I started working on T-1s in 1969. Actually four wire circuits go way back to analog trunk lines. An amplifier works in one direction only. Two wire circuits went through a two wire to four wire coil at each end.(can't remember the terminology). The circuit was four wire for the long haul. Each transmit was amplified. N carrier circuits again used four wire. The channels were seperated by frequency. L carrier used coax. Can't remember if one or two cables as I didn't work on it. > -----Original Message----- > From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]] m > Subject: Re: Serial links [7:28270] Each side has its own dedicated transmit pair. Big deal. That's been the case on WANs since like the 1940s or something. Well, maybe the 1970s.
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