> 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 multiplex channels

> | Voice calls incoming outgoing | Data / fax calls incoming outgoing | SMS incoming outgoing | GPRS connection | Phonebook management | AT commands
> Channel 1 | • | • | • | •1 | • | •
> Channel 2, 3 | • | - | • | •1 | • | •2

> 1
> Only two channels can be used in parallel to transmit GPRS data
> 2
> Except for AT commands related to data and fax calls
> • indicates that the functionality is available on the channel
> - indicates that the functionality is not available on the channel
> 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.

> • | The battery capacity can be queried from channel 2 or 3 while a voice, fax or data call is made on channel 1.

> 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 Section 3.1 and in [2].