> 5.5 | Siemens Multiplexer Protocol Version 4

> The major advantage of the proprietary Siemens multiplexer protocol version 4 is that it integrates the error recovery mechanism specified by the GSM 07.10 to provide better security: Modules with multiplexer protocol version 4 are using a different method of HDLC framing to enable more secure data transmission on the virtual ports and to avoid loss of data when using high data transfer rates and heavy data traffic. Multiplexer protocol version 4 also improves flow control.
> It is assumed that you are familiar with the GSM 07.10 specification and, in particular, its chapter 6 “Error recovery mode option”. Therefore, the present chapter discusses only the specifics of the Siemens implementation and the differences over GSM 07.10.