Subject: [AVT] Doubts regarding RFC 2833

From: Rama Lakshmi <[email-masked]>
Date: Mon, 28 Jan 2002 03:08:57 -0800 (PST)

Hi  all ,

         I have following doubts regarding RFC2833
1.What is the need for using in-band signalling when
out-of-band
signalling has so many advantages ?
2.what kind of signalling is used in PSTN ?
3.What is the  relation between PSTN  signalling(
in-band ) and SS7
signalling( out-of-band ) ?
4.When there is packet loss in transmission of  rfc
2833 packets 
whether
it should be retransmitted or  the data should be
recovered  from
redundant data ( as said in rfc 2198 )?
5.What is the gateway that should be  used when using
rfc 2833  ?

Thanks in advance ,
Rams

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From: Wayne Mills <[email-masked]>
Date: Mon, 28 Jan 2002 08:23:30 -0500

> signalling has so many advantages ?

I can think of one advantage.  RTP, through sequence numbers and other
timing info, allows the receiving party to more accurately reproduce the
timing of the in-band signals when regenerated on the PSTN side.  With
OOB signalling, it's more difficult to reproduce the timing of the
signal w/r/t the original media stream it came from, since media and
signalling may take different paths through the network and are less (or
not?) correlated.

Regards,
Wayne.

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From: "Chris Fulmer"<[email-masked]>
Date: Mon, 28 Jan 2002 10:18:50 -0500

Rama --

> signalling has so many advantages ?

Several...  First of all, the out-of-band signalling doesn't
necessarily terminate at the same place that your bearer
path does.  Secondly, many applications use DTMF tones
for the user to singal to the remote end (ie voice-mail systems,
IVR systems, etc...)  Third, you need to make sure that the
out-of-band DTMF arrives at the remote end at the correct
point in time in the call.

> 2.what kind of signalling is used in PSTN ?

The PSTN uses both in-band and out-of-band signalling.

> signalling( out-of-band ) ?

SS7 is a primary way of carrying signalling information
between switches.  It's one way of doing PSTN signalling,
but not the only way.

> redundant data ( as said in rfc 2198 )?

Depends on your application, but in general you don't
have time to ask for retransmission -- that's why the
redundant information is there.

> 5.What is the gateway that should be  used when using

Uhh...  Any gateway that supports RFC 2833.  2833 is a fairly
new RFC, so there are a lot of gateways on the market now
that don't do 2833, but if you ask the equipment providers,
they're probably adding it right now.  Your gateway choice
will be determined in large part by what control protocols
you want to use (are you doing a H.323 gateway, MGCP, H.248,
etc...) and what's your termination into the telephony world
(analog, PRI, T1/E1, SS7), as well as things like size, power
requirements, cost, etc....

(Apart from that, my answer is going to be "A Nortel Gateway,
of course....")

--
C