From: utzoo!watmath!watcgl!dmmartindale
Newsgroups: net.unix-wizards
Title: Re:  Padding on Ann Arbor Ambassadors &c
Article-I.D.: watcgl.222
Posted: Thu Mar  3 18:22:17 1983
Received: Thu Mar  3 23:47:43 1983
References: sri-unix.5221

I believe that the Request to Send and Clear to Send lines were provided
for use with half-duplex modems - RTS told the modem to turn on its carrier
and CTS indicated that the modem was stable enough for transmission of
data to begin.  Full-duplex modems may provide no useful information
on these signals.  In any case, they certainly aren't propagated
to the modem on the other end of the line, and there are many terminals
in the world connected to computers by modems.  The only possible means
of flow control under these circumstances is some form of "in-band"
signalling, whether it be XON/XOFF or ENQ/ACK or acknowledgement of
received data.  Modem control leads are useful for controlling modems,
but not for end-to-end things like flow control.