Multiplexer User's Guide
Confidential / Released
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mobile
4.2.1 Flag sequence
A flag sequence is a specific bit pattern (usually 11111001; hexadecimal: 0xF9) used to mark the beginning and the end of a frame of data.
Each frame begins and ends with a flag sequence. Only one flag sequence occurs between any two frames. If two successive flag sequences do occur, the frame is regarded as being empty and is discarded.
The flag sequence is used for the synchronization of frames.
4.2.2 Address field
Data link connection identifier is a frame relay term defining a
The values for the Data Link Connection Identifier (DLCI) are dynamically defined apart from DLCI = 0.
Table 2: Address field
EA
C/R
DLCI
DLCI: | Data Link Connection Identifier |
C/R: | Command / Response |
EA: | extension bit; EA = 1 |
Table 3: Assignment of the DLCI
|
|
| DLCI number (decimal) | Priority |
|
|
|
|
|
Multiplexer | control | channel | 0 | 0 |
(see chapter 4.3.6) |
|
| highest priority | |
|
|
|
| |
|
|
| ||
AT commands, data, fax, GPRS | 1 | 7 | ||
|
|
|
| |
AT commands, GPRS |
| 2,3 | 7 | |
|
|
|
|
|
The command/response bit identifies the frame as a command or response. A command contains the address of the data link connection to which the command is sent. A response contains the address of the data link connection sending the frame.
Table 4: Use of the command/response bit
Command/Response | Direction |
|
| C/R |
|
|
|
| |
Command | Customer µC | → GSM engine | 1 | |
(SABM, DISC) |
|
|
|
|
GSM engine | → | Customer µC | 0 | |
|
|
|
|
|
Response | Customer µC | → | GSM engine | 0 |
(UA, DM) |
|
|
|
|
GSM engine | → | Customer µC | 1 | |
|
|
|
|
|
Every command expects a response. No provision is made to repeat the command if no response is received.
Mux_guide_v06 | Page 18 of 36 | 30.06.2004 |
