When you define the server through the IXCSRVR macro, you can specify the range of server levels that the server supports through the MINLEVEL and MAXLEVEL keywords, the range of client levels whose requests it is willing to accept through the MINCLIENT and MAXCLIENT keywords, and the set of features that it supports through the FEATURES keywords.

When a client uses IXCSEND to send a request, it specifies its own level through the CLIENTLEVEL keyword and the routing criteria through the CRITERIA keyword that XCF is to use to determine which instances of a server are suitable for the request.

The routing criteria indicate the range of server levels that are suitable for the request and the features that the server must support in order to process the request. The desired server levels and features, as well as the client level are passed to the server exit routine when the request is presented for processing. The actual content and interpretation of the levels and features is determined by the client and server. As described below, XCF compares the requirements of the request against the support offered by the server to determine whether a given instance of the server is suitable for the request.