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Recommendation Q.764 - Signalling procedures
1. General........................................................... 7
2. Basic call control and signalling procedures...................... 8
2.1 Successful call set-up............................................ 8
2.2 Unsuccessful call set-up.......................................... 30
2.3 Normal call release............................................... 31
2.4 Transfer of user-to-user information.............................. 33
2.5 Suspend, resume................................................... 33
2.6 Delayed release................................................... 36
2.7 In call modification.............................................. 36
2.8 Echo control procedure............................................ 38
2.9 Network features.................................................. 41
2.10 Abnormal conditions............................................... 49
2.11 ISDN user part signalling congestion control...................... 63
2.12 Automatic congestion control...................................... 64
2.13 Unequipped circuit identification code message
(national option)................................................. 65
3. End-to-end signalling............................................. 77
3.1 Introduction...................................................... 77
3.2 Pass-along method................................................. 77
3.3 SCCP method....................................................... 78
3.4 Chaining of ISDN user part end-to-end signalling connection....... 80
3.5 Use of the Protocol Control Indicator (PCI)....................... 81
3.6 Operation of the pass-along method................................ 81
3.7 Operation of the SCCP method-connectionless services.............. 82
3.8 Operation of the SCCP method-connection-oriented service.......... 89
3.9 Interface elements between ISDN user part and SCCP
(embedded transfer)............................................... 93
Appendix I (to 3): Contents of the interface elements between
the ISDN user part and the SCCP.................. 97
Timers in Recommendation Q.764................... 98
Annex A: State transition diagrams (published in
Document AP IX-115/COM XI-R 166).............................
Recommendation Q.762 [1] and their format and content are given in
Recommendation Q.763 [2]. Recommendation Q.730 [3] contains the procedures
for supplementary services. (These were previously 4 of
Recommendation Q.764.)
d) Transfer of information not included in the Initial Address Message
As an alternative to the inclusion of call set-up user facility
information in the Initial Address Message, any call set-up user facility information that need not be examined at
intermediate exchanges and which can be requested from by
the destination exchange (see Recommendation Q.763, 3.22),
may be transported between the originating and destination
exchange. The method of transportation for this information
can be by the link-link method (see section 2.1.6) or via
the end-to-end methods (see section 3).
d) Transfer of information not included in the Initial Address Message
As an alternative to the inclusion of call set-up user facility
information in the Initial Address Message, any call set-up user facility information that need not be examined at
intermediate exchanges and which can be requested from by
the destination exchange (see Recommendation Q.763, 3.22),
may be transported between the originating and destination
exchange. The method of transportation for this information
can be by the link-link method (see section 2.1.6) or via
the end-to-end methods (see section 3).
when digit analysis or timer (T10), or
receipt of the Address Complete Message indicates that all digits
have beenreceived.
a) If an indication that the address is complete or no status
indication has been received from the ISDN access prior to
the destination exchange determining that the complete called
party number has been received, the indicators in the Address
Complete Message will be set as follows:
significant digits in the called party number may be
amended or omitted (see section 2.1.1.1 b)). A change of the
2.1.4.9 Return of sub-address information in Address Complete Message, Connect
Message or Call Progress Message
If sub-address information is received from the called access this information
is passed unchanged to the originating exchange in the access transport parameter
of the Address Complete Message, Connect Message or Call Progress Message.
- if all the information is not available locally or remotely, then an
Information Message containing only the available information is sent and the
requested but not delivered information is indicated as "not available",
using either the indication in the Information Indicator or an appropriate
coding in the requested parameter.
2.1.6.3 Sending unsolicited information
Information that is available at an exchange and that does not correspond to
information which can be or has been requested by an Information Request Message, can be
sent in the Information Message with the solicited information indicator set to
signify that the message has been sent unsolicited.
The unsolicited Information Message can be used only if the ISDN user part has
been used all the way. It can be sent in any direction in any call state (except in
the awaiting release complete state).
Solicited and unsolicited information must not be sent in the same Information
Message; if unsolicited information is to be sent at the same time together with
solicited information, this has to be done in a separate message with the Solicited
Information Indicator set to "Unsolicited".
2.1.6.4 Receiving an Information Message
Upon receipt of an Information Message which does neither contain the requested
information or an indication that the requested information is not available, the
actions taken will depend on whether the call can be progressed.
Address Message is the same as described in section 2.1.1.1 c).
The only purpose of the Subsequent Address Message is to carry
further digits.
The initiating exchange immediately starts the release of the switched path (if
established). The exchange sends a Release Message to the
preceding exchange and a timer (T1) is started to ensure that a Release
Complete Message is received from the preceding exchange within time T1.
