40 Questions
What is the primary function of an S-CSCF in IMS?
To provide session control services for a user
What is one of the main tasks of an S-CSCF during registration?
To make users' registration and location information available to location servers
What is the function of a P-CSCF in IMS?
To act as a SIP Proxy Server
What is an S-CSCF responsible for during session control?
Relaying SIP requests and responses between calling and called parties
What is an additional function of an S-CSCF?
To provide service-related event notifications to users
What does a P-CSCF include?
A Policy Control Function (PCF)
What does an S-CSCF act as during interactions with application servers?
An interface to application servers
What is generated by an S-CSCF for accounting and billing?
Call Detail Records (CDRs)
What is the main goal of IMS in the telecommunications industry?
To attract and retain subscribers by offering different services
What kind of services can IMS provide?
Real-time and non-real-time multimedia sessions
What is the main issue faced by fixed and mobile operators?
Subscriber churn
What is the focus of IMS architecture?
To provide a standardized solution for telecommunications
What is the advantage of IMS over proprietary solutions?
It is a standardized solution
What is the goal of IMS in terms of service convergence?
To converge services supplied by different types of networks
What kind of network does IMS support?
All-IP network
What is the benefit of IMS for subscribers?
It provides personalized services
What is the primary focus of IMS standardization in 3GPP Release 5?
Non-real time services
What is the main benefit of IMS from an end-user perspective?
New, exciting services and enhancements of existing services
What is the role of SIP in IMS?
Supporting signaling and session control for real-time services
What is the main benefit of IMS from an operator perspective?
Quality of Service
What is the main benefit of IMS from a general perspective?
Grow and protect subscriber base, increase ARPU
What is the primary focus of IMS standardization in 3GPP Release 6?
Real-time services
What is the main function of the Serving CSCF (S-CSCF)?
Dependent on the specific tasks performed
What is the scope of IMS extended in 3GPP Release 7?
Any IP access network, including fixed access networks
What type of information is stored in HSS?
User authentication data, service profile, and charging information
What is the primary function of the SLF?
To locate the correct HSS in a large network
What protocol is used for communication between HSS and SLF?
Diameter
What is the function of the Media Gateway Control Function (MGCF)?
Signaling inter-working between PS domain and CS networks
What information is used by the SLF to locate the correct HSS?
User-ID/ HSS-ID
Is the SLF a mandatory component in IMS?
No
What is the function of the IM Media Gateway (IM-MGW)?
Media inter-working between PS domain and CS networks
What is the primary function of the HSS?
To support IMS network entities and handle calls
What is the primary function of the MRFP?
To provide resources to be controlled by the MRFC
What is processed by the MRFP?
Media streams, including audio transcoding and media analysis
What is the role of the BGCF?
To select to which PSTN network a session should be forwarded
What is supported by the MRFP within the bearer path?
DTMF
What is the role of the MRFC?
To interpret signaling information from an S-CSCF or a SIP-based Application Server
What is responsible for interfacing with internal and external service platforms?
S-CSCF
What is forwarded by the I-CSCF?
SIP request to the S-CSCF
What type of platforms does the S-CSCF interface with?
SIP application servers, OSA Service Capability Servers, and IP Multimedia Service Switching Function
Study Notes
IMS (IP Multimedia Subsystem)
- IMS is a standardized solution in the telecommunications world that provides real-time multimedia sessions and non-real-time multimedia sessions over an all-IP network.
- IMS targets convergence of services supplied by different types of networks (fixed, mobile, Internet).
IMS Benefits
- Quality of Service enhancements
- New, exciting services and faster time to market with existing services
- Service integration and same services available regardless of terminal and access type
- Keeps charging relations with users and ease of use and security
- Controlling CAPEX and OPEX
IMS Standardization
- IMS was initially standardized by 3GPP (3rd Generation Partnership Projects) as part of its Release 5 specifications.
- 3GPP Release 6 targeted at supporting real-time services.
- 3GPP Release 7 standardization extended IMS scope to any IP access network, including fixed access networks (e.g., DSL).
IMS Architecture
- IMS provides all the network entities and procedures to support real-time voice and multimedia IP applications.
- IMS uses SIP to support signaling and session control for real-time services.
CSCF (Call State Control Function)
- Three types of CSCFs: Serving CSCF (S-CSCF), Proxy CSCF (P-CSCF), and Interrogating CSCF (I-CSCF).
- S-CSCF: provides session control services for a user, maintains session states, and performs registration, session control, proxy server, and interactions with application servers.
- P-CSCF: a mobile's first contact point inside a local IMS, acts as a SIP Proxy Server, and includes a Policy Control Function (PCF) to control policy regarding how bearers in the packet-switched network should be used.
Databases: HSS and SLF
- HSS (Home Subs Server): stores user data, authentication data, service profile, and charging information, and performs authentication and authorization of users.
- SLF (Subs Location Function): an optional component that helps locate the correct HSS in a large network, uses Diameter protocol to communicate with HSS.
IMS Entities
- MGCF (Media Gateway Control Function): responsible for signaling and media inter-working between PS domain and circuit-switched networks (e.g., PSTN).
- IM-MGW (IM Media Gateway): responsible for media inter-working between PS domain and circuit-switched networks.
- MRFP (Multimedia Resource Function Processor): provides resources to be controlled by the MRFC, sources media streams, processes media streams, and supports DTMF.
- MRFC (Multimedia Resource Function Controller): interprets signaling information from an S-CSCF or a SIP-based Application Server and controls the media streams resources in the MRFP.
- BGCF (Breakout Gateway Control Function): selects to which PSTN network a session should be forwarded.
Learn about the architecture of IMS, its core elements, interfaces, and application servers. Understand the basic call flow in IMS and its role in delivering various internet services.
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