/mcpmicroseconds/mile. Based on the equipment, the trans-switch delay in a frame relay network needs
to be in the order of 1 ms fixed and 5 ms variable for queuing. These figures are equipment and
traffic dependent. The delay figures for the Cisco MGX WAN Switches is less than 1 ms per switch
total if E1/T1 trunks are used. With the assumption of 500 miles of distance, with 1 ms fixed and 5
ms variable for each hop, the delay calculation becomes:
Table 6 .4: Two Hop Private Network Delay Calculation with PBX Tandem
Note: Since queuing delay and the variable component of the Network delay is already accounted
within the de-jitter buffer calculations, the Total delay is only the sum of all the Fixed Delay. In this
case the total delay is 191.1 ms.
When you run over a private frame relay network, it is possible to make a spoke-to-spoke connection
through the PBX at the hub site and stay within the 200 ms figure.
Effects of Multiple Compression Cycles
The CS-ACELP compression algorithms are not deterministic. This means that the input data stream
is not exactly the same as the output data stream. A small amount of distortion is introduced with
each compression cycle as shown in Figure 7-1.
Delay Type
Fixed
(ms)
Variable
(ms)
Coder Delay, χ1
18
Packetization Delay, π1
30
Queuing/Buffering, ß1
8
Serialization Delay (64 kbps), σ1
5
Network Delay (Private Frame),
ωS1 + ßS1+ ωS2 + ßS2
2
10
De-jitter Buffer Delay, Δ1
40
Coder Delay, χ2
15
Packetization Delay, π2
30
Queuing/Buffering, ß2
0.1
Serialization Delay (2 Mbps), σ2
0.1
Network Delay (Private Frame),
ωS3 + ßS3
1
8
Serialization Delay (64 kbps), σS3
5
De-jitter Buffer Delay, Δ2
40
Transmission/distance delay (not broken down) 5
Totals 191.1 26.1 Page 15 of 18 Cisco - Understanding Delay in Packet Voice Networks 7/31/2008 http://kbase.cisco.com/paws/servlet/ViewFile/5125/delay-details.xml?convertPaths=1