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ITG Engineering Guidelines Page 121 of
378
ITG Trunk 2.0 ISDN Signaling Link (ISL) Description, Installation and Operation
Queuin
g
dela
y
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 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 lies
between 250 and 500 bytes. Figure 18 displays the average queueing delay of
the network based on a 300-byte average packet size.
As can be seen in Figure 18, queueing delays can be significant for links with
bandwidth under 512 kbit/s, whereas with higher speed links they can tolerate
much higher utilization levels.
Figure 18
Queuing delay of various links
Queueing delay of various links
0
10
20
30
40
50
60
70
80
90
100
20% 30% 40% 50% 60% 70% 80% 90%
Utlization
Delay (ms)
64kbps
128kbps
256k
512kbps
T1
553-9183