolved at a very rapid rate, 10 Mbps … 100 Mbps … 1000Mbps - this is likely to continue Ethernet - Here to Stay !

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