DIT

Dar es Salaam institute of Technology (DIT)

ETU 08102

Digital Networks

Ally, J

jumannea@gmail.com

DIT

IP Multimedia Subsystem (IMS) Basics

Voice and Video over IP

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Voice and Video over IP After some early resistance, telecom

companies have embraced VoIP The VoIP standards war is over

The winner: Session Initiation Protocol (SIP) What if?

An architecture was designed to support services and multiple networks

The media is not just voice, but multi-media SIP signaling used throughout

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What is IMS? IMS is an architecture, it is not a protocol.

Open-systems architecture that supports a range of IP-based services over both Private and Carrier networks, employing both wireless and fixed access technologies.

IMS is defined by 3GPP.

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IMS Basic Concept IMS is an architecture that solves the continuing demands and

frustrations of users and enterprises. The ultimate goal of the architecture is to define a model that

separates the services offered by fixed-line (traditional telecom), mobile (traditional cellular), and converged service providers (cable companies and others who provide triple-play — voice, video, and data services) from the access networks used to receive those services.

For instance, a classic example would be the ability of a mobile cellular phone to switch to WiFi VoIP (mid-call) when it discovers a valid network to use.

In this scenario, your mobile phone would dynamically move your existing call over the cellular network to a valid WiFi network (for example, your home wireless network) when you came into range, saving your cellular airtime and providing additional bandwidth for data communications.

IMS, when fully deployed, will enable you to choose a Service Provider (SP) not by the quality or ubiquity of their network, but by the services they offer.

The “network,” or how you connect to those services, will become irrelevant.

AccessNetwork

OtherNetworks

Web PortalWeb Portal

ApplicationApplicationServersServers

Session Session ControlControl

CentralizedCentralizedDatabasesDatabases

Media Media Control &Control &GatewaysGateways

MediaMediaServerServer

AccessLayer

Session ControlLayer

Application Layer

Open Industry Standard Support for a Variety of

Applications:• Speed Applications to market

Common Session Control Element to Provide Service Interworking

• Predictable interactions between multiple services

Common Subscriber Database with Open

Interfaces

Service Consistency Across Wireless, Wireline and VoIP Endpoints:

•Retain ownership of the subscriber and their services

•Ability to provide differentiated services

Distributed Session Control• IMS flexibility and scalability reduce OPEX• Support mobility/portability

Common support for CoS, QoS, security,

scalability, reliability, and performance

Common OAM&P Environment• Ease integration into OSS/BSS/NMS

Common Common OAM&P,Billing, OAM&P,Billing,

etc.etc.

Capable of Interworking with the PSTN (i.e. legacy IN-

based services)

IP Multimedia Subsystem (IMS) - Key Attributes

RNCMSC(Server)

SGSNGGSN

CNCNMGW

BSC

UMTS/GPRSUMTS/GPRS

WLANWLAN

CorporateCorporate

P-CSCF

I-CSCFMRF

MGW

MGCF

IMSIMS

S-CSCF

SIP ApplicationServersSIP Application

ServersHSS

CDMA 2000CDMA 2000DSL/Cable ModemDSL/Cable Modem

DSLAM/CMTS

IMS Access Network Independence

Clie

nts

Clie

nts

Dev

ices

Dev

ices

Acc

ess

Acc

ess

Tran

spor

tTr

ansp

ort

Sess

ion

Sess

ion

Con

trol

Con

trol

App

licat

ions

App

licat

ions

Managed Core IP Network Media GWSignaling GW

MRFCMRFCCSCFCSCF

Service BrokerService BrokerHSSHSS

Pres.Data

Loc.Data

SubsData

Micro BillingMicro BillingIntegrated Integrated Pre-paid & Pre-paid & PostpaidPostpaid

AAAGroupLists

MediaServer

POTSphone

GGSNPDSN

MSCCellular

AccessPoint

WiFi/802.11x Local Loop

VoIPhandset

Ckt-PBXIP-PBX

IP-phonesISDN-phones

IP-phones

DSL/CableIP LAN

WirelessRouter Base

Station

5ESS

(IP-Centrex)

