InfoMagic Standards 1994 January/InfoMagic Standards - January 1994.iso/ccitt/1988/troff/6_12_02.tro

Text File | 1991-12-13 | 78KB | 2,614 lines

.rs
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.\"                 Not Copyright ( c) 1991
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.EN
.nr LL 40.5P
.nr ll 40.5P
.nr HM 3P
.nr FM 6P
.nr PO 4P
.nr PD 9p
.po 4P

.rs
\v | 5i'
.sp 2P
.LP
\fBRecommendation\ Q.1004\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBLOCATION\ REGISTER\ RESTORATION\ PROCEDURES\fR
.EF '%    Fascicle\ VI.12\ \(em\ Rec.\ Q.1004''
.OF '''Fascicle\ VI.12\ \(em\ Rec.\ Q.1004    %'
.ce 0
.sp 1P
.LP
\fR \fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
The data stored in the location registers are automatically
updated and the main information is related to the location of the mobile
station. The data is updated when the mobile station moves from one area to
another. The loss of this information would have an important impact on the
service provided to the relevant mobile subscribers. It is therefore necessary
to define solutions to limit the perturbations following a register failure
and to restore automatically these tables.
.PP
This Recommendation describes some methods that could be
implemented in order to provide a good security of the data stored in the
location registers and procedures that could be performed to restore the
location data and supplementary services data after a location register
failure.
.PP
However, the implementation of these methods and procedures are not
mandatory and are open to technical innovation.
.RT
.sp 2P
.LP
\fB2\fR     \fBTechnical realizations to achieve the objectives\fR
.sp 1P
.RT
.PP
To avoid a loss of all the data stored in a location register when a failure
occurs, it is necessary to implement a periodic safeguard of the
memories. This method is normally used in the telephone exchanges where
a copy of the tables is made periodically in order to allow a restart if
a control
unit failure occurs. This back\(hyup can be made on either a disc device or a
magnetic tape.
.RT
.sp 2P
.LP
\fB3\fR     \fBRestoration of the location register memories\fR
.sp 1P
.RT
.PP
The perturbations due to a deterioration of the location tables and the
restoration procedures are different if the equipment affected is a home
or a Visitor Location Register.
.RT
.sp 2P
.LP
3.1
    \fIThe\fR
\fIvisitor location register\fR
.sp 1P
.RT
.sp 1P
.LP
3.1.1
    \fIStatus of the data after a failure\fR
.sp 9p
.RT
.PP
When a visitor location register failure occurs, some
discrepancies between the actual location of the mobile station and the
location information stored may appear in the following cases:
.RT
.LP
    i)
    since the last safeguard, the mobile moved to another
location area in the same MSC area; the allocated roaming
number remains correct but the location area information is
wrong;
.LP
    ii)
    the mobile appeared in the MSC area after the last
safeguard; this mobile is then unknown by the visited location
register while the home location register stored a roaming
number corresponding to this new location;
.LP
    iii)
    the mobile left the MSC area; a roaming number is
allocated in the visitor register but the updating was made in
the home register;
.LP
    iv)
    the mobile left the MSC area and then came back; for the
visitor register, the mobile did not leave the MSC area and the
previous roaming number is considered as correct by the visitor
register while the home register stored another roaming number
given during the last updating made before the failure.  The
location area information saved may not be the relevant
one.
.sp 1P
.LP
3.1.2
    \fIRestoration procedures\fR
.sp 9p
.RT
.PP
When a failure occurs, the data concerning only a small part of
the mobiles located in the relevant area are lost. Therefore, it seems
that a systematic restoration method such as a general interrogation of
the home
location registers would load the network and the equipments for so small a
result.
.bp
.PP
The restoration process is then the following:
.PP
At the restart of the register each element of the memory is pointed out
by an indicator. This indicator is turned out when the relevant location
information has been checked.
.RT
.LP
    a)
    \fIOutgoing calls\fR
.LP
    When the restart occurs, each outgoing call from a mobile
will initiate the checking operation of its location
information:
.LP
    \(em
    if the mobile is already registered in the MSC area,
the location area information is updated, if necessary,
but the location updating procedure is not initiated with
the home register (case\ i) solved);
.LP
    \(em
    if the mobile is unknown in this MSC area, a roaming
number is allocated to that station and a location
updating procedure is started with the home register
(case\ ii) solved).
.LP
    b)
    \fIIncoming calls\fR
.LP
    Concerning the incoming calls, in the cases ii) and iv)
described above, the roaming number received by the MSC in the
IAM does not correspond to the right mobile station. In some
cases, it is not allocated or it may be allocated to another
mobile; this depends on the method used to allocate this number.
The normal solution (see also note) to detect this difficulty is
that the Initial Address Message received by the MSC during the
call set\(hyup contains also the international ISDN number of the
called subscriber. If this is the case, the visitor location
register can check the couple to detect a possible mistake.
If an inconsistency is noticed, the MSC sends then an
Unsuccessful Backward Message to inform the originating exchange
that it is unable to complete the call. The VLR interrogates the
relevant HLRs (the mobiles may be attached to two different
HLRs) to correct its tables. Two interrogations have to be
performed:
.LP
    \(em
    one about the mobile station to which the VLR
allocated this wrong roaming number (MS\ 1);
.LP
    \(em
    the other about the station to which the call was
destined (MS\ 2).
.LP
    i)
    The MS 1 left its MSC area; the VLR erases it from
its table and updates it by allocating the roaming
number to MS\ 2 which is introduced in the VLR tables.
The data attached to that station are requested from its
HLR;
.LP
    ii)
    The MS 1 is still in the MSC area:
.LP
    \(em
    the VLR allocates a new roaming number to that
station and then updates the relevant HLR;
.LP
    \(em
    the MS 2 is introduced in the VLR table and
the parameters attached to that station are
requested from its HLR.
.LP
    If the mobile station left its location area since the last
safeguard, the paging message sent will remain unanswered and
the mobile will be considered as lost or out of service. To
improve the service, the call message may be sent in all the
location areas controlled by the MSC. If the mobile answers, the
location information is then updated. If not, the mobile is
considered out of reach and the appropriate unsuccessful
end\(hyof\(hyselection message is sent backwards.
.LP
    If the mobile is switched off when it is called, the result
is the same as the above.
.LP
    \fINote\fR \ \(em\ As a national option, the HLR may use the \*Qsend
parameter from VLR\*U operation of MAP to obtain the MSRN from the
VLR on a per call basis. This is normally allowed only within a
PLMN.
.LP
    c)
    \fIParticular cases\fR
.LP
    In case iii), as the mobile leaves the area, no traffic is
related to that mobile; restoration is then impossible and a
roaming number is frozen for nothing. To solve this problem, if
the validation of the location information does not
occur after a certain delay (in the order of one day or more),
the VLR may then interrogate the HLR to know if this station is
still located in its area. This method can also solve cases\ ii)
and\ iv) if the corresponding mobiles have a very low
traffic.
.sp 1P
.LP
3.2
    \fIThe home location register\fR
.sp 9p
.RT
.PP
The deterioration of the data contained in the home location
register is of concern not only for the PLMN but also for the whole service.
The home location register needs the help of all the visitor registers in
charge of the MSC areas where its mobiles are located.
.bp
.PP
When a restart of the home location register occurs, a specific reset message
is sent to all the visitor location registers to inform them about the
failure. As the home register is unable to know the addresses of all the
visitor registers in service, the only solution is to send the message
only to the registers known. The list is extracted from the tables saved
previously; of course some modifications occurring since the last back\(hyup
are lost and
therefore some visitor registers involved in the control of mobiles managed
by this home register will not be contacted. But the number of registers
forgotten will be very low. Another solution could be that the reset message
is sent only to the \*Qneighbour\*U VLRs; a specific table giving the addresses
of these VLRs
is then contained in the HLR memories. The content of that table is defined
by the operating people according to the roaming traffic of the mobile
managed
by this HLR. In that case too, the number of forgotten registers will be
very low.
.PP
After receiving this reset message, when a mobile concerned by the
failure sends a radio message, to update its location, to set up an outgoing
call, to answer an incoming call or a request coming from the MSC or to
activate or request a supplementary service, the relevant visitor location
register will initiate a location updating procedure with the home location
register. The latter then updates its tables and validates the relevant data.
.PP
If, after a certain delay, the location of some mobiles is not
confirmed, the home register interrogates the relevant visitor registers.
If a positive answer can be obtained, the location information is validated.
If not, because the mobile left the MSC area between the back\(hyup and
the failure, an
alarm message may be given to the technical staff in order to inform them
about the loss of the location of this subscriber.
.RT
.sp 1P
.LP
3.3
    \fIPeriodic registration\fR
.sp 9p
.RT
.PP
The delay to confirm the location of a subscriber after a failure depends
on the traffic of this station. If a station is silent for a long time,
it would be difficult to know if the location information stored is correct
or not during this period.
.PP
A solution to reduce this delay is to force the mobile to send a
message when it remains still during a long time. For that purpose, a time\(hyout
is reinitiated at each message sent by the mobile. When this time\(hyout
expires, the station sends a location updating message to the base station.
