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4.2.2.2 Override Category between ISDN's
When a call originates in one ISDN network and terminates in another ISDN
network and CLIR is applicable, the rules and regulations of the destination
(host) network should apply.
For example, if an override category is not available in the originating
network but is available in the destination network. The destination network can
still override the presentation restriction whenever CLI is available at this
network.
As a national option the originating network can restrict the CLI to the
destination network if the CLIR is applicable.
4.2.2.3 Interworking with non-ISDN or via non-ISDN
On calls to or via non-ISDN networks, it cannot be guaranteed that the
CLIR indication will be carried to the destination network.
As a national option the originating network can restrict the CLI to the
destination network if CLIR is applicable.
If the destination network receives a Calling Line Identity without any
indication of presentation allowed or restricted, the destination network will
act according to its rules and regulations.
4.2.2.4 Restriction of Additional Address Information
Any additional address information provided by the calling party, i.e.
sub-address, will also be subject to the CLIR supplementary service as indicated
in the Presentation Restriction Indicator in the Calling Party Number Parameter
field.
4.2.2.5 Message Sequence diagrams for CLIR
Figure 8/Q.730 describes the message flow for CLIR.
Figure 8/Q.730 - T1121510-89
4.3 Nodal signalling function SDLs for CLIP and CLIR
Nodal signalling function procedures for CLIP and CLIR are described in
Figures 9/Q.730 to 13/Q.730.
Figure 9/Q.730 - T1121520-89
Figure 10/Q.730 - T1121530-89
Figure 11/Q.730 - T1115781-89
Figure 12/Q.730 - T1116220-88
Figure 13/Q.730 - T1115790-88
4.4 Interaction of CLIP with other supplementary services
4.4.1 Calling Line Identification Restriction
The calling line identification will not be present if the calling user
has an arrangement to inhibit the presentation of his number to the called party.
4.4.2 Call Forwarding
If the call has been redirected the CLI presented to the user will be the
originating CLI.
Fascicle VI.8 - Rec. Q.730 PAGE23
4.4.3 Call Waiting
No interaction.
4.4.4 Closed User Group
No interaction.
4.4.5 Direct Dialling In
No interaction.
4.4.6 User to User Information
No interaction.
4.5 Interaction of CLIR with other supplementary services
4.5.1 Calling Line Identification Presentation
Calling Line Identification Restriction will take precedence over Calling
Line Identification Presentation.
The only occasion when a user subscribing to Calling Line Identification
Presentation can take precedence over Calling Line Identification Restriction is
when the user has override category. This is a national option.
4.5.2 Call Forwarding
If the call has been re-directed the CLI presented to the user will be the
originating CLI. When Calling Line Identification Restriction is applicable and
activated, the calling party's ISDN number will not be presented to the
"forwarded to" user unless this user has an override category. The latter is a
national option.
4.5.3 Call Waiting
When Calling Line Identification Restriction is applicable and activated,
no number will be presented to a called user subscribing to Call Waiting.
4.5.4 Closed User Group
It is an option to allow invocation of Calling Line Identification
Restriction in connection with a CUG call.
4.5.5 Direct Dailling In
No interaction.
4.5.6 User to User Information
No interaction.
5 Direct Dialling In (DDI)
5.1 Definitions
Direct Dialling In (DDI) enables a user to call directly another user on a
PABX or other private system without attendant intervention, the DDI digit(s)
being the least significant digit(s) of the called ISDN number.
The stage 1 definition of DDI is to be found in Recommendation I.251, S A.
The stage 2 description is included in Recommendation Q.81, S 1. This stage 3
description of DDI compliments the ISDN User Part protocol as defined in
Recommendations Q.761-Q.764 and Q.766.
PAGE24 Fascicle VI.8 - Rec. Q.730
5.2 Procedures
The procedures to set up a call are in general the same as the basic
procedures. A distinction is made whether DDI is applied to an analogue or an
ISDN PABX and whether the destination local exchange is aware of the number of
DDI digits required by the called PABX.
