G.4 Immediate TFO establishment for AMR

28.0623GPPInband Tandem Free Operation (TFO) of speech codecsService descriptionStage 3TS

G.4.1 Con_Req / Con_Ack used on the TFO Interface

The following protocol flow shows the example where immediate TFO setup is possible, either because both sides use identical Codec Types and Configurations, or because the Codec Types and/or Configurations are compatible in the "lower, contiguous subset". In the latter case potentially an optimisation phase might follow after TFO has been set up.

Figure G.4.1-1: Immediate TFO establishment for AMR with Con_Req / Con_Ack

NOTE: The round trip delay is important for the GSM side for optimal Link Adaptation. It should be as precise as possible and therefore the RNC on the distant side is taken into consideration, but not the Node B or the UE, because that would be too complicated. The round trip delay is not important on the UMTS side, since this radio channel is more stable due to fast power control.

G.4.2 TFO_REQ_L / TFO_ACK_L used on the TFO Interface

The following protocol flow shows the same example as above. This version shows the option with TFO_REQ_L / TFO_ACK_L instead of Con_Req / Con_Ack on the TFO Interface. Please note that these TFO Messages take about 300ms for transmission, while Con_Req / Con_Ack need about 20ms.
In addition this example shows how the Optimal Configuration is reported to the BSC / MSC.

Figure G.4.2-1: Immediate TFO establishment for AMR with TFO_REQ_L / TFO_ACK_L

NOTE: The round trip delay measurement could be done without Config parameters (Par_Type = 00).