A rough
estimate of this time\(hyout value may be a few hours (this value is to
be fixed according to traffic simulations and it seems that it could be
comprised
between 12\ and 24\ hours); if the IMSI detach procedure when switched
off is not used, to avoid an overload of the control channel in the morning,
this time\(hyout runs only when the station is switched on. With this method,
the delay during which the mobile can be lost is less than the duration
of this time\(hyout. The
interruption of the time\(hyout when the station is switched off is not
a problem because it is then unable to receive any call; therefore, the
service provided to that subscriber is not degraded. If the IMSI detach
procedure is used, the first message sent by the mobile when it is switched
on is the IMSI attach;
in that case the interruption of the time\(hyout may or may not be
implemented.
.RT
.sp 2P
.LP
\fB4\fR     \fBRestoration of the supplementary service parameters\fR
.sp 1P
.RT
.PP
As well as the location data, the supplementary service parameters may
be disturbed when a register failure occurs. Therefore, it is necessary
to define methods to restore them.
.RT
.sp 1P
.LP
4.1
    \fIVLR fault recovery\fR
.sp 9p
.RT
.LP
    a)
    When the VLR fails, the HLR is able to retrieve the
activation status of the supplementary services. However, if the
visitor location register does not require any information from
the home location register in order to comply with a MS
supplementary services activation request, the involved data
are not available in the HLR when the VLR fails. This situation
cannot appear if the location area is the only information in
the VLR which is unknown from the HLR. Otherwise, it would be
necessary to include in the deregistration request and in the
location cancellation acknowledge messages sent by the VLR to
HLR the parameters of activations which would be only known from
the VLR.
.LP
    b)
    After the restart of a VLR, risks of inconsistency appear
between the tables of the VLR and of the HLR:
.LP
    \(em
    relating to incoming calls, the mobile may have
recently modified activation status of supplementary
services; reverse charging acceptance, diversion call on
no reply, connect when free. |  | ;
.bp
.LP
    \(em
    relating to outgoing calls, this method allows
checking of other parameters; conditional barring of
outgoing calls, preferential closer used
group. |  |
.PP
Two few mobiles are involved in this situation to justify the
systematic interrogation of the HLR by the VLR so it is suggested that
the VLR sends an information request message to the HLR if, and only if,
one SS at
least was registered in the saved tables of the VLR. This message must
request from the HLR all parameters of supplementary services that are
related to the mobile. Moreover, as soon as the data of supplementary services
are validated in the tables of the VLR, an indicator has to be turned out.
.PP
The retrieval procedures are not influenced by handover.
.RT
.sp 1P
.LP
4.2
    \fIHLR fault recovery\fR
.sp 9p
.RT
.PP
When the restart of a home location register occurs, the loading of a previously
saved state is useful. However, the mobile may have changed its
parameters of registration or activation since the last back\(hyup of the HLR;
these cases are presented here.
.RT
.sp 1P
.LP
4.2.1
    \fIRetrieval of SS\(hyregistration status\fR
.sp 9p
.RT
.PP
If the mobile station changed recently, by administrative means,
the list of the supplementary services for which it contracts a subscription,
the operation can be lost by the system when the HLR fails. It seems important
to avoid this situation with a high security.
.PP
When the MS requests, by signalling means, the HLR to provide a
registration for a specific supplementary service, this capability being
additional to that of providing subscriptions by administrative means,
the HLR has to save this command with a high level of security, against
an eventual HLR failure. After that, the HLR can send back a categoryB/Fsupplementary
services
information acknowledge message to the VLR.
.RT
.sp 1P
.LP
4.2.2
    \fIRetrieval of SS\(hyactivation status\fR
.sp 9p
.RT
.PP
After the HLR failure, the information which is related to the
activations of supplementary services by a not\(hyregistered station are
available in no VLR.
.PP
Therefore, the reset message which is sent by the reinitialized
HLR to all VLRs should contain implicitly an information request about the
current activation status of the supplementary services. Since in some cases
the VLR may not know these data, the relevant parameters should be held
in the mobile equipment. To recover them, two possibilities are
available:
.RT
.LP
    \(em
    to include this request into a \*Qsearch\*U message, from the
VLR towards the MSC, and then to send a category/supplementary
services information message to the HLR; however, the HLR cannot
recover by this method the data associated with the
non\(hyregistered mobiles;
.LP
    \(em
    to wait for the next mobile originating message and to
indicate to the mobile the loss of supplementary services status
in the system; the simplest solution is that the information is
only given after a status request message from the mobile; but
the quality of the service would be improved if the information
was introduced into a field of any originating mobile message
acknowledgement. It may be envisaged, too, that the mobile
station equipment or the subscriber card contain the description
of all supplementary service parameters.
.sp 1P
.LP
4.3
    \fIMSC fault recovery\fR
.sp 9p
.RT
.PP
No information is stored in the home or visitor location register for the
following services:
.RT
.LP
    \(em
    charging information (different forms of facilities);
.LP
    \(em
    credit card call;
.LP
    \(em
    debit card call;
.LP
    \(em
    reverse charging, MS originating call;
.LP
    \(em
    completion of calls to busy subscriber, MS orig. and term.
calls.
.PP
All these services are invoked on a call per call basis; if the
VMSC fails, the location registers cannot help the MSC to recover the contexts
of the established calls. There is no difference with a normal fixed
exchange.
.bp
.sp 2P
.LP
\fBRecommendation\ Q.1005\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBHANDOVER PROCEDURES\fR
.EF '%    Fascicle\ VI.12\ \(em\ Rec.\ Q.1005''
.OF '''Fascicle\ VI.12\ \(em\ Rec.\ Q.1005    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
This Recommendation contains a detailed description of handover
procedures to be used in PLMNs.
.PP
The following cases are considered:
.RT
.LP
    i)
    handover between radio channels of the same base station;
.LP
    \fINote\fR \ \(em\ This capability is mandatory and could be used in
the following situations:
.LP
    \(em
    when the radio channel carrying the call is subject to
interference or other disturbances, and/or
.LP
    \(em
    when a radio channel or channel equipment carrying a
call  has to be taken out of service for maintenance
or other reasons;
.LP
    ii)
    handover between base stations of the same MSC in
order to ensure continuity of the connection
when an MS moves from one BS area to another;
.LP
    iii)
    handover between base stations of different MSCs of the
same PLMN; and
.LP
    iv)
    handover between base stations of MSCs in different
PLMNs.
.PP
The same procedures can be used on the radio path for all four
cases.
.PP
Cases i) and ii) involve only one MSC.
.PP
\fINote\fR \ \(em\ Depending on the handover criteria, case ii) may involve
measurements in other MSCs.
.PP
Cases iii) and iv) involve more than one MSC. For these cases, two
procedures are defined requiring the use of the mobile application
part:
.RT
.LP
    a)
    \fBbasic handover procedure\fR where the call is handed over
from the controlling MSC (MSC\(hyA) to another MSC (MSC\(hyB);
and
.LP
    b)
    \fBsubsequent handover procedure\fR where the call is
handed over from MSC\(hyB to MSC\(hyA or from MSC\(hyB to a third MSC
(MSC\(hyB`).
.PP
In most respects case iv) is similar to case iii). However, any
additional aspects of case iv) not covered by the specification of case\ iii)
will not be included in this Recommendation for the time being.
.PP
The procedures in the mobile application part for supporting handover are
specified in Recommendation\ Q.1051.
.PP
In the following, the controlling MSC will be referred to as MSC\(hyA
also when the handover only involves this MSC [cases\ i) and\ ii) above]. For
cases\ iii) and\ iv), the controlling MSC (MSC\(hyA) is the MSC on which
the call
was originally established.
.PP
All MSCs should be capable of acting as MSC\(hyA and
MSC\(hyB.
.RT
.sp 2P
.LP
\fB2\fR     \fBFunctional composition of MSCs and interfaces for handover\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fIMSC\(hyA\fR
.sp 9p
.RT
.PP
For handover the controlling MSC can be regarded as being composed of functional
units as shown in Figure\ 1/Q.1005.
.RT
.sp 1P
.LP
    \fISignalling functions\fR
.sp 9p
.RT
.LP
    1)
    The \fIBS/MSC (MS/BS) procedures MSC\(hyA\fR  | for signalling
between the MSC and the BS and between the MSC and the MS.
The functional unit interfaces the BSs through interfaces\ A`
(to the previous BS)  and, for case\ ii), also through
interface\ A`` (to the new BS). Interworking with other
functional units takes place through the internal interface\ X.
.bp
.LP
    2)
    The \fIcall control procedures MSC\(hyA\fR  | for normal call control
functions (interface\ B`) and for signalling and call control of
connections to other MSCs (interfaces\ B`` and B```).
Interfaces\ B`` and\ B``` apply only to handover
cases\ iii) and\ iv)  where interface\ B``` is required for
subsequent handover.
.LP
    3)
    The \fIhandover control procedures MSC\(hyA\fR  | or overall
control of the handover including interworking with other
functional units (interfaces\ X, Y and\ Z).
.LP
    4)
    The \fIMAP procedures MSC\(hyA\fR  | for information exchange with
other MSCs and location registers. This function is required
for handover cases\ iii) and\ iv). The external interface is
interface\ c and the internal interface to the handover control
functions is interface\ Z. Interface\ C represents the interface
to all entities with which MSC\(hyA is communicating during
handover (other MSCs, location registers).
.LP
\fI
    \fINote\fR \ \(em\ This functional unit may also be required for
cases\ i) and\ ii) if measurements have to be performed in other
MSCs for determining the new BS (see below).