(Expiration of Timer (T1) is covered in 2.10.6)
(i.e. the exchange controlling the call)
(see section 2.2.4); or
(as described in section 2.2.4).
(ed note word PROCEDURES removed)
The Suspend Message indicates a temporary cessation of communication
without releasing the call. It can only be accepted during the
conversation/data phase. A Suspend Message can be either generated in
response to a suspend request from the calling/called party or generated
by the network in response to a clearback indication from an interworking
node or an on-hook condition from an analogue called (telephone) party.
(ed note 'called party' removed)
A suspend Message can be generated by the network in response to a
clearback indication from an interworking node or an on hook condition
from an analogue called party.
a) Action at the terminating exchange (destination) or an interworking
exchange
On receipt of the on hook condition or clearback indication or Suspend
Message, the controlling exchange starts a timer (T6) to ensure that an
off hook condition, a re-answer indication, a Resume (network) Message or
a Release Message is received. The value of this timer (T6) is covered in
Q.118 [11]. If the timer (T6) expires, the procedures in Section 2.5.3. [1]
apply.
Having initiated a suspend condition, a calling party may request a
reconnection within timer T2. The procedures in Section 2.5.1.1 items a),
b) and c) apply except that the Resume Message replaces the Suspend Message.
On receipt of the Resume Message, the controlling exchange cancels the
timer. (T2)
A Resume Message is initiated by the network, if a Suspend Message had
previously been sent, in response to a reanswer indication from an
interworking node or an off hook condition from an analogue called party.
a) Action at the terminating exchange or interworking exchange
On receipt of a reanswer indication at the interworking exchange or
an off hook condition in the terminating exchange, the exchange may
send a Resume (network) Message to the preceding exchange if a
Suspend (network) Message had previously been sent.
c) Action of the controlling exchange (i.e. that exchange
controlling the call)
Recommendation Q 118) [11] then the controlling exchange will initiate the release
procedure outlined in section 2.3.3.
At the start of the call, it is required to know whether the call is
an alternate speech/64 kbit or alternate 64 Kbit/speech unrestricted call
request. If this is the case then the following procedures apply:
On receipt of a Call Modification Completed Message,
the intermediate exchange modifies the resource and,
when complete, sends a Call Modification Completed
Message to the next exchange.
Actions required at the local exchange receiving the request call
for in-call modification
2.7.2.3 Action required at the remote local exchange
receiving the call modification request from the netowork.
If at the remote local exchange the in call modification cannot be
performed, the characteristics of the transmission path are kept in
the current mode and the Call Modification Reject Message is returned
to the netowrk. If resources have been reserved upon reception of the
Call modification Request Message, they are released.
2.8 Echo Control Procedure
2.7.2.1 Actions required at the local exchange initiating the
call modificationn
a) When the nature of connection indicators parameter field in
the IAM indicates that an echo control device is already included:
- no change to the nature of connection indicators parameter
field in the IAM is made;
- an incoming half echo control device is reserved; and
- any outgoing half echo control device is disabled.
b) When the nature of connection indicators parameters in the IAM does
not indicate that an echo control device is already included:
- an outgoing half echo control device is enabled; and
- the echo control device indicator in the Nature of connection
indicators parameter field is set.
a) When the nature of connection indicators parameter field the IAM
indicates that echo control device is already included:
- no change to the nature of connection indicators parameter field
in the IAM is made; and
- an incoming half echo control device is reserved.
b) When the nature of connection indicator parameters field in the
IAM does not indicate that an echo control device is already
included:
- no additional action is required.
Upon the receipt of an IAM with the indication "outgoing half echo
control device included" in the nature of connection indicators
parameter field, the following action is taken:
- the echo control device indicator of the backward call
indicators parameter field in the first backward message
(i.e. ACM or Connect or Call Progress) is set.
If the destination exchange is unable to include an incoming half echo
control device, the information is conveyed to the preceding exchange by
echo a control device indicator in the nature of connection indicators field
not being set in the first backward message.
Upon receipt of the first backward message (i.e. ACM or Connect or
Call Progress) in response to an IAM with echo control indication, then
one of the following action can occur:
a) When the backward call indicators parameter field indicates that
incoming half echo control device is already included:
b) When the backward call indicators parameter field indicates that an
incoming half echo control device is already included:
is made.
Automatic repeat attempt, as defined in Recommendation Q.12 [12], is
provided in signalling system No 7. An automatic repeat attempt will
be made (up to the point when the Initial Address Message information
is released. See section 2.3.4.
In the event of a Blocking Message being received:- after an Initial
Address Message has been sent in the opposite direction on that circuit,
and before a backward message relating to that call has been received, an
automatic repeat attempt will be made on another circuit. The exchange
receiving the Blocking Message releases the original call attempt in the
normal manner after sending the Blocking Acknowledgement message and will
not seize that circuit for subsequent calls.
