RFC 2705
Media Gateway Control Protocol (MGCP) Version 1.0
2.3. Gateway Control Commands
This section describes the commands of the MGCP. The service consists of connection handling and endpoint handling commands. There are nine commands in the protocol: * The Call Agent can issue an EndpointConfiguration command to a gateway, instructing the gateway about the coding characteristics expected by the "line-side" of the endpoint. * The Call Agent can issue a NotificationRequest command to a gateway, instructing the gateway to watch for specific events such as hook actions or DTMF tones on a specified endpoint . * The gateway will then use the Notify command to inform the Call Agent when the requested events occur. * The Call Agent can use the CreateConnection command to create a connection that terminates in an "endpoint" inside the gateway. * The Call Agent can use the ModifyConnection command to change the parameters associated to a previously established connection. * The Call Agent can use the DeleteConnection command to delete an existing connection. The DeleteConnection command may also be used by a gateway to indicate that a connection can no longer be sustained. * The Call Agent can use the AuditEndpoint and AuditConnection commands to audit the status of an "endpoint" and any connections associated with it. Network management beyond the capabilities provided by these commands are generally desirable, e.g. information about the status of the gateway. Such capabilities are expected to be supported by the use of the Simple Network Management Protocol (SNMP) and definition of a MIB which is outside the scope of this specification. * The Gateway can use the RestartInProgress command to notify the Call Agent that the gateway, or a group of endpoints managed by the gateway, is being taken out of service or is being placed back in service. These services allow a controller (normally, the Call Agent) to instruct a gateway on the creation of connections that terminate in an "endpoint" attached to the gateway, and to be informed about events occurring at the endpoint. An endpoint may be for example:
* A specific trunk circuit, within a trunk group terminating in a
gateway,
* A specific announcement handled by an announcement server.
Connections are grouped into "calls". Several connections, that may
or may not belong to the same call, can terminate in the same
endpoint . Each connection is qualified by a "mode" parameter, which
can be set to "send only" (sendonly), "receive only" (recvonly),
"send/receive" (sendrecv), "conference" (confrnce), "data",
"inactive" (inactive), "loopback", "continuity test" (conttest),
"network loop back" (netwloop) or "network continuity test"
(netwtest).
The handling of the audio signals received on these connections is
determined by the mode parameters:
* Audio signals received in data packets through connections in
"receive", "conference" or "send/receive" mode are mixed and sent
to the endpoint.
* Audio signals originating from the endpoint are transmitted over
all the connections whose mode is "send", "conference" or
"send/receive."
* In addition to being sent to the endpoint, audio signals received
in data packets through connections in "conference" mode are
replicated to all the other connections whose mode is
"conference."
The "loopback" and "continuity test" modes are used during
maintenance and continuity test operations. There are two flavors of
continuity test, one specified by ITU and one used in the US. In the
first case, the test is a loopback test. The originating switch will
send a tone (the go tone) on the bearer circuit and expect the
terminating switch to loopback the circuit. If the originating switch
sees the same tone returned (the return tone), the COT has passed. If
not, the COT has failed. In the second case, the go and return tones
are different. The originating switch sends a certain go tone. The
terminating switch detects the go tone, it asserts a different return
tone in the backwards direction. When the originating switch detects
the return tone, the COT is passed. If the originating switch never
detects the return tone, the COT has failed.
If the mode is set to "loopback", the gateway is expected to return
the incoming signal from the endpoint back into that same endpoint.
This procedure will be used, typically, for testing the continuity of
trunk circuits according to the ITU specifications.
If the mode is set to "continuity test", the gateway is informed that the other end of the circuit has initiated a continuity test procedure according to the GR specification. The gateway will place the circuit in the transponder mode required for dual-tone continuity tests. If the mode is set to "network loopback", the audio signals received from the connection will be echoed back on the same connection. If the mode is set to "network continuity test", the gateway will process the packets received from the connection according to the transponder mode required for dual-tone continuity test, and send the processed signal back on the connection.2.3.1. EndpointConfiguration
The EndpointConfiguration commands are used to specify the encoding of the signals that will be received by the endpoint. For example, in certain international telephony configurations, some calls will carry mu-law encoded audio signals, while other will use A-law. The Call Agent will use the EndpointConfiguration command to pass this information to the gateway. The configuration may vary on a call by call basis, but can also be used in the absence of any connection. ReturnCode <-- EndpointConfiguration( EndpointId, BearerInformation) EndpointId is the name for the endpoint in the gateway where EndpointConfiguration executes, as defined in section 2.1.1. The "any of" wildcard convention shall not be used. If the "all of" wildcard convention is used, the command applies to all the endpoint whose name matches the wildcard. BearerInformation is a parameter defining the coding of the data received from the line side. These information is encoded as a list of sub-parameters. The only sub-parameter defined in this version of the specification is the encoding method, whose values can be set to "A-law" and "mu-law". ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary.
2.3.2. NotificationRequest
The NotificationRequest commands are used to request the gateway to send notifications upon the occurrence of specified events in an endpoint. For example, a notification may be requested for when a gateway detects that an endpoint is receiving tones associated with fax communication. The entity receiving this notification may decide to use a different type of encoding method in the connections bound to this endpoint. ReturnCode <-- NotificationRequest( EndpointId, [NotifiedEntity,] [RequestedEvents,] RequestIdentifier, [DigitMap,] [SignalRequests,] [QuarantineHandling,] [DetectEvents,] [encapsulated EndpointConfiguration]) EndpointId is the name for the endpoint in the gateway where NotificationRequest executes, as defined in section 2.1.1. NotifiedEntity is an optional parameter that specifies where the notifications should be sent. When this parameter is absent, the notifications should be sent to the originator of the NotificationRequest. RequestIdentifier is used to correlate this request with the notifications that it triggers. RequestedEvents is a list of events that the gateway is requested to detect and report. Such events include, for example, fax tones, continuity tones, or on-hook transition. To each event is associated an action, which can be: * Notify the event immediately, together with the accumulated list of observed events, * Swap audio, * Accumulate the event in an event buffer, but don't notify yet, * Accumulate according to Digit Map, * Keep Signal(s) active,
* process the Embedded Notification Request,
* Ignore the event.
