Preservation of SNA transmission priority

In Logmode/COS assignment, every session is assigned an APPN COS with an associated transmission priority so that data flowing over that session is one of the four transmission priorities (network, high, medium, or low). EE attempts to preserve that transmission priority across the WAN by mapping the transmission priority to an appropriate IP type of service (ToS) byte setting and UDP port. Configure IP WAN routers to handle appropriate transmission priorities.

Guideline: EE also attempts to preserve SNA transmission priority by mapping each SNA TP to a corresponding UDP port. However, traffic prioritization using ToS byte management is generally preferable to port-based prioritization, because port-based prioritization schemes do not work well in the presence of IP fragmentation or IPSec-encrypted traffic.