McDewey

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 effectively only the sum of all the Fixed Delay. In this case the total delay is 209.1 ms. Two-Hop Connection over a Public Network with a PBX Tandem Switch
Figure 6-3: Two Hop Public Network Example with PBX Tandem

Consider a branch-to-branch connection in a branch-to-headquarters network where the C7200 at the headquarters site passes the connection through to the headquarters PBX for switching. Here the voice signal has to be decompressed and de-jittered and then re-compressed and de-jittered a second time. This results in extra delays relative to the previous example. Additionally, the two CS-ACELP compression cycles reduce voice quality (see Effects Of Multiple Compression Cycles).
Table 6.3: Two Hop Public Network Delay Calculation with PBX Tandem
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 (Public Frame), ω1
40 25 De-jitter Buffer Delay, Δ1

40 Coder Delay, χ2
15

Packetization Delay, π2
30

Queuing/Buffering, ß2

0.1 Serialization Delay (2 Mbps), 0.1

Page 13 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