ANNEX B
(to Recommendation Q.764)
State transition diagrams
	Note – Should any conflict arise between the text and the SDL definition, the textual description is taken as definitive.
B.1	General
	This Annex contains the description of the signalling procedures described in this Recommendation in the form of state transition diagrams according to the CCITT Specification and Description Language (SDL). In order to facilitate functional description, the ISDN User Part (ISDN–UP) signalling procedure is divided into main functional blocks, as shown in Figure B–1/Q.764. These blocks are as follows:
1)	Signalling procedure control (SPRC)
	SPRC provides procedures for sending ISDN–UP messages to Level 3 (SCCP or MTP) and distributing received messages to the other ISDN–UP functional blocks.
2)	Call processing control (CPC)
CPC provides call control procedures for realizing basic circuit switched service according to user's request.
3)	Circuit supervision control (CSC)
	CSC provides procedures for circuit supervision control for maintenance purpose and for recovery from abnormal situation.
B.2	Drafting convention
a)	External inputs and outputs are used for interactions with a remote exchange and interaction between SPRC and the other functional blocks. Internal inputs and outputs are used for interactions within each functional block, e.g., to indicate control of time–out. For these interactions, input and output symbols are used as shown in Figure B–2/Q.764.
b)	Inputs and outputs symbols contain as part of their name acronyms of their source and destination functional block names with an arrow in between, e.g., Blocking BLS -> CPC.
c)	A simple example of SDL diagram according to the above conventions is shown in Figure B–3/Q.764.
B.3	Abbreviations, timers and primitives
B.3.1	Abbreviations
1)	Table B–1/Q.764:
Signalling procedure control.
2)	Table B–2/Q.764:
Call processing control.
3)	Table B–3/Q.764:
Circuit supervision control.
B.3.2	Timers
	Timers used in the ISDN–UP SDL diagrams are shown in Table B–4/Q.764.
B.3.3	Primitives
	Primitives used over the interface between call control and ISDN–UP are shown in Table B–5/Q.764.
B.4	State transition diagrams and SDL diagrams
	Each ISDN–UP main functional block is further subdivided into the functional blocks. Functional diagrams and simple state transition diagrams for each main functional block are shown below:
1)	Signalling procedure control (SPRC)
–	Figure B–4/Q.764
	Functional diagrams
–	Figure B–5/Q.764
	State transition diagrams
2)	Call processing control (CPC)
–	Figure B–6/Q.764
	Functional diagrams
–	Figures B–7/Q.764 to B–9/Q.764
	State transition diagrams
3)	Circuit supervision control (CSC)
–	Figure B–10/Q.764
	Functional diagrams
–	Figures B–11/Q.764 to B–18/Q.764
	State transition diagrams
	The ISDN–UP SDL diagrams are described based on the three–blocks approach. In this approach, call control, which provides signalling–independent functions such as connect–through, circuit selection and digits analysis, is outside the ISDN–UP. These functions are described only in §§ 1–3. The ISDN–UP diagrams are provided for the above subdivided functional blocks, as shown below:
1)	Signalling procedure control (SPRC)
–	Figure B–19/Q.764
	Message sending control
–	Figure B–20/Q.764
	Message distributing control
2)	Call processing control (CPC)
–	Figure B–21/Q.764
	Call processing control incoming (CPCI)
–	Figure B–22/Q.764
	Call processing control outgoing (CPCO)
–	Figure B–23/Q.764
	Continuity check incoming (CCI)
–	Figure B–24/Q.764
	Continuity check outgoing (CCO)
3)	Circuit supervision control (CSC)
–	Figure B–25/Q.764
	Blocking/unblocking message sending (BLS)
–	Figure B–26/Q.764
	Blocking/unblocking message reception (BLR)
–	Figure B–27/Q.764
	Maintenance oriented circuit group blocking/unblocking sending (MGBS)
–	Figure B–28/Q.764
	Blocking/unblocking reception (MGBR)
–	Figure B–29/Q.764
	Hardware failure oriented locally blocking state (HLB)
–	Figure B–30/Q.764
	Hardware failure oriented remotely blocking state (HRB)
–	Figure B–31/Q.764
	Hardware failure oriented circuit group blocking/unblocking sending (HGBS):
–	Figure B–32/Q.764
	Hardware failure oriented circuit group blocking/unblocking reception (HGBR)
–	Figure B–33/Q.764
	Circuit reset sending (CRS)
–	Figure B–34/Q.764
	Circuit reset reception (CRR)
–	Figure B–35/Q.764
	Circuit group reset sending (CGRS)
–	Figure B–36/Q.764
	Circuit group reset reception (CGRR)
–	Figure B–37/Q.764
	Continuity recheck sending (CRCS)
–	Figure B–38/Q.764
	Continuity recheck reception (CRCR)
–	Figure B–39/Q.764
	Circuit group query sending (CQS)
–	Figure B–40/Q.764
	Circuit group query reception (CQR)
Figure B–1/Q.764 - T1116960-88

