2009年12月29日

ICS (1) - IMS Centralized Services OV

ICS (1) - IMS Centralized Services OV

Alternatives for Delivering Voice in FTTP

1.1) ICS OV


§ ICS Applicability: IMS Centralized Services is an approach to the provision of communication services wherein services and service control are based on IMS mechanisms and enablers

§ ICS enables the delivery of IMS based services to users regardless of the attached access network type; e.g. CS domain access or IP Based Access Networks.

§ ICS as an enabler for wireless-wireline convergence (like FMC)

§ With ICS, IMS sessions using CS media are treated as standard IMS sessions for the purpose of service control and service continuity.


Service Consistency:

§ Service Consistency: The subscriber’s service experience is the same regardless of the domain (CS, PS).

§ Service Consistency - Consistent User Experience-same services in All Domains

§ Subscribers shall have a consistent user experience regardless of the domain used, subject to the constraints of the UE and access network.

§ The ICS user shall receive both registered and unregistered services in a consistent manner when the user is accessing IMS regardless of CS or PS domain.


Service Continuity:

§ Service Continuity: The subscriber’s services are maintained seamlessly and transparently when transitioning across domains while in an active session.

§ Service continuity shall be provided when underlying mobility results in a change of access network capabilities, e.g. support of Gm reference point in conjunction with CS bearer may not be possible after handover from UTRAN to GERAN

§ Service Continuity between domains (CS, PS) is also provided.

§ The VCC function provides PS-CS Mobility for Voice functions.

§ The VCC AS capability will evolve into the SCC AS capability to additionally support CS-PS and PS-PS functionality with service continuity across the transfers.


ICS - Centralized IMS Application for all Telephony calls

§ Services supported by ICS should include at least: IMS supplementary services defined within 3GPP MMTel and other IMS hosted services

§ IMS multimedia telephony service (MMTel) is the main interest to ICS. ICS also supports IMS service continuity (VCC or SCC)

§ While in Release 7, the hot application specifications for IMS services were Multi Media Telephony (MMTel) and device centric Voice Call Continuity (VCC).

§ The work in Release 8 seems to have to have shifted towards IMS Centralized Services (ICS) and a network centric Voice Call Continuity.

§ IMS Centralized Services (ICS) allow mobile operators to connect and deliver IMS services to any device by connecting the IMS core to 2G, 3G, UMA Macro, Pico and Femto cells.

§ Call Routing is done in IMS. The Cs-Domain MSC role reduces to Inter-MSC Mobility within the 2G/3G Handover.

§ The ICS is an interim solution for a transition period when VoIP is not generally available due to lack of VoIP capable radio accesses (e.g. LTE, HSPA).

§ This will enable carriers to transition the voice core to all-IP, eliminating the need for legacy MSCs.

§ Certain operators would like to discontinue the investments to the CS network and develop all services in IMS as instead, but since the VoIP is not yet possible everywhere, the UE must have other means to access the IMS services while “roaming” in those areas.

§ In those (Not-VoIP-available) areas, the UE must use CS domain for voice calls, but still at the same time, be able to control the mid-call services residing in IMS.

§ Such mid-call services are e.g. conferencing, call transfer, call hold and resume, that in GSM (global system for mobile communication) are executed in the CS domain in a VMSC (visited mobile switching center), but in the ICS system, these should be executed in the IMS as instead.

§ For this purpose, the ICS has described two main solutions, I1-cs and I1-ps, that are protocol alternatives what a so-called ICS UE can use to control the IMS services while engaged to a CS call.


1.2) ICS - Service consistency


§ IMS services shall be consistently provided when using a CS or a PS access network for the media of the IMS service subject to the capability of the UE and the access network.

§ ICS shall be available from any access network, domain and UE.

§ A reduced set of services may be offered subject to constraints of the UE, access network and domain.


1.3) ICS - Service Continuity


§ IMS Centralized Services across different access networks, service continuity between domains is also considered

§ In ICS, the Service Continuity between access networks and domains (CS or PS) is also considered.

§ ICS provides mechanisms to support the use of CS media bearer for IMS sessions.

