Transcoder selection in media resource group/list

Hi all,

I read some documents for Transcoder. But, I still concern about Transcoder/media resource group/list selection. For Example:

Phone1 with:

  region: re1

  transcoder : xcoder1

  Media resource group: mrg1

  Media resource group list: mrgl1

CUE  support only G711 codec with:

  region: re2

  transcoder : xcoder2

  Media resource group: mrg2

  Media resource group list: mrgl2

Inter region between re1 and re2 : G729.

So, When Phone 1 makes call to CUE, which xcoder is involved?

Please clarify for me?

Thanks

Thuc