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Local Area Network(LAN)

Sarawuth Chaimoolศราวธุ ชยัมลู

jaounarak@hotmail.com

Wireless Communications Research Group (WCR)Department of Electrical Engineering

King Mongkut’s Institute of Technology North Bangkok,Thailand

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Objective

Understand Basic LAN Devices.Understand the Evolution of NetworkDevices.Understand the Basics of Data FlowThrough LANs.Understand the Building of LANs.

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Outline

Basic NetworkBasic LAN DevicesBasics of Data Flow Through LANs.Building of LANs.

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Network Topologies

PAN

LAN-PAN

MAN-LANMAN

WAN-MANWAN

PAN(Personal Area Network)LAN(Local Area Network)MAN(Metro Area Network)WAN(Wide Area Network)

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Local Area Network

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Local Area Network

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Metropolitan Area Network

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Wide Area Network

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Internetwork (Internet)

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LAN Topologies

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Bus Topologies

Single cable connects all computersEach computer has connector to sharedcableComputers must synchronize and allowonly one computer to transmit at a time

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Ring Topology

Computers connected in a closed loop First passes data to second, second passes data tothird, and so onIn practice, there is a short connector cable fromthe computer to the ringRing connections may run past offices withconnector cable to socket in the office:

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Star Topology

Previous diagram is idealized; usually,connecting cables run in parallel to computers:Result is:

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Multiple Topologies

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Multiple Topologies

Each has advantages and disadvantages:Ring ease synchronization; may be disabled ifany cable is cutStar easier to manage and more robust;requires more cablesBus requires fewer cables; may be disable ifcable is cut

Bucknell has used all three; now almost entirelystar topologyIndustry is settling on star topology as mostwidely used

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Networking Media

basic functions of mediacarry a flow of information, in the form ofbits and bytes, through a LAN

confine network signals to a wire, cable,or fiberLayer 1 components of LANs

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Networking Media

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LAN Wiring

ThickNet – 10Base5 ;Thick coax cable

ThinNet – 10Base2 ;“Thin” coax cableUse BNC connectors, “T” connectors for bus

10BaseT, 100BaseT ;Twisted PairUse central hub

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Typical Media

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LAN Devices

Physical featuresFunctions (on a network)OSI layers on which the devices operate

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Function of Computers on the LAN

provide the user with an almost limitlessset of applications

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Network Interface Cards (NICs)

Separate processor, buffers incoming/outgoingdataCPU might not be able to keep up networkspeeds!Distributes processing to avoid overburdeningCPUTypically has DMA access

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NICs

Layer 2 devices :MAC address

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RepeaterMay want to extend LAN medium

Ethernet - timing constraints allow longer mediumSignal strength constraints limit length

Repeater – simplest form is a bidirectional, analogamplifier that retransmits analog signals

Simply copy signals between segments; includesnoise/collisionDo not understand frame formats or addresses

• Not the case with digital repeatersHub acts as a repeater

One repeater can effectively double the length of anLAN segment, e.g. 100m to 200m

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Repeater

Layer 1 devicesREPEATER

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Limits on RepeatersCan't extend Ethernet with repeaters indefinitelyCSMA/CD requires low delay; if medium is too long, CSMA/CDwon't work

Run into the problem of not being able to detect collisionswhile transmitting the frame

Ethernet standard includes limit of 4 repeaters between any twoEthernet stationsReasons for limitations

Ethernet was designed to connect a floor of a building, or acouple floors, but not across wider distancesWill need to go to routers to cross larger distances (connecttwo separate LANs)

Aside from hubs, bridges are used today in favor of repeaters

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Hub

a multi-port repeaterpurpose

amplify and re-time network signals, at the bitlevela large number of users (e.g. 4, 8, or even 24)connect to one shared device

concentration

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Hub

Layer 1 devices

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Bridge

Copies frames from one network to anotherCan operate selectively - does not copy allframes (must look at data-link headers).Extends the network beyond physical lengthlimitations.

BRIDGE

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Layer of Bridge

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Bridges

Looks like one LAN to all systems

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Switch

concentrate connectivity, whileguaranteeing bandwidthable to combine the connectivity of ahub with the traffic regulation of abridge on each portswitches packets from incoming ports(interfaces) to outgoing ports

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Layer of Switch

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Switches

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Routerpath selection, and switching of routerroutes, and packetsEach router interface is connected to adifferent network or network segmentit is considered an inter-networkingdeviceexamine incoming packets, choose thebest path for them through the network,and then switch them to the properoutgoing port

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Layer of Router

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Gateway

Operates as a routerData conversions above the network layer.Conversions:encapsulation - use an intermediate networktranslation - connect different application

protocolsencrpyption - could be done by a gateway

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Encapsulation Example

Gateway Gateway

Provides service connectivity eventhough intermediate network does notsupport protocols.

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Translation

Translate from green protocol to brownprotocol

Gateway

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Encryption gateway

Encryption/DecryptionGateways

SecureNetwork

Secure Network

GWGW ? ??

Insecure Network

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Summary of Network Devices