Switching Techniques

Switching Techniques

In network communication, the switching technique determines how data travels through the network. Each technique has its own characteristics and its own range of applications.

1. Circuit Switching

Circuit switching establishes a dedicated physical path between the two parties, and that path is used exclusively for the whole session.

1.1 How It Works

1. Set up the connection: the caller requests a connection and the network establishes a dedicated path for the two parties
2. Transfer the data: the data travels over the dedicated path
3. Release the connection: the path is released when the communication ends

1.2 Characteristics

Advantages:

• Low transmission delay, good real-time behaviour
• High transmission quality, no congestion
• Well suited to real-time traffic such as voice and video

Disadvantages:

• Low resource utilisation, because an idle path cannot be used by anyone else
• Long connection setup time
• Unsuitable for bursty traffic

1.3 Applications

• Traditional telephone networks: PSTN (Public Switched Telephone Network)
• Video conferencing: real-time transfer is required
• Dedicated lines: leased connections between organisations

2. Message Switching

Message switching stores and forwards each message as a whole; a node receives the complete message before forwarding it.

2.1 How It Works

1. Receive the message: the node receives the complete message
2. Store the message: the message is kept in a buffer
3. Look up the route: the next hop is found from the destination address
4. Forward the message: the message is forwarded to the next node

2.2 Characteristics

Advantages:

• No connection needs to be set up, which suits bursty traffic
• Multiplexing is possible
• Fairly high transmission reliability

Disadvantages:

• High transmission delay, unsuitable for real-time traffic
• Large buffers are required
• Packets are easily lost when the network is congested

2.3 Applications

• Electronic mail: non-real-time data transfer
• File transfer: transfer of large files
• Early computer networks: ARPANET and similar systems

3. Packet Switching

Packet switching splits the data into small packets, and each packet is transmitted independently.

3.1 How It Works

1. Split the data: a large block of data is split into small packets
2. Transmit the packets: each packet chooses its route independently
3. Reassemble the packets: the data is reassembled at the destination

3.2 Characteristics

Advantages:

• High resource utilisation, because several users share the network resources
• Flexible transmission, since packets can take different routes
• Well suited to bursty traffic
• Less affected by congestion

Disadvantages:

• The transmission delay is unpredictable
• Packets have to be reassembled
• The protocols are complex

3.3 Applications

• The Internet: TCP/IP networks
• Local area networks: Ethernet
• Mobile communication: 4G and 5G networks

4. Comparing the Three Techniques

5. Datagrams and Virtual Circuits

Packet switching works in two ways: datagrams and virtual circuits.

5.1 Datagram

Characteristics:

• Each packet chooses its route independently
• Packets may reach the destination by different paths
• Packets may arrive out of order
• No connection needs to be set up

How it works:

1. The sender splits the data into packets
2. Each packet chooses its route independently
3. The packets may take different paths
4. The destination reassembles the data

Advantages:

• Flexible transmission
• Little impact when the network fails
• Simple to implement

Disadvantages:

• Packets may arrive out of order
• The transmission delay is unpredictable
• Packets have to be reassembled

5.2 Virtual Circuit

Characteristics:

• A logical connection is established first
• All packets follow the same path
• Packets arrive in order
• The connection has to be established and released

How it works:

1. The virtual circuit is established
2. All packets follow the same path
3. Packets are transmitted in order
4. The virtual circuit is released

Advantages:

• Packets arrive in order
• The transmission delay is relatively predictable
• Better quality of service

Disadvantages:

• Large impact when the network fails
• Complex to implement
• Connection management is required

5.3 Comparing Datagrams and Virtual Circuits

6. Modern Switching Techniques

6.1 ATM (Asynchronous Transfer Mode)

Characteristics:

• Fixed-length small cells (53 bytes)
• Connection-oriented
• Quality of service guarantees
• High-speed transmission

Applications:

• Broadband Integrated Services Digital Network (B-ISDN)
• High-speed backbone networks

6.2 MPLS (Multiprotocol Label Switching)

Characteristics:

• Adds a label layer between IP and the link layer
• Fast forwarding based on labels
• Supports traffic engineering
• Quality of service guarantees

Applications:

• Enterprise networks
• Service provider networks

6.3 Software-Defined Networking (SDN)

Characteristics:

• Separates the control plane from the data plane
• Centralised control
• Programmable network
• Flexible network management

Applications:

• Data centre networks
• Campus networks
• Enterprise networks

7. Choosing a Switching Technique

7.1 Factors to Consider

1. Type of traffic

   • Real-time traffic: choose circuit switching
   • Non-real-time traffic: choose packet switching

2. Size of the network

   • Small network: choose a simple technique
   • Large network: choose a sophisticated technique

3. Cost

   • Low cost: choose packet switching
   • High performance: choose circuit switching

4. Reliability requirements

   • High reliability: choose packet switching
   • Simple and reliable: choose circuit switching

7.2 Trends

1. All-IP: more and more traffic moves onto IP networks
2. Packetisation: circuit switching evolves into packet switching
3. Intelligence: network devices become more capable
4. Virtualisation: network functions are virtualised