The RTCIceCandidatePairStats property bytesSent indicates the total number of payload bytes—that is, bytes which aren't overhead such as headers or padding—that have been sent so far on the connection described by the candidate pair.

The bytesReceived property reports the number of bytes received so far on the described connection.

An integer value indicating the total number of bytes sent so far on the connection described by this candidate pair. Only data bytes are counted; overhead such as padding, headers, and the like are not included in this count.