Transcript IMS
IP Multimedia Subsystems By Vamsee K Pemmaraju Agenda IMS Example Overview Basic Principles Architecture Access, Core Networks and User databases Call and Session Control Service Interoperability Migrating Application to IMS SIP Architecture Advantages Issues Conclusion. IMS Example ANNA ANDREW COLLEAGUES OVERVIEW The IP Multimedia Subsystem (IMS) standard defines a generic architecture for offering Voice Over IP (VoIP) and Multimedia services It uses a Voice-Over -IP (VoIP) implementation based on a 3GPP standardized implementation of SIP, and runs over the standard Internet Protocol (IP). Existing phone systems (both packet switched and circuit switched are supported. The aim of IMS is not only to provide new services but all the services, current and future, that the Internet provides. To achieve these goals, IMS uses open standard IP protocols, defined by the IETF Designed for both wireless and wire line networks. BASIC PRINCIPLES Access independence: IMS will eventually work with any network (fixed, mobile or wireless) with packet switching functions, such as GPRS, UMTS, CDMA 2000, WLAN, WiMAX, DSL cable. Older circuit switched phone systems (POTS, GSM) are supported through gateways. Open interfaces between control and service layers allow elements and calls/sessions from different access networks to be mixed. Different network architectures: IMS allows operators and service providers to use different underlying network architectures. Extensive IP-based services: IMS should make it easier to offer just about any IP-based service. Examples include voice over IP (VOIP), Push to talk over Cellular(POC), multiparty gaming, video conferencing, Messaging, community services, Presence Information and content sharing. IMS Network (Access Independent Service Enabled) In Release 6 of the 3GPP specifications, the IMS has been specified to be access independent. This means that the access technology used to transport user SIP messages to the IMS network does not impact the functionality of the IMS network itself. Consequently, any access can be used, examples being DSL, Cable, WLAN, GPRS, etc. This is obviously a key step in the move towards converged network architectures IMS Services Examples •Presence (Is the user available) • Voice and Video Telephony • Instant Messaging • Push to talk, push to see • Conferencing • Gaming • Convergence of all of the above Architecture AL comprises of application and content servers to execute value added services to the user. SCL comprises network control servers for managing call or session set-up. It contains CSCF (Call Session Control Function) also know as SIP server. CL comprises of routers, and switches. IMS Access Network The user can connect to an IMS network using various methods, all of which are using the standard Internet Protocol(IP). Direct IMS terminals (mobile phones, computers, ...), can register directly into an IMS network, even when they are roaming in another network or country (the visited network). Fixed access (e.g., DSL, Cable Modems, Ethernet ...), mobile access (W-CDMA, CDMA, GSM, GPRS ...) and wireless access (WLAN, WiMAX ...) are all supported. Other phone systems like the POTS (the old analogue telephones), and non IMS-compatible VoIP systems are supported through gateways. Control Network The HSS (Home Subscriber Server) is the master user database that supports the IMS network entities that are actually handling the calls or sessions. It contains the subscription-related information (user profiles), performs authentication and authorization of the user, and can provide information about the physical location of user. It's similar to the GSM . An SLF (Subscriber Location Function) is needed when multiple HSSs are used. Both the HSS and the SLF implement the DIAMETER protocol (Cx, Dx and Sh interfaces). Call or Session Control Functions P-CSCF: Proxy Call Session Control Function: This is the first point of contact within the IMS for a User Element (UE). It ensures that the registration of the user is passed to the correct home network and that SIP session messages are passed to the correct Serving CSCF (S-CSCF) once registration has occurred PDF (Policy Decision Function): This function takes a service level policy request from the application layer (for example P-CSCF) and translates it into IP QoS parameters. IBCF Interconnect Border Control Function: This standard is to specify the detection of failure of interconnect points. I-CSCF Interrogating Call Session Control Function: This is the function that is able to determine the S-CSCF (Serving-Call Session Control Function) with which a user should register. This is achieved by querying the Home Subscriber Server (HSS). Serving Call Session Control Function: This is the function that registers the user and provides service to them even though these services may be on separate application platforms. Service interoperability