rfc3054.txt

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   elements to which they map on the physical device have very different
   functional significance to the end-user, yet they may be represented
   in the protocol using exactly the same sets of Packages.  Naming
   conventions allow the controlling MGC to distinguish this end-user
   meaning without specific advance knowledge of physical device
   configuration and without the requirement to provide different
   Packages for each audio input/output type.

   Using these same TerminationID naming conventions in combination with
   wildcards, the MGC application can target commands to groups of
   related Terminations, for example the collection of all Audio
   Transducer Terminations ("at/*").  This is especially useful during
   the discover phase, for example to efficiently Audit all available
   Audio Transducer Terminations, and to efficiently send commands to a
   set of related Terminations in a single command, for example to



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   simultaneously Subtract all Audio Transducer Terminations from a
   particular Context.  Further information on TerminationID naming
   conventions and their use can be found under the sections on Control
   Interaction and Capability Discovery (next two subsections) and under
   Termination Types.

4.4.  Control Interaction

   To provide control of audio paths, Audio Transducer Terminations are
   manipulated using Contexts in the normal way, by sending Add, Move,
   Subtract and Modify commands addressed to the specific Terminations
   being manipulated.  For example creating a Context (Context A)
   containing an RTP Termination (Tr) and a Handset Audio Transducer
   Termination (Ta1) creates a voice connection to/from the handset.
   Moving a Handsfree Audio Transducer Termination (Ta2) into the
   Context, and removing the Handset, sets up a handsfree conversation.
   This situation is shown in Figure 1.  See the section on Audio
   Transducer Termination Types for further details on specific Package
   support requirements.

   User input elements, such as Keypad or Function Keys, generate Events
   through Notify commands sent from the User Interface Termination of
   the Megaco IP Phone MG to the controlling MGC for handling.  These
   Events are according to the specific set of Packages supported by the
   User Interface Termination of the device.  See the section on User
   Interface Termination Type for further details on specific Package
   support requirements.

   User output elements such as the Text Display or Indicators are
   controlled by Signals sent by the MGC, addressed to the User
   Interface Termination of the Megaco IP Phone MG, generally as part of
   a Modify command, using syntax defined in the corresponding Packages.
   Since the User Interface Termination cannot be part of any context,
   Add, Move and Subtract commands sent to it are not valid.  See the
   section on User Interface Termination Type for further details on
   specific Package support requirements.

   Some elements, for example Softkeys, have both user input and output
   aspects, so both react to Signals and generate Events as above.

   The TerminationID naming conventions may be used to target commands
   to specific Terminations by well known name, for example to Add the
   Handsfree Audio Transducer Termination ("at/hf") to a Context.  The
   naming conventions in combination with wildcards may be used to
   efficiently send commands to groups of related Terminations, for
   example to simultaneously Subtract all Audio Transducer Terminations
   ("at/*") from a particular Context.




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4.5.  Capability Discovery

   At startup or service change, the Megaco IP Phone MG identifies
   itself to its controlling MGC as being a Megaco IP Phone class of
   device by use of the IPPhone Protocol Profile.  This is the first and
   most important stage of capability discovery, and implicitly provides
   a great deal of the necessary information in a single step.
   Thereafter, the MGC can make a large number of assumptions regarding
   organization and behavior of the MG.  See the section on IPPhone
   Protocol Profile for further details of ServiceChange operation.

   Device capabilities, including the list of all Terminations and
   supported Packages for each, are queried through the AuditValue
   command.  Wildcarded AuditValue commands targeted at the whole MG
   (i.e., addressed to ContextID=Null, TerminationID=ALL) return the
   list of all Terminations, including the User Interface Termination
   and all supported Audio Transducer Terminations.  Since the returned
   TerminationIDs use well known identifier names, the MGC can derive
   the specific audio input/output elements available on the physical
   device, and their intended purpose.  Further AuditValues commands on
   individual named Terminations provide further details of each, for
   example for the MGC to query user interface support Packages
   available on the User Interface Termination ("ui").  TerminationID
   naming conventions in combination with wildcards can be used with
   AuditValues commands to query specific Package support for the
   collection of all Audio Transducer Terminations ("at/*").

   Since the structure of the Megaco IP Phone MG is well known in
   advance, by virtue of the IPPhone Protocol Profile, audits can be
   efficiently directed at discovering only what additional information
   is required by the MGC.  Thus the MGC is able to efficiently and
   unambiguously discover both the specific user interface capabilities
   and the supported audio input/outputs of the Megaco IP Phone MG,
   without specific advance knowledge of physical device configuration.
   It is not necessary for the MGC to attempt to infer function from
   supported Packages within a random collection of Terminations, and a
   great deal of behavior common to all Megaco IP Phone MGs can simply
   be assumed.  This pre-determined organization and behavior therefore
   greatly reduces design complexity of both MG and MGC, and greatly
   improves interoperability.

