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) V(M)], then set V(M) equal to the N(S) of the received frame. Blanc APPENDIX II (to Recommendation Q.921) Occurrence of MDL-ERROR-INDICATION within the basic states and actions to be taken by the management entity II.1 Introduction Table II-1/Q.921 gives the error situations in which the MDL-ERROR-INDICATION primitive will be generated. This primitive notifies the data link layer's connection management entity of the occurred error situation. The associated error parameter contains the error code that describes the unique error conditions. Table II-1/Q.921 also identifies the associated connection manage- ment actions to be taken from the network and the user side, based on the types of error conditions reported. This appendix does not incorporate the retransmission of REJ response frames described in Appendix I. II.2 Layout of Table II-1/Q.921 The "Error code" column gives the identification value of each error situation to be included as a parameter with the MDL-ERROR-INDICATION primitive. The column entitled "Error condition" together with the "Affected states" describes unique protocol error events and the basic state of the data link layer entity at the point that the MDL-ERROR-INDICATION primitive is generated. For a given error condition, the column entitled "Network management action" describes the preferred action to be taken by the network management entity. The column entitled "User management action" describes the preferred action to be taken by the user side management entity on a given error condition. II.3 Preferred management actions The various preferred layer management actions on an error situation may be described as one of the following: a) Error log This suggests that the network side connection management entity has the preferred action of logging the event into an error counter. The length and the operation of the counter mechanisms for the error situations is implementation dependent. b) TEI check This means that the network side layer management entity invokes the TEI check procedure. c) TEI verify This means that the user side layer management entity may optionally invoke a TEI verify request procedure that asks the net- work side layer management entity to issue a TEI check procedure. d) TEI remove This means that the user side layer management entity may directly remove its TEI value from service. In most of the described error situations, there is either no action to be taken on the user side layer management or the action to be taken is implementation dependent, as Table II-1/Q.921 shows. "Implementation dependent" means that it is optional whether the user side layer management has incorporated any form of error counter to log (store) the reported event. If action is taken, the layer management has to take into account that the data link layer will have initiated a recovery procedure. Blanc H.T. [T22.921] TABLE II-1/Q.921 Management Entity Actions for MDL Error Indications ____________________________________________________________________________________ Error Type Error Code Error Condition { Affected states (See Note 1) } { Network Management Action } { User Management Action } ____________________________________________________________________________________ { ____________________________________________________________________________________ Unable to convert table ____________________________________________________________________________________ | | | | | | | | | | | | | | | | | | | | | | | | | | | | Table II-1/Q.921 [T22.921] + Notes, p. Blanc APPENDIX III (to Recommendation Q.921) Optional basic access deactivation procedures III.1 Introduction This appendix provides one example of a deactivation procedure which can be used by the network side system management to control deactivation of the access. Figure III-1/Q.921 provides a concep- tual model of the interactions which are required for this deac- tivation procedure. Figure III-1/Q.921, p. III.2 Description of the Conceptual Model The monitor function uses layer 2 activity as the basis for establishing whether deactivation of the access can take place. The signal INFORMATION is used to report the layer 2 activity in the following manner: - INFORMATION (FREE) indicates that there is no data link connection in the multiple-frame mode of operation; - INFORMATION (IN USE) indicates that there is at least one data link connection in the mode-setting or multiple-frame mode of operation; and - INFORMATION (UNIT DATA) indicates that a UI frame is about to be transmitted, or has just been received. Within the data link layer entity the DL-ESTABLISH-REQUEST/INDICATION primitives and DL-RELEASE-INDICATION/CONFIRM mark the duration of the multiple-frame mode of operation, and the MDL/DL/UNIT DATA-REQUEST/INDICATION primitives mark the transmission and recep- tion of UI frames. A signal Status is used to represent the ability of higher layers to enable or disable the deactivation procedures: - STATUS (ENABLE) deactivation procedures enabled; and - STATUS (DISABLE) deactivation procedures dis- abled. The MPH-DEACTIVATE-REQ, MPH-DEACTIVATE-IND and MPH-ACTIVATE-IND primitives are used as described in S 4. The definition and usage of these