Packet Switching Techniques

Fragmentation

• Fragmentation is a process of breaking packets into the smallest individual data units that travel through different networks.

Network Layer Services

• Forwarding: a router forwards a packet by examining a packet's header field and then using the header field value to index into the forwarding table.
• Routing: the process of moving data from one device to another device, finding the best possible route.
• Packet forwarding: the action applied by each router when a packet arrives at one of its interfaces.

Network Layer Design Issues

• Store and Forward packet switching: a mechanism where the host sends the packet to the nearest router, which stores it until it has fully arrived, verifies the checksum, and then forwards it to the next router until it reaches the destination.
• Packet switching involves packet forwarding from an entry interface out to an exit interface.

Packet Switching Techniques

• There are two approaches to Packet Switching: Datagram Packet switching and Virtual Circuit Switching.

Advantages of Packet Switching

• Delay in delivery of packets is less, since packets are sent as soon as they are available.
• Switching devices don’t require massive storage, since they don’t have to store the entire messages before forwarding them to the next node.
• Data delivery can continue even if some parts of the network faces link failure.
• Packets can be routed via other paths.
• It allows simultaneous usage of the same channel by multiple users.
• It ensures better bandwidth usage as a number of packets from multiple sources can be transferred via the same link.

Disadvantages of Packet Switching

• Unsuitable for applications that cannot afford delays in communication like high-quality voice calls.
• High installation costs.
• Requires complex protocols for delivery.
• Network problems may introduce errors in packets, delay in delivery of packets, or loss of packets.

Datagram Packet Switching

• A packet switching technology in which packet is known as a datagram, is considered as an independent entity.
• Also known as connectionless switching.
• Traffic congestion can be reduced because the message is temporarily stored in the nodes.
• Message priority can be used to manage the network.
• The size of the message which is sent over the network can be varied.
• Supports the data of unlimited size.

Disadvantages of Datagram Packet Switching

• Every switch in transit path needs enough storage to accommodate entire message.
• Message switching is very slow due to the store-and-forward technique and waits until resources are available.
• Not a solution for streaming media and real-time applications.

Packet Switching Techniques

• In packet switching, the message is sent in one go, but it is divided into smaller pieces, known as packets, and they are sent individually.
• Packets are given a unique number to identify their order at the receiving end.
• Every packet contains some information in its headers such as source address, destination address, and sequence number.
• Packets travel across the network, taking the shortest path as possible.
• All the packets are reassembled at the receiving end in correct order.
• If any packet is missing or corrupted, the message will be sent to resend the message.