[RTPproxy Users] About Jitter

[Maxim Sobolev]

Ronald Voermans wrote:
> Maksym,
> 
> Thank you for your answer. I'll go and try it. One other question about it:
> 
> The call is exactly as described below. With every call I see the following:
> 
> every third or fourth RTP packet has a arrival time (Delta) of around 11 ms instead of around 20-23 ms.
> 
> When I capture the traffic *before* it enters RTPproxy, every RTP packet has a normal arrival time (Delta) of around 20-23ms.
> 
> Why does this happen?

The RTPproxy processes incoming packets in "batches", with roughly 10ms 
interval between batches (by default). Let's say first packet arrives at 
9th ms, while the second at 21st ms. As a result, the first will get to 
the first "batch" and will be sent out almost immediately at 10th ms 
with the 1ms of delay, while the second will only get to the third 
"batch", and therefore will go out around 30th ms with 9ms of additional 
delay. Interval between first and the second would be 12ms in and 20ms 
out. This is the mechanism that causes jitter to be slightly higher 
after rtpproxy processing.

As I have said, you can decrease this effect by increasing the value of 
POLL_LIMIT.

Regards,
-- 
Maksym Sobolyev
Sippy Software, Inc.
Internet Telephony (VoIP) Experts
T/F: +1-646-651-1110
Web: http://www.sippysoft.com