Subject: [AVT] Missing events in RFC 2833

From: Tom Taylor <[email-masked]>
Date: Mon, 01 Dec 2003 11:36:34 -0500

I'm finding it a little difficult to see how some of the applications 
supported by RFC 2833 work without a few more events.  Here are some 
examples:

1. V.18 text telephones interwork with a number of other text telephone 
types.  The only event defined specifically for V.18 operation seems 
rather arbitrarily chosen: the ANS2225 event for Bell 103 answer tone. 
There don't seem to be any events for Baudot or V.23 or for Bell 103 in 
calling mode.

2. Signalling System No. 5 has two sets of signals: line signals, which 
are tones controlling trunk state, and register signals, which convey 
digits with some supporting information.  There is a timing constraint 
that register signalling must begin within 80 +/- 20 ms of the end of 
the "seize" line signal.  Yet no event is defined for "seize", only for 
the register signals.  It's a little hard to see how the receiving 
gateway can propagate KPx (the initial register signal) on time if it 
doesn't know that "seize" was playing, even if the sending end can 
recognize and report the start of KPx within the 20 ms tolerance.  As I 
see it, the present set of events is useful only to transfer the 
register events from one gateway to another which will report them to 
call control rather than propagating them as tones.

These missing events raise the issue of whether proposals to add events 
to RFC 2833 should be backed up by requirements documents describing 
their use.  I have been adding brief application descriptions in my 
rewrite of 2833bis, as justification for the normative text which I have 
also been adding.  (Basically just obvious stuff, missing the first time 
around and highlighted by Flemming's comments earlier this year.)  I am 
hoping that this additional information prompts a critical review of the 
current set of 2833/2833bis events, with a view to rounding them out as 
necessary to make applications work well.

Tom Taylor

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

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From: "Gunnar Hellstrom" <[email-masked]>
Date: Mon, 1 Dec 2003 23:20:15 +0100

Below, Tom Taylor asks if there is any interest to complete the textphone
related tone events in RFC2833 so that all V.18 submodes can be transported
with RFC2833.

We have to verify that we have satisfying detection and transport methods in
RFC2793, and e.g. V.18 or the H.248.2 package descriptions, so that we can
leave RFC2833 half done for text transport.

I would like to do so, but then the market forces must be strong enough to
make RFC2793 and textphone detection commonplace.

Using RFC2833 will place a task similar to V.18 logic on the IP endpoint,
but with less exact information than the native V.18 has. We have no
analysis if that task is realistic, nor if it is likely to be implemented by
IP endpoint developers.

( The missing events for complete text transport are probably:
V.21 data in lo channel at 110 bits/s
Bell 103 hi channel data at 300 bits/s
Bell 103 lo channel data at 300 bits/s
V.23 data at 1200 bits/s
V.23 data at 75 bits/s
Baudot data at 45.45 bits/s
Baudot data at 50 bits/s

(assuming that V.8 signals and V.21 at 300 bits/s in both directions and
DTMF are covered )

Gunnar

-------------------------------------------
Gunnar Hellstrom
Omnitor AB
Renathvagen 2
SE 121 37 Johanneshov
SWEDEN
+46 8 556 002 03
Mob: +46 708 204 288
www.omnitor.se
[email-masked]
--------------------------------------------

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of Tom
Taylor
Sent: Monday, December 01, 2003 5:37 PM
To: [email-masked]
Subject: [AVT] Missing events in RFC 2833

Tom Taylor