(56)is　a　one-way　function　that　takes　an　arbitrarily　long　piece　of　plaintext　and　from　it　computes　a　fixed-length　bit　string.(57)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.(58)is　an　approach　preferred　by　cable　TV　providers.　In　this　solution　the　fiber　terminates　at　an　opto-electrical　converter　and　the　final　segment　is　a　shared　coaxial　cable.(59)is　a　device　used　to　connect　two　separate　network　that　use　different　communication　protocol.(60)is　a　digital-to-digital　polar　encoding　method　in　which　the　signal　level　is　always　either　positive　or　negative.