IMS Standards

Marie-Paule Odini - HP

IP Multimedia Subsystem (IMS)

standards

2010 Telecom Master Class


Agenda

•2G - 3G – 4G : UMTS & IMS

•IMS Overview and components

•Architecture & Call flows

•Migration to IMS

•Summary


Simple 2G Mobile Network


3GPP Standard evolution


BTS — Base Transceiver Station

BSC — Base Station Controller

Typical 2G ArchitectureFixe + Mobile layer

MSC — Mobile Switching Center

VLR — Visitor Location Register

HLR — Home Location Register

BTS

BSCMSC/VLR

HLRBSC

GMSC

CO

BSC

BSCMSC/VLR

CO

PSTN

PLMN

CO

Tandem Tandem

SMS-SC

PSDN


SS7BTS

BSCMSC

VLR

HLRAuC

GMSC

BSS

PSTN

NSS

AE

CD

PSTNAbis

B

H

MS

BSS — Base Station System



NSS — Network Sub-System

MSC — Mobile-service Switching Controller



AuC — Authentication Server

GMSC — Gateway MSC

2.5G Architectural Detail

SGSN — Serving GPRS Support Node

GGSN — Gateway GPRS Support Node

GPRS — General Packet Radio Service

IP

2G+ MS (voice & data)

PSDNGi

SGSN

Gr

Gb

Gs

GGSN

Gc

Gn

2G MS (voice only)

+ DATA - IP


3G rel99 Architecture (UMTS)

SS7

IP

BTS

BSCMSC

VLR

HLRAuC

GMSC

BSS

SGSN GGSN

PSTN

PSDN

CN

CD

GcGr

Gn Gi

Abis

Gs

B

H




RNS — Radio Network System

RNC — Radio Network Controller

CN — Core Network








AE PSTN

2G MS (voice only)


UMTS — Universal Mobile Telecommunication System

Gb

3G UE (voice & data)

Node B

RNC

RNS

Iub

IuCS

ATM

IuPS

+ 3G Radio



SS7

IP/ATM

BTS

BSCMSC Server

VLR

HLRAuC

GMSC server

BSS

SGSN GGSN

PSTN

PSDN

CN

CD

GcGr

Gn Gi

Gb

Abis

Gs

B

H




RNS — Radio Network System

RNC — Radio Network Controller

CN — Core Network








ANc

2G MS (voice only)


Node B

RNC

RNS

Iub

IuCS

IuPS


Mc

CS-MGW

CS-MGWNb

PSTNMc

ATM

+ Soft-switching



Gb/IuPS

A/IuCS

SS7

IP/ATM

BTS

BSCMSC Server

VLR

HSSAuC

GMSC server

BSS

SGSN GGSN

PSTN

CN

CD

GcGr

Gn Gi

Abis

Gs

B

H

IMS — IP Multimedia sub-system

MRF — Media Resource Function

CSCF — Call State Control Function

MGCF — Media Gateway Control Function (Mc=H248,Mg=SIP)

IM-MGW — IP Multimedia-MGW

Nc

2G MS (voice only)


Node B

RNC

RNS

Iub


Mc

CS-MGW

CS-MGWNb

PSTNMc

IuCS

IuPS

ATM

IMS

IPPSTN

Mc

MGCF

IM-MGW

MRF

CSCF

Mg

Gs

IP Network

+IMS


3GPP view of IMS


IMS : IP and PSTN convergence


LTE architectureMME : Mobility Management Entity


LTE and Voice

MSCSMSC

MAP

Gs

SG

Lu-csA

For SMS – light MSC enough For Voice – need MSC upgrade to support SRVCC (SV protocol support)Note : if VoIP is used on 3G, no need for SRVCC – using PS HO (HO = hand over = address mapping )

SV

S-Gw P-Gw

F


VoLTE : LTE and IMS


LTE and Policies (QoS)

Sp

eNB

PCRF: Policy Charging and Rules Functions(policy decisions based on HSS/sp, applications/Rx )

P-GW : Policy Gwy= policy enforcerPacket filtering

P-GW

Gx

S-GW

S1

S5/S8


IMS overview


What is IMS all about?