IMS enables the reuse of inter-operator relations. Rather than develop different interconnect relations and agreements for each service, IMS enables a single interoperator relationship to be established and built upon for each service. Many functions can be reused for fast service creation and delivery. IMS services are hosted by an Application Server, they are implicitly placed in the IMS application layer. IMS defines how service requests are routed, which protocols are supported etc. Service Architectures Migrating applications to IMS. SIP (Session Initiation Protocol) SIP is an application layer protocol that can establish, modify and can terminate multimedia sessions and conferences over the internet. SIP messages could contain session descriptions such that participants can negotiate with media types and other parameters of the session. SIP provides its own mechanisms for reliability and can run on top of several different transport protocols such as TCP, UDP and SCTP (Stream Control Transmission Protocol) Establish a session between the originating and target end point—If the call can be completed, SIP establishes a session between the end points. SIP also supports mid-call changes, such as the addition of another end point to the conference or the changing of a media characteristic or codec. Handle the transfer and termination of calls—SIP supports the transfer of calls from one end point to another. During a call transfer, SIP simply establishes a session between the transferee and a new end point (specified by the transferring party) and terminates the session between the transferee and the transferring party. At the end of a call, SIP terminates the sessions between all parties. SIP Elements User Agent Client / Server user agent client and server are logical entities, whose roles last only for the duration of the transaction Proxy Server forward SIP requests and responses Redirect Server receive requests and then return the location of another SIP user agent or server where the user might be found Registrar accept REGISTER requests and places the information into the location service for the domain it handles. SIP Architecture SIP Request through a Proxy Server If a proxy server is used, the caller UA sends an INVITE request to the proxy server, the proxy server determines the path, and then forwards the request to the cal lee SIP Response through a Proxy Server The cal lee responds to the proxy server, which in turn, forwards the response to the caller SIP Session through a Proxy Server The proxy server forwards the acknowledgments of both parties. A session is then established between the caller and callee. Real-time Transfer Protocol (RTP) is used for the communication between the caller and the cal lee Interfaces Click here Interfaces.htmfor Different Interfaces and their Description Advantages The core network is independent of a particular access technology Integrated mobility for all network applications Easier migration of applications from fixed to mobile users Faster deployment of new services based on standardized architecture An end to unique or customized applications, leading to lower CAPEX and OPEX New applications such as presence information, videoconferencing, Push to talk over cellular (POC), multiparty gaming, community services and content sharing. Evolution to combinational services, for example by combining instant messaging and voice User profiles are stored in a central location The architecture is designed for easy scalability and redundancy Issues Benefits need to be further articulated in terms of actual savings. IMS is "operator friendly" which means that it provides the operator with comprehensive control of content at the expense of the consumer. IMS uses the 3GPP variant of SIP, which needs to interoperate with the IETF SIP. IMS is an optimization of the network, and investments for such optimization are questionable. Some IMS proponents are trying to push it as the total solution for IP-based systems such as IPTV, which is causing push-back from companies wanting a much richer experience in land-line environments that don't have mobile constraints; There are no products available other than paper machine; The new services are the same of ISDN services, i.e, voice calls, video calls, etc. All the supposed new services already exists; QoS is not a problem for voice calls. Skype's revenue shows that; Subscribers won't accept that service providers controls what application they are running; It's a useless control-layer. Conclusion Thus IMS plays a vital role in transferring multimedia messages easily. References http://en.wikipedia.org/wiki/IP_Multime dia_Subsystem http://www.cisco.com/univercd/cc/td/doc/pr oduct/voice/sipsols/biggulp/bgsipov.htm www.empirix.com Questions What is IMS and explain different elements in IMS? What SIP? How call is initiated using SIP? Differences between IMS and pre-IMS?