If the Blocking Message is received:
A circuit is controlled by the ISDN User Part if it can be used by
the ISDN User Part as a circuit switched bearer. Hence, time slots in
a digital path that are used for synchronisation (e.g. time slot 0 in
a 2048 kbit/s digital path) or as signalling channels are not circuits
whose control is allocated to the ISDN User Part.
be received from the called party. If a destination exchange
[9], section 7. [9], section 9.
all parameters in the Initial Address Message. The contents of the
Initial Address Message information shall be updated, if the value
of parameters change during the call set-up.
have chosen a suitable route (e.g. 64 kbit/s and ISDN user part signalling
used all the way) according to information included in the Initial Address
Message. Message, the controlling exchange starts a timer (T2) to ensure that a
resume request or Resume Message is received within timer T2). If the
timer (T2) expires, the procedures in section 2.5.3 apply.
a) Action at the terminating exchange or interworking exchange
On receipt of a re-answer indication at the interworking exchange or an
off-hook condition in the terminating exchange, the exchange may send
a Resume (network) Message to the preceding exchange if a Suspend (network)
Message had previously been sent.
b) Actions of the intermediate exchange
On receipt of a Resume Message the exchange will send a Resume Message to
the preceding exchange.
c) Action of the controlling exchange (i.e. that exchange
controlling call)
On receipt of the off-hook condition, re-answer signal, Release message or
Resume Message the controlling exchange stops the timer (T6) (started in
paragraph 2.5.1.3. b).
2.5.3 Expiration of timer (T2) or timer T6
If a request for reconnection or a Resume Message is not received within
timer (R2) or timer (T6) covered in Recommendation Q 118 [11] then the
controlling exchange will initiate the release procedure outlined in
section 2.3.3.
condition is removed or the
timer (T3) *) matures, the network generates the normal release sequence(section 2.3.3).
AP IX-114-E
a) When the nature of connection indicators parameter field
in the IAM indicates that an echo control device is already
included
- no change to the nature of connection indicators parameter field
in the IAM is made;
- an incoming half echo control device is reserved; and
- any outgoing half echo control device is disabled.
b) When the nature of connection indicators parameters in the
IAM does not indicate that an echo control device is already
included:
- an outgoing half echo control device is enabled; and
- the echo control device indicator in the Nature of connection
indicators parameter field is set.
If the intermediate exchange has sufficient information to to determine that echo
control is not required for the outgoing circuit then one of the following actions
can occur:
a) When the nature of connection indicators parameter field in the
IAM indicates that echo control device is already included:
- no change to the nature of connection indicators parameter field
in the IAM is mad; and
- an incoming half echo control device is reserved.
b) When the nature of connection indicator parameter field in the IAM
does not indicate that an echo control device is already included:
- no additional action is required.
REFERENCES
[1] CCITT Recommendation Q.762 - General functions of messages and
signals.
[2] CCITT Recommendation Q.763 - Formats and codes.
[3] CCITT Recommendation Q.730 - ISDN supplementary services.
[4] CCITT Recommendation E.163 - Numbering plan for the international telephone service.
[5] CCITT Recommendation E.164 - Numbering plan for the ISDN era.
[6] CCITT Recommendation Q.107 - Standard sending sequence of forward address
information.
[7] CCITT Recommendation E.172 - Call routing in the ISDN era.
[8] CCITT Recommendation Q.33 - Protection against the effects of faulty
transmission on groups of circuits.
[9] CCITT Recommendation Q.724 - Signalling procdedures.
[10] CCITT Recommendation Q.543 - Digital exchange performance design
objectives.
[11] CCITT Recommendation Q.118 - Special release arrangements.
[12] CCITT Recommendation Q.12 - Overflow-alternative routing-rerouting- automatic repeat attempt.
AP IX-114-E
[13] CCITT Recommendation Q.706 - Message Transfer Part signalling
performance.
[14] CCITT Recommendation Q.714 - Signalling Connection Control Part
procedures.
[15] CCITT Recommendation Q.711 - Functional description of the Signalling
Connection Control Part.
xxxxxxxxxx
Annex A - (to Recommendation Q.764)
STATE TRANSITION DIAGRAMS
Page
A.1 General........................................................6
A.2 Drafting convention............................................6
A.3 Abbreviations, timers and primitives...........................7
A.4 State transition diagrams and SDL diagrams.....................7
AP IX-114-E
ANNEX A
(to Recommendation Q.764)
State transition diagrams
Should any conflict arise between the text and the SDL definition, the
textual description is taken as definitive.
