gtpd2m23Data Communications Services Reference

Local vs. Remote Routing

Message routing can be divided into two levels: Local Routing and Remote Routing.

Previously, local routing meant the situation in which an application is communicating with another application in the same TPF processor. This definition is expanded to include the routing of messages between an application residing in one processor of an loosely coupled complex and an application belonging to another processor within the same complex. For simplicity, the examples used to illustrate local routing in this document will show routing in a Single Processor System.

Remote routing comes into play when an application is communicating with an application or terminal outside of the loosely coupled complex. Remote routing, in this context, implies processor-to-processor communication where RCPLs are used in message headers to adhere to a format known as Processor to Processor Message Format. The processor-to-processor communications lines used for remote routing must be SDLC.

The distinction between local routing and remote routing is made on the basis of a CPU ID. Each control point in a TPF network must have a unique CPU ID. The CPU ID associated with a destination determines whether or not remote routing is used. Procedures are available for reaching a remote SNA domain without the use of PPMSG header. A PPMSG message header identifies the remote routing performed by the TPF Message Router.

BSC lines used for local routing have each station permanently attached to one application program which is given all the data received from the station. This application can, of course, reroute the message but as far as the TPF system is concerned, the line is used for local routing. A BSC line cannot be used for remote routing.