5.  Termination Types

   The Termination types defined for use in the Megaco IP Phone MG are:

   *  User Interface (implements user interface);





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   *  Audio Transducer (implements audio input/output to the user, and
      potentially appears as several individual Terminations
      corresponding to individual audio input/outputs on the physical
      device);

   *  RTP (transport of audio streams over IP).

   These Termination types represent minimal capabilities to support
   fully featured business telephones.  Additional Termination types can
   be defined to extend these capabilities.

   The following subsections describe requirements and constraints on
   each type in further detail.

5.1.  User Interface Termination Type

   The User Interface Termination represents the Megaco IP Phone MG user
   interface elements.  Megaco IP Phone MGs MUST support exactly one
   User Interface Termination.

   TerminationID of the User Interface Termination MUST be "ui", used
   for both command addressing and command response return.  ABNF text
   encoding for this MUST be as described in Megaco/H.248 Protocol
   Appendix B.1 [3].

   Note: If ASN.1 binary encoding is used (OPTIONAL in this
   specification), TerminationID for the User Interface Termination MUST
   be encoded as described in Megaco/H.248 Protocol Appendix A.1 [3],
   with alphabetic characters of the identifier given above mapping to
   the equivalent octet string in the ASN.1 encoding.

   The User Interface Termination cannot be part of any context, hence
   Add, Move and Subtract commands are invalid for this Termination.

   The User Interface Termination MAY support the following Packages,
   defined in Megaco/H.248 Protocol H.248 Annex G: "User Interface
   Elements and Actions Packages" [4].














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       __________________________________________________________
      | Package           | Name   | Support in User Interface   |
      |                   |        | Termination                 |
      |___________________|_______ |_____________________________|
      | Text Display      | dis    | OPTIONAL                    |
      | Keypad            | kp     | OPTIONAL                    |
      | Function Key      | kf     | OPTIONAL                    |
      | Indicator         | ind    | OPTIONAL                    |
      | Softkey           | ks     | OPTIONAL                    |
      | Ancillary Input   | anci   | OPTIONAL                    |
      |___________________|________|_____________________________|

   Additional Packages not listed above MAY also be provided where these
   are defined to extend to additional user interface elements.

   Note: The reasoning to make all Packages optional in the User
   Interface Termination is to allow maximum flexibility to create a
   very broad range of Internet telephones and similar devices.  For
   example, anything from a simple hotel lobby phone (handset and
   hookswitch only), to conferencing units (handsfree unit and one or
   two buttons) to fully featured business telephones (display, rich set
   of keys and indicators, both handset and handsfree, etc) could be
   designed.

5.2.  Audio Transducer Termination Types

   The Audio Transducer Terminations are used to control audio
   input/output to/from the end user of the device.  Megaco IP Phone MGs
   MUST support at least one Audio Transducer Termination, which MAY be
   chosen from the following well known types (with identifier name):

      *  Handset ("hs")    -- input/output,
      *  Handsfree ("hf")  -- input/output,
      *  Headset ("ht")    -- input/output,
      *  Microphone ("mi") -- input only,
      *  Speaker ("sp")    -- output only.

   TerminationIDs of the Audio Transducer Terminations MUST be of the
   form "at/<name>", where <name> is the 2 character identifier listed
   above, used for both command addressing and command response return.
   If more than one Audio Transducer Termination of a particular type is
   implemented, the TerminationIDs of each MUST be of the form
   "at/<name>/<num>", where <num> is a 2 digit index number in
   hexadecimal format beginning at 01.  Examples of valid TerminationIDs
   include: "at/hs" (handset), "at/mi/02" (microphone 2), "at/*" (all
   audio input/outputs).  ABNF text encoding for this MUST be as
   described in Megaco/H.248 Protocol Appendix B.1 [3].




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   Note: If ASN.1 binary encoding is used (OPTIONAL in this
   specification), TerminationIDs and wildcards MUST be encoded as
   described in Megaco/H.248 Protocol Appendix A.1 [3], with alphabetic
   characters of the identifiers given above mapping to octet sub-
   strings in the ASN.1 encoding and the '/' character not used.

   Additional Audio Transducer Termination types MAY also be defined by
   the implementer, however well know identifier names for these are
   outside the scope of this specification.

   All Audio Transducer type Terminations MUST support the following
   Packages, defined in Megaco/H.248 Protocol Annex E [3].

       ____________________________________________________________
      | Package             | Name   | Support in Audio Transducer |
      |                     |        | Terminations                |