• Full IP network and service infrastructure for converged services

• Providing a new wave of sticky services that– Seamlessly integrate multimedia, data and

voice within a single user session– Are instant, real time in nature – Focus on customer environments and their

lifestyles– Are complex in nature, but simplistic to use– Are device and network agnostic– Can be easily enhanced and expanded as the

IMS network and standards evolve


IMS Drivers and Caveats

23 April 11, 2023

• Data obtained from Frost &Sullivan Report “ IMS Ready for Primetime” – Feb. 07


Viable IMS Applications by SegmentApplication %** Wireless Wireline Cable

FMC – Seamless Roaming 75% X X

Instant Multimedia Messaging 73%X

XX

Video Telephony (mobile video/TV) 68% X X X

IP - Centrex 55% X

Video Streaming (Push to see,mobile video,etc.)

48%X X X

Interactive Gaming 38% X X X

Push to Talk (POC) 33% X

Rich Voice (enhanced QoS) 32% X X X

Audio Streaming 29%X X X

Location Services 28% X

Push to talk enhanced (QoS) for Enterprise

------X

Cable Applications – Caller ID, Presence change, etc.

------X

• Data obtained from Frost &Sullivan Report “ IMS Ready for Primetime” – Feb. 07


Why IMS? Overall Value Proposition

• Convergence (fixe, mobile, BB)• Faster time to revenue• Investment protection (standard)• Cost containment (standard IT, IP)• Provides a flexible, scalable architecture • Service innovation enablement (multimedia)• Unprecedented flexibility (IP, enablers)• New services can be developed rapidly and trialed

economically• Large developer community (standard API, open)


IMS Components

CSCF


Proxy-CSCF• A first contact point inside a local (or visited) IMS • Acts as a SIP Proxy Server

– accepts SIP requests from User Equipment (UE) and then either serves these requests or forwards them to other servers

• Functions include:– Forward SIP REGISTER request from UE to the home network – Forward other SIP messages from a UE to a SIP server (e.g.,the

mobile’s S-CSCF in the mobile’s home network).– Forward SIP messages from the network to a device – Perform necessary modifications to the SIP requests before

forwarding them to other network entities – Maintain a security association with the mobile– Detect emergency session– Create CDRs


Interrogating-CSCF (I-CSCF)• Contact point within an operator’s network for

– all connections destined to a user of that network operator – For a roaming user currently located within that network operator’s service

area.

• Multiple I-CSCFs may exist within any given network

• Functions – Registration

• Assigning a S-CSCF to a user performing SIP registration – Session-related and session-unrelated flows

• Route a SIP request received from another network to the S-CSCF • Obtain from HSS the address of S-CSCF • Forward the SIP request or response to the S-CSCF

– Generation of CDRs

• Topology Hiding Inter-network Gateway– Acts has a firewall


Serving - CSCF• Maintains session states for a registered user ’s on-going sessions and performs

the following main tasks – Registration

• Can act as a SIP Registrar to accept users’ SIP registration requests & make users registration & location information available to location servers such as Home Subscriber Server

– Session Control• Can perform SIP session control functions for a registered user• Relay SIP requests and responses between calling & called parties

– Proxy Server• May act as a SIP Proxy Server that relays SIP messages between users & other

CSCFs or SIP servers

– Interactions with Application Servers• Acts as the interface to application servers & other IP or legacy service platforms

– Other functions• Performs a range of other functions not mentioned above

– For example, it provides service-related event notifications to users & generates Call Detail Records (CDR)


CSCF : orchestration flows


IMS Component

HSS


Home Subscriber Server • Provides customer

Authentication Accounting and Authorization (AAA)

• Provides subscriber master database – Calls, sessions– Info for roaming

• Responsible for holding user related info – Id, Security,Location, Profile

• One IMS network may include multiple HSS’s

SGSN GGSN

CSCF

D

C Gr GcCx

HSSSubscriptio

n Information

Location Informatio

n

GMSC Serve

r

MSC Server


Logical Functions of an HSS

CS Domain PS Domain IM CN Subsystem

C GrD Gc ShSi

Cx

GGSNSGSNCSCF

IM-SSFSIP AS

OSA -SCS

GMSCMSC/VLR

GSM SCF

Mobility Manageme

nt

Home Subscriber Server

Identification Handling

Access Authorizatio

n

User Security Info.

