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Local Area Networks

LANs are designed to: Operate within a limited geographic area Allow multi-access to high-bandwidth media Control the network privately under local

administration Provide full-time connectivity to local services Connect physically adjacent devices

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Local-Area Network LAN

What is a LAN? A collection of computers, printers, modems,

and other devices that can communicate witheach other in a small area (< ~ 1000 feet)

Small area-low cost, high speed, reliablecommunication is possible.

How is a LAN controlled? Protocols Formal sets of rules that govern

how devices on a network exchangeinformation

Standards

Sets of rules or procedures thatare either widely used or officially specified-

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Connector Port

PC or Workstation

Loaded with NOS

Network InterfaceCard (NIC)

Network Interface Card Amplifies electronic signals Packages data for transmission Physically connects computer to

transmission media (cable)

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Network Interface Card

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OSI Model and Project 802

1985 IEEE started with a project, to set standards to enable interconnectivity.

Does not seek to replace modelsWay of specifying functions of the physical layer &data link layer of LAN protocols.

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Project 802

ach subdivision is identified with a number.

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PDU Format

Defines the upper layer protocol at the source and destination that uses these LLC.

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PDU Control Field

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MAC Frame

46 to 1500 bytes

frame

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Common LAN Technologies

Ethernet

Token Ring

FDDIFiber Distributed Data Interface

FDDIDual Ring

TokenRing

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How media access is controlled?- how devices access thecommunication channel in LAN.

Multiple users have unregulatedaccess to channel. LAN needs mechanism to coordinate

traffic and reduce collision. Accessmechanism used in Ethernet CSMA/CD.

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MEDIA ACCESS

Random access protocols Controlled access protocols Token

passing Cannelization protocols- FDMA , TDMA

Random access- all devices have equalaccess to medium.

2 features:-1) there is no scheduled time fora device to transmit.

2) No rule concerning which device shouldtransmit first.

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When should a device attempt toaccess the medium?

What should a system do if it wishes tosend a data frame and the medium isbusy?

How should a device determine whetherthe transmission was successful? How a device know when a collision has

occurred? When a collision occurs, how a device

know if it was involved in it? What should a device do if it detect a

collision.

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Evolution of CSMA/CDALOHA was the 1 st random access usedFor broadband wireless LAN

Developed by university of Hawaii in 1970.

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Ethernet Operation

AA BB CC DD

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Ethernet Operation

AA BB CC DD

D

Data LinkNetworkTransportSession

PresentationApplication

Physical

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Ethernet Operation

AA BB CC DD

D



Physical

B and C



Physical

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Ethernet Broadcast

D

Data LinkNetworkTransportSessionPresentationApplication

Physical

C


Physical

B


Physical

A


Physical

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Ethernet Reliability

B C DA

B C DA Figure 1

Figure 2

Collision

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Collision

C

B C DA

BA D

JAMJAMJAMJAMJAM JAM

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B C DA

Collision

B C DA

JAMJAMJAMJAMJAM JAM

Carrier sense multiple access with

collision detection (CSMA/CD)

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Project 802

ach subdivision is identified with a number.

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10

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Base band systems use Manchester digitalcoding.

Ethernet LANs can support data ratesbetween 1 and 10Mbps.

IEEE defines types of cable, connectionsand signals that are to be used in each offive different Ethernet implementations.

All Ethernet LANs are configured as logicalbuses, although they may be physicallyimplemented in bus or star topologies.

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Ethernet and IEEE 802.3 Benefits and background

Ethernet is the most popular physical layer LANtechnology because it strikes a good balancebetween speed, cost, and ease of installation

Supports virtually all network protocols Revisions of Ethernet specification

Fast Ethernet (IEEE 802.3u) raises speed from

10 Mbps to 100 Mbps Gigabit Ethernet is an extension of IEEE 802.3

which increases speeds to 1 Gbps

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LANspeed (Mbps)

100BaseFX

Base = baseband Broad = broadband

Indicates type of cableand maximum length.If a number,

max. length = # x 100 m

Ethernet Protocol Names

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Bus topology LAN

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10BASE5

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Ethernet Segments

Attachment unit interface transceiver cable. AUIs are restricted to a maximumlength of 50 meters.Medium attachment unit transceiver. Performs CSMA/CD function.

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10BASE2

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10BASET

Instead of individual transceivers, 10 Base T Ethernet places all of its networking

Operations in an Intelligent hub with a port for each station.

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Unshielded Twisted-Pair Cable

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Schemes to improve performanceand speed of Ethernet LAN

Bridged Ethernet

Switched Ethernet Fast Ethernet Gigabit Ethernet

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Switched Ethernet

Entire media is involved in each transmission.- one transmission uses the entirecapacity of 10Mbps.

