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Versions: (draft-blatherwick-megaco-ipphone) 00 01 02 RFC 3054

Internet Engineering Task Force                              Robert Bell
INTERNET DRAFT                                             Cisco Systems
June 25, 1999                                 Peter Blatherwick (editor)
Expires December 25, 1999                                Nortel Networks
<draft-ietf-megaco-ipphone-00.txt>                          Phil Holland
                              Circa Communications (Chair TIA TR-41.3.4)
                                                            Richard Bach
                                                         Nortel Networks

                     Megaco IP Phone Media Gateway

Status of this document

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other
groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at

The list of Internet-Draft Shadow Directories can be accessed at


This document is a proposal to add new event/signal packages and
termination classes to the Megaco protocol [3], to support an IP
telephone MG.  The proposal covers the requirements (section 3), design
approach (section 4) and package/termination model (section 5) to be
used for IP telephones. The new event/signal packages and termination
classes are defined in sections 6 and 7 respectively.

The proposal represents the current view from the TIA working group on
IP telephone specification, 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.

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Industry feedback has made it clear that interoperability and acoustic
performance of IP telephones will be 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 standard for IP
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 will be provided.  Where possible, the requirements
will be based on existing standards, which will be included by

The TIA TR-41.3.4 working group has also recognized that the 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 and SIP and "Master/Slave"
architectures that use the Megaco protocol are both necessary and

In support of the Megaco 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 protocol for IP
telephone device control.  The following represents the working group's
current view.

NOTE: This document is a work in progress, known to be incomplete in
some areas, and leaves several issues unresolved.  However, it is
believed that sufficient details are included to allow integration with
the main Megaco protocol document, initial implementations and
interoperability testing to proceed.

[[ Editorial comments and issues are marked like this. ]]


The following general requirements drive the Megaco-based 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.   Simple, minimal design;

4.   Allow device cost to be appropriate to capabilities provided;

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5.   Packages and termination classes must have characteristics that
     enable reliability;

6.   The IP Phone shall also meet the appropriate Megaco protocol
     requirements as provided in the Megaco requirements document [2].


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

The approach to achieve this goal is to provide a very simple and
direct master/slave control model in which very little intelligence is
required in the end device.  This design intent matches the Megaco
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 manufacturer, by defining additional termination
classes, event/signal packages, or providing built-in application
capability.  This document defines the minimal design.


5.1.  Organization

As shown in Figure 1 below, the Megaco IP Phone is organized as a Media
Gateway (MG) that consists of a root termination class and a hierarchy
of audio-related terminations.  The root termination represents the IP
Phone MG itself, and includes packages to implement control of the
telephone user interface.  The audio terminations represent the
telephone audio transducer elements, including Handset, Headset,
Speakerphone etc, and DTMF tone generator.  These audio terminations
are subordinate to the root termination.

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                              |               |
                              |      MGC      |
                              |               |
                                    ^ \ \ \
              |       IP Phone MG                            |
              |                           Audio elements     |
              |                           (Terminations):    |
              | Audio context(s):         +----------------+ |
              | +---------------------+   | +------------+ | |
              | |     Context A       |   | | Handset    | | |
              | |                     |   | +------------+ | |
         RTP  | |  +-----+   +-----+  |   | +------------+ | |
     <--------+-+->| Tr  |   | Ta2 |<-+---+-| Handsfree  | | |
       audio  | |  +-----+   +-----+  |   | +------------+ | |
      stream  | |                     |   | +------------+ | |
              | |            +-----+  |   | | Headset    | | |
              | |            | Td  |  |   | +------------+ | |
              | |            +-----+  |   | ETC.           | |
              | |               ^     |   +----------------| |
              | |               |     |                      |
              | +---------------+-----+   Tone generator     |
              |                 |         (Termination):     |
              |                 |          +------------+    |
              |                 +----------| DTMF Tone  |    |
              |                            +------------+    |
              | - - - - - - - - - - - - - - - - - - - - - - -|
              |   User interface elements                    |
              |   (Packages of root termination):            |
              |   +---------------+      +---------------+   |
              |   |Text Display   |      | Dialpad       |   |
              |   +---------------+      +---------------+   |
              |   +---------------+      +---------------+   |
              |   | Softkeys      |      | Indicators    |   |
              |   +---------------+      +---------------+   |
              |   +---------------+                          |
              |   | Function Keys |      ETC.                |
              |   +---------------+                          |

Figure 1) Megaco IP Phone Package / Termination Model

Several - potentially thousands - of IP Phone MGs are 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

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collection of telephone devices in question.  In the case of a Megaco
IP Phone MG, the MG directly controls the media terminations like
handset, speakerphone and headset, and implements the user interface.
In this case, the IP Phone *is* the MG.

