Dynamic Jitter Buffer Operation - AudioCodes Mediant 3000 User Manual

SIP User's Manual
Below is an example of SIP messages implementing the X-Detect header:
INVITE sip:101@10.33.2.53;user=phone SIP/2.0
Via: SIP/2.0/UDP 10.33.2.53;branch=z9hG4bKac5906
Max-Forwards: 70
From: "anonymous" <sip:anonymous@anonymous.invalid>;tag=1c25298
To: <sip:101@10.33.2.53;user=phone>
Call-ID: 11923@10.33.2.53
CSeq: 1 INVITE
Contact: <sip:100@10.33.2.53>
X- Detect: Request=CPT,FAX
SIP/2.0 200 OK
Via: SIP/2.0/UDP 10.33.2.53;branch=z9hG4bKac5906
From: "anonymous" <sip:anonymous@anonymous.invalid>;tag=1c25298
To: <sip:101@10.33.2.53;user=phone>;tag=1c19282
Call-ID: 11923@10.33.2.53
CSeq: 1 INVITE
Contact: <sip:101@10.33.2.53>
X- Detect: Response=CPT,FAX
INFO sip:101@10.33.2.53;user=phone SIP/2.0
Via: SIP/2.0/UDP 10.33.2.53;branch=z9hG4bKac5906
Max-Forwards: 70
From: "anonymous" <sip:anonymous@anonymous.invalid>;tag=1c25298
To: <sip:101@10.33.2.53;user=phone>
Call-ID: 11923@10.33.2.53
CSeq: 1 INVITE
Contact: <sip:100@10.33.2.53>
X- Detect: Response=CPT,FAX
Content-Type: Application/X-Detect
Content-Length: xxx
Type = CPT
Subtype = SIT
9.8

Dynamic Jitter Buffer Operation

Voice frames are transmitted at a fixed rate. If the frames arrive at the other end at the
same rate, voice quality is perceived as good. In many cases, however, some frames can
arrive slightly faster or slower than the other frames. This is called jitter (delay variation),
and degrades the perceived voice quality. To minimize this problem, the device uses a jitter
buffer. The jitter buffer collects voice packets, stores them and sends them to the voice
processor in evenly spaced intervals.
The device uses a dynamic jitter buffer that can be configured using the following two
parameters:
Minimum delay: DJBufMinDelay (0 msec to 150 msec)
Defines the starting jitter capacity of the buffer. For example, at 0 msec, there is no
buffering at the start. At the default level of 10 msec, the device always buffers
incoming packets by at least 10 msec worth of voice frames.
Optimization Factor: DJBufOptFactor (0 to 12, 13)
Defines how the jitter buffer tracks to changing network conditions. When set at its
maximum value of 12, the dynamic buffer aggressively tracks changes in delay (based
on packet loss statistics) to increase the size of the buffer and doesn't decay back
down. This results in the best packet error performance, but at the cost of extra delay.
At the minimum value of 0, the buffer tracks delays only to compensate for clock drift
and quickly decays back to the minimum level. This optimizes the delay performance
but at the expense of a higher error rate.
Version 5.8 471
9. IP Telephony Capabilities
September 2009