CN LAN Networks

8/11/2019 CN LAN Networks

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Computer Networks

Module 5 - LAN Networks


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Key features of LANs

Limited geographical area High Speed

High Reliability

Transmission Media

Topology

Medium-Access Control Techniques


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What is LAN? (Local Area Netw

A LAN consists of shared transmissiomedium and a set of hardware and so

for interfacing devices to the medium

regulating the ordering access to the

medium.

Used to share resources and to excha

information.


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IEEE 802


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IEEE 8021. The 802.1 sublayer - provides relation

between the OSI model and the 802standards.

2. 802.2sublayer describes the LLC (log

link layer) - facilitate error control and controla. Unreliable datagram service

b. Acknowledged datagram service

c. Reliable connection oriented service


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IEEE CSMA/CD based LANs

Three data rates over optical fiber and tpair cables

1. 10 Mbps10Base-T Ethernet

2. 100 MbpsFast Ethernet

3. 1000 MbpsGigabit Ethernet


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Ethernet Architecture

Physical layer:this layer takes care of folfunctions.

Encoding and decoding

Collision detection

Carrier sensing Transmission and receipt


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Ethernet Architecture

Data link layer:Following are the majorfunctions of this layer.

Station interface

Data Encapsulation /Decapsulation

Link management Collision Management


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ypes o me um an conven oused to represent them


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10Base-T


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IEEE 802.3 - EncodingBi-phase Manchester Coding - ensures frequent

voltage transitions, directly proportional to the clocthis helps clock recovery. original data = clock XOR Manch
http://en.wikipedia.org/wiki/Clock_recoveryhttp://en.wikipedia.org/wiki/Clock_recovery


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Manchester Coding

original data = Clock XOR Manchester value

0 0 0

0 1 1

1 0 1

1 1 0

0 0 0


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The Ethernet MAC Sublayer

Two primary responsibilities:Data encapsulation, including frame ass

before transmission, and frame parsing/e

detection during and after reception

Media access control, including initiationframe transmission and recovery from

transmission failure


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The Basic Ethernet Frame Form


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EthernetCSMA/CD


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Token Ring (IEEE 802.5)

A Token is passed in the network and thstation that gets the token can only trans

Stations are connected by point-to-point

using repeaters


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Token Ring Working


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Advantages of Token Ring

collisions cannot occur in Token Ringnetworks.

token-passing networks are determini

which means that it is possible to calc

the maximum time that will pass beforend station will be capable of transmit


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Priority System in Token Ri


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Token - Ring 2 Error Condition

1. Lost token - No token the ring

2. Busy tokenToken circulates endlessly

IEEE 802 standard - one of the stations be desi

as active monitor

detects the lost condition using a timer by time-mechanism

detect a circulating busy token, the monitor set

monitor bit


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Token Ring - Physical Laye


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Token Ring - Frame Forma

Two basic frame types:1. tokens

2. data/command frames.


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Wireless LAN 802.11- Advantag

1. Availability of low-cost portable equip2. Mobility

3. Installation speed and simplicity

4. Installation flexibility

5. Reduced cost of ownership6. Scalability


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Transmission Media for 802.11

1. InfraredSimple in design and therefore inexpensiveRequire an unobstructed line of sight

2. Microwavehigher throughput achieved because they do n

the overhead involved with spread spectrum sy

3. Radio1. Direct Sequence Spread Spectrum (DSSS) Scheme

2. Frequency Hopping Spread Spectrum (FHSS)


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Direct Sequence Spread Spectrum (DSSS) s


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DSS Encoding Scheme

Frequency Hopping Spread Spectrum (FH


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Frequency Hopping Spread Spectrum (FH

Topology


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Topology


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Wireless LANs 802.11

CSMA/CA Back-off algorithm


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Framing

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