Before a session is established, both session partners must agree on a common Class of Service that defines a particular ordered list of virtual routes. They do this by specifying a Class of Service name. Within an SNA network, both session partners can use the same Class of Service name, thus ensuring that the correct Class of Service is used. When you connect independent SNA networks, however, a given Class of Service might be known by different names in different networks, or the same name might be used for different Classes of Service. When the alias name translation facility is used, a Class of Service name in one network can be mapped to a different name in each adjacent network along a cross-network session path to provide equivalent service. This translation can occur in any SSCP on the setup path. For SLU initiated sessions, you must also map the COS name for the origin logical unit (OLU) to the destination logical unit (DLU).

The COS name entry used for the session must exist in the COS table of the primary logical unit SSCP and in the gateway VTAM® that performs the SETCV. For information about determining which gateway VTAM performs the SETCV, see Cross-network routing.

The NetView® alias name translation facility can be used to establish equivalence for the required session parameters. The NetView alias name translation facility maps the logon mode name in one network to the logon mode name used in the other network. The same process is used for the COS name. If the COS name needed to establish a virtual route and transmission priority in one network does not exist in the COS table of the PLU in the other network, the NetView alias name translation facility can be used.

This alias name translation facility maps the COS name in one network to the COS name in the other network that provides a network route with equivalent characteristics (for example, high speed, high availability, and security).

A substitute COS entry can also be used. The substitute COS entry, chosen by specifying the SUBSTUT operand on the COS macroinstruction for one COS entry, indicates the COS entry to be used when the COS specified in a session request is unknown. For more information about how the substitute COS works, see "Substituting Class of Service Parameters" in How session traffic is assigned to a specific route.