Besides sending the Address Complete Message and possibly Call Progress
Message(s) the subsequent messages will be the same as for a normal call without
DDI.
5.2.1 Analogue PABX
An Address Complete Message is sent as soon as the destination local
exchange has received the complete called party number and has selected a free
circuit to the PABX. The Called Line Status is set to "no indication".
If the destination local exchange has no knowledge about the number of DDI
digits required to set up the call it selects a free circuit, sends the received
DDI digits to the PABX and returns an Address Complete Message as soon as it has
received a signal to that effect from the PABX. The Called Line Status is set to
either "no indication" or "subscriber free" according to the signal received from
the PABX.
5.2.2 ISDN PABX
An Address Complete Message is sent as soon as the destination local
exchange has received the complete called party number with the Called Line
Status set to "no indication".
If the destination local exchange has no knowledge about the number of DDI
digits required to set up the call it sends an Address Complete Message as soon
as it has received the relevant information (Call Proceeding) from the PABX. The
Called Line Status is set to "no indication".
On receipt of an "alerting" indication from the PABX the destination local
exchange sends a Call Progress Message with the Called Line Status set to
"subscriber free".
If tones and/or announcements are provided from the destination local
exchange the transmission path is through connected on receipt of the relevant
information (Connect) from the PABX before sending the Answer Message to the
preceding exchange. If tones and/or announcements are provided from the PABX the
destination local exchange connects the backward path on receipt of an indication
to that effect from the PABX and sends a Call Progress Message to the preceding
exchange. The transmission path is fully through connected on receipt of the
relevant information (Connect) from the PABX.
5.3 Interactions with sub-addressing
The use of DDI has no impact on the use of sub-addressing and vice versa.
6 Call Forwarding services
6.1 General description of Call Forwarding services
The Call Forwarding services involve the redirection of a call originally
intended for one destination, towards another destination. The stage 1
definitions for the Call Forwarding services are given in Recommendation I.252
and the stage 2 descriptions are contained in Recommendation Q.82, S 2.
This section gives the ISDN User Part procedures to support the Call
Forwarding Unconditional, Call Forwarding Busy, and Call Forwarding No Reply
services. The functional description, formats and codes and general procedures
for the ISDN User Part are contained in Recommendations Q.761-764 and Q.766. This
section does not cover the optional validation procedure of Recommendation I.252.
One possible method of performing this validation is to use a courtesy call at
call forwarding activation time.
6.2 Definition of Call Forwarding services
The Call Forwarding Unconditional service permits a served user to have
the network send all incoming calls, or just those associated with a specified
basic service, addressed to the served user's ISDN number to another Number. This
forwarding occurs regardless of the condition of the termination (busy or idle)
and without the subscriber being given the opportunity to answer the call.
Fascicle VI.8 - Rec. Q.730 PAGE23
The Call Forwarding Busy service permits a served user to have the network
send all incoming calls, or just those associated with a specified basic service,
addressed to the served user's ISDN number, to another Number if the served user
is in the busy state (user busy, either Network Determined User Busy (NDUB) or
User Determined User Busy (UDUB). Recommendation I.252 contains the definitions
for busy in an ISDN environment (NDUB occurs when both B-channels are busy for
example).
The Call Forwarding No Reply service permits a served user to have the
network send all incoming calls, or just those associated with a specified bearer
service, addressed to the served user's ISDN number to another Number if the
served user does not respond to the alerting within a specified time period.
A terminating exchange that determines that Call Forwarding may occur will
not discard the setup information until the exchange determines that Call
Forwarding will not occur in this particular instance.
6.3 Procedures for Call Forwarding
The following three sections detail the ISDN-User Part procedures
associated with the Call Forwarding services. The first section gives a high
level view of ISDN User Part Call Forwarding procedures. The section consists of
a figure that demonstrates the parameters and parameter values that occur in an
Initial Address Message as a call undergoes a series of call forwardings. The
second section gives the procedures for an exchange that determines that a call
it has received should be forwarded. The third section gives the procedures for
notification of the calling user.