We can theoretically increase the capacity of network with N devices to N X 10Mbps.

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Fast Ethernet operates at 100 mbps. It is easy to increase the speed if the

collision domain is decreased.

Collision domain of ethernet is limited to2500meters. Needed to achieve data rate

of 10Mbps using the CSMA/CD accessmethod.

U hi ld d T i t d P i

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Unshielded Twisted-Pair(UTP)

Speed and throughput: 10 100 Mbps Average cost per node: Least expensive Media and connector size: Small Maximum cable length: 100 m (short)

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USES TWISTED PAIR CABLE

Star LAN

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1BASE5

Daisy chaining starLAN allows as many as 10 stations to be linked, each to the next,In a chain in which only the lead device connects to the hub.

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Switched Ethernet

Entire media is involved in each transmission.- one transmission uses the entirecapacity of 10Mbps.

We can theoretically increase the capacity of network with N devices to N X 10Mbps.

MAC F

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MAC Frame

46 to 1500 bytes

frame

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Minimum size of frame 72 bytes .ie 576 bits.To send 576bits at data rate of 10 mbps takes57.6 us.

Collision must be detected during 57.6us. Thistime is sufficient to allow a signal to make around trip of 5000 meters at a propagationspeed in a typical medium.

To increase data rate without changingminimum size of frame . We decrease round

trip time. With 100mbps the round trip timereduces to 5.76us(576 bits/100mbps). Thismeans collision domain must be decreased 10times, from 2500 to 250 meters.

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Printer (Also has a NIC)

NIC

PC or WorkstationLoaded with NOS

Wiring Hub

Cables or Transmission Media

Physical environments through

which transmission signals pass Twisted pair Coaxial cable

Connectors (RJ-11, RJ-45, etc.)

Cable

Fiber-optic cable Atmosphere

Connectors

RJ-45Connector

RJ = Registered Jack

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Network Cabling Media connecting network components

NIC cards take turns transmitting on the cable LAN cables only carry one signal at a time WAN cables can carry multiple signals simultaneously

Three primary types of cabling Twisted-pair (or copper) Coaxial cable Fiber-optic cable

Twisted-Pair Cable

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Twisted-Pair Cable

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Twisted-Pair (UTP and STP)

Speed and throughput: 10/100 Mbps

Relative cost: Least costly

Media and connector size: Small

Maximum cable length: 100 m

RJ-45Connector

Color-CodedPlastic Insulation

Twisted-Pair

Outer Jacket

STP only:Shielded Insulationto Reduce EMI

EMI = Electromagnetic Interference

Unshielded Twisted Pair

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Unshielded Twisted-Pair(UTP)

Speed and throughput: 10 100 Mbps Average cost per node: Least expensive Media and connector size: Small Maximum cable length: 100 m (short)

1 2 3 6 normally used for data transmission.

Most common UTPConnector.Registered jack

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The Electronic Industries association hasdeveloped standards to grade UTP cables byquality. With 1 the lowest and 5 as highest.

Category1 basic twisted pair cabling used intelephone systems. This level of quality is finefor voice communication.

Category2 next higher grade, suitable for voiceand data transmission up to 4 Mbps.

Category3 used for data transmission of up to10 Mbps.

Category4 up to 16Mbps Category5 used for data transmission up to

100Mbps

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UTP Connectors

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Shielded Twisted-Pair (STP)

Speed and throughput: 10 100 Mbps Average cost per node: Moderately expensive Media and connector size: Medium to Large Maximum cable length: 100 m (short)

Coaxial Cable

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Coaxial Cable

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Coaxial Cable

Speed and throughput: 10/100 MbpsRelative cost: More than UTP, but still low

Media and connector size: Medium

Maximum cable length: 200/500 m

Outer Jacket Braided Copper ShieldingPlastic Insulation

Copper Conductor

BNC Connector

BNC = Bayonet Neill Concelman

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Fiber-Optic CableOuter Jacket Kevlar ReinforcingMaterial

PlasticShield Glass Fiber

and Cladding

Single mode: One stream of laser-generated light (100 km)

Multimode: Multiple streams of LED-generated light (2 km)

Speed and throughput: 100+ MbpsAverage cost per node: Most expensive

Media and connector size: Small

Maximum cable length: Up to 2 km

MultimodeConnector

LED = Light Emitting Diode

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LANspeed (Mbps)

100BaseFX

Base = baseband Broad = broadband

Indicates type of cableand maximum length.If a number,max. length = # x 100 m

Ethernet Protocol Names

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10BASE5

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10BASE5

Transceiver

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Transceiver

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10BASET

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10BASET

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Unshielded Twisted-Pair Cable

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Go back-N Damaged Frame

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g

Selective Reject

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Selective Reject

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L t F

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Lost Frame

CH-3.1 LAN

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