Transport classes are used to group messages. Using the CLASSDEF parameter in the COUPLExx parmlib member, you can assign messages to a transport class based on the group name, the message size, or both.

Each transport class has its own resources that consist of a buffer pool and one or more outbound signaling paths. It is recommended you keep the number of transport classes small. In most cases, it is more efficient to pool the resources and define the transport class based on message size. Some initial product documentation recommended separate transport classes for global resource serialization or RMF™. These recommendations are no longer advised. If you do have separate transport classes for specific groups based on early product recommendations, you should consider changing these recommendations.