5.2.  Control Interaction

Audio-related (and other media) terminations are manipulated using
contexts in the normal way to provide control of audio paths.  For
example, creating a context (Context A) containing an RTP termination
(Tr) and a handset termination (Ta1) creates a voice connection to/from
the handset.  Moving a handsfree unit termination (Ta2) into the
context, and removing the handset, could set up a handsfree
conversation.  Moving a DTMF tone generator termination (Td) into the
context allows tone generation on the audio paths.  This situation is
shown in Figure 1.

User interface elements are associated with the root termination.
Elements like Keypad generate events that are passed to the MGC.
Elements like the Text Display are controlled by signals sent by the
MGC.  Where applicable, user interface packages return Events through
the Notify command according to the defined Event Packages.

User interface elements are controlled through Modify commands
addressed to the root class of the IP Phone MG, using syntax defined in
the Signals and Events of Packages used by each new Termination class.
(Since the user interface elements do not appear in a context, Modify
is the only applicable command.)

Termination properties can be queried through the Audit command.  This
allows the MGC to discover capability of each termination class
supported by the MG.  Using addressing, Audit commands may be targeted
at the whole MG, which returns the list of user interface packages
supported and all terminations contained.  Further Audits on individual
Terminations provide further details.

Modify State parameters can be used to set configuration of a

6.  Business IP Phone Packages

This section defines a basic set of packages that may be supported by
an IP business telephone.  This constitutes a flexible "toolkit" from
which a very wide range of telephones and similar devices could be
defined.  The packages were also defined with reuse in mind for other
similar applications.  Additional packages can of course be defined as
per the mechanism provided by Megaco.

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A Megaco IP Phone may support following packages.

Support for audio-related terminations:

   * Audio Package (used in audio transducer terminations)
   * DTMF Tone Generator Package (used in DTMF Tone Generator

User interface elements of root termination class:

   * Function Key Package
   * Indicator Package
   * Text Display Package
   * Softkey Package
   * Dialpad Package
   * Ancillary Input Package

The package definitions contained in the subsequent subsections specify
audit information, events, and signals supported by each of these
packages.  Audit information listed under each package specifies the
information returned when the corresponding termination is audited.
Event and signal information specifies the legal properties (values)
for event and signal descriptors applied to the corresponding

[[ *** IMPORTANT NOTE:  There is currently a problem defining aspects
of the IP Phone protocol, for such  things as parameterized Signals and
Events.  We have chosen to document Packages here as if the protocol
was described as an API.  The intent should be clear enough until
complete Package description and encoding rules for Megaco are
settled. *** ]]

6.1.  Audio Package (aud)

The Audio package contains information, events and signal descriptions
related to the audio transducer terminations in an IP Phone, including:

   * Handset,
   * Handsfree,
   * Headset,
   * Microphone,
   * Speaker.

6.1.1.  Audit Information

The following is returned as a result of Audit command at the root MG:

   * Transducer list.

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The following is returned as a result of Audit command at a particular
audio transducer termination (see also definitions of these
terminations, next section):

   * Tones list,
   * Cadences list.

The standard audio transducers include:

   * Handset
   * Handsfree
   * Headset
   * Microphone
   * Speaker

The standard audio codecs include:

   * G.711
   * G.723.1
   * G.729

[[ Note: Do we need the codecs here?  Likely not.  Needs to be aligned
with RTP Package, but left here for now for completeness. ]]

The standard audio call progress tones include:

   * Dialtone
   * Ringback
   * Busy
   * Re-order
   * Call Waiting

[[ ISSUE: Tone list is known to be incomplete.  Needs alignment with
signals below and with other existing Megaco packages.  Do we need a
separate Tone Package for Megaco, to handle this in an international
context?  ]]

6.1.2.  Configuration

[[ ISSUE: How and where to specify what can be configured.  Presumably
through Modify(T,<state>,...) ?!).  Same issue appears in all
packages/termination classes.  Each Package or Termination needs
configuration specified.  ]]

6.1.3.  Signals

PlayTone( toneId, duration )

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Note: Audio PlayTone command follow the conventions contained in the
Megaco Protocol.  The following is a list of toneIds correspond to
audio signals which may be applied to an audio transducer termination.

   aw     - Answer Tone
   bz     - Busy Tone
   wt     - Call Waiting Tone
   dl     - Dial Tone
   rb     - Ringback
   nbz    - Network Busy Tone (reorder or fast cycle busy)
   rs     - Ring Splash Tone
   p      - Prompt Tone
   e      - Error Tone
   sdl    - Stutter Dial Tone (??)
   v      - Alerting Tone
   y      - Recorder Warning Tone (??)
   sit    - SIT Tone (??)
   z      - Calling Card Service Tone (??)
   ot     - Off Hook Warning Tone
   s(###) - Distinctive Tone Pattern Tone

[[ Note: these tones are defined in <draft-ietf-megaco-protocol-01.txt>
Megaco Protocol Draft document, in sections 7.1.5 and 7.1.6.  These
need to be rationalized and aligned.  A subset is applicable here. ]]

Note: DTMF tones are controlled through the DTMF Tone Generator
package, next subsection.

6.1.4.  Events


Note: Hookswitch, often associated with handset, is found in the
Function Key Package, since it is not always associated with audio
handling and can be used as a separate user interface element.  Other
possibly related keys are also found there.  This strict separation
allows greater flexibility in device configuration.

6.2.  DTMF Tone Generator Package (dtmftone)

The DTMF Tone Generator package contains information, events and signal
descriptions related to the DTMF Tone Generator termination class.
This can be used to inject DTMF tones into audio contexts towards the
network (over RTP) and/or audio transducers (heard by the user).  This
can also be used for keypad echo.  Note that Keypad events will
normally be sent to the MGC when digits are entered.  This provides a
means to play the tones.

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6.2.1.  Audit Information


6.2.2.  Configuration


6.2.3.  Signals

InjectTone( toneId, direction, duration )

KeypadEcho( on/off, direction, duration )
            default = on, upstream

Where: toneId    = DTMF0-9, *, #, A-D  (see DTMF Event package)
       direction = upstream, downstream, both  (default = upstream)
       duration  = tone duration in ms (default = "brief" for InjectTone
                   or track keypad for KeypadEcho)

Note: Direction parameter is intend specify how the context streams the
injected tones, upstream (towards the audio transducer), or downstream
(towards the network through RTP).  DTMF tones are played through the
audio transducers at reduced amplitude.

[[ ISSUE: There is currently no means to control the context to allow
this. ]]

[[ ISSUE: Is it worth considering if keypad echo should be a state
variable of root termination? ]]

6.2.4.  Events


6.3.  Function Key Package (fkey)

Events associated with the common telephone function keys are defined
in this package.  This allows, for example, line keys to be implemented
without specific knowledge of the physical layout of the telephone.
Function keys may have well known names, for example: Hookswitch, Hold,
or Handsfree.  Function keys may also be assigned an name identifier by
the MGC, which is returned as part of the key events.

Function keys with an associated indicator share the same name
identifier.  For example, if the identifier for a function key is "Call
Forward" then the indictor identifier is also "Call Forward".  This
allows the MGC to determine that these keys and indicators are

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physically related.  If such a relationship exists, the implementation
MUST use the naming convention.

6.3.1.  Audit Information

Return list of keys (id, name if assigned).

The standard function keys include:

   * Hookswitch
   * Hold
   * Conference
   * Forward
   * Transfer
   * LineKey<n>
   * FunctionKey<n>

6.3.2.  Signals

Function key mapping commands:

SetName( keyId, nameStr )

Where: nameStr = 'C' string, 8-bit Unicode UTF-8.

6.3.3.  Events

keyDown( keyId, nameStr )

keyUp( keyId, nameStr, duration )

Where: duration = key press duration in ms

6.4.  Indicator Package (ind)

Signals associated with the common telephone indicators are defined in
this package. This allows, for example, indicators to be implemented
without specific knowledge of the physical layout of the telephone.
Indicators may have well known identifier names, for example: message
waiting, hold, line active, and may be alterable as in Function Key

[[ ISSUE: Should we combine indicator package and function key package?
Another possibility is a separate package for Key/Indicator pairs to
resolve key/indicator pairs.  Leave separate for now.  Use naming
convention to associate keys with corresponding indicators.  Left for
further study. ]]

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6.4.1.  Audit Information

Returns a list of indicators and supported attributes (id, name if
assigned, attributes).

