IP Multimedia SubsystemPart 1

Marek Średniawamareks@tele.pw.edu.pl

Institute of Telecommunications

1EIMS - 2019/2020

Introduction

3

Evolution of telecomService Delivery Platforms (SDPs)

INAP, CAP, CAMEL, GSM

SIP, OSA/PARLAY, JAIN, UMTS

INSCP & CSE

Switching system software

3G, NGN, IMS

Intelligenceembedded in

software of switchingsystems

Intelligencein a separateservice node

Intelligenceof cooperating

components

PSTN, ISDN

IP TV, RCS, IoT, … )

4G/5G, LTE, EPC, SDP, NFV

Converged &virtualized

communications

EIMS - 2019/2020

4

Evolution of service implementation model

Traditional closed model New open model

Physical transport

Call control and switching

Services and applications

Physical transport

Multimedia session control

Services & applications +management

API

API

Service interface

Network interface

Opening of the control infrastructure and service architecture using standard APIs - Parlay OSA/X APIs and JAIN APIs. Breaking of the classic value chain. Separation of service development, deployment and operation. VNO and MVNOmodels. EIMS - 2019/2020

5

Change of model: „Spaghetti” →„Lasagna”

„Spaghetti” type architecture „Lasagna” type architecture

Pri

va

te n

etw

ork

s

Fix

ed

ne

two

rks

Mo

bil

e n

etw

ork

s

Common service capabilities

Transport and access

Application and content

EIMS - 2019/2020

6

Convergence - a buzzword …

• Overloaded concept – many flavours of „convergence”

• Voice - data– Common transport network

• FMC– ETSI TISPAN NGN

• Terminal convergence– GSM/UMTS + WLAN

– Session continuity

– Single address (ENUM)

• Application convergence– Context and presence embedded in applicatiions

– Click-to-call

EIMS - 2019/2020

7

Open source+

Web 2.0/3.0

Mobility VirtualizationNFV / SDN

Broadbandand/or wireless

access

Convergence

Securityand

privacy

CloudComputing

Presenceand

context

Multimedia

Convergence – key factors

Computer science and Internet – Content, media, networked IT services

Telecommunications – A mix of solutions, technical and legal aspects

EIMS - 2019/2020

EIMS - 2019/2020 8

Areas of convergence

Convergence planes

NetworkServices andapplications

Terminals Charging Contents

Everybody can offer (almost) everything …

EIMS - 2019/2020

9

Internet

TV

Mobile

Fixed

Internet

TV

Mobile

Fixed

Internet

TV

Mobile

Fixed

Internet

TV

Mobile

Fixed

Market liberalization (LLU, BSA, ...) + business models (MVNO/MVNE, networked IT services…) + resource sharing (fibers, lambdas, ducts, masts, servers, …)

EIMS - 2019/2020 10

IP Multimedia (IM) Domain• Implementation of multimedia services

• Integration of PS and CS domains and services

UMTS RNS (UTRAN)

GSM BSS

PDN(IP)

PSTN

Core network

PS Domain

CS DomainME

Home

Domain

IM Domain - IMS

EIMS - 2019/2020 11

IMS integrates services

Voice

SMS

Instant Messaging

MMS

Pre-IMS - „islands of services” IMS – integration of services and combinational services

Voice / Video

SMS

Instant Messaging

MMS

From separate usage of standalone services ... to integrated usage of services

based on presence

In groups – communities

PoC

TV

EIMS - 2019/2020 12

IMS - requirements

• Support for:– establishing IP Multimedia sessions

– mechanism to negotiate Quality of Service

– interworking with the Internet and circuit-switched networks

– Roaming

– strong control imposed by the operator with respect to the services delivered to the end-user

– rapid service creation without requiring standardization (service capability standardization)

– access from networks other than GPRS

3GPP IP Multimedia Subsystem (1/2)

• IMS standardized by 3GPP as part of UMTS Release 5

– Basic VoIP, IM, Presence support on top of GPRS

– Adaptations to “real word” made in Release 6 (QoS, PoC support)

– Release 7 - unified IMS for all IP access networks (DSL, WLAN, etc.)

