An apparatus and a method for processing messages. A transport protocol stack receives messages from senders. The transport protocol stack comprises a concurrent stack having an out of band thread pool and a non-out of band thread pool. A channel is formed with a thread from the non-out of band thread pool of the concurrent stack for each sender. Non-out of band messages are processed in parallel for each scope of an application with a non-out of band thread. Non-out of band messages pertains to processes of the application from a same sender. Processes from a scope of the application are unrelated to processes from another scope of the application. Non-out of band messages within a same scope are processed in a predefined order.