Switching

A method used in networks to connect a sender to a receiver so that data can travel from source to destination.

Without switching every pair of devices would require a direct connection, which is impractical and inefficient. Switching allows multiple devices to share a single link, which reduces overall cost and complexity.

Routing

Identifies the route traversed by data to get from source to destination.

Types of Network

Unswitched

A network where each device is directly connected to every other device or a common medium. No switching devices are used. When one device transmits data, all devices can receive the message.

Simple design. Low cost. Easy to setup for small networks.

Collisions are highly likely. More devices mean more collisions. Not good in terms of security. Not reliable.

Examples:

• Point-to-point
• Multi-point
• Broadcast

Switched

Data passes through one or more intermediate nodes between the sender and receiver.

Types

Circuit Switching

A dedicated communication path is established between sender and receiver before data transfer. The path remains reserved for the entire duration of the session. The circuit is released after the session ends.

Requires caller (sender), callee (receiver) and all intermediate nodes and links to be available at the same time.

Constant, guaranteed bandwidth. Delay occurs only during setup.

Inefficient if data is bursty. Setup time required before data transmission begins. Cannot be optimized while data is being transmitted. Not suitable for computer communications.

Used in human-to-human telephone calls.

Space-division switching

Each call uses a separate physical path through the switch. Implemented using crossbar or matrix switches.

Used in analog systems.

Time-division switching

Same physical path shared by multiple calls in different time-slots. Uses TDM.

Used in digital systems.

Message Switching

Entire message is stored and forwarded at intermediate nodes. Message is sent progressively as each hop becomes available.

End-to-end delivery time cannot be guaranteed. Very long messages can hog buffers and links.

Packet Switching

Data is divided into smaller units aka. packets and transmitted over the network. Packets are variable-length.

Each packet contains:

• a header to identify the source and destination of the data
• a sequence number that allows the receiver to reassemble the data in the correct order
• data

Each intermediate nodes switches incoming packet through a link to another node.

No need of dedicated paths. Ideal for bursty data. Jitter is possible. Packets may arrive out of order.

More flexible than circuit switching. Because it allows multiple devices to share a single link. More efficient than circuit switching. Can handle bursty data more effectively.

Virtual Circuit Packet Switching

Establishes a temporary virtual path between sender and receiver. All packets follow the same virtual path. Similar to circuit switching but with less overhead.

Packets are assigned to virtual circuits. Each VC has a virtual circuit identifier. Different VCIs are used in different links. Incoming and outgoing VCIs are managed by intermediate nodes using a table.

Datagram Switching

Packets are routed independently. No initial setups or delays.

Destination address of a packet stays the same throughout the transmission. Datagram switch uses a routing table to store destination address and output port.

Adapts to node or link failure during transmission. Switching each packets is relatively expensive.

Label Switching

A label is attached to packets, when they arrive at the switch. Each core switch switches the packet based on the label, and then substitutes a new label for the next hop.

Cell Switching

Similar to packet switching but uses fixed-size cells instead of variable length packets.