ACC HDLC/LAP-B (ABM) User's Guide

Using HDLC/LAP-B (ABM) Protocol
Request Specific Processing
Chapter 3 33
Request Specific Processing
Control Requests
All control writes to this protocol share a common format as shown in
Figure 3-1. Control writes are issued to the card using the zcntl() API
call.
Figure 3-1 Control Request Format
The first four bytes are defined as a header:
Control Code Defines the action to be taken by this request.
Control Length The length of the data for this control request. This
data immediately follows the header.
Packet Length Some protocols allow packet data (data to be
transmitted over the wire) to be passed to a control
write following the control request data. For this
protocol, these two bytes must be zero because the
protocol does not allow packet data within a control
write.
15 10987654321011121314
Control Code Control Length
(0)Packet Length