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

Ethernet - Here to Stay

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 HawaiiFirst 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


Early History

Robert Metcalfe - Inventor of EthernetAlso 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


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

Experimental Version 1.0

Data Rate 2.94 Mbps 10 Mbps Max Network Span 1 Km 2.5 KmMax Segment Length 1 Km 500 mEncoding Type Manchester ManchesterCoax Cable Impedance 75 ohms 50 ohmsSignalling Levels 0 to +3 volts 0 to -2 voltsPreamble Length 1 bit 64 bitsCRC Length 16 bits 32 bitsAddress Length 8 bits 48 bits

First generation successfully proved concept … ran between two computers called Michelson and Morley, who proved “Ether” did not exist!


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


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



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



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



Market Trends do not always follow technoloy (VHS Vs Betamax!)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1995 1996 1997 1998 1999 2000

Ethernet Token Ring

Industry analysis has shown that Ethernet continued to win the battle of the desktop technologies

Token Ring really only significant in vertical markets


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 m10BASE2 30 185 m10BASE-FL 2 2000 m10BASE-T 2 100 m


Fast Ethernet

Same Ethernet but 10 times faster !!IEEE802.3u 100BaseT Standard approved in 1995Employs 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


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


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


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


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


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


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


Conclusions

Ethernet has evolved at a very rapid rate, 10 Mbps … 100 Mbps … 1000Mbps

- this is likely to continue

Documents

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