> 3.1.2 | Restrictions

> If the GSM engine is operated in multiplexer mode, the following restrictions apply:

> • | MO and MT circuit-switched data and fax calls can only be set up on channel 1.

> • | It is not recommended to use AT+CFUN=<n> for selecting one of the SLEEP modes. For products supporting multiplexer protocol version 3 or 4, the best approach to properly control SLEEP mode in this case is to issue the PSC messages described in Section 4.3.10.

> • | During heavy traffic, the performance of the other multiplexer interfaces might be impaired. Some AT commands may behave differently than normal.

> The multiplexer cannot be started if one of the following features is activated, nor can these features be used when multiplexer is active:

> • | Multiplex mode cannot be started while autobauding (AT+IPR=0) is enabled.

> • | XON/OFF flow control is not supported in multiplexer mode.

> • | The multiplexer is not available in charge-only mode and in alarm mode (support of both modes is product specific).

> The maximum frame size N1 (defined in GSM 07.10) is fixed to 98 bytes and cannot be changed if the product supports multiplexer protocol versions 1 - 3. With multiplexer protocol version 4, the frame size is adjustable as described in Section 5.5.2. The maximum frame size is the same for sending and receiving. For general explanations regarding frames see also Chapter 4 in this manual and GSM 07.10.