3G is the third generation of tele standards and technology for mobile networking, superseding 2.5G. It is based on the International Telecommunication Union (ITU) family of standards under the IMT 3G networks enable network operators to offer users a wider range of more advanced services while achieving greater network capacity through improved spectral efficiency. 3G networks are wide-area cellular telephone networks that evolved to incorporate high-speed Internet access and video telephony. IEEE networks are short range, high-bandwidth networks primarily developed for data.
Access Network CS Domain PS Domain Internet PSTN IMS
Access network provides radio connectivity and most of the mobility handling CS domain provides traditional mobile voice service plus some new 3G services like video call PS domain provides packet based connectivity to existing packet based networks, that is the Internet IMS provides introduces the IP multimedia services, like VoIP. It provides SIP based signalling. The public switched telephone network (PSTN) is the worldwide collection of interconnected public telephone networks that was designed primarily for voice traffic.
The IP Multimedia Subsystem (IMS) is the technology that will merge the Internet (packet switching) with the cellular world (circuit switching). It will make Internet technologies, such as the web, , instant messaging, presence, and videoconferencing available nearly everywhere. It is a core network technology, that can serve as a low-level foundation for technologies like Voice over IP (VoIP), Push-To-Talk (PTT), Push-To-View, Video Calling, and Video Sharing. IMS is based primarily on SIP (session initiation protocol).
CSCF (Call/Session Control Function) is a SIP (Session Initiation Protocol) server which processes SIP signalling in the IMS. There are 3 types of CSCFs depending on the functionality they provide. P-CSCF is the first point of contact between the IMS terminal and the IMS network. All the requests initiated by the IMS terminal or destined to the IMS terminal traverse the P-CSCF. This node provides several functions related to security. I-CSCF (Interrogating-CSCF) provides the functionality of a SIP proxy server. It also has an interface to the SLF (Subscriber Location Function) and HSS (Home Subscriber Server).
S-CSCF (Serving-CSCF) is a SIP server that performs session control. It maintains a binding between the user location and the user’s SIP address of record Like the I-CSCF, the S-CSCF also implements a Diameter interface to the HSS. SIP AS (Application Server): The AS is a SIP entity that hosts and executes IP Multimedia Services based on SIP. IM-SSF (IP Multimedia Services Switching Function acts as an Application Server on one side and on the other side, it acts as an SCF (Service Switching Function) interfacing the gsmSCF (GSM Service Control Function) with a protocol based on CAP (CAMEL Application Part). MRF (Media Resource Function) provides a source of media in the home network. It is further divided into a signalling plane node called the MRFC (Media Resource Function Controller) and a media plane node called the MRFP (Media Resource Function Processor)
BGCF (Breakout Gateway Control Functions): BGCF a SIP server that includes routing functionality based on telephone numbers. SGW (Signalling Gateway): SGW performs lower layer protocol conversion. MGCF (Media Gateway Control Function) implements a state machine that does protocol conversion and maps SIP to either ISUP (ISDN User part) over IP or BICC (Bearer Independent Call Control) over IP. The Home Subscriber Server (HSS) contains all the user related subscription data required to handle multimedia sessions. These data include, among other items, location information, security information
SESSION CONTROL ON THE INTERNET Regular transaction Invite ack transaction
UAC which is the user agent client where as uas is the user agent server. In the session control UAC sends a bye request to the UAS and if the UAS accepts it then the regular transaction takes place in the session control. In the INVITE ACK transaction UAC sends a request to the UAS and in this process the ringing takes place and if it is accepted by the UAS the ACK is taken place between UAC and UAS.
Regular transactions are initiated by any request but INVITE, ACK, or CANCEL shows a regular BYE transaction. In a regular transaction, the user agent server receives a request and generates a final response that terminates the transaction. An INVITE–ACK transaction involves two transactions; an INVITE transaction and an ACK transaction The user agent server receives an INVITE request and generates zero or more provisional responses and a final response.
MESSAGE FLOW FOR SESSION ESTABLISHMENT Cancel transaction
In the message flow UAC sends a request to the proxy and then it sends the message to UAS and then the ringing takes places in this process. In this if the UAS can cancel the request or just can ok the request. If the UAS cancel the request then the request gets terminated and in this way the cancel transaction takes place in the message flow process in IMS.
CANCEL transactions are initiated by a CANCEL request and are always connected to a previous transaction (i.e., the transaction to be cancelled). CANCEL transactions are similar to regular transactions, with the difference that the final response is generated by the next SIP hop (typically a proxy) instead of by the user agent server. Canceltransaction cancelling an INVITE transaction. Note that the INVITE transaction, once it is cancelled, terminates as usual (i.e., final response plus ACK).
Interactive Gaming Shared folders Instant Messaging services Voice Messaging Voice and Video Telephony Video-conferencing
IP Multimedia Subsystem Benefits Lower Costs Best of Breed Value Chain Control Integrated, Interoperable Services End-user benefits
Cisco Systems has developed an architecture called the Cisco IP Next-Generation Network for IMS. Cisco IP NGN helps service providers develop and plan their organizations, their specific network architectures, and business models for the future HP Service Delivery Platform for IP Multimedia Subsystem The future of telecommunications resides in a new network architecture, the IP Multimedia Subsystem IMS. This new advanced architecture facilitates the creation and delivery of new real-time, person-to-person, multimedia services
IMS is the Universal base for other services It has many Advantages for users and operators. In this way IMS plays a key role in the mobile communication and it also used for Instant Messaging services.
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