RS232 Multiplexer Feature
3-448 AT Commands Reference Manual June 30, 2008
MUX Customer Open Source Code Packet
The MUX is provided with an open source code packet to help speed the development process
and reduce the incompatible interpretations of the protocol specifications. This source code
packet is saved in the VOBS and supports both Basic and Advanced modes.
When implementing the MUX feature, the user should have the MUX entity installed with the
product. The following two MUX integration options are available to the user:
•MIP (Mux Integration Packet): The user receives the source code, which is provided by
Motorola, with known APIs for the MUX. The MIP is a Motorola open source code packet
for the GSM 27.010 protocol with API functions provided for the user.
•MUI (Mux User Implementation): The GSM 27.010 protocol is implemented by the user.
The MUI is the user implementation device for the GSM 27.010 protocol.
APIs
There are five API user integrations, as follows:
•Open service
•Close service
•Sending Data service
•Receiving Data service
•MUX service test, MSC, FC and so on (refers only to the control channel)
MUX Channels (Information Data Link Control - IDLC)
The following sections describe the MUX channels.

Basic MUX Channel Definitions

•Each MUX channel functions as a regular RS232 connection that follows ETSI 07.07 and
ITU V.25 standards. However, there are some limitations, as described in this paragraph.
•The G24 IDLC channel switches to Data mode as specified in ETSI 07.07 [4].
•When the MUX protocol layer releases the IDLC channel, any GPRS/DATA session or
established call is hung up. Only active voice calls remain connected.
•AT command requests by an IDLC may result in an ERROR, while in PREMUX state the
same request would never have returned an ERROR. This may happen because the addressed
resource in the G24 is busy with a second IDLC request. For example, if two channels send
the AT+CLIP? command, which addresses the GSM engine, only one channel receives the
+CLIP: response, while the other receives an ERROR.

Channel Priorities

The control channel has the highest priority. All other IDLCs have the same priority.
Note: All control frames are processed before any other channels. IDLC frame validation is also
performed after all control frames are processed.