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From: CERF@A.ISI.EDU
Newsgroups: comp.protocols.tcp-ip
Subject: Re: DSU/CSU units
Message-ID: <[A.ISI.EDU]23-Sep-87.13:22:49.CERF>
Date: Wed, 23-Sep-87 13:22:00 EDT
Article-I.D.: <[A.ISI.EDU]23-Sep-87.13:22:49.CERF>
Posted: Wed Sep 23 13:22:00 1987
Date-Received: Sat, 26-Sep-87 11:02:50 EDT
References: <876@saturn.ucsc.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 11

Sorry to seem dense, but I thought the idea behind 8ZBS was to force
some ones in the stream to maintain sync - but that this was done in
a way which the telco did NOT see anything funny. The telco equipment
usually requires that there be some 1s in the data stream every so
often to assure clock synchronization. If a data stream threatens to
send a long sequence of zeros (as a crypto stream might), one puts in
a gadget that will convert 8 zeroes into a different bit pattern, and
on the receiving side, turn them back into zeroes. Why would the telco
see that as lots of line errors?

Vint Cerf