a) Circuit selection
When the originating exchange has received the complete selection information from the calling party, and has determined that the call is to be routed to another exchange, selection of a suitable, free, inter-exchange circuit takes place and an initial address message is sent to the succeeding exchange.
Appropriate routeing information is either stored at the originating exchange or at a remote database to which a request may be made.
The selection of the route will depend on the called party number, connection type required and the network signalling capability required. This selection process may be performed at the exchange or with the assistance of the remote database.
In addition, in the case of a subscriber with digital access, the set-up message contains bearer capability information which is analysed by the originating exchange to determine the correct connection type and network signalling capability. The bearer capability information will be mapped into the user service information parameter of the initial address message. When the user teleservice information is present in the initial address message, it shall contain the high layer compatibility information. If two high layer compatibility information elements are received from the access, the second received information element, carrying the preferred HLC, is mapped into the user teleservice information parameter. The information received from the access interface is used to set the value of the transmission medium requirement parameter.
The connection types allowed are:
– speech;
– 3.1 kHz audio;
– 64 kbit/s unrestricted;
– 64 kbit/s unrestricted preferred;
– 2 ´ 64 kbit/s unrestricted;
– 384 kbit/s unrestricted;
– 1536 kbit/s unrestricted;
– 1920 kbit/s unrestricted;
– N ´ 64 kbit/s unrestricted (N = 2-30).
NOTE – The procedure assumes that Recommendation E.172 will at an appropriate time include routeing rules for the transmission medium requirement parameter value "N ´ 64 kbit/s unrestricted".
The network signalling capabilities allowed are:
– ISDN-User Part preferred;
– ISDN-User Part required;
– ISDN-User Part not required (any signalling system).
The information used to determine the routeing of the call by the originating exchange will be included in the initial address message, (as transmission medium requirement and forward call indicators), to enable correct routeing at intermediate exchanges. The initial address message conveys implicitly the meaning that the indicated circuit has been seized.
b) Address information sending sequence
The sending sequence of address information on international calls will be the country code followed by the national (significant) number. On national connections, the address information may be the subscriber number or the national (significant) number as required by the Administration concerned. For calls to international operator positions (Code 11 and Code 12) refer to Recommendation Q.107 [8].
The end-of-pulsing (ST) signal will be used when ever the originating exchange is in a position to know by digit analysis that the final digit has been sent.
c) Initial address message
The initial address message in principle contains all the information that is required to route the call to the destination exchange and connect the call to the called party.
If the initial address message would exceed the 272 octet limit for Message Transfer Part transfer, it shall be segmented by use of the segmentation message; see 2.1.12.
All initial address messages will include a protocol control indicator (in the forward call indicator parameter) and a transmission medium requirement parameter.
The originating exchange will set the parameters in the protocol control indicator and in the ISDN-User Part preference indicator to indicate:
i) the type of end-to-end method that can be accommodated (see Recommendation Q.730 [16]);
ii) the availability of Signalling System No. 7 signalling;
iii) the use of the ISDN-User Part;
iv) network signalling capability required, e.g. ISDN-User Part required all the way.
The ISDN-User Part preference indicator is set according to the bearer service, teleservice and supplementary service(s) requested. The exact setting depends on the service demand conditions and may be different depending on individual cases. In principle, if the service demand requires ISDN-User Part to be essential then the indicator is set to "required", if the service required is optional but preferred it is set to "preferred", otherwise it is set to "not required". The indicator is set to either "required" or "preferred", or "not required", according to the most stringent condition required by one or more of the parameters in the initial address message.
The nature of connection indicators are set appropriately based on the characteristics of the selected outgoing circuit.
The transmission medium requirement parameter contains the connection type required information, e.g. 3.1 kHz audio.
The propagation delay counter is included according to 2.6.
The originating exchange may also include in the initial address message:
i) a call reference (including the point code of the originating exchange) to enable the destination exchange to establish an end-to-end connection (see Recommendation Q.730 [16]);
ii) the calling party number if this is to be passed forward without being requested. The calling party number could contain Code 11 or 12 if the call is from an international operator;
iii) an SCCP connection request parameter (see Recommendation Q.730 [16]); and
iv) other information related to supplementary services and network utilities.
The initial address message can contain an access transport parameter.
d) Completion of transmission path
Through connection of the transmission path will be completed in the backward direction (the transmission path is completed in the forward direction on receipt of a connect or answer message) at the originating exchange immediately after the sending of the initial address message, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
It is also acceptable that on speech or 3.1 kHz audio calls, through-connection of the transmission path will be completed in both directions immediately after the initial address message has been sent, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
e) Network protection timer
When the originating exchange has sent the Initial Address Message the awaiting address complete timer (T7) is started. If timer (T7) expires the connection is released and an indication is returned to the calling subscriber.
a) Circuit selection
An intermediate national exchange, on receipt of an initial address message, will analyse the called party number and the other routeing information [see 2.1.1.1 a)] to determine the routeing of the call. If the intermediate national exchange can route the call using the connection type specified in the transmission medium requirement parameter, a free inter-exchange circuit is seized and an initial address message is sent to the succeeding exchange. Within a network if the intermediate national exchange does not route the call using just the connection type specified in the transmission medium requirement parameter, the exchange may also examine the user service information containing the bearer capability information and/or the user teleservice information containing the high layer compatibility information, if available, to determine if a suitable route can be selected. In this case if a new connection type is provided the transmission medium requirement parameter is modified to the new connection type.
b) Parameters in the initial address message
An intermediate national exchange may modify signalling information received from the preceding exchange according to the capabilities used on the outgoing route. Signalling information that may be changed are nature of connection indicator and propagation delay counter. Other signalling information is passed on transparently, e.g. the access transport parameter, user service information, etc. The order of information elements carried in the access transport parameter received from the incoming exchange shall be retained.
