> 4 | Structure of the Multiplexer Protocol

> 4.1 | Introduction of the Multiplexer Protocol

> The supported multiplexer protocol conforms to the GSM 07.10 Multiplexer Protocol. Multiplexer protocol version 1 - 3 supports the non-recovery mode available with the basic option of the multiplexer described in GSM 07.10. The proprietary Siemens multiplexer protocol version 4 enables an error recovery mode which is a subset of the GSM 07.10 advanced option and is designed to provide good performance at low CPU usage. See Section 5.5 for further detail.
> The frames have a start and a stop byte. A checksum is calculated to protect the transferred data.
> Data and fax calls are transferred in the logical channel DLCI = 1 (DLCI: Data Link Connection Identifier). The remaining DLCIs are in AT command mode; two GPRS connections can be established simultaneously on every channel. The multiplexer protocol must be started and the logical channels opened in compliance with specified procedures.
> This chapter also discusses the following issues:

> • | Opening logical channels without parameter negotiation

> • | Opening logical channels with parameter negotiation

> • | Closing of logical channels