U.S. patent application number 13/098985 was filed with the patent office on 2011-11-03 for handling a registration timer to provide service continuity in ims.
Invention is credited to Ralf Keller, Fredrik Lindholm.
Application Number | 20110268098 13/098985 |
Document ID | / |
Family ID | 43302877 |
Filed Date | 2011-11-03 |
United States Patent
Application |
20110268098 |
Kind Code |
A1 |
Keller; Ralf ; et
al. |
November 3, 2011 |
Handling a registration timer to provide service continuity in
IMS
Abstract
The invention relates to a method for providing service
continuity with respect to a registration of a mobile terminal, UE,
at a control server of an IP Multimedia Subsystem, IMS, network,
while a CS-communication session between the UE and a switching
server, MSC, of a circuit-switched, CS, network is established. The
control server comprises a registration timer which is used for
initiating a termination of the registration of the UE at the IMS
network, when the registration timer expires, wherein the control
server updates the registration timer in dependence of a control
information received from the MSC. The invention further relates to
a MSC providing such service.
Inventors: |
Keller; Ralf; (Wurselen,
DE) ; Lindholm; Fredrik; (Stockholm, SE) |
Family ID: |
43302877 |
Appl. No.: |
13/098985 |
Filed: |
May 2, 2011 |
Current U.S.
Class: |
370/338 |
Current CPC
Class: |
H04W 60/00 20130101;
H04L 65/1073 20130101; H04W 36/0022 20130101; H04W 60/04
20130101 |
Class at
Publication: |
370/338 |
International
Class: |
H04W 4/00 20090101
H04W004/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 3, 2010 |
EP |
PCT/EP2010/055988 |
Claims
1. A method of providing service continuity with respect to a
registration of a mobile terminal (UE) at a control server of an IP
Multimedia Subsystem (IMS) network, while a CS-communication
session between the UE and a switching server (MSC) of a
circuit-switched (CS) network is established, the method
comprising: the control server utilizing a registration timer for
initiating a termination of the registration of the UE at the IMS
network, when the registration timer expires, and the control
server updating the registration timer independent of a control
information received from the MSC.
2. The method according to claim 1, wherein the control information
is sent to the control server before the registration timer
expires.
3. The method according to claim 1, wherein the control information
comprises an information that the UE cannot update the registration
timer.
4. The method according to claim 3, wherein the control information
additionally comprises information about a user identity of the UE
or an equipment identity of the UE.
5. The method according to claim 3, wherein the control server,
after receiving the control information from the MSC, updates the
registration timer prior to the registration timer expiring.
6. The method according to claim 5, wherein the MSC triggers the
control server to terminate updating the registration timer in the
control server after the communication session between the UE and
the MSC is released.
7. The method according to claim 1, wherein the MSC initiates the
update of the registration timer in the control server by
requesting the registration timer value from the control server of
the IMS network and, after receiving the registration timer value
and detecting that the registration timer is near expiration,
triggering the control server of the IMS network to update the
registration timer.
8. The method according to claim 7, wherein the request of the
registration timer value also comprises the user identity of the UE
or the equipment identity of the UE.
9. The method according to claim 1, wherein the control server,
after updating the registration timer, sends a notification message
to a serving node of the IMS network to trigger an update of an
additional registration timer in the serving node.
10. The method according to claim 8, wherein the serving node is a
Server Call Session Control Function (S-CSCF) server.
11. The method according to claim 1, wherein the control server of
the IMS is a Proxy Call Session Control Function (P-CSCF)
server.
12. The method according to claim 1, wherein the MSC receives the
address of the control server of the IMS network in response to the
registration of the UE at the control server of the IMS
network.
13. The method according to claim 1, wherein the MSC receives the
address of the control server of the IMS network, when the
communication session has been established.
14. A method for providing service continuity with respect to a
registration of a mobile terminal (UE), at a control server of an
IP Multimedia Subsystem (IMS) network, while a CS-communication
session between the UE and a switching server (MSC), of a
circuit-switched (CS) network is established, the method
comprising: the MSC sending for the duration of the established
CS-communication session, a control information to the control
server to update a registration timer in the control server; and
the control information initiating a termination of the
registration of the UE at the IMS network, when the registration
timer expires.
15. The method according to claim 14, wherein the control server,
after receiving the control information from the MSC, updates the
registration timer when the registration timer approaches
expiration.
16. The method according to claim 14, wherein the MSC initiates the
update of the registration timer in the control server by
requesting the registration timer value from the control server of
the IMS network and, after receiving the registration timer value
and detecting that the registration timer is near expiration,
triggering the control server of the IMS network to update the
registration timer.
17. A switching server (MSC), of a circuit-switched network (CS)
for providing service continuity with respect to a registration of
a mobile terminal (UE), at a control server of an IP Multimedia
Subsystem (IMS) network, while a communication session between the
UE and the MSC is established, wherein the control server comprises
a registration timer which is used for initiating a termination of
the registration of the UE at the IMS network, when the
registration timer expires, the MSC comprising: a transmitting unit
for sending a control information to the control server, the
control information including information that the UE to update the
registration timer.
18. The switching server, MSC, according to claim 17, wherein the
transmitting unit of the MSC is adapted to trigger the control
server to terminate an updating of the registration timer in the
control server after the communication session between the UE and
the MSC is released.
19. A switching server (MSC), of a circuit-switched (CS) network
for providing service continuity with respect to a registration of
a mobile terminal (UE), at a control server of an IP Multimedia
Subsystem (IMS) network, for the duration of a CS-communication
session between the UE and the MSC, wherein the control server
comprises a registration timer which is used for initiating a
termination of the registration of the UE at the IMS network, when
the registration timer expires, the MSC comprising: a transmitting
unit for sending to the control server a request for the
registration timer value from of the IMS network and a trigger to
update the registration timer when the registration timer is near
expiration a receiving unit for receiving the registration timer
value from the control server of the IMS network, a decision unit
for making a decision to trigger an update of the registration
timer, when the registration timer is near expiration.
Description
TECHNICAL FIELD
[0001] The present invention relates to providing service
continuity with respect to a registration of a mobile terminal, UE,
at a control server of an IP Multimedia Subsystem, IMS, network.
The invention further relates to switching servers, MSCs, providing
such service.
BACKGROUND
[0002] Mobile communication networks are currently evolving from
circuit switched (CS) networks towards packet switched (PS)
networks, and by that integrate into IP based infrastructure that
are e.g. used for the Internet, the World Wide Web and the datacom
industry. With this trend mobile networks closely follow the
evolution steps of the wireline networks, where Voice over IP
(VoIP) via DSL access or via WLAN access is existing technology
today.
[0003] So-called IP Multimedia Subsystem (IMS) networks have been
developed for delivering multimedia services to mobile terminals
(e.g. to GSM terminals) being designed according to the well-known
standard named Global System for Mobile Communication (GSM), or to
Wideband Code Division Multiplex Access (WCDMA) stations. Hereto,
calls from and to subscribers of the multimedia services using a CS
access are routed through the IMS network in order to reach an IMS
service engine. This concept is called IMS Centralized Services
(ICS) being described in the standardization document TS 23.292,
release 8, of the so-called Third Generation Partnership Project
(3GPP) that is a standardization body to produce globally
applicable technical specifications.
[0004] A further 3GPP standard document in this scope is TS 23.237
(current release 10.1) specifying architectural requirements and
procedures for delivery of PS-CS or CS-PS IMS Service
Continuity.
[0005] In the frame of the 3GPP, further a project called Long Term
evolution (LTE) has been established to enhance the UMTS mobile
phone standard to cope with future requirements. Within this
project, the packet core is being developed to the so-called
Evolved Packet Core (EPC) forming a part of the Evolved Packet
System (EPS) that supports the so-called evolved UMTS Terrestrial
Radio Access Network (eUTRAN) being a new packet oriented radio
access (PS access network).
[0006] As part of the 3GPP standardization, e.g. being described in
the document TS 23.216 (current release 9.3), work on call
continuity for terminals equipped with single radio means (i.e.
terminals with one single radio transmitter and one single radio
receiver thus being capable of transmitting/receiving on only one
of PS- or CS-access at a given time) being referred to as Single
Radio Voice Call Continuity (SR-VCC) is ongoing, enabling to
transfer an IMS voice call from the EPS to the CS and vice
versa.
[0007] According methods described in the above-cited document TS
23.216, SR-VCC between PS access and CS access is based on the
principle that an MSC being enhanced for SR-VCC, also being
referred to as evolved MSC (eMSC), initiates a session transfer
towards an application server being dedicated to maintain service
continuity when handing over from an actual access network to a
target access network, also being referred to as Service
Centralization and Continuity Application Server (SCC-AS).
[0008] To perform a fast handover from the CS network to the PS
network and vice versa, the UE should preferably already be
registered in the IMS network and having at least a signaling
bearer in the PS network when the handover takes place.
[0009] When the UE moves from one access network to another access
network, there is a possibility that the registration of the UE in
the IMS network will expire because of a missing PS bearer support
for an IMS re-registration. This could happen if the UE, having an
ongoing CS call, enters an access network, which does not support
simultaneous PS and CS bearers, e.g. Global System for Mobile
communications (GSM) networks or Enhanced Radio Access Networks
(GERAN) not having a Dual Transfer Mode (DTM) support.
SUMMARY
[0010] It is an object of the present invention to perform an
improved registration of a mobile terminal in an IMS network. This
object is achieved by the independent claims. Advantageous
embodiments are described in the dependent claims.
[0011] According to embodiments of the invention, it is assumed
that a CS-communication session between a mobile terminal, UE, and
a switching server, MSC, of a circuit-switched, CS, network is
established and that the UE is registered at a control server of an
IP Multimedia Subsystem, IMS, network. The CS-communication session
between the UE and the MSC can either has been initiated when the
UE is camping on CS or has been initiated in a PS network, and then
transferred to the CS network using the Single Radio Voice Call
Continuity (SR-VCC) procedure. The SR-VCC procedure as e.g. been
mentioned in the 3GPP standard TS 23.216, Version 9.3.0, provides a
service continuity of Multicast and Broadcast services, when the
access system changes and the corresponding services are provided
in the target access system. Therefore the call of the UE is
anchored in the IMS network. The MSC, enhanced for SR-VCC,
initiates the session transfer procedure to IMS and coordinates it
with the CS handover procedure to the target cell. It then sends a
PS-CS handover response to a Mobility Management Entity (MME) of
the PS network, which includes the necessary CS handover command
information for the UE to access the CS network.
[0012] Further more, the control server comprises a registration
timer which is used for initiating a termination of the
registration of the UE at the IMS network, when the registration
timer expires. To provide a service continuity for the registration
of the UE at IMS network, the control server updates the
registration timer in dependence of a control information received
from the MSC.
[0013] The update procedure of the registration timer of the
control server can be executed even if the UE is not able to
refresh the IMS registration status over a packet switched PS
network. The ongoing registration of the UE in the IMS network will
speed up the SR-VCC procedure switching from a CS network to a PS
network because no re-registration has to be initiated.
[0014] In an embodiment of the invention, the MSC sends the control
information to the control server before the registration timer in
the control server expires. This will prevent the loss of
registration of the UE in the IMS network. A loss of registration
during a CS call session of the UE will hamper a possible rSR-VCC
(return SR-VCC) procedure when the communication is switched back
from a CS network to a PS network.
[0015] In an embodiment of the invention, the MSC initiates the
update of the registration timer in the control server by sending
control information to the control server which comprises the
information about the lack of possibility of the UE to update the
registration timer. This control information comprises the
information that an ongoing CS-communication session between the
MSC and the UE is established. The control server takes over the
responsibility to update its registration timer for the IMS
registration of the UE before it expires without further involving
the MSC and the UE in the updating procedure. This will reduce the
traffic load in the IMS network because a re-registration of the
IMS registration due to the expiry of the registration timer is not
necessary.
