X25AM Configuration and Management Manual

Attribute Descriptions
X25AM Configuration and Management Manual—523424-004
5-19
The Call User Data (CUD) Attribute
The Call User Data (CUD) Attribute
The Call User Data (CUD) attribute is present only in incoming calls and call requests.
For the Process-To-Process (PTP) protocol, the CUD field of a subdevice can:
•
Be totally absent
•
Contain a protocol ID (the first 4 bytes of the CUD)
•
Contain up to 16 bytes of user-defined information
For the Interactive Terminal Interface (ITI) protocol, the CUD field of a subdevice:
•
Always contains a protocol ID or 4 bytes of zeros (the default)
•
Can contain a protocol ID followed by up to 12 bytes of user-defined information
Figure 5-1. Call User Data (CUD)
VST0501.vsd
Logical
Channel Identifier
Facility Length
Facility Fields
Call User Data 1–16 Octets
present in call request and
incoming call packets only
Bits
876543 21
1
2
3
4
0D SN
Packet Type Identifier (PTI)
Calling DTE
Called DTE
DTE Addresses
00
Octet
0 = The initial bit (Q bit) is set to zero in call-setup packets.
D = The delivery bit (D bit).
SN = Sequence numbering information
(either module 8 or modulo 128).