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terminate in analog signal systems. For historical reasons, mobile phone calls that cross network or carrier boundaries use an analog network backbone and are converted from digital to analog signals on one network and converted back to digital signals on the receiving network.
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If one phone uses a high-bitrate codec, and the other a low-bitrate, the user with the high bitrate will be able to hear the user with the low bitrate, but possibly not the reverse.
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Even if all phones used the same audio codec, packet retransmission and re-encoding are still required. When a user makes a call to a
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phone, the audio is digitized into packets that are transmitted from the mobile device and are then decoded into 64 kbit/s
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