G711 as a codec does not replay the last packet received. There are no codecs that have error recovery built into the standard. It is the vendor’s implementation that decides it. That would be the function of the playout buffer no matter which codec you use. G711 is tolerant to packet loss because a sample only amounts ot 125 microseconds of voice where as a sample at other codecs are a much longer sample i.e. g729 10ms. That being said most vendors do not ship a single 125 microsecond sample per RTP packet and buffer at least 10 samples per frame.
G711 is built on nyquist’s theorum stating “in order to accurately reproduce a waveform one must sample twice the frequency” Voice being 3.1khz (in general) and rounded up to 4khz gives us 8000 samples per second. This is what TDM was built upon. 8000 samples at 8 bits per sample give us 64k per channel.