The satellite indicator in the nature of connection parameter should be incremented if the selected outgoing circuit is a satellite circuit. Otherwise, the indicator is passed on unchanged.
c) Completion of transmission path
Through-connection of the transmission path in both directions will be completed at an intermediate national exchange immediately after the initial address message has been sent, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
a) Circuit selection
An outgoing international exchange, on receipt of an initial address message, will analyse the called party number and the other routeing information [see 2.1.1.1 a)] to determine the routeing of the call. If the outgoing international exchange can route the call using the connection type specified in the transmission medium requirement parameter, a free inter-exchange circuit is seized and an initial address message is sent to the succeeding exchange.
If the outgoing international exchange cannot trust that the transmission medium requirement value received from the national network reflects the minimum value of the information transfer susceptance, then the transmission medium requirement value may be modified according to the contents of the information transfer capability and information transfer rate fields of the user service information parameter (if available).
The outgoing international exchange must ensure that the transmission medium requirement parameter is set according to the service requested by the customer (see Recommendation E.172 [2]). More specifically this parameter is carried unchanged within the international network.
b) Parameters in the initial address message
An outgoing international exchange may modify signalling information received from the preceding exchange according to the capabilities used on the outgoing route. Signalling information that may be changed are nature of connection indicator and propagation delay counter; the most significant digits in the called party number may be amended or omitted (country code is removed at the last exchange before the incoming international exchange). Other signalling information is passed on transparently, e.g. the access transport parameter, user service information, etc. The order of information elements carried in the access transport parameter received from the incoming exchange shall be retained.
If the outgoing international exchange belongs to a country using -law PCM encoding nationally and the transmission medium requirement indicates speech or 3.1 kHz audio then the user information layer 1 protocol identification field of the user service information parameter must be checked, if it indicates "Recommendation G.711 [4] -law" this must be changed to "Recommendation G.711 [4] A-law" and a -law to A-law convertor must be enabled.
The satellite indicator in the nature of connection parameter should be incremented if the selected outgoing circuit is a satellite circuit. Otherwise, the indicator is passed on unchanged.
The outgoing international gateway exchange should include the origination ISC point code parameter in the initial address message. This information is used for statistical purposes, e.g. accumulation of the number of incoming calls on an originating international switching centre basis.
If a location number parameter is received, the nature of address indicator is checked. If the nature of address indicator is set to "international number" then the parameter is passed unchanged, otherwise the number is modified to the international number format and the nature of address is set to "international number" before being passed.
The end-of-pulsing (ST) signal will be used whenever the outgoing exchange is in a position to know by digit analysis that the final digit has been sent.
c) Completion of transmission path
Through-connection of the transmission path in both directions will be completed at an outgoing international exchange immediately after the initial address message has been sent, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
d) Network protection timer
When an outgoing international exchange has sent the initial address message the awaiting address complete timer (T7) is started. If timer (T7) expires the connection is released and an indication is returned to the calling subscriber.
a) Circuit selection
An intermediate international exchange, on receipt of an initial address message, will analyse the called party number and the other routeing information [see 2.1.1.1 a)] to determine the routeing of the call. If the intermediate international exchange can route the call using the connection type specified in the transmission medium requirement parameter, a free inter-exchange circuit is seized and an initial address message is sent to the succeeding exchange.
b) Parameters in the initial address message
An intermediate international exchange may modify signalling information received from the preceding exchange according to the capabilities used on the outgoing route. Signalling information that may be changed are nature of connection indicator and propagation delay counter; the most significant digits in the called party number may be amended or omitted (country code is removed at the last exchange before the incoming international exchange). Other signalling information is passed on transparently, e.g. the access transport parameter, user service information, etc. The order of information elements carried in the access transport parameter received from the incoming exchange shall be retained.
The satellite indicator in the nature of connection parameter should be incremented if the selected outgoing circuit is a satellite circuit. Otherwise, the indicator is passed on unchanged.
c) Completion of transmission path
Through-connection of the transmission path in both directions will be completed at an intermediate international exchange immediately after the initial address message has been sent, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
d) Network protection timer
When an intermediate international exchange has sent the initial address message the awaiting address complete timer (T7) is started. If timer (T7) expires the connection is released and an indication is returned to the calling subscriber.
a) Circuit selection
An incoming
international exchange, on receipt of an initial address message, will analyse
the called party number and the other routeing information [2.1.1.1 a)] to
determine the routeing of the call. If the incoming international exchange can
route the call using the connection type specified in the transmission medium
requirement parameter, a free
inter-exchange circuit is seized and an initial address message is sent to the
succeeding exchange.
b) Parameters in the initial address message
An incoming international exchange may modify signalling information received from the preceding exchange according to the capabilities used on the outgoing route. Signalling information that may be changed are nature of connection indicator and propagation delay counter. Other signalling information is passed on transparently, e.g. the access transport parameter, user service information, etc. The order of information elements carried in the access transport parameter received from the incoming exchange shall be retained.
The satellite indicator in the nature of connection parameter should be incremented if the selected outgoing circuit is a satellite circuit. Otherwise, the indicator is passed on unchanged.
If the incoming international exchange belongs to a country using -law PCM encoding nationally and the transmission medium requirement indicates speech or 3.1 kHz audio then the user information layer 1 protocol identification field of the user service information parameter must be checked, if it indicates "Recommendation G.711 [4] A-law" this must be changed to "Recommendation G.711 [4] -law" and a -law to A-law converter must be enabled.
The incoming international gateway exchange should delete the origination ISC point code parameter from the initial address message and set up a connection to the national network. This information is used for statistical purposes, e.g. accumulation of the number of incoming calls on an originating international switching centre basis.
c) Completion of transmission path
Through-connection of the transmission path in both directions will be completed at an incoming international exchange immediately after the initial address message has been sent, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
d) Network protection timer
When an incoming international exchange has sent the initial address message the awaiting address complete timer (T7) is started. If timer (T7) expires the connection is released and an indication is returned to the calling subscriber.
a) Selection of called party
Upon receipt of an initial address message the destination exchange will analyse the called party number to determine to which party the call should be connected. It will also check the called party's line condition and perform various checks to verify whether or not the connection is allowed. These checks will include correspondence of compatibility checks, e.g. checks associated with supplementary services.
