RFC 3015
Megaco Protocol Version 1.0
7. COMMANDS
The protocol provides commands for manipulating the logical entities of the protocol connection model, Contexts and Terminations. Commands provide control at the finest level of granularity supported by the protocol. For example, Commands exist to add Terminations to a Context, modify Terminations, subtract Terminations from a Context, and audit properties of Contexts or Terminations. Commands provide for complete control of the properties of Contexts and Terminations. This includes specifying which events a Termination is to report, which signals/actions are to be applied to a Termination and specifying the topology of a Context (who hears/sees whom). Most commands are for the specific use of the Media Gateway Controller as command initiator in controlling Media Gateways as command responders. The exceptions are the Notify and ServiceChange commands: Notify is sent from Media Gateway to Media Gateway Controller, and ServiceChange may be sent by either entity. Below is an overview of the commands; they are explained in more detail in section 7.2. 1. Add. The Add command adds a termination to a context. The Add command on the first Termination in a Context is used to create a Context. 2. Modify. The Modify command modifies the properties, events and signals of a termination.
3. Subtract. The Subtract command disconnects a Termination from its
Context and returns statistics on the Termination's participation
in the Context. The Subtract command on the last Termination in a
Context deletes the Context.
4. Move. The Move command atomically moves a Termination to another
context.
5. AuditValue. The AuditValue command returns the current state of
properties, events, signals and statistics of Terminations.
6. AuditCapabilities. The AuditCapabilities command returns all the
possible values for Termination properties, events and signals
allowed by the Media Gateway.
7. Notify. The Notify command allows the Media Gateway to inform the
Media Gateway Controller of the occurrence of events in the Media
Gateway.
8. ServiceChange. The ServiceChange Command allows the Media Gateway
to notify the Media Gateway Controller that a Termination or group
of Terminations is about to be taken out of service or has just
been returned to service. ServiceChange is also used by the MG
to announce its availability to an MGC (registration), and to
notify the MGC of impending or completed restart of the MG. The
MGC may announce a handover to the MG by sending it a
ServiceChange command. The MGC may also use ServiceChange to
instruct the MG to take a Termination or group of Terminations in
or out of service.
These commands are detailed in sections 7.2.1 through 7.2.8
7.1 Descriptors
The parameters to a command are termed Descriptors. A Descriptor
consists of a name and a list of items. Some items may have values.
Many Commands share common Descriptors. This subsection enumerates
these Descriptors. Descriptors may be returned as output from a
command. In any such return of descriptor contents, an empty
descriptor is represented by its name unaccompanied by any list.
Parameters and parameter usage specific to a given Command type are
described in the subsection that describes the Command.
7.1.1 Specifying Parameters
Command parameters are structured into a number of descriptors. In
general, the text format of descriptors is
DescriptorName=<someID>{parm=value, parm=value_.}.
Parameters may be fully specified, over-specified or under-specified:
1. Fully specified parameters have a single, unambiguous value that
the command initiator is instructing the command responder to use
for the specified parameter.
2. Under-specified parameters, using the CHOOSE value, allow the
command responder to choose any value it can support.
3. Over-specified parameters have a list of potential values. The
list order specifies the command initiator's order of preference
of selection. The command responder chooses one value from the
offered list and returns that value to the command initiator.
If a required descriptor other than the Audit descriptor is
unspecified (i.e., entirely absent) from a command, the previous
values set in that descriptor for that termination, if any, are
retained. A missing Audit descriptor is equivalent to an empty Audit
Descriptor. The behavior of the MG with respect to unspecified
parameters within a descriptor varies with the descriptor concerned,
as indicated in succeeding sections. Whenever a parameter is
underspecified or overspecified, the descriptor containing the value
chosen by the responder is included as output from the command.
Each command specifies the TerminationId the command operates on.
This TerminationId may be "wildcarded". When the TerminationId of a
command is wildcarded, the effect shall be as if the command was
repeated with each of the TerminationIds matched.
7.1.2 Modem Descriptor
The Modem descriptor specifies the modem type and parameters, if any,
required for use in e.g. H.324 and text conversation. The descriptor
includes the following modem types: V.18, V.22, V.22bis, V.32,
V.32bis, V.34, V.90, V.91, Synchronous ISDN, and allows for
extensions. By default, no modem descriptor is present in a
Termination.
7.1.3 Multiplex Descriptor
In multimedia calls, a number of media streams are carried on a
(possibly different) number of bearers. The multiplex descriptor
associates the media and the bearers. The descriptor includes the
multiplex type:
* H.221
* H.223,
* H.226,
* V.76,
* Possible Extensions
and a set of TerminationIDs representing the multiplexed inputs, in
order. For example:
Mux = H.221{ MyT3/1/2, MyT3/2/13, MyT3/3/6, MyT3/21/22}
7.1.4 Media Descriptor
The Media Descriptor specifies the parameters for all the media
streams. These parameters are structured into two descriptors, a
Termination State Descriptor, which specifies the properties of a
termination that are not stream dependent, and one or more Stream
Descriptors each of which describes a single media stream.
