Good point. I was thinking the 1970s might be too late, even if the 1940s was too early. ;-)
The 4-wire to 2-wire connection is important to know about because it represents an impedance mismatch and may cause echo. It's called the hybrid. The change from 2 wire to 4 wire lets the network apply amplification in just one direction, from what I understand. For the various Cisco classes that cover voice, you need to know about the hybrid. I mostly work above the physical layer, as you can probably tell. ;-) But even a minimal understanding of the physical layer is helpful for understanding full duplex, half duplex, etc. Priscilla At 05:01 PM 12/7/01, Daniel Cotts wrote: >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. ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=28477&t=28270 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