.LP
.rs
.sp 38P
.ad r
\fBFigure 1/Q.1005, (N), p.1\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
    \fISwitching functions\fR
.sp 9p
.RT
.LP
    5)
    The \fIswitch and handover device MSC\(hyA\fR  | for connecting the
new path. This function is additional to normal switching
functions in the MSC. The handover device has interfaces to the
previous BS (interface\ A`) and the new BS (interface\ A``) for
handover case\ ii). Interface\ B` represents the original
connection with the fixed network and interface\ B`` represents
the new connection to and MSC\(hyB for handover between MSCs
(cases\ iii) and\ iv)). Interface\ B``` represents the connection
to a third MSC (MSC\(hyB`) for subsequent handover from MSC\(hyB to
MSC\(hyB`. The connections which can exist in the handover device
are shown in Figure\ 2/Q.1005.
.LP
.rs
.sp 27P
.ad r
\fBFigure 2/Q.1005, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The connection via interface A` is released after completion of a successful
handover (Figures\ 2a and\ 2b/Q.1005).
.PP
For MS to MS calls in the same MSC the configuration in
Figure\ 2b/Q.1005 applies. Then interface B`` is not to another MSC but
internal to MSC\(hyA.
.RT
.ce
\fBH.T. [T1.1005]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(60p) | cw(60p) .
Case    Initial connection    Resulting connection
_
.T&
cw(60p) | cw(60p) | cw(60p) .
Figure 2a)/Q.1005    A` to B`    A`` to B`
_
.T&
cw(60p) | cw(60p) | cw(60p) .
Figure 2b)/Q.1005    A` to B`    B` to B``
_
.T&
cw(60p) | cw(60p) | cw(60p) .
Figure 2c)/Q.1005    B` to B``    B` to B```
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau [T1.1005], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.2
    \fIMSC\(hyB\fR
.sp 9p
.RT
.PP
The functional composition of an MSC acting as MSC\(hyB is essentially
the same as that of MSC\(hyA. However, there are some differences. The
functional units are as follows (see Figure\ 3/Q.1005).
.RT
.LP
.rs
.sp 39P
.ad r
\fBFigure 3/Q.1005, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
    \fISignalling functions\fR
.sp 9p
.RT
.LP
    1)
    The \fIBS/MSC (MS/BS) procedures MSC\(hyB\fR  | or signalling
between the MSC and the new BS and between the MSC and the
MS (interface\ A``).
.LP
    2)
    The \fIcall control procedures MSC\(hyB\fR  | for normal call control
functions and for signalling between MSC\(hyA and MSC\(hyB.
.LP
    3)
    The \fIhandover control procedures MSC\(hyB\fR  | for control of the
handover in MSC\(hyB.
.LP
    4)
    The \fIMAP procedures MSC\(hyB\fR  | for information exchange with
MSC\(hyA and the VLR of MSC\(hyB.
.bp
.sp 1P
.LP
    \fISwitching functions\fR
.sp 9p
.RT
.LP
    5)
    The \fIswitch MSC\(hyB\fR  | for connecting the circuit from MSC\(hyA
(interface\ B``) to the circuit to the BS (interface\ A``).
.PP
MSC\(hyB will also require a handover device for subsequent handovers to
BSs (or to another channel of the same BS) in the MSC area of MSC\(hyB.
Subsequent handovers to other MSCs will not require switching in MSC\(hyB (see
below).
.sp 2P
.LP
\fB3\fR     \fBInitiation\fR
.sp 1P
.RT
.PP
The decision that a handover shall take place can be made by both the MS
and the BS by monitoring the channel quality. If the decision is made
by the MS, a handover request message should be provided to the BS.
.PP
Depending on the radio sub\(hysystem arrangement the new BS, to which
the call is to be handed over, can either be determined by the MS or the
MSC. If determined by the MS, the indication of the BS candidates will
be providing to the MSC by signalling on the radio path.
.PP
If the new BS is to be determined by the MSC, this may require
measurements on its own BSs and BSs in other MSCs. Procedures defined in
Recommendation\ Q.1051 are used for initiating measurements on BSs in other
MSCs.
.PP
The initiation procedures are for further study.
.RT
.sp 2P
.LP
\fB4\fR \fBGeneral description of the procedures for handover to another
MSC\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
    \fIBasic handover procedure\fR
.sp 9p
.RT
.PP
The procedure which takes place after initiation, i.e.\ after the
identity of the new BS has been determined, is shown in Figure\ 4/Q.1005
for a successful handover. The procedure makes use of messages of the Mobile
Application Part (MAP) of Recommendation\ Q.1051.
.RT
.LP
.rs
.sp 25P
.ad r
\fBFigure 4/Q.1005, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
Firstly, MSC\(hyA sends a \fIradio channel request\fR  | essage to MSC\(hyB.
The message will contain all parameters needed by MSC\(hyB for allocating
a radio channel (see Recommendation\ Q.1051). The message will also identify
the BS to which the call is to be handed over. MSC\(hyB will return the
\fIradio channel\fR
\fIacknowledge\fR  | essage after having received the mobile station roaming
number from its VLR (exchange of the messages \fIrequest for handover number\fR
 | nd
\fIhandover number acknowledge\fR ). The roaming number is to be used for
routing
the call from MSC\(hyA to MSC\(hyB. If a traffic channel is available in
MSC\(hyB the
\fIradio channel acknowledge\fR  | essage will contain the identity of the new
radio channel and the mobile station roaming number. Other parameters may
also be included (see Recommendation\ Q.1051).
.PP
If there is no free traffic channel in MSC\(hyB, this will be indicated
to MSC\(hyA and MSC\(hyA will terminate the handover procedure. The existing
connection to the MS will not be cleared.
.PP
At this point, MSC\(hyA establishes a connection between MSC\(hyA and MSC\(hyB
by signalling procedures supported by the network to which MSC\(hyA is
connected. In Figure\ 4/Q.1005 this is illustrated by the messages IAM
(Initial Address
Message) and the ACM (Address Complete Message) of Signalling System No.\ 7.
MSC\(hyB initiates the handover procedure on the radio path when the ACM
is sent and MSC\(hyB initiates the procedure when the ACM is received (illustrated
by
HB\(hy and HA\(hyINDICATION, respectively).
.PP
The connection is through\(hyconnected in MSC\(hyA by use of a handover
device. The through\(hyconnection is done and the old radio channel is released
when MSC\(hyA receives an acknowledgement from the MS (HA\(hyCONFIRM) or
when the
\fIsuccessful handover\fR message is received from MSC\(hyB. MSC\(hyB sends
this message when it receives an acknowledgement from the MS (HB\(hyCONFIRM).
.PP
In order not to conflict with the PSTN/ISDN signalling system(s) used between
MSC\(hyA and MSC\(hyB, MSC\(hyB must generate an answer signal when HB\(hyCONFIRM
is received.
.PP
If the connection between MSC\(hyA and MSC\(hyB cannot be established
(e.g. an unsuccessful backward message is received instead of the ACM),
MSC\(hyA terminates the procedure without clearing the radio path.
.PP
MSC\(hyA will have the overall call control until the call is cleared by
the fixed subscriber or the MS and there are no further call control functions
to be performed (e.g.\ servicing waiting calls). MSC\(hyA then releases
the
connection to MSC\(hyB and also sends an \fIend signal\fR message which
terminates
the MAP procedure. When receiving this message MSC\(hyB will release all
call control functions and send the message \fIremove handover number\fR
to its VLR.
.PP
MSC\(hyA may terminate the procedure at any time by sending the MAP
message \fIhandover cancellation\fR  | to MSC\(hyB. If establishment of
the physical
connection between MSC\(hyA and MSC\(hyB has been initiated, the physical
connection must also be cleared by procedures defined for the signalling
system used
between MSC\(hyA and the fixed network. The VLR of MSC\(hyB is also informed
by using the \fIremove handover number\fR message.
.PP
The \fIhandover cancellation\fR  | essage is sent when MSC\(hyA detects
clearing or interruption of the radio path before the call has been established
on MSC\(hyB. The message is also sent in order to terminate the MAP procedure
in MSC\(hyB when it is not possible to establish a connection between MSC\(hyA
and
MSC\(hyB.
.RT
.sp 1P
.LP
4.2
    \fIProcedure for subsequent handover\fR
.sp 9p
.RT
.PP
When an MS, after the call has been handed over from MSC\(hyA to
MSC\(hyB, leaves the area of MSC\(hyB during the same call, subsequent
handover is
necessary in order to continue the connection.
.PP
The following cases are identified:
.RT
.LP
    i)
    the MS moves back to the area of MSC\(hyA, and
.LP
    ii)
    the MS moves into the area of a third MSC
(MSC\(hyB`).
.PP
In both cases the call is redirected in MSC\(hyA using the handover device;
the connection between MSC\(hyA and MSC\(hyB can be released after a
successful subsequent handover has been performed.
.sp 1P
.LP
4.2.1
    \fIDescription of subsequent handover procedure\fR
.sp 9p
.RT
.LP
    i)
    \fIMSC\(hyB to MSC\(hyA\fR
.PP
The procedure which takes place after the initiation procedure has indicated
that a handover has to be made back to MSC\(hyA is shown in
Figure\ 5/Q.1005 for the case of successful handover.
.bp
.LP
.rs
.sp 16P
.ad r
\fBFigure 5/Q.1005, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The procedure is as follows.
.PP
MSC\(hyB sends the \fIsubsequent handover request\fR  | essage to MSC\(hyA
indicating that the new MSC is MSC\(hyA. Because MSC\(hyA is the call controlling
MSC, this MSC needs no roaming number for routing purposes; MSC\(hyA can
directly search for a free radio channel at the desired BS.