A stream is identified by a StreamID. The StreamID is used to link
the streams in a Context that belong together. Multiple streams
exiting a termination shall be synchronized with each other. Within
the Stream Descriptor, there are up to three subsidiary descriptors,
LocalControl, Local, and Remote. The relationship between these
descriptors is thus:
Media Descriptor
TerminationStateDescriptor
Stream Descriptor
LocalControl Descriptor
Local Descriptor
Remote Descriptor
As a convenience a LocalControl, Local, or Remote descriptor may be
included in the Media Descriptor without an enclosing Stream
descriptor. In this case, the StreamID is assumed to be 1.
7.1.5 Termination State Descriptor
The Termination State Descriptor contains the ServiceStates property,
the EventBufferControl property and properties of a termination
(defined in Packages) that are not stream specific.
The ServiceStates property describes the overall state of the
termination (not stream-specific). A Termination can be in one of
the following states: "test", "out of service", or "in service". The
"test" state indicates that the termination is being tested. The
state "out of service" indicates that the termination cannot be used
for traffic. The state "in service" indicates that a termination can
be used or is being used for normal traffic. "in service" is the
default state.
Values assigned to Properties may be simple values
(integer/string/enumeration) or may be underspecified, where more
than one value is supplied and the MG may make a choice:
* Alternative Values: multiple values in a list, one of which must
be selected
* Ranges: minimum and maximum values, any value between min and max
must be selected, boundary values included
* Greater Than/Less Than: value must be greater/less than specified
value
* CHOOSE Wildcard: the MG chooses from the allowed values for the
property
The EventBufferControl property specifies whether events are
buffered following detection of an event in the Events Descriptor, or
processed immediately. See section 7.1.9 for details.
7.1.6 Stream Descriptor
A Stream descriptor specifies the parameters of a single bi-
directional stream. These parameters are structured into three
descriptors: one that contains termination properties specific to a
stream and one each for local and remote flows. The Stream Descriptor
includes a StreamID which identifies the stream. Streams are created
by specifying a new StreamID on one of the terminations in a Context.
A stream is deleted by setting empty Local and Remote descriptors for
the stream with ReserveGroup and ReserveValue in LocalControl set to
"false" on all terminations in the context that previously supported
that stream.
StreamIDs are of local significance between MGC and MG and they are
assigned by the MGC. Within a context, StreamID is a means by which
to indicate which media flows are interconnected: streams with the
same StreamID are connected.
If a termination is moved from one context to another, the effect on
the context to which the termination is moved is the same as in the
case that a new termination were added with the same StreamIDs as the
moved termination.
7.1.7 LocalControl Descriptor
The LocalControl Descriptor contains the Mode property, the ReserveGroup and ReserveValue properties and properties of a termination (defined in Packages) that are stream specific, and are of interest between the MG and the MGC. Values of properties may be underspecified as in section 7.1.1. The allowed values for the mode property are send-only, receive-only, send/receive, inactive and loop-back. "Send" and "receive" are with respect to the exterior of the context, so that, for example, a stream set to mode=sendonly does not pass received media into the context. Signals and Events are not affected by mode. The boolean-valued Reserve properties, ReserveValue and ReserveGroup, of a Termination indicate what the MG is expected to do when it receives a local and/or remote descriptor. If the value of a Reserve property is True, the MG SHALL reserve resources for all alternatives specified in the local and/or remote descriptors for which it currently has resources available. It SHALL respond with the alternatives for which it reserves resources. If it cannot not support any of the alternatives, it SHALL respond with a reply to the MGC that contains empty local and/or remote descriptors. If the value of a Reserve property is False, the MG SHALL choose one of the alternatives specified in the local descriptor (if present) and one of the alternatives specified in the remote descriptor (if present). If the MG has not yet reserved resources to support the selected alternative, it SHALL reserve the resources. If, on the other hand, it already reserved resources for the Termination addressed (because of a prior exchange with ReserveValue and/or ReserveGroup equal to True), it SHALL release any excess resources it reserved previously. Finally, the MG shall send a reply to the MGC containing the alternatives for the local and/or remote descriptor that it selected. If the MG does not have sufficient resources to support any of the alternatives specified, is SHALL respond with error 510 (insufficient resources). The default value of ReserveValue and ReserveGroup is False. More information on the use of the two Reserve properties is provided in section 7.1.8. A new setting of the LocalControl Descriptor completely replaces the previous setting of that descriptor in the MG. Thus to retain information from the previous setting the MGC must include that information in the new setting. If the MGC wishes to delete some
information from the existing descriptor, it merely resends the descriptor (in a Modify command) with the unwanted information stripped out.7.1.8 Local and Remote Descriptors
The MGC uses Local and Remote descriptors to reserve and commit MG resources for media decoding and encoding for the given Stream(s) and Termination to which they apply. The MG includes these descriptors in its response to indicate what it is actually prepared to support. The MG SHALL include additional properties and their values in its response if these properties are mandatory yet not present in the requests made by the MGC (e.g., by specifying detailed video encoding parameters where the MGC only specified the payload type). Local refers to the media received by the MG and Remote refers to the media sent by the MG. When text encoding the protocol, the descriptors consist of session descriptions as defined in SDP (RFC2327). In session descriptions sent from the MGC to the MG, the following exceptions to the syntax of RFC 2327 are allowed: * the "s=", "t=" and "o=" lines are optional, * the use of CHOOSE is allowed in place of a single parameter value, and * the use of alternatives is allowed in place of a single parameter value. When multiple session descriptions are provided in one descriptor, the "v=" lines are required as delimiters; otherwise they are optional in session descriptions sent to the MG. Implementations shall accept session descriptions that are fully conformant to RFC2327. When binary encoding the protocol the descriptor consists of groups of properties (tag-value pairs) as specified in Annex C. Each such group may contain the parameters of a session description. Below, the semantics of the local and remote descriptors are specified in detail. The specification consists of two parts. The first part specifies the interpretation of the contents of the descriptor. The second part specifies the actions the MG must take upon receiving the local and remote descriptors. The actions to be taken by the MG depend on the values of the ReserveValue and ReserveGroup properties of the LocalControl descriptor.
