Routing & Switching Concepts

Network Switching

1. Circuit Switching

• How it works: A dedicated, physical path (circuit) is established between the sender and receiver before any data is transferred. This path remains locked for them until the communication ends.
• Example: Traditional telephone networks (Landlines).
• Pros: Guaranteed bandwidth, no delay once connected.
• Cons: Highly inefficient. If no data is being sent during the connection, the bandwidth is wasted because nobody else can use that circuit.

2. Packet Switching

• How it works: No dedicated path is established. Data is broken down into small chunks called Packets. Each packet is tagged with the destination address and sent independently. Packets may take completely different routes to reach the destination, where they are reassembled.
• Example: The Internet.
• Pros: Extremely efficient use of network resources. Multiple users can share the same physical lines simultaneously.
• Cons: Packets can arrive out of order or get lost, requiring protocols like TCP to organize and recover them.

Routing Concepts

1. Static vs Dynamic Routing

• Static Routing: Paths are manually configured by a network administrator. If a cable breaks, the network administrator must manually update the router.
• Dynamic Routing: Routers use protocols to automatically discover the network topology and calculate the best paths. If a cable breaks, routers automatically calculate a new path.

2. Dynamic Routing Algorithms

A. Distance Vector Routing

• Routers only know their immediate neighbors.
• Every router periodically shares its entire routing table (list of known distances) but only to its neighbors.
• It relies on the 'Bellman-Ford' algorithm. (Example Protocol: RIP - Routing Information Protocol).
• Problem (Count-to-Infinity): A routing loop where routers keep telling each other incorrect, increasing distances to a dead node.

B. Link State Routing

• Every router knows the exact topology of the entire network.
• A router only shares information about its own immediate links (is the link up or down?), but it broadcasts this info to every router in the network.
• It relies on Dijkstra's Shortest Path algorithm. (Example Protocol: OSPF - Open Shortest Path First).
• Pros: Faster convergence, no count-to-infinity problem. Scales better for large networks like the Internet.