[asterisk-dev] Off the wall idea - transmit wideband G722 or Speex over ISDN

[asterisk at ntplx.net]

G.722 is used as an ISDN codec. It is (or was) used a lot in remote
radio broadcasts and then they mostly moved to MPEG (MP3) over ISDN.

The codec used could be sent in the bearer capability field of
the Q.931 call setup message. There are voice/data types but
the only codecs defined for voice/speech are G.711A and G.711u.

I have seen a few places where there has been an update to the
types to allow G.722/G.725 as an additional speech codec type.

You can see the info at:
http://www.ciscopress.com/articles/article.asp?p=29737&seqNum=3

I looks like additional information was added to the call
setup in a GTD message which includes more detailed codec settings.
http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ftgtdisd.html


BUT, if you look at libpri, you'll see G.722 is already defined
as a PRI Layer 1 type....
http://svn.digium.com/svn/libpri/branches/1.4/



Quoting Stephen Davies <stephen.l.davies at gmail.com>:

> Hi,
> Off the wall idea that I'd like to hear comments about:
>
> End-to-end ISDN call is basically a 64k data pipe.
> Can we find a way to stay within the rules of ISDN, but "discover" that our
> call is from an Asterisk box and to another.  Once we discover we are
> talking to a friend, we could do things like switch to encoding with G722 or
> Wideband Speex.
>
> "Discovery" could be to send and detect a special bit-pattern (selected to
> be inaudible or innocuous), and a similar response.  It needs to only be
> detectable if the link is really 64k "bit clear".
>
> How nifty would it be to pick up your SIP phone, dial a remote party and
> suddenly find yourself on a wideband call...
>
> Steve
>