In this case where the connection is allowed, the destination exchange will set up a connection to the called party. If a continuity check has to be performed on one or more of the circuits involved in a connection, setting up of the connection to the called party must be prevented until the continuity of such circuits has been verified.
b) Segmented initial address message
If the initial address message had been segmented by the use of the segmentation message; the remainder of the call set-up information is awaited; see 2.1.12.
International gateways should support access to operators equipment as specified in Recommendation Q.101 [7].
The sending sequence of specific forward address information to be sent for calls to operators (incoming, delay or particular delay operator) is shown below. The other parameters of the initial address message are coded as the ones for an automatic call initial address message (e.g. nature of connection indicators, transmission medium requirement, etc.).
i) Called party number:
• Nature of address indicator: "0000100" international number.
• Address:
– country code: I1, I1I2, I1I2I3;
– extra digit designating the incoming international exchange N1 (Note 1);
– access to operator's position: Code 11 or Code 12 or special number (Note 2);
– number of a particular position: x1(x2x3...);
– sending finished: ST.
NOTE 1 – The extra digit (N1) designating the incoming international exchange is used in cases where more than one incoming international exchange can be reached in the country of destination. The insertion of the extra digit is not mandatory (see Recommendation Q.107 [8]).
NOTE 2 – The incoming operator or the delay operator may be obtained by using a special number (see Recommendation Q.101 [7]).
ii) Calling party category:
"00000001" operator, language French;
"00000010" operator, language English;
"00000011" operator, language German;
"00000100" operator, language Russian;
"00000101" operator, language Spanish.
i) Called party number:
• Nature of address indicator: "0000011" national (significant) number.
• Address:
– extra digit designating the incoming international exchange N1 (Note 1 in 2.1.1.7.1);
– access to operator's position: Code 11 or Code 12 or special number (Note 2 in 2.1.1.7.1);
– number of a particular position: x1(x2x3...);
– sending finished: ST.
ii) Calling party category:
"00000001" operator, language French;
"00000010" operator, language English;
"00000011" operator, language German;
"00000100" operator, language Russian;
"00000101" operator, language Spanish.
This subclause only describes the standard sending sequence of forward address information in the case of calls to testing and measuring devices.
i) Called party number:
• Nature of address indicator: "0000011" national (significant) number.
• Address:
– access code for particular testing or measuring device: XY (as given in Recommendation Q.107 [8]);
– sending finished: ST.
ii) Calling party category:
"00001101" test call.
NOTE – The principles in Recommendation Q.107 [8] are not always applicable to the international network.
a) Circuit selection
When the originating exchange has received sufficient information [see 2.1.2.1 c)] from the calling party to determine that the call is to be routed to another exchange, selection of a suitable, free, inter-exchange circuit takes place and an initial address message is sent to the succeeding exchange.
Appropriate routeing information is either stored at the originating exchange or at a remote database to which a request may be made.
The selection of the route will depend on the called party number, connection type required and the network signalling capability required. This selection process may be performed at the exchange or with the assistance of a remote database.
In addition, in the case of a subscriber with digital access, the set-up message contains bearer capability information which is analysed by the originating exchange to determine the correct connection type and network signalling capability. The bearer capability information will be mapped into the user service information parameter of the initial address message. When the user teleservice information is present in the initial address message, it shall contain the high layer compatibility information. If two high layer compatibility information elements are received from the access, the second received information element, carrying the preferred HLC, is mapped into the user teleservice information parameter. The information received from the access interface is used to set the value of the transmission medium requirement parameter.
The connection types allowed are:
– speech;
– 3.1 kHz audio;
– 64 kbit/s unrestricted;
– 64 kbit/s unrestricted preferred;
– 2 × 64 kbit/s unrestricted;
– 384 kbit/s unrestricted;
– 1536 kbit/s unrestricted;
– 1920 kbit/s unrestricted;
– N ´ 64 kbit/s unrestricted (N = 2-30).
NOTE – The procedure assumes that Recommendation E.172 will at an appropriate time include routeing rules for the transmission medium requirement parameter value "N ´ 64 kbit/s unrestricted".
The network signalling capabilities allowed are:
– ISDN-User Part preferred;
– ISDN-User Part required;
– ISDN-User Part not required (any signalling system).
The information used to determine the routeing of the call by the originating exchange will be included in the IAM, (as transmission medium requirement and forward call indicators), to enable correct routeing at intermediate exchanges. The initial address message conveys implicitly the meaning that the indicated circuit has been seized.
b) Address information sending sequence
The sending sequence of address information on international calls will be the country code followed by the national (significant) number. On national connections, the address information may be the subscriber number or the national (significant) number as required by the Administration concerned. For calls to international operator positions (Code 11 and Code 12) refer to Recommendation Q.107 [8].
The end-of-pulsing (ST) signal will be used whenever the originating exchange is in a position to know by digit analysis that the final digit has been sent.
c) Content of initial and subsequent address messages
The initial and subsequent address messages in principle contain all of the information that is required to route the call to the destination exchange and connect the call to the called party. The contents of the initial address message is the same as described in 2.1.1.1 c). The only purpose of the subsequent address message is to carry further digits.
If the initial address message would exceed the 272 octet limit for Message Transfer Part transfer, it shall be segmented by use of the segmentation message; see 2.1.12.
Within national networks the address information contained within the initial address message may vary depending on the routeing requirement within the network.
The remaining digits of the number may be sent in subsequent address messages containing one or several digits as they are received. Efficiency can be gained by grouping together as many digits as possible. However, to prevent an increase in post sending delay in those cases where overlap operation with subscribers' dialling is used, it may be desirable to send the last few digits individually.
The end-of-pulsing (ST) signal is always sent in the following situations:
i) semi-automatic calls;
ii) test calls; and
iii) when the end-of-pulsing (ST) signal is received.