6.3.1 Call Forwarding related parameters in the Initial Address Message during
Multiple Forwardings
Figure 14/Q.730 - T1121540-89
PAGE24 Fascicle VI.8 - Rec. Q.730
6.3.2 Procedures for an exchange that determines that a call it has received
should be forwarded
6.3.2.1 General overview
When an exchange determines that it must forward a call, it first checks
to see if forwarding the call would result in the call exceeding the number of
forwardings allowed within the network. The second action that needs to be
undertaken, given that the limit was not exceeded, is the setting of the
parameters that would be used in an Initial Address Message for the forwarded
call. Even if the forwarding is intra-exchange this parameter information is set
and retained. The reason for the retention is that, if subsequent forwarding
occurs, the information is required to guarantee that the forwarding completes
correctly. Finally the exchange attempts to set up the forwarded call. Any
parameters received in the Initial Address Message not associated with forwarding
(e.g., Calling Number, Higher Layer Compatibility etc.) are included unchanged in
the Initial Address Message used to set up the forwarded call.
6.3.2.2 Checking the forwarding limit
If the call has already undergone forwarding, the redirection counter is
examined to see if another forwarding would take the counter above the network
specified limit. If it would, but the reason for the forwarding is Call
Forwarding No Reply, the call should be left in its current state with the
calling party continuing to receive ringing (the call is not cleared as the
calling user would get a confusing sequence of tones and announcements e.g.
ringing to network busy). In all other cases the call is cleared. The cause value
used in the Release message depends upon which of the Call Forwarding services it
is that would take the call over the limit. The mapping is as follows:
a) Call Forwarding Busy, the cause value "user busy" is used;
b) Call Forwarding No Reply, the cause value "no answer from user" is
used;
c) Call Forwarding Unconditional, the cause value "no user responding" is
used.
6.3.2.3 Setting the parameters associated with call forwarding
The parameters to be set depend upon the number of forwardings that the
call has undergone. The following three sections give the procedures for the case
where this is the first forwarding, the second forwarding and the third or
greater forwarding that the call has undergone.
6.3.2.3.1 This is the first forwarding that the call has undergone
There are three parameters to set: the redirection information, the called
party number and the original called number. Their values are set as follows:
1) Redirection information. The redirection counter is one. The
redirecting reason and redirecting indicator are set according to the
forwarding conditions.
2) Original called number. This is equal to the first number that was
called.
3) Called party number. This is equal to the number that the call is to be
forwarded to.
6.3.2.3.2 This is the second forwarding that the call has undergone
There are three parameters to set: the redirection information, the called
party number, and the redirecting number. Their values are set as follows:
1) Redirection information. The redirection counter is two. The
redirecting reason and redirecting indicators are set according to the
forwarding conditions.
2) Redirecting number. This is equal to the number that is doing the
redirecting.
3) Called number. This is equal to the number that the call is to be
forwarded to.
6.3.2.3.3 This is the third or greater forwarding that the call has undergone
There are three parameters that must be set: the redirection information,
the called party number and the redirecting number. Their values are set as
follows:
1) Redirection information. The redirection counter is incremented. The
redirecting reason and redirecting indicators are set according to the
Fascicle VI.8 - Rec. Q.730 PAGE23
forwarding conditions.
2) Redirecting number. This is equal to the number that is doing the
redirecting.
3) Called number. This is equal to the number that the call is to be
forwarded to.
6.3.2.4 Forwarding procedures at the forwarding exchange
The exchange continues based on the service that is causing the
forwarding. The procedures to be followed if the cause of the forwarding was
either Busy (Network Determined) or Unconditional are given below. These are
followed by the procedures for No Reply. Lastly the procedures for Busy (User
Determined) are given.
6.3.2.4.1 Call Forwarding Unconditional or Busy (Network Determined)
The exchange continues in the following fashion:
1) If the number that the call is to be forwarded to resides at another
exchange, an Initial Address Message is sent to continue the call on to
that exchange. The incoming trunk or line should be connected to the
chosen outgoing trunk immediately. The Initial Address Message includes
the parameter information as shown in S 6.3.1.
