Multiplexer User's Guide
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Mux_guide_v06 Page 10 of 36 30.06.2004
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
Voice calls
incoming
outgoing
Data / fax calls
incoming
outgoing
SMS
incoming
outgoing
GPRS
connection
Phonebook
management
AT
commands
Channel 1 ! ! ! !2) ! !
Channel 2, 3 ! - ! !2) ! !1)
! indicates that the functionality is available on the channel
--- indicates that the functionality is not available on the channel
1) except for AT commands related to data and fax calls
2) only two channels can be used parallel to transmit GPRS data
Examples
• 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.
Note
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 [2].