W4_JTO_Ph2_Datacom_IT-part-13.pdf

JTO Phase II Data Network & IT IMS 13 IMS 13.1 Learning Objectives  Learn about the Architecture of IMS  Different working elements of IMS Core  IMS interfaces ...

JTO Phase II Data Network & IT IMS 13 IMS 13.1 Learning Objectives  Learn about the Architecture of IMS  Different working elements of IMS Core  IMS interfaces  Application Servers to provide functionality.  Basic Call Flow in IMS 13.2 INTRODUCTION Many successful services are available today on the Internet, including e-mail, web browsing, chat, and audio and video downloading/streaming, Internet telephony and Multimedia Communications Services. Both fixed and mobile operators face problem of subscriber churn, and the issue is getting worse as new service providers offers cheap, or free, calls over the Internet continue to arrive on the scene and gain market share.  One key way to attract and retain subscribers is to offer differentiation in areas like personalization, service bundling, co-branding, business-to-business relations, tariffs, single sign-on and quality of service.  Another key way to retain subscribers is to build on and strengthen the customer relationship so that subscribers are far more reluctant to switch suppliers, even if switching means lower call charges in the short term. In this case, they will have to rapidly push IMS before proprietary solutions become largely adopted. IMS is the only standardized solution in the telecommunications world. 13.3 What is IMS? IMS – IP Multimedia Subsystem standardized by the telecommunications world is a new architecture based on new concepts, new technologies, new partners and ecosystem. IMS provides real-time multimedia sessions (voice session, video session , conference session, etc) and non real-time multimedia sessions (Push to talk, Presence, instant messaging) over an all-IP network. IMS targets convergence of services supplied indifferently by different types of networks fixed, mobile, Internet. IMS is also called Multimedia NGN (Next Generation Network). IMS deployment is a strategic decision, not a network technology decision. It can be taken either by a traditional service provider in the context of repositioning its business on IP services or by any entity that would decide to start an activity in IP services even without owning an access or transport network. IMS offers standardized service enablers and network interfaces that will make interoperability of new MM services easier to achieve. JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 165 of 174 For Restricted Circulation JTO Phase II Data Network & IT IMS IMS is a tool for operators that enable the creation and delivery of PS based person-to- person MM services in a way that protects the operator business model and generates new revenue. Service scalability is solved by the IMS architecture. It offers support to compose services and expand existing services. The core of IMS is combining the best of two worlds datacom industry & telecom industry. 13.4 Why IMS? Operator perspective End-user perspective General Quality Of Service New, exciting services and Faster time to market with enhancements of existing new services services Service Integration Same services available Grow and protect subscriber regardless of terminal and base, increase ARPU access type Keeps charging relation Ease of use & Security Controlling CAPEX with user and OPEX 13.4.1 IMS Standardization The IMS was initially standardized by the 3rd Generation Partnership Projects (3GPP) as part of its Release 5 specifications & is practically speaking targeted at supporting non – real time services.The second release is 3GPP Release 6 & is targeted at supporting real time services.3GPP release added inter-working with WLAN. With the increasing penetration of Wireless Local Area Networks (WLANs) and emerging Wireless Metropolitan Area Networks (WiMax) as access network technologies, the IMS scope is now extended within the ongoing Release 7 standardization for any IP access network, including fixed access networks, i.e. DSL. 13.4.2 IMS Architecture As Defined By 3 GPP The IMS provides all the network entities and procedures to support real-time voice and multimedia IP applications. It uses SIP to support signaling and session control for real- time services Depending on the specific tasks performed by a CSCF, CSCFs can be divided into three different types.  Serving CSCF (S-CSCF).  Proxy CSCF (P-CSCF).  