letters, hyphens and digits, with the restriction that hyphens shall
never be the first or last characters in a name. Package or event
names are not case sensitive - values such as "hu", "Hu", "HU" or
"hU" should be considered equal.
Examples of package names are "D" (DTMF), "M" (MF), "T" (Trunk) or
"L" (Line). Examples of event names can be "hu" (off hook or "hang-
up" transition), "hf" (flash hook) or "0" (the digit zero).
In textual representations, the package name, when present, is
separated from the event name by a slash ("/"). The package name is
in fact optional. Each endpoint-type has a default package associated
with it, and if the package name is excluded from the event name, the
default package name for that endpoint-type is assumed. For example,
for an analog access line, the following two event names are equal:
l/dl dial-tone in the line package for an analog access line.
dl dial-tone in the line package (default) for an analog access
line.
This document defines a basic set of package names and event names.
Additional package names and event names can be registered with the
IANA. A package definition shall define the name of the package, and
the definition of each event belonging to the package. The event
definition shall include the precise name of the event (i.e., the
code used in MGCP), a plain text definition of the event, and, when
appropriate, the precise definition of the corresponding signals, for
example the exact frequencies of audio signal such as dial tones or
DTMF tones.
In addition, implementers can gain experience by using experimental
packages. The names of experimental packages must start with the two
characters "x-"; the IANA shall not register package names that start
with these characters.
Digits, or letters, are supported in many packages, notably "DTMF"
and "MF". Digits and letters are defined by the rules "Digit" and
"Letter" in the definition of digit maps. This definition refers to
the digits (0 to 9), to the asterisk or star ("*") and orthotrope,
number or pound sign ("#"), and to the letters "A", "B", "C" and "D",
as well as the timer indication "T". These letters can be combined in
"digit string" that represent the keys that a user punched on a dial.
In addition, the letter "X" can be used to represent all digits, and
the sign "$" can be used in wildcard notations. The need to easily
express the digit strings has a consequence on the form of event
names:
An event name that does not denote a digit should always contain at
least one character that is neither a digit, nor one of the letters
A, B, C, D, T or X. (Such names should not contain the special
signs "*", "#", "/" or "$".)
A Call Agent may often have to ask a gateway to detect a group of
events. Two conventions can be used to denote such groups:
* The wildcard convention can be used to detect any event belonging
to a package, or a given event in many packages, or event any
event in any package supported by the gateway.
* The regular expression Range notation can be used to detect a
range of digits.
The star sign (*) can be used as a wildcard instead of a package
name, and the keyword "all" can be used as a wildcard instead of an
event name:
A name such as "foo/all" denotes all events in package "foo"
A name such as "*/bar" denotes the event "bar" in any package
supported by the gateway
The names "*" or "*/all" denote all events supported by the
gate way.
The call agent can ask a gateway to detect a set of digits or letters
either by individually describing those letters, or by using the
"range" notation defined in the syntax of digit strings. For example,
the call agent can:
Use the letter "x" to denote "any letter or digit."
Use the notation "[0-9#]" to denote the digits 0 to 9 and the pound
sign.
In some cases, Call Agents will request the gateway to generate or
detect events on connections rather than on the end point itself.
For example, gateways may be asked to provide a ringback tone on a
connection. When an event shall be applied on a connection, the name
of the connection is added to the name of the event, using an "at"
sign (@) as a delimiter, as in:
G/rt@0A3F58
The wildcard character "*" (star) can be used to denote "all
connections". When this convention is used, the gateway will generate
or detect the event on all the connections that are connected to the
endpoint. An example of this convention could be:
R/qa@*
The wildcard character "$" can be used to denote "the current
connection." It should only be used by the call agent, when the event
notification request is "encapsulated" within a command creation or
modification command. When this convention is used, the gateway will
generate or detect the event on the connection that is currently
being created or modified. An example of this convention is:
G/rt@$
The connection id, or a wildcard replacement, can be used in
conjunction with the "all packages" and "all events" conventions.
For example, the notation:
*/all@*
can be used to designate all events on all connections.
Events and signals are described in packages. The package description
must provide, for each events, the following informations:
* The description of the event and its purpose, which should mean
the actual signal that is generated by the client (i.e., xx ms FSK
tone) as well as the resulting user observed result (i.e., MW
light on/off).
* The detailed characteristics of the event, such as for example
frequencies and amplitude of audio signals, modulations and
repetitions,
* The typical and maximum duration of the event.
Signals are divided into different types depending on their behavior:
* On/off (OO) Once applied, these signals last forever until they
are turned off. This may happen either as the result of an event
or a new SignalRequests (see later).
* Time-out (TO) Once applied, these signals last until they are
either turned off (by an event or SignalRequests) or a signal
specific period of time has elapsed. Depending on package
specifications, a signal that times out may generate an "operation
complete" event.
* Brief (BR) The duration of these signals is so short, that they
stop on their own. If an event occurs the signal will not stop,
however if a new SignalRequests is applied, the signal will stop.
(Note: this point should be debated. One could make a case that
events such as strings of DTMF digits should in fact be allowed to
complete.)
TO signals are normally used to alert the endpoints' users, to
signal them that they are expected to perform a specific action,
such as hang down the phone (ringing). Transmission of these
signals should typically be interrupted as soon as the first of
the requested events has been produced.
Package descriptions should describe, for all signals, their type
(OO, TO, BR). They should also describe the maximum duration of
the TO signals.
2.2. Usage of SDP
The Call Agent uses the MGCP to provision the gateways with the
description of connection parameters such as IP addresses, UDP port
and RTP profiles. These descriptions will follow the conventions
delineated in the Session Description Protocol which is now an IETF
proposed standard, documented in RFC2327.
SDP allows for description of multimedia conferences. This version
limits SDP usage to the setting of audio circuits and data access
circuits. The initial session descriptions contain the description
of exactly one media, of type "audio" for audio connections, "nas"
for data access.
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 RFC2327. 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 RFC1889. 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: