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Network Working Group                            P. Blatherwick (Editor)Request for Comments: 3054                               Nortel NetworksCategory: Informational                                         R. Bell                                                           Cisco Systems                                                              P. Holland                                                    Circa Communications                                                   (Chair TIA TR-41.3.4)                                                            January 2001Megaco IP Phone Media Gateway Application ProfileStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2001).  All Rights Reserved.Abstract   This document specifies a particular application of the Megaco/H.248   Protocol for control of Internet telephones and similar appliances:   the Megaco IP Phone Media Gateway.  The telephone itself is a Media   Gateway (MG), controlled by the Megaco/H.248 Protocol, with   application control intelligence located in the Media Gateway   Controller (MGC).  To achieve a high degree of interoperability and   design efficiency in such end-user devices, a consistent   architectural approach, a particular organization of Terminations and   Packages, and a Protocol Profile are described.  The approach makes   use of existing Protocol features and user interface related   Packages, and is thus a straight-forward application of the   Megaco/H.248 Protocol.1.  Introduction   This document represents the current view from the TIA working group   on VoIP (Voice over IP) telephone specification [1], TIA TR-41.3.4,   with the intent of using this as part of its "whole device"   specification as an optional method of device control.   Industry feedback has made it clear that interoperability and   acoustic performance of Internet telephones is key to the rapid and   extensive commercialization of these products.  To facilitate this,   the TIA has established working group TR-41.3.4 to develop a standardBlatherwick, et al.          Informational                      [Page 1]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 2001   for VoIP telephones.  The TR-41.3.4 working group has included the   "whole device" within the scope of the standard, so a full range of   requirements including acoustic performance, protocols, methods for   powering and safety are provided.  Where possible, the requirements   are based on existing standards, which are included by reference.   The TIA TR-41.3.4 working group has also recognized that its proposed   standard must enable creative application of the equipment, encourage   the development of new capabilities and allow for high levels of   product customization.  To achieve this, peer to peer architectures   that are based on protocols such as H.323 or SIP and master/slave   architectures such as Megaco/H.248 Protocol are both necessary and   complementary.   In support of the Megaco/H.248 Protocol development effort, the TR-   41.3.4 working group has considered product enabling issues and   requirements, and has developed an approach to use the Megaco/H.248   Protocol for Internet telephone device control.  This document   represents the working group's current view.   This document covers the general requirements of the Megaco IP Phone   application (section 3), architectural approach and MG organization   (section 4), details of specific Termination types used and Packages   supported by each (section 5), and the Megaco IP Phone Protocol   Profile (section 6).2.  Conventions   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this   document, are to be interpreted as described inRFC 2119 [5].3.  General Requirements   The following general requirements were identified to drive the   Megaco IP Phone design [1]:   1. The Megaco IP Phone must meet the basic needs of the business user      from day one;   2. Provide a path for rapid expansion to support sophisticated      business telephony features;   3. Flexibility to allow for a very wide range of telephones and      similar devices to be defined, from very simple to very feature      rich;   4. Simple, minimal design;Blatherwick, et al.          Informational                      [Page 2]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 2001   5. Allow device cost to be appropriate to capabilities provided;   6. Packages and Termination types must have characteristics that      enable reliability;   7. The IP Phone MG shall meet the appropriate Megaco/H.248 Protocol      requirements as provided in the Megaco Requirements document [2]      and be a straight-forward application of the Megaco/H.248 Protocol      [3].4.  Architecture Description   The following subsections describe the general design approach and   organization of the Megaco IP Phone MG.4.1.  Design Approach   Design intent of the Megaco IP Phone is to keep it determinedly   simple while providing required support for fully featured business   telephones and the flexibility to allow for a very wide range of   telephone configurations and similar appliances.   The approach to achieve this goal is to provide a very simple and   direct master/slave control model in which very little feature   intelligence is required in the end device.  This design intent   matches the Megaco/H.248 Protocol approach well.   It is important to note that additional functionality, built-in   feature capability or system-specific optimization can easily be   provided, at the option of the implementer, by defining additional   Termination types, Event/Signal Packages, or providing built-in   application capability.  This document defines the minimal design   only.4.2.  General Structure   As shown in Figure 1 below, the Megaco IP Phone is organized as a   Media Gateway (MG) that consists of a User Interface Termination and   a set of Audio Transducer Terminations.   Several - potentially thousands - of Megaco IP Phone MGs may be   controlled by a single Media Gateway Controller (MGC).  This is   distinguished from the organization between traditional analog or PBX   telephones behind an IP network, where the MGC would control an MG   which in turn controls the collection of telephone devices in   question.  