.PP
When a radio channel can be assigned in time, MSC\(hyA will return the
\fIsubsequent handover acknowledgement\fR  | essage containing the new
radio channel number and possibly other information to MSC\(hyB. If a radio
channel cannot be assigned, a no channel available indication will be given
to MSC\(hyB and MSC\(hyB
has to maintain the connection with the MS as long as possible.
.PP
If a radio channel has been reserved in MSC\(hyA, both MSC\(hyA and
MSC\(hyB can start the handover procedure on the radio path (in Figure\
5/Q.1005
indicated by the interworking messages HB\(hyINDICATION and HA\(hyINDICATION
respectively).
.PP
After handover, MSC\(hyA has to release the connection with MSC\(hyB by
the procedures relevant to the PSTN/ISDN signalling system(s) used between
MSC\(hyA and MSC\(hyB.
.PP
MSC\(hyA must also terminate the MAP procedure for the basic handover
between MSC\(hyA and MSC\(hyB. This is done by MSC\(hyA by sending the
\fIend signal\fR
 | essage to MSC\(hyB. When receiving this signal, MSC\(hyB sends the \fIremove\fR
\fIhandover number\fR  | essage to its VLR.
.RT
.sp 1P
.LP
4.2.2
    \fIDescription of the subsequent handover procedure\fR
.sp 9p
.RT
.LP
    ii)
    \fIMSC\(hyB to MSC\(hyB`\fR
.PP
The procedure which takes place after the initiation procedure has indicated
that the call has to be handed over to MSC\(hyB` is shown in
Figure\ 6/Q.1005 in the case of successful handover.
.PP
The procedure consists of two parts:
.LP
    \(em
    subsequent handover as described in \(sc\ 4.2.1 between MSC\(hyA
and MSC\(hyB, and
.LP
    \(em
    a basic handover procedure as described in \(sc\ 4.1 between
MSC\(hyA and MSC\(hyB`.
.PP
MSC\(hyB sends the \fIsubsequent handover request\fR  | essage to MSC\(hyA
indicating a new MSC which is not MSC\(hyA. The message contains the identity
of MSC\(hyB` and of the new BS. MSC\(hyA then starts a basic handover procedure
towards MSC\(hyB`.
.PP
When MSC\(hyA receives the ACM from MSC\(hyB`, MSC\(hyA informs MSC\(hyB that
MSC\(hyB` has started the handover procedure on the radio path by sending the
\fIsubsequent handover acknowledgement\fR message to MSC\(hyB containing
the new
radio channel number. Now MSC\(hyB can start the procedure on the radio
path.
.bp
.RT
.LP
.rs
.sp 30P
.ad r
\fBFigure 6/Q.1005, (N), p.7\fR
.sp 1P
.RT
.ad b
.RT
.PP
For MSC\(hyA the handover is completed when it has received the
\fIsuccessful handover\fR  | essage from MSC\(hyB`. The connection between
MSC\(hyA and
MSC\(hyB is released by normal clearing procedures applicable for the PSTN/ISDN
signalling system(s) on the connection between MSC\(hyA and MSC\(hyB. MSC\(hyA
also
sends the \fIend signal\fR message to MSC\(hyB in order to terminate the
original
handover procedure between MSC\(hyA and MSC\(hyB. Receiving this message,
MSC\(hyB
releases the radio path.
.PP
In case no radio channel can be allocated in time or the connection
between MSC\(hyA and MSC\(hyB` cannot be established, MSC\(hyA informs
MSC\(hyB by a
\fIcongestion\fR message. MSC\(hyB has then to maintain the existing connection
with the MS as long as possible. When necessary, MSC\(hyA sends the \fIhandover\fR
\fIcancellation\fR message to MSC\(hyB`.
.PP
When the MS again passes the MSC boundary, MSC\(hyB` is considered as
an MSC\(hyB so that the subsequent handover procedures given above are
applicable for any series of handover between MSCs.
.RT
.sp 1P
.LP
4.3
    \fIHandover procedure using subscriber information transfer\fR
\fI(optional procedures)\fR
.sp 9p
.RT
.PP
This procedure is a handover procedure with subscriber information transfer
during handover. To realize this handover procedure, only the
following additional procedure will be needed.
.RT
.sp 1P
.LP
4.3.1
    \fIBasic handover procedure (optional)\fR
.sp 9p
.RT
.PP
In addition to the basic handover procedure, described in \(sc\ 4.1,
this optional procedure is illustrated in Figure\ 7/Q.1005. MSC\(hyA sends a
handover completion message which contains subscriber information as soon as
MSC\(hyA receives the successful handover message. MSC\(hyB informs its
VLR to send a roaming number to the HLR to support supplementary services
(e.g.,\ call
waiting), after receiving the handover completion message.
.bp
.RT
.LP
.rs
.sp 21P
.ad r
\fBFigure 7/Q.1005, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
4.3.2
    \fISubsequent handover procedure (optional)\fR
.sp 1P
.RT
.sp 1P
.LP
4.3.2.1
    \fIDescription of the subsequent handover procedure\fR
\fI(optional)\fR
.sp 9p
.RT
.LP
    i)
    \fIMSC\(hyB to MSC\(hyA\fR
.PP
In addition to the subsequent handover procedure, described in
\(sc\ 4.2.1, this optional procedure is illustrated in Figure\ 8/Q.1005. When
receiving the end signal, MSC\(hyB sends the remove handover number message
to its VLR and the handover completion message to MSC\(hyA. MSC\(hyA informs
its VLR to send a roaming number to the HLR, after receiving the handover
completion
message.
.RT
.LP
.rs
.sp 17P
.ad r
\fBFigure 8/Q.1005, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
4.3.3.2
    \fIDescription of the subsequent handover procedure\fR
\fI(optional)\fR
.sp 9p
.RT
.LP
    ii)
    \fIMSC\(hyB to MSC\(hyB`\fR
.PP
In addition to the subsequent handover procedure, described in
\(sc\ 4.2.2, this optional procedure is illustrated in Figure\ 9/Q.1005. After
receiving the end signal, MSC\(hyB releases the radio path and sends handover
completion message to MSC\(hyB`. MSC\(hyB` informs its VLR to send a roaming
number to the HLR, after receiving the handover completion message.
.RT
.LP
.rs
.sp 32P
.ad r
\fBFigure 9/Q.1005, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
\fINote\fR \ \(em\ Implementation of this procedure requires careful
consideration of the handling of some supplementary services (e.g.,\ call
waiting, conference calling or call completion to busy subscriber) at handover,
since these aspects have not been studied in detail. The procedure is not
included in the current version of the MAP (Recommendation\ Q.1051).
.sp 2P
.LP
\fB5\fR     \fBDetailed procedures in MSC\(hyA\fR
.sp 1P
.RT
.sp 1P
.LP
5.1
    \fIBS/MSC (MS/BS) procedures MSC\(hyA (functional unit 1)\fR
.sp 9p
.RT
.PP
The handover procedures in this functional unit consist
of:
.RT
.LP
    i)
    signalling between the MS and the MSC; and
.LP
    ii)
    signalling between the BS and the MSC for
.LP
    \(em
    initiation of quality measurements, and
.LP
    \(em
    access management.
.PP
Signals sent to and received from functional unit 3 (handover
control procedures MSC\(hyA) are indicated in \(sc\ 5.3 below.
.bp
.sp 1P
.LP
5.2
    \fICall control procedures MSC\(hyA (functional unit 2)\fR
.sp 9p
.RT
.PP
Related to handover the call control procedures in MSC\(hyA can be
divided into two functional entities.
.PP
The first entity is the call control procedure as part of the
normal interworking between the PSTN/ISDN and the PLMN; for an MS originating
call MSC\(hyA is the originating exchange, for an MS terminating call MSC\(hyA
is the destination exchange.
.PP
The second entity is the call control procedure for the connection
between MSC\(hyA and MSC\(hyB in case of a handover from MSC\(hyA to MSC\(hyB.
For the
latter call control procedure the following applies.
.RT
.sp 1P
.LP
\fICall set\(hyup\fR
.sp 9p
.RT
.PP
The connection to MSC\(hyB is set up by procedures relevant to the
signalling system used in the PSTN/ISDN to which MSC\(hyA is connected.
The call is set up by using the MS roaming number received from MSC\(hyB
as part of the MAP procedures.
.PP
The call set\(hyup direction will always be from MSC\(hyA to MSC\(hyB,
i.e.\ also when the call was originally established by the MS. Functional
unit\ 2 should therefore keep information on call set\(hyup direction in
order to be able to correctly interpret any clearing signals (see below).
.PP
The unit should indicate the address\(hycomplete condition to functional
unit\ 3 and through connect without waiting for the answer signal from
MSC\(hyB.
This applies also to signalling systems where address\(hycomplete signals
are not supported. In such cases, an artificial address complete is established
by
functional\ unit\ 2.
.RT
.sp 1P
.LP
\fICall clearing\fR
.sp 9p
.RT
.PP
The call clearing consists of two parts after inter MSC handover, clearing
of the BS\(hyMS connection and clearing of the inter MSC connection.
.PP
The MAP is used to transfer information between MSC\(hyB and MSC\(hyA in
order to maintain full control with MSC\(hyA. MSC\(hyA determines, based on
information received from MSC\(hyB, the appropriate signals to be sent
to the MS, and sends this information to MSC\(hyB.