In automatic
working, the end-of-pulsing (ST) signal will be sent whenever the originating
exchange is in a position to know, by digit analysis, that the final digit has
been sent. Digit analysis may consist of an examination of the country code and
counting the maximum (or fixed) number of digits of the national number. In
other cases, the end-of-pulsing signal is
not sent and the end-of-address information is determined by the receipt of the
address complete message or connect message from the incoming exchange.
d) Completion of transmission path
Through-connection of the transmission path in the backward direction (the transmission path is completed in the forward direction on receipt of connect or answer message) at the originating exchange will be completed except in the cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]):
i) immediately after the sending of the initial address message; or
ii) when digit analysis or timer (T10), or receipt of the address complete message indicates that all digits have been received. It is also acceptable that on speech or 3.1 kHz audio calls, through-connection of the transmission path will be completed in both directions immediately after the initial address message has been sent, except in the cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
e) Network protection timer
Each time when the originating exchange has sent an address message the awaiting address complete timer (T7) is started. If timer (T7) expires the connection is released and an indication is sent to the calling subscriber.
a) Circuit selection
An intermediate national exchange, on receipt of an initial address message, will analyse the digits available and the other routeing information [see 2.1.2.1 a)] to determine the routeing of the call. If the intermediate national exchange can route the call using the connection type specified in the transmission medium requirement parameter, a suitable free inter-exchange circuit is seized and an initial address message is sent to the succeeding exchange. If the number of digits in the called party number is not sufficient to route the call the routeing will be carried out when the intermediate national exchange has received additional digits in subsequent address message(s). Any address digits received in subsequent address messages during the circuit selection process may be included in this initial address message. Any subsequent address messages received after the initial address message has been sent are forwarded to the succeeding exchange as subsequent address message(s).
Within the network if the intermediate national exchange does not route the call just using the connection type specified in the transmission medium requirement parameter, the exchange may also examine the user service information containing the bearer capability information and/or the user teleservice information containing the high layer compatibility information, if available, to determine if a suitable route can be selected. In this case the transmission medium requirement parameter is modified to the new connection type.
b) Parameters in the initial address message
An intermediate national exchange may modify signalling information received from the preceding exchange according to the capabilities used on the outgoing route. Signalling information that may be changed are nature of connection indicator and propagation delay counter. Other signalling information is passed on transparently, e.g. the access transport parameter, user service information, etc. The order of information elements carried in the access transport parameter received from the incoming exchange shall be retained.
The satellite indicator in the nature of connection parameter should be incremented if the selected outgoing circuit is a satellite circuit. Otherwise, the indicator is passed on unchanged.
c) Completion of transmission path
Through-connection of the transmission path in both directions will be completed at an intermediate national exchange immediately after the initial address message has been sent, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
a) Circuit selection
An outgoing international exchange, on receipt of an initial address message, will analyse the digits available and the other routeing information [see 2.1.2.1 a)] to determine the routeing of the call. If the outgoing international exchange can route the call using the connection type specified in the transmission medium requirement parameter, a suitable free inter-exchange circuit is seized and an initial address message is sent to the succeeding exchange. All digits required for routeing the call through the international network will be sent in the initial address message. On calls with a country code in the number (except in the case of calls to special operators), the initial address message will contain a minimum of 4 digits and should contain as many digits as are available. If the number of digits in the called party number is not sufficient to route the call the routeing will be carried out when the outgoing international exchange has received additional digits in subsequent address message(s). Any address digits received in subsequent address messages during the circuit selection process may be included in this initial address message. Any subsequent address messages received after the initial address message has been sent, are forwarded to the succeeding exchange as subsequent address message(s).
If the outgoing international exchange cannot trust that the transmission medium requirement value received from the national network reflects the minimum value of the information transfer susceptance, then the transmission medium requirement value may be modified according to the contents of the information transfer capability and information transfer rate fields of the user service information parameter (if available).
The outgoing international exchange must ensure that the transmission medium requirement parameter is set according to the service requested by the customer (see Recommendation E.172 [2]). More specifically this parameter is carried unchanged within the international network.
b) Parameters in the initial address message
An outgoing international exchange may modify signalling information received from the preceding exchange according to the capabilities used on the outgoing route. Signalling information that may be changed are nature of connection indicator and propagation delay counter; the most significant digits in the called party number may be amended or omitted (country code is removed at the last exchange before the incoming international exchange). Other signalling information is passed on transparently, e.g. the access transport parameter, user service information, etc. The order of information elements carried in the access transport parameter received from the incoming exchange shall be retained.
In automatic working, the end-of-pulsing (ST) signal will be sent whenever the outgoing international exchange is in a position to know, by digit analysis, that the final digit has been sent. Digit analysis may consist of an examination of the country code and counting the maximum (or fixed) number of digits of the national number. In other cases, the end-of-pulsing signal is not sent and the end-of-address information is determined by the receipt of the address complete message or connect message from the incoming exchange.
If the outgoing international exchange belongs to a country using -law PCM encoding nationally and the transmission medium requirement indicates speech or 3.1 kHz audio, then the user information layer 1 protocol identification field of the user service information parameter must be checked, if it indicates "Recommendation G.711 [4] -law" this must be changed to "Recommendation G.711 [4] A-law" and a -law to A-law convertor must be enabled.
The satellite indicator in the nature of connection parameter should be incremented if the selected outgoing circuit is a satellite circuit. Otherwise, the indicator is passed on unchanged.