Figure B–2/Q.764 - T6970-88

Figure B–3/Q.764 - T1116980-88

TABLE B–1/Q.764
Signalling procedure control acronym
	Acronym	 Description	
	BLR	Blocking/Unblocking Message Reception	
	 BLS	 Blocking/Unblocking Message Sending	
	 CCO	 Continuity Check Outgoing	
	 CCI	 Continuity Check Incoming	
	 CGRS	 Circuit Group Reset Sending	
	 CGRR	 Circuit Group Reset Reception	
	 CPC	 Call Processing Control	
	 CRR	 Circuit Reset Reception	
	 CRS	 Circuit Reset Sending	
Functional 	 CSC	 Circuit Supervision Control	
block name	 SPRC	 Signalling Procedure Control	
	 MGBR	 Maintenance Oriented Circuit Group Blocking/Unblocking Reception	
	 HGBR	 Hardware Failure Oriented Circuit Group Blocking/Unblocking Reception	
	 MGBS	 Maintenance Oriented Circuit Group Blocking/Unblocking Sending	
	 HGBS	 Hardware Failure Oriented Circuit Group Blocking/Unblocking Sending	
	 CRCR	 Continuity Recheck Control Reception	
	 CRCS	 Continuity Recheck Control Sending	
	 CQR	 Circuit Group Query Reception	
	 CQS	 Circuit Group Query Sending	
	 MSDC	 Message Sending Control	
	 MDSC	 Message Distributing Control	
	BLA	 Blocking Acknowledgement	
	 BLO	 Blocking	
	 GRA	 Group Reset Acknowledgement	
	 GRS	 Group Reset	
	 CQR	 Circuit Group Query Response	
	 CQM	 Circuit Group Query	
	 UBA	 Unblocking Acknowledgement	
Message type	 UBL	 Unblocking	
	 CCR	 Continuity Check Request	
	 CGB	 Circuit Group Blocking	
	 CGBA	 Circuit Group Blocking Acknowledgement	
	 CGU	 Circuit Group Unblocking	
	 CGUA	 Circuit Group Unblocking Acknowledgement	
	 RSC	 Reset Circuit	
	 CFN	 Confusion	

TABLE B–2/Q.764
Call processing control acronym
	Acronym	 Description	
	OGC	 Outgoing Trunk Circuit	
General	 ICC	 Incoming Trunk Circuit	
	CCH	 Continuity Check Indicator	
	CC	 Call control	
	 SPRC	 Signalling Procedure Control	
	 CPC	 Call Processing Control	
	 BLR	 Blocking/Unblocking Message Reception	
	 BLS	 Blocking/Unblocking Message Sending	
	 CCO	 Continuity Check Outgoing	
	 CCI	 Continuity Check Incoming	
	 CGRR	 Circuit Group Reset Reception	
 Functional	 CRR	 Circuit Reset Reception	
 block name	 CRS	 Circuit Reset Sending	
	 CPCI	 Call Processing Control Incoming	
	 CPCO	 Call Processing Control Outgoing	
	 MGBR	 Maintenance Oriented Circuit Group Unblocking/Blocking Reception	
	 HGBR	 Hardware Failure Oriented Circuit Group Blocking/Unblocking Reception	
	 MGBS	 Maintenance Oriented Circuit Group Unblocking/Blocking Sending	
	 HGBS	 Hardware Failure Oriented Circit Group Blocking/Unblocking Sending	
	 CRCR	 Continuity Recheck Reception	
	 CRCS	 Continuity Recheck Sending	
	ACM	 Address Complete	
	 ANM	 Answer	
	 COT	 Continuity	
	 CPG	 Call Progress	
	 IAM	 Initial Address	
 Message type	 SUS	 Suspend (network–or user–initiated)	
	 RES	 Resume (network–or user–initiated)	
	 REL	 Release	
	 RLC	 Release Complete	
	 FOT	 Forward Transfer	
	 SAM	 Subsequent Address	
	 CON	 Connect	