Generation

Service Authorization

Support

Application Service Support

Service Provisioning

Support

Call/Session Establishmen

t Support

Camel Services Support

User Security Support


IMS Components

SIP AS


What is an Application Server (AS)?• An Application Server offers value added IMS services. It may be

– SIP Application Server– Open Service Access (OSA) Service Capability Server (OSA Gateway)– CAMEL IM-SSF

• An AS can communication with the HSS• The Serving-CSCF to AS interface is used to provide services

residing in an AS. Two cases are possible – Serving-CSCF to an AS in Home Network– Serving-CSCF to an AS in a trusted External Network

• Some vendors already integrate in their IMS solution some SIP AS among which – OSA SCS– SIP AS for presence– SIP AS for instant messaging– SIP AS for Push To Talk– Etc.


OSA AS

IMS Application Server (AS) Architecture

OSA AS

SIP App. Server

SIP App. Server

AS : SCIM (broker)

ISC

Cx

OSA SCS

Legacy Network Element

OSA API

S-CSCF

(Service Capability Interaction Manager)

IM-SSF

SS7

Mr

MRF

ISC

Sh

Si

HSS

Sh

SIP App. Server


Legacy integration :

* Parlay Application Server* IM-SSF to Camel


Parlay Service Capability Server(SCS)

• Parlay is an OMA standard • Focus on legacy services

integration : – SMS– MMS– Location– Call control with legacy

• Can sit within or outside network domain

• Is the controlling mechanism to the network (security, etc.)

• Has interfaces to network – can connect to wireline, wireless or Voip, IMS

• Normally uses off the shelf hardware and software

OSASCS

MRF

S-CSCF

HSSDiameter

Sh

IMS Network

CxISC

OMA : Open Mobile Alliance

legacy


Open Service Access (OSA) Parlay AS

• Part of the “Virtual Home Environment”• Open, standardized API for 3rd party application developers

– Developed in the Parlay group• “Exports” typical network functionality

– Call Control– QOS– User Location– Terminal Capabilities– Content based charging

Open Service Access

Interface Class

OSA API

Application

Application Server

Framework

Discovery

Service Capability Server(s)Call

ControlUser

Location

HLR CSEWGW WPP

Servers


IP Multimedia – Services Switching Function (IM-SSF)

• Provides the interworking of a SIP message to the corresponding customized applications for Mobile Networks Enhanced Logic (CAMEL) – ANSI-41, Intelligent Network Application Protocol (INAP) – Transaction Capabilities Application Part (TCAP) messages

• Enables UE access to legacy services such as – Calling name service – Freephone services– Number Portability – One number services– Etc.

SIP App. Server

SIP App. Server

SIP App. Server

App. Server

ISC

Legacy Networ

k Elemen

t

OSA AS

OSA AS

OSA SCS

OSA API

S-CSCF

(Service Capability Interaction Manager)

IM-SSF

ISC

SS7

IMS Network ElementsNon IMS Network Elements

MRFMr


Media Resource Function MRF

media server(serveur vocal)

conference server


Standard Media Server functionality

• Announcements (audio and video)• Automated Speech Recognition (ASR)• Billing Record Creation (CDR, IPDR)• Fax Detection• Interactive Voice Response (IVR)• Recording• Text-To-Speech conversion (TTS)• Transcoding between different codecs or

rates• Multi-unicasting (replicating the audio and

video payload of RTP)• Open Standard interfaces (SIP, VXML)


IMS - Media Resource Function • Two components per standards

– MRF Controller (MRFC) • Controls the media stream resources in

the MRFP• Interprets information coming from an AS

and S-CSCF (e.g. session identifier) and control MRFP accordingly

• Generates CDRs– MRF Processor (MRFP)

