WAN Technologies

ABOUT WAN

The Wide Area Network (WAN) is a type of network that covers a large geographical area.  It consists many more LANs which allow the users or the computers at the different locations to communicate. Networking devices like computers or routers are connected through a public network such as the telephone system, leased lines or satellites. one of the most common example of WAN is the internet.  

WAN technologies function at the lower three layers of the OSI reference model, the physical layer, the data link layer, and the network layer. WAN services are provided by different technologies such as circuit switching, packet switching, X.25 protocol, frame relay, Asynchronous Transfer Mode (ATM), Integrated Services Digital Network (ISDN), and Fiber Distributed Data Interface (FDDI).

TYPES OF SWITCHING

Switching is a process of moving the data through a series of intermediate steps rather than moving from the start point directly to the end point. Network switching does not rely on permanent connection between the source and the destination. It rely on a series of temporary connection. WAN uses some of following types of switching:

1. Circuit Switching

2. Message Switching

3. Packet Switching 
4. Cell Switching

1. Circuit Switching

In the circuit switching, a directly physical temporary connection is established between the sender and the receiver before the communication occurs. Data Connection is initiated when the sender wants to transmit data and is terminated after the communication is completed. The sender and receiver must have the same data transfer speeds.   

The drawback of circuit switching is that the unused transmission is wasted, as the connection is reserved only for two communication parties. 

The most common example of circuit switching is the telephone system. The other example is narrow ISDN.

Public Switch Telephone Network (PSTN) is an example of circuit switching

2. Message Switching

In message switching, direct physical connection is not established between sender and receiver before data transmission. This message is routed through the intermediate nodes or station such as a central network computer. Each intermediate node accepts the entire message, checks the address and then forwards the message to the next node. This technology is also known as store and forward method.   

3. Packet Switching

In packet switching, the message to be transmitted are broken into small units called packets. Each packet contains address information which identifies both the source and destination nodes. These packets are then routed through the intermediate nodes. These nodes are known as Packet Switching Exchanges (PSEs). 

Connection-less service

In connection-less service, an actual connection is not established between sender and receiver before the packets are transmitted. Each packet is considered as an independent unit and is treated as a complete message. This message is then routed through different paths to reach the destination. The connection-less means that the switch does not keep information about the connection state.   

Connection-oriented service

In connection-oriented service, a communication link is established before the transmission of packets. Since the path is established before the transmission begins, all the packets comprising the message follow the same route to reach the destination.

The connection oriented service, use either the SVCs or PVCs circuit for transmission.

Switched Virtual Circuits (SVCs)

In switch virtual circuits, a connection is first established then the packets are transmitted. After the packets are transmitted, the connection is then terminated.

Permanent Virtual Circuits (SVCs)

The permanent virtual circuit uses leased line for transmission. A connection is available between the sender and the receiver at all times even through no data is transmitted. 

Cell Switching

In cell switching, packets are divided into fixed length called "cells" to transport data from one device to another. Cell switching is associated with Asynchronous Transmission Mode (ATM) which is considered to be a high speed switching technology. Total length of cell is 53 Bytes (48 Bytes date + 5 Bytes header).