.PP
MSC\(hyA shall initiate inter MSC connection release and send the \fIend\fR
\fIsignal\fR  | o release any resource attached to the call.
.PP
The clearing of the connection is by procedures relevant to the
signalling system in the PSTN/ISDN to which MSC\(hyA is connected.
.PP
When the Signalling System No. 7\(hyISDN User Part is used, the normal
symmetric release procedures apply on both the connection to the fixed
network and to MSC\(hyB.
.PP
When a signalling system is used with a symmetric release possibility,
some notice should be given to the clear\(hyforward and clear\(hyback procedures.
.PP
For \fIMS terminating calls\fR  | he following conditions apply on
clear\(hyforward and clear\(hyback:
.RT
.LP
    \(em
    when a clear\(hyforward signal is received on interface\ B` (see
Figure\ 1/Q.1005), MSC\(hyA clears the circuit to MSC\(hyB by normal
clear\(hyforward procedures; and
.LP
    \(em
    when a clear\(hyback signal is received from MSC\(hyB, MSC\(hyA
starts normal clear\(hyback procedures towards the fixed network
(interface\ B`) and sends the clear\(hyforward signal on
interface\ B`` in order to clear the connection with MSC\(hyB.
.LP
    \fINote\fR \ \(em\ This case corresponds to a fault situation. O&M
actions are for further study.
.PP
For \fIMS originated calls\fR  | he following applies:
.LP
    \(em
    when an MSC\(hyA receives a clear\(hyback signal from MSC\(hyB, this
signal must be interpreted as indicating clear\(hyforward
condition. MSC\(hyA then clears both the connection on interface\ B`
(see Figure\ 1/Q.1005) and to MSC\(hyB by normal clear\(hyforward
procedures; and
.LP
    \fINote\fR \ \(em\ This case corresponds to a fault situation. O&M
actions are for further study.
.bp
.LP
    \(em
    when MSC\(hyA receives a clear\(hyback signal on interface\ B`,
MSC\(hyA should distinguish between national and international
connections:
.LP
    \(em
    for \fIinternational\fR  | onnections MSC\(hyA sends a
clear\(hyforward signal on both interface\ B` to the fixed
network and interface\ B`` to MSC\(hyB; and
.LP
    \(em
    for \fInational\fR  | connections a timer is started
according to national practice for clear\(hyback supervision
and MSC\(hyA proceeds as follows:
.LP
    i)
    if a clear\(hyback signal is received from MSC\(hyB,
MSC\(hyA interprets this as indicating a clear\(hyforward
condition and proceeds by clearing the connections
on interface\ B` and to MSC\(hyB by normal clear\(hyforward
procedures, or
.LP
    ii)
    if the timer expires, MSC\(hyA proceeds by normal
clear\(hyforward of the connections on interface\ B`
to MSC\(hyB.
.sp 1P
.LP
5.3
    \fIHandover control procedures MSC\(hyA (functional unit\ 3)\fR
.sp 9p
.RT
.PP
The procedures of functional unit\ 3 are given in terms of SDL
diagrams in Figure\ 10/Q.1005. For all signals sent to or received from
another functional unit the source or sink of the signal is indicated (e.g.\
from\ 4, to 2,\ etc.).
.RT
.PP
The procedures of functional unit 3 include the
following:
.LP
    i)
    Initiation (states\ 1, 2 and 3). The initiation condition is
shown by the signal HA\(hyREQUEST. This may either be generated by
the MS or the BS depending on the initiation condition
(see \(sc\ 3). The diagram includes all possibilities described in
\(sc\ 3, i.e.\ the MS identifies the new BS, or the new BS is
identified by the MSC by measurements in adjacent BSs. These may
include BSs in other MSCs.
.LP
    The diagram also includes queuing when there is no channel
available. Calls for which handover had been initiated should be
queued with priority higher than normal calls. They should have
lower priority than emergency calls.
.LP
    ii)
    Handover of calls within the area of MSC\(hyA, i.e.\ handover
cases\ i) and\ ii) (states\ 1, 2, 3 and\ 4). MSC\(hyA controls the
procedures on both the previous and the new radio channel. Both
signals HA\(hyINDICATION and HB\(hyINDICATION are required. The
handover procedure is completed when HB\(hyCONFIRM is received. If
this signal is not received, the radio path and the connection
on interface\ B` are either released or the original connection
is maintained depending on national choice.
.LP
    The handover device is first set up so that
all interfaces\ A`, A`` and\ B` are connected (illustrated by the
signal \fIset up handover device\fR ). This is done when
HA\(hyINDICATION is sent. The device is connected in its final
position (i.e.\ A`` to\ B` for case\ ii)) (illustrated by the
signal \fIconnect handover device\fR ) either when HA\(hyCONFIRM is
received or when HB\(hyCONFIRM is received.
.LP
    iii)
    Handover to MSC\(hyB (states\ 1, 2, 5, 6 and 7). This
procedure is the one described in \(sc\ 4.1. The handover device is
set up when MSC\(hyA send the HA\(hyINDICATION, i.e.\ the
interfaces\ A`, B` and\ B`` are connected. The device is connected
in its final position (i.e.\ B` to\ B``) when either the
HA\(hyCONFIRM signal is received from the MS or the successful
procedure indication is received from functional unit\ 4.
.LP
    iv)
    Subsequent handover to MSC\(hyA (states\ 7 and 9). This
procedure is described in \(sc\ 4.2. When a handover to MSC\(hyA
indication is received from functional unit\ 4, the handover
device is set up so that interfaces\ B`, B`` and\ A` are
connected. When HB\(hyCONFIRM is received, the device is connected
in its final position (i.e.\ B` to\ A`).
.LP
    If HB\(hyCONFIRM is not received (expiry of timer\ T104), the
handover device releases interface\ A` and returns to a position
where B` and\ B`` are connected. A congestion
indication is returned via functional unit\ 4 to MSC\(hyB.
.LP
    v)
    Subsequent handover to a third MSC (MSC\(hyB`) (states\ 7
and\ 8). The procedure is described in \(sc\ 4.2. The handover device
is set up in its initial position, i.e.\ interconnection of
interfaces\ B`, B`` and\ B```, when the connection to MSC\(hyB` has
been established (indicate by the signal connection
established from functional unit\ 2). MSC\(hyB is informed via
functional unit\ 4 (send acknowledge) that the connection has
been established and that the procedure on the radio path can be
initiated. The device is connected in its final position
(i.e.\ B` to\ B```) when a successful procedure indication in
received from functional unit\ 4. MSC\(hyB is informed that
all procedures in MSC\(hyB can be terminated (illustrated by the
send\(hyend signal indication). The device returns to the state
where B` and\ B`` are connected if the subsequent handover
procedure fails.
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 10/Q.1005 (1/9), (N), p.11\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 10/Q.1005 (2/9), (N), p.12\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 10/Q.1005 (3/9), (N), p.13\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 10/Q.1005 (4/9), (N), p.14\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 10/Q.1005 (5/9), (N), p.15\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 10/Q.1005 (6/9), (N), p.16\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 10/Q.1005 (7/9), (N), p.17\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 10/Q.1005 (8/9), (N), p.18\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 10/Q.1005 (9/9), (N), p.19\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
\fITimers in MSC\(hyA\fR
.sp 9p
.RT
.PP
The procedures are supervised by timers in order to avoid deadlock when
responses are not received or the procedures fail. The following timers
are defined:
.RT
.LP
\fIT100:\fR     This timer supervises the time between sending a request for
measurements to a BS or an MSC and the receipt of the results. Results
received after time out are ignored. T100\ =\ (FS)
.LP
\fIT101:\fR     This timer supervises the queuing time for a free channel.
If T101 expires, a no channel indication is generated.
T101\ =\ (FS)
.LP
\fIT102:\fR     This timer supervises the time for handover completion for
handover between BSs in MSC\(hyA. If T102 expires, the radio path and the
connection on interface\ B` are released. T102\ =\ (FS)
.LP
\fIT103:\fR     This timer supervises the time between issuing a
HA\(hyINDICATION in MSC\(hyA and receiving a successful procedure indication
from MSC\(hyB. If T103 expires, the handover procedure is cancelled and
either the radio channel is released (if HA\(hyCONFIRM has been received)
or it continues on the old channel (if HA\(hyCONFIRM has not been
received). T103\ =\ (FS)
.LP
\fIT104:\fR     This timer supervises the time between sending an
HB\(hyINDICATION and receiving the HB\(hyCONFIRM for a subsequent handover
from MSC\(hyB to MSC\(hyA. If T104 expires, the new radio channel is released
and the existing handover device connection to MSC\(hyB is maintained.
T104\ =\ (FS)
.sp 1P
.LP
5.4
    \fIMAP procedures in MSC\(hyA (functional unit\ 4)\fR
.sp 9p
.RT
.PP
The MAP procedures for handover are defined in
Recommendation\ Q.1051. They include:
.RT
.LP
    \(em
    requesting measurements in other MSCs;
.LP
    \(em
    procedures for basic handover; and
.LP
    \(em
    procedures for subsequent handover.
.PP
These procedures are as outlined in \(sc\ 4.
.sp 2P
.LP
\fB6\fR     \fBDetailed procedures in MSC\(hyB\fR
.sp 1P
.RT
.sp 1P
.LP
6.1
    \fIBS/MSC (MS/BS) procedures MSC\(hyB (functional unit\ 1)\fR
.sp 9p
.RT
.PP
The handover procedures in this functional unit consist
of:
.RT
.LP
    i)
    signalling between the MS and the MSC; and
.LP
    ii)
    signalling between the BS and the MSC for
.LP
    \(em
    initiation of quality measurements, and
.LP
    \(em
    access management.