A.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 A-1/Q.764. These blocks are as follows:
1) Signalling Procedure Control (SPRC)
SPRC provides procedures for sending ISUP messages to Level 3 (SCCP or MTP)
and distributing received ISUP messages to the other ISUP 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.
A.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 A-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 A-3/Q.764.
A.3 Abbreviations, timers and primitives
A.3.1 Abbreviations
1) Signalling Procedure Control: Table A-1/Q.764
2) Call Processing Control: Table A-2/Q.764
3) Circuit Supervision Control: Table A-3/Q.764
A.3.2 Timers
AP IX-114-E
Timers used in the ISDN-UP SDL diagrams are shown in Table A-4/Q.764.
A.3.3 Primitives
Primitives used over the interface between Call Control and ISDN-UP are
shown in Table A-5/Q.764.
A.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)
- Functional diagrams: Figure A-4/Q.764
- State transition diagrams: Figure A-5/Q.764
2) Call Processing Control (CPC)
- Functional diagrams: Figure A-6/Q.764
- State transition diagrams: Figure A-7 - 9/Q.764
3) Circuit Supervision Control (CSC)
- Functional diagrams: Figure A-10/Q.764
- State transition diagrams: Figure A-11 - 18/Q.764
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 sections 1-4. The ISDN-UP diagrams are
provided for the above subdivided functional blocks, as shown below:
1) Signalling Procedure Control (SPRC)
- Message Sending Control: Figure A-19/Q.764
- Message Distributing Control: Figure A-20/Q.764
2) Call Processing Control (CPC)
- Call Processing Control Incoming
(CPCI): Figure A-21/Q.764
- Call Processing Control Outgoing
(CPCO): Figure A-22/Q.764
- Continuity Check Incoming (CCI): Figure A-23/Q.764
- Continuity Check Outgoing (CCO): Figure A-24/Q.764
3) Circuit Supervision Control (CSC)
- Blocking/Unblocking Message Sending
(BLS): Figure A-25/Q.764
- Blocking/Unblocking Message
Reception (BLR): Figure A-26/Q.764
- Maintenance Oriented Circuit Group
Blocking/Unblocking Sending (MGBS): Figure A-27/Q.764
- Maintenace Oriented Circuit Group
Blocking/Unblocking Reception
(MGBR): Figure A-28/Q.764
- Hardware Failure Oriented Locally
Blocking State (HLB): Figure A-29/Q.764
- Hardware Failure Oriented Remotely
Blocking State (HRB): Figure A-30/Q.764
- Hardware Failure Oriented Circuit
AP IX-114-E
Group Blocking/Unblocking Sending
(HGBS): Figure A-31/Q.764
- Hardware Failure Oriented Circuit
Group Blocking/Unblocking Reception
(HGBR): Figure A-32/Q.764
- Circuit Reset Sending (CRS): Figure A-33/Q.764
- Circuit Reset Reception (CRR): Figure A-34/Q.764
- Circuit Group Reset Sending (CGRS): Figure A-35/Q.764
- Circuit Group Reset Reception
(CGRR): Figure A-36/Q.764
- Continuity Recheck Sending (CRCS): Figure A-37/Q.764
- Continuity Recheck Reception
(CRCR): Figure A-38/Q.764
- Circuit Group Query Sending (CQS): Figure A-39/Q.764
- Circuit Group Query Reception
(CQR): Figure A-40/Q.764
AP IX-114-E
FIGURE A-1/Q.764
Overview Functional Block Diagram for ISDN-UP
AP IX-114-E
Note - Input which is not shown in SDL diagrams should be discarded.
FIGURE A-2/Q.764
Symbols Used In SDL Diagrams
AP IX-114-E
FIGURE A-3/Q.764
SDL Convention Example
AP IX-114-E
TABLE A-1/Q.764
Signalling Procedure Control Acronym
AP IX-114-E
TABLE A-2/Q.764
Call Processing Control Acronym
AP IX-114-E
TABLE A-3/Q.764
Circuit Supervision Control Acronym
AP IX-114-E
TABLE A-4/Q.764
Timers
AP IX-114-E
TABLE 1-5/Q.764
Primitives
AP IX-114-E
FIGURE A-4/Q.764
Functional Block Diagram for SPRC
FIGURE A-5/Q.764
State Transition Diagrams for SPRC
AP IX-114-E
FIGURE A-6/Q.764
Functional Block Diagram for CPC
AP IX-114-E
FIGURE A-7/Q.764
State Transition Diagrams for CPC Incoming (CPCI)
AP IX-114-E
FIGURE A-8/Q.764
State Transition Diagrams for CPC Outgoing (CPCO)