HP UX 11.x Operating Systems manual Introduction, Application Message Headers

Using HDLC.FRAME Protocol

Introduction

Introduction

For a complete description of the communications formats and protocol disciplines, the reader is referred to the ISO standard mentioned in the first chapter of this manual.

The HDLC.FRAME protocol is a non-polled, bit oriented protocol. Each unit transmitted over a Level 1 link is termed a frame. A frame consists of the following components:

•Opening flag (one byte binary 01111110)

•Data (supplied by higher layer)

•Frame check sequence (2 bytes)

•Closing flag (one byte binary 01111110).

A number of parameters can be configured to control the operation of ports which make use of the HDLC.FRAME protocol. These parameters are fully described in Chapter 4 , “Protocol Specific Configuration.”

Application Message Headers

The HDLC.FRAME protocol does not use application message headers. Both transmitted and received messages contain only the data portion of frames sent across the link. The protocol adds leading and trailing flags and the checksum to transmitted messages, and removes the same from received messages.

20 Chapter 3