Local Area Networks

Local Area Networks (LAN)

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A local area network (LAN) encompasses a limited distance, usually one building or several buildings in close proximity. Most LAN’s connect devices located within a 2000-foot radius, and they have been widely used to link personal computers and associated devices. Common LAN Configurations and LAN technologies include Ethernet, Token Ring, and FDDI.

Ethernet Most widely used with a good balance between speed, cost, and ease of installation and speed ranges of 10 Mbps to 1000 Mbps.
	Token Ring Token Ring is primarily used with IBM networks with speed ranges of 4 Mbps to 16 Mbps.
Fiber Distributed Data Interface (FDDI) FDDI is primarily used for corporate backbones and supports longer distances with speeds of 100 Mbps.

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Ethernet LAN

Benefits and background

Ethernet is the most popular physical layer LAN technology because it strikes a good balance between speed, cost, and ease of installation

Supports virtually all network protocols

Xerox initiated, then joined by DEC & Intel in 1980

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 1000 Mbps, or 1 Gbps

Fast Ethernet

Gigabit Ethernet

» 1000 Mbps data rate

» 802.3/Ethernet frames

» Full duplex or half duplex

» 100% compatible with existing:
     - Network protocols
     - Network operating systems
     - Network applications
     - Network management

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Token Ring

History
· Developed by IBM in the 1970s, IEEE 802.5 spec is totally compatible with Token Ring
· Second to Ethernet in popularity

Features
· Token determines transmission so no collisions
· Ideal for applications (such as factory automation) where delay must be predictable and robust network operation is important
· More difficult and costly than Ethernet, but little impact as more users are added to system.

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FDDI Fiber Distributed Data Interface

History

Defined by ANSI X3T9.5 spec in mid 1980s
100-Mbps token-passing network
Fiber-optic cable with max. distance of 2 km
Dual-ring architecture for redundancy
Used for corporate and carrier backbones

FDDI

Implements FDDI over (STP) Shielded Twisted Pair and (UTP) Unshielded Twisted Pair cable
Transmits at 100 Mbps over about 100 m

Features

Dual-ring architecture

Primary ring for data transmissions
Secondary ring for reliability and robustness

Components

Single attachment station (SAS)—PCs
Dual attachment station (DAS)—Servers
Concentrator

FDDI concentrator

Also called a dual-attached concentrator (DAC)

Building block of an FDDI network

Attaches directly to both rings and ensures that any SAS failure or power-down does not bring down the ring.

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