Interrogating CSCF (I-CSCF). JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 166 of 174 For Restricted Circulation JTO Phase II Data Network & IT IMS Figure 66: GPP IP Multimedia Subsystems 13.4.3 S-CSCF (Serving Call State Control Function) An S-CSCF provides session control services for a user. It maintains session states for a registered user‘s on-going sessions and performs the following main tasks. a. Registration: An S-CSCF can act as a SIP Registrar to accept users‘ SIP registration requests and make users‘ registration and location information available to location servers such as the HSS (Home Subscriber Server). b. Session Control: An S-CSCF can perform SIP session control functions for a registered user. Relay SIP requests and responses between calling and called parties. c. Proxy Server: An S-CSCF may act as a SIP Proxy Server that relays SIP messages between users and other CSCFs or SIP servers. d. Interactions with Application Servers: An S-CSCF acts as the interface to application servers and other IP or legacy service platforms. e. Other functions: An S-CSCF performs a range of other functions not mentioned above. For example, it provides service-related event notifications to users and generates Call Detail Records (CDRs) needed for accounting and billing 13.4.4 P-CSCF A P-CSCF is a mobile‘s first contact point inside a local (or visited) IMS. It acts as a SIP Proxy Server. In other words, the P-CSCF accepts SIP requests from the mobiles and then either serves these requests internally or forwards them to other servers. The P-CSCF includes a Policy Control Function (PCF) that controls the policy regarding how bearers in the packet-switched network should be used. The P-CSCF performs the following specific functions: o Forward SIP REGISTER request from a mobile to the mobile‘s home network. If an I-CSCF is used in the mobile‘s home network, the P-CSCF will forward the SIP REGISTER request to the I-CSCF. Otherwise, the P- CSCF will forward the SIP JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 167 of 174 For Restricted Circulation JTO Phase II Data Network & IT IMS REGISTER request to an S-CSCF in the mobile‘s home network. The P-CSCF determines where a SIP REGISTER request should be forwarded based on the home domain name in the SIP REGISTER Request received from the mobile. o Forward other SIP messages from a mobile to a SIP server (e.g. the mobile‘s S- CSCF in the mobile‘s home network). The P-CSCF determines to which SIP server the messages should be forwarded based on the result of the SIP registration process. o Forward SIP messages from the network to a mobile. o Compression and decompression of SIP messages. Compression is required to minimize the air-interface time. o Perform necessary modifications to the SIP requests before forwarding them to other network entities. o Maintain a security association with the mobile. o Detect emergency session. o Create CDRs. 13.4.5 I-CSCF An I-CSCF is an optional function that can be used to hide an operator networks internal structure from an external network when an I-CSCF is used. It serves as a central contact point within an operator‘s network for all sessions destined to a subscriber of that network or a roaming user currently visiting that network. Its main function is to select an S-CSCF for a user‘s session, route SIP requests to the selected S-CSCF. The I-CSCF selects an S- CSCF based primarily on the following information: o Capabilities required by the user. o Capabilities and availability of the S-CSCF and o Topological information, such as the location of an S-CSCF and the location of o the users P-CSCFs if they are in the same operators network as the S-CSCF. 13.4.6 The Databases: (HSS And SLF) HSS (Home Subs Server): It is just like HLR & Authentication Centre (AuC). All the database of users are stored in HSS ie, authentication data , service profile ,charging etc will be in HSS. No VLR concept in IMS. HSS is mandatory. Whereas SLF is optional. HSS is master user database that supports IMS N/W entities that actually handle call. It contain subscriber profile , perform authentication & authorisation of the user & can provide information about subscriber location & IP information. SLF ( Subs Location Function) Whenever n/w size is so big that if one HSS cannot store data then SLF is required ,this is an addl. Component. Suppose S-CSCF has done some authorisation then it has to contact HSS for downloading ,authentication etc. JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 168 of 174 For Restricted Circulation JTO Phase II Data Network & IT IMS –If one HSS is there then no ambiguity. –But if more than one HSS then SLF will check which HSS. Both HSS & SLF communicate through Diameter protocol. This diameter is called as AAA protocol. SLF will have -(User-ID/ HSS-ID ). Both the HSS and the SLF implement the Diameter protocol (RFC 3588) with an IMS- specific Diameter application.  The Media Gateway Control Function (MGCF) and the IM Media Gateway (IM-MGW) are responsible for signaling and media inter-working, respectively, between the PS domain and circuit-switched networks (e.g. PSTN).  Multimedia Resource Function Processor (MRFP) –Provides resources to be controlled by the MRFC  Sources media streams (for multimedia announcements)  Processes media streams (e.g. audio transcoding, media analysis)  Tones and announcements –Applied on receipt of ACK, self-timed with BYE or stopped on BYE  Support DTMF within the bearer path.  