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TR 23.771 (SA2)
Study on system impacts of
IMS Emergency Sessions over WLAN

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(W-zip) V13.0.0    2016/06    64 p.

Rapporteur:  Mr. Thiebaut, Laurent
See also:  IMS-Emergency-related TS/TR    

The present document studies the mechanisms needed to support IMS Emergency sessions over WLAN (both in the Trusted -S2a - and in the untrusted -S2b- cases)

The study is split up into 2 phases corresponding to 2 SID (FS_SEW1 and FS_SEW2).

Topics to be studied in phase 1 (FS_SEW1) are:
  • Providing access to EPC over WLAN in order to support an emergency session only in case of "Valid" UEs as in the case 1 in clause of TS 23.401: the support of emergency session is only studied for UEs which (a) have valid credentials to access EPC over WLAN and (b) are authorized to connect to EPC over WLAN in the location where they initiate an emergency session.
  • Providing Location information (in particular for untrusted WLAN). Only existing location determination mechanisms are considered i.e. location determination mechanisms that should not require standard effort. No location accuracy requirements are considered in phase 1.
Phase 1(FS_SEW1) will not consider solutions that imply specification activities in other SDO(s).

Topics to be studied in phase 2 (FS_SEW2) correspond to all the features not covered by phase 1, e.g.:
  • Support of other cases for the access to EPC over WLAN (e.g. the UE is authenticated but is in a location where it is restricted from regular service, or is unauthenticated or has no USIM).
  • Roaming cases (user not in his / her home country).
  • Support of session continuity of emergency sessions at inter-access mobility.
  • TWAN access.


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1 Scope    2 References    3 Definitions and abbreviations    3.1 Definitions    3.2 Abbreviations    4 Architectural assumptions    4.1 General architectural assumptions    4.2 Architectural assumptions for phase 1    5 Key issues    5.1 Key Issue #1: ePDG Selection for emergency services    5.2 Key Issue 2: Providing priority to emergency services especially in case of control plane congestion    5.3 Key Issue 3: providing location information to IMS nodes    5.4 Key Issue 4: Location Privacy    5.5 Key Issue 5: Location at Initial Connection for Voice Service    5.6 Key Issue 6: Determination of Emergency Call Support    5.7 Key Issue 7: Determine if TWAN supports emergency service    5.8 Key Issue 8: Support of unauthenticated emergency session over Trusted WLAN    5.9 Key Issue 9: Support of "unauthenticated" emergency session over Untrusted WLAN    5.10 Key Issue 10: Support for IMS based Non-Voice Emergency Services    5.11 Key Issue 11: Means by which the order in which an emergency session is attempted over the available networks    5.12 Key Issue 12: Handover Active Emergency call from WLAN to 3GPP    5.13 Key Issue 13: Handover Active Emergency call from 3GPP to WLAN    5.14 Key Issue 14: Determine if ePDG supports emergency service    5.15 Key Issue 15: Stay connected to an ePDG that supports emergency service    5.16 Key issue 16: Determine Emergency Call Numbers    5.17 Key issue 17: IMEI check    6 Solutions    6.1 Solution 1: ePDG selection when UE can detect being in the home country    6.2 Solution 2: ePDG selection when the UE cannot know it is in Home Country    6.3 Solution 3 for key issue #3: UPLI via SIP for untrusted WLAN    6.4 Solution 4 for key issue #3: UPLI via EPC for untrusted WLAN    6.5 Solution 5 for key issue #3: UPLI via IKEV2 for untrusted WLAN    6.6 Solution 6 for key issue #3: UPLI to OMA server    6.7 Solution 7 for key issue #3: UPLI to OMA server (fallback use case)    6.8 Solution 8: Location information from LRF for s2a   


1   Scope   Word-p. 7
2   References
3   Definitions and abbreviations   Word-p. 8
4   Architectural assumptions
5   Key issues   Word-p. 10
6   Solutions   Word-p. 15

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