PackageName and a PropertyId. Most properties have default values
described in the Package description. Properties may be read-only or
read/write. The possible values of a property may be audited, as can
their current values. For properties that are read/write, the MGC
can set their values. A property may be declared as "Global" which
has a single value shared by all Terminations realizing the package.
Related properties are grouped into descriptors for convenience.
When a Termination is added to a Context, the value of its read/write
properties can be set by including the appropriate descriptors as
parameters to the Add command. Similarly, a property of a
Termination in a Context may have its value changed by the Modify
command.
Properties may also have their values changed when a Termination is
moved from one Context to another as a result of a Move command. In
some cases, descriptors are returned as output from a command.
In general, if a Descriptor is completely omitted from one of the
aforementioned Commands, the properties in that Descriptor retain
their prior values for the Termination(s) upon which the Command
acts. On the other hand, if some read/write properties are omitted
from a Descriptor in a Command (i.e., the Descriptor is only
partially specified), those properties will be reset to their default
values for the Termination(s) upon which the Command acts, unless the
package specifies other behavior. For more details, see clause 7.1
dealing with the individual Descriptors.
The following table lists all of the possible descriptors and their
use. Not all descriptors are legal as input or output parameters to
every command.
Descriptor name Description
Modem Identifies modem type and properties when
applicable
Mux Describes multiplex type for multimedia
Terminations (e.g., H.221, H.223, H.225.0) and
Terminations forming the input mux
Media A list of media stream specifications (see 7.1.4)
TerminationState Properties of a Termination (which can be defined
in Packages) that are not stream specific
Stream A list of remote/local/localControl descriptors for
a single stream
Local Contains properties that specify the media flows
that the MG receives from the remote entity.
Remote Contains properties that specify the media flows
that the MG sends to the remote entity.
LocalControl Contains properties (which can be defined in
packages) that are of interest between the MG and
the MGC.
Events Describes events to be detected by the MG and what
to do when an event is detected.
EventBuffer Describes events to be detected by the MG when
Event Buffering is active.
Signals Describes signals (see 7.1.11) applied to
Terminations.
Audit In Audit commands, identifies which information is
desired.
Packages In AuditValue, returns a list of Packages realized
by Termination.
DigitMap Defines patterns against which sequences of a
specified set of events are to be matched so they
can be reported as a group rather than singly.
ServiceChange In ServiceChange, what, why service change
occurred, etc.
ObservedEvents In Notify or AuditValue, report of events observed.
Statistics In Subtract and Audit, report of Statistics kept on
a Termination.
Topology Specifies flow directions between Terminations in a
Context.
Error Contains an error code and optionally error text;
it may occur in command replies and in Notify
requests.
6.2.5 Root Termination
Occasionally, a command must refer to the entire gateway, rather than
a Termination within it. A special TerminationID, "Root" is reserved
for this purpose. Packages may be defined on Root. Root thus may
have properties, events and statistics (signals are not appropriate
for root). Accordingly, the root TerminationID may appear in:
- a Modify command - to change a property or set an event
- a Notify command - to report an event
- an AuditValue return - to examine the values of properties and
statistics implemented on root
- an AuditCapability - to determine what properties of root are
implemented
- a ServiceChange - to declare the gateway in or out of service.
Any other use of the root TerminationID is an error. Error code
410 - Incorrect identifier shall be returned in these cases.
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
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 a 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 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 subclause 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 subclause 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, overspecified or underspecified:
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) Underspecified parameters, using the CHOOSE value, allow the
command responder to choose any value it can support.
3) Overspecified 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. In commands other than Subtract, a missing Audit
descriptor is equivalent to an empty Audit descriptor. The Behaviour
of the MG with respect to unspecified parameters within a descriptor
varies with the descriptor concerned, as indicated in succeeding
subclauses. 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.22 bis,
V.32, V.32 bis, 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 bearers, 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
TerminationState 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
TerminationState Descriptor
Stream descriptor
LocalControl descriptor
Local descriptor
Remote descriptor
As a convenience, LocalControl, Local, or Remote descriptors 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 TerminationState descriptor
The TerminationState 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 7.1.9 for details.
7.1.6 Stream descriptor
A Stream descriptor specifies the parameters of a single
bidirectional 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 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. The default value for the mode property is "Inactive".
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 media begins to flow while more than a single alternative is
reserved, media packets may be sent/received on any of the
alternatives and must be processed, although only a single
alternative may be active at any given time.
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, it 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
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 RFC2327 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.
A Stream Descriptor specifies a single bi-directional media stream
and so a single session description MUST NOT include more than one
media description ("m=" line). A Stream Descriptor may contain
additional session descriptions as alternatives. Each media stream
for a termination must appear in distinct Stream Descriptors. 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:
1) unspecified (i.e., absent);
2) empty;
3) underspecified through use of CHOOSE in a property value;
4) fully specified; or
5) 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 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. The RequestIdentifier is omitted if the
EventsDescriptor is empty (i.e., no events are specified).
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 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 MGC.
Notification may be deferred if the event is absorbed into the
current dial string of an active digit map (see 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 subclause. Unless the Events Descriptor is replaced by another
Events Descriptor, it remains active after an event has been
recognized.
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 of an embedded EventsDescriptor being activated, the MG
continues event processing based on the newly activated
EventsDescriptor.
NOTE 1 - 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 or Recommendation of the H.248 sub-series for
specific transport considerations.
The default value of EventBufferControl is Off.
NOTE 2 - 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.
An empty Events Descriptor disables all event recognition and
reporting. An empty EventBuffer Descriptor clears the EventBuffer
and disables all event accumulation in LockStep mode: the only events
reported will be those occurring while an Events Descriptor is
active. If an empty Events Descriptor is activated while the
Termination is operating in LockStep mode, the events buffer is
immediately cleared.
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
Signals are MG generated media such as tones and announcements as
well as bearer-related signals such as hookswitch. More complex
signals may include a sequence of such simple signals interspersed
with and conditioned upon the receipt and analysis of media or
bearer-related signals. Examples include echoing of received data as
in Continuity Test package. Signals may also request preparation of
media content for future signals.
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 (or
otherwise completed on its own), 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
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 will stop on its own unless a new Signals
descriptor is applied that causes it to stop; no timeout value is
needed.
If a signal of default type other than TO has its type overridden to
type TO in the Signals descriptor, the duration parameter must be
present.
If the signal type is specified in a SignalsDescriptor, it overrides
the default signal type (see 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 and a
sequence of signals to be played sequentially. Only the trailing
element of the sequence of signals in a sequential signal list may be
an on/off signal. The duration of a sequential signal list is the
sum of the durations of the signals it contains.
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 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 flag shall 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
any descriptor containing the current values of its properties,
events, signals and statistics even if that descriptor was not
present in the command, 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 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. If the start timer is overridden with the value set to
zero (T=0), then the start timer shall be disabled. This implies
that the MG will wait indefinitely for digits.
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. Default values
of these timers should be provisioned on the MG, but can be
overridden by values specified within the DigitMap.
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, overriding 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 long timer
shall be used.
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. The
digit map completion event contains an eventDM field in the requested
actions field. 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.
A digit map completion event that does not contain an eventDM field
in its requested actions field is considered an error. Upon receipt
of such an event in an EventsDescriptor, a MG shall respond with an
error response, including Error 457 - Missing parameter in signal or
event.
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 have no side-effects unless separately
enabled; 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; to that end, the
event specification must include an eventDM field according to
section 7.1.14.6. 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.