Saturday, 6 November 2010

LTE CS Fallback Procedure

From a 3GPP presentation by Hannu Hietalahti:

1. CS FallBack from EPS to CS domain
2. CSFB reuses voice and other CS-domain services provided by legacy CS infrastructure
3. EPS redirects the UE to CS Domain for CS services
3a. SMS can be delivered to the UE without redirecting to CS Domain
3b. After CS service the UE returns to LTE, depending on coverage and policy
4. User can decide, based on CLI, whether to accept CSFB request
5. Application of CSFB:
5a. CS capable device camping on LTE cell can establish/receive CS services
5b. Reuse of existing CS infrastructure for voice service until IMS VoIP is deployed
5c. Provide voice roaming support with LTE
5d. Support E911 using existing CS infrastructure
5e. Rel-9 IMS provides full emergency call support
5f. Requires overlapping CS domain coverage

Note: CSFB applies between LTE and GSM, WCDMA and 1xRTT

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