Multiplexer User's Guide
Confidential / Released
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mobile
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
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 a data link frame.
Figure 3: Data link layer
Flag | Address | Control | Length | Information | FCS | Flag |
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1 Octet | 1 Octet | 1 Octet | 1 or 2 Octets | n Octets | 1 Octet | 1 Octet | of | ||
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Checksum for address, control and length fields, also for the information field in the case of UI frames FCS.
EA |
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Length: Length Information | |||
EA: | extension bit; | ||
| EA = 1 | ||
| EA = 0 | ||
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| SABM | Set Asynchronous Balanced Mode | |
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| UA | Unnumbered Acknowledgement | |
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| DM | Disconnected Mode | |
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| DISC | Disconnect | |
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| UIH | Unnumbered Information with Header check | |
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| UI | Unnumbered Information | |
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EA |
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| DLCI |
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DLCI: | Data Link Connection Identifier | ||||
C/R: | Command / Response | ||||
EA: | extension bit; EA = 1 | ||||
0xF9
Mux_guide_v06 | Page 17 of 36 | 30.06.2004 |