Concurrent and iterative servers

An iterative server handles both the connection request and the transaction involved in the call itself. Iterative servers are fairly simple and are suitable for transactions that do not last long.

However, if the transaction takes more time, queues can build up quickly. In Figure 1, once Client A starts a transaction with the server, Client B cannot make a call until A has finished.

Figure 1. An iterative server
The diagram shows that an iterative server can only process a call from one client at a time.

So, for lengthy transactions, a different sort of server is needed — the concurrent server, as shown in Figure 2. Here, Client A has already established a connection with the server, which has then created a child server process to handle the transaction. This allows the server to process Client B’s request without waiting for A’s transaction to complete. More than one child server can be started in this way.

TCP/IP provides a concurrent server program called the IMS Listener. It is described in How to customize and operate the IMS Listener.

Figure 2. A concurrent server
A concurrent server

Figure 1 illustrates a concurrent server at work.