Network Working Group A. Srinath
Request for Comments: 3149 G. Levendel
Category: Informational K. Fritz
Sylantro Systems
R. Kalyanaram
Wipro Systems
September 2001
MGCP Business Phone Packages
Status 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 describes a collection of MGCP (Media Gateway Control
Protocol) packages that can be used to take advantage of the feature
keys and displays on digital business phones and IP-Phones.
IESG Note
This document is being published for the information of the
community. It describes a non-IETF protocol that is currently being
deployed in a number of products. Implementers should be aware that
the IETF Megaco working group and the ITU-T Study Group 16 have
produced a standards track RFC "Megaco Protocol Version 1.0" (RFC
3015, also published as ITU recommendation H.248) which addresses the
same problem space and are developing extensions to that protocol for
functions of this type.
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 General Information. . . . . . . . . . . . . . . . . . 4
1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . 5
2. MGCP Packages for Business Phones . . . . . . . . . . . . . 5
2.1 Feature Key Package. . . . . . . . . . . . . . . . . . 6
2.2 Business Phone Package . . . . . . . . . . . . . . . . 9
2.3 Display XML Package. . . . . . . . . . . . . . . . . . 9
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3. Endpoint Naming and Phone Type Determination. . . . . . . .10
4. Functions that should be Locally Implemented. . . . . . . .11
4.1 Volume Control . . . . . . . . . . . . . . . . . . . .11
4.2 Audio Path . . . . . . . . . . . . . . . . . . . . . .11
4.3 Microphone mute button and light . . . . . . . . . . .11
5. XML Package Support . . . . . . . . . . . . . . . . . . . .12
5.1 XML Documents. . . . . . . . . . . . . . . . . . . . .12
5.2 XML Requests . . . . . . . . . . . . . . . . . . . . .13
5.3 XML Request History. . . . . . . . . . . . . . . . . .15
5.4 XML Events . . . . . . . . . . . . . . . . . . . . . .15
5.5 XML Tags . . . . . . . . . . . . . . . . . . . . . . .15
5.5.1 XML Tag. . . . . . . . . . . . . . . . . . . . . . .17
5.5.2 Card Tag . . . . . . . . . . . . . . . . . . . . . .18
5.5.3 P Tag. . . . . . . . . . . . . . . . . . . . . . . .18
5.5.4 Select Tag . . . . . . . . . . . . . . . . . . . . .18
5.5.5 Option Tag . . . . . . . . . . . . . . . . . . . . .19
5.5.6 Input Tag. . . . . . . . . . . . . . . . . . . . . .20
5.5.7 Echo Tag . . . . . . . . . . . . . . . . . . . . . .20
5.5.8 Calltimer Tag. . . . . . . . . . . . . . . . . . . .21
5.5.9 Time Tag . . . . . . . . . . . . . . . . . . . . . .21
5.5.10 Timer Tag . . . . . . . . . . . . . . . . . . . . .21
5.5.11 Do Tag. . . . . . . . . . . . . . . . . . . . . . .22
5.5.12 Go Tag. . . . . . . . . . . . . . . . . . . . . . .22
5.5.13 Prev Tag. . . . . . . . . . . . . . . . . . . . . .23
6. Security Considerations . . . . . . . . . . . . . . . . . .23
7. Acknowledgements. . . . . . . . . . . . . . . . . . . . . .23
8. References. . . . . . . . . . . . . . . . . . . . . . . . .23
9. Authors' Addresses. . . . . . . . . . . . . . . . . . . . .24
Appendix A: BNF description of XML grammar . . . . . . . . . .25
Appendix B: Sample XML Documents, Renderings and Events. . . .27
B.1 Sample Deck 1 (Itemized List Box). . . . . . . . . . .27
B.2 Sample Deck 2 (Enumerated List Box). . . . . . . . . .28
B.3 Sample Deck 3 (Text Box) . . . . . . . . . . . . . . .29
B.4 Sample Deck 4 (Echo Box) . . . . . . . . . . . . . . .30
B.5 Sample Deck 5 (Input Box). . . . . . . . . . . . . . .31
B.6 Sample Deck 6 (Timers) . . . . . . . . . . . . . . . .32
Appendix C: Example usage of MGCP extension packages . . . . .33
C.1 Setting Labels on Phone. . . . . . . . . . . . . . . .33
C.2 Activating a Feature on a Feature Key. . . . . . . . .33
C.3 Generating a Call using Feature Key as a Line Key. . .35
C.4 Determining Make and Model of a Phone. . . . . . . . .38
Appendix D: BNF Description of X-UA Parameter. . . . . . . . .39
Full Copyright Statement . . . . . . . . . . . . . . . . . . .41
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1. Introduction
The Media Gateway Control Protocol (MGCP) Version 1.0 defines a
protocol for controlling Voice over IP Telephony Gateways from
external call control elements. As defined, it supports external
call control elements called Media Gateway Controllers and assumes
that these Gateways can support collections of endpoints. The
endpoint type known as an "analog line" can be used as a client
interface to provide service to a basic analog telephone unit. The
packages that are currently defined to handle events and signals
allow for only a basic level of audio connection and signaling to
such endpoints. To handle more advanced capabilities commonly found
on business phones such as feature keys, speaker phones and displays,
it is necessary to define additional packages as extensions to the
MGCP protocol.