Office/Hotel HotspotHome On the Road Home/Office

Dual-modeWiFi phoneSoft-phones

PSTN SS7

SIP Clients

Ckthandset

Multiple user interfaces with common look and feel

Other Clients

IMS Converged Communications Services Vision

LucentLucentPresencePresence

ServerServer

ActiveActivePhonebookPhonebook

ServerServer

BroadSoftBroadSoftTelephonyTelephony

ServerServer

AnyPathAnyPathUnified Unified

Messaging Messaging SvrSvr

OtherOtherApp Servers App Servers (PTT, IM etc.)(PTT, IM etc.)

EBS Web PortalEBS Web Portal

Parlay/OSAParlay/OSAMediationMediation

Gateway (ISG)Gateway (ISG) Network Operations, Applications Mgt, Subscriber registration/

authorization

PresencePresenceServersServers

TelephonyTelephonyServersServers

UnifiedUnifiedMessagingMessaging

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Roles of Standards Bodies for IMS

ServicesServices

Open Mobile AllianceOpen Mobile Alliance Defining IMS services

The Parlay GroupThe Parlay Group Integral to IMS architecture, define standard API frameworks

Mobile Mobile ArchitectureArchitecture

3rd Generation 3rd Generation Partnership ProjectPartnership Project

Define IMS network elements and infrastructure

Architecture Architecture for Wirelinefor Wireline

ETSI TISPAN - Merger of ETSI TISPAN - Merger of TIPHON (VoIP) and SPAN TIPHON (VoIP) and SPAN (Fixed)(Fixed)

Defines SIP, SDP and other protocols underlying IMSIMS is driving some of the work in IETF

CornerstoneCornerstone Internet Engineering Internet Engineering Task ForceTask Force

Agreement on reuse of 3GPP IMS in comprehensive NGN plans

IMS Building Blocks1. An all-IP Core Network (CN)

2. An all-IP Radio Access network (RAN)

3. Multimedia call control based on SIP

4. Quality of Service (QoS) support for IP

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3GPP IMS Network Elements

HSSHSS

I-CSCFI-CSCF S-S-CSCFCSCF

VisitedNetwork

Home Network

SIP

ASASASASASAS

Home Subscriber Server• Centralized DB• HLR successor• User profile• Filter criteria (sent to S-CSCF)

• Which applications• Which conditions

Application Servers• Push-to-talk• Instant messaging• Telephony AS• 3rd party or Lucent

P-P-CSCFCSCF

BackboneBackbonePacketPacket

NetworkNetwork

AccessAccess

MGCFMGCF

MGWMGWPSTNPSTN

H.248ISUP

BGCFBGCF

SIP

SIPSIP

SS7SS7

SIP

SIP

SIP

SIP

SIPSIPSIP

Diameter

RTP TDM

RTPRTP

Call SessionControl Function• SIP registration • SIP session setup

MRFMRF

Media GatewayControl Function• Interfaces to PSTN/PLMN by

• Converting SIP <-> ISUP• Interworking RTP to circuit

• H.248 control of MGW

Breakout Gateway Control Function• Selects network (MGCF or other BGCF) in which PSTN/ PLMN breakout is to occur

Media Resource Function Pooling of Media servers

Proxy CSCF• 1st contact point for UE• QoS• Routes to I-CSCF

Interrogating CSCF• Entry point for incoming calls• Determines S-CSCF for Subscribers• Hides network topology

Serving CSCF• Registrar• Session control• Application Interface

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Brief Explanation IMS Network Elements The Call Session Control Function (CSCF) is a SIP server which processes the IMS signaling traffic in order to control multimedia sessions.There are three types of CSCF:

Proxy CSCF (P-CSCF): The initial point of contact for signaling traffic in to the IMS.

Serving CSCF (S-CSCF): Provides the service coordination logic to invoke the application servers needed to deliver the requested service.