In the case of a Megaco IP Phone MG, the MG directlyBlatherwick, et al.          Informational                      [Page 3]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 2001   implements the media terminations like handset, handsfree and   headset, as well as the user interface.  In this case, the Megaco IP   Phone itself is the MG.                             +---------------+                             |               |                             |      MGC      |                             |               |                             +---------------+                                     ^ \ \ \                                     |                                     v               +---------------------------------------------+               |                                             |               |   Megaco IP Phone MG                        |               |   ==================      Audio Transducer  |               |                           Terminations:     |               | Audio context(s):         + - - - - - - - + |               | +---------------------+     +-----------+   |               | |     Context A       |   | | Handset   | | |               | |                     |     +-----------+   |          RTP  | |  +-----+   +-----+  |   | +-----------+ | |      <--------+-+->| Tr  |   | Ta2 |<-+-----| Handsfree |   |        audio  | |  +-----+   +-----+  |   | +-----------+ | |       stream  | |                     |     +-----------+   |               | +---------------------+   | | Headset   | | |               |                             +-----------+   |               |                           |               | |               |                              ETC.           |               |                           + - - - - - - - + |               |                                             |               |  +----------------------------------------+ |               |  | User Interface Termination             | |               |  | +--------------+      +--------------+ | |               |  | | Text Display |      | Keypad       | | |               |  | +--------------+      +--------------+ | |               |  | +--------------+      +--------------+ | |               |  | | Softkeys     |      | Indicators   | | |               |  | +--------------+      +--------------+ | |               |  | +--------------+                       | |               |  | | Function Keys|       ETC.            | |               |  | +--------------+                       | |               |  +----------------------------------------+ |               +---------------------------------------------+             Figure 1: Megaco IP Phone Termination / Package ModelBlatherwick, et al.          Informational                      [Page 4]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 20014.3.  Termination / Package Organization   As shown in Figure 1, each Audio Transducer Termination represents an   individually controllable audio input/output element of the telephone   device, such as Handset, Handsfree, Headset, etc.  By separating each   audio element as a distinct Termination, more flexible applications   can be easily implemented, such as paging, group listening, and so   on. Since this is actually only the logical view of the device,   represented by protocol, it is also quite possible to simplify   representation of the device by hiding all available audio   input/outputs behind a single Audio Transducer Termination, for   example the Handset, and implement control of multiple real   input/outputs locally inside the device.   All non-audio user interface elements are associated with the User   Interface Termination.  This special Termination supports Packages to   implement all user interaction with the telephone user interface,   including Function Keys, Indicators, the Dialpad, etc, as appropriate   for the specific device capabilities (within constraints given in the   section on User Interface Termination).  The User Interface   Termination cannot be placed in any Context.  This grouping of user   interface elements behind a well-know Termination greatly simplifies   audits to determine actual device configuration, and reduces the   number of Terminations involved in representing user interface.   In addition, TerminationID naming conventions are provided to   identify specific Terminations within the Megaco IP Phone MG and   group them into related sets.  These conventions use a set of well   known identifier names to specify the individual Terminations, for   example the User Interface Termination ("ui"), the Handset Audio   Transducer ("at/hs"), or the Handsfree Audio Transducer ("at/hf").   This specific naming is important in this application, especially for   the Audio Transducer Terminations, since the real input/output   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 toBlatherwick, et al.          Informational                      [Page 5]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 2001   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.Blatherwick, et al.          Informational                      [Page 6]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 20014.5.  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);Blatherwick, et al.          Informational                      [Page 7]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 2001   *  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 ProtocolAppendix 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 ProtocolAppendix 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].Blatherwick, et al.          Informational                      [Page 8]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 2001       __________________________________________________________      | 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 ProtocolAppendix B.1 [3].Blatherwick, et al.          Informational                      [Page 9]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 2001   Note: If ASN.1 binary encoding is used (OPTIONAL in this   specification), TerminationIDs and wildcards MUST be encoded as   described in Megaco/H.248 ProtocolAppendix 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                |      |_____________________|_______ |_____________________________|      | Basic DTMF Generator| dg     | REQUIRED                    |      | Call Progress Tones | cg     | REQUIRED                    |      |   Generator         |        |                             |      |_____________________|________|_____________________________|   Additional Packages not listed above MAY also be provided where   applicable to audio input/output functions.5.3.  