These packages, when used in conjunction with the packages currently
defined in RFC 2705 (Media Gateway Control Protocol Version 1.0) [1],
allow an MGCP Call Agent to control business phone endpoints.
The MGCP extension packages defined here are as follows:
- Feature Key Package
o Groups events and signals associated with the additional
keys available on business phones that are non-DTMF and not
locally-implemented. These include:
- Feature Key event to allow mapping of key numbers to
features.
- Key State signal to indicate the state of feature keys.
- Set Label signal to display a label on the LCD next to a
feature key.
- Business Phone Package
o Groups signals that are not related to feature keys,
including:
- Force Off-hook and Force On-hook signals to allow
application integration with speaker phone capabilities.
- Beep signal to play a beep on the phone.
- Display XML Package
o Used to convey XML [2] script data to and from the phone to
control the display and assign functions to the display
soft-keys for event reporting. These include:
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- XML event to report user input or selection.
- XML signal to render text to the LCD display.
An MGCP experimental parameter is also defined here:
- User Agent Parameter
o Used to determine the make and model of a phone
1.1 General Information
A generic business phone typically includes a number of features that
provide access to additional functionality useful in a business
environment. Beyond the basic handset and dial pad, a business phone
may optionally include a number of fixed buttons, line keys and
programmable feature keys, along with an LCD display and soft-keys.
Specific examples of items that may be included on a business phone
are:
- Speaker phone microphone and speaker
- Speaker phone button and light
- Messages button and light
- Redial button
- Volume up and down buttons
- Hold button and light
- Transfer button and light
- Forward button and light
- Conference button and light
- Microphone mute button and light
- Multiple feature keys with lights
- Multi-line LCD Display
- Multiple soft-keys next to the LCD display
- Navigation keys
Examples of fixed buttons functionality are 'hold', 'transfer',
'redial', 'conference', 'call-logs', 'directories', and 'messages'.
Fixed buttons may vary from phone to phone. While the packages
described here would allow these to be reported to a Call Agent, the
Call Agent would also need to determine which feature key number
corresponds to a particular pre-assigned function.
Since MGCP assumes a call control architecture where the call control
"intelligence" is outside the Gateways and handled by external call
control elements, the programming of the feature keys would be
resident in the Call Agent. If the user were to press the 'hold'
button, the phone would simply report the key number, and the burden
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of recognizing that this feature key is assigned to the 'hold'
function, and providing such functionality, is left to the Call
Agent.
1.2 Objectives
The high level objectives that were considered in generating the
packages described here are:
- Provide a minimum set of extension packages to the MGCP Version
1.0 protocol to allow applications to take advantage of generic
business phone capabilities.
- Provide event and control extensions at a sufficiently low level
for an application to implement generic business phone functions
without generating excessive or redundant data traffic. (e.g.,
sending feature key information on both press and release would be
a "don't care" for a Call Agent. All it cares about is that the
key was pressed.)
- Provide a mechanism to interface with LCD displays and allow the
flexibility to accommodate a variety of application needs and the
different types of displays available.
2. MGCP Packages for Business Phones
The following packages should be implemented for business phones.
The G,D,L, and H packages are defined in RFC 2705 [1]. Packages KY,
BP and XML are defined in this specification.
