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Quality of Service guidelines
Figure 83: Differentiated Services (DiffServ) TOS byte
A DiffServ Code Point (DSCP) of 46 (101110), referred to as expedited forwarding (EF), is
suggested for the proper treatment of voice and signaling packets. However, with
Communication Manager, one can set any DSCP value as desired 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
DiffServe is implementation- dependent.
Note that older routers might require a DSCP setting of 40 (101000), which is backward
compatible to the original TOS byte definition of critical. But again, Avaya products and software
allows users to set any of the 64 possible DSCP values to work with your voice quality policy.
The TOS byte is an OSI model Layer 3 solution, and works on IP packets on the LAN and
possibly the WAN, depending upon the service provider.
318 Avaya Application Solutions IP Telephony Deployment Guide
Table 74: Original TOS specification
Bit
Value
description
000
001
Bits 0-2IP
010
011
precedence
100
101
110
111
Bit 3
0
delay
1
Use
Routine
Priority
Immediate
Flash
Flash Override
CRITIC/ECP
Internetwork control
Network control
Normal
Low
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