CHAPTER 8WIDE AREA NETWORK (WAN)

INTRODUCTION Wide Area Network (WAN) is a data

communications network that covers a relatively broad geographic area & that often uses transmission facilities provided by common carriers such as telephone companies. Ex: Internet

Most WANs are combination of LANs & other communication components connected by communication links known as ‘ Wan Links’.

WAN link includes: Packet switching networks Fiber optic cable Satellite links Cable television coaxial systems

WHY WE NEED A WAN?

Any businesses/organizations/governments with offices scattered everywhere over a wide geographical area need a way to exchange data between those sites.

Some of the scenarios where you need a WAN : A bank with branches all over the world – gather

transactions into central database. Regional sales representatives needing to submit sales

files to their HQ in other states/countries A clothing manufacturer selling products through

Internet to their customers through out the world. Factors in choosing WAN type: traffic load, budget,

geographical area & commercially available technology.

SWITCHING TECHNOLOGIES

Following are the switching techniques used for WAN: Circuit Switching Packet Switching Message Switching Cell Switching

CIRCUIT SWITCHING NETWORK Establishes a dedicated circuit (or channel)

between nodes & terminals before the users may communicate.

Each circuit that is dedicated cannot be used by other callers until the circuit is released & a new connection is set up.

Has been used since the first communication network in the nineteenth century & a dominant technology for voice communication today.

CIRCUIT SWITCHING NETWORKS

CIRCUIT SWITCHING NETWORKS

Communication via circuit switching networks involves 3 phases: Circuit establishment – an end-to-end connection

must be established before any signal can be transmitted via the channel.

Data transfer – the transmission may be analog voice, digitalized voice or binary data depending on the nature of the network.

Circuit disconnection – once the transmission is complete, the connection will be terminated by one of the end station.

CIRCUIT SWITCHING NETWORKS

Advantages Disadvantages

Compatible with voice No routing techniques, call subject to blockage

No special training / protocols are needed to handle data traffic

Devices at both ends must be compatible in terms of protocols & data flow.

Predictable, constant rate of data traffic

Large processing & signal burden on the network

PACKET SWITCHING NETWORK Fast, convenient & reliable technology which is used

to transmits data over extensive areas such as across cities, states or countries.

It is a network technology that breaks up a message into smaller packets for transmission.

Unlike circuit switching which requires point to point connection establishment, each packet in the packet switched network contains a destination address.

Thus, each packets in a single message do not have to travel the same path & can arrive out of order.

Destination computer reassembles them into proper sequence.

Network protocols used: IP & IPX

PACKET SWITCHING NETWORK

HOW PACKET SWITCHING NETWORK WORKS

Original message is broken into smaller packets & tagged with destination address & other information (allows them to travel separately)

Packets are relayed through station in a network & the path selected for packet to travel depends on the bandwidth between stations.

Each packet travels separately & reach the same destination.

Receiving computer can reassemble the original message by looking at information contained in the packet

PACKET SWITCHING NETWORK

DATAGRAM & VIRTUAL CIRCUIT

Packet switching networks supports 2 service:

Datagram In which each packet is treated independently &

packet path is chosen based on the information received from neighboring nodes on traffic, line failures etc. Each independent packet referred as a datagram !

Virtual circuit Pre-planned route is established before sending any

packets. Once the route is stabled, all packets follow the route but it is logical connection for fix duration and referred as virtual circuit.

VIRTUAL CIRCUIT

MESSAGE SWITCHING NETWORK

Originally used in data communications. Ex: ‘store and forward’ paper tape relay systems, email delivery, ‘forward voice mail’.

HOW MESSAGE SWITCHING NETWORK WORKS?

Not necessary to establish circuit all over the network from source to destination. Consider a connection between A & D represented in a series of links (AB, BC & CD).

When email sent from A to D, it first passes a local connection (AB), then passed to station C via link BC, then finally to station D.

At each message switch, received message is stored & a connection is made to deliver the message to neighboring switch.

Message switch is also known as store-and-forward switching.

CELL SWITCHING NETWORK

Similar to packet switching, except that the cell relay refers to a method of statistically multiplexing fixed-length packets. Ie, cells to transport data between computers / network equipment.