primitives are also described in Recommendation I.430 [4] which specifies layer 1. Since, in Recommendation I.430, the usage of the MPH-DEACTIVATE-IND primitive is an implementation option, two cases of deactivation are described below. S III.3 provides a description of the deactivation procedure when the MPH-DEACTIVATE-IND primitive is delivered to the system management entity. S III.4 provides a description of the deactivation procedure when the MPH-DEACTIVATE-IND primitive is not delivered to the sys- tem management entity. Note - These procedures require that all layer 3 entities making use of the acknowledged information transfer service, must release the data link connection at an appropriate point after the completion of the information transfer. III.3 Deactivation procedure with MPH-DEACTIVATE-IND This deactivation procedure makes use of the MPH-DEACTIVATE-IND primitive to provide an option of layer 1 imple- mentation. Figure III-2/Q.921 provides a state transition diagram of the deactivation procedure with the MPH-DEACTIVATE-IND primitive. This deactivation procedure can be represented by six states: State 1 Information transfer not available and free; (No info xfer and free ) State 2 Information transfer available and free; (Info xfer and free ) State 3 Information transfer available and in use; (Info xfer and in use ) State 4 Information transfer not available and in use; (No info transfer and in use ) State 5 Information transfer interrupted and free; (Info interrupted and free ) State 6 Information transfer interrupted and in use; (Info interrupted and in use ) These six states are described as follows: - State 1 represents the state where the access is assumed to be deactivated and no data link connections are in a mode setting or multiple-frame mode of operation. - State 2 represents the state where the access is activated and no data link connection is in a mode setting or multiple-frame mode of operation. Timer TM01 is running, and upon its expiry, if deactivation is enabled, then an MPH-DEACTIVATE-REQ primitive may be issued to layer 1. The access is then assumed to be deactivated. - State 3 represents the state where the access is activated and at least one data link connection is in a mode set- ting or multiple-frame mode of operation. - State 4 represents the state where the access is regarded as being in an transient state (neither deactivated nor activated) and at least one data link connection is in a mode set- ting or multiple-frame mode of operation. [This state can be entered, for example, due to the arrival of an INFORMATION (IN USE) signal before an MPH-ACTIVATE-IND primitive.] - State 5 represents the state where the access is regarded as being in a transient state (neither deactivated nor activated) and no data link connection is in a mode setting or multiple-frame mode of operation. Timer TM01 is running and upon its expiry, if deactivation is enabled, then an MPH-DEACTIVATE-REQ primitive will be issued to layer 1. The access is assumed to be deactivated. - State 6 represents the state where the access is regarded as being in the transient state (neither deactivated nor activated) and at least one data link connection is in a mode set- ting or multiple frame mode of operation. Timer TM01 is started whenever state 2 is entered: - on receipt of an MPH-ACTIVATE-IND primitive in state 1; and - on receipt of an INFORMATION (FREE) signal in state 3. Timer TM01 is started whenever state 5 is entered: - on receipt of an INFORMATION (FREE) signal in state 6. Timer TM01 is restarted in states 2 and 3 when: - TM01 expires while deactivation is disabled by the receipt of a STATUS (DISABLE) signal; and - an INFORMATION (UNIT DATA) signal is received in order to allow sufficient time for current and further unack- nowledged information transfer. Timer TM01 has a value of ten seconds at the network side. Blanc Figure III-2/Q.921, p. III.4 Deactivation procedure without MPH-DEACTIVATE-IND This deactivation procedure does not make use of the MPH-DEACTIVATE-IND primitive to provide an option of layer 1 imple- mentation. Thus this procedure can be represented by only four states, i.e. state 1, state 2, state 3, and state 4. States 5 and 6 have disappeared. Figure III-3/Q.921 provides a state transition diagram of this deactivation procedure without the MPH-DEACTIVATE-IND primitive. Figure III-3/Q.921, p. APPENDIX IV (to Recommendation Q.921) Automatic negotiation of data link layer parameters IV.1 General Each data link layer entity has an associated data link con- nection management entity. The data link connection management entity has the responsibility for initializing the link parameters necessary for correct peer-to-peer information transport. The method of initialization of the parameters follows one of the two methods below: - initialization to the default values as specified in S 5.9; or - initialization based on the values supplied by its peer entity. The latter method utilizes the parameter negotiation procedure described in this appendix. Typically, after the assignment of a TEI value to the management entity, the data link connection management entity is notified by its layer management entity that parameter initialization is required. The data link