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DiffServ
Issue 6 January 2008 321
Recommendations for end-to-end QoS
When end-to-end QoS is desired, Avaya recommends using DiffServ, a Layer 3 CoS method.
Modern routers can map DiffServ Code Points (DSCP) to 802.1p priority values, so 802.1p tags
can be recreated on each Ethernet link. This functionality is supported in Avaya Layer 3
switches, and the X330 WAN module.
IEEE 802.1p states a standard according to which these bits are used for CoS. The precedence
is listed in Table 54:
IEEE 802.1 precedence and service mapping.
DiffServ
The Differentiated Services (DiffServ) prioritization scheme redefines the existing TOS byte in
the IP header (Figure 90:
Differentiated Services (DiffServ) TOS byte on page 322) by
combining the first 6 bits into 64 possible combinations. This use of the TOS byte is still
evolving, but can be used now by Communication Manager, IP Telephones, and other network
elements such as routers and switches in the LAN and WAN.
Table 54: IEEE 802.1 precedence and service mapping
User priority Service mapping
000 Default, assumed to be best effort
001 Reserved, less than best effort
010 Reserved
011 Reserved
100 Delay sensitive, no bound
101 Delay sensitive, 100 ms bound
110 Delay sensitive, 10 ms bound
111 Network control