ROUTE_SETUP process

When an RTP connection starts, there is a new flow called a ROUTE_SETUP command that occurs after the APPN search (LOCATE flows) and before the BIND request is sent out. The purpose of the ROUTE_SETUP process is to gather the HPR information for the route, including:
  • The list of ANR labels in the forward direction (the path from the node containing the PLU to the remote RTP endpoint)
  • The list of ANR labels in the reverse direction (the path from the remote RTP endpoint to the node containing the PLU)
  • The maximum packet size, which is the value of the smallest link size along the route between the RTP endpoints.
  • The maximum amount of time that the remote RTP endpoint requires for a path switch.

The ROUTE_SETUP request is sent by the node containing the PLU and is processed by every node along the route, up to and including the remote RTP endpoint, to obtain the forward route information. When the ROUTE_SETUP request reaches the remote RTP endpoint, a ROUTE_SETUP reply is sent back to gather the reverse route information.

Figure 1 shows an example of the flows during the ROUTE_SETUP process.
Figure 1. ROUTE_SETUP process
Alternative text description not available.
In the figure, a session between LUa (the PLU) in the z/TPF system and LUd in node D is starting. The RSCV calculated by the network is a three-hop route, the z/TPF system determined that HPR support can be used for the entire route, and a new RTP connection will be started. The step-by-step description of the ROUTE_SETUP process is as follows:
  1. The z/TPF system receives a LOCATE command on the CP-CP sessions containing the RSCV.
  2. The z/TPF system builds the ROUTE_SETUP request; the following information is included:
    Req
    The ROUTE_SETUP command is marked as a request.
    PCIDx
    A new procedure correlation identifier (PCID) to identify this ROUTE_SETUP process. This is not the PCID of the LU-LU session being started.
    RSCV
    The route for the LU-LU session.
    DLU
    Name of the destination LU, which, in this example, is LUd.
    FANR
    Forward ANR field. The z/TPF system includes the ANR label for the first link (which is A1) here. Each node along the route will add to this field.
  3. Node B adds ANR label B2 to the FANR field and then, using the RSCV, passes the ROUTE_SETUP request to node C.
  4. Node C adds ANR label C1 to the FANR field and then, using the RSCV, passes the ROUTE_SETUP request to node D.
  5. Node D builds the ROUTE_SETUP reply; the following fields are included:
    Rep
    The ROUTE_SETUP command is a reply.
    PCIDx
    The PCID from the ROUTE_SETUP request.
    CP_DLU
    CP name of the remote RTP endpoint (CP name of node D).
    FANR
    Forward ANR field. This is copied from the ROUTE_SETUP request.
    NCE_DLU
    NCE identifier assigned to the destination LU in the remote RTP endpoint, which is D4 in this example.
    RANR
    Reverse ANR field. The remote RTP endpoint puts ANR label D1 here. Each node along the route will add to this field.
  6. Because the ROUTE_SETUP command is a reply, intermediate nodes add to the RANR field rather than the FANR field. Node C adds ANR label C2 to the RANR field.
  7. Node B adds ANR label B1 to the RANR field.

When the ROUTE_SETUP reply is received by the z/TPF system, the RTP connection is started by sending out an NLP marked as a new connection. The NLP also contains the BIND request to start the new LU-LU session.

The ROUTE_SETUP process is also used during the path switch process. See Path switches for more information about the path switch process.