[Asterisk-Users] PLC (Packet loss cancel) questions

[Chris Shaw]

> This is nothing to do with SIP. It is an RTP issue, common to everything
> which uses RTP - SIP and H.323 included.

I have been reading the RFCs and I'm a bit more familiar with how it works
now although the algorithms are a bit over my head. I am somewhat new to
RTP/VoIP, but I have a strong telecom/networking background so it makes
things a bit easier to understand since they share a lot of common
features.. I just thought from the post mentioning only IAX2 and "some of
the other codecs" that SIP et. al. would be ignored...

>Sending no packets is perfectly valid, and normal, in RTP. If the receiving
>end takes no packets (other  than, perhaps, an extremely long silence) as a
>disconnect it does not comply with the RTP spec. DTX is much despised,
>and CNG only slightly better. They just sound good (pun intende) on paper.

While I realize that hanging up on silence is not a desired behavior,
unfortunately lots of things are out of spec... Look at Cisco's POE
implementation for example, it's completely reversed from 802.3af specs...
If * had at least some kind of continuous CNG capability it would help in
these situations... Silence should be acceptable and even desired because it
saves bandwidth, but apparently some people (and switches) find it
uncomfortable...

-Chris