Either the local or the remote descriptor or both may be
* unspecified (i.e., absent),
* empty,
* underspecified through use of CHOOSE in a property value,
* fully specified, or
* overspecified through presentation of multiple groups of
properties and possibly multiple property values in one or more of
these groups.
Where the descriptors have been passed from the MGC to the MG, they
are interpreted according to the rules given in section 7.1.1, with
the following additional comments for clarification:
(a) An unspecified Local or Remote descriptor is considered to be a
missing mandatory parameter. It requires the MG to use whatever was
last specified for that descriptor. It is possible that there was no
previously-specified value, in which case the descriptor concerned is
ignored in further processing of the command.
(b) An empty Local (Remote) descriptor in a message from the MGC
signifies a request to release any resources reserved for the media
flow received (sent).
(c) If multiple groups of properties are present in a Local or Remote
descriptor or multiple values within a group, the order of preference
is descending.
(d) Underspecified or overspecified properties within a group of
properties sent by the MGC are requests for the MG to choose one or
more values which it can support for each of those properties. In
case of an overspecified property, the list of values is in
descending order of preference.
Subject to the above rules, subsequent action depends on the values
of the ReserveValue and ReserveGroup properties in LocalControl.
If ReserveGroup is true, the MG reserves the resources required to
support any of the requested property group alternatives that it can
currently support. If ReserveValue is true, the MG reserves the
resources required to support any of the requested property value
alternatives that it can currently support.
NOTE - If a Local or Remote descriptor contains multiple groups of
properties, and ReserveGroup is true, then the MG is requested to
reserve resources so that it can decode or encode the media stream
according to any of the alternatives. For instance, if the Local
descriptor contains two groups of properties, one specifying
packetized G.711 A-law audio and the other G.723.1 audio, the MG
reserves resources so that it can decode one audio stream encoded in
either G.711 A-law format or G.723.1 format. The MG does not have to
reserve resources to decode two audio streams simultaneously, one
encoded in G.711 A-law and one in G.723.1. The intention for the use
of ReserveValue is analogous.
If ReserveGroup is true or ReserveValue is true, then the following
rules apply.
* If the MG has insufficient resources to support all alternatives
requested by the MGC and the MGC requested resources in both Local
and Remote, the MG should reserve resources to support at least
one alternative each within Local and Remote.
* If the MG has insufficient resources to support at least one
alternative within a Local (Remote) descriptor received from the
MGC, it shall return an empty Local (Remote) in response.
* In its response to the MGC, when the MGC included Local and Remote
descriptors, the MG SHALL include Local and Remote descriptors for
all groups of properties and property values it reserved resources
for. If the MG is incapable of supporting at least one of the
alternatives within the Local (Remote) descriptor received from
the MGC, it SHALL return an empty Local (Remote) descriptor.
* If the Mode property of the LocalControl descriptor is RecvOnly,
SendRecv, or Loopback, the MG must be prepared to receive media
encoded according to any of the alternatives included in its
response to the MGC.
* If ReserveGroup is False and ReserveValue is false, then the MG
SHOULD apply the following rules to resolve Local and Remote to a
single alternative each:
* The MG chooses the first alternative in Local for which it is able
to support at least one alternative in Remote.
* If the MG is unable to support at least one Local and one Remote
alternative, it returns Error 510 (Insufficient Resources).
* The MG returns its selected alternative in each of Local and
Remote.