Some actions can be combined. In particular:
* The "swap audio" action can be combined with "Notify",
"Accumulate" and "Ignore."
* The "keep signal active" action can be combined with "Notify",
"Accumulate", "Accumulate according to Digit Map", "Ignore" and
"Embedded Notification Request."
* The "Embedded Notification Request" can be combined with
"Accumulate" and with "Keep signals active." It can also be
combined with Notify, if the gateway is allowed to issue several
Notify commands in response to a single Notification request.
In addition to the requestedEvents parameter specified in the
command, some profiles of MGCP have introduced the concept of
"persistent events." According to such profiles, the persistent event
list is configured in the endpoint, by means outside the scope of
MGCP. The basic MGCP specification does not specify any persistent
event.
If a persistent event is not included in the list of RequestedEvents,
and the event occurs, the event will be detected anyway, and
processed like all other events, as if the persistent event had been
requested with a Notify action. Thus, informally, persistent events
can be viewed as always being implicitly included in the list of
RequestedEvents with an action to Notify, although no glare
detection, etc., will be performed.
Non-persistent events are those events explicitly included in the
RequestedEvents list. The (possibly empty) list of requested events
completely replaces the previous list of requested events. In
addition to the persistent events, only the events specified in the
requested events list will be detected by the endpoint. If a
persistent event is included in the RequestedEvents list, the action
specified will then replace the default action associated with the
event for the life of the RequestedEvents list, after which the
default action is restored. For example, if "Ignore off-hook" was
specified, and a new request without any off-hook instructions were
received, the default "Notify off-hook" operation then would be
restored. A given event MUST NOT appear more than once in a
RequestedEvents.
The gateway will detect the union of the persistent events and the requested events. If an event is not specified in either list, it will be ignored. The Swap Audio action can be used when a gateway handles more than one active connection on an endpoint. This will be the case for three-way calling, call waiting, and possibly other feature scenarios. In order to avoid the round-trip to the Call Agent when just changing which connection is attached to the audio functions of the endpoint, the NotificationRequest can map an event (usually hook flash, but could be some other event) to a local function swap audio, which selects the "next" connection in a round robin fashion. If there is only one connection, this action is effectively a no-op. If signal(s) are desired to start when an event being looked for occurs, the "Embedded NotificationRequest" action can be used. The embedded NotificationRequest may include a new list of RequestedEvents, SignalRequests and a new digit map as well. The semantics of the embedded NotificationRequest is as if a new NotificationRequest was just received with the same NotifiedEntity, and RequestIdentifier. When the "Embedded NotificationRequest" is activated, the "current dial string" will be cleared; the list of observed events and the quarantine buffer will be unaffected. MGCP implementations shall be able to support at least one level of embedding. An embedded NotificationRequest that respects this limitation shall not contain another Embedded NotificationRequest. DigitMap is an optional parameter that allows the Call Agent to provision the gateways with a digit map according to which digits will be accumulated. If this optional parameter is absent, the previously defined value is retained. This parameter must be defined, either explicitly or through a previous command, if the RequestedEvent parameters contain an request to "accumulate according to the digit map." The collection of these digits will result in a digit string. The digit string is initialized to a null string upon reception of the NotificationRequest, so that a subsequent notification only returns the digits that were collected after this request. Digits that were accumulated according to the digit map are reported as any other accumulated event, in the order in which they occur. It is therefore possible that other events be accumulated may be found in between the list of digits. SignalRequests is a parameter that contains the set of signals that the gateway is asked to apply to the endpoint, such as, for example ringing, or continuity tones. Signals are identified by their name, which is an event name, and may be qualified by parameters.
The action triggered by the SignalRequests is synchronized with the
collection of events specified in the RequestedEvents parameter. For
example, if the NotificationRequest mandates "ringing" and the event
request ask to look for an "off-hook" event, the ringing shall stop
as soon as the gateway detect an off hook event. The formal
definition is that the generation of all "Time Out" signals shall
stop as soon as one of the requested events is detected, unless the
"Keep signals active" action is associated to the specified event.
The specific definition of actions that are requested via these
SignalRequests, such as the duration of and frequency of a DTMF
digit, is out side the scope of MGCP. This definition may vary from
location to location and hence from gateway to gateway.
The RequestedEvents and SignalRequests refer to the same event
definitions. In one case, the gateway is asked to detect the
occurrence of the event, and in the other case it is asked to
generate it. The specific events and signals that a given endpoint
can detect or perform are determined by the list of event packages
that are supported by that end point. Each package specifies a list
of events and actions that can be detected or performed. A gateway
that is requested to detect or perform an event belonging to a
package that is not supported by the specified endpoint shall return
an error. When the event name is not qualified by a package name, the
default package name for the end point is assumed. If the event name
is not registered in this default package, the gateway shall return
an error.
The Call Agent can send a NotificationRequest whose requested signal
list is empty. It will do so for example when tone generation should
stop.
The optional QuarantineHandling parameter specifies the handling of
"quarantine" events, i.e. events that have been detected by the
gateway before the arrival of this NotificationRequest command, but
have not yet been notified to the Call Agent. The parameter provides
a set of handling options:
* whether the quarantined events should be processed or discarded
(the default is to process them.)
* whether the gateway is expected to generate at most one
notification (step by step), or multiple notifications (loop), in
response to this request (the default is exactly one.)
When the parameter is absent, the default value is assumed.
We should note that the quarantine-handling parameter also governs
the handling of events that were detected but not yet notified when
the command is received.
DetectEvents is an optional parameter that specifies a list of events
that the gateway is requested to detect during the quarantine period.
When this parameter is absent, the events that should be detected in
the quarantine period are those listed in the last received
DetectEvents list. In addition, the gateway should also detect the
events specified in the request list, including those for which the
"ignore" action is specified.
