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Ethernet - Here to Stay Ethernet LAN Technologies John A.Clark.

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Presentation on theme: "Ethernet - Here to Stay Ethernet LAN Technologies John A.Clark."— Presentation transcript:


2 Ethernet - Here to Stay Ethernet LAN Technologies John A.Clark

3 Ethernet - Here to Stay Agenda Early History Ethernet Vs Token Ring Structured Cabling Fast Ethernet Gigabit Ethernet GigE Vs ATM

4 Ethernet - Here to Stay 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

5 Ethernet - Here to Stay 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

6 Ethernet - Here to Stay 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 ExperimentalVersion 1.0 Data Rate 2.94 Mbps10 Mbps Max Network Span1 Km2.5 Km Max Segment Length1 Km500 m Encoding TypeManchester Manchester Coax Cable Impedance75 ohms50 ohms Signalling Levels0 to +3 volts0 to -2 volts Preamble Length 1 bit64 bits CRC Length16 bits32 bits Address Length8 bits48 bits First generation successfully proved concept … ran between two computers called Michelson and Morley, who proved Ether did not exist!

7 Ethernet - Here to Stay 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

8 Ethernet - Here to Stay 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 2 n 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)=x 32 +x 26 +x 23 +x 22+ x 16 +x 12 +x 11 +x 10+ x 8 +x 7 +x 5 +x 4+ x 2 +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 XORd to check for a 0 remainder

9 Ethernet - Here to Stay 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

10 Ethernet - Here to Stay 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

11 Ethernet - Here to Stay 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

12 Ethernet - Here to Stay 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

13 Ethernet - Here to Stay 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

14 Ethernet - Here to Stay 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). 1000 Mbps Ethernet !! Gigabit Ethernet

15 Ethernet - Here to Stay 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 Standards Modifications Gigabit Ethernet

16 Ethernet - Here to Stay 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 - OC12c 800m MM/15km SM 2.4Gbps - OC48c … no theoretical limit No Network Diameter Restrictions

17 Ethernet - Here to Stay 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

18 Ethernet - Here to Stay 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

19 Ethernet - Here to Stay 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

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

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