User's Manual

Chapter 3 29

Using HDLC/LAP-D Protocol

Request Specific Processing

Terminal Enable/Disable R equests

Enabling a non-UI terminal causes the protocol to attempt to enter

multiple frame acknowledged operation (the state that allows

Information frames to be exchanged). Di sabling a terminal causes the

non-UI terminal to exit multiple frame acknowledgedoperation. A newly

created terminal is initially disabled. Enabling/disabling UI terminals

simply allows/disallows the transmission and reception of UI frames.

These requests cause unsolicited status messages to be sent by the

protocol. For details regarding status codes and messages, see “Status

and Error Messages”, later in this chapter.

Terminal Activate/Deactivate Requests

Activating a non-UI terminal allows t he terminal to receive data (the

protocol sends Receive Ready frames to indicate it is ready to receive

Information frames). Deactivating the terminal prevents the terminal

from receiving data (the p rotocol send Receive Not Ready frames). A

newly created terminal is initially deactivated. For UI terminals , these

requests only toggle the terminal activated flag; they do not affect the

reception of data .

Write (Transmit) Requests

The data sent to the protocol via a write request becomes the information

field within an I-frame or UI-frame.

The terminal must be enabled before any write requests may be sent to

the terminal. In addition, for an Information frame to be sent, multiple

frame acknowledged operation must have been established.