IP Multimedia Subsystem (IMS) Emergency Services

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IP Multimedia Subsystem (IMS)

Emergency Services

Christian Militeau

Director, IEN Services Development

ESIF 16
-

January 2006





2

Objectives

Highlight Current Standards Activity

Present an Overview of IMS Architecture

Define IMS Core Network Elements

Illustrate Registration and Call Flow

Present an Overview of IMS in the context of
Emergency Services


3

Where does IMS come from?

In Wireline there has been a long term move towards a Voice
over Packet (VoIP) replacement for the PSTN

Drivers have always been to reduce OPEX in fixed line
networks by optimising bandwidth usage, and replacing
outdated TDM switching fabric


Compressed speech into less than 64kbps channels (G Standards)


Further optimisation using VAD, Silence Suppression, ATM AAL2 or IP
multiplexing yields significant reduction in core network bandwidth
requirements.

Drivers in 3GPP for Wireless are more service related


IMS is born out of a need for ‘feature rich’ services


Bandwidth requirements and their impact on capacity for the Radio interface
(GSM, GPRS, 3G).

IMS provides the final piece in the business case for the NGN

4

IMS
-
Related Standards Initiatives

5

IMS Releases

6

What is IMS?

An Industry Standard Service
Architecture (SA) and Core
Network (CN) architecture

An IP Multimedia Services
Architecture

Defined with Open Standards
from 3GPP and ETSI

Based on IETF Protocols
(SIP, RTP, RTSP, COPS,
DIAMETER, etc.)

Designed for both Wireless
and Wireline Networks and
for Fixed and Mobile
Convergence (FMC)

A Solution for Service
Transparency

Capable of Interworking with
PSTN (i.e. legacy IN
-
based
services)

CSCF


Call Session Control Function

HSS


Home Subscriber Server

Access & Transport

Plane

Core Network

Session

Control Plane

Service Architecture

Applications/Services

Plane

HSS

CSCF

Access

Network

Other

Networks

Web Portal

Application

Servers

Session
Control

Centralized

Databases

Media
Control &

Gateways

Media

Server

7

Access

Network

Other

Networks

Web Portal

Application

Servers

Session
Control

Centralized

Databases

Media
Control &

Gateways

Media

Server

Access

Layer

Session

Control

Layer

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
OAM&P,Billing,
etc.

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

IP Multimedia Subsystem (IMS)
-

Key Attributes

8

RNC

MSC(Server)

SGSN

GGSN

CN

MGW

BSC

UMTS/GPRS

WLAN

Corporate

P
-
CSCF

I
-
CSCF

MRF

MGW

MGCF

IMS

S
-
CSCF

SIP Application

Servers

SIP Application

Servers

HSS

CDMA 2000

DSL/Cable Modem

DSLAM/CMTS

IMS Access Network Independence

9

Clients

Devices

Access

Transport

Session

Control

Applications

Managed Core IP Network

Media GW

Signaling GW

MRFC

CSCF

Service Broker

HSS

Pres.

Data

Loc.

Data

Subs

Data

Micro Billing

Integrated
Pre
-
paid &
Postpaid

AAA

Group

Lists

Media

Server

POTS

phone

GGSN

PDSN

MSC

Cellular

Access

Point

WiFi/802.11x

Local Loop

VoIP

handset


Ckt
-
PBX

IP
-
PBX

IP
-
phones

ISDN
-
phones

IP
-
phones

DSL/Cable

IP LAN

Wireless

Router

Base

Station

5ESS

(IP
-
Centrex)

Office/Hotel

Hotspot

Home

On the Road

Home/Office

Dual
-
mode

WiFi phone

Soft
-
phones

PSTN

SS7

SIP Clients

Ckt

handset


Multiple user interfaces with common look and feel

Other Clients

IMS Converged Communications Services Vision

Network Operations, Applications
Mgt, Subscriber registration/
authorization

Presence

Servers

Telephony

Servers

Unified

Messaging

10

IMS Functional Elements

Session Management (SIP)

Routing

Databases

Network Interoperability Elements

Services and Support Components

Charging Components

11

IMS Functional Elements

Application Server (AS)

Breakout Gateway Control Function (BGCF)

Call Session Control Function (CSCF)

Home Subscriber Server (HSS)

Media Gateway Function (MGW)

Media Gateway Control Function (MGCF)

Multimedia Resource Function Controller (MRFC)

Multimedia Resource Function Processor (MRFP)

Security Gateway (SEG)

Serving/Gateway GPRS Support Node (SGSN/GGSN)

Signaling Gateway (SGW)

Subscription Locator Function (SLF)

Service Capability Interaction Manager (SCIM)

Policy Decision Function (PDF)


“Bandwidth Manager” (CoS & QoS)


