[asterisk-users] RTP Timestamp rewind

[Steve Davies]

Mark,

You have cropped the image you inserted above and removed a very important
part of the line you highlighted. I think is says ",Mark" after the time
value - You can even see the un-cropped comma in your picture.

RTP timestamps can be reset mid-stream if needed - It is part of the spec,
and most commonly happens when initially (eg Asterisk) generated audio is
replaced with audio from an external source once the call is bridged. The
early timestamp comes from Asterisk, and the subsequent timestamp is
retained from the new source of the RTP.

No packets should be dropped though in my experience some jitter buffers
can handle it poorly.

Hope that helps,
Steve

On Tue, 29 Aug 2017 at 19:39 Mark Wiater <mark.wiater at greybeam.com> wrote:

> Hi folks.
>
> I have a couple of questions regarding RTP.
>
> The background of my inquiry is that I have packet captures of SIP and RTP
> traffic on an Asterisk and Broadworks SIP trunk and the RTP many times has
> a time stamp that rewinds by 480 using g.711u. The Sequence number
> continues to increment appropriately, but the timestamp just rewinds.
>
>
>
> It doesn't happen on every call, but it's frequent enough to make me want
> to understand it better.
>
> My questions are:
>
> Is there ever a circumstance where it would be normal or logical to see
> the RTP timestamp go backwards during the RTP stream?  Consistently by 480,
> 3 voice frames?
>
> Will Asterisk just drop the packets that compromise the rewind?
>
> Thanks
>
> Mark
>
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