– Release 8 – Common IMS

– Releases 9-16 – Common IMS with updates and extensions -> cloudification/virtualization of IMS

• The IMS is based on the IP family of protocols:

– Adapted SIP (Session Initiation Protocol) for Session Control

– Diameter for AAA (Authentication, Authorization & Accounting)

– Others: SDP, RTP, RTCP, MGCP, etc.

EIMS - 2019/2020 13

3GPP IP Multimedia Subsystem (2/2)

• Key components of the IMS architecture:

– Extended AAA Server - Home Subscriber System – as evolution of the HLR)

– SIP servers / softswitches

– Media Servers & Media Gateways

– Application Servers

EIMS - 2019/2020 14

Evolution from 2G to 5G

15

2011 2013 2016 … 202020102009200820072006200520042003200220012000

R99 R4 R5 R6 R7 R8 R9 R10

High speed

Migration to ALL IP network

Convergentservices

WC

DM

A

HSP

AD

L

HSP

AU

L

LTE

LTE

Ad

v

HSP

A+

EPC

Co

mm

on

IMS

MM

Tel

IM&

P

R11 R13R12 R14/15/16

MIM

O

NG

CN

NR

1990 …

EDG

EC

AM

EL

IMS

Vir

tual

ized

SDP

s

LTE

Ad

vP

ro

BIC

N

GSM/GPRS

GSM/GPRS network architecture

16

GSM/GPRS core networkRadio access network

BSS

database

IP Backbone

Internet

PS

TN

, ISD

N

BTS

BTS

BSC

MSC

VLR

SGSN

GMSC

HLR

AuC

EIR

GGSN

MS

PCU

3GPP Rel.99 UMTS 3G network architecture

17

GSM/GPRS core networkRadio access network

BSS

database

IP Backbone

Internet

PS

TN

, ISD

N

BTS

BTS

BSC

MSC

VLR

SGSN

GMSC

HLR

AuC

EIR

GGSN

MS

PCU

3GPP Rel.99 UMTS 3G network architecture

18

Radio access network

UTRAN

UE Iur

Iub

Uu

BS

BS

RNC

RNC

Iub

2G => 3G MS => UE (User

Equipment), often also called

(user) terminal

New air (radio) interface based

on WCDMA access technology

New RAN architecture

(Iur interface is available for soft

handover,

BSC => RNC)

3GPP Rel.99 UMTS 3G network architecture

19

Core network (GSM/GPRS-based)

Iu CS

GnIu PS

IP Backbone

Internet

PS

TNMSC

VLR

SGSN

GMSC

HLR

AuC

EIR

GGSN

Changes in the core

network:

MSC is upgraded to 3G

MSC

SGSN is upgraded to 3G

SGSN

GMSC and GGSN remain

the same

AuC is upgraded (more

security features in 3G)

3GPP Rel.4 UMTS 3G network architecture

20

Circuit Switched (CS) ore

network

UTRAN

(UMTS Terrestrial Radio

Access Network)

PS

TN

MSC

Server

New option in Rel.4:

GERAN

(GSM and EDGE Radio

Access Network)PS core as in Rel.’99

GMSC

Server

SGW

MGW

SGW

MGW

3GPP Rel.4 UMTS 3G network architecture

21

Circuit Switched (CS) core

networkP

ST

N

MSC

Server

PS core as in Rel.’99

GMSC

Server

SGW

MGW

SGW

MGW

MSC Server takes care of

call control signalling

The user connections are set

up via MGW (Media

GateWay)

“Lower layer” protocol

conversion in SGW

(Signalling GateWay)

RANAP / ISUP

SS7

MTP

IP

SIGTRAN

HSS – Home Subscriber System PS – Packet Switching

MGW – Media Gateway SGW – Signaling Gateway

MTP – Message Transfer Part MSC – Mobile Switching Center

3GPP Rel.5 UMTS 3G network architecture

22

CS core

PS

TN

SGSN GGSN

GW

Inte

rnet

HSS

IMS (IP

Multimedia

System)

PS core

UTRAN

(UMTS Terrestrial Radio

Access Network)

GERAN

(GSM and EDGE Radio

Access Network)

New core

network part:

HSS – Home Subscriber System PS – Packet Switching

GW – Gateway CS – Circuit Switching

3GPP Rel.5 UMTS 3G network architecture

23

CS core

PS

TN

SGSN GGSN

Inte

rnet / o

ther IM

S

HSS

PS core

The IMS can establish

multimedia sessions (using

IP transport) via PS core

between UE and Internet (or

another IMS)

Call/session control using

SIP (Session Initiation

Protocol)

Interworking with the PSTN

may be required for some

time ...

