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MEGACO - CALEA - Topology descriptor
SPLIT-IN CALEA
SPLIT-OUT CALEA
MIXED CALEA
7.1.18 Topology descriptor (From RFC 3525 Gateway Control Protocol Version 1)
A Topology descriptor is used to specify flow directions between Terminations in a Context. Contrary to the descriptors in previous subclauses, 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. An MG that does not support Topology descriptors, but receives a command containing one, returns Error 444 Unsupported or unknown descriptor, and optionally includes a string containing the name of the unsupported Descriptor ("Topology") in the error text in the error descriptor.
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.
SPLIT-OUT CALEA
MIXED CALEA
7.1.18 Topology descriptor (From RFC 3525 Gateway Control Protocol Version 1)
A Topology descriptor is used to specify flow directions between Terminations in a Context. Contrary to the descriptors in previous subclauses, 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. An MG that does not support Topology descriptors, but receives a command containing one, returns Error 444 Unsupported or unknown descriptor, and optionally includes a string containing the name of the unsupported Descriptor ("Topology") in the error text in the error descriptor.
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.
MEGACO/H.248
Introduction
A Context is an association between a number of Terminations. Null Context is a special context that contains Terminations that are not associated to any other Termination.
In general, an Add command is used to add Terminations to Contexts. If the MGC does not specify an existing Context to which the Termination is to be added, the MG creates a new Context. A Termination may be removed from a Context with a Subtract command, and a Termination may be moved from one Context to another with a Move command. A Termination SHALL exist in only one Context at a time.
Commands:
Add
The Add Command adds a Termination to a Context.
Modify
The Modify Command modifies the properties of a Termination.
Subtract
The Subtract Command disconnects a Termination from its Context and
returns statistics on the Termination's participation in the Context.
Move
The Move Command moves a Termination to another Context from its
current Context in one atomic operation.
AuditValue
The AuditValue Command returns the current values of properties,
events, signals and statistics associated with Terminations.
AuditCapabilities
The AuditCapabilities Command returns the possible values of
properties, events, signals and statistics associated with
Terminations.
Notify
The Notify Command allows the Media Gateway to notify the Media
Gateway Controller of events occurring within the Media Gateway.
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.
Example Call Flow: Initiating a telephone call
Power point slide of the pictures of this calls flow: MEGACO-Call-Flow.ppt
Initial assumptions:
One MGC controlling both ends
Both gateways have associated with the MGC
MG1 and MG2 have TDM terminations programmed to listen to events
STEP1: MG1 detects an offhook event and notifies MGC
STEP2: MGC modifies MG1 to collect digits
STEP3: MG1 notifies when digits are collected
STEP4: MGC analyzes the digits and begins to connect MG1 and MG2
STEP5: MGC adds a TDM and RTP termination to context in MG1
STEP6: MG1 replies with local IP address, UDP port and choice of codec
STEP7: MGC adds a TDM(recvonly) and RTP termination to context in MG2
STEP8: MG2 replies with local IP address, UDP port and choice of codec
STEP9: MGC modifies the RTP termination at MG1 to sendrecv.
STEP10: User 1 hears ringback and User 2 hears phone ringing
STEP11: User 2 lifts up the phone
STEP12: The telephone call is initiated
Abbreviations/Terms
Package :
The primary mechanism for extension is by means of Packages.Packages define additional Properties, Events, Signals and Statistics that may occur on Terminations.
Examples of packages -
Tone Generator Package
Tone Detection Package
Basic DTMF Generator Package
DTMF detection Package
Network Package
RTP Package
Events: Events are detected at MG and reported to MGC. (example: inband signaling). MGC controls what events it wants to learn about at any given time sets the termination Events descriptor
Signals: Signals cause things to happen on terminations. For e.g. play a tone, display text, ...
DTMF: Dual Tone Multi Frequency
RTP: Real Time Protocol
Packetization Time (ptime):
A Context is an association between a number of Terminations. Null Context is a special context that contains Terminations that are not associated to any other Termination.
In general, an Add command is used to add Terminations to Contexts. If the MGC does not specify an existing Context to which the Termination is to be added, the MG creates a new Context. A Termination may be removed from a Context with a Subtract command, and a Termination may be moved from one Context to another with a Move command. A Termination SHALL exist in only one Context at a time.
Commands:
Add
The Add Command adds a Termination to a Context.
Modify
The Modify Command modifies the properties of a Termination.
Subtract
The Subtract Command disconnects a Termination from its Context and
returns statistics on the Termination's participation in the Context.
Move
The Move Command moves a Termination to another Context from its
current Context in one atomic operation.
AuditValue
The AuditValue Command returns the current values of properties,
events, signals and statistics associated with Terminations.
AuditCapabilities
The AuditCapabilities Command returns the possible values of
properties, events, signals and statistics associated with
Terminations.
Notify
The Notify Command allows the Media Gateway to notify the Media
Gateway Controller of events occurring within the Media Gateway.
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.
Example Call Flow: Initiating a telephone call
Power point slide of the pictures of this calls flow: MEGACO-Call-Flow.ppt
Initial assumptions:One MGC controlling both ends
Both gateways have associated with the MGC
MG1 and MG2 have TDM terminations programmed to listen to events
STEP1: MG1 detects an offhook event and notifies MGC
STEP2: MGC modifies MG1 to collect digits
STEP3: MG1 notifies when digits are collected
STEP4: MGC analyzes the digits and begins to connect MG1 and MG2
STEP5: MGC adds a TDM and RTP termination to context in MG1
STEP6: MG1 replies with local IP address, UDP port and choice of codec
STEP7: MGC adds a TDM(recvonly) and RTP termination to context in MG2
STEP8: MG2 replies with local IP address, UDP port and choice of codec
STEP9: MGC modifies the RTP termination at MG1 to sendrecv.
STEP10: User 1 hears ringback and User 2 hears phone ringing
STEP11: User 2 lifts up the phone
STEP12: The telephone call is initiated
Abbreviations/Terms
Package :
The primary mechanism for extension is by means of Packages.Packages define additional Properties, Events, Signals and Statistics that may occur on Terminations.
Examples of packages -
Tone Generator Package
Tone Detection Package
Basic DTMF Generator Package
DTMF detection Package
Network Package
RTP Package
Events: Events are detected at MG and reported to MGC. (example: inband signaling). MGC controls what events it wants to learn about at any given time sets the termination Events descriptor
Signals: Signals cause things to happen on terminations. For e.g. play a tone, display text, ...
DTMF: Dual Tone Multi Frequency
RTP: Real Time Protocol
Packetization Time (ptime):
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