Avaya 555-245-600 manual QoS guidelines, Serialization delay matrix

Quality of Service guidelines

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

	Serialization Delay =			Packet Size (bits)
				-----------------------------------------
					Line Speed
Table 53: Serialization delay matrix
WAN	Packet size
line
	64	128	256		512	1024	1500
speed
	bytes	bytes	bytes		bytes	bytes	bytes
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

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.

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.

318 Avaya Application Solutions IP Telephony Deployment Guide