12

Visited

Network

IMS Home Network
-

Functional Elements

HSS

DNS

ENUM

I
-
CSCF

S
-
CSCF

Home Network

AS

AS

AS

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



3
rd

party or IMS Vendor

Domain Name Server

P
-
CSCF

MGCF

MGW

PSTN

H.248

ISUP

BGCF

SIP

SS7

SIP

SIP

SIP

SIP

SIP

SIP

SIP

Diameter

RTP

TDM

Call Session

Control Function



SIP registration



SIP session setup

MS

MS

MRFC

Media Gateway

Control 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 Controller



Pooling of Media servers (e.g. conference)


Proxy CSCF



1
st

contact point for UA



QoS



Routes to S
-
CSCF

Interrogating CSCF



Entry point for incoming calls



Determines S
-
CSCF for Subscribers



Hides network topology

Serving CSCF



Registrar



Session control



Application Interface

P
-
CSCF

SIP

SIP

UA/UE

UA/UE

13

IMS Network
-
to
-
Network Connectivity

HSS

DNS

ENUM

I
-
CSCF

S
-
CSCF

Visited

Network

Home

Network

SIP

AS

AS

AS

P/S
-
CSCF

Backbone

Packet

Network

Access

MGCF

MGW

PSTN

H.248

ISUP

BGCF

SIP

SIP

SIP

SS7

SIP

SIP

SIP

SIP

SIP

SIP

Diameter

RTP

TDM

RTP

RTP

MS

MS

MRFC

P
-
CSCF

SIP

SIP

Proxy/Serving CSCF


Manages call origination


Selects destination network



Routes to I
-
CSCF


Interrogating CSCF



Entry point for incoming calls



Determines S
-
CSCF for Subscribers



Hides network topology

UA/UE

14

IMS UE Registration

HSS

S
-
CSCF

P
-
CSCF

UA/UE

Register

Register


The UA/UE Registers with the S
-
CSCF

MAR/MAA


The S
-
CSCF consults HSS for Authentication

Unauth

Unauth


The S
-
CSCF Challenges the UA/UE

Register

Register


The UA/UE Registers with Credentials to the S
-
CSCF

MAR/MAA


S
-
CSCF Authenticates with HSS and Downloads User Profile

15

IMS Subscription to UE State Changes

HSS

S
-
CSCF

P
-
CSCF

UA/UE

Subscribe



The P
-
CSCF Subscribes to the UA/UE Registration State

Notify



S
-
CSCF Notifies the P
-
CSCF of Registration State

Subscribe

Subscribe



The UA/UE Subscribes to its Registration State

Notify

Notify



S
-
CSCF Notifies the UA/UE of Registration State

Now the Elements can Inform Each Other of Registration State Changes

16

A Typical Example of an IMS Call

User B

DSL/Cable Modem

DSLAM/CMTS

RNC

GGSN

Network Z (UMTS/GPRS)

Network X

User A

SGSN

Network Y

GRX

P
-
CSCF

P
-
CSCF

I
-
CSCF

I
-
CSCF

S
-
CSCF

S
-
CSCF

HSS

HSS

AS

AS

17

IMS (3G) Emergency Services Architecture

18

3GPP IMS R7 Emergency Sessions

HSS

DNS

ENUM

S
-
CSCF

IMS Core Network

AS

AS

AS

P
-
CSCF

MGCF

MGW

Selective

Router

H.248

ISUP

BGCF

SIP

SS7

SIP

SIP

SIP

SIP

SIP

Diameter

TDM

MS

MS

MRFC

SIP

CAMA

E
-
MF

IP PSAP

Connectivity to Network

Capable of Delivering

Call to IP PSAP

Connectivity to

Legacy Emergency

Services Network



3GPP View of Emergency Sessions

RTP

IP Access Network

Initiates Emergency

Call

PSAP Selection

Left to Implementation

IP Connectivity

Access Network (ICAN)

IP
-
PBX

IP
-
phones

IP
-
phones

(IP
-
Centrex,

DSL, Cable)

Legacy PSAP

19

Potential Long Term

IMS Emergency Services Network

HSS

DNS

ENUM

I
-
CSCF

S
-
CSCF

Customer

Home

Network

IMS Emergency

Services Network

SIP

AS

AS

PSAP
Selection

AS

P/S
-
CSCF

Backbone

Packet

Network

Access

MGCF

MGW

BGCF

SIP

SIP

SIP

SIP

SIP

SIP

SIP

SIP

SIP

Diameter

RTP

RTP

RTP

MS

MS

MRFC

P
-
CSCF

SIP

SIP

IP PSAP

Call Delivered to

IP PSAP with

Location

Call Enters IMS ESNet

With Location

Location is Used to

Determine PSAP

H.248

Selective Router

ISUP

SS7

TDM

CAMA

E
-
MF

Legacy PSAP

CAMA

E
-
MF

OR

Call Delivered to Legacy
Network Without Location

(Query for Location Needed)

