The Differentiated Services (DiffServ) prioritization scheme redefines the existing ToS byte in the IP header (Differentiated Services (DiffServ) ToS byte) by combining the first 6 bits into 64 possible combinations. The ToS byte can be used by Communication Manager, IP telephones, and other network elements such as routers and switches in the LAN and WAN.

A DiffServ Code Point (DSCP) of 46 (101110), referred to as expedited forwarding (EF), is used for the proper treatment of voice packets. Signaling packets can also be marked with DSCP 46 if there is sufficient bandwidth to prevent dropped packets. To assure that voice and signaling packets are not in contention, mark signaling packets with a different DSCP value. With Communication Manager, you can set any DSCP value needed to work with a company’s QoS scheme.

Some common DiffServ Code Points are defined in RFCs 2474 and 2475. Although DSCPs are specified in IETF RFCs, the treatment of packets that are tagged with DiffServ depends on implementation.

Note that older routers might require a DSCP setting of 40 (101000), which is backward compatible with the original ToS byte definition of critical. But again, Avaya products and software allows you to set any of the 64 possible DSCP values to work with your voice quality policy. You must use DSCP-46 for both bearer and control for simplicity. The default values are: Bearer-46, Control-34, Video-26. The ToS byte is an OSI model Layer 3 solution and works on IP packets on the LAN and WAN, depending upon the service provider.