Some events and signals, such as the in-line ringback or the quality
alert, are performed or detected on connections terminating in the
end point rather than on the endpoint itself. The structure of the
event names allow the Call Agent to specify the connection (or
connections) on which the events should be performed or detected.
The command may carry an encapsulated EndpointConfiguration command,
that will apply to the same endpoint. When this command is present,
the parameters of the EndpointConfiguration command are inserted
after the normal parameters of the NotificationRequest, with the
exception of the EndpointId, which is not replicated.
The encapsulated EndpointConfiguration command shares the fate of the
NotificationRequest command. If the NotificationRequest is rejected,
the EndpointConfiguration is not executed.
ReturnCode is a parameter returned by the gateway. It indicates the
outcome of the command and consists of an integer number optionally
followed by commentary. .NH 3 Notifications
Notifications are sent via the Notify command and are sent by the
gateway when the observed events occur.
ReturnCode
<-- Notify( EndpointId,
[NotifiedEntity,]
RequestIdentifier,
ObservedEvents)
EndpointId is the name for the endpoint in the gateway which is
issuing the Notify command, as defined in section 2.1.1. The
identifier should be a fully qualified endpoint identifier, including
the domain name of the gateway. The local part of the name shall not
use the wildcard convention.
NotifiedEntity is an optional parameter that identifies the entity to which the notifications is sent. This parameter is equal to the last received value of the NotifiedEntity parameter. The parameter is absent if there was no such parameter in the triggering request. The notification is sent to the "current notified entity" or, if no such entity was ever specified, to the address from which the request was received. RequestIdentifier is parameter that repeats the RequestIdentifier parameter of the NotificationRequest that triggered this notification. It is used to correlate this notification with the request that triggered it. ObservedEvents is a list of events that the gateway detected. A single notification may report a list of events that will be reported in the order in which they were detected. The list may only contain the identification of events that were requested in the RequestedEvents parameter of the triggering NotificationRequest. It will contain the events that were either accumulated (but not notified) or treated according to digit map (but no match yet), and the final event that triggered the detection or provided a final match in the digit map. ReturnCode is a parameter returned by the call agent. It indicates the outcome of the command and consists of an integer number optionally followed by commentary.2.3.3. CreateConnection
This command is used to create a connection between two endpoints. ReturnCode, ConnectionId, [SpecificEndPointId,] [LocalConnectionDescriptor,] [SecondEndPointId,] [SecondConnectionId] <--- CreateConnection(CallId, EndpointId, [NotifiedEntity,] [LocalConnectionOptions,] Mode, [{RemoteConnectionDescriptor | SecondEndpointId}, ] [Encapsulated NotificationRequest,] [Encapsulated EndpointConfiguration])
A connection is defined by its endpoints. The input parameters in
CreateConnection provide the data necessary to build a gateway's
"view" of a connection.
CallId is a globally unique parameter that identifies the call (or
session) to which this connection belongs. Connections that belong to
the same call share the same call-id. The call-id can be used to
identify calls for reporting and accounting purposes. It does not
affect the handling of connections by the gateway.
EndpointId is the identifier for the connection endpoint in the
gateway where CreateConnection executes. The EndpointId can be
fully-specified by assigning a value to the parameter EndpointId in
the function call or it may be under-specified by using the "anyone"
wildcard convention. If the endpoint is underspecified, the endpoint
identifier will be assigned by the gateway and its complete value
returned in the SpecificEndPointId parameter of the response.
The NotifiedEntity is an optional parameter that specifies where the
Notify or DeleteConnection commands should be sent. If the parameter
is absent, the Notify or DeleteConnection commands should be sent to
the last received Notified Entity, or to originator of the
CreateConnection command if no Notified Entity was ever received for
the end point.
LocalConnectionOptions is a parameter used by the Call Agent to
direct the handling of the connection by the gateway. The fields
contained in LocalConnectionOptions are the following:
* Encoding Method,
* Packetization period,
* Bandwidth,
* Type of Service,
* Usage of echo cancellation,
* Usage of silence suppression or voice activity detection,
* Usage of signal level adaptation and noise level reduction, or
"gain control."
* Usage of reservation service,
* Usage of RTP security,
* Type of network used to carry the connection.
This set of field can be completed by vendor specific optional or
mandatory extensions. The encoding of the first three fields, when
they are present, will be compatible with the SDP and RTP profiles:
* The encoding method shall be specified by using one or several
valid encoding names, as defined in the RTP AV Profile or
registered with the IANA.
* The packetization period is encoded as either the length of time
in milliseconds represented by the media in a packet, as specified
in the "ptime" parameter of SDP, or as a range value, specifying
both the minimum and maximum acceptable packetization periods.
* The bandwidth is encoded as either a single value or a range,
expressed as an integer number of kilobit per seconds.
For each of the first three fields, the Call Agent has three options:
* It may state exactly one value, which the gateway will then use
for the connection,
* It may provide a loose specification, such as a list of allowed
encoding methods or a range of packetization periods,
* It may simply provide a bandwidth indication, leaving the choice
of encoding method and packetization period to the gateway.
The bandwidth specification shall not contradict the specification of
encoding methods and packetization period. If an encoding method is
specified, then the gateway is authorized to use it, even if it
results in the usage of a larger bandwidth than specified.
The LocalConnectionOptions parameter may be absent in the case of a
data call.
The Type of Service specifies the class of service that will be used
for the connection. When the connection is transmitted over an IP
network, the parameters encodes the 8-bit type of service value
parameter of the IP header. When the Type of Service is not
specified, the gateway shall use a default or configured value.