Interrogating CSCF (I-CSCF): A SIP proxy that provides a gateway to other domains, such as other service provider networks.

The Home Subscriber Server (HSS) is a centralized database storing the subscriber profile information.

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Brief Explanation IMS Network Elements (2) An Application Server (AS) hosts and executes services and can run in a number of classical SIP operational modes. The application servers mentioned above are attached to the S-CSCFs to

host and serve IMS services. The Media Resource Function (MRF) comprises two nodes: the

Controller and Processor. The MRFC (controller) is situated in the signaling plane as a SIP User

Agent; and the MRFP (processor) is situated in the media plane and provides media related functions, such as serving voice announcements, voice mixing (for conferencing) and video conferencing.

A Border Gateway Control Function (BGCF) identifies if a session terminates on the PSTN and determines which MGCF should handle it.

The Media Gateway (MGW)/Media Gateway Control Function (MGCF) collectively represent equipment that provides interworking with the legacy PSTN.

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IMS Protocol Session Initiation Protocol (SIP): An application layer protocol

for establishing, terminating and modifying multimedia sessions within an IP network. SIP has been embraced as the specified protocol in support

of session control protocol for IMS which follows a client server model.

Session Description Protocol (SDP): is a text based protocol which describes the multimedia session. For example, when initiating a session the caller and callee

indicate and exchange their media capabilities as well as receive address and port number.

Real-Time Protocol (RTP): provides a mechanism to transport real-time multimedia traffic including video and audio over unreliable transport mediums such as User Datagram Protocol (UDP).

Diameter: The Diameter protocol was chosen for use with IMS as the AAA (Authentication, Authorization and Accounting) protocol.

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SIP Protocol IMS builds on the Session Initiation Protocol (SIP), which

has emerged as the crucial technology for controlling communications in IP -Based Next-Generation Networks (NGNs).

The advantages for adopting the SIP as control layer protocol:

Advantages in convergence and interworking of voice and data services

Supports the development of IN network towards the application and terminal sides

Supports mobility function at the application layer Simple protocol with recognized potential for extension.

A Typical Example of an IMS Call

User B

DSL/Cable ModemDSL/Cable Modem

DSLAM/CMTS

RNC

GGSN

Network Z (UMTS/GPRS)Network Z (UMTS/GPRS)

Network XNetwork X

User A

SGSN

Network YNetwork Y

GRXGRXP-CSCF

P-CSCF

I-CSCFI-CSCF

S-CSCFS-CSCF

HSSHSS

ASAS

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Imagine starting a voice call on you home phone and transferring it seamlessly to your mobile as you drive to work.

Imagine sending a multimedia message from your car that later appears on your TV screen.

Imagine watching a movie on that same TV, pausing it in mid-show and then watching it on a wireless PDA as you relax in the garden.

Imagine having a cell phone conversation with two or three friends and simultaneously sharing a video of the football match you are attending.

Imagine that all of the above can be done with a single account, on a single log-in with multiple devices over any number of access networks

These are only a few examples of seamless multimedia services that IMS will allow users to access “anywhere” at “anytime”

Why all of the excitement?

Who needs IMS?Fixed Network Users wantMultimedia conferencing: With PC or SIP phone user can participate in a video conference with mobile or WLAN users. Voice over IP: Cable providers will become phone providers.Streaming Services: Video on demand, wake-up call with music video or latest news.Mobile Network Users wantPush-to-X: PTtalk, PTVideo.Location Based Services: Which of my friends is nearby? Mobile Gaming: Gaming on your mobile, while you chat with a friend you play against.Network Providers wantFixed Mobile Convergence.A service needs to be implemented only once for all kind of access networks.New business models by offering my services to users from other access networks.

