 Figure 3.3 Conventions used for signal naming A request on one side is generally followed by an indication on the other side of the con- nection; then, if the layer above accepts, it transmits a response, translated into a confirm on the side originator of the request. 3.2 SPECIFICATION OF THE V.76 PROTOCOL 3.2.1 Abbreviations used DISConnect Data Link Connection entity Disconnect Mode The V.76 Protocol Case Study 27 Information SABME SET ASYNCHRONOUS BALANCED MODE EXTENDED Service User eXchange IDentification 3.2.2 Exchange identification procedures (XID) Upon receipt of an L-SETPARM request primitive from its SU (the layer on top of V.76), the DLC entity shall transmit an XID command frame. On receipt of an XID command frame, the DLC shall issue an L-SETPARM indication primitive to its SU. Upon receipt of an L-SETPARM response primitive from its SU, the DLC shall transmit an XID response frame. On receipt of an XID response frame, the DLC shall inform its SU by an L-SETPARM confirm primitive. 3.2.3 Establishment of a data link connection Establishing a DLC2 means going from a disconnected to a connected state to allow the transfer of user data. On receipt of an L-ESTABLISH request primitive from its SU, the V.76 shall attempt to establish the DLC. The DLC entity transmits a Set Asynchronous Balanced Mode Extended (SABME) frame, the retransmission counter shall be reset and timer T320 shall then be started. A DLC entity receiving an SABME command, if it is able to establish the DLC (as indi- cated by receipt of an L-ESTABLISH response primitive from the SU in response to an L-ESTABLISH indication primitive), shall respond with an Unnumbered Acknowledge (UA) response; consider the DLC as established and enter the connected state. If the SU is unable to accept establishment of the DLC (as indicated by an L-RELEASE request primitive from the SU in response to an L-ESTABLISH indication primitive), the DLC entity shall respond to the SABME command with a Disconnect Mode (DM) response. Upon reception of the UA, the o