Chapter 14 LAN Systems

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William Stallings

Data and Computer

Communications

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Ethernet (CSAM/CD)

 _{Carriers Sense Multiple Access with}

Collision Detection

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IEEE802.3 Medium Access Control

 _{Random Access}

 Stations access medium randomly

 _Contention

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ALOHA

 _{Packet Radio}

 _{When station has frame, it sends}

 _{Station listens (for max round trip time)plus small}

increment

 _{If ACK, fine. If not, retransmit}

 _{If no ACK after repeated transmissions, give up}  _{Frame check sequence (as in HDLC)}

 _{If frame OK and address matches receiver, send ACK}  _{Frame may be damaged by noise or by another station}

transmitting at the same time (collision)

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Slotted ALOHA

 _{Time in uniform slots equal to frame}

transmission time

 _{Need central clock (or other sync}

mechanism)

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CSMA

 _{Propagation time is much less than transmission time}  _{All stations know that a transmission has started}

almost immediately

 _{First listen for clear medium (carrier sense)}  _{If medium idle, transmit}

 _{If two stations start at the same instant, collision}

 _{Wait reasonable time (round trip plus ACK contention)}  _{No ACK then retransmit}

 _{Max utilization depends on propagation time (medium}

length) and frame length

 _{Longer frame and shorter propagation gives better}

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If Busy?

 _{If medium is idle, transmit}

 _{If busy, listen for idle then transmit}

immediately

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CSMA/CD

 _{With CSMA, collision occupies medium for}

duration of transmission

 _{Stations listen whilst transmitting}

 _{If medium idle, transmit}

 _{If busy, listen for idle, then transmit}  _{If collision detected, jam then cease}

transmission

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Collision Detection

 On baseband bus, collision produces much

higher signal voltage than signal

 _{Collision detected if cable signal greater}

than single station signal

 _{Signal attenuated over distance}

 _{Limit distance to 500m (10Base5) or 200m}

(10Base2)

 _{For twisted pair (star-topology) activity on}

more than one port is collision

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10Mbps Specification (Ethernet)

10Base2 10Base-T 10Base-FP

Medium Coaxial Coaxial UTP 850nm

fiber Signalin

g Baseband Manchest er

Baseband Manchest er

Baseband

y Bus Bus Star Star

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100Mbps (Fast Ethernet)

100Base-TX 100Base-FX 100Base-T4

2 pair, STP

2 optical

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Gigabit Ethernet - Diferences

 _{Carrier extension}

 _{At least 4096 bit-times long (512 for}

10/100)

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Gigabit Ethernet - Physical

 _1000Base-SX

 _{Short wavelength, multimode fiber}

 _1000Base-LX

 _{Long wavelength, Multi or single mode fiber}

 _1000Base-CX

 _{Copper jumpers <25m, shielded twisted}

pair

 _1000Base-T

 _{4 pairs, cat 5 UTP}

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Token Ring (802.5)