The gateways can be instructed to perform a reservation, for example
using RSVP, on a given connection. When a reservation is needed, the
call agent will specify the reservation profile that should be used,
which is either "controlled load" or "guaranteed service." The
absence of reservation can be indicated by asking for the "best
effort" service, which is the default value of this parameter. When
reservation has been asked on a connection, the gateway will:
* start emitting RSVP "PATH" messages if the connection is in
"send-only", "send-receive", "conference", "network loop back" or
"network continuity test" mode (if a remote connection descriptor
has been received,)
* start emitting RSVP "RESV" messages as soon as it receives "PATH"
messages if the connection is in "receive-only", "send-receive",
"conference", "network loop back" or "network continuity test"
mode.
The RSVP filters will be deduced from the characteristics of the
connection. The RSVP resource profiles will be deduced from the
connection's bandwidth and packetization period.
By default, the telephony gateways always perform echo cancellation.
However, it is necessary, for some calls, to turn off these
operations. The echo cancellation parameter can have two values,
"on" (when the echo cancellation is requested) and "off" (when it is
turned off.)
The telephony gateways may perform gain control, in order to adapt
the level of the signal. However, it is necessary, for example for
modem calls, to turn off this function. The gain control parameter
may either be specified as "automatic", or as an explicit number of
decibels of gain. The default is to not perform gain control, which
is equivalent to specifying a gain of 0 decibels.
The telephony gateways may perform voice activity detection, and
avoid sending packets during periods of silence. However, it is
necessary, for example for modem calls, to turn off this detection.
The silence suppression parameter can have two values, "on" (when the
detection is requested) and "off" (when it is turned off.) The
default is "off."
The Call agent can request the gateway to enable encryption of the
audio Packets. It does so by providing an key specification, as
specified in RFC 2327. By default, encryption is not used.
The Call Agent may instruct the gateway to prepare the connection on
a specified type of network. The type of network is encoded as in
the "connection-field" parameter of the SDP standard. Possible
values are IN (Internet), ATM and LOCAL. The parameter is optional;
if absent, the network is determined by the type of gateway.
RemoteConnectionDescriptor is the connection descriptor for the remote side of a connection, on the other side of the IP network. It includes the same fields as in the LocalConnectionDescriptor, i.e. the fields that describe a session according to the SDP standard. This parameter may have a null value when the information for the remote end is not known yet. This occurs because the entity that builds a connection starts by sending a CreateConnection to one of the two gateways involved in it. For the first CreateConnection issued, there is no information available about the other side of the connection. This information may be provided later via a ModifyConnection call. In the case of data connections (mode=data), this parameter describes the characteristics of the data connection. The SecondEndpointId can be used instead of the RemoteConnectionDescriptor to establish a connection between two endpoints located on the same gateway. The connection is by definition a local connection. The SecondEndpointId can be fully- specified by assigning a value to the parameter SecondEndpointId in the function call or it may be under-specified by using the "anyone" wildcard convention. If the secondendpoint is underspecified, the second endpoint identifier will be assigned by the gateway and its complete value returned in the SecondEndPointId parameter of the response. Mode indicates the mode of operation for this side of the connection. The mode are "send", "receive", "send/receive", "conference", "data", "inactive", "loopback", "continuity test", "network loop back" or "network continuity test." The expected handling of these modes is specified in the introduction of the "Gateway Handling Function" section. Some end points may not be capable of supporting all modes. If the command specifies a mode that the endpoint cannot support, and error shall be returned. The gateway returns a ConnectionId, that uniquely identifies the connection within one endpoint, and a LocalConnectionDescriptor, which is a session description that contains information about addresses and RTP ports, as defined in SDP. The LocalConnectionDescriptor is not returned in the case of data connections. The SpecificEndPointId is an optional parameter that identifies the responding endpoint. It can be used when the EndpointId argument referred to a "any of" wildcard name. When a SpecificEndPointId is returned, the Call Agent should use it as the EndpointId value is successive commands referring to this call.
When a SecondEndpointId is specified, the command really creates two
connections that can be manipulated separately through
ModifyConnection and DeleteConnection commands. The response to the
creation provides a SecondConnectionId parameter that identifies the
second connection.
After receiving a "CreateConnection" request that did not include a
RemoteConnectionDescriptor parameter, a gateway is in an ambiguous
situation. Because it has exported a LocalConnectionDescriptor
parameter, it can potentially receive packets. Because it has not yet
received the RemoteConnectionDescriptor parameter of the other
gateway, it does not know whether the packets that it receives have
been authorized by the Call Agent. It must thus navigate between two
risks, i.e. clipping some important announcements or listening to
insane data. The behavior of the gateway is determined by the value
of the Mode parameter:
* If the mode was set to ReceiveOnly, the gateway should accept the
voice signals and transmit them through the endpoint.
* If the mode was set to Inactive, Loopback, Continuity Test, the
gateway should refuse the voice signals.
* If the mode was set to Network Loopback or Network Continuity
Test, the gateway should perform the expected echo or Response.
Note that the mode values SendReceive, Conference, Data and SendOnly
don't make sense in this situation. They should be treated as errors,
and the command should be rejected (Error code 517).
The command may optionally contain an encapsulated Notification
Request command, in which case a RequestIdentifier parameter will be
present, as well as, optionally, the RequestedEvents DigitMap,
SignalRequests, QuarantineHandling and DetectEvents parameters. The
encapsulated NotificationRequest is executed simultaneously with the
creation of the connection. For example, when the Call Agent wants to
initiate a call to an residential gateway, it should:
* ask the residential gateway to prepare a connection, in order to
be sure that the user can start speaking as soon as the phone goes
off hook,
* ask the residential gateway to start ringing,
* ask the residential gateway to notify the Call Agent when the
phone goes off-hook.