______________________________________________________
| Package | Name | Defined |
|______________________________|_________|_____________|
| Generic Media Package | G |in RFC 2705 |
| DTMF package | D |in RFC 2705 |
| Line Package | L |in RFC 2705 |
| Handset Package | H |in RFC 2705 |
| Feature Key Package | KY |in this spec |
| Business Phone Package | BP |in this spec |
| Display XML Package | XML |in this spec |
|______________________________|_________|_____________|
In the tables of events for each package, there are five columns:
Symbol: the unique symbol used for the event
Definition: a short description of the event
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R: an x appears in this column if the event can be requested by the
Call Agent.
S: if nothing appears in this column for an event, then the event
cannot be signalled on command by the Call Agent. Otherwise, the
following symbols identify the type of signal:
OO On/Off signal. The signal is turned on until requested by the
Call Agent to turn it off, and vice versa.
TO Timeout signal. The signal lasts for a given duration unless
it is superseded by a new signal.
BR Brief signal. The event has a short, known duration.
Duration: specifies the duration of TO signals.
2.1 Feature Key Package
Package Name: KY
The Feature Key Package groups events and signals that are associated
with the additional keys that are available on business phones.
____________________________________________________________________
| Symbol | Definition | R | S Duration |
|__________|____________________________|_____|______________________|
| fk1-fk99 | Feature Key | x | |
| ks | Key State | | OO |
| ls | Set Label | | OO |
|__________|____________________________|_____|______________________|
Feature Key (fk1-fk99)
These events map to all the keys on the phone that are not DTMF
keys or locally implemented functions (such as volume). The
mapping of fk number to key is expected to vary between phones.
Note: Some have suggested parameterizing the fk event, i.e.,
sending an RQNT with "R: KY/fk" and an NTFY with "O: KY/fk(1)",
but this is problematic; It is desirable to request only the keys
that can be pressed in a given state, to eliminate the chance that
a mis-pressed button will cancel a timeout signal, as well as to
reduce message traffic. This is not possible within the confines
of MGCP, as requested events cannot be parameterized.
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Key State (ks)
This signal is used to indicate the state of a feature key. It
should be ignored by phones without this capability.
This signal has two parameters: key number and state. The key
number maps directly to the feature key number. The state is a
high level description of the state of the key. This allows
different phones to implement different indications of state. For
example, Phone A may have a multi-color LED associated with
feature keys that can blink at different cadences. Phone B might
have an LCD beside the keys that can display text or icons. It is
up to each phone vendor to determine how to present the state
indication.
The following states are used:
______________________
| State | Definition |
|_______|______________|
| en | enabled |
| db | disabled |
| id | idle |
| dt | dial tone |
| cn | connected |
| dc | disconnected |
| rg | ringing |
| rb | ringback |
| ho | holding |
| he | held |
|_______|______________|
For example: an RQNT with "S: KY/ks(5,en)" will cause an indicator
corresponding to fk5 to indicate that it is enabled. An RQNT with
"S: KY/ks(2,rg)" will cause an indicator corresponding to fk2 to
indicate that it is ringing.
"en" state
The associated feature is enabled. Used for keys that turn a
feature on or off, such as "Do Not Disturb."
"db" state
The associated feature is disabled. Used for keys that turn a
feature on or off, such as "Do Not Disturb."
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"id" state
The specified line appearance is in the idle state, available for
a call.
"dt" state
The specified line appearance is providing dial-tone.
"cn" state
The specified line appearance is actively in a call, in the
connected state.
"dc" state
The specified line appearance is disconnected, but the
corresponding line is still active (the user is still offhook).
"rg" state
The specified line appearance is terminating an incoming call, in
the ringing state.
"rb" state
The specified line appearance is originating an outgoing call, in
the ringing-back state.
"ho" state
The specified line appearance is in the holding state, with the
far end held.
"he" state
The specified line appearance is in the held state, with the far
end holding.
Set Label (ls)
This signal is used to set the label on a key. This is used for
phones that have an LCD next to the feature keys. It should be
ignored by phones without this capability.
This signal has 2 parameters: key number and label. The key
number maps directly to the feature key number. The label is free
form text, restricted to the capabilities of the phone.
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For example, an RQNT with "S: KY/ls(1,2200)" sets the label next
to the fk1 feature key to the string "2200" (a phone extension).
2.2 Business Phone Package
Package Name: BP
The Business Phone Package groups signals other than those related to
feature keys and displays.
