Suggested Modifications to draft-ietf-megaco-reqs-03.txt For text telephone support.
Issued by Gunnar Hellström L M Ericsson Gunnar.hellstrom@omnitor.se
The following additions to the megaco requirements spec are intended to cover the needs from text telephony, and its gatewaying to IP text conversation.
They are now concentrated in the Application-specific requirements section. Since many of the requirements could as well have been specified under Termination Class Requirements for an Analogue Gateway, section 11.1.5, I want to leave it to the authors of the main document to insert the information where it is appropriate.
<<<<<<In 11.2.4, add information about a text telephone capable gateway >>>> 11.2.4. Trunking/Access Gateway with text telephone access ports
An access gateway with ports capable of text telephone communication, shall provide communication between text telephones in the SCN and text conversation channels in the packet network.
Text telephone capability of ports is assumed to be possible to combine with other options for calls as described in the section on "Adaptable NASes".
The port is assumed to adjust for the differences in the supported text telephone protocols, so that the text media stream can be communicated T.140 coded in the packet network without further transcoding.
The protocol must be capable of reporting the type of text telephone that is connected to the SCN port. The foreseen types are the same as the ones supported by ITU-T V.18: DTMF, EDT, Baudot-45, Baudot-50, Bell, V.21, Minitel and V.18. It should be possible to control which protocols are supported. The SCN port is assumed to contain ITU-T V.18 functionality.
The protocol must be able to control the following functionality levels of text telephone support:
a. Simple text-only support: The call is set into text mode from the beginning of the call, in order to conduct a text-only conversation.
b. Alternating text-voice support: The call may begin in voice mode or text mode and, at any moment during the call, change mode on request by the SCN user. On the packet side, the two media streams for voice and text must be opened, and it must be possible to control the feeding of each stream by the protocol.
c. Simultaneous text and voice support: The call is performed in a mode when simultaneous text and voice streams are supported. The call may start in voice mode and during the call change state to a text-and-voice call.
A port may implement only level a, or any level combination including level a.
The protocol must support:
a. A text based alternative to the IVR functionality of the gateway when the port is used in text telephone mode.
b. Selection of what national translation table to be used between the Unicode based T.140 and the 5-7 bit based text telephone protocols.
c. Control of the V.18 probe message to be used on incoming calls.
<<<< End of 11.2.4 addition >>>>>>>
<<< IN 11.2.6 e, add ",text telephone" after "fax" to read like this: >>
e. Adaptable NASes: The protocol must be able to support multiple options for an incoming call to allow the NAS to dynamically select the proper type of call. For example, an incoming ISDN call coded for "Speech" Bearer Capability could actually be a voice, modem, fax, text telephone or 56 kbit/s synchronous call. The protocol should allow the NAS to report back to the MGC the actual type of call once it is detected. <<<< end of change for 11.2.6 >>>>>
Regards
Gunnar Hellström
------------------------------------- Gunnar Hellström
Ericsson Home Systems
Tel +46 751 100 501 Fax +46 8 556 002 06
e-mail gunnar.hellstrom@omnitor.se Video +46 8 556 002 05 -------------------------------------