Transcript 3GPP IMS Emergency Calls Stage 3 Update

3GPP IMS Emergency
Calls Stage 3 Update
Georg 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
Specified emergency categories
Fixed Broadband
Access
PSAP= Public Safety
Answering Point
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WLAN 3GPP IP
access
3GPP IMS
core
PSA
P
Emergency
Control Centre
Emergency
Control Centre
Emergency
Control Centre
IWF
GPRS access
PSTN/ CS core
3GPP LTE
access
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Emergency
Control Centre
h
p
f
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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Emergency Registration and Emergency Call
GGSN in Home Network
Home Network
P
I
S
Emergency Call
P
E
Emergency CSCF
Visited Network
IMS Emergency APN
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Public Safety
Answering Point
(PSAP)
Emergency Registration and Initiating the E-Call
• If UE detects, that emergency call needs to be made (based on dialled number / URI), it
shall
• 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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