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Packet Switching and Circuit Switching

The switching function provides communication pathways between two endpoints and manages how data flows between them. The two most common switching methods are circuit switching and packet switching.

Integrated Service Digital Network (ISDN), shown in Figure 29-1, is an example of a circuit-switched network.

Figure 29-1

Figure 29-1 Circuit Switching ISDN Topology

Circuit switching requires a dedicated physical connection between the sending and receiving devices. For example, parties involved in a phone call have a dedicated link between them for the duration of the conversation. When either party disconnects, the circuit is broken, and the data path is lost. This is an accurate representation of how circuit switching works with network and data transmissions. The sending system establishes a physical connection, and the data is transmitted between the two. When the transmission is complete, the channel is closed.

A Frame Relay network, shown in Figure 29-2, is an example of a packet-switched network.

Figure 29-2

Figure 29-2 Packet Switching Frame Relay Topology

In packet switching, messages are broken into smaller pieces called packets. Each packet is assigned source and destination addresses. Packets are required to have this information because they do not always use the same path or route to get to their intended destination. Packets can take an alternative route if a particular route is unavailable for some reason.

Table 29-1 compares circuit switching and packet switching.

Table 29-1 Circuit Switching and Packet Switching Comparison

Switching Method



Key Features

Circuit switching

Offers a dedicated transmission channel that is reserved until it is disconnected.

Dedicated channels can cause delays because a channel is unavailable until one side disconnects. Uses a dedicated physical link between the sending and receiving devices.

Offers the capability of storing messages temporarily to reduce network congestion.

Packet switching

Packets can be routed around network congestion. Packet switching makes efficient use of network bandwidth.

Packets can become lost while taking alternative routes to the destination. Messages are divided into packets that contain source and destination information.

The two types of packet switching are datagram and virtual circuit. Datagram packets are independently sent and can take different paths throughout the network. Virtual circuit uses a logical connection between the source and destination device.

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