Implement QoS in IP networks 133
Serialization delay
Serialization delay is the time it takes to transmitthe voice packet one bit at
a time over a WANlink. The serialization delay depends on the voice packet
size and the link bandwidth, and is calculated using the following formula:
Serialization delay in ms = 8 * (IP packet size in bytes)/(link bandwidth in
kbit/s)
Table27 "Serialization delay" (page 133) shows what the serialization delay
for voice packetson a 64 kbit/s and 128 kbit/s link. The serialization delay
on higher speed links are considered negligible.
Table 2 7
Serialization delay
Codec Frame
duration
Serialization
delay over
64 kbit/s link
(ms)
Serialization
delay over
128 kbit/s link
(ms)
10 ms 14.00 0.88
20 ms 24.00 1.50
G.711A/
G.711U
30 ms 34.00 2.13
10 ms 5.25 0.33
20 ms 6.50 0.41
G.729A/
G.729AB
30 ms 7.75 0.48
G.723.1 5.3
kbit/s 30 ms 6.50 0.41
G.723.1 6.3
kbit/s 30 ms 7.00 0.44
Queuing delay
Queueing delay is the time it takes fora packetto wait in transmission queue
of the link before it is serialized. On a link where packets are processed in
first-come-first-serve order,the average queueing time in ms is estimated by
the following formula:
p*p*(average intranet packet in bytes)/(1-p)/(link speed in kbit/s)
where p is the link utilization level.
The average size of intranet packets carried over WANlinks generally is
between 250 and 500 bytes. Figure 26 "Queuing delay of various links"
(page 134) displays the average queueing delayof the network based on a
300-byte average packetsize.
Nortel Communication Server 1000
IP TrunkFundamentals
NN43001-563 02.01 Standard
Release 5.5 21December 2007
Copyright© 2007, Nor tel Networks
.