.PP
Signals exchanged with functional unit\ 3 are indicated in \(sc\ 6.3
below.
.sp 1P
.LP
6.2
    \fICall control procedures MSC\(hyB (functional unit\ 2)\fR
.sp 9p
.RT
.PP
These procedures relate to the call control in MSC\(hyB of the
\*Qhandover\*U connection with MSC\(hyA. For these procedures the following
apply.
.RT
.sp 1P
.LP
\fICall set\(hyup\fR
.sp 9p
.RT
.PP
The connection is set\(hyup by MSC\(hyA. MSC\(hyB should provide, if
possible, the following backward signals:
.RT
.LP
    \(em
    signals indicating unsuccessful call set\(hyup and, if possible,
the cause of call failure;
.LP
    \(em
    address complete signal; and
.LP
    \(em
    answer signal (see note).
.LP
    \fINote\fR \ \(em\ The answer signal is not related to answering by
the MS and it has no meaning in the handover procedure between
MSC\(hyA and MSC\(hyB. But after successful handover this signal is
needed for bringing the connection in the answered state in the
intermediate PSTN/ISDN exchanges.
.PP
There will be no indication that the call applies to a handover. This information
has to be derived from the MS roaming number received during call set\(hyup
in relation to the earlier radio channel request/radio channel
acknowledgement procedure between MSC\(hyA and MSC\(hyB (MAP\(hyprocedure).
.PP
When the connection has been established an indication should be given
to functional unit\ 3 (illustrated by the signal \*Qconnection established\*U
in
Figure\ 11/Q.1005).
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBFigure 11/Q.1005 (1/8), (N), p.20\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 11/Q.1005 (2/8), (N), p.21\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 11/Q.1005 (3/8), (N), p.22\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 43P
.ad r
\fBFigure 11/Q.1005 (4/8), (N), p.23\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 11/Q.1005 (5/8), (N), p.24\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 11/Q.1005 (6/8), (N), p.25\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 11/Q.1005 (7/8), (N), p.26\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 11/Q.1005 (8/8), (N), p.27\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
\fICall clearing\fR
.sp 9p
.RT
.PP
The call clearing consists of two parts after inter MSC handover, clearing
of the BS\(hyMS connection and clearing of the inter MSC
connection.
.PP
The MAP is used to transfer information between MSC\(hyB and MSC\(hyA in
order to make it possible for MSC\(hyB to send the appropriate signals
and still leave the call control to MSC\(hyA.
.PP
MSC\(hyA initiates release of the connection between MSC\(hyA and
MSC\(hyB.
.PP
MSC\(hyB is only allowed to initiate inter MSC connection release after
the \fIend signal\fR  | s received.
.PP
When the Signalling System No. 7\(hyISDN User Part is used, the normal
symmetric release procedures apply.
.PP
When a signalling system is used without a symmetric release
possibility, the following applies.
.RT
.LP
    \(em
    When MSC\(hyB receives a clear\(hyforward signal from MSC\(hyA, it
shall release the radio path.
.LP
    \(em
    In fault situations, e.g. machine malfunction or loss of
the connection on interface\ A, MSC\(hyB may send a clear\(hyback
signal to MSC\(hyA.
.sp 1P
.LP
6.3
    \fIHandover control procedures MSC\(hyB (functional unit\ 3)\fR
.sp 9p
.RT
.PP
The procedures of functional unit\ 3 are given in the form of SDL
diagrams in Figure\ 11/Q.1005. For all signals sent to or received from
another functional unit the source or sink of the signal is indicated (e.g.\
from 4,
to\ 2,\ etc.).
.PP
The procedures in functional unit\ 3 include the
following.
.RT
.LP
    i)
    Handover from MSC\(hyA (states\ 1, 2, 3 and 4). This case
includes initiation by MSC\(hyA (indicated by the allocate radio
channel signal received from functional unit\ 4) and allocation
and establishment of the new radio channel. The procedure is
outlined in \(sc\ 4.1.
.LP
    ii)
    Subsequent handover within the area controlled by MSC\(hyB
(states\ 4, 5, 6 and\ 7). This procedure is essentially the same
as that of\ ii) of \(sc\ 5.3.
.LP
    iii)
    Subsequent handover to another MSC (MSC\(hyA or MSC\(hyB`)
(states\ 4, 8 and\ 9). The initiation procedure is essentially
the same as that of\ i) of \(sc\ 5.3. The HA\(hyINDICATION is now
generated by MSC\(hyB after a subsequent handover accepted
indication is received from MSC\(hyA (via functional unit\ 4).
The procedure is terminated in MSC\(hyB when MSC\(hyB receives a
terminate procedure indication from functional
unit\ 4.
.sp 1P
.LP
\fITimers in MSC\(hyB\fR
.sp 9p
.RT
.PP
The procedures are supervised by timers in order to avoid deadlock when
responses are not received or the procedures fail. The following timers
are defined.
.RT
.LP
\fIT200:\fR     This timer is the same as T100 (\(sc\ 5.3).
.LP
\fIT201:\fR     This timer is the same as T101 (\(sc\ 5.3).
.LP
\fIT202:\fR     This timer is the same as T102 (\(sc\ 5.3).
.LP
\fIT204:\fR     This timer is the same as T104 (\(sc\ 5.3).
.LP
\fIT210:\fR     This timer is used to supervise the time for establishing a
connection from MSC\(hyA to MSC\(hyB after an allocate radio
channel request has been received. When T210 expires, the allocated
channel in MSC\(hyB is released. T210\ =\ (FS)
.LP
\fIT211:\fR     This timer is used to control the time between requesting
a subsequent handover and receiving the response from MSC\(hyA. If T211
expires, the existing connection with the MS is maintained.
T211\ =\ (FS)
.sp 1P
.LP
6.4
    \fIMAP procedures MSC\(hyB (functional unit\ 4)\fR
.sp 9p
.RT
.PP
The MAP procedures for handover are defined in
Recommendation\ Q.1051. They include:
.RT
.LP
    \(em
    requesting measurements in other MSCs,
.LP
    \(em
    procedures for basic handover,
.LP
    \(em
    procedures for subsequent handover, and
.LP
    \(em
     procedures for obtaining and releasing MS roaming number for handover
from the VLR.
.PP
These procedures are outlined in \(sc\ 4.
.bp
.sp 2P
.LP
\fB7\fR     \fBAuthentication\fR
.sp 1P
.RT
.PP
Authentication will be performed after handover (for further
study).
.RT
.sp 2P
.LP
\fB8\fR     \fBHandling of supplementary services\fR
.sp 1P
.RT
.PP
This is for further study. MAP procedures for supporting such
functions are contained in Recommendation\ Q.1051.
.PP
MSC\(hyA will maintain call control until all operations, i.e.\ the
existing call and any supplementary service operation have been terminated.
At this instant, MSC\(hyB is informed by the \fIend signal\fR message of
the MAP that
all functions in MSC\(hyB can be released.
.PP
If the call waiting service is provided for the called MS, and there are
calls waiting at the time of a handover to another MSC, these calls should
be established by MSC\(hyA using normal call forwarding to MSC\(hyB. If
the MS
requests holding of the existing call and connection of a waiting call,
the MAP is used to provide the necessary exchange of information between
MSC\(hyA and the MS.
.RT
.sp 2P
.LP
\fB9\fR     \fBLocation updating after handover\fR
.sp 1P
.RT
.PP
MSC\(hyB (or VLR\(hyB) should not initiate automatic updating of the HLR
at the end of the call. The procedures in the MS should be such that the
MS
should initiate updating after the call has been completed and the MS has
tuned to a common control channel.
.PP
Automatic updating by MSC\(hyB (or VLR\(hyB) is for further study.
.RT
.LP
.rs
.sp 31P
.ad r
BLANC
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 10P
.LP
\fBMONTAGE:\ \
PAGE PAIRE = BLANCHE\fR
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 3
.ce 0
.sp 1P
.ce 1000
\fBINTERWORKING WITH ISDN AND PSTN\fR \v'1P'
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.1031\fR
.RT
.sp 2P
.ce 1000
\fBGENERAL\ SIGNALLING\ REQUIREMENTS\ ON\
\fBINTERWORKING\fR
.EF '%    Fascicle\ VI.12\ \(em\ Rec.\ Q.1031''
.OF '''Fascicle\ VI.12\ \(em\ Rec.\ Q.1031    %'
.ce 0
.sp 1P
.ce 1000
\fBBETWEEN\ THE\ ISDN\ OR\ PSTN\ AND\ THE\ PLMN\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
The purpose of this Recommendation is to present the general
requirements for the PSTN and the ISDN as well as for the mobile network
to be met in order to ensure a correct integration of the mobile service
in the fixed network.
.PP
This Recommendation covers only the signalling aspects of the
interworking between the mobile service and fixed network.
.RT
.sp 2P
.LP
\fB2\fR     \fBGeneral requirements\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fIRequirements for the mobile system\fR
.sp 9p
.RT
.PP
In order to be integrated in the fixed network the PLMN must comply with
the following requirements:
.RT
.LP
    a)
    The MAP which supports information exchanges between the
nodes of the mobile service uses the facilities of Transactions Capabilities
of Signalling System No.\ 7. Therefore the equipment of the mobile network
must
comply with the specification of the interface between TCAP and the application
user. If TCAP functions are integrated in the mobile network equipment,
the
latter must comply with the relevant specifications (Recommendations\ Q.771
to\ Q.774).
