X25AM Configuration and Management Manual

PTrace for the X25AM Subsystem
X25AM Configuration and Management Manual—523424-004
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Terminals and PAD Parameters
2. At record 74, it sent the saved Q packet because the SETMODE posted at record
66. This Q packet is different from the initial one sent at record 40 because it sends
parameter (2,0), which should turn off echo mode at the PAD (the default value of
2,1 means echo on).
The Q packet was not sent immediately after the SETMODE because Q packets
are normally saved until a WRITE or READ operation is posted to allow X25AM to
do several SETMODEs with one Q packet.
3. At record 78, the WRITE portion of the WRITEREAD operation (found at record
70) is performed when level 3 sends out a data packet to the PAD, which then
writes the data to the terminal in asynchronous mode.
4. At record 86, the terminal responds with data and the PAD forwards it in a data
packet, which level 3 verifies and forwards to our level 4 (ITI mode).
5. At record 89, the data from the incoming packet is returned to the application in a
WRITELINK operation (note the same LCB address, 6560). Then the operation is
completed. The application can determine that the operation completed
successfully by the presence of error FEOK (0).
The following is one more analysis example from the same trace. In this case, an error
is detected by level 3 and passed to the application.
1. At record 136, the application posts a READ in order to receive data (LCB address
62F0).
2. At record 139, the application receives a clear packet instead of data, meaning that
the network disconnected the circuit prematurely.
3. At record 144, the READ is completed by X25AM, which returns error 140 (circuit
disconnected). The application now has to do its own error recovery, which
probably means posting another CONTROL to wait for a new terminal to log onto
the PAD. The PAD forwards the CONTROL as a call request packet.
4. At record 147, level 3 continues, as the protocol dictates, to respond to the clear
packet by sending a clear confirmed packet. When the network and PAD receive
this packet, they know that the circuit is officially cleared and is available to the
next user.
Terminals and PAD Parameters
In ITI mode, which usually has a PAD device as an interface, a common problem is
how to set the PAD parameters correctly so that the PAD can communicate with a
particular terminal. The BPADPARMS and CPADPARMS (block and conversational
PAD parameters, respectively) should be set to match the terminal’s requirements. You
can also use SETMODEs to set these parameters. In ITI mode, some SETMODES
cause a Q data packet to be sent which signals the PAD to configure itself to the
parameters in the data portion of the packet. The Q packets generally follow a
successful call request-call accept sequence. They can also appear later as a result of
the SETMODEs.