Qos Guidelines - Avaya Application Solutions Deployment Manual

Quality of Service guidelines
serialization delay for a variety of packet sizes and line speeds. The formula for determining
serialization delay is:
Table 72: Serialization delay matrix
WAN
line
speed
56 kbps
64 kbps
128 kbps
256 kbps
512 kbps
768 kbps
Because of all these configuration variables, properly implementing QoS on a router is no trivial
task. However, QoS is needed most on the router where, because most WAN circuits terminate
on routers.

QoS guidelines

There is no all-inclusive rule regarding the implementation of QoS because all networks and
their traffic characteristics are unique. It is good practice to baseline the IP Telephony response
on a network without QoS, and then apply QoS as necessary. Avaya Network Consulting
Services can help with baselining services. Conversely, it is bad practice to enable multiple QoS
features simultaneously, not knowing what effects, if any, each feature is introducing.
Generally, for newer network equipment, best practices involve enabling Layer 3 (DiffServ) QoS
on WAN links traversed by voice. Tag voice and data with DiffServ Code Point 46 (Expedited
Forwarding), and set up a strict priority queue for voice. If voice quality is still not acceptable, or
if QoS is desired for contingencies such as unexpected traffic storms, QoS can then be
implemented on the LAN segments as necessary.
314 Avaya Application Solutions IP Telephony Deployment Guide
Serialization delay
Packet size
64 128 256
bytes bytes bytes
9 ms 18 ms 36 ms
8 ms 16 ms 32 ms
4 ms 8 ms 16 ms
2 ms 4 ms 8 ms
1 ms 2 ms 4 ms
640 µs 1.28 ms 2.56 ms
Packet size (bits)
---------------------------------------- -
=
Line speed
512 1024
bytes bytes
72 ms 144 ms
64 ms 128 ms
32 ms 64 ms
16 ms 32 ms
8 ms 16 ms
5.12 ms 10.24 ms
1500
bytes
214 ms
187 ms
93 ms
46 ms
23 ms
15 ms