Nortel Networks NN43001-563 User Manual download pdf (Page 133)

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101

Implement QoS in IP networks 133

Serialization delay

Serialization delay is the time it takes to transmit the voice packet one bit at

a time over a WAN link. 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)

Table 27 "Serialization delay" (page 133) shows what the ser ialization delay

for voice packets on a 64 kbit/s and 128 kbit/s link. The serialization delay

on higher speed links are considered negligible.

Table 27

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 for a packet to 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 WAN links generally is

between 250 and 500 bytes. Figure 26 "Queuing delay of various links"

(page 134) displays the average queueing delay of the network based on a

300-byte average packet size.

Nortel Communication Server 1000

IP Trunk Fundamentals

NN43001-563 02.01 Standard

Release 5.5 21 December 2007

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