IMS (IP

Multimedia

System)

GW

HSS – Home Subscriber System PS – Packet Switching

GW – Gateway CS – Circuit Switching

3GPP Rel.8 UMTS 4G network architecture

24

25

IMS as a component of UMTS Rel.5-16

Architecture of IMS [3GPP 23.002]

S-CSCFMGCF HSS

CxIM

MGWMn

Mb

Mg

MRFP

MbI-CSCF

Mw

Mw

Gm

MjMi

BGCF

Mk

UE

Mb

Mb

MbSLFDx

CS

CS

Cx

AS

ISC

Sh

Ut

BGCF

Mg

Dh

Ma

P-CSCF

Mx

Mx

Mx

Legacy CS network MmMm Mm

TrGW

Multimedia IP networks

IBCF

Ix

Ici, MmIzi

MRB

Rc

ISC

Mr

MRFC

Cr, Mr’

Mb

IMS

AGW

Mp

Mw

Iq

Ms

EIMS - 2019/2020 26

Main 3GPP IMS standards

• 22.228: IP multimedia subsystem; Stage 1• 23.207: End-to-end QoS Concepts and Architecture• 23.218: IP Multimedia (IM) session handling; IM call model• 23.228: IP Multimedia Subsystem (IMS); Stage 2• 24.228: Signalling flows for the IP multimedia call control based on SIP and SDP; Stage 3• 24.229: IP Multimedia Call Control Protocol based on SIP and SDP; Stage 3• 29.228: IP Multimedia (IM) Subsystem Cx Interface; Signalling flows and message contents• 29.229: Cx Interface based on the Diameter protocol; Protocol details• 29.328: IP Multimedia Subsystem (IMS) Sh Interface; Signalling flows and message contents• 29.329: Sh interface based on the Diameter protocol; Protocol details• 29.207: Policy Control over Go Interface• 29.208: End-to-end Quality of Service (QoS) signalling flows• 32.200: Telecommunications management; Charging management; Charging principles• 32.225: Telecommunications management; Charging management; Charging data description for the IMS domain• 33.203: 3G security; Access security for IP-based services• 33.210: 3G security; Network Domain Security (NDS); IP network layer security

An IMS concept: taking control of IP based services

27

IMScontrol

Application Server

Application Server

• IP network enables unrestricted communication between the endpoints

• IMS takes control over services using SIP protocol

IP

BA

BA

IMS – control of IP based services

28

IP Core Network

UMTS access

IMS

SIP signaling

RTP Transport

IMS motivation – „rich” servicese.g. presence based VoLTE

29

IP core network

IMS

SIP signaling

RTP Transport

IM server

Presenceserver

Call/sessionserver

…

Other ASs

Application servers (AS)

IMS as an enabler for convergence of services

PSTN

IP Transport

PLMNIP

Session Control

IN Services MMTelTAS/VAS

IMS provides an access neutral unified architecture for both mobile and fixed network services

› Common service layer, Common session control Layer, common IP transport layer for all access networks

Key characteristics

› Access Convergence

› Services Convergence

› Open architecture

› Vendor independence

PST

N

IP

PLM

N

Aol.

31

Protocols related to IMS services

• Instant messaging and presence

– SIP – Multimedia Messaging (MMS)

– MSRP

• Conversational multimedia services – MMTel, videoconferencing, VoLTE, VoWiFI

– SIP

• Video streaming

– SIP

– RTSP (IP TV, monitoring)

• IPTV

– RTSP

• Multimedia games

– SIP

EIMS - 2019/2020 32

From IETF SIP ….

