Encoding message lengths for data transmission (Corresp.)

Two familiar techniques for encoding message lengths are considered. One technique breaks messages into packets, with each but the last message packet having the same length. The message length is encoded by specifying the last packet and its length. The other technique uses a special bit sequence called a flag to terminate the message and slightly re-encodes the message to prevent the flag from appearing within the message. For a geometric message length distribution and for properly chosen parameters, it is shown that the packet strategy is optimal in the Huffman coding sense and that the flag strategy is very close to optimal. Moreover, for a given expected message length the expected codeword lengths are quite insensitive to the message length distribution.