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www.newport-networks.com/whitepapers/IMS-1.html

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Posted by crouse

IMS Telephone On-Hold Player.It can also be used to define longer text answer questions with marking

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Posted by waqasahmad

Here we see how TISPAN has specified the IMS architecture (i.e. “core IMS”). The TISPAN IMS architecture is a service control infrastructure. It can be divided in:

• An Application layer consisting of Application Servers (AS) that host the IMS services and a Home Subscriber Server (HSS),
• A Control layer made of several service subsystems
among which the IMS core,
• A Transport layer consisting of the user equipment (UE), Access Network, Next Generation Network (NGN) core, NASS and RACS.

The Resource Admission Control Subsystem (RACS) and the Network Attachment Subsystem (NASS) are two important non IMS subsystems standardized at ETSI TISPAN.

Several service subsystems can coexist in IMS architecture, for example the IMS core and the PSTN emulation function.

Because IMS is still being defined (TISPAN Release 2 is underway), and because it describes several interfaces and functional entities, a complete IMS system is quite difficult to represent. It should nevertheless be kept in mind that IMS is a part of a functional architecture, and several of its components can be bundled in a single hardware.

Lets see some of the protocols used in the IMS:
Signaling and media flow description is done by using the Session Initiation Protocol (SIP). SIP borrows the principles used in HTTP and SMTP, the two most successful Internet protocols. SIP has been chosen in IMS mainly because it complies with the various requirements of IMS and is considered flexible and secured. The main purpose of SIP is the establishment, modification and termination of multimedia services between two terminals. It is perhaps the key protocol for IMS as it can handle Subscriber management, Service control, Single sign on, QoS authorization, Charging, etc.

Another important protocol that is a classic example of Authentication, Authorization and Accounting is DIAMETER. It is mainly used for security. Another protocol called the Common Open Policy Service (COPS) supports control over Quality of Service (QoS), signaling protocols (e.g. RSVP). Thus, this is a protocol developed for policy support. Other protocols for media control such as Megaco, also called H248, (which is a successor of Media Control Gateway Protocol (MGCP)) used for controlling media serving functions in the IMS. The Real Time Transport Protocol (RTP) is the transport protocol that is used for transporting real time media. It is used in conjunction with Real Time Control Protocol (RTCP) in order to monitor data delivery.

Finally, the idea of transforming a best effort IP network by introducing end-to-end QoS guarantees is an important driver for the development of IMS. This is important because the level of QoS the IMS architecture is able to provide determines the services that can be deployed on it, and the value is assumed to lie in real time multimedia services.

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Posted by Fangzhou