Request

SIP Proxy server

IP/Internet

Response

DNSAS – SIP application server

SIP User Agent- UA

SIP User Agent- UA SIP User Agent- UA

SIP User Agent- UA

EIMS - 2019/2020 33

… to 3GPP IMS SIP

P-CSCF

I-CSCFS-CSCF

Application server

DNS

SLF

DNS HSS

IP Core Network with QoSsupport

AS – SIP application serwer

SIP User Agent- UA

SIP User Agent- UA

EIMS - 2019/202034

IMS in UMTS Rel.5

CS Domain

PS Domain

“call”

“session”

IP core network

TDM, ATM or IP

MSC GMSC

SCP

IMS

HLR ???HSS

SGSN GGSN

MGW MGW

PSTN

Intranet/Internet

CSCF

MGCF “IP based”

GMSCServer

MSCServer

35Mobile

IP

Residential

Wi-Fi / WiMax wireless IMS access

PoC MessagingGLMS MultimediaTelephony

Licensed radio IMS

PresenceCSI

WLAN Access to IMS

VCC MultimediaTelephony

MultimediaTelephony

IMS standardization activities

EIMS - 2019/2020

EIMS - 2019/2020 36

Protocols related to IMS services

• Instant messaging and presence

– SIP/PoC i 3G H.324M – Video Mail (VM)

– SIP – Multimedia Messaging (MMS)

– 3G-H.324M – Multimedia advertising

• Conversational multimedia services

– SIP/PoC – Push-To-Talk (PTT) over Cellular (PoC)

– SIP i 3G-H.324M – videotelephony and videoconferencing

• Video streaming

– SIP 3G-H.324M (based on DTMF video portals)

– RTSP (IP TV, monitoring)

• Multimedia games

– SIP/JSR-180 (J2ME)

– SIP/PoC

3GPP IMS architecture

37

control

transport

Visited network Home network

P-CSCF

HSS

S-CSCF BGCF MGCF

MGW

PSTN

H.248

SIPSIP SIP

SIPISUP/IP

AS

Diameter

IP corenetwork

Accessnetwork

PCM

I-CSCF

Diameter

SIP

Diameter

HSS – Home Subscriber Server

CSCF – Call Session Control Function

BGCF – Breakout Gateway Control Function

MGCF – Media Gateway Control Function

VoIP – RTP – transport of media streams

Service plane

Control plane

Transport plane

SGW ISUP/MTP

EIMS - 2019/2020

EIMS - 2019/2020

38

IMS layers: transport, session control, applications

Transport/user layer

Application layer

Control layer

S-CSCF

HSS

SIP AS SIP AS

MRFC

B-GW

SIP Diameter PSTN

RTP

I-CSCFP-CSCF

MRFP

H.248 / MEGACO

Parlay ASCAMEL

CSE

OSA GW IM SSF

Parlay API CAP API

ISC interface

EIMS - 2019/2020 39

Three layer architecture of IMS (1/3)

• Unified architecture that supports a wide range of services enabled by the flexibility of Session Initiation Protocol (SIP)

• Transport and Endpoint Layer– Initiates and terminates SIP signaling to set up sessions and provide bearer services such as conversion of

voice from analog or digital formats to IP packets using Real time Transport Protocol (RTP)

– Provides the media gateways for converting the VoIP bearer streams to the PSTN TDM format.

– The media server provides many media related services including conferencing, playing announcements, collecting in-band signaling tones, speech recognition, speech synthesis, etc.

EIMS - 2019/2020 40

Three layer architecture of IMS (2/3)

• Session Control Layer– Call Session Control Function (CSCF)

• provides the registration of the endpoints and routing of the SIP signaling messages to the appropriate application server

• interworks with the transport and endpoint layer to guarantee QoS across all services

– Home Subscriber Server (HSS) database• maintains the unique service profile for each end user

• By centralizing this information, applications can share information to create unified personal directories, multi client type presence information and blended services.

– Media Gateway Control Function (MGCF)• Interworks SIP signaling with the signaling used by the media gateway

EIMS - 2019/2020 41

Three layer architecture of IMS (3/3)

• Application Server Layer

– Contains application servers, which provide the end-user service logic

• Telephony Application Server

• IP Multimedia – Services Switching Function (IM-SSF)

• Supplemental Telephony Application Servers

• Non Telephony Application Servers

• Open Service Access – Gateway (OSA-GW)

EIMS - 2019/2020

42

IMS architecture

UE

P-CSCF I-CSCF S-CSCF

BGCF MGCF

HSS

Visited network Home network

AS

Gm

Mw

ISC

Mj

Mi

MRF

Cx

Sh

<SIP>

<DIAMETER>

<SIP>

<SIP>

EIMS - 2019/2020 43

Terminal - User Equipment (UE)