This can be accomplished in a single CreateConnection command, by also transmitting the RequestedEvent parameters for the off hook event, and the SignalRequest parameter for the ringing signal. When these parameters are present, the creation and the NotificationRequests should be synchronized, which means that bothshould be accepted, or both refused. In our example, the CreateConnection may be refused if the gateway does not have sufficient resources, or cannot get adequate resources from the local network access, and the off-hook Notification-Request can be refused in the glare condition, if the user is already off-hook. In this example, the phone should not ring if the connection cannot be established, and the connection should not be established if the user is already off hook. The NotifiedEntity parameter, if present, applies to both the CreateConnection and the NotificationRequest command. It defines the new "notified entity" for the endpoint. The command may carry an encapsulated EndpointConfiguration command, that will apply to the same endpoint. When this command is present, the parameters of the EndpointConfiguration command are inserted after the normal parameters of the CreateConnection with the exception of the EndpointId, which is not replicated. The EndpointConfiguration command may be encapsulated together with an encapsulated NotificationRequest command. The encapsulated EndpointConfiguration command shares the fate of the CreateConnection command. If the CreateConnection is rejected, the EndpointConfiguration is not executed. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary.2.3.4. ModifyConnection
This command is used to modify the characteristics of a gateway's "view" of a connection. This "view" of the call includes both the local connection descriptors as well as the remote connection descriptor.
ReturnCode,
[LocalConnectionDescriptor]
<--- ModifyConnection(CallId,
EndpointId,
ConnectionId,
[NotifiedEntity,]
[LocalConnectionOptions,]
[Mode,]
[RemoteConnectionDescriptor,]
[Encapsulated NotificationRequest,]
[Encapsulated EndpointConfiguration])
The parameters used are the same as in the CreateConnection command,
with the addition of a ConnectionId that identifies the connection
within the endpoint. This parameter is returned by the
CreateConnection function, as part of the local connection
descriptor. It uniquely identifies the connection within the context
of the endpoint.
The EndpointId should be a fully qualified endpoint identifier. The
local name shall not use the wildcard convention.
The ModifyConnection command can be used to affect parameters of a
connection in the following ways:
* Provide information about the other end of the connection, through
the RemoteConnectionDescriptor.
* Activate or deactivate the connection, by changing the value of
the Mode parameter. This can occur at any time during the
connection, with arbitrary parameter values.
* Change the sending parameters of the connection, for example by
switching to a different coding scheme, changing the packetization
period, or modifying the handling of echo cancellation.
Connections can only be activated if the RemoteConnectionDescriptor
has been provided to the gateway. The receive only mode, however, can
be activated without the provision of this descriptor.
The command will only return a LocalConnectionDescriptor if the local
connection parameters, such as RTP ports, were modified. (Usage of
this feature is actually for further study.)
The command may optionally contain an encapsulated Notification
Request command, in which case a RequestIdentifier parameter will be
present, as well as, optionnally, the RequestedEvents DigitMap,
SignalRequests, QuarantineHandling and DetectEvents parameters. The
encapsulated NotificationRequest is executed simultaneously with the modification of the connection. For example, when a connection is accepted, the calling gateway should be instructed to place the circuit in send-receive mode and to stop providing ringing tones. This can be accomplished in a single ModifyConnection command, by also transmitting the RequestedEvent parameters, for the on hook event, and an empty SignalRequest parameter, to stop the provision of ringing tones. When these parameters are present, the modification and the NotificationRequests should be synchronized, which means that both should be accepted, or both refused. The NotifiedEntity parameter, if present, applies to both the ModifyConnection and the NotificationRequest command. The command may carry an encapsulated EndpointConfiguration command, that will apply to the same endpoint. When this command is present, the parameters of the EndpointConfiguration command are inserted after the normal parameters of the ModifyConnection with the exception of the EndpointId, which is not replicated. The EndpointConfiguration command may be encapsulated together with an encapsulated NotificationRequest command. The encapsulated EndpointConfiguration command shares the fate of the ModifyConnection command. If the ModifyConnection is rejected, the EndpointConfiguration is not executed. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary.2.3.5. DeleteConnection (from the Call Agent)
This command is used to terminate a connection. As a side effect, it collects statistics on the execution of the connection. ReturnCode, Connection-parameters <-- DeleteConnection(CallId, EndpointId, ConnectionId, [Encapsulated NotificationRequest,] [Encapsulated EndpointConfiguration]) The endpoint identifier, in this form of the DeleteConnection command, shall be fully qualified. Wildcard conventions shall not be used.
In the general case where a connection has two ends, this command has to be sent to both gateways involved in the connection. Some connections, however, may use IP multicast. In this case, they can be deleted individually. After the connection has been deleted, any loopback that has been requested for the connection should be cancelled. When all connections to an endpoint have been deleted, that endpoint should be placed in inactive mode. In response to the DeleteConnection command, the gateway returns a list of parameters that describe the status of the connection. These parameters are: Number of packets sent: The total number of RTP data packets transmitted by the sender since starting transmission on this connection. The count is not reset if the sender changes its synchronization source identifier (SSRC, as defined in RTP), for example as a result of a Modify command. The value is zero if the connection was set in "receive only" mode. Number of octets sent: The total number of payload octets (i.e., not including header or padding) transmitted in RTP data packets by the sender since starting transmission on this connection. The count is not reset if the sender changes its SSRC identifier, for example as a result of a ModifyConnection command. The value is zero if the connection was set in "receive only" mode. Number of packets received: The total number of RTP data packets received by the sender since starting reception on this connection. The count includes packets received from different SSRC, if the sender used several values. The value is zero if the connection was set in "send only" mode. Number of octets received: The total number of payload octets (i.e., not including header or padding) transmitted in RTP data packets by the sender since starting transmission on this connection. The count includes packets received from different SSRC, if the sender used several values. The value is zero if the connection was set in "send only" mode.
