Many early communications protocol standards, such as RFC 780, 788, 821, 2821, 5321 (for SMTP), RFC 977 (for NNTP) and RFC 1056, were designed to work over such "7-bit" communication links. They specifically require the use of ASCII character set "transmitted as an 8-bit byte with the high-order bit cleared to zero" and some of these[1] explicitly restrict all data to 7-bit characters.