LOCAL AREA NETWORKLOCAL AREA NETWORK A A local area network (lan)local area network (lan) is a communication network that is a communication network that

interconnects a variety of data communicating devices within a small interconnects a variety of data communicating devices within a small geographic area. geographic area.

A lan broadcasts data at high data transfer rates with very low error A lan broadcasts data at high data transfer rates with very low error rates.rates.

lan enables the sharing of resources such as files or hardware lan enables the sharing of resources such as files or hardware devices that may be needed by multiple users.devices that may be needed by multiple users.

It is limited in size, typically spanning a few It is limited in size, typically spanning a few hundred meters, and no more than a mile.hundred meters, and no more than a mile.

Is fast, with speeds from 10 Mbps to 10 Gbps.

• Requires little wiring, typically a single cable connecting to each device.

Has lower cost compared to MAN’s or WAN’s

PRIMARY FUNCTION OF PRIMARY FUNCTION OF LANLAN File servingFile serving

large storage disk drive acts as a central storage repositorylarge storage disk drive acts as a central storage repository

Print servingPrint serving Providing authorization to access a printer, accept and queue print jobs, Providing authorization to access a printer, accept and queue print jobs,

and administer printing dutiesand administer printing duties

Email servingEmail serving Interconnecting multiple systemsInterconnecting multiple systems Video transferVideo transfer

High speed LANs support image and video streamingHigh speed LANs support image and video streaming

Distributed computation (e.g., gridDistributed computation (e.g., grid computing)computing) Applied fields:Applied fields:

E.g., Manufacturing, office, academicsE.g., Manufacturing, office, academics

Basic LAN TopologiesBasic LAN Topologies

Bus/treeBus/treeStar-wired busStar-wired busStar-wired ringStar-wired ringWireless Wireless

Bus/Tree TopologyBus/Tree Topology

Original topology in 70s, almost extinct for LAN, but still Original topology in 70s, almost extinct for LAN, but still

used in cable televisionused in cable television signalingsignaling Workstation’s Network Interface Card (NIC) attaches to Workstation’s Network Interface Card (NIC) attaches to

bus (e.g., a coaxial cable) via a tap.bus (e.g., a coaxial cable) via a tap. Two signaling technologies:Two signaling technologies:

Baseband digital signaling: bidirectional (broadcast)Baseband digital signaling: bidirectional (broadcast) Broadband analog signaling: FDM, unidirectional Broadband analog signaling: FDM, unidirectional

(require special wiring)(require special wiring) Forming Trees: buses can be split and joinedForming Trees: buses can be split and joined Disadvantage: difficult to add if there is no tap, but Disadvantage: difficult to add if there is no tap, but

anticipate tap need in advance is difficultanticipate tap need in advance is difficult

Star-wired Bus TopologyStar-wired Bus Topology Differs from Star LAN, an old star topologyDiffers from Star LAN, an old star topology Logically operates as a bus, but physically looks like a starLogically operates as a bus, but physically looks like a star Components:Components:

HubHub non-intelligent, takes incoming signal and immediately retransmit it non-intelligent, takes incoming signal and immediately retransmit it

to all connected linksto all connected links Workstations linked to Hub via Unshielded TWPWorkstations linked to Hub via Unshielded TWP

Hubs can be interconnected to extend network sizeHubs can be interconnected to extend network size e.g., 24-port hube.g., 24-port hub

Inter hub connections can use TWP, coaxial, or fiber optic Inter hub connections can use TWP, coaxial, or fiber optic cablecable

Adv: simple installation & maintenance, low-cost, biggest Adv: simple installation & maintenance, low-cost, biggest market sharemarket share

Biggest disadv: – Shared NetworkBiggest disadv: – Shared Network one talks, everyone hears itone talks, everyone hears it

Star-wired Ring TopologyStar-wired Ring Topology

Logically operates as a ring, but physically looks like a starLogically operates as a ring, but physically looks like a star Use baseband signals which has only one channel, signals Use baseband signals which has only one channel, signals

are unidirectionalare unidirectional Components:Components:

MAU (Multistation Access Unit)MAU (Multistation Access Unit) similar to Hub, but only retransmit in unidirectionsimilar to Hub, but only retransmit in unidirection

TWP wiringTWP wiring MAUs can be interconnected to increaseMAUs can be interconnected to increase network sizenetwork size Adv: simple installation & maintenanceAdv: simple installation & maintenance Disadv: slower transmission, higher cost,Disadv: slower transmission, higher cost, more more complex complex

software – close to extinctionsoftware – close to extinction

Wireless LANsWireless LANs No cabling, No any set physical patternNo cabling, No any set physical pattern

Workstation within acceptable transmission rangeWorkstation within acceptable transmission range to AP;to AP; aa few few feet up to 800 feetfeet up to 800 feet

3 Components: 3 Components: User device/wireless station: e.g., NIC w/ antennaUser device/wireless station: e.g., NIC w/ antenna Access Point (AP) – e.g., Ethernet port plus transceiverAccess Point (AP) – e.g., Ethernet port plus transceiver

AP acts as a bridge betw. wireless and wired networks AP acts as a bridge betw. wireless and wired networks Can perform basic routing functionsCan perform basic routing functions

Wired LAN which links to servicesWired LAN which links to services 3 Configurations: 3 Configurations:

BSS: single-cell w/ one APBSS: single-cell w/ one AP ESS: multiple-cell w/ multiple APsESS: multiple-cell w/ multiple APs Peer-to-peer or Ad-hoc: no APPeer-to-peer or Ad-hoc: no AP

ADVANTAGES OF LANADVANTAGES OF LAN Share resources efficiently.Share resources efficiently. hardware, softwarehardware, software

Individual workstation might survive network failure if it Individual workstation might survive network failure if it doesn’t rely upon othersdoesn’t rely upon others

Component evolution independent of system evolutionComponent evolution independent of system evolution Support heterogeneous hardware/softwareSupport heterogeneous hardware/software Access to other LANs and WANsAccess to other LANs and WANs High transfer rates with low error ratesHigh transfer rates with low error rates Private ownership vs. lease vs. outsourcingPrivate ownership vs. lease vs. outsourcing

DISADVANTAGES OF LANDISADVANTAGES OF LAN

Equipment and support can be costlyEquipment and support can be costly Network server, NOS, cabling, security, maintenance, etcNetwork server, NOS, cabling, security, maintenance, etc ..

Management and control can be costlyManagement and control can be costly Licensing issues for network applicationsLicensing issues for network applications Some types of hardware/software may not Some types of hardware/software may not

interoperateinteroperate Upgrades may have ripple effectsUpgrades may have ripple effects

A LAN is only as strong as it weakest link, and there are A LAN is only as strong as it weakest link, and there are many linksmany links