Routing and Switching Overview
The simplest way to define the function of both the processes of routing and switching in telecommunication is that routing acts to move a telephone call to the access layer, typically to a telephone exchange whereas the final deliverance and decision is made by using the switching process.
Theoretically, switching is defined as a process of actually moving bits in any point on the network where communication lines interface i.e. from an input port to an output port.
In telecommunication, this point of interface is in general termed as the network node and may be a Private Branch Exchange (PBX), a modem, a host computer, a multiplexer or any other similar device.
Normally a switching process relies on the information that is gathered through a routing process and the infrastructure constitutes of specialized computers used to link multiple transmission lines. These specialized computers may be termed as the switching elements that make use of a number of tables formed on the general record of the number dialed and help determine the most gainful and inexpensive trunk over which the call is forwarded. As compared to the complex path determination strategies used by IP routers in the Internet, this process of switching is quite simple and uncomplicated.
Even though both routing and switching are used to transfer information source to destination, the main difference lies in the fact that routing works across an internetwork which means that typically at least one intermediate node is involved in its path. Practically the number of these intermediate nodes may be numerous depending on the network and the path followed. A router is a device that serves to perform two major functions i.e. determining the best possible path in terms of distance and cost effectiveness and the efficient transfer of data or information through this path across an internetwork.
Routers generally make use of multiple routing algorithms which are needed to initialize and uphold the routing tables. These routing algorithms operate on information related to a number of metric variables which may be destination, reliability, load, path length, next-hop associations, delay, bandwidth, and communication cost. A router may use one or more of these variables in order to determine the most effective path for packet transfer.
When it comes to switching in telecommunication it becomes crucially important to mention the circuit switching mode which is the center of voice networks infrastructure worldwide. A circuit switched connection is a temporarily reserved network resource that is dedicated to two subscribers for the complete duration of a conversation. This is why a conversation is continuous and exclusive. However, as soon as the conversation ends, the connection is removed.
In circuit switching, the exclusive connection requires that a preset share of network resources are held in reserve for the call, and during that duration, no other call is permitted to utilize those resources.
The call request is sent to the destination and only when it is acknowledged by the destination, the data transmission begins.
A huge number of lines are used in circuit switching so as to make the switching and routing computation more cost-effective. Once the connection is established, there is no further need of routing calculations based on complicated algorithms as the line itself becomes dedicated.