Message Switching

Message Switching

Message switching treats each message as an independent entity. Each message carries address information that describes the message’s destination, and this information is used at each switch to transfer the message to the next switch in the route. Message switches are programmed with information concerning other switches in the network that can be used to forward messages to their destinations. Message switches also may be programmed with information about the most efficient routes. Depending on network conditions, different messages may be sent through the network by different routes, as shown in Figure 2.5.

Message switching transfers the complete message from one switch to the next, where the message is stored before being forwarded again. Because each message is stored before being sent on to the next switch, this type of network frequently is called a store-and-forward network. The message switches often are general-purpose computers and must be equipped with sufficient storage (usually hard drives) to enable them to store messages until forwarding is possible.

Message switching commonly is used in e-mail because some delay is permissible when delivering mail, unlike the requirements when two computers exchange data in real time. Message switching uses relatively low-cost devices to forward messages and can function well with relatively slow communication channels. Other applications for message switching include group applications such as workflow, calendaring, and groupware.

Message switching offers the following advantages:

Data channels are shared among communicating devices, improving the efficiency of using available bandwidth.
Message switches can store messages until a channel becomes available, reducing sensitivity to network congestion.
Message priorities can be used to manage network traffic.
Broadcast addressing uses network bandwidth more efficiently by delivering messages to multiple destinations.

The chief disadvantage of message switching is that message switching is not suited for real-time applications, including data communication, video, and audio.