3. Comparison of Client/Server Model Implementation

3.2 Discussion of Mechanisms Used in Comparison Models

For comparative purposes I have chosen to use a traditional mechanism, Sockets. The sockets mechanism is more primitive in its application than RMI and it is this quality that makes it an ideal comparison model. The limited complexity of the Socket mechanisms emphasis's the greater functionality of RMI and significantly highlights the potential problems presented by the increased complexity of the RMI mechanism.

3.2.1 Sockets

As with RMI, sockets are used to create a communication channel between two processes. Sockets establish a communication channel between server and client as follows. The server listens on a certain port to see if any processes are interested in communicating with it. When another process, the client, wishes to communicate, it first notifies its OS. The OS assigns the client an unused port to use. The client then contacts the server, using the servers IP address and port number, to notify the server process of its wish to communicate, at the same time identifying itself and its port number [3]. This is illustrated in Figure 7.

Figure 7. Client requesting connection on server port [4]

If all goes well the server will accept the connection. As the original port the server was listening on is now used for the connection to the client a new port is assigned to the server for the purpose of listening for connection requests. This is illustrated in Figure 8.

Figure 8. Server establishing connection [4]

The client and server can now communicate by reading from or writing to their sockets [4].
Communication between client and server is done through the sending of packets of data. Sockets present data packets as a stream of bytes.

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