.LP
    b)
    FOR MAP messages routing purpose, the mobile nodes must
provide the SCCP via TCAP with an address complying with the
relevant specifications (Recommendations\ Q.711
to\ Q.714).
.LP
    c)
    For call set\(hyup, the MSCs must interface with the fixed
exchanges. In the detailed interworking Recommendations, the
fixed network signalling considered are Signalling System
No.\ 7 and its User Parts (TUP or ISUP). The MSCs must comply
with the same signalling interface specifications as the
fixed exchanges.
.LP
    d)
     The PLMN and the signalling on the radio path must provide the information
needed to ensure a correct interworking with
the fixed network. The interworking in the MCSs must occur with
a minimum loss of information.
.LP
    e)
    The PLMN nodes must interface with the No.\ 7 signalling
network.  For that, they must comply with the MTP specifications
(Recommendations\ Q.701 to\ Q.707).
.bp
.sp 1P
.LP
2.2
    \fIRequirements for the fixed network\fR
.sp 9p
.RT
.PP
The adaptations of the fixed network needed for the integration of the
mobile service have to be minimized. However, some facilities foreseen
for other services will also facilitate the access to the mobile service
or the
operation of the PLMN.
.RT
.LP
    a)
     The implementation of the No.\ 7 signalling network could be useful for
the mobile service. Before the No.\ 7 Signalling System is
implemented, a dedicated signalling network, using a subset of Signalling
System No.\ 7, could be used as an interim solution for transporting the data
between functional units of PLMNs.
.LP
    b)
    It will be useful that, in addition to the signalling
network, the SCCP facilities be available in order to avoid a specific
implementation of such a service in the PLMN equipments.
.LP
    c)
    The interrogation procedure based on TCAP prior to
connection set up to a mobile would save circuits resources
in the network and would increase the service quality
provided to the fixed calling subscriber by e.g., reducing
the post dialling delay in such kinds of calls. From a
signalling point of view the best way is to introduce this
procedure as near as possible to the local originating exchanges (see
Recommendation\ Q.1032).
.sp 2P
.LP
\fB3\fR     \fBInterworking with the PSTN for call set\(hyup\fR
.sp 1P
.RT
.PP
The interworking with the Telephone User Part of Signalling System No.\
7 is the only case considered here.
.PP
\fIParticular aspects\fR :
.RT
.LP
    a)
    The fixed telephone network provides an end\(hyto\(hyend
transparent link at least for speech use. It is then possible to have a data
transmission communication on a telephone call. This would not be the case
with a mobile subscriber: the radio path would not be transparent. Therefore,
if a calling subscriber wishes to have a data transmission call with a
mobile it
would be necessary to inform the network concerning the precise characteristics
of this transmission: the mobile system will then be able to replace the
speech coder by a data coder adapted to the type of transmission modem
used. One
solution could be that the mobile station has one telephone number per
type of data transmission service it can use.
.LP
    b)
    The usual routing of a call to a mobile includes a
re\(hyrouting according to the roaming number allocated to that
mobile. This number is temporarily allocated and
difficulties could appear in some cases such as a failure of
a register. It would then be useful that the
number dialled by the calling subscriber appears in the
Initial Address Message received by the VMSC. This
transmission can be used as a solution to avoid the
allocation of one roaming number for each telephone number
in the case of data transmission to a mobile
station.
.sp 2P
.LP
\fB4\fR     \fBInterworking with the ISDN for call set\(hyup\fR
.sp 1P
.RT
.PP
Since the radio path cannot economically provide a transparent
64\ kbB/Fs channel to mobile subscribers all the time, all the ISDN services
foreseen in the fixed network will not be available to the mobile subscribers.
The Quality of Service in land mobile networks may also in some cases not
meet the Quality of Service requirement for certain ISDN services. Therefore
some service limitations need to be introduced in the access to mobile
stations.
.PP
Different methods may be foreseen to implement this
limitation:
.RT
.LP
    a)
    The interrogation is used also to check the service
capabilities of the mobile access. This procedure can also be used to perform
a compatibility check between the parties. But this test is only possible
if the HLR knows the relevant characteristics of the mobile station and
cannot be used with card operated stations; in that case a mobile subscriber
can use different stations.
.LP
    b)
     The simplest solution is that normal mobile call set\(hyup be processed
and controlled by the incoming MSC. As such the incoming MSC can
also provide a compatibility check for card operated stations.
.LP
    c)
     The call setup is normally performed up to the mobile. The IAM contains
the characteristics of the service requested and on the terminal needed
by the calling party. The network, MSC included, is transparent in the
compatibility check. This method is the same as that defined in the
ISDN.
.bp
.sp 2P
.LP
\fB5\fR     \fBImpact of the off\(hyair call set\(hyup on the interworking\fR
.sp 1P
.RT
.PP
The use of the off\(hyair call set\(hyup in the PLMN has an impact on the
interworking with the fixed network. Both outgoing and incoming calls have
to be considered: the consequences are not the same.
.PP
As it was stated before, the use of the Off\(hyAir Call Set\(hyUp procedure
is optional and must be limited to national telephone calls only (see
Recommendation\ Q.1002).
.RT
.sp 1P
.LP
5.1
    \fIDefinition of the off\(hyair call set\(hyup\fR
.sp 9p
.RT
.PP
To save the radio resources the radio traffic channel may be
allocated to the communication only when both calling and called parties are
present i.e.,\ at the answer instant. This method called \*QOff\(hyAir
Call Set\(hyUp\*U (OACSU) has some implication on the interworking with
the fixed network. The consequences are not the same whether the mobile
subscriber is the calling or the called party.
.RT
.sp 1P
.LP
5.2
    \fIOutgoing call from a mobile station\fR
.sp 9p
.RT
.PP
Upon initiation of an outgoing call, a traffic channel is allocated to
the communication when the called subscriber answer is received in the
MSC. In some cases, no idle traffic channel may be available when necessary.
Therefore, an appropriate announcement must be given to the called party
when no idle traffic channel is available within a certain interval upon
receipt of the called party's answer.
.PP
Whenever the announcement is used, it must always be played through in
its entirety, even if a traffic channel becomes available before it is
completed.
.PP
If the ADDRESS COMPLETE message indicates that there will possibly be no
ANSWER message upon the connection of the called party (e.g., ADC without
any information), the radio path must be established immediately upon receipt
of the ADC.
.PP
Due to interworking constraints coming from the characteristics of the
different signalling systems used in countries, the OACSU technique should
only be used for national calls.
.RT
.sp 1P
.LP
5.3
    \fIIncoming call to a mobile station\fR
.sp 9p
.RT
.PP
For incoming calls, the impact is not so important, but some rules must
be applied in order to limit the influence on the service quality.
.PP
Concerning the sending instant of the answer message, the normal
operating rules apply. If the call is successfully set\(hyup to the mobile
station, the answer message must be sent to the originating exchange only
when the traffic channel is established upon recognition of the called
party
connection.
.RT
.sp 2P
.LP
\fB6\fR     \fBSpecial arrangements\fR
.sp 1P
.RT
.sp 1P
.LP
6.1
    \fIControl of speech processing and echo control devices\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
6.2
    \fIInterworking for non\(hyvoice calls\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 2P
.LP
\fBRecommendation\ Q.1032\fR
.RT
.sp 2P
.ce 1000
\fBSIGNALLING\ REQUIREMENTS\ RELATING\ TO\ ROUTING\ OF\fR
.EF '%    Fascicle\ VI.12\ \(em\ Rec.\ Q.1032''
.OF '''Fascicle\ VI.12\ \(em\ Rec.\ Q.1032    %'
.ce 0
.sp 1P
.ce 1000
\fBCALLS\ TO\ MOBILE\ SUBSCRIBERS\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
When a subscriber wants to call a mobile subscriber, the fixed
network needs to know the actual location of the MS in order to route the
connection to the relevant Mobile Services Switching Centre (see
Recommendation\ Q.1003 on location registration). This contribution tries to
present the signalling requirements the fixed network has to comply with for
that purpose. The document considers the different assumptions concerning
the capabilities of the fixed exchanges to perform some signalling procedures
prior to call set\(hyup.
.bp
.PP
This Recommendation assumes that the routing analysis requirements
specified in Recommendation\ Q.107\fIbis\fR  | are fulfilled.
.PP
This Recommendation assumes that the ISDN number of the mobile
contains a specific National Destination Code. The cases where the mobile
numbering plan is fully integrated in the fixed numbering plan are for
further study.
.RT
.sp 2P
.LP
\fB2\fR     \fBGeneral routing rules\fR
.sp 1P
.RT
.PP
The number dialled by the calling subscriber contains no indication concerning
the actual location of the called MS. Therefore, to set up the
complete connection, it is necessary to know the location of the MS and the
routing address to be used,\ i.e. the Mobile Station Roaming Number. The only
equipment able to provide this information is the Home Location Register.
Therefore to route the call to the Mobile Services Switching Centre where
the MS is located, it is necessary to interrogate the HLR.
.PP
The preferred procedure with regard to signalling is the
following:
.RT
.LP
    1)
    When a subscriber wants to call a mobile station he dials
the ISDN number of that station.
