Avaya 555-245-600 Benutzerhandbuch

serialization delay for a variety of packet sizes and line speeds. The formula for determining 
serialization delay is:

Because of all these configuration variables, properly implementing QoS on a router is no trivial 
task. However, QoS is needed most on the router because most WAN circuits terminate on 
routers.

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. 

56 kbps

9 ms

18 ms

36 ms

72 ms

144 ms

214 ms

64 kbps

8 ms

16 ms

32 ms

64 ms

128 ms

187 ms

128 kbps

4 ms

8 ms

16 ms

32 ms

64 ms

93 ms

256 kbps

2 ms

4 ms

8 ms

16 ms

32 ms

46 ms

512 kbps

1 ms

2 ms

4 ms

8 ms

16 ms

23 ms

768 kbps

640 µs

1.28 ms

2.56 ms

5.12 ms

10.24 ms

15 ms

Serialization Delay

Packet Size (bits)

Line Speed

------------------------------------------

=