The outgoing international gateway exchange should include the origination ISC point code parameter in the initial address message. This information is used for statistical purposes, e.g. accumulation of the number of incoming calls on an originating international switching centre basis.
c) Completion of transmission path
Through-connection of the transmission path in both directions will be completed at an outgoing international exchange immediately after the initial address message has been sent, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
d) Network protection timer
Each time when an outgoing international exchange has sent an address message the awaiting address complete timer (T7) is started. If timer (T7) expires the connection is released and an indication is returned to the calling subscriber.
a) Circuit selection
An intermediate international exchange, on receipt of an initial address message, will analyse the digits available and the other routeing information [see 2.1.2.1 a)] to determine the routeing of the call. If the intermediate international exchange can route the call using the connection type specified in the transmission medium requirement parameter, a suitable free inter-exchange circuit is seized and an initial address message is sent to the succeeding exchange. If the number of digits in the called party number is not sufficient to route the call the routeing will be carried out when the intermediate international exchange has received additional digits in subsequent address message(s). Any address digits received in subsequent address messages during the circuit selection process may be included in this Initial address message. Any subsequent address messages received after the initial address message has been sent, are forwarded to the succeeding exchange as subsequent address message(s).
b) Parameters in the initial address message
An intermediate international exchange may modify signalling information received from the preceding exchange according to the capabilities used on the outgoing route. Signalling information that may be changed are nature of connection indicator and propagation delay counter; the most significant digits in the called party number may be amended or omitted (country code is removed at the last exchange before the incoming international exchange). Other signalling information is passed on transparently, e.g. the access transport parameter, user service information, etc. The order of information elements carried in the access transport parameter received from the incoming exchange shall be retained.
The satellite indicator in the nature of connection parameter should be incremented if the selected outgoing circuit is a satellite circuit. Otherwise, the indicator is passed on unchanged.
c) Completion of transmission path
Through-connection of the transmission path in both directions will be completed at an intermediate international exchange immediately after the initial address message has been sent, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724).
d) Network protection timer
Each time when an intermediate international exchange has sent an address message the awaiting address complete timer (T7) is started. If timer (T7) expires the connection is released and an indication is returned to the calling subscriber.
a) Circuit selection
An incoming international exchange, on receipt of an initial address message, will analyse the digits available and the other routeing information [see 2.1.2.1 a)] to determine the routeing of the call. If the incoming international exchange can route the call using the connection type specified in the transmission medium requirement parameter a suitable free inter-exchange circuit is seized and an initial address message is sent to the succeeding exchange. If the number of digits in the called party number is not sufficient to route the call, the routeing will be carried out when the incoming international exchange has received additional digits in subsequent address message(s). Any address digits received in subsequent address messages during the circuit selection process may be included in this initial address message. Any subsequent address messages received after the initial address message has been sent are forwarded to the succeeding exchange as subsequent address message(s).
Selection of the outgoing national circuit normally can start at an incoming international exchange on receipt of the initial address message and signalling can proceed on the first national link.
b) Parameters in the initial address message
An incoming international exchange may modify signalling information received from the preceding exchange according to the capabilities used on the outgoing route. Signalling information that may be changed are nature of connection indicator and propagation delay counter. Other signalling information is passed on transparently, e.g. the access transport parameter, user service information, etc. The order of information elements carried in the access transport parameter received from the incoming exchange shall be retained.
If the incoming international exchange belongs to a country using -law PCM encoding nationally and the transmission medium requirement indicates speech or 3.1 kHz audio then the user information layer 1 protocol identification field of the user service information parameter must be checked, if it indicates "Recommendation G.711 [4] A-law" this must be changed to "Recommendation G.711 [4] -law" and a -law to A-law converter must be enabled.
The satellite indicator in the nature of connection parameter should be incremented if the selected outgoing circuit is a satellite circuit. Otherwise, the indicator is passed on unchanged.
Incoming international gateway exchanges may delete the origination ISC point code parameter in the initial address message and set up a connection to the national network. This information is used for statistical purposes, e.g. accumulation of the number of incoming calls on an originating international switching centre basis.
c) Completion of transmission path
Through-connection of the transmission path in both directions will be completed at an incoming international exchange immediately after the initial address message has been sent, except in those cases where conditions on the outgoing circuit prevent it (see clause 7/Q.724 [15]).
d) Network protection timer
Each time when an incoming international exchange has sent an address message the awaiting address complete timer (T7) is started. If timer (T7) expires the connection is released and an indication is returned to the calling subscriber.
a) Selection of called party
Upon the receipt of the sufficient called party number information the destination exchange will analyse the called party number to determine to which party the call should be connected. It will also check the called party's line condition and perform various checks, to verify whether or not the connection is allowed. These checks will include correspondence of compatibility checks, e.g. checks associated with supplementary services.
In the case where the connection is allowed, the destination exchange will set up a connection to the called party. If a continuity check has to be performed on one or more of the circuits involved in a connection, setting up of the connection to the called party must be prevented until the continuity of such circuits has been verified.
b) Segmented initial address message
If the initial address message had been segmented by the use of the segmentation message, the remainder of the call set-up information is awaited; see 2.1.12.
See 2.1.1.7.
See 2.1.1.8.
a) International network
The calling party number can only be included in the initial address message [see 2.1.1.1 c) and 2.1.2.1 c)].
b) National networks
The calling party
number can either be included in the initial address message [see 2.1.1.1 c) and
2.1.2.1 c)] or requested by the destination exchange (see 2.1.6). If the calling
party number is required at the destination exchange but is not included in the
initial address message, the destination exchange may request the calling party
number. The destination exchange will investigate the presence/absence of the
calling party number parameter to determine whether a request is useful or not.
Further it may be necessary to withhold the
sending of the address complete message until the calling party number has been
successfully delivered.
If the address complete or connect messages would exceed the 272 octet limit for Message Transfer Part transfer, it shall be segmented by use of the segmentation message; see 2.1.12.
i) An address complete message will be sent from the destination exchange as soon as it has been determined that the complete called party number has been received, or an indication received from the called party that an in-band tone is being connected (for this case, see 2.1.5 and 2.2.4). However there is no direct mapping from alerting, received from the access signalling system, to address complete in the network. In the case that the continuity check is performed the destination exchange will withhold sending the address complete message until a successful continuity indication has been received (see clause 7/Q.724 [15]).
