DiffServ

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.

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

 

 

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.

Issue 6 January 2008 321

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Avaya 555-245-600 manual DiffServ, Recommendations for end-to-end QoS