Number of packets lost: The total number of RTP data packets that have been lost since the beginning of reception. This number is defined to be the number of packets expected less the number of packets actually received, where the number of packets received includes any which are late or duplicates. The count includes packets received from different SSRC, if the sender used several values. Thus packets that arrive late are not counted as lost, and the loss may be negative if there are duplicates. The count includes packets received from different SSRC, if the sender used several values. The number of packets expected is defined to be the extended last sequence number received, as defined next, less the initial sequence number received. The count includes packets received from different SSRC, if the sender used several values. The value is zero if the connection was set in "send only" mode. This parameter is omitted if the connection was set in "data" mode. Interarrival jitter: An estimate of the statistical variance of the RTP data packet interarrival time measured in milliseconds and expressed as an unsigned integer. The interarrival jitter J is defined to be the mean deviation (smoothed absolute value) of the difference D in packet spacing at the receiver compared to the sender for a pair of packets. Detailed computation algorithms are found in RFC 1889. The count includes packets received from different SSRC, if the sender used several values. The value is zero if the connection was set in "send only" mode. This parameter is omitted if the connection was set in "data" mode. Average transmission delay: An estimate of the network latency, expressed in milliseconds. This is the average value of the difference between the NTP timestamp indicated by the senders of the RTCP messages and the NTP timestamp of the receivers, measured when this messages are received. The average is obtained by summing all the estimates, then dividing by the number of RTCP messages that have been received. This parameter is omitted if the connection was set in "data" mode. When the gateway's clock is not synchronized by NTP, the latency value can be computed as one half of the round trip delay, as measured through RTCP. When the gateway cannot compute the one way delay or the round trip delay, the parameter conveys a null value. For a detailed definition of these variables, refer to RFC 1889.
When the connection was set up over an ATM network, the meaning of
these parameters may change:
Number of packets sent: The total number of ATM cells transmitted
since starting transmission on this connection.
Number of octets sent:
The total number of payload octets transmitted in ATM cells.
Number of packets received:
The total number of ATM cells received since starting reception on
this connection.
Number of octets received:
The total number of payload octets received in ATM cells.
Number of packets lost:
Should be determined as the number of cell losts, or set to zero
if the adaptation layer does not enable the gateway to assess
losses.
Interarrival jitter:
Should be understood as the interarrival jitter between ATM cells.
Average transmission delay:
The gateway may not be able to assess this parameter over an ATM
network. It could simply report a null value.
When the connection was set up over an LOCAL interconnect, the
meaning of these parameters is defined as follows:
Number of packets sent:
Not significant.
Number of octets sent:
The total number of payload octets transmitted over the local
connection.
Number of packets received:
Not significant.
Number of octets received:
The total number of payload octets received over the connection.
Number of packets lost:
Not significant. A value of zero is assumed.
Interarrival jitter:
Not significant. A value of zero is assumed.
Average transmission delay:
Not significant. A value of zero is assumed.
The standard set of connection parameters can be extended by the
creation of extension parameters.
The command may optionally contain an encapsulated Notification
Request command, in which case a RequestIdentifier parameter will be
present, as well as, optionnally, the RequestedEvents DigitMap,
SignalRequests, QuarantineHandling and DetectEvents parameters. The
encapsulated NotificationRequest is executed simultaneously with the
deletion of the connection. For example, when a user hang-up is
notified, the gateway should be instructed to delete the connection
and to start looking for an off hook event.
This can be accomplished in a single DeleteConnection command, by
also transmitting the RequestedEvent parameters, for the off hook
event, and an empty SignalRequest parameter.
When these parameters are present, the DeleteConnection and the
NotificationRequests should be synchronized, which means that both
should be accepted, or both refused.
The command may carry an encapsulated EndpointConfiguration command,
that will apply to the same endpoint. When this command is present,
the parameters of the EndpointConfiguration command are inserted
after the normal parameters of the DeleteConnection with the
exception of the EndpointId, which is not replicated. The
EndpointConfiguration command may be encapsulated together with an
encapsulated NotificationRequest command.
The encapsulated EndpointConfiguration command shares the fate of the
DeleteConnection command. If the DeleteConnection is rejected, the
EndpointConfiguration is not executed.
ReturnCode is a parameter returned by the gateway. It indicates the
outcome of the command and consists of an integer number optionally
followed by commentary.
2.3.6. DeleteConnection (from the VoIP gateway)
In some circumstances, a gateway may have to clear a connection, for example because it has lost the resource associated with the connection, or because it has detected that the endpoint no longer is capable or willing to send or receive voice. The gateway terminates the connection by using a variant of the DeleteConnection command: ReturnCode, <-- DeleteConnection( CallId, EndpointId, ConnectionId, Reason-code, Connection-parameters) In addition to the call, endpoint and connection identifiers, the gateway will also send the call's parameters that would have been returned to the Call Agent in response to a DeleteConnection command. The reason code indicates the cause of the disconnection. ReturnCode is a parameter returned by the call agent. It indicates the outcome of the command and consists of an integer number optionally followed by commentary.2.3.7. DeleteConnection (multiple connections, from the Call Agent)
A variation of the DeleteConnection function can be used by the Call Agent to delete multiple connections at the same time. The command can be used to delete all connections that relate to a Call for an endpoint: ReturnCode, <-- DeleteConnection( CallId, EndpointId) It can also be used to delete all connections that terminate in a given endpoint: ReturnCode, <-- DeleteConnection( EndpointId) Finally, Call Agents can take advantage of the hierarchical naming structure of endoints to delete all the connections that belong to a group of endpoints. In this case, the "local name" component of the EndpointID will be specified using the "all value" wildcarding convention. The "any value" convention shall not be used. For example, if endpoints names are structured as the combination of a physical interface name and a circuit number, as in "X35V3+A4/13",
the Call Agent may replace the circuit number by a wild card character "*", as in "X35V3+A4/*". This "wildcard" command instructs the gateway to delete all the connections that where attached to circuits connected to the physical interface "X35V3+A4". After the connections have been deleted, the endpoint should be placed in inactive mode. Any loopback that has been requested for the connections should be cancelled. This command does not return any individual statistics or call parameters. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary.2.3.8. Audit Endpoint
The AuditEndPoint command can be used by the Call Agent to find out the status of a given endpoint. ReturnCode, EndPointIdList|{ [RequestedEvents,] [DigitMap,] [SignalRequests,] [RequestIdentifier,] [NotifiedEntity,] [ConnectionIdentifiers,] [DetectEvents,] [ObservedEvents,] [EventStates,] [BearerInformation,] [RestartReason,] [RestartDelay,] [ReasonCode,] [Capabilities]} <--- AuditEndPoint(EndpointId, [RequestedInfo]) The EndpointId identifies the endpoint that is being audited. The "all of" wildcard convention can be used to start auditing of a group of endpoints. If this convention is used, the gateway should return the list of endpoint identifiers that match the wildcard in the EndPointIdList parameter. It shall not return any parameter specific to one of these endpoints.
