Prerequisites for TFO/TrFO

The TFO/TrFO function takes effect only when the calling party and the called party use the same AMR rate. To enable the rate adjustment between two parties, IuUP v2 that supports bidirectional AMR rate adjustment between the RNC  and CN must be used over the Iu interface.

Restrictions:

>>If there are two or more rates in the current AMR rate set and the AMRC function is not enabled, the TFO/TrFO function cannot take effect because the rate of the calling UE may be different from that of the called UE.
>> If the TFO/TrFO function is to be used between a UMTS UE and a GSM UE, the TFO/TrFO function must be supported on the GSM side.

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