4-2 Message structure and function
297-2521-106 Standard 23.01 March 2001
Call Reference
The Call Reference information element identifies the call request at the
local user-network interface to which the particular message applies. The
call reference does not have end-to-end significance across ISDN.
Message Type
The Message Type information element identifies the function of the
message.
Other information elements
There are other information elements that may be required for specific
messages. These elements are assigned code values. The code values of the
information element identified for the variable length formats are assigned in
ascending numerical order, according to the actual order of appearance of
each information element in a message. This allows the receiving equipment
to detect the presence or absence of a particular information element without
scanning through the entire message. These information elements are listed
as follows.
Bearer Capability
The Bearer Capability (BC) information element lets subscribers specify (on
a per-call basis) the type of communication required for a call. BCs are
further discussed in Chapter 7, “Feature interaction.” No default BC may be
assumed by the absence of this information element.
Call State
The Call State information element describes the current status of a call.
Called Party Number
The Called Party Number information element is the digits dialed to access a
terminal in the public switched telephone network or the private network.
For details on how the DMS-250 switch uses the Called Party Number for
routing the call, refer to “Translations and routing options” in Chapter 7,
“Feature interaction.”
Called Party Subaddress
The Called Party Subaddress information element allows the originating
user to further identify the called user.
Calling Party Number
The Calling Party Number information element identifies the origin of a
call.
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