When a non-wildcard EndpointId is specified, the (possibly empty)
RequestedInfo parameter describes the information that is requested
for the EndpointId specified. The following endpoint info can be
audited with this command:
RequestedEvents, DigitMap, SignalRequests, RequestIdentifier,
NotifiedEntity, ConnectionIdentifiers, DetectEvents, ObservedEvents,
EventStates, RestartReason, RestartDelay, ReasonCode, and
Capabilities.
The response will in turn include information about each of the items
for which auditing info was requested:
* RequestedEvents: The current value of RequestedEvents the endpoint
is using including the action associated with each event.
Persistent events are included in the list.
* DigitMap: the digit map the endpoint is currently using.
* SignalRequests: A list of the; Time-Out signals that are currently
active, On/Off signals that are currently "on" for the endpoint
(with or without parameter), and any pending Brief signals. Time-
Out signals that have timed-out, and currently playing Brief
signals are not included.
* RequestIdentifier, the RequestIdentifier for the last Notification
Request received by this endpoint (includes NotificationRequest
encapsulated in Connection handling primitives). If no
notification request has been received, the value zero will be
returned.
* QuarantineHandling, the QuarantineHandling for the last
NotificationRequest received by this endpoint.
* DetectEvents, the list of events that are currently detected in
quarantine mode.
* NotifiedEntity, the current notified entity for the endpoint.
* ConnectionIdentifiers, the list of ConnectionIdentifiers for all
connections that currently exist for the specified endpoint.
* ObservedEvents: the current list of observed events for the
endpoint.
* EventStates: For events that have auditable states associated with
them, the event corresponding to the state the endpoint is in,
e.g., off-hook if the endpoint is off-hook. The definition of the
individual events will state if the event in question has an
auditable state associated with it.
* BearerInformation: the value of the last received
BearerInformation parameter for this endpoint.
* RestartReason: the value of the restart reason parameter in the
last RestartInProgress command issued by the endpoint, "restart"
indicating a fully functional endpoint.
* RestartDelay: the value of the restart delay parameter if a
RestartInProgress command was issued by the endpoint at the time
of the response, or zero if the command would not include this
parameter.
* ReasonCode:the value of the Reason-Code parameter in the last
RestartInProgress or DeleteConnection command issued by the
gateway for the endpoint, or the special value 000 if the
endpoint's state is nominal.
* The capabilities for the endpoint similar to the
LocalConnectionOptions parameter and including event packages and
connection modes. If there is a need to specify that some
parameters, such as e.g., silence suppression, are only compatible
with some
* codecs, then the gateway will return several capability sets:
Compression Algorithm: a list of supported codecs. The rest of
the parameters will apply to all codecs specified in this list.
Packetization Period: A single value or a range may be
specified.
Bandwidth: A single value or a range corresponding to the range
for packetization periods may be specified (assuming no silence
suppression).
Echo Cancellation: Whether echo cancellation is supported or
not.
Silence Suppression: Whether silence suppression is supported
or not.
Type of Service: Whether type of service is supported or not.
Event Packages: A list of event packages supported. The first
event package in the list will be the default package.
Modes: A list of supported connection modes.
The Call Agent may then decide to use the AuditConnection command to
obtain further information about the connections.
If no info was requested and the EndpointId refers to a valid
endpoint, the gateway simply returns a positive acknowledgement.
If no NotifiedEntity has been specified in the last
NotificationRequest, the notified entity defaults to the source
address of the last NotificationRequest command received for this
connection.
ReturnCode is a parameter returned by the gateway. It indicates the
outcome of the command and consists of an integer number optionally
followed by commentary.
2.3.9. Audit Connection
The AuditConnection command can be used by the Call Agent to retrieve
the parameters attached to a connection:
ReturnCode,
[CallId,]
[NotifiedEntity,]
[LocalConnectionOptions,]
[Mode,]
[RemoteConnectionDescriptor,]
[LocalConnectionDescriptor,]
[ConnectionParameters]
<--- AuditConnection(EndpointId,
ConnectionId,
RequestedInfo)
The EndpointId parameter specifies the endpoint that handles the
connection. The wildcard conventions shall not be used.
The ConnectionId parameter is the identifier of the audited
connection, within the context of the specified endpoint.
The (possibly empty) RequestedInfo describes the information that is
requested for the ConnectionId within the EndpointId specified. The
following connection info can be audited with this command:
CallId, NotifiedEntity, LocalConnectionOptions, Mode,
RemoteConnectionDescriptor, LocalConnectionDescriptor,
ConnectionParameters
The AuditConnectionResponse will in turn include information about
each of the items auditing info was requested for:
* CallId, the CallId for the call the connection belongs to.
* NotifiedEntity, the current notified entity for the Connection.
* LocalConnectionOptions, the LocalConnectionOptions that was
supplied for the connection.
* Mode, the current mode of the connection.
* RemoteConnectionDescriptor, the RemoteConnectionDescriptor that
was supplied to the gateway for the connection.
* LocalConnectionDescriptor, the LocalConnectionDescriptor the gate-
way supplied for the connection.
* ConnectionParameters, the current value of the connection
parameters for the connection.
If no info was requested and the EndpointId is valid, the gateway
simply checks that the connection exists, and if so returns a
positive acknowledgement.
If no NotifiedEntity has been specified for the connection, the
notified entity defaults to the source address of the last connection
handling command received for this connection.
ReturnCode is a parameter returned by the gateway. It indicates the
outcome of the command and consists of an integer number optionally
followed by commentary.
