Parallel TGs for multiple connections between APPN nodes are supported. This support means that a node can have multiple links to the same adjacent node. Parallel TGs have different TG numbers and can have different TG characteristics assigned to them. Multiple-link TGs (many links with one TG number) are not supported in APPN by VTAM®. The support for parallel TGs matches that of most other APPN products.

If you have parallel TGs with CONNTYPE=APPN coded on the adjacent link stations, you can establish one or more APPN connections or one LEN connection between the two nodes. You cannot combine LEN and APPN connections or establish more than one LEN connection to the same adjacent node over APPN-capable TGs.

Support for multiple connections allows an independent LU in the APPN network to establish sessions through or into the subarea network by using several boundary-function TGs. An LU can have multiple sessions with one or more LUs through multiple boundary-function TGs and through different physical paths that function as parallel TGs. This support is also available for TGs attached to LEN nodes.

When coding CONNTYPE=APPN (or letting it default to that value), XID exchange rules for parallel TGs are enforced. This means that if you have PUs with duplicate CPNAMES, you should resolve this duplication before that node becomes an APPN node. If the node is to remain a LEN node, then CONNTYPE=LEN should be coded on the PU statement. Coding CONNTYPE=LEN results in VTAM avoiding the test for duplicate CPNAMEs.