Switching Techniques

Switching techniques are the methods used to route the data from one node to another in a switched communication network. Switching techniques are categorized into three types circuit switching, packet switching, and message switching. The first two switching technologies are commonly used in networking nowadays.

Switching Techniques in Networking

1. Why Switching?
2. Circuit Switching
   • Space Division Switching
   • Time Division Switching
3. Message Switching
4. Packet Switching
   • Datagram
   • Virtual Circuit
     1. Permanent Virtual Circuit
     2. Switched Virtual Circuit

Why Switching?

Internet is a combination of different types of networks (LAN and WANs) that are connected together with the help of connecting devices. The devices attached to the network that has to communicate through this network can be referred to as end nodes and the switching devices whose only purpose is to provide communication through the network are referred to as nodes.

To achieve one-to-one communication between the nodes a point-to-point connection can be established but this is literally impractical when it comes to large networks. A point-to-point network increases the number of links in the network which increases the cost of the infrastructure.

The length of links also puts a limitation on the size of the network. Moreover, most of the links in the network are idle when there is no communication between the nodes. So, an alternative option to avoid this is switching.

Switched network routes data from one node to another node by switching it through the nodes. The nodes are also referred to as switches. The switches are able to create a temporary connection between the two end nodes that are linked through these switches.

Now the switching can be performed in three different ways circuit switching, packet switching, and message switching. The first two techniques are common nowadays. Still, we will study all three techniques.

Circuit Switching Techniques

In circuit switching, whenever a source end node wants to send a message to the destination end node a physical link has to be established between the source and the destination.

Once the link is established the entire message is transmitted from source to destination through this link. Remember the messages are not divided into packets here. After the message is transferred the source node informs the network to open all the switches to terminate this physical link.

Next time when the same source and destination have to communicate again, they have to establish a dedicated physical link between them before they start communication and have to terminate the link after the communication gets completed.

The circuit switch is further classified into two types space division switching and time-division switching.

1. Space Division Switching

The space division switching involves a separate path for each connection where each connection is dedicated for connecting two end nodes in the network.

2. Time Division Switching

In time-division switching the intermediatory nodes in the network performs time-division multiplexing to implement switching.

Advantages of Circuit Switching

1. 1. • In circuit switching, there is a dedicated path between sender and receiver.
      • The transmission speed is high as the message does not have to wait at any intermediatory switch.

Disadvantages of Circuit Switching

1. 1. • When the communication is going on the path between the sender and receiver is blocked.
      • More bandwidth is required as an entire message is sent at once.

Message Switching

In message switching, no dedicated physical link is established between the sender and the receiver end nodes during the communication. Instead, the message is forwarded in a hop-to-hop fashion.

The sender node transmits the message to the available switch in the network. The switch accepts the entire message and stores the message until the next-hop switch in the network is available to accept the message. Because of this behavior the message switching technique is also referred to as the store and forward technique.

Advantages of Message Switching

1. 1. • As no dedicated link is established between the sender and receiver the links in the network are not blocked.
      • Message switching allows more devices to share the links in the network.
      • Reduces traffic as the switches are capable to store the message until sufficient resources are available to transfer the message.

Disadvantages of Message Switching

1. 1. • The intermediary switches in the network require a storage facility so that they can store messages during the transmission.
      • The message switching is slow as compared to other switching techniques due to its store and forward feature.

Packet Switching Techniques

In the packet switching technique, the whole message is split to form small packets. Now, these packets are transmitted one by one from sender to the receiver through the intermediatory switches in the network.

The receiver waits until all the packets of the same message arrive at the receiver end before it transmits the message to the upper layer. Once all the packets arrive at the receiver end the packets are assembled and then delivered to the upper layer.

Still, the intermediatory switches in the network require some mechanism to route the packets from source to destination and for this, packet switching employs two techniques i.e., datagram and virtual circuit switching.

1. Datagram

In the datagram technique, each packet belonging to the same message follows a different routing path through the network and reaches the destination node. When all the packets of the same message reach the destination node they are assembled and then delivered to the upper layer.

2. Virtual Circuit Switching

In virtual circuit switching, when a message is split into multiple packets, the first packet establishes a path through the intermediatory switches in the network. And the rest of the packets of the same message have to follow the same path established by the first packet of the message. The virtual circuit switching can be further implemented into two methods switched virtual circuit and permanent virtual circuit.

2.1 Permanent Virtual Circuit (PVC)

In the permanent virtual circuit, a permanent virtual path is established between the sender and the receiver. This path exists even if the sender and receiver are not communicating. If the source node wants to communicate with other destination nodes, then it has to establish a separate PVC connection.

Establishing a PVC connection is costlier as compared to an SVC connection as the sender and receiver both have to pay for the connection even if they are not communicating.

2.2 Switched Virtual Circuit (SVC)

In the switched virtual circuit, every time the sender and receiver are communicating, they have to establish a new virtual circuit. This virtual circuit exists only when the sender and the receiver are communicating.

Advantages of Packet Switching

1. 1. • Requires less bandwidth as compared to circuit and packet switching.
      • End nodes or intermediatory nodes do not require more storage space.

Disadvantages of Packet Switching

1. 1. • Packet switching is not suitable for the network that does not afford any kind of delay such as voice calls.
      • There can be issues like delays in the delivery of packets, loss of packets, errors.

So, these are the switching techniques that are useful for establishing a connection between the end nodes in the network. We have studied all kinds of switching techniques along with their further classification.