2.3.10. Restart in progress
The RestartInProgress command is used by the gateway to signal that
An endpoint, or a group of endpoint, is taken in or out of service.
ReturnCode,
[NotifiedEntity]
<------- RestartInProgress ( EndPointId,
RestartMethod,
[RestartDelay,]
[Reason-code])
The EndPointId identifies the endpoint that are taken in or out of
service. The "all of" wildcard convention may be used to apply the
command to a group of endpoint, such as for example all endpoints
that are attached to a specified interface, or even all endpoints
that are attached to a given gateway. The "any of" wildcard
convention shall not be used.
The RestartMethod parameter specified the type of restart. Three
values have been defined:
* A "graceful" restart method indicates that the specified endpoints
will Be taken out of service after the specified delay. The
established connections are not yet affected, but the Call Agent
should refrain to establish new connections, and should try to
gracefully tear down the existing connections.
* A "forced" restart method indicates that the specified endpoints
are taken abruptely out of service. The established connections,
if any, are lost.
* A "restart" method indicates that service will be restored on the
endpoints after the specified "restart delay." There are no
connections that are currently established on the endpoints.
* A "disconnected" method indicates that the endpoint has become
disconnected and is now trying to establish connectivity. The
"restart delay" specifies the number of seconds the endpoint has
been disconnected. Established connections are not affected.
* A "cancel-graceful" method indicates that a gateway is canceling a
previously issued "graceful" restart command.
The optional "restart delay" parameter is expressed as a number of
seconds. If the number is absent, the delay value should be
considered null. In the case of the "graceful" method, a null delay
indicates that the call agent should simply wait for the natural
termination of the existing connections, without establishing new
connections. The restart delay is always considered null in the case
of the "forced" method.
A restart delay of null for the "restart" method indicates that
service has already been restored. This typically will occur after
gateway startup/reboot.
The optional reason code parameter the cause of the restart.
Gateways SHOULD send a "graceful" or "forced" RestartInProgress message as a courtesy to the Call Agent when they are taken out of service, e.g., by being shutdown, or taken out of service by a network management system, although the Call Agent cannot rely on always receiving such messages. Gateways MUST send a "restart" RestartInProgress message with a null delay to their Call Agent when they are back in service according to the restart procedure specified in Section 4.3.4 - Call Agents can rely on receiving this message. Also, gateways MUST send a "disconnected" RestartInProgress message to their current "notified entity" according to the "disconnected" procedure specified in Section 4.3.5. The "restart delay" parameter MUST NOT be used with the "forced" restart method. The RestartInProgress message will be sent to the current notified entity for the EndpointId in question. It is expected that a default Call Agent, i.e., notified entity, has been provisioned for each endpoint so, after a reboot, the default Call Agent will be the notified entity for each endpoint. Gateways should take full advantage of wild- carding to minimize the number of RestartInProgress messages generated when multiple endpoints in a gateway restart and the endpoints are managed by the same Call Agent. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. A NotifiedEntity may additionally be returned with the response from the Call Agent: * If the response indicated success (return code 200 - transaction executed), the restart procedure has completed, and the NotifiedEntity returned is the new "notified entity" for the endpoint(s). * If the response from the Call Agent indicated an error, the restart procedure is not yet complete, and must therefore be initiated again. If a NotifiedEntity parameter was returned, it then specifies the new "notified entity" for the endpoint(s), which must consequently be used when retrying the restart procedure.2.4. Return codes and error codes.
All MGCP commands are acknowledged. The acknowledgment carries a return code, which indicates the status of the command. The return code is an integer number, for which four ranges of values have been defined:
* values between 100 and 199 indicate a provisional response,
* values between 200 and 299 indicate a successful completion,
* values between 400 and 499 indicate a transient error,
* values between 500 and 599 indicate a permanent error.
The values that have been already defined are listed in the following
list:
100 The transaction is currently being executed. An actual
completion message will follow on later.
200 The requested transaction was executed normally.
250 The connection was deleted.
400 The transaction could not be executed, due to a transient error.
401 The phone is already off hook
402 The phone is already on hook
403 The transaction could not be executed, because the endpoint does
not have sufficient resources at this time
404 Insufficient bandwidth at this time
500 The transaction could not be executed, because the endpoint is
unknown.
01 The transaction could not be executed, because the endpoint is
not ready.
502 The transaction could not be executed, because the endpoint does
not have sufficient resources
510 The transaction could not be executed, because a protocol error
was detected.
11 The transaction could not be executed, because the command
contained an unrecognized extension.
512 The transaction could not be executed, because the gateway is
not equipped to detect one of the requested events.
513 The transaction could not be executed, because the gateway is
not equipped to generate one of the requested signals.
514 The transaction could not be executed, because the gateway
cannot send the specified announcement.
515 The transaction refers to an incorrect connection-id (may have
been already deleted)
516 The transaction refers to an unknown call-id.
517 Unsupported or invalid mode.
518 Unsupported or unknown package.
519 Endpoint does not have a digit map.
520 The transaction could not be executed, because the endpoint is
"restarting".
521 Endpoint redirected to another Call Agent.
522 No such event or signal.
523 Unknown action or illegal combination of actions
524 Internal inconsistency in LocalConnectionOptions
525 Unknown extension in LocalConnectionOptions
526 Insufficient bandwidth
527 Missing RemoteConnectionDescriptor
528 Incompatible protocol version
529 Internal hardware failure
530 CAS signaling protocol error.
531 failure of a grouping of trunks (e.g. facility failure).
2.5. Reason Codes
Reason-codes are used by the gateway when deleting a connection to inform the Call Agent about the reason for deleting the connection. They may also be used in a RestartInProgress command, to inform the gateway of the Restart's reason. The reason code is an integer number, and the following values have been defined: 000 Endpoint state is nominal. (This code is used only in response to audit requests.) 900 Endpoint malfunctioning 901 Endpoint taken out of service 902 Loss of lower layer connectivity (e.g., downstream sync)
(page 61 continued on part 3)