Address complete is sent from the destination exchange in the following conditions:
1) In the case where the terminating access is non-ISDN the following action takes place at the destination exchange:
a) In all cases an address complete message is sent as soon as it has been determined that the complete called party number has been received, and the destination exchange established that the subscriber is free. Indicators in the address complete message will be set to indicate:
– called line status: "Subscriber free".
– ISDN access indicator: "Non-ISDN".
b) In the case of a PBX an address complete message is sent as soon as it has been determined that the called party number has been received. Indicators in the address complete message will be set to indicate:
– called line status: "No indication".
– ISDN access indicator: "Non-ISDN".
2) In the case where the terminating access is ISDN, the following conditions can apply:
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:
– called line status: "No indication".
– ISDN access indicator: "ISDN".
NOTE – In case a) the indication that the destination user is being alerted is transferred in a call progress message (see 2.1.5).
b) The destination exchange concludes from the receipt of an indication from the ISDN access that the complete called party number has been received. In this case the indicators in the address complete message will be set as follows:
– called line status: "Subscriber free".
– ISDN access indicator: "ISDN".
ii) If a connect indication is received from the ISDN access under the following conditions:
– no alerting indication received from the ISDN access; and
– an address complete message has not yet been sent by the destination exchange,
a connect message is sent by the destination exchange. This connect message signifies both address complete and answer conditions. Indicators in the connect message will indicate:
– called line status: "Subscriber free".
– ISDN access indicator: "ISDN".
The destination exchange will through connect before the connect message is sent.
Call history information is included in the connect message.
Upon receipt of an address complete message an intermediate national exchange will send the corresponding address complete message to the preceding exchange, and if this is the exchange controlling charging, the awaiting answer timer T9 is started. If timer (T9) expires, the connection is released and an indication is sent to the calling subscriber.
If a connect message is received at an intermediate national exchange instead of an address complete message, a connect message will be sent to the preceding exchange.
Upon receipt of an address complete message, the awaiting address complete timer () is stopped and the awaiting answer timer (T9) is started. If timer (T9) expires, the connection is released and an indication is sent to the calling subscriber.
If the connect message is received, then the awaiting address complete timer (T7) is stopped.
See also 2.1.4.2.
Upon receipt of an address complete or connect message, the awaiting address complete timer (T7) is stopped.
See also 2.1.4.2.
Upon receipt of an address complete or connect message, the awaiting address complete timer (T7) is stopped.
See also 2.1.4.2.
a) On receipt of an address complete message with the called line status indicator set to "subscriber free" an alerting indication is passed to the calling party if possible.
b) On receipt of the address complete message the awaiting address complete timer (T7) is stopped and the awaiting answer timer (T9) is started. If timer (T9) expires the connection is released and an indication is sent to the calling subscriber.
c) If the connect message is received, then the awaiting address complete timer (T7) is stopped (see 2.1.7.6).
The sending of the awaiting answer indication (e.g. ring
tone) at the destination exchange depends on the type of call. On speech, 64
kbit/s unrestricted preferred, 3.1 kHz calls and calls to an analogue called
party the awaiting answer indication is applied to the transmission path to the
calling party
from the destination exchange on receipt of an alerting indication from the
called party or from information contained within the destination exchange that
the called party will not or is prohibited from providing in-band tone.
Regardless of whether tones are to be provided or not, the destination exchange will through connect after the reception of the connection indication from the called party and before sending the answer/connect message to the preceding exchange.
If the destination exchange does not send the awaiting answer indication because the destination user provides for the sending of tones, then the destination exchange will through connect the transmission path in the backward direction on receipt of the progress indication.
The complete through-connection of the transmission path at answer is covered in 2.1.7.
An address complete message will not be sent until the cross-office check is made, if applicable (see Recommendation Q.543 [12]). If the succeeding network does not provide electrical called-party's-line-condition indications the last Signalling System No. 7 exchange shall originate and send an address complete message when the end of address signalling has been determined:
a) by receipt of an end-of-pulsing (ST) signal; or
b) by receipt of the maximum number of digits used in the national numbering plan; or
c) by analysis of the national (significant) number to indicate that a sufficient number of digits has been received to route the call to the called party; or
d) by receipt of an end-of-selection signal from the succeeding network (e.g. number received signal in Signalling System No. 5); or
e) exceptionally, if the succeeding network uses overlap signalling and number analysis is not possible, by observing that timer (T10) has elapsed since the last digit was received, and that no fresh information has been received; in such circumstances, transmission to the national network of the last digit received must be prevented until the end of the waiting period which causes an address complete message to be sent backward. In this way, it is ensured that no national answer signal can arrive before an address complete message has been sent.
If in normal operation, a delay in the receipt of an address complete signal from the succeeding network is expected, the last common channel signalling exchange will originate and send an address complete message 15 to 20 seconds (timer T11) after receiving the latest address message. The time-out condition is an upper limit considering the subclauses of 2.9.8.3 (20 to 30 seconds waiting for address complete message timer (T7) for outgoing international exchanges in abnormal release conditions).
When the T11 expires, an ACM is sent to the preceding exchange. Exchanges that run T11 do not run T7. In addition, the wait for answer timer (4.3.1/Q.118 [10]) shall be started at the sending of ACM.
In case the destination exchange delivered any call set-up information at the ISDN access, this will be indicated in the access delivery indicator in the first backward message (address complete, connect or release).
Only the destination exchange can generate the access delivery indicator.
An intermediate exchange (e.g. an outgoing international exchange) is required to recognise the access delivery indicator when it is received, and pass it on if possible.
When an intermediate exchange does not receive the access delivery indicator, no action is required. This would be the case when the destination exchange or the network between the destination exchange and the intermediate exchange does not support the access delivery indicator.
The procedure for use of the indication is for further study.
The call progress message is sent (only after the address complete message) from an exchange in the backward direction indicating that an event has occurred during call set-up which should be relayed to the calling party.
If the call progress message would exceed the 272 octet limit for Message Transfer Part transfer, it shall be segmented by use of the segmentation message; see 2.1.12.
