VTAM® refers to a communication network management (CNM) routing table to determine which CNM application program is to receive an unsolicited network services request unit (NSRU) requiring further processing.

An application program can put its own procedure-related identifier (PRID) in each request sent to VTAM. When a reply to the request is returned, VTAM uses the PRID to route the reply to the application program. However, unsolicited request units contain network information, but they do not have a PRID. Therefore, VTAM needs the CNM routing table to determine which application program is to receive the unsolicited request unit.

VTAM provides default routing information for IBM® CNM licensed programs, such as the NetView® program. If you authorize a user-written application program to use the CNM interface, you should write a supplementary CNM routing table to route unsolicited requests to that application program.

For information about the request units for which VTAM provides default routing, see z/OS Communications Server: SNA Customization.