[0016] Advantageously the control information additionally
comprises information about the user identity of the UE and/or the
equipment identity of the UE. The information about the identity of
the user and/or the identity of the user equipment can be used by
the control server of the IMS network to check the identity of the
PS registration of the user. The control server of the IMS network
doesn't need to request additional authentication information which
can result in a time delay and additional network traffic.
[0017] In a further embodiment after receiving the control
information from the MSC, the control server updates the
registration timer when the registration timer is close to expire.
In other words, the update should be initiated at the latest in due
time before the expiry of the registration timer might trigger the
termination of the registration. Otherwise a re-registration
procedure would have to be initiated when the communication is
switched back from a CS network to a PS network which results in
additional network traffic and a time delay or interruption in the
communication session of the UE. The control server is responsible
for the supervision of his local registration timer. No further
action is needed from the MSC to supervise this timer. This will
reduce the internal workload of the MSC. When a registration timer
counts (e.g. counts down) from a start-value to an end-value (e.g.
"0") and, after reaching the end-value, initiating a termination of
the registration of the UE in the IMS network, an update of the
registration timer means to reset the registration timer value to a
start-value.
[0018] In a further embodiment the MSC triggers the control server
to terminate the updating of the registration timer in the control
server after the CS-communication session between the UE and the
MSC is released. After the release of the communication session,
the UE is able to update the registration in IMS on its own.
[0019] In a further embodiment of the invention, the MSC requests
the registration timer value from the control server of the IMS
network and, after receiving the registration timer value and
detecting that the registration timer is close to expire, triggers
the control server of the IMS network to update the registration
timer. The MSC is responsible for the supervision of the
registration timer which is located in the control server. The
workload for the control server is reduced.
[0020] In a further embodiment, the request of the registration
timer value also comprises the user identity of the UE and/or the
equipment identity of the UE.
[0021] In a further embodiment of the invention, the control
server, after updating the registration timer, sends a notification
message to a serving node of the IMS network which triggers an
update of an additional registration timer in the serving node.
This additional registration timer in the serving node of the IMS
network is needed for managing additional registration purposes in
the IMS network.
[0022] In a further embodiment the control server of the IMS is a
Proxy Call Session Control Function, P-CSCF, server. In a further
embodiment the serving node is a Server Call Session Control
Function, S-CSCF, server.
[0023] In a further embodiment of the invention, the MSC receives
the address of the control server of the IMS network, when the
registration of the UE at the control server of the IMS network has
been established.
[0024] In an alternative embodiment of the invention the MSC
receives the address of the control server of the IMS network, when
the communication session has been established. The MSC requires
the address of the control server to build up a communication
session between the MSC and the control server.
[0025] The present invention also concerns a method for providing
service continuity with respect to a registration of a mobile
terminal, UE, at a control server of an IP Multimedia Subsystem,
IMS, network, while a CS-communication session between the UE and a
switching server, MSC, of a circuit-switched, CS, network is
established. The MSC sends, for the duration of the established
CS-communication, control information to the control server to
update a registration timer in the control server which is used for
initiating a termination of the registration of the UE at the IMS
network, when the registration timer expires.
[0026] In an embodiment of the invention, the control server, after
receiving the control information from the MSC, updates the
registration timer when the registration timer is close to
expires.
[0027] The present invention also concerns a switching server, MSC,
of a circuit-switched network, CS, for providing service continuity
with respect to a registration of a mobile terminal, UE, at a
control server of an IP Multimedia Subsystem, IMS, network, while a
communication session between the UE and the MSC is established.
The control server comprises a registration timer which is used for
initiating a termination of the registration of the UE at the IMS
network, when the registration timer expires. The MSC comprises a
unit which is adapted to send control information to the control
server. The control information comprises the information about the
lack of possibility of the UE to update the registration timer.