• SIP UA

• Establishes GPRS PDP context for– signaling

– media transport

• ISIM for authentication– Public and Private User identity

– User Network address

– Security algorithms and keys

– At least USIM

• Corellation of session control with QoS reservation

EIMS - 2019/202044

IMS components

UE

P-CSCF I-CSCF S-CSCF

BGCF MGCF

HSS

AS

Gm

Mw

ISC

Mj

Mi

MRF

Cx

Sh

<SIP>

<DIAMETER>

<SIP>

<SIP>

Home networkVisited network

EIMS - 2019/2020 45

Proxy Call Session Control Function - P-CSCF

• P-CSCF (Proxy Call Session Control Function) – entry point of user terminal into the IMS world

– acting as an outbound/inbound SIP proxy server

– an IMS terminal communicates with a single P-CSCF during the registration

– establish IPsec security associations toward the IMS terminal

– verify the correctness of SIP request sent by the IMS terminal

– compressor and a decompressor of SIP messages

– may include PDF (Policy Decision Function) to authorize media plane

– generate charging information

EIMS - 2019/202046

IMS components

UE

P-CSCF I-CSCF S-CSCF

BGCF MGCF

HSS

AS

Gm

Mw

ISC

Mj

Mi

MRF

Cx

Sh

<SIP>

<DIAMETER>

<SIP>

<SIP>

Visited network Home network

EIMS - 2019/2020 47

Interrogating Call Session Control Function (I-CSCF)

• A SIP proxy located at the edge of an administrative domain

• The address of the I-CSCF is listed in the DNS records of the domain

• I-CSCF has an interface to the SLF and HSS and route the SIP request to the appropriate destination (typically S-CSCF)

EIMS - 2019/2020

48

IMS components

UE

P-CSCF S-CSCF

BGCF MGCF

HSS

AS

Gm

Mw

ISC

Mj

Mi

MRF

Cx

Sh

Visited network Home network

I-CSCF

EIMS - 2019/2020 49

Serving Call Session Control Function S-CSCF

• S-CSCF (Serving Call Session Control Function)

– Central node of the signaling plane

– Acts as a SIP server and a SIP registrar

•Maintains binding between the user location (e.g. IP address of the terminal) and the user’s SIP address of record (Public User Identity)

– Diameter interface to the HSS

•To download the authentication vectors of the user

•To download the user profile including service profile

•To inform the HSS of S-CSCF allocated to the user

– All the SIP signaling the IMS terminals sends and receives traverse the allocated S-CSCF

– Provides SIP routing (e.g. translation from phone number to SIP URI)

– Enforces the policy of the network operator

EIMS - 2019/2020

50

IMS components

UE

P-CSCF I-CSCF S-CSCF

BGCF MGCF

HSS

AS

Gm

Mw

ISC

Mj

Mi

MRF

Cx

Sh

Visited network Home network

EIMS - 2019/2020 51

Breakout Gateway Control Function (BGCF)

• Selects PSTN/CS domain to forward a call– local MGCF

– another BGCF

• MGCF selection process not defined– configuration

– TRIP or a similar solution

Media Gateway Control Function (MGCF)

• Gateway to PSTN

– SIP - PSTN mapping

– Establishes appropriate bearer capabilities

– Transcoding

– Acts as UA (registration not required)

EIMS - 2019/2020 52

EIMS - 2019/2020

53

IMS components

UE

P-CSCF I-CSCF S-CSCF

BGCF MGCF

HSS

AS

Gm

Mw

ISC

Mj

Mi

MRF

Cx

Sh

Visited network Home network

EIMS - 2019/2020 54

Media Resource Function (MRF)

• Supports conference services and announcements

• Multimedia Resource Control Function (MRFC)

– Interprets information from S-CSCF andAS

• e.g. conference reservation

– controls MRPF

• Multimedia Resource Processor Function (MRPF)

– Sets bearer capabilities based on MRFCrequests

– Mixing and distribution of media

– Media streaming for user interaction

• Uses H.248 (MEGACO)