TABLE B–3/Q.764
Circuit supervision control acronym
	Acronym	 Description	
	BLR	Blocking/Unblocking Reception	
	 BLS	 Blocking/Unblocking Sending	
	 CRS	 Circuit Reset Sending	
	 CRR	 Circuit Reset Reception	
	 CGRS	 Circuit Group Reset Sending	
	 CGRR	 Circuit Group Reset Reception	
	 MGBR	 Maintenance Oriented Circuit Group Blocking/Unblocking Reception	
 Functional	 HGBR	 Hardware Failure Oriented Circuit Group Blocking/Unblocking Reception	
 block name	 MGBS	 Maintenance Oriented Circuit Group Blocking/Unblocking Sending	
	 HGBS	 Hardware Failure Oriented Circuit Group Blocking/Unblocking Sending	
	 CRCR	 Continuity Recheck Reception	
	 CRCS	 Continuity Recheck Sending	
	 CQR	 Circuit Group Query Reception	
	 CQS	 Circuit Group Query Sending	
	 HRB	 Hardware Failure Oriented Remotely Blocking	
	 HLB	 Hardware Failure Oriented Locally Blocking State	
	BLA	 Blocking Acknowledgement	
	 BLO	 Blocking	
	 COT	 Continuity	
	CQR	 Circuit Group Query Response	
	 CQM	 Circuit Group Query	
	 GRA	 Group Reset Acknowledgement	
	 GRS	 Group Reset	
	 RLC	 Release Complete	
 Message type	 RSC	 Reset Circuit	
	 UBA	 Unblocking Acknowledgement	
	 UBL	 Unblocking	
	 CGB	 Circuit Group Blocking	
	 CGBA	 Circuit Group Blocking Acknowledgement	
	 CCR	 Continuity Check Request	
	 CGU	 Circuit Group Unblocking	
	 CGUA	 Circuit Group Unblocking Acknowledgement	
	 REL	 Release	

TABLE B–4/Q.764
Timer
Timer	 Symbol	 Time–out value	
 First RLC timer	 T1 	 4–15 s	
 Second RLC timer	 T5 	 1 min	
 RES timer (network)	 T6 	 Covered in Q.118	
 ACM timer	 T7 	 20–30 s	
 COT timer	 T8 	 10–15 s	
 ANM timer	 T9 	 Interval specified in Q.118	
 First BLA timer	 T12	 4–15 s	
 Second BLA timer	 T13	 1 min	
 First UBA timer	 T14	 4–15 s	
 Second UBA timer	 T15	 1 min	
 First RSC response timer	 T16	 4–5 s	
 Second RSC response timer	 T17	 1 min	
 First CGBA timer	 T18	 4–15 s	
 Second CGBA timer	 T19	 1 min	
 First CGUA timer	 T20	 4–15 s	
 Second CGUA timer	 T21	 1 min	
 First GRA timer	 T22	 4–15 s	
 Second GRA Timer	 T23	 1 min	
 Continuity tone timer	 T24	  2 s	
 CCR timing timer	 T25	 1–10 s	
 CCR response timer	 T26	 1–3 min	
 CCR receive timer	 T27	 4 min	
 CQR timer	 T28	 10 s	

TABLE B–5/Q.764
Primitives
Primitive		 ISDN–UP message	 Interface	
SETUP	 REQUEST	 IAM	Interface between 	
	 INDICATION	ANM, CON	CC and CPC	
	 RESPONSE			
RELEASE	 CONFIRMATION	REL, RLC		
 RESET	 INDICATION	 RSC, RLC		
	 RESPONSE	GRS, GRA		
 FORWARD TRANSFER	 REQUEST	FOT		
	 INDICATION			
 PROC		 ACM (Other)		
 ALERT	 	CPG, ACM (Subscriber free)		
 INFO	 	SAM		
 PROG a)	 	CPG, ACM (Interworking, Q.931 progress indicator)		
 IBI b)	 	CPG (In–band information)		
		ACM (In–band information		
 SUSPENDED		 SUS		
 RESUMED		 RES		
 BLOCKING	 REQUEST	BLO, BLA	Interface between	
	 INDICATION	CGB, CGBA	CC and CSC	
	RESPONSE			
	 CONFIRMATION			
 UNBLOCKING		 UBL, UBA		
		 CGU, CGUA		
 CCT GROUP QUERY		 CQM, CQR		
 STOP c)	 REQUEST	 –		
	 CONFIRMATION			
 CONTINUITY RECHECK		 CCR		
 RESET		 GRS, GRA		
		 RSC, RLC		

TABLE B–5/Q.764 (cont.)
Primitive		 ISDN–UP message	 Interface	
 CALL FAILURE c)	 INDICATION	 –	 Interface between 
CC and CPC	
 REATTEMPT c)				
 CONTINUITY REPORT	 REQUEST	COT		
	 INDICATION			
MAINTENANCE SYSTEM c)	 INDICATION	 –	 Interface between
CC and CSC	
 START RESET c)			 CC and CPC	
a	Prog (network): Interworking
	Prog (access): Q.931 progress indivator
b)	IBI: In–band information available
c)	Locale primitive
Figure B–4/Q.764 - T1116990-88