/mcpThe lumped Coder delay for G.729 that is used for the remainder of this document is:
Worst Case Compression Time Per Block: 10 ms
Decompression Time Per Block x 3 Blocks 3 ms
Algorithmic Delay 5 ms ---------------------------
Total (χ) 18 ms
Packetization Delay
Packetization delay (πn) is the time taken to fill a packet payload with encoded/compressed speech.
This delay is a function of the sample block size required by the vocoder and the number of blocks
placed in a single frame. Packetization delay can also be called Accumulation delay, as the voice
samples accumulate in a buffer before they are released.
As a general rule you need to strive for a packetization delay of no more than 30 ms. In the Cisco
router/gateways you need to use these figures from Table 5.2 based on configured payload size:
Table 5 .2: Common Packetization
You have to balance the Packetization delay against the CPU load. The lower the delay, the higher
the frame rate, and the higher the load on the CPU. On some older platforms, 20 ms payloads can
potentially strain the main CPU.
Pipeline Delay in the Packetization Process
Though each voice sample experiences both algorithmic delay and packetization delay, in reality, the
processes overlap and there is a net benefit effect from this pipelining. Consider the example shown
in Figure 2-1.
Figure 5-2 : Pipelining and Packetization
Coder
Payload
Size
(Bytes)
Packetization
Delay (ms)
Payload
Size
(Bytes)
Packetization
Delay (ms)
PCM,
G.711
64
Kbps 160
20
240
30
ADPCM,
G.726
32
Kbps 80
20
120
30
CS-
ACELP,
G.729
8.0
Kbps 20
20
30
30
MP-
MLQ,
G.723.1
6.3
Kbps 24
24
60
48
MP-
ACELP,
G.723.1
5.3
Kbps 20
30
60
60
Page 6 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