RTP Termination Type   Megaco IP Phone MGs MUST support at least one RTP Termination in   order to support audio streams to/from the device, as defined in   Megaco/H.248 Protocol Annex E.12 [3].   No special TerminationID naming convention is defined for RTP   Terminations as part of this specification.6.  IPPhone Protocol Profile   The following subsections provide details of the IPPhone Protocol   Profile, used between Megaco IP Phone MGs and their controlling MGCs.   This includes implicit application-level agreements between the   Megaco IP Phone MG and its controlling MGC on organization and   behavior of the MG, types of Terminations used and the specific   minimum Package support for each, and specific minimum selections on   the transport and encoding methods used.   Use of a this Profile greatly simplifies assumptions necessary by the   MGC regarding MG organization, thereby reducing complexity and cost   of both MG and MGC, and improves interoperability for the specific   Megaco IP Phone application.  Since the Profile is specific to theBlatherwick, et al.          Informational                     [Page 10]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 2001   Megaco IP Phone MG, no other applications of Megaco/H.248 Protocol   are affected.   It is important to note that the IPPhone Profile specifies minimum   functionality only, for interoperability purposes.  Additional   Termination types, Package support, transport or encoding methods, or   other capabilities MAY be added at the discretion of the implementer   within the general structure described.6.1.  Profile Descriptor and Usage   Profile name: "IPPhone"   Version: 1   The Megaco/H.248 Protocol [3] describes startup and service change   procedures in detail, including use of Profiles.   In brief, the above Profile name and version are supplied by the   Megaco IP Phone MG on startup or at service change, in the   ServiceChangeDescriptor parameter of the ServiceChange command,   issued to the controlling MGC as part of the registration procedure.   In response, the MGC may 1) accept control by acknowledging the   Service Change, 2) pass control to a different MGC by replying with a   new MGC to try, or 3) refuse control entirely by rejecting the   Service Change.  If MGC control is refused, the Megaco IP Phone MG   may attempt registration with other MGCs in its list of MGCs to try.   Once a controlling MGC accepts the IPPhone Profile, both it and the   Megaco IP Phone MG become bound by the Profile rules and constraints   described in subsequent subsections as well as Megaco IP Phone   Termination/Package organization and behavior rules described in   previous sections of this document.  Thereafter, any protocol use   outside these rules is considered an error.6.2 Termination Organization and Package Support   Termination organization, required Termination types, and the   specific Packages supported by each MUST be as described in sections   4 - 5 of this document.   Note that additional Termination types and Package support MAY also   be provided within the general structure described.6.3.  Transport   Megaco IP Phone MGs MUST support Application Layer Framing (ALF) over   UDP transport, as specified in the Megaco/H.248 ProtocolAppendix D.1   [3].Blatherwick, et al.          Informational                     [Page 11]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 2001   Note that this does not imply that the Megaco IP Phone MG cannot   support other transport methods as well.  TCP transport is OPTIONAL,   but if used MUST conform to Megaco/H.248 ProtocolAppendix D.2 [3].6.4.  Message Encoding   Megaco IP Phone MGs MUST support ABNF text encoding of the protocol,   as specified in the Megaco/H.248 ProtocolAppendix B [3].   Note that this does not imply that the Megaco IP Phone MG cannot   support ASN.1 binary encoding as well.  ASN.1 binary encoding is   OPTIONAL, but if used MUST conform to Megaco/H.248 ProtocolAppendixA [3].7.  Security Considerations   The Megaco IP Phone Media Gateway Application Profile adds no new   security issues beyond those endemic to all applications of   Megaco/H.248 Protocol [3].8.  References   [1] TIA/EIA, IS-811, Performance and Interoperability Requirements       for Voice-over-IP (VoIP) Feature Telephones,http://www.tiaonline.org/standards/ip/voip/tia-eia-is-811-final.pdf   [2] Greene, N., Ramalho, M. and B. Rosen, "Media Gateway Control       Protocol Architecture and Requirements",RFC 2805, April 2000.   [3] Cuervo, F., Greene, N., Rayhan, A., Huitema, C., Rosen, B. and J.       Segers, "Megaco Protocol Version 1.0",RFC 3015, November 2000.   [4] ITU-T SG16, H.248 Annex G: User Interface Elements and Actions       Packages, Brown, M. & P. Blatherwick, November 2000.http://www.itu.int/itudoc/itu-t/rec/h/h248anxg.html   [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement       Levels",BCP 14,RFC 2119, March 1997.Blatherwick, et al.          Informational                     [Page 12]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 20019.  Authors' Addresses   Peter Blatherwick (Editor)   Nortel Networks   P.O. Box 3511, Stn C   Ottawa, Ontario,   Canada K1Y 4H7   Phone: (613) 763-7539          (613) 724-4726   EMail: blather@nortelnetworks.com          peter.blatherwick@home.com   Bob Bell   Cisco Systems Inc.   576 S. Brentwood Ln.   Bountiful, UT 84010   USA   Phone: (801) 294-3034   EMail: rtbell@cisco.com   Phil Holland   Circa Communications Ltd.   1000 West 14th Street   North Vancouver, British Columbia,   Canada V7P 3P3   Phone: (604) 924-1742   EMail: phil.holland@circa.caBlatherwick, et al.          Informational                     [Page 13]

RFC 3054      Megaco IP Phone Media GW Application Profile  January 200110.  Full Copyright Statement   Copyright (C) The Internet Society (2001).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Blatherwick, et al.          Informational                     [Page 14]