§ With ICS, the user services are provided and executed in the IMS. ICS users are IMS subscribers. User sessions are controlled in IMS via PS or CS access.

§ Service continuity availability depends on the capability of the user equipment (UE).

§ ICS shall support service continuity between different 3GPP access networks, subject to the constraints of the UE and access networks.

§ The service continuity shall include:

o Basic services

o Non mid call services

o Mid call services

§ ICS enables both service consistency and service continuity.

§ IMS centralized services (ICS, 3GPP TR 23.892) describes a solution which can offer service consistency and service continuity between CS (circuit switched) and PS packet switched (IP-CAN) accesses.


2.1) Coexistence of an ICS UE and a non ICS UE


§ It shall be possible to provide ICS for an ICS UE and a non ICS UE in home and in visited networks.

§ An ICS UE is basically a user equipment that is capable of receiving telephony services and other services offered by IMS while the voice bearer is established via CS.

§ An ICS UE can also be a UE which can access IMS via an IP-CAN that supports the full duplex speech component of the IMS multimedia telephony service.

§ Home and visited networks with an MSC Server enhanced for ICS (IMSC) shall support call originations and terminations for ICS UEs and non ICS UEs.

§ When the ICS UE establishes the Service Control Signalling Path over I1 or Gm prior to the CS Bearer Control Signalling Path, the ICS UE shall use the routing number for establishing the CS Bearer Control Signalling Path.


2.2). ICS UE Scenarios:


§ IMS Centralized Services may be supported across different three types of UEs attached through different types of access networks.

§ But those different types of UEs may or may not be VCC/SCC capable

§ Three Scenarios of ICS UE: http://docs.google.com/View?id=ddh56dhg_307fkbdxqw8


Scenario A ICS UE: (IMS services via PS access / domain – VoIP Capable)

§ The network is an IP CAN capable of transporting bi-directional speech media.

§ Here both media transport and session control signalling is carried over the IP CAN.

§ In this scenario IP based services are being provided over a fully supportive IP capable network.

§ For IMS centralized services there are no issues associated with enabling ICS under this scenario.


Scenario B ICS UE: (IMS voice services via CS access / domain)

§ The UE is served through the CS domain.

§ In this scenario, both the media transport and session control signalling is carried through the CS domain.


Scenario C ICS UE: (IMS services with voice via CS access / domain)

§ Both CS domain and a non bi-directional speech media capable IP CAN are available in the network:

§ The media transport is carried through the CS domain and

§ The session and media control signalling is carried over CS domain or over the non bi-directional speech media capable IP CAN.

§ Note that PS domain may be VoIP capable in this scenario as well.


2.3) Administration of supplementary services via UE


§ The device may probably support Ut for user administration of supplementary services

§ The Ut is defined and supported between an IMS terminal and user service management system in the IMS service layer.

§ If Ut is NOT supported, the operator may support user administration via other suitable means from the device, for example, using a web page.

§ If the device does not support any of these above methods, an MSC that has been enhanced for ICS may also be called on to translate between DTAP and Ut (for user administration of supplementary services).

§ Then, all supplementary services can be executed in IMS and administered from GSM and IMS.


2.4) ICS UE Session Scenarios


The following IMS session scenarios shall be supported

§ Basic voice or voice and video service origination and terminating sessions.

§ Voice or voice and video origination and termination service sessions with Line ID services (e.g. OIP, OIR, TIP, TIR) controlled in IMS.

§ Voice or voice and video origination and termination service sessions with Communication Barring services controlled in IMS.

§ Voice or voice and video origination and termination service sessions with mid-call services (e.g. Hold/Resume, Conferencing, CW, ECT) controlled in IMS.

§ Voice or voice and video termination service sessions with Communication Diversion services controlled in MS.

§ Adding/removing real time video media flow over CS access to/from an IMS session

§ Communication services setting modifications (e.g., changing forwarding info or activating barring services, etc).

§ The solution shall provide generic capabilities to enable introduction of new IMS services utilizing CS bearers without further standardization.


2.5) Non-ICS UE Session Scenarios


If CS networks are upgraded with ICS capability: the following services will be supported

§ Basic voice service origination and terminating sessions.