A new setting of a Local or Remote Descriptor completely replaces the
previous setting of that descriptor in the MG. Thus to retain
information from the previous setting the MGC must include that
information in the new setting. If the MGC wishes to delete some
information from the existing descriptor, it merely resends the descriptor (in a Modify command) with the unwanted information stripped out.7.1.9 Events Descriptor
The EventsDescriptor parameter contains a RequestIdentifier and a list of events that the Media Gateway is requested to detect and report. The RequestIdentifier is used to correlate the request with the notifications that it may trigger. Requested events include, for example, fax tones, continuity test results, and on-hook and off-hook transitions. Each event in the descriptor contains the Event name, an optional streamID, an optional KeepActive flag, and optional parameters. The Event name consists of a Package Name (where the event is defined) and an EventID. The ALL wildcard may be used for the EventID, indicating that all events from the specified package have to be detected. The default streamID is 0, indicating that the event to be detected is not related to a particular media stream. Events can have parameters. This allows a single event description to have some variation in meaning without creating large numbers of individual events. Further event parameters are defined in the package. If a digit map completion event is present or implied in the EventsDescriptor, the EventDM parameter is used to carry either the name or the value of the associated digit map. See section 7.1.14 for further details. When an event is processed against the contents of an active Events descriptor and found to be present in that descriptor ("recognized"), the default action of the MG is to send a Notify command to the MG. Notification may be deferred if the event is absorbed into the current dial string of an active digit map (see section 7.1.14). Any other action is for further study. Moreover, event recognition may cause currently active signals to stop, or may cause the current Events and/or Signals descriptor to be replaced, as described at the end of this section. If the value of the EventBufferControl property equals LockStep, following detection of such an event, normal handling of events is suspended. Any event which is subsequently detected and occurs in the EventBuffer Descriptor is added to the end of the EventBuffer (a FIFO queue), along with the time that it was detected. The MG SHALL wait for a new EventsDescriptor to be loaded. A new EventsDescriptor can be loaded either as the result of receiving a command with a new EventsDescriptor, or by activating an embedded EventsDescriptor.
If EventBufferControl equals Off, the MG continues processing based
on the active EventsDescriptor.
In the case that an embedded EventsDescriptor being activated, the MG
continues event processing based on the newly activated
EventsDescriptor (Note - for purposes of EventBuffer handling,
activation of an embedded EventsDescriptor is equivalent to receipt
of a new EventsDescriptor).
When the MG receives a command with a new EventsDescriptor, one or
more events may have been buffered in the EventBuffer in the MG. The
value of EventBufferControl then determines how the MG treats such
buffered events.
Case 1
If EventBufferControl equals LockStep and the MG receives a new
EventsDescriptor it will check the FIFO EventBuffer and take the
following actions:
1. If the EventBuffer is empty, the MG waits for detection of events
based on the new EventsDescriptor.
2. If the EventBuffer is non-empty, the MG processes the FIFO queue
starting with the first event:
a) If the event in the queue is in the events listed in the new
EventsDescriptor, the MG acts on the event and removes the
event from the EventBuffer. The time stamp of the Notify shall
be the time the event was actually detected. The MG then waits
for a new EventsDescriptor. While waiting for a new
EventsDescriptor, any events detected that appear in the
EventsBufferDescriptor will be placed in the EventBuffer. When
a new EventsDescriptor is received, the event processing will
repeat from step 1.
b) If the event is not in the new EventsDescriptor, the MG SHALL
discard the event and repeat from step 1.
Case 2
If EventBufferControl equals Off and the MG receives a new
EventsDescriptor, it processes new events with the new
EventsDescriptor.
If the MG receives a command instructing it to set the value of
EventBufferControl to Off, all events in the EventBuffer SHALL be
discarded.
The MG may report several events in a single Transaction as long as this does not unnecessarily delay the reporting of individual events. For procedures regarding transmitting the Notify command, refer to the appropriate annex for specific transport considerations. The default value of EventBufferControl is Off. Note - Since the EventBufferControl property is in the TerminationStateDescriptor, the MG might receive a command that changes the EventBufferControl property and does not include an EventsDescriptor. Normally, recognition of an event shall cause any active signals to stop. When KeepActive is specified in the event, the MG shall not interrupt any signals active on the Termination on which the event is detected. An event can include an Embedded Signals descriptor and/or an Embedded Events Descriptor which, if present, replaces the current Signals/Events descriptor when the event is recognized. It is possible, for example, to specify that the dial-tone Signal be generated when an off-hook Event is recognized, or that the dial-tone Signal be stopped when a digit is recognized. A media gateway controller shall not send EventsDescriptors with an event both marked KeepActive and containing an embedded SignalsDescriptor. Only one level of embedding is permitted. An embedded EventsDescriptor SHALL NOT contain another embedded EventsDescriptor; an embedded EventsDescriptor may contain an embedded SignalsDescriptor. An EventsDescriptor received by a media gateway replaces any previous Events Descriptor. Event notification in process shall complete, and events detected after the command containing the new EventsDescriptor executes, shall be processed according to the new EventsDescriptor.7.1.10 EventBuffer Descriptor
The EventBuffer Descriptor contains a list of events, with their parameters if any, that the MG is requested to detect and buffer when EventBufferControl equals LockStep (see 7.1.9).7.1.11 Signals Descriptor
A SignalsDescriptor is a parameter that contains the set of signals that the Media Gateway is asked to apply to a Termination. A SignalsDescriptor contains a number of signals and/or sequential
signal lists. A SignalsDescriptor may contain zero signals and
sequential signal lists. Support of sequential signal lists is
optional.
