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 trans missi on queue
of the link before it is serialized. On a link where packets are processed in
first-come-first -serve order, the avera ge queueing time in ms is e stimated by
the formula:
p*p*(average intran et pa ck e t in by t es) / ( 1- p )/ (l i nk sp ee d 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. Figure18 displays the average queueing delay of
the network based on a 300-byte average packet size.
As can be seen in Figure18, queueing delays can be significant for links with
bandwidth under 512 kbit/s, whereas with higher speed links they can tolera te
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%
Utliz ation
Delay (ms)
64kbps
128kbps
256k
512kbps
T1
553-9183