X25AM Programming Manual

X3PAD Interface
X25AM Programming Manual—527201-001
4-7
Establishing a Call
X25AM process that X3PAD accesses is the one that has been configured to
control $line.
command-list
is a list of one or more terminal commands, separated by commas. You can
execute the RUN command non-interactively by specifying X3PAD terminal
commands in the run command rather than the input file. When the command
string completes, the X3PAD process stops.
Establishing a Call
To establish a virtual circuit, the X3PAD (the calling DTE,) sends a Call Request
packet. The packet will vary slightly from the standard X25AM packet.
For packets sent from a PAD, the first four octets of the CUD are the protocol identifier.
The Q-bit, located in the Message Control Word (MCW), distinguishes a data packet
from a control packet. Set to 0, it identifies a data packet; set to 1, it identifies a control
packet.
Figure 4-2. X3PAD Call Request Packet Format
0 DSN
0 000
1011
0 0
0 000
0000
VST0402.vsd
Bits
Address
Lengths
upto
12 Octets
Facility Fields
Octet
Call User
Data Field
Call Data
(maximum of 12 octets)
~
~
1
0 000
0000
0 000
0000
0 000
0000
~
~
Facility Length
DTE Addresses
Calling DTE
Called DTE
Channel Identifier
Logical
2
3
4
Octet 1
2
3
4
8765
4321
~
~
~
~