2) If the number resides in the same exchange, the exchange tries to set
up a call to that number. If the attempt is successful and neither Call
Forwarding Busy or Call Forwarding Unconditional occurs, the incoming
line or trunk should be connected to the destination line. If Call
Forwarding Busy or Call Forwarding Unconditional occurs when the
attempt is made, the Call Forwarding procedures should be re-entered.
6.3.2.4.2 Call Forwarding No Reply
The exchange continues in the following fashion:
1) If the number that the call is to be forwarded to resides at another
exchange, an Initial Address Message is sent to continue the call on to
that exchange. The incoming trunk or line is not connected to the
chosen outgoing trunk yet as it could result in confusing sequences of
in band tones or announcements (e.g., ringing going to busy). The
Initial Address Message includes the parameter information as shown in
S 6.3.1. If the exchange receives an alerting indication it should
connect the incoming trunk or line to the outgoing trunk, in at least
the backward direction. If the exchange receives an answer indication
it should connect in both directions. If the exchange receives a
release indication - called party busy for instance, the current
connections should simply be left intact, until timer expiry or calling
user disconnect.
2) If the original called user answers prior to receipt of alerting
indication from the forwarded-to exchange, this user is awarded the
call and the connection toward the forwarded-to exchange is released.
3) If the number resides in the same exchange, the exchange tries to set
up a call to that number. If the attempt is successful and neither Call
Fowarding Busy or Call Forwarding Unconditional occurs, the incoming
line or trunk is connected to the destination line. If Call Forwarding
Busy or Call Forwarding Unconditional occurs when the attempt is made,
the Call Forwarding procedures should be re-entered. If the exchange
cannot complete the call (e.g., destination is busy and No Call
Forwarding on Busy active), the current connections are left intact.
6.3.2.4.3 Call Forwarding Busy (User Determined)
The exchange continues in the following fashion:
1) An Address Complete Message with no indication of the called party's
status in the backward call indicators parameter should be returned to
the calling party's exchange.
2) If the number that the call is to be forwarded to resides at another
exchange, an Initial Address Message is sent to continue the call on to
that exchange. The Initial Address Message includes the parameter
information as shown in S 6.3.1. If the exchange receives an alerting
indication it should connect the incoming trunk or line to the outgoing
trunk. If the exchange receives a release indication - called party
busy for instance, the call should be released with the cause value
"user busy".
3) If the number resides in the same exchange, the exchange tries to set
up a call to that number. If the attempt is successful and neither Call
PAGE24 Fascicle VI.8 - Rec. Q.730
Forwarding Busy or Call Forwarding Unconditional occcurs, the incoming
line or trunk is connected to the destination line. If call Forwarding
Busy or Call Forwarding Unconditional occurs when the attempt is made,
the Call Forwarding procedures should be re-entered. If the exchange
cannot complete the call (e.g., destination is busy and no Call
Forwarding on Busy active) the call should be released with the cause
value "user busy".
Fascicle VI.8 - Rec. Q.730 PAGE23
6.3.3 Notification procedures for the forwarding exchange
An exchange forwarding a call sends a call progress message in the
backward direction if the forwarding (served) user does not subscribe to
notification (to the calling party) of the forwarded-to number. Procedures for
users subscribing to the notification of forwarded-to number are for further
study.
6.3.3.1 Forwarding user subscribes to redirection information presentation
restricted
The call progress message contains an event indicator of the "Event
Information Presentation Restricted Type". The value is set according to the
redirecting reason.
6.3.3.2 Forwarding user does not subscribe to redirection information
presentation restricted
The call progress message contains an event indicator that is not of the
"Event Information Presentation Restricted" type. The value is set according to
the redirecting reason.
6.3.3.3 Nofitification for Call Forwarding No Reply
If Call Forwarding No Reply is in effect, and the exchange alerts the
called party, the Address Complete message sent including the Backward and
Optional Backward Call indicators set to the appropriate values. In this case,
the Call Progress message is delayed until receipt of an alerting indication from
the forwarded-to exchange.
