5i' ANNEX D (to Recommendation Q.921) State transition table of the point-to-point procedures of the data link layer D.1 The state transition table presented in Tables D-1/Q.921 to D-3/Q.921 is based on the eight basic states (see S B.2) recog- nized in the SDL representation and the related transmitter and receiver conditions. The state transition table relinquishes to any partitioning of the procedures. It is conceptual and does not prevent a designer from partitioning in his implementation. Moreover, all the processes related to primitive procedures, the management of queues and the exchange of information between adjacent layers are concep- tual, not visible from outside of the system and would not impose any constraints on the implementation. The eight basic states apply to both the transmitter and the receiver within one data link layer entity. However, some of the conditions are confined to the transmitter (e.g. "peer receiver busy"), whilst some are confined to the receiver (e.g. "REJ recovery"). This implies, if the concept of non-partitioning is adopted, that each transmitter condition has to be combined with each receiver condition resulting in composite states. This state transition table comprises 24 composite states representing the 8 basic states and the related combinations of transmitter and receiver conditions. Events are defined as follows: a) primitives; b) repertoire of frames to be received; - unnumbered frames (SABME, DISC, UA, DM, UI, FRMR) - supervisory frames (RR, REJ, RNR) - information frame (I); c) internal events (servicing of queues, expiry of timers, receiver busy condition). The actions to be taken when an event occurs whilst in a specific state comprise: i) transition to another state ii) peer-to-peer frame to be transmitted iii) primitives to be issued iv) timer actions v) retry counters vi) state variables vii) P/F bit setting viii) discarding contents of queues. D.2 Key to the state transition table D.2.1 Definition of a cell of the state transition table Diagram [T17.921], p. D.2.2 Key to the contents of a cell | Impossible by the definition of the data link layer service. / Impossible by the definition of the peer-to-peer data link procedures. - No action, no state change. V(S) = V(A) = N(R) Collective term for the two actions V(S) = N(R) and V(A) = N(R). Timer T200 Start timer T200 if not already running. TX ACK The acknowledgement of the received I frame may be conveyed by an I frame associated with the information flow in the opposite direction or a supervisory response frame, as appropriate. "DISCARD" Indicates the discarding of the informa- tion contained in the information field of the I frame. (A-O) The codes used in MDL-ERROR-INDICATION sig- nals are defined in Table II-1/Q.921 in Appendix II. When multiple codes are shown, only one applies. Diagram [T18.921] + Note, p. blanc H.T. [1T19.921] _________________________________________________ TABLE D-1/Q.921 (1 of 10) { State transition table: receiving primitive } _________________________________________________ | | | | | | | | | | BASIC STATE TEI UNASSIGNED ASSIGN AWAITING TEI ESTABLISH AWAITING TEI TEI ASSIGNED AWAITING ESTABLISHMENT AWAITING RELEASE RECEIVER CONDITION See Note STATE NUMBER 1 2 3 4 5.0 5.1 5.2 6 DL-ESTABLISH-REQUEST { MDL-ASS-IDN | | | | 3 } | | | | | | 3 I { RC=0 TX SABME P=1 START T200 5.0 } I { | | DISC. I QUEUE | | 5.0 } I I ______________________________________________________________________________________________________________________________________________________________________________________________ DL-RELEASE-REQUEST I I I DL-REL-CONF I | | 5.2 I I ______________________________________________________________________________________________________________________________________________________________________________________________ DL-DATA-REQUEST I I I I I DATA INTO I QUEUE I I ______________________________________________________________________________________________________________________________________________________________________________________________ I FRAME IN QUEUE V(S)