Multiplexer User's Guide
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mo b i l e
Mux_guide_v06 Page 17 of 36 30.06.2004
Address
1 Octet
Control
1 Octet
Flag
1 Octet
0xF9
DLCI
DLCI: Data Link Connection Identifier
C/R: Command / Response
EA: extension bit; EA = 1
Frame type:
SABM Set Asynchronous Balanced Mode
UA Unnumbered Acknowledgement
DM Disconnected Mode
DISC Disconnect
UIH Unnumbered Information with Header check
UI Unnum bered Information
P/F-Bit Poll- /Final - Bit
Length
1 or 2 Octets
Information
n Octets
FCS
1 Octet
Flag
1 Octet
0xF9
Checksum for address,
control and length
fields, also for the
information field in the
case of UI frames FCS.
LengthEA
Length:Length Information
EA: extension bit;
EA = 1 -> 1 octet length information
EA = 0 -> >2 octets length information
EA C/R
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
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
4.2 Data link layer
The following sections
show the detailed structure of
a data link frame.
Figure 3: Data link layer