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ATM traffic descriptor IE: Specifies the traffic parameters in the forward and backward direction of the connection.
Broadband bearer capability IE: Used to define the ATM service requested for a new connection.
SIGNALING IN ATM NETWORKS
Broadband high-layer IE, broadband low-layer IE: Used to check compatibility by the called user.
Broadband repeat indicator IE: Indicates how repeated IEs are to be interpreted.
Call state: Describes the current status of the call.
Called party number IE, and called party subaddress IE: Identify the called user.
Calling party number IE, and calling party subaddress IE: Identify the calling user.
Cause IE: Describes the reason for generating certain messages and indicates the location of the cause originator.
Connection identifier IE: Identifies the VPI/VCI allocated to the connection at the UNI.
End-to-end transit delay IE: Indicates the maximum acceptable transit delay and the cumulative transit delay to be expected for the connection.
Extended QoS parameters IE: Specifies the acceptable values and the cumulative values of some of the QoS parameters.
Transit network selection IE: Identifies a transit network that the call can cross.
An ATM end device or an ATM switch might not be able to process every information element included in a signaling message. In this case, the ATM equipment simply uses only the information elements that it needs, and it ignores the rest of them.
5.7.2 Q.2931 Messages
The Q.2931 messages can be grouped into the following three categories: call establishment, call clearing, and miscellaneous. The messages for each category are given in Table 5.2. Each Q.2931 message uses the signaling message format described in Section 5.6, with the protocol discriminator set to 00001001, and contains a set of information elements. Below, we describe the function of each message, and then we show how they are used to establish and clear a call.
ALERTING: This message is sent by the called user to the network and by the network to the calling user to indicate that called user alerting has been initiated. Called user
Table 5.2 Q.2931 messages.
Message category Message
Call establishment messages ALERTING
Call clearing messages RELEASE
Miscellaneous messages NOTIFY
THE SIGNALING PROTOCOL Q.2931
alerting is used for calls that require human interface, such as voice. The information element used in this message is the connection identifier.
CALL PROCEEDING: The message is sent by the called user to the network or by the network to the calling user, to indicate that the requested establishment of the call has been initiated and no more call information is accepted. The information element used in this message is the connection identifier.
CONNECT: The message is sent by the called user to the network, or by the network to the calling user to indicate that the called user has accepted the call. The following information elements are used in this message: AAL parameter, broadband low-layer, connection identifier, and end-to-end transit delay.
CONNECT ACKNOWLEDGEMENT: This message is sent by the network to the called user to indicate that the user has been awarded the call. It is also sent by the calling user to the network to allow symmetrical call control procedures.
RELEASE: This message is sent by the user to request the network to clear an end-to-end connection. It is also sent by the network to indicate that an end-to-end connection is cleared. It also indicates that the receiving equipment is to release the connection identifier, and to prepare to release the call reference value after sending RELEASE COMPLETE. The cause information element is carried in this message.
RELEASE COMPLETE: This message is sent by the calling user or the network to indicate that the equipment sending the message has released its call reference value and, if appropriate, the connection identifier. The cause information element is carried in this message.
SETUP: This message is sent by the calling user to the network and by the network to the called user to initiate the establishment of a new call. The following information elements are used: AAL parameter, ATM traffic descriptor, broadband bearer capability, broadband high-layer, broadband low-layer, called party number, called party subaddress, calling party number, calling party subaddress, connection identifier, end-to-end transit delay, extended QoS parameters, and transit network selection.