The standard indicators include:

   * Message waiting indicator
   * Hold On/Off
   * Conference
   * Ringer/Alerter
   * Line<n>
   * Function Indicator<n>

The standard attributes include:

   * on, off, blink, fast blink, slow blink, invert, color.

[[ Note: Need to define attributes appropriate for audible alerts such
as ringing, page, possibly error tones etc.  These may need to be
aligned with other Megaco packages. ]]

[[ ISSUE: Should consider additional package specifically for audible
indicators.  Left for further study. ]]

6.4.2.  Signals

Indicator state control commands:

SetIndicator( indicatorId, attribute ) : Set state of indicator

Where: attribute = on, off, blink, fast_blink, slow_blink, invert,

Indicator mapping commands:

SetName( indicatorId, nameStr )

Where: nameStr = 'C' string of Unicode UTF-8.

6.4.3.  Events


6.5.  Text Display Package (tdisp)

The text display package supports signals associated with the text
display elements.

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Carriage return <Unicode U+000D> is supported in-string, and moves the
text input to the beginning of the next line, clearing the remainder
(if any) of the current line. Text wrapping is not provided.

One or more languages are supported, one of which must provide US ASCII
or equivalent character set.  Unicode is supported to provide support
for multiple languages.  The Unicode Standard, Version 2.0 or ISO/IEC
10646-1:1993 shall be the definitive standard intended when the term
Unicode is used within the context of this document.  All text display
elements shall support the Unicode pages U+0000 -> U+00ff as the basic
character set.  All of the text strings shall be encoded using UTF-8 as
defined in ISO/IEC 10646 AM1.

6.5.1.  Audit Information

Returns the number of displays and display parameters for each (number
of rows, columns, color).

If a text display element supports more than the mandatory U+0000 ->
U+00ff symbol set, it shall respond to an Audit query of the supported
character sets by providing the high order octet plus the high order
bit of the lower octet of each supported character set.  For example,
if the text display element supports U+2500 ->U+25ff, U+2600 ->U+26ff
and U+2700 -> U+277f, it would return 250, 258, 260, 268, 270 in
response to the query.

6.5.2.  Signals

Text display commands:

Display( row, column, str, attribute )

ClearDisplay() : Clear entire display

Where: str = 'C' string UTF-8 characters
       attribute = OR of blink, invert, underline, color (details TBD)

[[ Note: Should consider keypad character echo here.  Left for further
study. ]]

[[ Note: Should consider color (foreground and background) here.  Left
for further study. ]]

6.5.3.  Events


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6.6.  Softkey Package (skey)

Softkeys are a combination of a function key and a display element,
sharing some behavior of each.  Softkeys are dynamically configured by
the MGC based on the current state and context of the application
controlling the IP Phone MG.

Softkey identifiers are indexed 1,2...N.  N is the maximum number of
softkeys supported by a specific IP Phone MG.

6.6.1.  Audit Information

Returns the number of softkeys, display size and Unicode character sets
supported for all Softkeys.  Additionally, the name and display content
of each soft key id is returned.

6.6.2.  Signals

Softkey mapping commands:

SetName( softkeyId, nameStr )

Note: SetName with a null string clears the softkey, ie. the softkey
becomes blank and inactive.

Softkey control commands:

Display( softkeyId, row, column, str, attribute )
                                          : Set softkey display text

Where: str = 'C' string, 8-bit UTF-8 encoding
       attribute = OR of blink, invert (TBD)

[[ Note: Should consider color (foreground and background) here.  Left
for further study. ]]

6.6.3.  Events

keyDown( softkeyId, nameStr )

keyUp( nameStr, duration )

6.7.  Dialpad Package (dpad)

The dialpad package is used to represent a standard 10 digit key pad
plus the '*', '#', A, B, C, and D keys.

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Standard dialpad identifiers (dialpadId) include:

   * '0','1','2','3','4','5','6','7','8','9','*','#','A','B','C','D'

6.7.1.  Audit Information


6.7.2.  Signals


6.7.3.  Events

keyDown( dialpadId )

keyUp( dialpadId, duration )

6.8.  Ancillary Input Package (anci)

The ancillary input package is used to enter user alphanumeric
information such as teletext input or scan data, which is forwarded to
the MGC for processing.  The information is presented as a Unicode
character encoded in UTF-8 format.

