[SR-Users] Robust header compression (RFC 3095) with Kamailio +rtpproxy

[Ovidiu Sas]

Without RoHC, the only 'cheap' way to save on bandwidth is to increase
the packetization time, which leads to delays.  Also, if a packet is
dropped, a big chunk of media is lost.
With RoHC, packetization time doesn't really matter.  Choosing a low
value for packetization (10-20ms) reduce the latency a lot and if a
packet is discarded, the effect is negligible.

RoHC makes a lot of sense in scenarios where bandwidth is expesive
(wireless transmissions).  It can save a lot of bandwidth and it can
improve the voice quality (low delay by choosing a low value for
packetization and better tolerance for packet loss).


Regards,
Ovidiu Sas

On Tue, May 18, 2010 at 4:00 PM, Jeff Brower <jbrower at signalogic.com> wrote:
> Alex-
>
>> It is not supported by rtpproxy.  But you could run all that traffic
>> inside a high-compression IP-in-IP UDP tunnel, though there would be
>> an overhead penalty there too.
>
> We've already extended rtpproxy for transcoding and encryption, we're thinking to continue with that approach for
> header compression.
>
>> Doesn't seem to me like this stuff really saves a lot of bandwidth,
>> especially in a way that has meaningful network oversubscription
>> returns.  You might be better off just using a low-bandwidth codec
>> than worrying about all this.
>
> Yes we're wondering also.  The main customer concern seems to be physically slow networks rather than
> oversubscription.  I.e. geographical regions and/or equipment where voice channels are well under 50 kbps.  But you
> make a good point, and we're trying to evaluate this carefully.
>
> It does seem valuable if we can get down (and stay down) to a few bytes for all headers instead of 40.  Also it seems
> a lot of work has gone in the area over the last few years.  For example, initial RFCs were sensitive to packet loss,
> later revisions have improved this.
>
> -Jeff
>
>> On May 18, 2010, at 3:10 PM, Vikram Ragukumar
>> <vragukumar at signalogic.com> wrote:
>>
>>> Hello,
>>>
>>> We are looking into bandwidth conservation by implementing RTP/UDP/
>>> IP header compression.
>>>
>>> Has anybody implemented ROHC or another header compression scheme in
>>> combination with kamailio + rtpproxy ? Could you please point us to
>>> online documentation or other useful resources ?
>>>
>>> Thanks and Regards,
>>> Vikram.
>
>
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