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Why do we need IMS? Challenges in services

Difficulty and slowly delivery of new services Single services experience

Challenges from Internet Internet has been competitor of legacy operator Legacy operator must learn from Internet

Challenges in OPEX/CAPEX More network technologies and more network

deployment Duplicated development and deployment leads to higher

CAPEX and OPEX Challenges in Average Revenue Per User (ARPU)

Voice ARPU is decreasing Difficulty for legacy networks to introduce abundant

services and charge for content and service

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Characteristic of IMS - More Convergence

Network resource sharing greatly reduces CAPEX\OPEX Reduce customer churn and improve loyalty

Unified services deliver any application to any terminal Multimedia experience Single user profile, single sign on

Fixe

d N

etw

ork

Mob

ile N

etw

ork

Mob

ile D

ata

Inte

rnet

Multi-ServiceTraditional Network Converged Network

Convergence

Terminal

IP Connectivity

GSM/UMTS BroadbandWLAN

Services & Content

Session Control

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User-Centric NetworkUser-centric network: One network for all services Single Sign-On

IMSService-centric network: Services provided by different network. Sign-On for each service;

Services

Address book

ProfileBillMy rings

Profile

Address book

Bill

User identity, profile, address book and bill are different by each service; Services can’t be customized, or difficult to be customized.

One user identity, one profile, one address book and one bill for all services Customized services

Benefits of IMS User experience in mobility and multimedia Richer services

Abundant and attractive services will boost ARPU Sustained service revenue

Telecom Operators will generate much more revenue by operators always be on top of IP service value chain

Common shared subscriber data Better investment protection

Common IMS Core infrastructure and service Enablers will remain unchanged when new services and access types are introduced.

Initial network investment on IMS Core will be protected during later stages of network deployment

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Subscribers want access to communications services from many places… Home, office, or on-the-go: mobility

isn’t just wireless voice anymore!

from several devices… Telephones, PCs, mobile phones,

PDAs

without needing separate accounts

Single sign-on, common contacts, and “access-aware” information delivery

Home Office Moving Travel

Convergence Networks

Fixed NetworksMobile

Networks

Benefit of IMS-User Experience: Wider Mobility

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Benefit of IMS-User Experience: MultimediaToday

Limited video introducedYesterday

voice leadingTomorrow

User-centric multimedia experience

1.Hi, I am RobertLet us have a talk about our next film

2.Hi, I am Richard

Rich voice, VoD, internet applications, etc

Still can not flexibly add/drop multiple media types, or switch between them within single session

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IP Backbone

IMS Core

Presence

Chat

Media Push

Game

CALL WHITEBOARDRich Call

Push To Talk

6

Video

Music Voice

Enterprise AD

Cartoon

Greeting

Play Your True Color

Multimedia RBT

Benefit of IMS - Richer Services

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Benefits of IMS - Sustained Service Revenue

RAN

SGSNSGSN

GGSNGGSN

RAN

SGSNSGSN

GGSNGGSN

ApplicationsApplicationsHSSHSS

CSCFCSCF

RAN

SGSNSGSN

GGSNGGSN

Internet

ApplicationsApplications

Domain Controlled by OperatorOperator risks itself to be a bit pipe

IMS

PS only

Domain Controlled by OperatorEnd-to-End service control

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Benefits of IMS - Common Shared Subscriber Data

Replicated Data

HSSHSS

Now IMS

SESSION CONTROL

Application 1

Application 2

Application X

Application 1

Application 2

Application X

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NAT controlAuth SigComp

Routing Charging

New EnablerMessaging Conference

Presence Group Mngt

Common Functions

Service Enablers

QOS Control Service Trigger

Broadband WLANGSM/UMTS CDMA2000

Application1 Application2 Application3 More Apps

Benefits of IMS - Better Investment Protection

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V2CC - Seamless Multimedia communication

Single Number for both GSM/UMTS and WLAN/WiMAX Bi-directional smooth handover: less than 200ms, no interruption Excellent voice quality: better than GSM Multi-media service enabled

Application & Service

IMS VCC

IMS core network

Public/PrivateWiFi/WiMAX newtwork

CellularNetwork

Indoors OutdoorsVoice Call Continuity

VCC Application Server

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IMS Terminals

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