The Multimedia Resource Function Controller (MRFC) interprets signaling information from an S-CSCF or a SIP-based Application Server and controls the media streams resources in the MRFP accordingly. The Breakout Gateway Control Function (BGCF) selects to which PSTN network a session should be forwarded. IT will then be responsible for forwarding the session signaling to the appropriate MGCF and BGCF in the destination PSTN network JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 169 of 174 For Restricted Circulation JTO Phase II Data Network & IT IMS Figure 67: Service architecture With both service architectures, the initial SIP request from a mobile travels from the originating mobile to the visited P-CSCF first, which then forwards the request to the I- CSCF (if used) in the originating mobiles home network. This I-CSCF selects an S- CSCF in the home network for this user session and forwards the SIP request to session will travel directly between the visited P-CSCF and the S-CSCF in the mobiles home network. The S-CSCF is responsible for interfacing with internal and external service platforms as illustrated in Fig. 3. There are three types of standardized platforms: (1) SIP application server (2) Open Service Access (OSA) Service Capability Server (SCS) and (3) IP Multimedia Service Switching Function (IM-SSF). JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 170 of 174 For Restricted Circulation  JTO Phase II Data Network & IT IMS OSA Application Servers MAP CAMEL Service OSA API HSS Environment Sh Sh SI CAP OSA SCS Cx IM-SSF SIP (for Providing (for Interface withLegacy Application Servers Open Access to 3rd Service Platform) Party Service Providers) ISC ISC ISC S-CSCF IIP multimedia Subsystems Figure 68: Interaction between SCSCF and service platforms The services offered by them are value-added services (VAS or operator-specific services. The S-CSCF uses the same interface, IMS Service Control (ISC) interface, to interface with all service platforms. The signaling protocol over the ISC interface is SIP. The OSA SCS and IM-SSF by themselves are not application servers. Instead, they are gateways to other service environments. As depicted in Fig. 3, the OSA SCS and IM- SSF interface to the OSA application server and CAMEL Service Environment (CSE), respectively. From the perspective of the S-CSCF, however, they all exhibit the same ISC interface behavior. The services are briefly described: 13.5 SIP Application Server: In addition to session control, a SIP server can also provide various value-added services. A lightweight SIP-based server enables the CSCF to utilize the SIP-based services and interact with the ISP application servers without additional components 13.5.1 Camel Service Environment (CSE): The CSE provides legacy Intelligent Network (IN) services. It allows operators leverage existing infrastructure for IMS services. As specified earlier, the CSCF interacts with CSE through IM-SSF. The IM-SSF hosts the CAMEL features and interfaces with CSE by CAP (CAMEL Application Part). JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 171 of 174 For Restricted Circulation JTO Phase II Data Network & IT IMS 13.5.2 OSA Application Server: Applications may be developed by a third party that is not the owner of the network infrastructure. The OSA application server framework provides a standardized way for a third party to secure access to the IMS. The OSA reference architecture defines an OSA Application Server as the service execution environment for third-party applications. The OSA application server then interfaces with the CSCF through the OSA SCS by OSA API (Application Programming Interface). Figure 69: Simplified 3GPP IMS Architecture Examples of Flow of Information: Registration and Re-Registration JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 172 of 174 For Restricted Circulation JTO Phase II Data Network & IT IMS Figure 70: Basic Message Flow JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 173 of 174 For Restricted Circulation JTO Phase II Data Network & IT IMS Figure 71: Routing of Mobile-To-Mobile Calls - Session Initiation 13.6 CONCLUSION: The IP Multimedia Subsystem (IMS) seems to be the technology that will prevail in Next Generation Networks (NGNs) and its main goal to make convergence between any IP networks and a vertical handoff may happening depend on the user requirements (services, QoS,. etc). In this chapter it was presented an IMS based interworking architecture for NGN networking through which it prevail that how any two user from any two different IP based network can be involved in a session under the umbrella of IMS management. By presenting a complete signaling flow for concerning the authorization, registration, session set up and vertical handoff processes between two networks. JTO Phase II (DNIT) Version 1.0 Sep 2021 Page 174 of 174 For Restricted Circulation