MRFC

MRPF

SIP

H.248

Media

Interworking with PSTN – PSTN/CS Gateway

• PSTN/CS = MGCF + SGW + MGW

• MGCF (Media Gateway Control Function)

– ISUP-SIP mapping

– MGW control for media transcoding

– Selection of I-CSCF for calls to PSTN

• SGW (Signalling Gateway Function)

– Supports interworking between SS7 and MGCF

– Transport of ISUP messages in SIP messages to MGCF MGCF (SIP-T orBICC)

– ISUP/BICC/MTP – ISUP/BICC/SCTP/IP

• MGW (Media Gateway)

– Termination of media streams

• RTP - PCM

• AMR - G.711 EIMS - 2019/2020 55

BGCF - Breakout Gateway Control Function

• SIP server – routing based on telephone numbering– Using of info delivered by TRIP protocol

• IMS – PSTN/PLMN calls

• Selection of an interworking network

• Selection of an appropriate PSTN/CS gateway (MGCF) ifinterworking refers to the same network in which BGCF islocated

EIMS - 2019/2020 56

EIMS - 2019/202057

Application Server (AS)• An SIP entity that hosts and executes

services

• Four modes of operation:

– AS acting as terminating UA, or redirect server

– AS acting as originating UA

– AS acting as a SIP proxy

– AS performing third party call control/ B2BUA mode

• ISC - SIP Interface to S-CSCF

• Implemetation variants of ASs– SIP AS

– OSA-SCS (Open Service Access-Service Capability Server)

– IM-SSF (IP Multimedia Service Switching Function)

S-CSCF

AS

ISC

1

2 3

4

EIMS - 2019/2020 58

Implementation variants of IMS AS

CSCFS-CSCF

SIP Application ServerSIP AS

HSSHSSOSA service

capability server(SCS)

OSA servicecapability server

(SCS)

IM-SSFIM-SSF

Camel Service

Environment

CAMEL ServiceEnvironment

OSA

application OSA AS

ISC

Cx ISC

ISC

CAP

MAP

Parlay OSA API

SCIM

Sh

Si

MRFCMRFC

Mr

AS AS

EIMS - 2019/2020 59

Parlay OSA application servers – third parties

Online &Offline

Charging (ECF, CCF)

Service Delivery Platform

(Application server) Parlay App 1

Service Platform Trigger PointsParlay API (MPCC, MMM, Presence, Charging ...

SIP Interface

HSS

S-CSCF

SPT

SPT Filtering criteria

ISC

SIP

SIP-Server

Sh =

Diameter

Cx =

DiameterRo + Rf =

Diameter

Diameter

Parlay X GWParlay App 2

Parlay App 3

Parlay X App 1Parlay X App 2

Other accessnetworks

Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)

EIMS - 2019/2020 60

IMS components

UE

I-CSCF

BGCF MGCF

HSS

AS

Gm

Mw

ISC

Mj

Mi

MRF

Cx

Sh

Visited network Home network

I-CSCF S-CSCF

AS

MRFI-CSCF

AS

P-CSCF S-CSCF

EIMS - 2019/2020 61

Home Subscription Server (HSS)

• HSS (Home Subscriber Server)– Technically, an evolution of the HLR– Central repository for user-related information

• location information• security information (authentication and authorization)• user profile information (the services that the user is

subscribed to)• S-CSCF allocated to the user

• SLF (Subscriber Location Function)– Simple database that maps users’ addresses to

HSSs

EIMS - 2019/2020 62

HSS – Home Subscriber Server

I-CSCF S-CSCF

Mw

SLF

Dx Cx

HSS AS

Cx

SIP

SIPDiameter

Sh

ISC

Diameter

GPRSaccess

MAP

SIP

Mw

The first registration

UAR: User-Authorization-RequestUAA: User-Authorization-AnswerMAR: Multimedia-Authentication-RequestMAA: Multimedia-Authentication-AnswerSAR: Server-Assignment-RequestSAA: Server-Assignment-AnswerRAND: Random challengeAUTN: Network Authorization TokenCK: Ciphering KeyIK: Integrity Key

