Multiplexer User's Guide
Confidential / Released
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. The
non-error recovery mode was implemented with the basic option.
The frames have a start and a stop byte. A checksum is calculated to protect the transferred
data. Frame repetition is not enabled.
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
This chapter also discusses the following issues:
Opening logical channels without parameter negotiation
Opening logical channels with parameter negotiation
Closing of logical channels
4.2 Data link layer
show the detailed structure
a data link frame.
Figure 3: Data link layer
DLCI: Data Link Connection Identifier
Command / Response
extension bit; EA = 1
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1 or 2 Octets
Length: Length Information
EA = 1 -> 1 octet length information
EA = 0 -> >2 octets length information
SABM Set Asynchronous Balanced Mode
Unnumbered Information with Header check
P/F-Bit Poll- /Final - Bit
o b i l e
Checksum for address,
control and length
fields, also for the
information field in the
case of UI frames FCS.