 _{MAC protocol}

 _{Small frame (token) circulates when idle}  _{Station waits for token}

 _{Changes one bit in token to make it SOF for data}

frame

 _{Append rest of data frame}

 _{Frame makes round trip and is absorbed by}

transmitting station

 _{Station then inserts new token when transmission has}

finished and leading edge of returning frame arrives

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Dedicated Token Ring

 _{Central hub}

 _{Acts as switch}

 _{Full duplex point to point link}

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802.5 Physical Layer

 _{Note: 1G bit in development}

Data Rate 4 16 100

Medium UTP,STP,Fiber UTP,STP,Fib

er UTP,STP,Fiber

Signaling Diferential

Manchester Diferential Manchester Diferential Manchester Max

Frame 4550 18200 18200

Access

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FDDI

 _100Mbps

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FDDI MAC Protocol

 _{As for 802.5 except:}

 _{Station seizes token by aborting token}

transmission

 _{Once token captured, one or more data}

frames transmitted

 _{New token released as soon as}

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FDDI

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FDDI Physical Layer

Medium Optical Fiber Twisted Pair

Data rate 100 100

Signaling 4B/5B/NRZI MLT-3

Max

repeaters 100 100

Between

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LAN Generations

 _First

 _{CSMA/CD and token ring}

 _{Terminal to host and client server}  _{Moderate data rates}

 _Second  _FDDI

 _Backbone

 _{High performance workstations}  _Third

 _ATM

 _{Aggregate throughput and real time support for}

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Third Generation LANs

 _{Support for multiple guaranteed classes of}

service

 _{Live video may need 2Mbps}

 _{File transfer can use background class}  _{Scalable throughput}

 _{Both aggregate and per host}

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ATM LANs

 _{Asynchronous Transfer Mode}

 _{Virtual paths and virtual channels}  _{Preconfigured or switched}

 _{Gateway to ATM WAN}  _{Backbone ATM switch}

 _{Single ATM switch or local network of}

ATM switches

 _{Workgroup ATM}

 _{End systems connected directly to ATM}

switch

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Compatibility

 _{Interaction between end system on ATM}

and end system on legacy LAN

 _{Interaction between stations on legacy}

LANs of same type

 _{Interaction between stations on legacy}

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Fiber Channel - Background

 _{I/O channel}

 _{Direct point to point or multipoint comms link}  _{Hardware based}

 _{High Speed}

 _{Very short distance}

 _{User data moved from source bufer to} destiation bufer

 _{Network connection}

 _{Interconnected access points}  _{Software based protocol}

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Fiber Channel

 _{Best of both technologies}  _{Channel oriented}

 _{Data type qualifiers for routing frame payload}

 _{Link level constructs associated with I/O ops}

 _{Protocol interface specifications to support}

existing I/O architectures  _{e.g. SCSI}

 _{Network oriented}

 _{Full multiplexing between multiple destinations}

 _{Peer to peer connectivity}

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Fiber Channel Elements

 _{End systems - Nodes}

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Fiber Channel Protocol

Architecture (1)

 _{FC-0 Physical Media}

 _{Optical fiber for long distance}

 _{coaxial cable for high speed short distance}  _{STP for lower speed short distance}

 _{FC-1 Transmission Protocol}

 _{8B/10B signal encoding}

 _{FC-2 Framing Protocol}

 _Topologies

 _{Framing formats}

 _{Flow and error control}

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 _{FC-3 Common Services}  _{Including multicasting}  _{FC-4 Mapping}

 _{Mapping of channel and network}

services onto fiber channel

 _{e.g. IEEE 802, ATM, IP, SCSI}

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Wireless LANs

 _{IEEE 802.11}

 _{Basic service set (cell)}

 _{Set of stations using same MAC protocol}

 _{Competing to access shared medium}

 _{May be isolated}

 _{May connect to backbone via access}

point (bridge)

 _{Extended service set}

 _{Two or more BSS connected by}

distributed system

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Types of station

 _{No transition}

 _{Stationary or moves within direct}

communication range of single BSS

 _{BSS transition}

 _{Moves between BSS within single ESS}  _{ESS transition}

 _{From a BSS in one ESS to a BSS in}

another ESS

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Wireless LAN - Physical

 _Infrared

 _{1Mbps and 2Mbps}

 _{Wavelength 850-950nm}

 _{Direct sequence spread spectrum}

 _{2.4GHz ISM band}  _{Up to 7 channels}

 _{Each 1Mbps or 2Mbps}

 _{Frequency hopping spread spectrum}

 _{2.4GHz ISM band}  _{1Mbps or 2Mbps}

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Media Access Control

 _{Distributed wireless foundation MAC}

(DWFMAC)

 _{Distributed coordination function (DCF)}  _CSMA

 _{No collision detection}

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Required Reading

 _{Stallings chapter 14}

 _{Web sites on Ethernet, Token ring, FDDI,}