Thread Subject: Re: RFC 4103 reference for real-time text.
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From: Paul E. Jones
Date: Wed, May 23 2007 4:40 PM
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Not to drive the committee into a deep hole on this much-debated issue, but
in spite of the many references to RFC 4103 (which I do favor for native IP
devices), there are concerns with the ability to utilize RFC 4103 on gateway
devices. When developing TIA-1001, we were presented with a laundry list of
requirements that, unfortunately, RFC 4103 could not always satisfy for
gateway devices (or not very well). Thus, TIA-1001 and V.151 prescribe
something different, yet very similar in capability, as a primary means of
relaying text over IP.
Perhaps more important is the loud voices I hear in the industry that are
actually deploying equipment. As much as I?ve pushed to get support for a
text relay mechanism between analog TTY devices over IP, it is very
difficult to even get DSPs in the market that can do proper tone detection,
let alone error-free character extraction. Even if that issue is solved
(which it could be), we?re still faced with other problems:
Â· RFC 4103 consumes more resources on large gateways, which would
lead to higher port costs and/or lower port density
Â· The PSTN circuit is a multiplex of voice and TTY signals.
Separating text and voice into separate steams on IP, only to put them back
together again on a remote gateway, is a zero-gain exercise (i.e., it?s a
Â· It takes time to establish an RFC 4103 stream, especially if there
are H.248 media gateways, two media gateway controllers, and one or more
proxies in the call path (and we have all of this and more in the IMS
architecture), so RFC 4103 might introduce delays in initial communication
which can be avoided with TIA-1001
Â· For legacy TTY devices, carriers seem to not favor text relay at
all, preferring to use G.711 and simply pass TTY signals over G.711 (much to
So, simply declaring that a gateway device shall support RFC 4103 and citing
standards references is insufficient. The problem is a complicated on a
number of levels, which is why carriers seem to favor treating TTY as voice.
Placing a requirement on gateway equipment to relay modulated TTY signals is
an uphill battle, and one that simply cannot be met with many of the tens of
thousands of already-deployed gateway devices in the field. When we can get
a foot in the door, to then further complicate the problem with multiple RTP
streams, multiplexing issues, and higher per-port costs, increased signaling
overhead, etc., will likely mean we stick with G.711 for legacy TTY support
So, if I were to place bets on what I think stands the greatest chance of
succeeding on gateway devices in the carrier space, it would be (in order):
Â· V.152 (Voice Band Data, i.e., use G.711 or better for
Â· TIA-1001 / V.151 (if we can convince folks to do relay at all)
Â· RFC 4103
From: = EMAIL ADDRESS REMOVED =
[mailto: = EMAIL ADDRESS REMOVED = ] On Behalf Of Gunnar
Sent: Wednesday, May 23, 2007 5:19 PM
Subject: [teitac-telecom] RFC 4103 reference for real-time text.
I want to comment on today?s meeting discussion on 1194.23(b), about the
explicit reference to RFC 4103 for real-time text.
It sounds good with many voices understanding the great benefits that are
within reach by moving to IP and getting a real-time text channel easily
integrated with other media in the calls.
However, Fred Lucas / TIA had some questions and concerns that I can answer
and hopefully resolve.
I will take them in portions.
Concern 1: ?RFC 4103 is not so much known protocol. Any protocol can be
decided now for this purpose.?
Answer: IETF RFC 4103 ?RTP Payload for text conversation? is an open
standard now referenced from at least 20 other standards from IETF, ITU-T,
3GPP and ETSI. It has for example been included as one of the three media
together with video and audio in IMS Multimedia Telephony. IMS is the next
environment we will see grow for establishing IP based telecom services.
These standards comprise:
No other standard for real-time text has the ambition to have this wide
coverage. It has taken some years to reach this acceptance level.
Here are a few excerpts:
1. From RFC 4305, SIP telephony device requirements:
?Req-55: SIP telephony devices that include a display, or have a
facility for connecting an external display, MUST include
protocol support as described in RFC 4103  for real-time
2. From ietf-draft-ecrit-requirements: ?Requirements for Emergency Context
Resolution with Internet Technologies?
?Emergency calling must support a variety of
media. Such media should include voice, conversational text
([RFC4103]), instant messaging and video.?
3. From ITU-T V.151 ?Procedures for the end-to-end connection of analogue
PSTN text telephones over an IP network utilizing text relay?
?In general, ITDs transmit text characters when communicating with other
ITDs using RFC 4103, which specifies the establishment of a separate RTP
stream specifically for transmitting text characters.? ( ITDs are IP text
Conclusion: Well covered in standards, ready for wider deployment.
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