Introduction to
WANS
Wide Area Networks
Introduction to WANS
1
WIDE AREA NETWORKS

Reasons for using WANs :

connecting distant computers together

connecting distant networks together
(LANs and WANs)

access to / sharing of remote services

Topology: Arbitrary

Size/Distance between nodes: from 10's of kilometres and up
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WAN ORGANISATION

WANs may be interconnected to form bigger WANs

WANs are usually owned / operated by

multinational corporations - private, secure

governments - military, academic, admin

service providers - re-sell connection to others

WANs tend to evolve over time, in an ad hoc manner (difficult to plan them)

The Internet is a collection of many Interconnected WANs
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COMMUNICATION USING WANS
Transmission Media:

copper

optical fibre

radio (terrestrial and satellite)
Transmission Rate: Usually slower than LANs, although high-speed WAN technologies
are available (for a price)
Slow speed

1200 - 56kbps (e.g. X.25)

64kbps (1 ISDN channel, BT kilostream)
High speed

1.544 Mbps (T1)

25 Mbps (e.g. ATM)

44.736 Mbps (T3)
Protocols used on WANs include:

Frame Relay

ATM (Asynchronous Transfer Mode)

SMDS (Switched Multi-megabit Data Service)

X.25
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EXAMPLE: SUPERJANET

JANet (Joint academic network) runs at 2Mbps

New netrwork is SuperJANET: 34Mbps or 140Mbps

Started in 1993/94 to allow high-speed communication between academic sites
e.g. cms.dmu.ac.uk domain to Manchester's WWW server (www.cs.man.ac.uk) cs-gate.cms.dmu.ac.uk
smds-gw.dmu.ac.uk
smds-gw.mcc.ja.net
gw-mcc.g-ming.net.uk
gw-mcc3.mcc.ac.uk
www.cs.man.ac.uk
average round-trip time 12ms


Applications

Distance Learning

Group Collaboration (e.g. using video-conferencing)

Fast access to High-bandwidth information (e.g. high resolution images)

High-speed access to supercomputer facilities
Plans to upgrade links to 600Mbps
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INTERNETWORKING
Joining networks together may be done in several ways, depending on whether
networks are similar or different
Repeater

Boosts network signal allowing LAN to be extended past normal size
Bridge

Connects two LANs (e.g. 2 ethernet buses)

Passes packets between the LANs based on address information in the packets
Router

Allows dissimilar LANs to be connected (converts protocols)

Generally connects more than 2 networks, holding information about how to
route the packets
Gateway

Provides more complex protocol conversion than Router

Used to connected LANs, MANs and WANs
In practice many commercial products
combine these functions, so things can
get very confusing!
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