> 3.1.5 | Timing Conditions

> Switching on the multiplexer with AT+CMUX=0 causes a 5s timer to start. If the multiplexer control channel is not established within this time, the module returns to “normal AT command mode” without multiplexer. This prevents the module from being blocked if, for example, AT+CMUX=0 is sent from an application that does not support the multiplexer protocol.
> Fax is based on a protocol, which needs to respect timings between the application and the module as well as between the module and the selected terminal equipment (TE). Hence, heavy parallel traffic load in the module can lead to mistiming. This may result in malfunction in both directions. Please consider the following recommendations:
> Using the multiplexer it is not possible to define bandwidth and delay time per channel. Therefore, the customer application should take care that the channels 2 and 3 are not heavily loaded when faxing on channel 1.
> Example 1: Checking the field strength every 2 seconds does not harm, sending an SMS every 10 seconds may lead to problems.
> Example 2: Reading a complete phone book, may cause problems if a fax transmission is ongoing at the same time.
> When switching on the module after a firmware update we recommend to wait 5 seconds before entering the first AT command.