20

Emergency Call Delivery

VoIP to IP PSAP

P
-
CSCF

I
-
CSCF

MRF

MGW

MGCF

IMS ES Network

S
-
CSCF

SIP Application

Servers

SIP Application

Servers

HSS

IP PSAP

Legacy ESNet/PSAP

PSTN

Legacy

EO

STP

VSP VoIP Network

PIDF
-
LO

PIDF
-
LO

ANI

ANI



Call Originates with Location



Location used for PSAP Selection



Call Delivered with Location

21

Emergency Call Delivery

VoIP to Legacy PSAP

P
-
CSCF

I
-
CSCF

MRF

MGW

MGCF

IMS ES Network

S
-
CSCF

SIP Application

Servers

SIP Application

Servers

HSS

IP PSAP

PSTN

Legacy

EO

STP

VSP VoIP Network

PIDF
-
LO

PIDF
-
LO

ANI

ANI



Call Originates with Location



Location Could be used for PSAP Selection



Call Delivered only w/Callback (ANI)



Query Mechanism Needed for Location

Legacy ESNet/PSAP

22

Emergency Call Delivery

Legacy PSTN to IP PSAP

P
-
CSCF

I
-
CSCF

MRF

MGW

MGCF

IMS ES Network

S
-
CSCF

SIP Application

Servers

SIP Application

Servers

HSS

IP PSAP

PSTN

Legacy

EO

STP

VSP VoIP Network

PIDF
-
LO

PIDF
-
LO

ANI

ANI



Call Originates with only Callback (ANI)



Mechanism to Provide Location and

PSAP Selection Required



Call Delivered with Location

Legacy ESNet/PSAP

23

Emergency Call Delivery

Legacy PSTN to Legacy PSAP

P
-
CSCF

I
-
CSCF

MRF

MGW

MGCF

IMS ES Network

S
-
CSCF

SIP Application

Servers

SIP Application

Servers

HSS

IP PSAP

PSTN

Legacy

EO

STP

VSP VoIP Network

PIDF
-
LO

PIDF
-
LO

ANI

ANI



Call Originates with only Callback (ANI)



Mechanism to Provide Location and

PSAP Selection Required



Call Delivered only w/Callback (ANI)



Query Mechanism Needed for Location

Legacy ESNet/PSAP

24

Emergency Services
-

Additional Topics

Bridge/Transfer


Including Location, if Feasible

Alternate Routing

Default Routing

Wireless Phase 2 Updates

TTY/TDD

3
rd

Party Call Centers

25

BACKUP SLIDES

26

FUNCTIONAL ELEMENTS DESCRIPTIONS

Home Subscriber Server (HSS)

Application Server (AS)

Call Session Control Function (CSCF)

Breakout Gateway Control Function (BGCF)

Media Gateway Function (MGW)

Media Gateway Control Function (MGCF)

Multimedia Resource Function Controller (MRFC)

Multimedia Resource Function Processor (MRFP)


27

Home Subscriber Server (HSS)

Presence, Location and Profile

End
-
User Identity

Private and Public End
-
User Information

Registration Information

Service Initiation Information

Subscriber Service Profile (SSP)


Downloaded to CSCF at Registration

HSS

Diameter

28

Application Server (AS)

Contains Call Related Application Logic

Facilitates a Service Creation Environment

Queried by S
-
CSCF in Real Time to Execute Logic

Generally Specialized for Each Service

May Provide Gateway to Legacy Applications (e.g.
AIN)

AS

AS

AS

SIP

Diameter

29

Call/Session Control Function (CSCF)

CSCF


Processes SIP Signaling

P
-
CSCF


First Point of User Contact


Authenticates user


May Include Policy Functions

C
-
CSCF


Central Node of Control Plane


Acts as Registar for User (Downloads SSP from HSS)


Invokes Application Servers


Performs Primary Routing Function

I
-
CSCF


Located at Edge of Administrative Domain


Is the Ingress Network Point Defined in DNS


Shields Network Topology from External Networks

I
-
CSCF

S
-
CSCF

P
-
CSCF

SIP

SIP

SIP

SIP

SIP

Diameter

30

PSTN (Circuit Switched) Gateway

BGCF


Routes to Gateway Based Upon Telephone
Number

MGCF


Controlling Function for SGW and MGW

SGW


Provides Signaling Conversion Between SIP
and ISUP

MGW


Provides Conversion between RTP and
TDM



MGCF

MGW

H.248

ISUP

BGCF

SIP

SIP

TDM

SGW

SIP

31

Multimedia Resource Function (MRF)

Offers Services Such as Conferencing

MRFC


SIP User Interface toward S
-
CSCF

MRFP


Controls the Media Server (MS)

SIP

MS

MS

MRFC