The call progress message is sent from the destination exchange if the address complete message has been sent and subsequently:
– an indication is received that the called party is being alerted, the call progress message contains an event indicator that is set to "alerting";
– a progress indication is received from the called party, the call progress message contains an event indicator that is set to "progress".
If the indication received from the called party contains a "progress indication", this is carried by the call progress message in the access transport parameter (transported unchanged across the public network).
The destination exchange may on receipt of the indication from the called party, that contains an appropriate progress indicator, through connect the speech path, see 2.1.4.7.
In the case of call failure and the connection of a tone or announcement being returned before the address complete message has been returned, see 2.2.4.
On receipt of a call progress message an intermediate exchange will send the corresponding call progress message to the preceding exchange.
On receipt of a call progress message at the originating exchange, no state change occurs, and the appropriate indication is sent to the calling user. If the call progress message contained information carried in the access transport parameter, it is transferred unaltered into the indication returned to the calling user.
An information request message may be sent to any exchange in the forward (backward) call establishment direction after sending (receiving) an initial address message until when routeing is complete i.e. when the address complete message or connect message is generated at the destination exchange or when it is received by the intermediate or originating exchange.
On sending an information request message a timer (T33) is started. No second information request message may be sent in the same direction until a response information message is received. If the timer (T33) expires before the response message is received, see 2.9.7. The value of this timer (T33) is 12-15 seconds to allow for a cascade of information request messages, as described in item ii). The response information message may be sent as follows:
i) if all the information requested is available locally, then an information message containing all the required information is sent in response;
ii) if all the information is not available locally, but may be available remotely, then an information request message may be sent to a subsequent exchange in the connection in an attempt to extract the information not locally available. (This information request message may be delayed if one has already been sent and the response not yet received.) On receipt of a response, all the information necessary to respond to the original information message is sent in an information message;
iii) 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.
Upon receipt of an information message timer T33 is stopped.
If this message neither contains the requested information nor an indication that the requested information is not available, the actions taken will depend on whether the call can be progressed. Any information which was not requested is discarded.
If the answer message would exceed the 272 octet limit for Message Transfer Part transfer, it shall be segmented by use of the segmentation message; see 2.1.12.
When the called party answers, the destination exchange connects through the transmission path and the ringing tone is removed if applicable. An answer message to the preceding exchange is sent. If the destination exchange is the exchange controlling charging, then charging may begin.
Upon receipt of an answer message, an intermediate national exchange sends the corresponding answer message to the preceding exchange and, if this is the exchange controlling charging, charging may begin, and timer (T9) is stopped.
Upon receipt of an answer message, an outgoing international exchange sends the corresponding answer message to the preceding exchange and timer (T9) is stopped.
Upon receipt of an answer message, an intermediate international exchange sends the corresponding answer message to the preceding exchange.
See 2.1.7.4.
When the originating exchange receives an answer message indicating the required connection has been completed, the transmission path is connected through in the forward direction, if not already connected. The awaiting answer timer (T9) is stopped. If the originating exchange is the exchange controlling charging, charging may begin if applicable.
When connections are set up to terminals having an automatic answer feature, the alerting indication may not be received from the called party. If a destination exchange receives an answer indication an answer message is sent provided that an address complete message has been sent, otherwise the connect message is sent.
Because the signalling in Signalling System No. 7 does not pass over the circuit, facilities should be provided for making a continuity-check of the circuit in the circumstances described below.
The application of the continuity-check depends on the type of the transmission system used for the circuit. For transmission systems having some inherent fault indication features giving an indication to the switching system in case of fault, a continuity-check is not required. However, a per call continuity-check may be needed on fully-digital circuits when circuits or bundles of circuits in primary multiplex groups are dropped and inserted en route between switches, and alarm indications carried on bits of the primary multiplex frame structure are lost in passing through an intermediate transmission facility that does not relay them transparently. Typical, per call continuity-checks may be needed when the transmission link between switches contains a TDMA satellite system, a digital circuit multiplication system or a digital access and cross connection system, where fault indications are lost (see Recommendation Q.33 [6]).
When an initial address message is received with a request for a continuity-check, a continuity-check loop is connected.
For exchanges having both analogue and digital circuits served by Signalling System No. 7, the continuity-check initiated by a continuity-check request message could be used to test for proper alignment of circuit code identities. On those exchanges, reception of a continuity-check request message should always cause a loop to be attached to the circuit.
Alternative methods for detection of circuit identity misunderstandings in exchanges with all digital circuits may be employed.
The continuity-check is not intended to eliminate the need for routine testing of the transmission path.
The continuity check of the circuit will be done, link-by-link, on a per call basis or by a statistical method prior to the commencement of conversation. Procedures and requirements are specified in clause 7/Q.724 [15].
The actions to be taken when pilot supervision is used are described in clause 9/Q.724 [15].
When an initial address message is received with a request for continuity check (either on this circuit or on a previous circuit), timer T8 is started. On receipt of a successful indication of continuity check in a continuity message, timer T8 is stopped. However, if timer T8 expires, the connection is cleared (cause 41).
If an indication of continuity check failure is received in a continuity message, timer T27 is started awaiting a continuity re-check request. Also, the connection to the succeeding exchange is cleared. Timer T27 is stopped when the continuity-check request Message is received and timer T36 is started awaiting a continuity or release message.
If either timer T27 or timer T36 expires, a reset circuit message is sent to the preceding exchange. On reception of the release complete message, the circuit is set to idle.
Where circumstances require per call continuity checking for multi-rate connection type calls, the continuity of the single 64 kbit/s circuit whose circuit identification code is contained in the initial address message shall be checked.
Charging indicators are basically defined for national use. Therefore, unless there is bilateral agreement, the decision to charge a call or not, or to start international accounting will not be decided upon reception of these indicators.
The forward transfer message may be sent in telephony semi-automatic working in either of the following two cases:
a) following a call switched automatically to a subscriber, or following a call established via a special operator, the controlling operator wishes to call in an assistance operator. On receipt of the forward transfer message at the incoming international exchange, an assistance operator is called in;
b) following a call via codes 11 and 12, the controlling operator wishes to recall the incoming international exchange. Receipt of the forward transfer message at the incoming international exchange recalls the incoming operator on calls completed via the operator positions at the exchange.
