Multiplexer User's Guide
Confidential / Released
2 Multiplexer protocol – an overview
2.1 Product concept and architecture
The multiplexer mode enables one serial interface to transmit data to three different custo-
mer applications. This is achieved by providing three virtual channels using a
This is especially advantageous when a fax/data/GPRS call is ongoing. Using the multiplexer
features, e.g. controlling the module or using the SMS service can be done via the additional
channels without disturbing the data flow; access to the second UART is not necessary.
Furthermore, several accesses to the module can be created with the multiplexer. This is of
great advantage when several independent electronic devices or interfaces are used.
To access the three virtual interfaces, both the GSM engine and the customer application
must contain Mux components which communicate over the multiplexer protocol.
In multiplexer mode, AT commands and data are encapsulated into packets. Each packet
has a channel identification and may vary in length.
All statements regarding GPRS are valid only for Siemens wireless products capable of
or internal programs
integrated in cus-
to GSM 07.10
Figure 1: Multiplexer architecture
Page 9 of 36
to GSM 07.10
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