13. UAR

1. Register

Visited network Home network

P-CSCF

2. Register

UA I-CSCF HSS

3. UAR

4. UAA

S-CSCF

Selection of r S-CSCF

5. Register

6. MAR

10. 401 UnauthorisedRAND||AUTN

12. RegisterRES

7. MAARAND||AUTN||XRES||CK||IK

9. 401 UnauthorisedRAND||AUTN

11. RegisterRES

Authenticationvector selection

8. 401 UnauthorisedRAND||AUTN

14. UAA

15. RegisterRES

22. OK20. OKCK||IK

21. OKCK||IK

Authentication

18. SAR

19. SAA

EIMS - 2019/202063

EIMS - 2019/2020 64

Home Network of Mobile A Home network of Mobile B

HSS - A

I-CSCF - A S-CSCF - A

HSS - B

S-CSCF - B I-CSCF - B

P-CSCF - A

Network Visited by Mobile A Network Visited by Mobile B

P-CSCF - B

Mobile A Mobile B

Call Control

11

22

33

4 4

5 5

Example: registration

EIMS - 2019/2020 65

Control

Bearer

Visited network

of callee

Home network of called userHome network of

calling user

Visited network of callerP-CSCF

HSS

S-CSCFSIP

SIP

Diameter

P-CSCF

AS

HSS

S-CSCF SIPAS

SIP

Diameter

I-CSCF

Diameter

DNS

Packet

CoreAccess Access

SIP INVITE1

1

Retrieving user’s profile2

2

3

3 Execution of a service scenario

Resolution of User B home network address and

INVITE forwarding

4

4

Identification of Registrar for user B and INVITE forwarding5

5

Retrieving user’s profile 6

6

7

7 Execution of a service scenario

INVITE forwarding to do User B 8

8

Ringing / Alerting10

10

SDP session negotiation /

Reservation of resources

9

9

RTP

Answer / call active11

11

IMS users session

Packet

Core

SIP UESIP UE

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66

Home Network of Mobile A Home network of Mobile B

HSS - A

I-CSCF - A S-CSCF - A

HSS - B

S-CSCF - B I-CSCF - B

P-CSCF - A

Network Visited by Mobile A Network Visited by Mobile B

P-CSCF - B

Mobile A Mobile B

Call Control

1

2

3

4

5

6

7

Example 2 – IMS mobile call

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Control

Bearer

Network vizited by the caller Home network of the caller

P-CSCF

HSS

S-CSCF

BGCFMGCF

MGW

H.248

SIP

SIP SIP

AS

BGCF

SIP

SIP

PSTN

ISUPDiameter

PacketCore

Access

SIP INVITE1

1

2 3

Selection of access to PSTN and selection of MGCF4

4

ISUP IAM7

75

Seizing of a link/trunk and determination of MGW capabilities5

PCM

SDP session negotiation / Reservation of resources6

6

RTP stream

Ringing / Alerting8

8 9

Answer / Connect9

IMS to PSTN call

Retrieving user’s profile 2

3 Execution of a service scenario

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P-CSCF - A

Network Visited by Mobile A

HSS - A

I-CSCF - A S-CSCF - A

BGCF - A

Home Network of Mobile A PSTN

MGW - B

MGCF - B

Mobile A

Gateway Control

User Profile

User Profile

1 2

3

4

5

Call to PSTN (CS domain)

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IMS Session Setup and Control

• Happens after user registration (and authentication!)

• Goals of IMS session setup– Capability and media negotiation (e.g. codecs, port numbers, addresses)

– Network resource reservation and the support of QoS preconditions

• Additional functions performed by the IMS during the IMS Session Setup:– Routing to the terminating IMS (= the IMS of the B-Party)

– Routing / Breakout to the PSTN / CS-Domain when the B-Party is not in the IMS, but in the PSTN / CS-Domain

– Service Control / Invocation of Application Servers to trigger the execution of Originating- and/or Terminating IMS Services

– Integrity/Confidentiality Protection of SIP Messages

– QoS/Media Authorization

– SIP Signaling Compression

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IMS Session Setup and Control 1/4

Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)

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IMS Session Setup and Control 2/4

Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)

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IMS Session Setup and Control 3/4

Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)

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IMS Session Setup and Control 4/4

Source: IMS Tutorial -T. Magedanz (TU Berlin / Fraunhofer FOKUS)

EIMS

Project is co-financed by European Union within European Social Fund74EIMS - 2019/2020