It breaks a data stream into packets & places them on line that are shared by several streams.

It is unreliable, connection oriented packet switched data communication protocol.

Ideal for integrated environment & ATM. International Telecommunication Union(ITU)

adopted cell switching technology called Asynchronous Transfer Mode (ATM).

CELL SWITCHING NETWORK

Major difference between packet switching and cell switching is that the cells have fixed size while packets have different sizes.

ATM is used for: Voice Data Fax Real-time video CD-quality audio Imaging Multi-megabit data transmission

INTEGRATED SERVICES DIGITAL NETWORK(ISDN)

A type of circuit switched telephone network system designed to allow digital transmission of voice & data over ordinary copper telephone wires for better quality & higher speed.

ISDN is a set of protocols for establishing and breaking circuit switched connections & for advanced call features for the end users.

Provides special services to the users such as call forwarding, voice mail and calling party identification.

ISDN connections are based on 2 types of channels: B Channel & D Channel

INTEGRATED SERVICES DIGITAL NETWORK(ISDN)

B (Bearer) channel Called bearer channel & employs circuit switching

techniques to carry voice, video, audio & other types of data over ISDN connection. Maximum throughput for B channel is 64Kbps & sometimes limited to 56Kbps. No of channels not fixed & may vary

D ( Data ) Channel Called data channel & it employs packet switching

techniques to carry information about the call such as session initiation & session termination signals. Caller identity, call forwarding & conference call signal are also handled by this channel. Maximum throughput for D channel is 16Kbps or 64Kbps depending on the ISDN connection type. No of channels is only ONE !

ISDN IMPLEMENTATION

There are 3 types: Basic Rate Interface (BRI)

(2B+D,2B1D) Consists of 2 B channels with bit rate of 64Kbps each & 1 D channel

with bit rate of 16Kbps. B channel used for voice / user data.

The 2 B channels can be bonded together resulting in 128Kbps.

D channel used for any combination of data control/signaling & x.25 packet networking.

Interface BRI intended for home 7 small enterprise users.

ISDN IMPLEMENTATION Primary Rate Interface (PRI)

A telecommunication standard for carrying multiple DS0 (Digital signal 0) voice & data transmission between 2 physical locations.

DS0 is a basic digital signaling rate of 64Kbps, corresponding to

the capacity of one voice frequency equivalent channel.

Number of B channels vary according to the nation: north america & japan = 23B+1D with bit rate 1.544Mbps(T1 line), europe & australia is 30B+1D with bit rate of 2.048 Mbps (E1 line)

ISDN IMPLEMENTATION

Broadband Integrated Services Digital Network (B-ISDN) It is another ISDN implementation & able to

manage different types of services at the same time.

Primarily used within network backbones and employs ATM

TRADITIONAL WAN ALTERNATIVES

Packet switching technology brought new alternatives for WAN like Public Data Network (PDN) & Value-added network (VAN).

Value-Added Network (VAN) - Privately owned or proprietary network. Provides specialized services such as electronic data interchange (EDI) / access to particular database. Such type of networks adds value to the existing transmission line hence its called value-added service

Public Data Network (PDN) – owned by government for specific purpose of providing data transmission services for the public.

CELLULAR WIRELESS NETWORKS Mobile wireless communication which we normally

use to contact friends & families are based on cellular technology.

Mobile phones, personal communications systems, wireless Internet & wireless web applications are all based on cellular technology.

It is comprised of multiple low power transmitters of 100W or less. Transmitter range is small & covers small area called as a cell.

Each cell has its own transmitter called base station.

A band of frequencies is allocated to each cell is different from the adjacent cells to avoid interference / crosstalk

CELLULAR WIRELESS NETWORKS

SATELLITE COMMUNICATION

Involves the transmission of information from the ground station to satellite, called uplink.

Retransmission from the satellite back to the ground station is called downlink (one station or many at the same time!)

Satellite has a receiver with receiving antenna & transmitter with a transmitting antenna.

It has method for connecting the uplink to the downlink for retransmission & prime electrical power (solar panels) to run all electrical systems.

All satellites must have all these basic components illustrated in the following picture.

SATELLITE COMMUNICATION