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.
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.
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
or SendRecv, 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.
The default action of the MG, when it detects an event in the Events
Descriptor, is to send a Notify command to the MG. Any other action
is for further study.
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 = 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 default action of the MG is to send a
Notify command to the MGC and remove the event from the
EventBuffer. Any other action is for further study. 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 matching the
EventsBufferDescriptor will be placed in the EventBuffer and
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, detection 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 detected. It is
possible, for example, to specify that the dial-tone Signal be
generated when an off-hook Event is detected, or that the dial-tone
Signal be stopped when a digit is detected. 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. When the MGC enables the signal completion event
(see section E.1.2) in an Events Descriptor, that event is detected
whenever a signal terminates and "notifyCompletion" for that signal
is set to TRUE. The signal completion event of section E.1.2 has a
parameter that indicates how the signal terminated: it played to
completion, it was interrupted by an event, it was halted because a
new SignalsDescriptor arrived, or the signal did not complete for
some other reason.
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
See section 7.2.8.
7.1.14 DigitMap Descriptor
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.
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.
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 the 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. A timer specifier following a dot
specifies inter-event timing for all events matching the dot as well
as for subsequent events. 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.
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.
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, 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 (because the
candidate set still contains more than one alternative event
sequence), processing returns to step 2.
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. 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.
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, this form of event specification will cause the individual
events to be reported to the MGC as they are detected.
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;
loopbacks are created by setting the TerminationMode. 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.
Context 1 Context 2 Context 3
+------------------+ +------------------+ +------------------+
| +----+ | | +----+ | | +----+ |
| | T2 | | | | T2 | | | | T2 | |
| +----+ | | +----+ | | +----+ |
| ^ ^ | | ^ | | ^ |
| | | | | | | | | |
| +--+ +--+ | | +---+ | | +--+ |
| | | | | | | | | |
| v v | | v | | | |
| +----+ +----+ | | +----+ +----+ | | +----+ +----+ |
| | T1 |<-->| T3 | | | | T1 |<-->| T3 | | | | T1 |<-->| T3 | |
| +----+ +----+ | | +----+ +----+ | | +----+ +----+ |
+------------------+ +------------------+ +------------------+
1. No Topology Desc. 2. T1, T2 Isolate 3. T3, T2 oneway
Context 1 Context 2 Context 3
+------------------+ +------------------+ +------------------+
| +----+ | | +----+ | | +----+ |
| | 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.
7.2 Command Application Programming Interface
Following is an Application Programming Interface (API) describing
the Commands of the protocol. This API is shown to illustrate the
Commands and their parameters and is not intended to specify
implementation (e.g. via use of blocking function calls). It
describes the input parameters in parentheses after the command name
and the return values in front of the Command. This is only for
descriptive purposes; the actual Command syntax and encoding are
specified in later subsections. All parameters enclosed by square
brackets ([. . . ]) are considered optional.
7.2.1 Add
The Add Command adds a Termination to a Context.
TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
Add( TerminationID
[, MediaDescriptor]
[, ModemDescriptor]
[, MuxDescriptor]
[, EventsDescriptor]
[, SignalsDescriptor]
[, DigitMapDescriptor]
[, AuditDescriptor]
)
The TerminationID specifies the termination to be added to the
Context. The Termination is either created, or taken from the null
Context. For an existing Termination, the TerminationID would be
specific. For a Termination that does not yet exist, the
TerminationID is specified as CHOOSE in the command. The new
TerminationID will be returned. Wildcards may be used in an Add, but
such usage would be unusual. If the wildcard matches more than one
TerminationID, all possible matches are attempted, with results
reported for each one. The order of attempts when multiple
TerminationIDs match is not specified.
The optional MediaDescriptor describes all media streams.
The optional ModemDescriptor and MuxDescriptor specify a modem and
multiplexer if applicable. For convenience, if a Multiplex Descriptor
is present in an Add command and lists any Terminations that are not
currently in the Context, such Terminations are added to the context
as if individual Add commands listing the Terminations were invoked.
If an error occurs on such an implied Add, error 471 - Implied Add
for Multiplex failure shall be returned and further processing of the
command shall cease.
The EventsDescriptor parameter is optional. If present, it provides
the list of events that should be detected on the Termination.
The SignalsDescriptor parameter is optional. If present, it provides
the list of signals that should be applied to the Termination.
The DigitMapDescriptor parameter is optional. If present, defines a
DigitMap definition that may be used in an EventsDescriptor.
The AuditDescriptor is optional. If present, the command will return
descriptors as specified in the AuditDescriptor.
All descriptors that can be modified could be returned by MG if a
parameter was underspecified or overspecified. ObservedEvents,
Statistics, and Packages, and the EventBuffer Descriptors are
returned only if requested in the AuditDescriptor. Add SHALL NOT be
used on a Termination with a serviceState of "OutofService".
7.2.2 Modify
The Modify Command modifies the properties of a Termination.
TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
Modify( TerminationID
[, MediaDescriptor]
[, ModemDescriptor]
[, MuxDescriptor]
[, EventsDescriptor]
[, SignalsDescriptor]
[, DigitMapDescriptor]
[, AuditDescriptor]
)
The TerminationID may be specific if a single Termination in the
Context is to be modified. Use of wildcards in the TerminationID may
be appropriate for some operations. If the wildcard matches more than
one TerminationID, all possible matches are attempted, with results
reported for each one. The order of attempts when multiple
TerminationIDs match is not specified. The CHOOSE option is an error,
as the Modify command may only be used on existing Terminations.
The remaining parameters to Modify are the same as those to Add.
Possible return values are the same as those to Add.
7.2.3 Subtract
The Subtract Command disconnects a Termination from its Context and
returns statistics on the Termination's participation in the Context.
TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
Subtract(TerminationID
[, AuditDescriptor]
)
TerminationID in the input parameters represents the Termination that
is being subtracted. The TerminationID may be specific or may be a
wildcard value indicating that all (or a set of related) Terminations
in the Context of the Subtract Command are to be subtracted. If the
wildcard matches more than one TerminationID, all possible matches
are attempted, with results reported for each one. The order of
attempts when multiple TerminationIDs match is not specified. The
CHOOSE option is an error, as the Subtract command may only be used
on existing Terminations. ALL may be used as the ContextID as well
as the TerminationId in a Subtract, which would have the effect of
deleting all contexts, deleting all ephemeral terminations, and
returning all physical terminations to Null context.
By default, the Statistics parameter is returned to report
information collected on the Termination or Terminations specified in
the Command. The information reported applies to the Termination's
or Terminations' existence in the Context from which it or they are
being subtracted.
The AuditDescriptor is optional. If present, the command will return
descriptors as specified in the AuditDescriptor. Possible return
values are the same as those to Add.
When a provisioned Termination is Subtracted from a context, its
property values shall revert to:
. the default value, if specified for the property and not