Signals are defined in packages. Signals shall be named with a
Package name (in which the signal is defined) and a SignalID. No
wildcard shall be used in the SignalID. Signals that occur in a
SignalsDescriptor have an optional StreamID parameter (default is 0,
to indicate that the signal is not related to a particular media
stream), an optional signal type (see below), an optional duration
and possibly parameters defined in the package that defines the
signal. This allows a single signal to have some variation in
meaning, obviating the need to create large numbers of individual
signals.
Finally, the optional parameter "notifyCompletion" allows a MGC to
indicate that it wishes to be notified when the signal finishes
playout. The possible cases are that the signal timed out, that it
was interrupted by an event, that it was halted when a Signals
Descriptor was replaced, or that it stopped or never started for
other reasons. If the notifyCompletion parameter is not included in
a Signals Descriptor, notification is generated only if the signal
stopped or was never started for other reasons. For reporting to
occur, the signal completion event (see section E.1.2) must be
enabled in the currently active Events Descriptor.
The duration is an integer value that is expressed in hundredths of a
second.
There are three types of signals:
* on/off - the signal lasts until it is turned off,
* timeout - the signal lasts until it is turned off or a specific
period of time elapses,
* brief - the signal duration is so short that it will stop on its
own unless a new signal is applied that causes it to stop; no
timeout value is needed.
If the signal type is specified in a SignalsDescriptor, it overrides
the default signal type (see Section 12.1.4). If duration is
specified for an on/off signal, it SHALL be ignored.
A sequential signal list consists of a signal list identifier, a
sequence of signals to be played sequentially, and a signal type.
Only the trailing element of the sequence of signals in a sequential
signal list may be an on/off signal. If the trailing element of the
sequence is an on/off signal, the signal type of the sequential
signal list shall be on/off as well. If the sequence of signals in a
sequential signal list contains signals of type timeout and the
trailing element is not of type on/off, the type of the sequential
signal list SHALL be set to timeout. The duration of a sequential
signal list with type timeout is the sum of the durations of the
signals it contains. If the sequence of signals in a sequential
signal list contains only signals of type brief, the type of the
sequential signal list SHALL be set to brief. A signal list is
treated as a single signal of the specified type when played out.
Multiple signals and sequential signal lists in the same
SignalsDescriptor shall be played simultaneously.
Signals are defined as proceeding from the termination towards the
exterior of the Context unless otherwise specified in a package. When
the same Signal is applied to multiple Terminations within one
Transaction, the MG should consider using the same resource to
generate these Signals.
Production of a Signal on a Termination is stopped by application of
a new SignalsDescriptor, or detection of an Event on the Termination
(see section 7.1.9).
A new SignalsDescriptor replaces any existing SignalsDescriptor. Any
signals applied to the Termination not in the replacement descriptor
shall be stopped, and new signals are applied, except as follows.
Signals present in the replacement descriptor and containing the
KeepActive flagshall be continued if they are currently playing and
have not already completed. If a replacement signal descriptor
contains a signal that is not currently playing and contains the
KeepActive flag, that signal SHALL be ignored. If the replacement
descriptor contains a sequential signal list with the same identifier
as the existing descriptor, then
* the signal type and sequence of signals in the sequential signal
list in the replacement descriptor shall be ignored, and
* the playing of the signals in the sequential signal list in the
existing descriptor shall not be interrupted.
7.1.12 Audit Descriptor
The Audit Descriptor specifies what information is to be audited. The
Audit Descriptor specifies the list of descriptors to be returned.
Audit may be used in any command to force the return of a descriptor
even if the descriptor in the command was not present, or had no
underspecified parameters. Possible items in the Audit Descriptor
are:
+----------------+
| Modem |
|----------------|
| Mux |
|----------------|
| Events |
|----------------|
| Media |
|----------------|
| Signals |
|----------------|
| ObservedEvents |
|----------------|
| DigitMap |
|----------------|
| Statistics |
|----------------|
| Packages |
|----------------|
| EventBuffer |
+----------------+
Audit may be empty, in which case, no descriptors are returned. This
is useful in Subtract, to inhibit return of statistics, especially
when using wildcard.
7.1.13 ServiceChange Descriptor
The ServiceChangeDescriptor contains the following parameters:
* ServiceChangeMethod
* ServiceChangeReason
* ServiceChangeAddress
* ServiceChangeDelay
* ServiceChangeProfile
* ServiceChangeVersion
* ServiceChangeMGCId
* TimeStamp
* Extension.
See section 7.2.8.
