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X25AM Programming Manual

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Introduction
X25AM Programming Manual—527201-001
1-8
Call User Data (CUD) in Call Setup Packets
only appears in the two call set-up packets CALL REQUEST and INCOMING CALL,
and it is optional.
An application can set or fetch the entire CUD field programmatically by calling
filesystem procedure SETPARAM 41. In addition, this field can be set or fetched using
SCF commands, and displayed using the SCF INFO,DETAIL command. If the SCF
ADD or ALTER commands are issued (for example, in a command file), the line or
subdevice must be stopped. When it is restarted the SCF-configured values take
effect.
Previous versions of X25AM only allowed specification of the protocol ID (the first four
bytes of the CUD) for a PTP subdevice by using SETPARAM 8. Moreover, this
information could not be set or fetched.
Enhanced Specification of CUD Field
The remaining bytes of the CUD field can only be used with a remote public data
network (PDN) that does not require a port number in the call user data field of a CALL
REQUEST packet.
•
The CUD field of a subdevice configured for the PTP protocol:
°
Can contain a protocol ID (first four bytes of the CUD)
°
Can contain up to sixteen bytes of user-defined information
°
Is optional
•
The CUD field of a subdevice configured for the ITI protocol:
°
Always contains a protocol ID or four zero bytes (default value)
°
Can follow the protocol ID with up to twelve bytes of user-defined information
Modifying Default CUD Values
The default values for the CUD are configured by the SYSGEN modifier
CALLUSERDATA/NOCALLUSERDATA. The default setting for this modifier is
CALLUSERDATA.
If the line is configured with the default setting (CALLUSERDATA), the default for the
CUD field is four bytes of zero (0000) for both PTP and ITI subdevices. If this modifier
is set to NOCALLUSERDATA, the default for PTP subdevices is no CUD field, and the
default for ITI subdevices is four zero bytes (0000).
Note. Do not confuse the Call User Data field with the User Data field. The User Data field
appears in data packets, while the Call User Data field appears only in call set-up packets.