Introduction

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

The HDLC-NRM (SDLC) protocol is a polled, bit oriented protocol. Each unit transmitted over an HDLC-NRM (SDLC) link is termed a frame. A frame consists of the following components:

The frame type is encoded in the control field. There are three types of frames:

Each line used for HDLC-NRM (SDLC) protocol has a primary and secondary end. The primary station (end) polls the secondary stations. The primary station sends frames to the secondary station. When a frame with the “poll bit” is sent to a secondary station, this station is allowed to send information frames to the primary station. When it has no more frames to send, the secondary sends a frame with the “final bit” set. The primary can then send a frame containing the poll to another secondary station on the line.

A number of parameters can be configured to control the operation of primary and secondary stations defined via the HDLC-NRM (SDLC) protocol. These parameters are fully described in Chapter 4 “Protocol Specific Configuration”