6.8.1.  Audit Information


6.8.2.  Signals


6.8.3.  Events

CharInput( char )

Where: char = UTF-8 character

7.  Termination Classes

The Termination classes for the IP Phone MG are:

   * Root (implements user interface),
   * Audio transducer (implements audio input/output to the user),
   * DTMF Tone Generator (implements tone injection and keypad echo),
   * RTP (transport of audio streams, defined elsewhere in Megaco
     protocol [3]).

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These Termination Classes represent minimal capabilities to support
fully featured business telephones with purely master/slave control.
Additional Termination Classes can of course be defined to extend this
capability set.

[[ Note: Audit information associated with the termination classes
described here is given under the individual package descriptions in the
previous section.  This keeps the information all in one place for each
specific element, which seems to give a clearer description. ]]

7.1.  Root Termination Class

The root termination class represents the IP Phone MG, including user
interfaces.  The root termination class cannot be part of a context and
hence add/subtract commands do not apply to this class.  The
LocalTerminationDescriptor and RemoteTerminationDescriptor parameters
are never used with this class.

[[ Note: Need a section to describe STATE of termination class.  No
clear way to specify this in current Megaco. ]]

This termination class may support following packages.
|Package               |   Name   |   Support in Root Class       |
|______________________|_________ |_______________________________|
|Function Key          |  fkey    |   Optional                    |
|Indicator             |  ind     |   Optional                    |
|Text Display          |  tdisp   |   Optional                    |
|Softkey               |  skey    |   Optional                    |
|Dialpad               |  dpad    |   Optional                    |
|Ancillary Input       |  anci    |   Optional                    |

Note: The reasoning to make all packages optional is to allow maximum
flexibility to create a very broad range of IP 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 full blown business telephones (display, rich set of
keys and indicators, both handset and handsfree, etc) could be designed.

7.2.  Audio Transducer Termination Class

The Audio Transducer Termination class is used to describe the local
terminations for audio input and output devices including:

   * Handset,
   * Handsfree,
   * Headset,
   * Microphone,
   * Speaker.

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The RemoteTerminationDescriptor parameter is never used.  The
LocalTerminationDescriptor may be used to specify the encoding of the
media.  This parameter is described using SDP, with the following

Same as LocalTerminationDescriptor from Analog Termination, section
7.2.2 of Megaco protocol [3].

This termination class may support following packages.

|Package               |   Name   |  Support in Audio Transducer  |
|                      |          |  Class                        |
|Audio                 |  aud     |   Mandatory                   |

7.3.  DTMF Tone Generator Termination Class

DTMF Tone Generator Termination class is used to control the DTMF Tone
Generator function.  Since this is a termination on its own, DTMF tone
generation can be moved in/out of multiple contexts, including contexts
with only audio transducers (tones play out to user only) contexts with
RTP streams only (tones played to network without user hearing them).
This allows a great deal of flexibility in usage of DTMF tones by
|Package               |   Name   |  Support in DTMF Tone         |
|                      |          |  Generator Class              |
|DTMF Tone Generator   | dtmftone |   Mandatory                   |

7.4.  RTP Termination Class

Refer to Megaco protocol section 7.2.3 [3].

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   1. [[ TIA TR-41.3.4 IP Telephone specification ]]

   2. Media Gateway Control Protocol Architecture and Requirements,
      draft-ietf-megaco-reqs-03.txt, Greene, Ramalho, Rosen,

   3. MEGACO Protocol, draft-ietf-megaco-protocol-01.txt, Cuervo,
      Huitema, et al., http://www.ietf.org/internet-drafts/draft-ietf-

   4. ISO/IEC 10646-1:1993 The Unicode Standard, http://www.unicode.org


        Bob Bell
        Cisco Systems Inc.
        640 N. Main St.
        Suite 2246
        North Salt Lake, Ut 84054
        Tel: (801) 294-3034
        Email: rtbell@cisco.com

        Peter Blatherwick (editor)
        Nortel Networks
        P.O. Box 3511, Stn C
        Ottawa, Ontario,
        Canada K1Y 4H7
        Tel: (613) 763-7539
        Email: blather@nortelnetworks.com

        Phil Holland
        Circa Communications Ltd.
        1000 West 14th Street
        North Vancouver,
        British Columbia, Canada.
        V7P 3P3
        Tel: (604) 924-1742

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