HP X.25/9000 Programmer's Guide

Chapter 4 55

Sending and Receiving Data

Data Transmission Requirements

time in the CALL REQUEST or CALL ACCEPTED packet.

Setting the D Bit in CALL REQUEST Packets

Use the ioctl(X25_SEND_TYPE) call to set the D bit in a CALL

REQUEST packet. After the D bit is set, issue the connect() call to

transmit the CALL REQUEST packet.

After the connect() call, turn the D bit off again by issuing an

ioctl(X25_SEND_TYPE) call so that the next message does not have its

D bit set. Refer to “Controlling the MDTF, D, and Q bits” below for the

syntax for ioctl(X25_SEND_TYPE)

Setting the D Bit in CALL ACCEPTED Packets

To set the D bit in CALL ACCEPTED packets:

1. First set the listen socket so that transmission of the CALL

ACCEPTED packet is controlled by the application. Use the

ioctl(X25_CALL_ACPT_APPROVAL) call.

2. When the accept() call returns, issue ioctl(X25_SEND_TYPE) on

the VC socket to set the D bit for the transmission of the CALL

ACCEPTED packet.

3. Finally, send the CALL ACCEPTED packet with the

ioctl(X25_SEND_CALL_ACEPT) call.

Turn off the D bit with the ioctl(X25_SEND_TYPE) call after the

ioctl(SEND_CALL_ACEPT) call. Otherwise, the next message you send

will have the D bit set. Refer to “Controlling the MDTF, D, and Q bits”

below for the syntax for ioctl(X25_SEND_TYPE)

Setting the D Bit in a Data Message

To use the D bit in a DATA packet, the D bit must have been set at

connection time in either the CALL REQUEST packet (on the calling

side) or the CALL ACCEPTED packet (on the called side).

Issue the ioctl(X25_SEND_TYPE) call to set the D bit immediately prior

to issuing a send() or write() call. In blocking mode, the process is

blocked until conﬁrmation is received. If the connection has been

established to use the D bit, the application can set the D bit for any data

message being transmitted. A data message may be a single packet or a

set of packets with the M bit set on all but the last packet.

The D bit is set on every data message transmitted until it is cleared

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