HP X.25/9000 Programmer's Guide

Appendix A 123
X.25 Packet Formats
DATA Packet
Receive Sequence
Number
Indicates the sequence number of the last packet received. It is
controlled by the subsystem and cannot be read or written by the
application.
M Bit Indicates that the packet is part of a group of packets (a message). The M
bit is set whenever the buffer specified in a send() or write() system
call is larger than the maximum packet size, or when the X25_MDTF_BIT
is set in the ioctl(X25_SEND_TYPE) system call. Packets with the M bit
set are part of a larger message. The entire message must be read by a
single recv() or read() system call, or as a series of fragments when the
ioctl(X25_SET_FRAGMENT_SIZE) system call is used. This field cannot
be directly read or written by an application.
Send Sequence
Number
Indicates the sequence number of this packet. It is controlled by the
subsystem and cannot be read or written by the application.
User Data Contains the data being transmitted in this packet.
To read this field on an incoming packet:
Use the recv() or read() system calls to read this field.
To write this field on an outgoing packet:
Use the send() or write() system calls to write this field.
36960-90061.bk Page 123 Friday, November 10, 2000 3:42 PM