Homework 9

22C:116, Fall 1998

Due Monday Nov 2, 1998, in class

1. Background Consider the following top-level design for the transport layer running on a computer. This transport layer offers datagram services to clients. This transport layer runs as a process, with all interprocess communications being through FIFO queues of messages. The queue operations are put(msg,queue) and get(msg,queue). The queue implementation considers each message to be an uninterpreted bit pattern of arbitrary size, and it guarantees that the put and get operations are atomic.

   This transport layer has a queue, transport-in, that is used by the session layer and by the network layer to pass messages to the transport layer. The network layer has a queue, network-in, that is available for passing messages to the network layer from the transport layer.

   The session layer is implemented by a number of processes, one per active session. When a session is initiated, the process for that session creates a queue, session-in, and then passes that queue and the globally unique session ID in a new-session message. At the end of a session, the session layer sends an end-of-session message with the session ID to the transport layer.

   Part A: Give, in reasonable detail, the formats of each messages the transport layer might send or receive in this system. Do not specify details that are not relevant to the transport layer.

   Part B: What crucial detail has been omitted from the above that would be essential for this implementation of the transport layer to be of any use?

2. The details of the implementation of client server interactions can be considered to be an example of something best dealt with at either the session layer or the presentation layer in the ISO OSI protocol hierarchy. Give a modestly detailed proposal suggesting how the UNIX socket kernel call can be used to implement client-server interactions.

3. Do problem 11 of Chapter 10, on page 461 of the text!

4. Do problems 13 and 14 on page 461 of the text!