• Controls RTP bearers• Provides resources to be controlled by

the MRFC• Mixes incoming media streams (e.g., for

multiple parties)• Sources media streams (for multimedia

announcements)• Processes media streams (e.g., audio

transcoding, media analysis)• Supports multiple audio and video codecs

AS

MRFP

ISC

Mr

S-CSCF MRFC

Mb

Mp

MRF

GGSN


IMS Components

BGCF


Breakout Gateway Control Function (BGCF)

C,D, Gc, Gr

UE

Mm

Mk

MkPstnPstn

Mj

Mg

Mr

Mp

Mw

Gm

Dx

Cx

Legacy mobile signaling networks

Mn

Mb

Mb

IMS

Mw

PTSN

HSS

SLF

P-CSCFMRFC

MGCF

BGCF

BGCF

IMS-MGW

MRFP

CSCF

CSCF

Gq

Mi

MbMb

Mb

Mb

Other IMS Networks


Breakout Gateway Control Function (BGCF)

• Process request from S-CSCF to select appropriate PSTN/CS domain breakout point

• Select the network in which the interworking with the PSTN/CS Domain is to occur. If the interworking is in another network, then the BGCF will forward the SIP signaling to the BGCF of that network

• If the interworking is in another network & network hiding is required, the BGCF will forward the SIP signaling via an I-CSCF toward BGCF of the other network

• Select MGCF in the network in interworking with PSTN/CS domain is to occur & forward the SIP signaling to that MGCF

• CDR generation


IMS architecture&

Call Flows


IMS full picture


IMS call flow


Registration processturn on phone : I am Here !


Incoming Call


IMS simplified architecture

Media


Registration


Registration : SIP register

?? ?? ?? ?? ??


Session set up : SIP invite

UE-1UE-2


Session set up

?? ?? ?? ??


Presence : SIP simpleSubscribe, Publish, Notify


AS to HSS : Diameter


Other examples


Push to talk session


From IMS user to CS user


Off-line charging


On-line charging


GSM to IMS network roaming


CS user calling IMS user


Toll-free thru TCAP Gwy


Off-line charging to CAP Gwy


SMS to IMS user


Summary : Key call flows

• 1- Registration : SIP-REGISTER– UE - P-CSCF - I-CSCF – S-CSCF - HSS – SIP 200 OK

• 2- Session Set up : SIP INVITE– UE1 – S-CSCF – ( I-CSCF - HSS – S-CSCF ) – UE2– SIP 200 OK – SIP ACK

• 3- Presence : SIP Simple Subscribe, publish, notify

• 4- AS-HSS : DIAMETER Protocol


Migration towards IMS


Different approaches to implementing IMS

• No IMS – Keep it simple– Proprietary path– Convergence is not important

• Full IMS – Technology follower– Must wait for IMS to mature

• Closed IMS– Wild card– Proprietary path

• Only IMS – Market follower– Must wait for IMS to mature

• Early IMS – Market leader– Use pre-IMS services– Evolution path to full IMS


Packet Network

IMS for Global Network as “Overlay”

Local Zone

SGSN

Central IMS Centre

App. Servers

MGW

GGSN

Circuit Network

CSCF

Mobility

Server

HSSHLR

CRM & Billing

MGCF

MGW

• All IP processing is in the new centre

• A single central HSS

Local Zone

Note : Local zone remainunchanged


Packet Network

IMS partial local implementation

Local Zone

SGSN

Central IMS Centre

App. Servers

MGW

GGSN

Circuit Network

CSCF HLR

CRM & Billing

MGCF

MGW

• Local HSS, possibly evolved from HLR

• SLF to select HSS

• Still central applications

SLF

Local

HSS

Note : - some local zone will have IMS service, and local HSS- others may not

Local Zone


IMS full local implementation

Circuit NetworkMGW

• Central SLF to select HSS

• Local session control (cscf)

• Some local applications

Local Zone

GGSN

HLR

CRM & Billing

Local HSS

CSCF

Local

AS

Central IMS Centre

App. Servers

SLF

Local Zone

GGSN

HLR

CRM & Billing

Local HSS

CSCF

Local

AS

MGW

Packet Network

MGW

SGSN

MGCF

CSCF

Note : IMS deployed everywhere

IMS Standards

Documents

Transcript of IMS Standards