[0028] In an embodiment, the switching server, MSC, comprises a
unit adapted to trigger the control server to terminate the
updating of the registration timer in the control server after the
CS-communication session between the UE and the MSC is
released.
[0029] In a further embodiment of the invention, the MSC initiates
the update of the registration timer in the control server by
requesting the registration timer value from the control server of
the IMS network and, after receiving the registration timer value
and detecting that the registration timer is close to expire,
triggers the control server of the IMS network to update the
registration timer
[0030] In a further embodiment the invention concerns a switching
server, MSC, of a circuit-switched network, CS, for providing
service continuity of a registration of a mobile terminal, UE, at a
control server of an IP Multimedia Subsystem, IMS, network, for the
duration of a CS-communication session between the UE and the MSC.
The control server comprises a registration timer which is used for
initiating a termination of the registration of the UE at the IMS
network, when the registration timer expires. The MSC comprises:
[0031] a transmitting unit (31) adapted to send to the control
server (3) a request for the registration timer value from of the
IMS network and to send a trigger to update the registration timer
when the registration timer is close to expire. [0032] a receiving
unit (32) adapted to receive the registration timer value from the
control server (3) of the IMS network, [0033] a decision unit (33)
adapted to make a decision to trigger an update of the registration
timer, when the registration timer is close to expire.
[0034] In a further embodiment, the request of the registration
timer value also comprises the user identity of the UE and/or the
equipment identity of the UE.
[0035] The present invention also concerns computer programs
comprising portions of software codes in order to implement the
method as described above when operated by a respective processing
unit of a user device and a recipient device. The computer program
can be stored on a computer-readable medium. The computer-readable
medium can be a permanent or rewritable memory within the user
device or the recipient device or located externally. The
respective computer program can also be transferred to the user
device or recipient device for example via a cable or a wireless
link as a sequence of signals.
[0036] In the following, detailed embodiments of the present
invention shall be described in order to give the skilled person a
full and complete understanding. However, these embodiments are
illustrative and not intended to be limiting.
BRIEF DESCRIPTION OF THE FIGURES
[0037] FIG. 1 shows a first exemplary sequence diagram of
embodiments of the invention;
[0038] FIG. 2 shows a second exemplary sequence diagram of an
alternative embodiment of the invention;
[0039] FIG. 3 shows an exemplary block diagram of a switching
server, MSC according to an embodiment of the invention;
[0040] FIG. 4 shows an exemplary flow chart of the functioning of
the MSC performing the alternative embodiment of FIG. 2.
DETAILED DESCRIPTION
[0041] FIG. 1 shows an exemplary sequence diagram of a first
embodiment of the invention and comprises a mobile terminal UE 1
which has established a circuit switched (CS) session. This CS
session has either been initiated in a CS network or has been
initiated in a PS network and then transferred to a CS network
using the Single Radio Voice Call Continuity (SR-VCC) procedure as
specified in the 3GPP standard TS 23.216 Version 9.3.0. The SR-VCC
procedure provides a service continuity of Multicast and Broadcast
services, when the access system changes and the corresponding
services are provided in the target access system. The call of the
UE 1, which supports the SR-VCC procedure, is always anchored in
the IMS network. The MSC 2, enhanced for SR-VCC, initiates the
session transfer procedure to IMS and coordinates it with the CS
handover procedure to the target cell. It then sends a PS-CS
handover response to a Mobility Management Entity (MME) of the PS
network, which includes the necessary CS handover command
information for the UE 1 to access the CS network. It is assumed
that the CS network does not support the Dual Transfer Mode, DTM,
which allows simultaneous transfer of CS and PS data over the same
network.
[0042] The communication session is established between the UE 1
and a switching server, MSC 2, of the CS network, whereas the MSC 2
is enhanced with the capability to use the Session Initiation
Protocol, SIP, or the XML Configuration Access Protocol, XCAP, for
the communication with a control server 3 of an IMS network to
provide SR-VCC functions.
