2.2.4.1 Callback Request Message

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The Callback Request message is sent by an answerer to a caller. This contains a list of configuration options available to the caller.

The message format is specified as follows.


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Code

Identifier

Length

Data (variable)

...

Code (1 byte): This MUST be 0x01.

Identifier (1 byte): This MUST specify a value that assists in matching the Callback Request message with the corresponding Callback Response message and Callback Acknowledgment message. For each new Callback Request message sent by the answerer, the Identifier MUST be different. This SHOULD be set to 1 in the initial Callback Request message and incremented for each subsequent retransmitted Callback Request message.

Length (2 bytes): This MUST specify the length of the message, including the Code, Identifier, Length, and Data fields.

Data (variable): This contains the list of configuration options available to the caller (section 2.2.3).

There MUST be at least one Callback Configuration Option specified in the Callback Request message. If multiple callback types are supported for the specific caller, all possible types (specified in the following table) SHOULD be specified as individual Callback Configuration Option (section 2.2.3).

Callback configuration option

Settings

No Callback

The Callback Delay and Callback Address fields MUST not be present.

Callback to a user-specified number

The Callback Delay field SHOULD be set to 0. The Address Type field of the Callback Address MUST be set to 0x01, and the Address field MUST be set to an empty null-terminated ASCII string.

Callback to a pre-specified or an administrator-specified number

The Callback Delay field SHOULD be set to 0. The Callback Address field MUST not be present.