7.1.14 DigitMap Descriptor
7.1.14.1 DigitMap Definition, Creation, Modification and Deletion
A DigitMap is a dialing plan resident in the Media Gateway used for detecting and reporting digit events received on a Termination. The DigitMap Descriptor contains a DigitMap name and the DigitMap to be assigned. A digit map may be preloaded into the MG by management action and referenced by name in an EventsDescriptor, may be defined dynamically and subsequently referenced by name, or the actual digitmap itself may be specified in the EventsDescriptor. It is permissible for a digit map completion event within an Events Descriptor to refer by name to a DigitMap which is defined by a DigitMap Descriptor within the same command, regardless of the transmitted order of the respective descriptors. DigitMaps defined in a DigitMapDescriptor can occur in any of the standard Termination manipulation Commands of the protocol. A DigitMap, once defined, can be used on all Terminations specified by the (possibly wildcarded) TerminationID in such a command. DigitMaps defined on the root Termination are global and can be used on every Termination in the MG, provided that a DigitMap with the same name has not been defined on the given Termination. When a DigitMap is defined dynamically in a DigitMap Descriptor: * A new DigitMap is created by specifying a name that is not yet defined. The value shall be present. * A DigitMap value is updated by supplying a new value for a name that is already defined. Terminations presently using the digitmap shall continue to use the old definition; subsequent EventsDescriptors specifying the name, including any EventsDescriptor in the command containing the DigitMap descriptor, shall use the new one. * A DigitMap is deleted by supplying an empty value for a name that is already defined. Terminations presently using the digitmap shall continue to use the old definition.7.1.14.2 DigitMap Timers
The collection of digits according to a DigitMap may be protected by three timers, viz. a start timer (T), short timer (S), and long timer (L). 1. The start timer (T) is used prior to any digits having been dialed.
2. If the Media Gateway can determine that at least one more digit is
needed for a digit string to match any of the allowed patterns in
the digit map, then the interdigit timer value should be set to a
long (L) duration (e.g. 16 seconds).
3. If the digit string has matched one of the patterns in a digit
map, but it is possible that more digits could be received which
would cause a match with a different pattern, then instead of
reporting the match immediately, the MG must apply the short timer
(S) and wait for more digits.
The timers are configurable parameters to a DigitMap. The Start
timer is started at the beginning of every digit map use, but can be
overridden.
7.1.14.3 DigitMap Syntax
The formal syntax of the digit map is described by the DigitMap rule
in the formal syntax description of the protocol (see Annex A and
Annex B). A DigitMap, according to this syntax, is defined either by
a string or by a list of strings. Each string in the list is an
alternative event sequence, specified either as a sequence of digit
map symbols or as a regular expression of digit map symbols. These
digit map symbols, the digits "0" through "9" and letters "A" through
a maximum value depending on the signalling system concerned, but
never exceeding "K", correspond to specified events within a package
which has been designated in the Events Descriptor on the termination
to which the digit map is being applied. (The mapping between events
and digit map symbols is defined in the documentation for packages
associated with channel-associated signalling systems such as DTMF,
MF, or R2. Digits "0" through "9" MUST be mapped to the
corresponding digit events within the signalling system concerned.
Letters should be allocated in logical fashion, facilitating the use
of range notation for alternative events.)
The letter "x" is used as a wildcard, designating any event
corresponding to symbols in the range "0"-"9". The string may also
contain explicit ranges and, more generally, explicit sets of
symbols, designating alternative events any one of which satisfies
that position of the digit map. Finally, the dot symbol "." stands
for zero or more repetitions of the event selector (event, range of
events, set of alternative events, or wildcard) that precedes it. As
a consequence of the third timing rule above, inter-event timing
while matching a terminal dot symbol uses the short timer by default.
In addition to these event symbols, the string may contain "S" and
"L" inter-event timing specifiers and the "Z" duration modifier. "S"
and "L" respectively indicate that the MG should use the short (S)
timer or the long (L) timer for subsequent events, over-riding the timing rules described above. If an explicit timing specifier is in effect in one alternative event sequence, but none is given in any other candidate alternative, the timer value set by the explicit timing specifier must be used. If all sequences with explicit timing controls are dropped from the candidate set, timing reverts to the default rules given above. Finally, if conflicting timing specifiers are in effect in different alternative sequences, the results are undefined. A "Z" designates a long duration event: placed in front of the symbol(s) designating the event(s) which satisfy a given digit position, it indicates that that position is satisfied only if the duration of the event exceeds the long-duration threshold. The value of this threshold is assumed to be provisioned in the MG.7.1.14.4 DigitMap Completion Event
A digit map is active while the events descriptor which invoked it is active and it has not completed. A digit map completes when: * a timer has expired, or * an alternative event sequence has been matched and no other alternative event sequence in the digit map could be matched through detection of an additional event (unambiguous match), or * an event has been detected such that a match to a complete alternative event sequence of the digit map will be impossible no matter what additional events are received. Upon completion, a digit map completion event as defined in the package providing the events being mapped into the digit map shall be generated. At that point the digit map is deactivated. Subsequent events in the package are processed as per the currently active event processing mechanisms.7.1.14.5 DigitMap Procedures
Pending completion, successive events shall be processed according to the following rules: 1. The "current dial string", an internal variable, is initially empty. The set of candidate alternative event sequences includes all of the alternatives specified in the digit map.
