Technical information

Table Of Contents
Appendix B: MUX
January 31, 2007 AT Commands Reference Manual B-5
Advance Mode Frame Unpacking
The receiver (referring to the receiver of a frame) examines the frame between the two flag octets.
Upon receipt of a control escape octet, and prior to FCS calculation, it does the following:
Discards the control escape octet.
Restores the octet that immediately follows by complementing its 6th bit (XOR with 0x20).
MUX State Procedures
Valid channel indexes in MUX state are 0 to 4, where 0 is the index of the control channel and
1-4 are indexes of the information channels (IDLC).
The following table describes the basic procedures (Open/Close/Err) performed when the G24 is
in MUX state.
Table B-3: MUX State Procedures
Procedure Description
Unrecognized
Frames/Invalid Frames
The G24 ignores unrecognized and invalid frames.
SABMi Reception –
Channel Establishment
Upon receiving a SABMi frame (i = channel index), the G24 checks
whether i is within the valid range and is not already established. It them
tries to establish the new channel.
If the G24 succeeds, it sends a UA frame. If it is not successful, it sends
a DM frame.
DISCi Reception –
Disconnect Channel
Upon receiving a DISCi frame (i = channel index), the G24 checks
whether i is within the valid range and represents an open channel. If so,
the G24 attempts to close the channel.
If the G24 is successful, it sends a UA frame. If it is not successful, it
sends a DM frame.
Closing a channel hangs up any active CDSs. However, active voice
calls are not hung up, even after the IDLC is closed. Any other AT
command can continue to control the voice call.