[asterisk-users] G.722 between Eyebeam and a Polycom IP650

[Michael Graves]

Hi All,

So I've been exploring the use of G.722 encoded wideband audio
recently. I have three different SIP devices that allow this: Eyebeam,
IP650 and a Siemens S865IP. The Siemens and IP650 seems to work fine
together. Calls pass between them in what the Polycom notes as "HD"
mode and the audio quality is certainly very good.

However, things are not so easy with Eyebeam and the IP650. When a call
is placed between those two the audio stream from Eyebeam to the IP650
is never heard. The audio from the IP650 to Eyebeam is heard, and very
good quality.

David Frankel of ZipDX tells me that there is an error in RFC3551 such
that G.722 RTP clock/timestamps are actually wrong. To quote the RFC
directly.

"Even though the actual sampling rate for G.722 audio is 16,000 Hz, the
RTP clock rate for the G722 payload format is 8,000 Hz because that
value was erroneously assigned in RFC 1890 and must remain unchanged
for backward compatibility.  The octet rate or sample-pair rate is
8,000 Hz."

It seems that some manufacturers adhere strictly to the RFC while
others correct for the error. As such there are problems with G.722
interoperability.

Counterpath defends their implementation as being according to the RFC.

This begs the question of what does Asterisk do with G.722? I've yet to
try v1.6 so I open the question to the group.

Michael

--
Michael Graves
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http://blog.mgraves.org
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sip:mjgraves at pixelpower.onsip.com
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