6.4 Interactions with other Supplementary Services where interaction has ISDN
User Part impact
6.4.1 User-to-User Signalling
6.4.1.1 Description of interaction
6.4.1.1.1 Call Forwarding Busy (Network Determined) or Call Forwarding
Unconditional
If the forwarding party does not subscribe to a Service requested as
"essential" the call is cleared. If the forwarding party inhibits User to User on
Forwarded calls and one or more User to User service was requested as
"essential", the call is cleared. The cause is "no user responding" in the case
of Call Forwarding Unconditional and "user busy" in the case of Call Forwarding
Busy.
If call clearing does not occur above and the forwarding party inhibits
User to User on Forwarded calls, the forwarding exchange will not include a User
to User indicators parameter in the Initial Address Message used to set up the
forwarded leg of the call. If the forwarding party does not subscribe to any of
the User to User services requested by the calling user, the forwarding exchange
will again not include a User to User indicators parameter in the Initial Address
Message used to set up the forwarded leg of the call. In both of these cases the
normal User to User procedures will ensure that the calling user is informed of
the lack of User to User signalling capability.
If the forwarding user subscribes to a requested user to user service and
does not inhibit it on forwarded calls, the forwarding exchange will try to
supply the user to user service requested. This will be accomplished by
requesting the user to user service in the outgoing Initial Address Message using
the same request information that was contained in the original Initial Address
Message. If the attempt is successful, user to user transfer will be available
between the calling user and forwarded to user.
PAGE24 Fascicle VI.8 - Rec. Q.730
6.4.1.1.2 Call Forwarding No Reply
Call Forwarding No Reply subscribers with Call Forwarding No Reply
activated can also be User to User Subscribers. They cannot however use the
Alerting (Address Complete) indication to indicate acceptance or rejection of
User to User Service requests. The Alerting (Address Complete) indication must
show a "no indication" response to any User to User service requests. Any other
response is a protocol error. Acceptance or rejection of User to User service
requests occurs in the Connect (Answer) indication.
If a Call is Forwarded No Reply and one or more of any requested User to
User services are essential and the forwarding user inhibits user to user on the
forwarding leg, then the call is cleared. If the forwarding party does not
subscribe to a Service requested as "essential" the call is cleared. The cause
used in both cases is "no answer from user".
Services 1 and 2 are not extended to the forwarded to party in the case of
Call Forwarding No Reply. Service 3 may be extended to the forwarded to party if
the forwarding user subscribes to User to User Service 3 and does not inhibit
User to User on the forwarded leg. The User to User indicators parameter for
service 3 in the Forwarding Initial Address Message should be set identically to
the values received in the Original Initial Address Message. If the Address
Complete Message received on the forwarded leg of the call indicates that service
3 was not provided, the call Forwarding No Reply exchange should retain this
indicator and insert it in the Answer Message when it is received. If the Address
Complete Message received on the forwarded leg of the call indicates that servive
3 is provided, the Call Forwarding No Reply exchange should retain this indicator
and insert it in the Answer Message when it is received.
6.4.1.1.3 Call Forwarding Busy (User Determined)
Call Forwarding Busy (User Determined) subscribers can also be User to
User Subscribers. The Address Complete Message sent back upon receipt of the
release from the originally called party should give "no information" in response
to any received User to User requests.
If a Call is Forwarded Busy (User Determined) and one or more of any
requested User to User services are essential and the forwarding user inhibits
user to user on the forwarding leg, then the call is cleared. If the fowarding
party does not subscribe to a Service requested as "essential" the call is
cleared. The cause used in both cases is "user busy".
Services 1 and 2 are not extended to the forwarded to party in the case of
Call Forwarding Busy (User Determined). Service 3 may be extended to the
forwarded to party if the forwarding user subscribes to User to User Service 3
and does not inhibit User to User on the forwarded leg. The User to User
indicators parameter for service 3 in the Forwarding Initial Address Message
should be set identically to the values received in the Original Initial Address
Message. If the Address Complete Message received on the forwarded leg of the
call indicates that service 3 was not provided, the Call Forwarding Busy (User
Determined) exchange should retain this indicator and insert it in the Answer
Message when it is received. If the Address Complete Message received on the
forwarded leg of the call indicates that service 3 is provided, the Call
Forwarding Busy (User Determined) exchange should retain this indicator and
insert it in the Answer Message when it is received.