2. At each step, a timer is set to wait for the next event, based
either on the default timing rules given above or on explicit
timing specified in one or more alternative event sequences. If
the timer expires and a member of the candidate set of
alternatives is fully satisfied, a timeout completion with full
match is reported. If the timer expires and part or none of any
candidate alternative is satisfied, a timeout completion with
partial match is reported.
3. If an event is detected before the timer expires, it is mapped to
a digit string symbol and provisionally added to the end of the
current dial string. The duration of the event (long or not long)
is noted if and only if this is relevant in the current symbol
position (because at least one of the candidate alternative event
sequences includes the "Z" modifier at this position in the
sequence).
4. The current dial string is compared to the candidate alternative
event sequences. If and only if a sequence expecting a long-
duration event at this position is matched (i.e. the event had
long duration and met the specification for this position), then
any alternative event sequences not specifying a long duration
event at this position are discarded, and the current dial string
is modified by inserting a "Z" in front of the symbol representing
the latest event. Any sequence expecting a long-duration event at
this position but not matching the observed event is discarded
from the candidate set. If alternative event sequences not
specifying a long duration event in the given position remain in
the candidate set after application of the above rules, the
observed event duration is treated as irrelevant in assessing
matches to them.
5. If exactly one candidate remains and it has been fully matched, a
completion event is generated indicating an unambiguous match. If
no candidates remain, the latest event is removed from the current
dial string and a completion event is generated indicating full
match if one of the candidates from the previous step was fully
satisfied before the latest event was detected, or partial match
otherwise. The event removed from the current dial string will
then be reported as per the currently active event processing
mechanisms.
6. If no completion event is reported out of step 5, processing
returns to step 2.
7.1.14.6 DigitMap Activation
A digit map is activated whenever a new event descriptor is applied to the termination or embedded event descriptor is activated, and that event descriptor contains a digit map completion event which itself contains a digit map parameter. Each new activation of a digit map begins at step 1 of the above procedure, with a clear current dial string. Any previous contents of the current dial string from an earlier activation are lost.7.1.14.7 Interaction of DigitMap and Event Processing
While the digit map is activated, detection is enabled for all events defined in the package containing the specified digit map completion event. Normal event behaviour (e.g. stopping of signals unless the digit completion event has the KeepActive flag enabled) continues to apply for each such event detected, except that: * the events in the package containing the specified digit map completion event other than the completion event itself are not individually notified, and * an event that triggers a partial match completion event is not recognized and therefore has no side effects until reprocessed following the recognition of the digit map completion event.7.1.14.8 Wildcards
Note that if a package contains a digit map completion event, then an event specification consisting of the package name with a wildcarded ItemID (Property Name) will activate a digit map if the event includes a digit map parameter. Regardless of whether a digit map is activated, if the package also contains the digit events themselves, this form of event specification will cause the individual events to be reported to the MGC as they are detected.
7.1.14.9 Example
As an example, consider the following dial plan: +------------------------+------------------------------------------+ | 0 | Local operator | |------------------------+------------------------------------------| | 00 | Long distance operator | |------------------------+------------------------------------------| | xxxx | Local extension number (starts with 1-7) | |------------------------+------------------------------------------| | 8xxxxxxx | Local number | |------------------------+------------------------------------------| | #xxxxxxx | Off-site extension | |------------------------+------------------------------------------| | *xx | Star services | |------------------------+------------------------------------------| | 91xxxxxxxxxx | Long distance number | |------------------------+------------------------------------------| | 9011 + up to 15 digits | International number | +------------------------+------------------------------------------+ If the DTMF detection package described in Annex E (section E.6) is used to collect the dialled digits, then the dialling plan shown above results in the following digit map: (0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)7.1.15 Statistics Descriptor
The Statistics parameter provides information describing the status and usage of a Termination during its existence within a specific Context. There is a set of standard statistics kept for each termination where appropriate (number of octets sent and received for example). The particular statistical properties that are reported for a given Termination are determined by the Packages realized by the Termination. By default, statistics are reported when the Termination is Subtracted from the Context. This behavior can be overridden by including an empty AuditDescriptor in the Subtract command. Statistics may also be returned from the AuditValue command, or any Add/Move/Modify command using the Audit descriptor. Statistics are cumulative; reporting Statistics does not reset them. Statistics are reset when a Termination is Subtracted from a Context.7.1.16 Packages Descriptor
Used only with the AuditValue command, the PackageDescriptor returns a list of Packages realized by the Termination.