____________________________________________________________________
| Symbol | Definition | R | S Duration |
|__________|____________________________|_____|______________________|
| hd | Force Offhook | | OO |
| hu | Force Onhook | | OO |
| beep | Beep | | BR |
|__________|____________________________|_____|______________________|
Force Offhook (hd)
This signal is used to force the phone offhook. If the phone has
a speaker phone, it should be activated. This signal can be
negated by the user by hanging up.
This can be used if a feature key causes a call to be initiated.
See the sample call flow in Appendix C.
This can also be used for application integration. For example, a
user could select a number in an application on their PC, and the
phone would be forced offhook and a call initiated.
Force Onhook (hu)
This signal forces the phone onhook. This can be used when the
far-end disconnects, or if a feature key causes a call to be
terminated.
Beep (beep)
Play a beep on the phone.
2.3 Display XML Package
Package Name: XML
The XML Package contains one event/signal that is used to convey XML
data to and from the phone.
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_____________________________________________________________________
| Symbol | Definition | R | S Duration |
|__________|____________________________|_____|______________________|
| xml | XML Data | x | OO |
|__________|____________________________|_____|______________________|
XML Data (xml)
As an event, if this event is requested in an RQNT with "R:
XML/xml", any posts of data from an XML script are returned in an
NTFY with "O: XML/xml(post data here)".
As a signal, the parameterized data indicates a URL to an XML
script (possibly local), as well as substitution values that
depend on the XML script selected. See section 5 for more
information.
3. Endpoint Naming and Phone Type Determination
Because the display state can be asynchronous from the signaling
state of the phone, it is desirable to address the display as a
separate MGCP endpoint.
For example, suppose a call is presented to the phone, and a display
is presented that gives the user the option of redirecting the caller
immediately to voice-mail. Selecting the option via the display
would cause an XML post to occur, cancelling any timeout signals (the
ringing).
In order to simplify the handling of such scenarios, it is expected
that the related display have a different MGCP endpoint name, created
by inserting a prefix before the phone endpoint name. The prefix
used shall be "disp/".
For example, if the phone endpoint has the name
"ep1@foo.whatever.net", the display endpoint would be named
"disp/ep1@foo.whatever.net".
The Call Agent must be able to determine which feature key number
corresponds to a particular pre-assigned function. For example, one
phone may have the pre-assigned functions of 'redial' and 'hold'
mapped to feature keys numbered fk1 and fk23, respectively. Another
phone may not report fk23 at all, and have the pre-assigned function
of 'transfer' mapped to fk1. Also, since the programming of feature
keys would be resident in the Call Agent, a user-interface that
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allows the programming of these keys must know the keys supported on
the phone, in order for the Call Agent to request the appropriate
feature keys.
Determination of such basic capabilities must occur at the moment
when the phone sends its first RSIP message to a Call Agent. While
it might be possible to define packages with events and signals that
allow for an exhaustive discovery of the layout of a particular
phone, a simpler and more reasonable approach would be for the Call
Agent to discover the make and model of the phone, and thus determine
the capabilities of the phone. To this end, an experimental
parameter, "X-UA" has been introduced for use in the Requested-Info
field (F:) of the AUEP method. The response to the "X-UA" is
expected to be a string that uniquely identifies the make and model
of the phone. Note that per RFC 2705, a Gateway must ignore
experimental parameters prefixed as "X-" that it cannot support,
versus respond with an error code such as 511 (Unrecognized
extension). See the sample call flow in Appendix C.
4. Functions that should be Locally Implemented
Some functions should be implemented locally on the Gateway. These
are listed in the following sections.
4.1 Volume Control
Volume for ringing, handset, and speaker phone should be implemented
locally on the Gateway.
4.2 Audio Path
If the phone includes a speaker phone, activating the speaker phone
from the idle state should generate an offhook (L/hd) event. The
user should then be able to switch to handset mode by lifting the
handset, and be able to switch back to speaker phone mode without any
interaction with the Call Agent. De-activating the speaker phone
with the handset on-hook should generate an onhook (L/hu) event.
4.3 Microphone mute button and light
If the phone includes a microphone mute button and (optionally) an
associated indicator (e.g., light), the functionality of these items
should be implemented locally on the Gateway.
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5. XML Package Support
Not all business phones have the same display and keypad
capabilities. To support these varying devices in a consistent
manner, this section outlines an XML framework that is used to drive
the phone. In this framework, the Call Agent pushes XML requests to
the Gateway using MGCP signals. These XML requests indicate the XML
document that is to be rendered on the phone.
When a user inputs data or makes a selection from a display, the
Gateway "posts" an XML request to the Call Agent using MGCP events.
5.1 XML Documents
When an XML signal request is sent to an endpoint, it indicates the
XML documents that the endpoint must process. These documents
contain tags that are a subset of the Wireless Markup Language (WML)
[3] plus some non-WML additions. These tags specify items to be
displayed as well as XML events that may be reported as the result of
user input.
Each XML document, known as a card, defines a user interaction. A
group of cards is called a deck. One or more decks define an
application. The cards define soft key behavior as well as display
behavior, and are mapped to components that implement the behavior of
a basic graphical user interface on the display phone. Based on the
available requirements, the components needed are:
- Input box:
allows user input, including editing capabilities, via the
keypad.
- Enumerated list box:
allows the user to select one of a list of items.
- Itemized list box:
allows the user to select an item using a soft key.
- Text box:
displays read-only text to the user.
- Echo box:
displays but does not process user input.
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A card may have the following properties.
1. Timed content (e.g., card expiration)
2. Static content (e.g., text)
3. Dynamic content (e.g., call timers/time)
Additionally, cards may also contain variables to be substituted for
values that are specified in an XML request. See section 5.2 for
details on variable substitution.
There are cases where the XML scripts handling the display need to
use keys that are also used by the phone. For example, the display
could present an enumerated list, where a particular item is selected
by pressing the associated number on the dial pad. All user key
presses must be routed through the XML component layer. The display
layer either consumes the key presses or passes them on to the phone
layer for consumption.
The code handling key presses should thus present a key press to the
display code first. If the display code does not "use" the key
press, then the key press should be presented to the phone code.
This gives precedence to the XML scripts for key presses.
5.2 XML Requests
The XML framework uses MGCP as its transport for making requests to
the display phone. MGCP is also used to receive asynchronous events
from the display phone (e.g., an item has been selected, or the user
has entered text).
An XML request is made to an endpoint using the XML/xml signal. The
signal has the following format:
S: XML/xml(??$=?$=)
The first component of the signal parameter is a URL to the deck. If
no scheme is indicated, the deck is assumed to be local to the phone.
Here are some examples:
ftp://server.company.com/deck1?card1?$var1=val1
http://www.company.com/deck1?card1?$var1=val1
file://deck1?card1?$var1=val1
deck1?card1?$var1=val1
A card identifier and a list of variable/value pairs follow the URL.
The card identifier indicates the card within the deck to display.
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The variable/value pairs are substituted into the deck before it is
rendered to the display. This means that the variables are deck-
scoped, and variables not defined in the requested card must be
populated in other cards in the same deck if defined therein.
For example, a deck may contain the following cards:
$line1
$line2
And an XML request may look like:
S: XML/xml(deck?one?$line1=abc$line2=xyz)
After variable substitution, the deck will look like:
abc
$line2
Once variable substitution is complete, the card is rendered. If a
parameter variable does not exist anywhere in the deck it should be
ignored.
When card two is invoked from card1 in response to the timeout
action, card two's variables are substituted with the variables
values passed as a request to card one. Card two will look like:
xyz
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5.3 XML Request History
In order to support navigation through a request history such as when
a user cancels a card, the XML layer must maintain a last-in-first-
out history of requests made for the endpoint. (See the tag
definition in section 5.5.13.)
5.4 XML Events
Whenever the XML layer determines that an event has occurred, it
reports the event using the MGCP observed event field:
O:
XML/xml(post???=?=)
Here, the event parameter contains the deck and card that generated
the event, as well as data that is to be processed by the Call Agent.
The data being posted is in the form of a list of variable/value
pairs.
In order for the Gateway to properly generate the XML event, it is
necessary for the Call Agent to request the event using the requested
events field:
R: XML/xml
This requested event should be combined with the signal request in an
RQNT.
5.5 XML Tags
Any XML implementation must at a minimum support the XML tags listed
in the table that follows. All tags have a terminator tag of the
form to indicate the end of the tag. See the XML grammar in
Appendix A.
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_____________________________________________________________________
| Name | Usage |
|_______________|_____________________________________________________|
| | Marks the beginning of a deck. |
|_______________|_____________________________________________________|
| | Marks the beginning of a card. |
|_______________|_____________________________________________________|
|
| Marks the beginning of a paragraph. |
|_______________|_____________________________________________________|
|