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LTE : How authentication is done when an UE moves from LTE to wifi network ?

+3 votes
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During the Handover from LTE to WiFi, how an UE is authenticated at WiFi network ?
Is there any difference in authentication procedure when UE is handed over to un-trusted or trusted WiFi network ?

posted Aug 18, 2016 by Neelam

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1 Answer

+1 vote

When a LTE UE moves from LTE network to trusted WLAN (handover), it should be authenticated. EAP (Extensible Authentication Protcol)-AKA is used for authentication. EAP-AKA is used for LTE subscribers whose devices have SIM card.
During authentication procedure, authentication messages are exchanged among UE, WiFi-AP (WiFi-access point), TWAG (Trusted Wireless Access Gateway), AAA and HSS.

TWAG is a WLAN core network node which has interfaces with AAA and PGW of LTE network. Interface "STa" is used to exchange authentication and authorization related messages with TWAG and AAA while interface "S2a" is used for establishing data tunnels by using GTPv2 protocol.

In case of un-trusted WLAN, LTE UEs are authenticated with ePDG node by using IPsec tunnel. ePDG node sits in home network while TWAG can be in visited network as well.

One more think, for EAP-AKA based authentication, UE should have support of 802.1x and 802.11i protocol.

For devices which do not have SIM, EAP-TLS and EAP-TTLS based authentication method is used.

Hope it will help you to understand up to some extent.

answer Aug 19, 2016 by Vimal Kumar Mishra
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+3 votes

When an UE moves from LTE to Wifi, how does authentication procedure work ?

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As per my knowledge, WiFI calling is supported over untrusted(using ePDG/S2b) networks from Rel 10 onwards.
But I am not sure about WiFi over trusted(TWAG/S2a) networks and having few doubts.

  1. Is VoWiFI is supported over trusted(using TWAG or S2a) networks, if not then what are the limitation?
  2. Is LTE to WiFI handover supported over S2a interface(TWAG) ?

Any help, pointers will be appreciated.

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