§ Voice origination and termination service sessions with Communication Barring services controlled in IMS.

§ Voice termination service sessions with Communication Diversion services controlled in IMS.

But if CS networks are not upgraded with ICS capability, then the following services will NOT be supported

§ Voice origination and termination service sessions with Line ID services (e.g. OIP, OIR, TIP, TIR) controlled in IMS.

§ Voice origination and termination service sessions with mid-call services (Hold/Resume, Conferencing, CW, ECT) controlled in IMS.

And support the following VCC session scenarios - when a non-ICS UE capable of VCC accesses IMS services via GSM/UMTS CS network:

§ Domain Transfers of basic voice service sessions in both directions.

§ Domain Transfers of voice sessions with non mid call services in both directions.


3). ICS - Services Supported


3.1). IMS services


§ ICS users receive IMS Services. IMS service control is always performed by the home IMS network except for emergency calls.

§ However the services themselves may be provided by the home IMS network, the visited IMS network or a 3rd party provider.

§ The set of IMS services supported by ICS should at least include: IMS Multimedia Telephony services (MMTel) and supplementary services (subject to the constraints of the UE and access networks)


3.2). Service provided on ICS:


IMS Centralized Services that may be provided using different access networks or solutions

Priority Service (ETS):

§ The IMS centralized services solution needs to support Domain Transfers of Priority Service

Supplementary services

§ The IMS centralized services solution needs to provide subscribers with a consistent supplementary service behavior upon Domain Transfers (e.g. Call Forwarding, Communication Waiting, Call Hold, etc.).

Service consistency in Emergency Call and Priority Service

§ Emergency calls and Priority services (if provided by the operator) shall be provided in a consistent manner regardless of domain


Some Service Requirement supports are required for ICS:

§ UE support

§ Roaming support

§ Service consistency

§ Service continuity

§ Emergency call

§ Priority service

§ IMS services: at least IMS Multimedia Telephony services and supplementary services


4). Managing Session via ICS


ICS offers a centralized services, which means an IMS Application Server for ICS manages sessions for a user in several respects:


4.1). Multiple Devices Allowed


§ Several devices can be associated to the same user account and can be active simultaneously. Incoming media sessions can then be forwarded to one, several or all of these devices. Devices can be switched during ongoing sessions.

§ Including GSM mobiles, the ICS has been designed not only to work with IP/IMS devices but also with "legacy" GSM phones without any special software on board.

§ For example, directing an incoming session to an ICS User and one or more UEs of an ICS User (multiple UEs allowed) is allowed.

§ When mobiles are switched on the MSC server communicates with the ICS Application Server on behalf of the mobile. This can be done via

o either directly - the MSC server has been enhanced to act as an IMS client for the mobile

o or via an Intelligent Network (IN) node that communicates with the MSC Server via CAP

§ The later one is probably preferred by many suppliers since IN nodes and CAP are used today for many applications such as prepaid billing. This has the advantage that the MSC software does not have to be extended for ICS.


4.2). Managing Supplementary Services


§ The ICS offers a standardized way of implementing services such as call forwarding, barring, hold, resume, 3-way calling.


4.3). Combination of Different Types of Media Supported


§ The ICS is not limited to voice telephony.

§ Video calling, picture sharing and other media streams can be added or removed from a session at any time.


4.4). Handover to 2G


§ Handover the voice portion of a session to a circuit switched bearer when the mobile reaches the limit of the broadband wireless networks.

o The ICS handover to a circuit switched channel is network initiated and controlled where VCC handover is mobile-controlled.

o IMS service continuity (SCC) is coupled with IMS Centralized Services (ICS) so that all session signaling is controlled in IMS whatever the type of access used by the terminal (i.e. CS or PS).

o The advantage of network-controlled is that the device does not have to be attached to two different radio networks simultaneously.

o This network control is important since like GSM/UMTS mobiles today, future LTE mobiles will also not be able to connect to two cellular network technologies simultaneously (for SRVCC). Currently, handovers from LTE are supported to GSM/UTRAN and 1xCDMA







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