The document discusses network layer design issues related to connectionless and connection-oriented services. Connectionless services route each packet independently, while connection-oriented services establish a logical connection and route all traffic for that connection along the same path. Virtual circuits use connection-oriented services, pre-determining the route and maintaining state information for each connection. Datagram subnets are connectionless, routing each packet independently without state information. Virtual circuits provide easier quality of service and congestion control while datagram subnets are more robust to router failures.

1. Network Layer Design Issues

4. Connectionless services

6. Implementation of Connectionless Service Routing within a d at agram subnet. (destined for, outgoing line)

8. Implementation of Connection-Oriented Service Routing within a VC subnet (incoming, connection id) (outgoing, connection id)

10. Comparison of Datagram Subnets and Virtual-Circuit Route chosen when VC is setup; all packet follow this route Each packet is routed independently Routing A table is needed to hold the state information Subnet does not hold state information State information Each packet contains a short VC number Each packet contains the source as well as destination address Addressing Required Not required Circuit set up Virtual-Circuit Subnet Datagram Subnets Issue

11. Comparison of Datagram Subnets and Virtual-Circuit All VCs which passed through failed router are terminated. No other effect except for the packets lost at the time of crash Effect of router failure Difficult Easy if enough resources can be allocated in advance for each VC. Quality of service Difficult Easy if enough resources can be allocated in advance for each VC. Congestion control Virtual-Circuit Subnet Datagram Subnets Issue