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2008 Nokia V1-Filename.ppt / YYYY-MM-DD / Initials1

3GPP IMS Emergency

Calls Stage 3 UpdateGeorg Mayer


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3GPP IMS Emergency Calls Status 10/2008

IMS Emergency Calls have been added in 3GPP Rel-7

Before: only fall-back to CS emergency all

Based on IETF specifications and 3GPP architecture (TS 23.167, TS 22.101)

Special treatment of e-calls from visited network

Special requirements due to PSAPs located in PSTN

Still

Rel-7 is frozen since December 2007

Major change since then: Removal of Emergency IMPU (see Milan Patels

presentation)

No news on IMS Emergency Calls in Rel-8 EPS (also known as SAE/LTE) added as an IMS access network


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IMS Emergency Calls Beyond Rel-8

Further alignment with latest IETF progress

E.g. how to handle e-calls from pure RFC 3261 clients via IMS

E.g. role of LOST protocol

Emergency Calls in Session Continutiy cases

e.g. ongoing e-call whilst user walks out of IMS coverage and call is transferred to CS

domain or to different IMS access network (e.g. GRPS -> I-WLAN)

Especially interesting when new 3GPP EPS is used as access network

Further issues may come up

Currently these issues are not discussed on a stage 3 (protocol) level


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Basic 3GPP IMS Architecture for Emergency

Calls

K

S

I

3GPP IMScore

Fixed BroadbandAccess

GPRS access

WLAN 3GPP IPaccess

PSAP

PSTN/ CS core

IWF

EmergencyControl Centre



PSAP= Public Safety

Answering Point

112

Specified emergency categories


3GPP LTEaccess


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IETF Specifications used for IMS Emergency

Calls Basic SIP specifications, such as RFC 3261

RFC 4119 A Presence-based GEOPRIV Location Object Format

RFC 5031 A Uniform Resource Name (URN) for Services

draft-ietf-sip-location-conveyance Location Conveyance for SIP

draft-holmberg-sip-keep Indication of support for keep-alive


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Entities

UE (SIP: UA) Initiates e-calls, if necessary also e-registration

May receive callbacks from PSAP

P-CSCF (SIP: Outbound Proxy)

Detects whether call is subject to emergecny treatment

Rejects e-calls if UE should e.g. use CS domain

Forwards e-calls to the E-CSCF

S-CSCF (SIP: Registrar, Home Service Proxy)

Registration of the user / always locates in users home network

Call-backs from PSAP take place via home network

E-CSCF

Routing to PSAP (based on e-URN, location information, etc.)

Can query LRF (Location Function in 3G networks) for user location information

PSAP No 3GPP specific requirements

MGCF / MGW (Interworking between IMS / CS)

No additional requirements due to e-calls


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Visited Network

Emergency Registration and Emergency Call

Home Network

P

IMS Emergency APN

E

Emergency CSCF

Emergency Call Public SafetyAnswering Point(PSAP)

I SP

GGSN in Home Network


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Emergency Registration and Initiating the E-Call

If UE detects, that emergency call needs to be made (based on dialled number / URI), itshall

Detect whether to use CS or IMS domain (based on operator preference)

If connected to home network and already IMS registered

Start IMS emergency call directly

If connected to home network and not registered

Perform emergency registration

Perform emergency call

If connected to visited network (roaming)

Perform emergency registration with home network

Perform emergency call via visited network

Emergency Calls for unregistered users are possible

P-CSCF can reject INVITE requests from the UE with 380 (Alternative Service) response,including a 3GPP specific XML document, which can indicate:

that the UE shall use the CS domain to perform the emergency call

that the UE shall perform IMS emergency registration before emergency call


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Thank You!

http://www.3gpp.org

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