Network Layer Design Issues

Summary

This video script covers essential concepts in the design of the network layer. It addresses four key design issues: 1) Store-and-Forward Packet Switching, where routers temporarily store packets before forwarding them to ensure error-free transmission; 2) Services provided to the transport layer, such as independence from router technology and uniform address numbering; 3) Connectionless service, where packets are routed independently, potentially via different paths; and 4) Connection-oriented service, where a virtual circuit is established to ensure reliable and ordered delivery. These concepts form the foundation of efficient and reliable network communication.

Takeaways

• 😀 The network layer focuses on four design issues: store-and-forward packet switching, services to the transport layer, connectionless service, and connection-oriented service.
• 😀 Store-and-forward packet switching involves routers storing packets temporarily, checking for errors, and forwarding them to the next router until they reach the destination.
• 😀 The network layer provides three key services to the transport layer: independence from router technology, shielding transport layer from router topology, and uniform addressing across networks.
• 😀 In connectionless service, there is no pre-established connection between source and destination. Packets are sent independently and may follow different paths.
• 😀 Connectionless service uses datagrams, where packets are routed based on current network conditions, with routing tables updated periodically based on congestion or traffic.
• 😀 The implementation of a connection-oriented service involves setting up a virtual circuit before transmitting data. This ensures all packets follow the same predefined path.
• 😀 Routers in connection-oriented services assign connection identifiers to packets, ensuring proper forwarding based on these identifiers rather than the packet’s content.
• 😀 The network layer's routing tables store both incoming and outgoing connection identifiers, helping routers manage data transmission in a connection-oriented service.
• 😀 A virtual circuit is set up between the source and destination, ensuring that all packets follow the same route, providing more reliable and consistent communication.
• 😀 The service provided by the network layer is independent of the router technology, ensuring that the transport layer operates uniformly across different types of networks and ISPs.

Q & A

What are the four key design issues that need to be addressed in the network layer?

The four key design issues are: 1) Store and forward packet switching, 2) Services provided to the transport layer, 3) Implementation of connectionless service, and 4) Implementation of connection-oriented service.

How does the store and forward packet switching mechanism work in the network layer?

In store and forward packet switching, routers store the packet temporarily before forwarding it to the next router. Each router checks for errors (using checksum) before forwarding the packet. This process continues until the packet reaches its destination.

What are the three service requirements provided by the network layer to the transport layer?

The three service requirements are: 1) Independence from router technology, 2) Shielding from the number, type, and topology of routers, and 3) Uniform addressing across LANs and WANs.

What does it mean for a network layer service to be independent of router technology?

It means that the network layer services should not depend on the specific type or technology of routers used in the network. This ensures that services remain consistent regardless of the underlying router infrastructure.

What is the primary characteristic of connectionless service in the network layer?

In connectionless service, there is no need for a connection between the source and destination before transmitting packets. Each packet (datagram) is forwarded independently through the network, and routers make independent routing decisions based on their current routing tables.

How do routing tables work in connectionless service?

In connectionless service, each router maintains a routing table that is periodically updated. The routing table helps the router determine where to forward incoming packets based on the destination address, independent of other packets in transit.

What are datagrams in the context of connectionless service?

Datagrams are individual packets in a connectionless network, where each packet is routed independently without the need for an established connection. The network is known as a datagram network.

What is a virtual circuit in connection-oriented service?

A virtual circuit is a dedicated path that is established between the source and destination before any data is transmitted. All packets follow this predefined path, ensuring consistent routing and delivery. This service requires a connection setup before transmitting any data.

What role do connection identifiers play in connection-oriented service?

Connection identifiers are used to label and distinguish different virtual circuits. Each packet transmitted through a virtual circuit is assigned a connection identifier, allowing routers to route packets along the correct path based on the established virtual circuit.

How does the routing table differ in connection-oriented service compared to connectionless service?

In connection-oriented service, the routing table includes connection identifiers that define the path for each packet based on its virtual circuit. In connectionless service, the routing table primarily deals with destination addresses, and packets are routed independently of each other without any predefined path.