> 4.2.2 | Address Field

> Data link connection identifier is a frame relay term defining a 10-bit field of the address field. The DLCI identifies the data link and its service parameters, including the frame size.
> The values for the Data Link Connection Identifier (DLCI) are dynamically defined apart from DLCI = 0.
> Figure 4: Address field

> Table 3: | Assignment of the DLCI

> | DLCI number (decimal) | Priority
> Multiplexer control channel (see Section 4.3.6) | 0 | 0 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 (SABM, DISC) | Customer µC → Module | 1
> Module → Customer µC | 0
> Response (UA, DM) | Customer µC → Module | 0
> Module → Customer µC | 1

> Every command expects a response. No provision is made to repeat the command if no response is received.