[0043] The control server 3 could be a Proxy Call Session Control
Function, P-CSCF, server, which is capable to act as a first point
of contact in an IMS network for the registration of a UE 1 to the
IMS network. The P-CSCF is a Proxy-Server and authenticates the UE
1. Because other nodes in the IMS trust the P-CSCF, they do not
have to authenticate the UE 1 again.
[0044] The serving node 4 could be a Server Call Session Control
Function, S-CSCF, server, which is capable to act as the central
node of an IMS network. The S-CSCF provides routing services and
decides which application server should provide their services to
the UE 1.
[0045] It will be further assumed that the UE 1 has an active IMS
registration that has not expired yet. The UE 1 which supports the
SR-VCC procedure comprises a local expiration timer which prevents
the release of an IMS registration locally in the UE 1 before it
expires. The UE 1 updates its expiration timer locally when a CS
session or call is ongoing. After the CS session or call is
completed, the UE 1 must re-register its registration in the IMS
within a given time interval to ensure that it re-synchronized its
expiration timer with the registration timer of the IMS. After the
CS session is established, the SCC AS 5 sends the address of the
P-CSCF 3 the UE 1 is registered through on the PS access to the
enhanced MSC 2.
[0046] Based on the P-CSCF address, the MSC 2 sends in a first step
11 of the MSC registration expiration update procedure, a
notification message of ongoing session to the P-CSCF 3. This
notification may include the user identity, the equipment identity
of the UE 1 and/or other information required to identify the IMS
registration of the user.
[0047] The second step 12 of the MSC registration expiration update
procedure comprises a supervision of the registration timer in the
P-CSCF 3. When the registration of the UE 1 on IMS is close to
expiring, the P-CSCF 3 updates its local registration timer. The
P-CSCF 3 must therefore be aware of the inability of the UE 1 to
update its PS registration. This could be provided by the
notification message the MSC 2 sends to the P-CSCF 3 in the first
step 11, which can include the information that the UE 1 is not
able to update its IMS registration.
[0048] The third step 13 is a further embodiment of the invention
and comprises the initiation of a re-registration procedure from
the P-CSCF 3 to update the registration timer also in the serving
node 4 of the IMS network. This serving node 4 can be a Call
Session Control Function server, S-CSCF 4. The P-CSCF 3 can
indicate in the re-registration message 13 to the S-CSCF 4 that
this re-registration is a P-CSCF-registration to avoid that the
S-CSCF 4 challenges the P-CSCF 3 for authentication. Another
possibility to inform the S-CSCF 4 about a registration timer
update is a special notification message 13, which could be sent
from the P-CSCF 3 to the S-CSCF 4. This would have the benefit of
not impacting the current registration process.
[0049] When the call is released 14 by the UE 1 in CS, the MSC 2
sends in a fourth step 15 a notification message to the P-CSCF 3 to
initiate a termination of the process of updating the registration
timer before expiry. The expiration of the local expiration timer
in the UE 1 leads to a re-registration of the UE 1 in the IMS. In a
preferred embodiment of this invention the update of registration
is performed immediately even if the local expiration timer in the
UE 1 is not expiring.
[0050] In a further embodiment of the invention, the MSC 2
established a relation to the P-CSCF 3 before the establishment of
a CS connection of the UE 1. This could happen if a call in the PS
network is initiated and later be transferred to the CS network
using a procedure according to the standard 4GPP 23.856, clause
6.4.3.1a. In this scenario, the UE 1 initiates an IMS multimedia
session to another UE and uses only PS media flow(s). The request
is forwarded to the S-CSCF 4 following normal IMS session set up
procedures. The P-CSCF 3 detects the IMS multimedia session and
based on the local policy it anchors the session in the MSC 2 prior
forwarding the invitation message to the S-CSCF 4. The P-CSCF 3
finds the correct MSC 2 to route to by applying procedures similar
to those defined for dynamic user allocation to application
servers. The difference to the first embodiment of the invention is
that the SCC-AS 5 does not need to send the address of the P-CSCF 3
to the MSC 2.
