X25AM Programming Manual

ITI Applications
X25AM Programming Manual—527201-001
2-9
Packet Exchange between the PAD and ITI
Packet Exchange between the PAD and ITI
The PAD and ITI exchange two packet types: data packets and packets containing
control information for the PAD or response information from the PAD.
The Q bit, also called a Data Qualifier bit, identifies the X.29 data that is not intended
for the end user. The Q bit indicates the packet type:
•
Q bit = 1 for PAD control and response packets.
•
Q bit = 0 for data packets.
The Q bit can also indicate any other data not intended for the end user. SNA-over-
X.25 (SNAX) is an example of this.
PAD Control Packets
PAD control packets are issued by ITI. This is done by ITI responding on its own or as
a result of the application using file-system procedures.
Figure 2-4. X.3, X.25, X.28, X.29, and the PAD
HP NonStop System (DTE)
Characters
A
VST0204.vsd
Application
X25AM
Data
PAD
(DTE)
B
X.28
Data
Packets
X.29
X.25
X.25
PSN
X.29
X.25
X.3
Remote Terminal
(DTE-C)