gtps2m1q | ACF/SNA Data Communications Reference |
In APPN support, a link is identified by its transmission group (TG) number and the control point (CP) name of the adjacent node. In HPR support, a link is identified by an automatic network routing (ANR) label.
ANR labels identify paths through the HPR network. There are two ANR labels assigned to each HPR-capable link, one label for each direction that data flows across the link. The ANR labels are created when an HPR link is activated during the exchange identifier (XID) process.
An ANR label is a 1- to 8-character identifier representing the path from node A to node B across a specific link. Because an ANR label implies direction, there are two ANR labels assigned to each link. When a link between node A and node B is activated, node A assigns the ANR label representing the path from node A to node B across the link. Node B assigns the ANR label representing the path from node B to node A across the link.
ANR labels are unique only per node; they are not necessarily unique in the whole network. Assume node A assigned ANR label 123 to a link connecting node A to node B. Next, a link from node B to node C is activated. Node B can assign ANR label 123 to this link. However, if node A activates a link to node C, node A cannot assign ANR label 123 because node A has already assigned this ANR label to another link.
Data sent on an RTP connection is called a network layer packet (NLP). There is a section at the beginning of each NLP called the network layer header (NHDR), which contains the list of ANR labels representing the path from the origin RTP endpoint to the destination RTP endpoint. Because ANR labels are sent in every NLP, it is desirable to create ANR labels that are as short as possible to reduce the size of NLPs. See NLPs for more information about NLPs.
A different link identification method (ANR labels) was created for HPR support because:
Besides having ANR labels assigned to HPR links, there are special ANR labels called network connection endpoint (NCE) identifiers. An NCE identifier is assigned to one or more logical units (LUs) in an RTP node. In the TPF system, there is one NCE representing all TPF applications.
Figure 63 shows the APPN and HPR view of a network:
Figure 63. Sample Network with APPN TGs and HPR ANR Labels
In Figure 63, there is one link connecting each of the following node pairs: A and B, B and C, C and D. In APPN terminology, the path from node A to node D is described as follows (assuming all nodes are in the NET1 network):
The reverse path (node D to node A) is:
In the HPR view of the network, there are two lines drawn between each pair of nodes, but the two lines represent one link. Each line is showing the ANR label assigned to that link in the indicated direction. In HPR support, ANR labels describe a route through the network, so the path from node A to node D is:
The reverse path (node D to node A) is:
Notice that this example uses ANR label N1 more than once in the HPR network.