riginator of the SABME command shall stop timer T320 and consider the DLC as established (i.e. enter the connected state) and inform the SU by using the L-ESTABLISH confirm primitive. Upon reception of a DM response, the originator of the SABME command shall inform its SU of a failure to establish the DLC (by issuing an L-RELEASE indication primitive). If timer T320 expires before the UA or DM response is received, the DLC entity shall retransmit the SABME command as above, restart timer T320 and increment the retransmis- sion counter. After retransmission of the SABME command N320 times and failure to receive a response, the DLC entity shall indicate this to the SU by means of the L-RELEASE indication primitive. The value of N320 is 3. 1 A data link connection can be established without being preceded by an XID procedure. 2 More than one DLC can run in parallel, numbered 0, 1 and SO on. This number is indicated in the L-ESTABLISH request. 28 Validation of Communications Systems with SDL 3.2.4 Information transfer modes Once in the connected state, information transfer may begin. 3.2.4.1 Transmitting I (Information) frames Data received by the DLC entity from the SU by means of an L-DATA request primitive shall be transmitted in an I frame3. 3.2.4.2 Receiving I frames When a DLC entity receives an I frame, it shall pass the information field of this frame to the SU using the L-DATA indication primitive. 3.2.5 Release of a DLC The SU requests release of a DLC4 by use of the L-RELEASE request primitive, then the DLC entity shall initiate a request for release of the connection by transmitting the disconnect (DISC) command. All outstanding L-DATA request primitives and all associated frames in queue shall be discarded. A DLC entity receiving a DISC command while in the connected state shall transmit a UA response. An L-RELEASE indication primitive shall be passed to the SU and the disconnected state shall be entered. If the originator of the DISC command receives either a UA response or a DM response, indicating tha