[0051] FIG. 2 discloses a third embodiment of the invention and
only shows the part of the MSC registration expiration update
procedure. It is assumed, that the UE 1 established a call in the
CS network. This establishment is according to the embodiments of
the invention as shown in FIG. 1. The MSC 2 has determined the
address of the P-CSCF. The MSC 2 requests in a first step 21 the
P-CSCF of the expiration timer value of the UE 1. This request may
also include the user and/or the equipment identity of the UE 1.
Also other information which could be required to identify the PS
registration of the user could be implemented in the request 21.
Ina second step 22 of the embodiment according FIG. 2, the P-CSCF 3
returns to the MSC 2 a timer value 22 which indicates the time left
the UE 1 has on prior its expiration timer will expire. The request
of the first step 21 can be a subscription of the MSC 2 to the
P-CSCF 3, i.e. the P-CSCF 3 will inform the MSC 2 about any
changes. This could happen e.g. if the coverage situation might
have changed and may have allowed that the UE 1 updates the IMS
registration on its own. This might be possible if the UE 1 is
switched to a network which can handle a PS request or supports
DTM. The MSC 2 can request the expiration timer value latest before
it expires and while the CS call is still ongoing.
[0052] The MSC 2 decides in a third step 23 of the MSC registration
expiration update procedure according the embodiment of FIG. 2 to
update the registration timer in the P-CSCF 3 prior to the expiry
of the expiration timer in the UE 1.
[0053] In a fourth step 24 of the embodiment according FIG. 2, the
MSC 2 initiates a re-registration to update the registration timer
in the P-CSCF 3. To avoid that the P-CSCF 3 will request the MSC 2
for authentication according to a normal re-registration procedure
to an IMS network, the MSC 2 may indicate the re-registration
procedure as an MSC initiated re-registration procedure.
Alternatively, the MSC 2 could send a special notification message
to the P-CSCF 3 to update its registration timer. This would
advantageously not impact the current registration procedure.
[0054] In the fifth step 13, after the P-CSCF 3 updates its local
registration timer, it forwards the notification message or the
notification of a re-registration procedure to the S-CSCF 4 to
update the local registration timer in the S-CSCF 4.
[0055] FIG. 3 shows a block diagram of a switching server, MSC 2,
according to an embodiment of the invention. The MSC 2 comprises a
transmitting unit 31, adapted to send a request for the
registration timer value to the control server 3 of the IMS network
and to trigger the control server 3 of the IMS network to update
the registration timer when the registration timer is close to
expire, a receiving unit 32, adapted to receive the registration
timer value from the control server 3 of the IMS network and a
decision unit, adapted to make a decision to trigger an update of
the registration timer, when the registration timer is close to
expire. The transmitting unit 31, receiving unit 32 and the
decision unit 33 of the MSC 2 are functional blocks and can be
integrated in one or more circuits or one or more other physical
entities.
[0056] FIG. 4 is a flow chart which shows the steps of an
embodiment of the invention performed by the switching server, MSC
2. This flow started with a first step 20, which requests a
positive indication in the MSC 2 of on ongoing call of a UE 1 in a
CS network. If this indication is given, the second step 21 will be
performed. The MSC 2 requests a registration timer value from the
P-CSCF 3. The third step 22 is a check whether the MSC 2 receives
the requested timer or not. If the MSC 2 does not receive the
requested registration timer from the P-CSCF 3, a new request is
started. If the MSC 2 receives a registration timer value from the
P-CSCF 3, it checks in the fourth step 23 if the registration timer
is close to expires. If the registration timer is close to expires,
the MSC 2 sends in the fifth step 24 a notification message to the
P-CSCF 3 to update the registration timer in the P-CSCF 3. When the
call of the UE in the CS network stops, the registration expiration
update procedure ends 25. The UE 1 is now able to update the
registration timer it selves.
* * * * *