MEXICO     |             BRAZIL             |      USA -------------------------------------------------------------------------   | | [VoiceGW1]-(WAN)-[VoiceGW2]-QSIG- PBX -ISDN-[VoiceGW3]-(WAN)-[VoiceGW4]     |        \       |                        /       |    FXO       /      MGCP                      \     T1 (ISDN)         |        \       |                        /       |   [PBX]      /     [CCM]                      \    [PBX]     |        \                                /      | [digitPhone] /                                \ [digitPhone]