Ethernet LAN Technologies John A Clark Ethernet Here

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

Agenda £ Early History £ Ethernet Vs Token Ring £ Structured Cabling £ Fast Ethernet £ Gigabit Ethernet £ Gig. E Vs ATM 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 u Had to deal with contention on the radio channel u Multiple stations attempting to transmit at once i. e. “a collision” u Packet transmissions repeated where collisions occurred u Remains in use today for "many to one" telecommunication applications e. g. GSM digital cellular standards … became the basis for Ethernet u 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 20 th century physics Ethernet - Here to Stay

Early History Robert Metcalfe - Inventor of Ethernet Also famous for founding a network/palm-top vendor! u u u Bob Metcalfe's Harvard Ph. D 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 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 1 st generation Ethernet Data Rate Max Network Span Max Segment Length Encoding Type Coax Cable Impedance Signalling Levels Preamble Length CRC Length Address Length Experimental Version 1. 0 2. 94 Mbps 1 Km Manchester 75 ohms 0 to +3 volts 1 bit 16 bits 8 bits 10 Mbps 2. 5 Km 500 m Manchester 50 ohms 0 to -2 volts 64 bits 32 bits 48 bits First generation successfully proved concept … ran between two computers called Michelson and Morley, who proved “Ether” did not exist! Ethernet - Here to Stay

Early History CSMA/CD - Carrier Sense Multiple Access/ Collision Detect u u u 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 Ethernet - Here to Stay

Early History Truncated Binary Exponential Back-off Algorithm Random retransmission delay before retrying after collision u u 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 11 th 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 u 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) u The remainder is placed in the CRC field, following the data. u During checking a recalculated CRC is- XOR’d check for a 0 remainder Ethernet Here toto. Stay

Ethernet Vs Token Ring IEEE 802. 5 Token Ring u u Signals travel around the network from one station to the next, the cabling forming a logical ring Networks originally operated at 4 Mbps, increasing to 16 Mbps Access method on token ring networks is by token passing Ensures only one station can transmit at a time 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 15 K+ MTU size Self-healing beaconing process Higher equipment costs Slower development of standards & products Ethernet - Here to Stay

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

Structured Cabling Ethernet over twisted pair “telephone cable” !! Thicknet 10 Base 5, Thinnet 10 base 2, optic fibre 10 Base. F u AT&T Systimax PDS (Premisis Distribution System) u Flood wiring of new buildings, grid pattern outlets per sq metre u u u Ronald Schmidt, technical director of Syn. Optics, creator of the Ethernet 10 base. T standard 10 megabits of baseband data over twisted pair Network Type 10 BASE 5 10 BASE 2 10 BASE-FL 10 BASE-T Max Nodes Per Segment 100 30 2 2 Max Distance Per Segment 500 m 185 m 2000 m 100 m Ethernet - Here to Stay

Fast Ethernet Same Ethernet but 10 times faster !! IEEE 802. 3 u 100 Base. T Standard approved in 1995 Employs original Ethernet CSMA/CD access method 100 Base. T supports 3 physical layers: 100 Base. Tx: two pair system for Category 5 cabling 100 Base. T 4: four pair system for Category 3, 4 and 5 cable 100 Base. Fx: A two strand optic fibre Ethernet - Here to Stay

Gigabit Ethernet 1000 Mbps Ethernet !! u 1996 Gigabit Ethernet developed IEEE 802. 3 z approved 1997 Leonard Kleinrock of UCLA helped define the mathematical limits of Ethernet, and for naming CSMA/CD). Ethernet - Here to Stay

Gigabit Ethernet Standards Modifications u u u u CSMA/CD method enhanced to maintain 200 m 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 Ethernet - Here to Stay

Gig. E Vs ATM Network Speed/Distance · · · Gigabit-Ethernet 1000 Base. CX: 25 m 1000 Base. SX: 500 m on 50 micron MM fibre, 160 m on 62. 5 micron (DMD) 1000 Base. LX: 550 m all MM fibre , 3 km SM fibre 1 Gbps limit Network Diameter Restrictions when Shared · · · ATM 25 Mbps 155 Mbps - OC 3 c 622 Mbps - OC 12 c 800 m MM/15 km SM 2. 4 Gbps - OC 48 c … no theoretical limit No Network Diameter Restrictions Ethernet - Here to Stay

Gig. E Vs ATM Network Resilience Gigabit-Ethernet · · · Spanning Tree Protocol blocks parallel links stability issues? No standards based loadsharing - 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 Ethernet - Here to Stay

Gig. E Vs ATM Standards Required Gigabit-Ethernet · · · 802. 3 z (1000 Base. LX/SX/CX) 802. 3 ab (1000 Base. TX) 802. 3 x (Flow Control), Standard since 3/97 802. 1 P (Prioritisation) 802. 1 Q (Vlan Queuing) RSVP (Resource re. Ser. Vation Protocol), RFC 2205 ATM · · · LANE 1. 0 IISP (PNNI Ph 0) PNNI LANE 2. 0 MPOA 1. 0 NHRP Ethernet - Here to Stay

Gig. E Vs ATM Routing/Layer 3 Switching Gigabit-Ethernet · · · Routing via high 100/1000 Mbps links VLAN trunks with IEEE 802. 1 Q coming Layer 3 hardware routing switches with n Mbps throughout/ n usec latency ATM · · · Routing via high 100 Mbps links (1000 Mbps to follow) VLAN trunks with ATM VNR proven Layer 3 switching via ATM Forum MPOA (Nortel/Bay) rolling out during Q 199 Ethernet - Here to Stay

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