The support of the forward transfer message in the international interface does not impose that the related functions are implemented in each incoming or outgoing international exchange (e.g. language assistance).
If transit network selection information is included in the set-up information from the calling party or is provided on a subscription basis, this information is carried in the transit network selection parameter, and is used for routeing of the call, e.g. to a specific carrier.
The simple segmentation procedure uses the segmentation message to convey an additional segment of an overlength message. Any message containing either the optional forward or backward call indicators can be segmented using this method. This procedure provides a mechanism for the transfer of certain messages whose contents are longer than 272 octets but not longer than 544 octets.
The procedure is as follows:
a) The sending exchange, on detecting that the message to be sent exceeds the 272 octet limit of the Message Transfer Part, can reduce the message length by sending some parameters in a segmentation message sent immediately following the message containing the first segment.
Note. The threshold for the initiation of the simple segmentation procedure may alternativily depend on network characteristics. The value of this threshold may vary per traffic relation depending on the typical network configuration and interconnection arrangements.
b) The parameters that may be sent in the second segment using the segmentation message are: the user-to-user information, generic digit, generic notification, generic number and access transport parameters. If the user-to-user information and access transport parameters cannot be carried in the original message and the two together do not fit in the segmentation message, the user-to-user information parameter is discarded.
c) The sending exchange sets the Simple Segmentation Indicator in the optional forward or backward call indicators to indicate that additional information is available.
d) When a message is received, at a local exchange, with the Simple Segmentation Indicator set to indicate additional information is available, the exchange starts timer T34 to await the segmentation message. This action may also take place at incoming or outgoing international exchanges if policing of information is required.
e) When the segmentation message is received timer T34 is stopped, and the call continues.
f) In case any other message except the ones listed below is received before the segmentation message containing the second segment the exchange should react as if the second segment is lost, i.e. the timer T34 is stopped and the call continues.
The messages are:
– Continuity.
– Blocking.
– Blocking acknowledgement.
– Circuit group blocking.
– Circuit group blocking acknowledgement.
– Unblocking.
– Unblocking acknowledgement.
– Circuit group unblocking.
– Circuit group unblocking acknowledgement.
– Circuit group query.
– Circuit group query response.
g) After expiry of timer T34 the call shall proceed and a received segmentation message containing the second segment of a segmented message is discarded.
h) At an incoming or outgoing international exchange, when following the simple segmentation procedure it is possible that the exchange has to reassemble an incoming message and subsequently re-segment it for onward transmission. In this case it has to be ensured that any unrecognised parameters received in the first, or second segment are transmitted in the first, or second, segment respectively, when the passing of the parameter is required by the compatibility procedure.
i) In case a segmentation message is received when not expected, see 2.9.5.1.
Note. Based on the set of services supported (e.g. ISDN end-to-end information, Call Diversion, User-to-user, etc.) and the set of APM applications (VPN, BICC, GAT, etc.), the exchange performing the segmentation is able to calculate the maximum length of the first segment, to leave enough space in a message for use by any subsequent. This maximum length may vary per traffic relation depending on the typical network configuration and interconnection arrangements.
For interworking with these ISDN User Part exchanges, no special action is required.
The originating exchange determines whether it is an N ´ 64 kbit/s connection type call by analysing the bearer capability information received in the access set-up message. The required number of timeslots and outgoing circuits are selected from available circuits within a 1544 or 2048 kbit/s G.704 [13] synchronous digital path. The principles of 2.9.1 (dual seizure) apply. The circuit identification code used in the ISUP messages shall be that of the lowest member circuit identification code. The timeslots and circuits selected need not be contiguous. When the non-contiguous circuit selection method is used, the selected circuits are indicated to the succeeding exchange in the circuit assignment map parameter carried in the outgoing initial address message.
On receipt of an initial address message at an intermediate exchange (intermediate national exchange, intermediate international exchange, or incoming international exchange) or a destination exchange, the circuit selection method used for the N ´ 64 kbit/s connection type call is determined as follows:
When the initial address message does not include the optional circuit assignment map parameter, contiguous circuit selection is implied. The circuits selected for the connection consist of the N contiguous circuits with the lowest member circuit identified by the circuit identification code.
When the initial address message does include the optional circuit assignment map parameter, non-contiguous circuit selection is indicated. The circuits selected for the connection consist of the N circuits specified by the circuit assignment map parameter.
If the N circuits as implicitly specified by the circuit identification code (contiguous) or explicitly specified by the circuit assignment map parameter (non-contiguous) of an incoming initial address message are idle, the incoming N ´ 64 kbit/s connection is selected. When the intermediate exchange selects outgoing N ´ 64 kbit/s non-contiguous circuits the outgoing circuit assignment map parameter shall be regenerated according to the selected outgoing circuits.
It is required that an ISC in a network supporting non-contiguous N ´ 64 kbit/s connection type procedures shall also support the fixed contiguous circuit selection connection type procedures described in this Recommendation, and have the capability of interworking between the two connection types. When interworking with an exchange (e.g. ISUP'92 exchange) which supports only the contiguous circuit selection method and 2 ´ 64 kbit/s, 384 kbit/s, 1536 kbit/s and 1920 kbit/s multirate connection types, only contiguous selection circuit and these connection types shall be used.
When either one call or both calls is/are using non-contiguous circuit selection, dual seizure cannot be detected until the exchange processes the contents of the circuit assignment map parameter in the incoming initial address message. Dual seizure occurs when there is at least one circuit in the N ´ 64 kbit/s connection types, either contiguous or non-contiguous, is selected at either end. The dual seizure resolution procedures described in 2.9.1.4 d) apply.
NOTE – In case of failure in the release or reset procedures, a momentary increase in signalling load can occur, the duration of which is dependent on the value of N.