Multiplexer User's Guide
Confidential / Released
2.2 Virtual channels and AT commands
Please note that a cellular engine designed for multiplex operation does not include three
different devices. Only one single air interface (RF part) is available.
As mentioned before the multiplexer enables one serial interface to run three sessions
simultaneously. All incoming or outgoing calls are connected to the device.
Channel 1 supports the full range of functions, which is available without multiplexer tool.
Channel 2 and 3 are connected to a different AT interpreter and support a subset of the
functional range of channel 1, for more details refer to Table 1.
Table 1: Comparison of multiplexer channels
Channel 2, 3
indicates that the functionality is available on the channel
indicates that the functionality is not available on the channel
except for AT commands related to data and fax calls
only two channels can be used parallel to transmit GPRS data
While a data call is in progress on channel 1, you can send a short message on channel
2 and edit the phonebook on channel 3.
When receiving a fax on channel 1, you are able to check the battery capacity using the
appropriate AT command on channel 2 or 3.
Due to the technical requirements of multiplexer mode, data and fax calls can only be set up
on logical channel 1 while GPRS connections can be established on every channel. Several
AT commands have a different behavior on channels 2 and 3. Additional information
regarding restrictions and interferences between the channels can be found in chapter 3.1
and in .
Data / fax calls
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