.LP
    2)
    The local exchange (or a transit exchange) analyzes the
number dialled and recognizes the mobile service National Destination Code
indicating that the call is destined to a mobile subscriber. In general this
complete routing analysis can be made for the national calls only: when the
outgoing exchange recognizes that the calling subscriber dialled the
international prefix, it routes the call directly to the outgoing International
Switching Centre (ISC) without any further analysis. This ISC can then
recognize the mobile national destination code.
.LP
    3)
     If the result of routing analysis shows that it is necessary to get additional
information to set up the complete connection to the MSC
where the called station is located, then this information must be obtained
from the HLR in charge of the mobile subscriber. If the interrogation procedure
is implemented in an exchange referred to in\ 2) above, this exchange then
performs the interrogation of the Home Location Register. The HLR sends back
the roaming number of the called MS. This procedure is supported by the
Transaction Capabilities of Signalling System No.\ 7.
.LP
    4)
    The connection is then set up in the fixed network to the
MSC according to the roaming number of the\ MS.
.sp 2P
.LP
\fB3\fR     \fBGeneral requirements for the fixed network\fR
.sp 1P
.RT
.PP
To route a call up to a mobile subscriber, an interrogation of the HLR
must be performed in order to get the roaming number allocated to that
MS. This interrogation procedure is supported by the Transaction
Capabilities of Signalling System No.\ 7. The preferred solution is that the
local exchanges be adapted to TC, and able to perform this interrogation:
then they can route the call directly to the called mobile according to
the roaming number they obtain from their interrogation of the HLR. The
following section of this document shows possible solutions if this assumption
is not
fulfilled.
.PP
As it is described below, in the case where there are no interrogation
facilities in the fixed network, on recognition that a call is destined
to a
mobile subscriber, the routing is first performed to a Gateway MSC. The
interrogation of the HLR is then performed by the MSC and the call proceeds
according to the Roaming Number received.
.PP
Section 5 deals with the routing of calls to foreign mobile stations: usually,
in this case, the local exchange does not analyze the national part of
the called address and routes directly to the outgoing International Switching
Centre which then performs the correct routing of the call.
.RT
.sp 2P
.LP
\fB4\fR     \fISignalling aspects on routing a call to a mobile managed by\fR
\fIa home PLMN situated in the same country\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
    \fIThe originating exchange is adapted to the interrogation\fR
\fIprocedure\fR  | (Figure\ 1/Q.1032)
.sp 9p
.RT
.PP
If the originating local exchange is able to perform the
interrogation procedure, the call set\(hyup occurs as it is specified in
section\ 2 of this document.
.RT
.sp 1P
.LP
4.2
    \fIThe originating exchange is not adapted to the interrogation\fR
\fIprocedure\fR
.sp 9p
.RT
.PP
If the originating exchange is unable to use TCAP, the following
cases can be considered:
.RT
.LP
    \(em
    the interrogation procedure is performed by a transit
exchange;
.LP
    \(em
    the call is re\(hyrouted by a Gateway MSC.
.bp
.LP
.rs
.sp 26P
.ad r
\fBFigure 1/Q.1032, (N), p.28\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.2.1
    \fIThe interrogation is performed by a transit exchange\fR  |
(Figure\ 2/Q.1032)
.sp 9p
.RT
.PP
If the originating exchange is unable to perform the interrogation of the
HLR, the connection is set up to a transit exchange. This exchange
analyzes the address received (the ISDN number of the subscriber) and notices
that the call is destined to a mobile subscriber. It then performs the
interrogation of the HLR and routes the call as it is described in
section\ 2.
.RT
.sp 1P
.LP
4.2.2
    \fIThe call is re\(hyrouted by a Gateway MSC\fR  |
(Figure 3/Q.1032)
.sp 9p
.RT
.PP
If the fixed network is unable to interrogate the HLR in order to route
the call to the actual location of the MS, the connection is set up to
a Gateway\ MSC.
.PP
The Gateway MSC interrogates the HLR of the called MS (using MAP in
general cases). It receives back the roaming number of the subscriber. With
this address, the GMSC set up a connection via the telephone (or ISDN)
network to the MSC where the mobile is located. If the called subscriber
is abroad, the connection is normally set up via the international network.
.RT
.sp 2P
.LP
\fB5\fR     \fBRouting a call to a foreign mobile subscriber\fR
.sp 1P
.RT
.PP
As for a normal telephone call, the calling subscriber, when he
wants to join a foreign mobile subscriber, dials the international access
prefix first. His local exchange, according to this prefix, routes the call
directly to the outgoing International Switching Centre without any further
analysis of the number dialled.
.PP
The routing of the call is then performed by the outgoing
international Switching Centre. Two assumptions can be envisaged:
.RT
.LP
    \(em
     the outgoing International Switching Centre recognizes that the called
party is a mobile subscriber and can perform the interrogation of
the HLR;
.LP
    \(em
    the outgoing International Switching Centre is unable to
perform the interrogation of the HLR.
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigure 2/Q.1032, (N), p.29\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 23P
.ad r
\fBFigure 3/Q.1032, (N), p.30\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
5.1
    \fIThe outgoing ISC can perform the interrogation of the HLR\fR  |
(Figure\ 4/Q.1032)
.sp 9p
.RT
.PP
When the outgoing International Switching Centre receives the call, for
routing purposes it analyzes the digits of the country code and the first
digits of the national significant number of the called party address.
It can then notice that the call is destined to a mobile subscriber and
needs a
preliminary interrogation transaction prior to setting up the connection.
.PP
With the roaming number, the ISC then routes the call to the MSC where
the mobile is actually located. The connection is set up via the international
network if the MS is not in the same country as the calling subscriber.
.RT
.LP
.rs
.sp 32P
.ad r
\fBFigure 4/Q.1032, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
5.2
     \fIThe outgoing International Switching Centre is unable to perform\fR
\fIthe interrogation of the HLR\fR  | (Figure 5/Q.1032)
.sp 9p
.RT
.PP
If the outgoing International Switching Centre is unable to perform the
interrogation procedure, it routes the call to the incoming ISC of the
country where the Home PLMN of the called mobile is situated according
to the telephone (or the ISDN) number dialled by the calling subscriber.
.PP
The incoming ISC receiving the call notices that it is destined to a mobile.
The following assumptions can be envisaged:
.RT
.LP
    \(em
    this ISC can perform the interrogation;
.LP
    \(em
    this ISC is unable to perform the interrogation: therefore
the interrogation has to be made either by a national transit exchange
or by a Gateway MSC.
.bp
.PP
In this assumption where the actual routing has to be made in the home
country of the mobile, the connection may comprise two international links
in tandem if the subscriber is roaming abroad. Therefore it would be better
that the interrogation is performed in the outgoing country; this method
would limit the length of the complete connection. The worst case will
appear when
the called mobile is roaming in the country of the calling subscriber: the
complete connection comprises two international links in tandem instead of a
simple national routing.
.LP
.rs
.sp 28P
.ad r
\fBFigure 5/Q.1032, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
5.3
    \fIThe International Switching Centre recognizes that it is a\fR
\fIcall to an MS but cannot perform the interrogation\fR
.sp 9p
.RT
.PP
In this case, the International Switching Centre routes the call to a Gateway
MSC which performs the interrogation:
.RT
.LP
    \(em
    if the GMSC is accessed by the outgoing ISC, see
Figure\ 6/Q.1032.
.LP
    \(em
    if the GMSC is accessed by the incoming ISC, see
Figure\ 7/Q.1032.
.sp 2P
.LP
\fB6\fR     \fBAlternative solution: re\(hyrouting of the call after clearing the
previous connection\fR  | (Figure\ 8/Q.1032)
.sp 1P
.RT
.PP
The ISUP provides a backward message to indicate that the call
should be re\(hyrouted and containing the new address. This facility may
be used in the case where a foreign MS is called and no interrogation functions
are
available in the fixed network to get the Roaming Number from the HLR.
A long international connection may be established before the location
of the MS is
determined but this facility could allow the call to be \*Qdropped back\*U
to the suitable MSC.
.bp
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure 6/Q.1032, (N), p.33\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 23P
.ad r
\fBFigure 7/Q.1032, (N), p.34\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 30P
.ad r
\fBFigure 8/Q.1032, (N), p.35\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB7\fR     \fBUnsuccessful call set\(hyup\fR
.sp 1P
.RT
.sp 1P
.LP
7.1
    \fIRoaming not allowed\fR
.sp 9p
.RT
.PP
If the MS is roaming in an area where it is not allowed to have
calls, the location is not stored in the HLR and an indication is set.
When a call is set up to this subscriber, the HLR will return an unsuccessful
indication to the originating exchange.
.RT
.sp 1P
.LP
7.2
    \fIRestart of the HLR\fR
.sp 9p
.RT
.PP
After a restart, the HLR considers that the information coming from the
back up is still valid. If an interrogation is related to a subscriber
whose information is not yet restored, the HLR gives back the Roaming Number
it has in its tables. If there is a mistake, the restoration
procedure specified in Recommendation\ Q.1004 will re\(hyestablish the correct
information.
.RT
.sp 1P
.LP
7.3
    \fIMobile station roaming number unallocated\fR
.sp 9p
.RT
.PP
If the incoming MSC receives a call which roaming number is
declared unallocated by the VLR, it sends back an unsuccessful call set\(hyup
indication to the outgoing exchange. This situation may occur after a restart
of the HLR or of the VLR (see Recommendation\ Q.1004).
.RT
.LP
.bp