is a one -way function that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string. (72) is a protocol that most USENET machines now use it to allow news articles to propagate from one machine to another over a reliable connection. (73) is an approach preferred by cable TV providers. In this solution the fiber terminates at an optoelectrical converter and the final segment is a shared coaxial cable. (74) is a device used to connect two separate network that use different communication protocol. (75) is a digital-to-digital polar encoding method in which the signal level is always either positive or negative.