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<h1>Enhanced Full Rate Codec (ANSI)</h1>

<p>The enhanced full rate codec (EFR) offers high speech quality
to end-users. Tests indicate that better quality or comparable to ADPCM could
be offered with this codec.</p>


<p>From the Air interface dimensioning point of view, EFR
channels need no special attention. The same applies to the A interface because
TCSM2 handles dynamically both FR and EFR coding on the same circuit.</p>


<p>If all the pre-requisites for EFR itself are fulfilled
(TCSM2 etc.), EFR can coexist with no limitations in the previous HR/FR ‘dual-codec’
system, that is, the whole BSS supports ‘triple codec’ approach.</p>


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<p>The basic information of a codec type comes from the MSC.
The BSC will make the final decision about the codec based upon input from
the MSC, the BSS speech coder capabilities and possibly radio channel conditions.</p>


<p>In case of handover, the BSC has the option to change the
speech coder at the time of handover. For intra-BSC handover, the BSC uses
the previously stored information from the MSC/VLR about the speech coder
preferences in the selection process.</p>


<p>The BSC forwards the information of the codec type to the
BTS in a channel activation message. The BTS uses this information to configure
the activated RTSL to support either conventional full rate codec or EFR.
Inband signalling between the transcoder, and the BTS is used to control the
transcoder codec selection on a call basis.</p>
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