7.1.17 ObservedEvents Descriptor
ObservedEvents is supplied with the Notify command to inform the MGC of which event(s) were detected. Used with the AuditValue command, the ObservedEventsDescriptor returns events in the event buffer which have not been Notified. ObservedEvents contains the RequestIdentifier of the EventsDescriptor that triggered the notification, the event(s) detected and the detection time(s). Detection times are reported with a precision of hundredths of a second. Time is expressed in UTC.7.1.18 Topology Descriptor
A topology descriptor is used to specify flow directions between terminations in a Context. Contrary to the descriptors in previous sections, the topology descriptor applies to a Context instead of a Termination. The default topology of a Context is that each termination's transmission is received by all other terminations. The Topology Descriptor is optional to implement. The Topology Descriptor occurs before the commands in an action. It is possible to have an action containing only a Topology Descriptor, provided that the context to which the action applies already exists. A topology descriptor consists of a sequence of triples of the form (T1, T2, association). T1 and T2 specify Terminations within the Context, possibly using the ALL or CHOOSE wildcard. The association specifies how media flows between these two Terminations as follows. * (T1, T2, isolate) means that the Terminations matching T2 do not receive media from the Terminations matching T1, nor vice versa. * (T1, T2, oneway) means that the Terminations that match T2 receive media from the Terminations matching T1, but not vice versa. In this case use of the ALL wildcard such that there are Terminations that match both T1 and T2 is not allowed. * (T1, T2, bothway) means that the Terminations matching T2 receive media from the Terminations matching T1, and vice versa. In this case it is allowed to use wildcards such that there are Terminations that match both T1 and T2. However, if there is a Termination that matches both, no loopback is introduced. CHOOSE wildcards may be used in T1 and T2 as well, under the following restrictions: * the action (see section 8) of which the topology descriptor is part contains an Add command in which a CHOOSE wildcard is used;
* if a CHOOSE wildcard occurs in T1 or T2, then a partial name SHALL
NOT be specified.
The CHOOSE wildcard in a topology descriptor matches the
TerminationID that the MG assigns in the first Add command that uses
a CHOOSE wildcard in the same action. An existing Termination that
matches T1 or T2 in the Context to which a Termination is added, is
connected to the newly added Termination as specified by the topology
descriptor. The default association when a termination is not
mentioned in the Topology descriptor is bothway (if T3 is added to a
context with T1 and T2 with topology (T3,T1,oneway) it will be
connected bothway to T2).
The figure below and the table following it show some examples of the
effect of including topology descriptors in actions. In these
examples it is assumed that the topology descriptors are applied in
sequence.
+------------------+ +------------------+ +------------------+ | +----+ | | +----+ | | +----+ | | | T2 | | | | T2 | | | | T2 | | | +----+ | | +----+ | | +----+ | | ^ ^ | | ^ | | ^ | | | | | | | | | | | | +--+ +--+ | | +---+ | | +--+ | | | | | | | | | | | | v v | | v | | | | | +----+ +----+ | | +----+ +----+ | | +----+ +----+ | | | T1 |<-->| T3 | | | | T1 |<-->| T3 | | | | T1 |<-->| T3 | | | +----+ +----+ | | +----+ +----+ | | +----+ +----+ | +------------------+ +------------------+ +------------------+ 1. No Topology Desc. 2. T1, T2 Isolate 3. T3, T2 oneway +------------------+ +------------------+ +------------------+ | +----+ | | +----+ | | +----+ | | | T2 | | | | T2 | | | | T2 | | | +----+ | | +----+ | | +----+ | | | | | ^ | | ^ ^ | | | | | | | | | | | | +--+ | | +---+ | | +--+ +--+ | | | | | | | | | | | | v | | v | | v v | | +----+ +----+ | | +----+ +----+ | | +----+ +----+ | | | T1 |<-->| T3 | | | | T1 |<-->| T3 | | | | T1 |<-->| T3 | | | +----+ +----+ | | +----+ +----+ | | +----+ +----+ | +------------------+ +------------------+ +------------------+ 4. T2, T3 oneway 5. T2, T3 bothway 6. T1, T2 bothway Figure 4: A Sequence Of Example Topologies
+----------+--------------------------------------------------+
| Topology | Description |
|----------+--------------------------------------------------|
| 1 | No topology descriptors |
|----------+--------------------------------------------------|
| When no topology descriptors are included, all terminations |
| have a both way connection to all other terminations. |
|----------+--------------------------------------------------|
| 2 | T1, T2, Isolate |
|----------+--------------------------------------------------|
| Removes the connection between T1 and T2. |
| T3 has a both way connection with both T1 and T2. T1 and |
| T2 have bothway connection to T3. |
|----------+--------------------------------------------------|
| 3 | T3, T2, oneway |
|----------+--------------------------------------------------|
| A oneway connection from T3 to T2 (i.e. T2 receives media |
| flow from T3). A bothway connection between T1 and T3. |
|----------+--------------------------------------------------|
| 4 | T2, T3, oneway |
|----------+--------------------------------------------------|
| A oneway connection between T2 to T3. |
| T1 and T3 remain bothway connected |
|----------+--------------------------------------------------|
| 5 | T2, T3 bothway |
|----------+--------------------------------------------------|
| T2 is bothway connected to T3. This results in the same |
| as 2.
|----------+--------------------------------------------------|
| 6 | T1, T2 bothway (T2, T3 bothway and T1,T3 bothway |
| | may be implied or explicit). |
|----------+--------------------------------------------------|
| All terminations have a bothway connection to all other |
| terminations. |
|----------+--------------------------------------------------|
| A oneway connection must implemented in such a way that the |
| other Terminations in the Context are not aware of the |
| change in topology. |
+-------------------------------------------------------------|
(page 45 continued on part 3)
