ADTRAN AOS Version R10.1.0 Command Reference Manual page 3280

Command Reference Guide
Equipment following the DiffServ model (DSCP-compliant nodes) must use the entire 6-bit DSCP value to
determine the appropriate PHB. The PHBs are defined as the following:
• Default PHB
• Class selector PHB
• Assured forwarding PHB (RFC 2597)
• Expedited forwarding PHB (RFC 2598)
Default PHB
All DSCP-compliant nodes must provide a default PHB to offer best-effort forwarding service. For default
PHBs, the DSCP value is 0. Any packet that does not contain a standardized DSCP should be mapped to
the default PHB and handled accordingly.
Class Selector PHB
In the class selector PHB, the first three bits in the DSCP value are used for backwards compatibility to
systems implementing IP precedence. In this scenario, all but the first three bits of the DS field are set to 0.
This compatibility requires DSCP-compliant nodes to provide the same data services as are provided by
nodes implementing IP precedence. The following table is a comparison of IP precedence values to their
corresponding DSCP values.
Assured Forwarding PHB
The flexibility of DiffServ allows for more developed subclasses of service within each main class using the
last three bits of the DSCP. As defined in RFC 2597, the assured forwarding PHB creates four main
classes of service:
60000CRG0-35E
IP Precedence Value (bits)
0 (000)
1 (001)
2 (010)
3 (011)
4 (100)
5 (101)
6 (110)
7 (111)
Class
AF1
AF2
AF3
AF4
X indicates a do not care value.
Copyright © 2012 ADTRAN, Inc.
Quality of Service Map Command Set
DSCP Value (bits)
0 (000000)
8 (001000)
16 (010000)
24 (011000)
32 (100000)
40 (101000)
48 (110000)
56 (111000)
DSCP Bits
001XX0
010XX0
011XX0
100XX0
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