Multiplexer User's Guide
Confidential / Released
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mobile
4.3.1 Start-up procedure
The only approach to activate the multiplexer protocol is entering the appropriate AT command AT+CMUX=0. This enables the multiplexer control channel. The next step is to set up the multiplexer control channel as described in Chapter 4.3.2.
4.3.2 DLC establishment
The multiplexer control channel must be set up as the first channel followed by all other DLCIs. To do so, a SABM frame (see Chapter 4.2.3) must be sent to the GSM engine.
The module responds either with a UA frame if the DLCI was set up, or with a DM frame if the DLCI was not set up.
No provision is made for repeating the request if a response is not received.
The state machine requesting the multiplexer control channel DLCI = 0 is the "initiating station", while the other is called the "responding station".
Customer
µC
SABM: P = 1
Address Field = DLCI of channel to be established
UA: F = 1, DLCI is being established
DM: F = 1, not ready, DLCI is not established Address Field = DLCI of requested channel
GSM
engine
Figure 7: DLC establishment
4.3.3 Information transfer
A response is not essential for every command – for example, an unsolicited result code does not require a response.
Customer | UIH: | P = 0, C/R = 1 | |
| GSM engine | ||
µC |
| ||
| (Responder) | ||
(Initiator) |
| ||
UIH: | P = 0, C/R = 0 | ||
|
Figure 8: Information transfer
Mux_guide_v06 | Page 25 of 36 | 30.06.2004 |