6.4.1.1.4 Message length
There is a further implication in that multiple forwarding adds to the
length of the Initial Address Message. If the Initial Address Message that is to
be used on a call setup is within 32 octets of the 272 octet message length
limit, the user to user information should be dropped. This will result in a
guarantee that the Initial Address Message will not subsequently exceed the
length limit.
6.4.2 Closed User Group
6.4.2.1 Description of interaction
Closed User Group restrictions must be met on each leg of the call. In
addition, CUG restrictions must be met end-to-end. If the call is forwarded
multiple times, CUG restrictions have to be met between the calling user and
every intermediate forwarding user.
Fascicle VI.8 - Rec. Q.730 PAGE23
Calling User/Forwarded-to User: When a call is forwarded a new check of
the CUG restrictions is made at the forwarded-to destination. The CUG information
sent to the forwarded-to destination is the same CUG information that was sent
from the originating exchange.
6.4.2.2 Actions at a forwarding exchange
For a subscriber who has both CUG interlock and Call Forwarding services,
checks will have to be made prior to entering the Call Forwarding procedures. The
forwarding users CUG interlock code(s) will have to be checked against the
calling user CUG interlock code. The check would be done at the exchange for the
decentralized case and at a database after a TCAP query response sequence for the
centralized case. If the check is passed, the Call Forwarding procedures may be
entered. If the call proceeds onwards from the forwarding exchange the CUG
interlock code and outgoing access indication, which was included in the Initial
Address Message received, is included in the Initial Address Message transmitted.
6.4.2.3 Actions at a destination exchange
If an exchange receives a call for a CUG member it will have to check
against the calling user CUG code. The check would be done at the exchange for
the decentralized case and at a database after a TCAP query response sequence for
the centralized case. The check would have to be passed for the call to complete.
6.4.3 Calling Line Identification Presentation
When an exchange receives a call for a Call Forwarding No Reply
Subscriber, Address Complete is not returned until alerting is received from the
called party. Address Complete messages returned for Call Forwarding No Reply or
Call Forwarding (user determined) Busy. Subscribers contain an optional backwards
call indicators parameter. The value of this parameter should indicate "Call
Forwarding may occur". This indication alerts the transit and originating
exchanges that the call is not yet in a stable state as Call Forwarding No Reply
may occur. This is used to allow the request/response cycle to be used to obtain
the calling number for the forwarded to party if Call Forwarding No Reply occurs.
6.5 Message flow diagrams
The messages over the access are included as examples only and are not
exhaustive.
Call release procedures are as per normal call.
Abbreviations used in Figures 15/Q.730 to 22/Q.730 are the following:
IAM Initial Address Message
CPG Call Progress Message
ACM Address Complete Message
ANM Answer Message
REL Release
RLC Release Complete
LE Local Exchange
TE Terminal Entity
TR Transit Exchange
Figure 15/Q.730 - T1115800-88
Figure 16/Q.730 - T1115810-88
Figure 17/Q.730 - T1115820-88
Figure 18/Q.730 - T1115830-88
Figure 19/Q.730 - T1115840-88
Figure 20/Q.730 - T1115850-88
Figure 21/Q.730 - T1115860-88
Figure 22/Q.730 - T1115870-88
7 Time-out table
Table 5/Q.730 specifies the timers to be used in conjunction with the
supplementary services defined in this Recommendation. (This requires further
study.)
TABLE 5/Q.730
Symbol Time-out Significa Cause for Normal At the At the Section
value nce initiatio terminati first following
n on expiry expiry
T3 U-U Receipt "Protocol
facility of error"
request facility passed to
Acceptanc call
e or control
reject
message
PAGE24 Fascicle VI.8 - Rec. Q.730
Fascicle VI.8 - Rec. Q.730 PAGE23
PAGE24 Fascicle VI.8 - Rec. Q.730