connection management entity will invoke the peer-to-peer notification procedure the data link connection management entity will notify the layer management entity that parameter initialization has occurred, and the layer management entity will issue the MDL-ASSIGN-REQUEST. IV.2 Parameter initialization The parameter initialization procedure may invoke either the internal initialization procedure or the automatic notification of data link parameter procedure. IV.3 Internal parameter initialization When the layer management entity notifies the connection management entity of TEI assignment, the connection management entity shall initialize the link parameters to the default values and notify the layer management of task completion. IV.4 Automatic notification of data link layer parameter values For each data link layer an exchange of certain data link layer parameters may take place between the peer data link connec- tion management entities before entering the TEI-assigned state. This exchange may be initiated after acquiring a TEI, that is, after: - receipt of a DL-ESTABLISH-REQUEST or a DL-UNIT DATA-REQUEST primitive following a power-up condition associated with non-automatic TEI user equipment. - receipt of the Identity assigned response for automatic TEI assignment user equipment. This message contains the TEI received by the layer management entity. The data link connection management entity, following assign- ment of a TEI from the layer management entity, shall issue an XID command with the P bit set to 0 and containing the parameter mes- sage shown in Figure IV-1/Q.921, and start the connection manage- ment timer TM20. The I field of the XID command frame shall reflect the parame- ters desired for future communications across this data link layer connection. The peer data link connection management entity, upon receipt of this XID command frame, shall transmit an XID response with the F bit set to 0 containing the list of parameter values that the peer can support. If the data link connection management entity receives the above XID response prior to expiry of timer TM20, it shall stop the timer, and shall notify the layer management entity of a successful parameter exchange. However, if timer TM20 expires before receiving the XID response, the data link connection management entity shall retransmit the XID command, increment the retransmission counter and restart timer TM20. This retransmission process is repeated if timer TM20 expires again. Should the retransmission counter equal NM20, or an XID response frame with a zero length I field be received, the data link connection management entity shall issue an indication to the layer management entity and initialize the param- eters to the default values. The layer management entity may log this condition and then issue the MDL-ASSIGN-REQUEST primitive to the data link layer. The timer TM20 is set to 2.5 seconds and NM20 is set to 3. Figure IV-3/Q.921 [T23.921], p. ABBREVIATIONS AND ACRONYMS USED IN RECOMMENDATION Q.921 Abbreviation Meaning of acronym Ai Action indicator ASP Assignment source point CEI Connection endpoint identifier CES Connection endpoint suffix C/R Command/response field bit DISC Disconnect DL- Communication between Layer 3 and data link layer DLCI Data link connection identifier DM Disconnected mode EA Extended address field bit ET Exchange termination FCS Frame check sequence FRMR Frame reject I Information ID Identity ISDN Integrated Services Digital Network L1 Layer 1 L2 Layer 2 L3 Layer 3 LAPB Link access procedure - Balanced LAPD Link access procedure on the D-channel M Modifier function bit MDL- Communication between management entity and data link layer MPH- Communication between system management and physical layer N(R) Receive sequence number N(S) Send sequence number P/F Poll/Final bit PH- Communication between data link layer and physical layer RC Retransmission counter REC Receiver REJ Reject Ri Reference number RNR Receive not ready RR Receive ready S Supervisory S Supervisory function bit SABME Set asynchronous balanced mode extended SAP Service access point SAPI Service access point identifier TE Terminal equipment TEI Terminal endpoint identifier TX Transmit U Unnumbered UA Unnumbered acknowledgement UI Unnumbered information V(A) Acknowledge state variable V(M) Recovery state variable V(R) Receive state variable V(S) Send state variable XID Exchange identification References [1] CCITT Recommendation Q.920 (I.440), ISDN user-network _________________________ A different acronym has to be found for Supervisory function bit. interface data link layer - General aspects . [2] CCITT Recommendation Q.930 (I.450), ISDN user-network interface layer 3 - General aspects . [3] CCITT Recommendation Q.931 (I.451), ISDN user-network interface layer 3 specification . [4] CCITT Recommendation I.430, Basic user-network inter- face layer 1 specification . [5] CCITT Recommendation I.431, Primary rate user-network interface layer 1 specification . [6] CCITT Recommendation X.25, Interface between data ter- minal equipment (DTE) and data circuit terminating equipment (DCE) for terminals operating in the packet mode and connected to public data networks by dedicated circuit . MONTAGE: PAGE PAIRE = PAGE BLANCHE