[Asterisk-code-review] codecs: Add Codec 2 mode 2400. (asterisk[master])

[Matt Jordan]

Matt Jordan has posted comments on this change.

Change subject: codecs: Add Codec 2 mode 2400.
......................................................................


Patch Set 6: Code-Review+2

> Related only indirectly to this issue here, however, because Codec
 > 2 or SILK is going to get 120 by using -1 after this is included,
 > there was a reason why 120 is free: <https://github.com/asterisk/asterisk/commit/7ba7ec9c976b44ba7cdf21b7c7cb8ab8aaf20b44>
 > at least there was in the year 2003 because iLBC got moved to 97
 > back then.
 > 
 > Yet, I was not able to find an issue report or another comment
 > related to that change. Can somebody ask Mark? Some Cisco phones
 > seem to use 120 for DTMF but in Asterisk the payload type 121 was
 > appointed to that. I am confused.

I would suspect that Asterisk used 97 for iLBC due to this example in RFC 3952:

   When conveying information by SDP, the encoding name SHALL be "iLBC"
   (the same as the MIME subtype).

   An example of the media representation in SDP for describing iLBC
   might be:

      m=audio 49120 RTP/AVP 97
      a=rtpmap:97 iLBC/8000

https://tools.ietf.org/html/rfc3952

Poor implementations may have hardcoded that format mapping (a relatively common error), and Mark was working around it.

Granted, all of that was back in 2003, which is practically antiquity.

At this point, I would suspect that all reasonable equipment can handle basic SDP parsing and handle mappings correctly.

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Gerrit-MessageType: comment
Gerrit-Change-Id: I1e45d8084683fab5f2b272bf35f4a149cea8b8d6
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