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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: net.ham-radio
Subject: Re: Re: leased lines
Message-ID: <182@kitty.UUCP>
Date: Tue, 30-Jul-85 23:42:11 EDT
Article-I.D.: kitty.182
Posted: Tue Jul 30 23:42:11 1985
Date-Received: Thu, 1-Aug-85 06:17:44 EDT
References: <103@biomed.UUCP> <207@steinmetz.UUCP>
Organization: Recognition Research Corp., Clarence, NY
Lines: 73

> >      ...  (when she asked me if it would be used for voice, it made me
> > wonder if they sell different kinds of lines , like, voice-quality, and not
> > voice-quality?? What good is a non-voice quality line anyway????) 
> > Bob Lagasse  N 1 A L G
> 
> They were probably wondering if you wanted voice quality or data quality.
> Data quality lines are less noisy than voice quality.  It sounds like you
> want a data-quality leased line.

	There are several basic categories of leased lines:

(1) 	SIGNAL GRADE lines provide metallic continuity and will generally
	provide a frequency response up to 30 Hz.  There is absolutely no
	attempt at loading or other circuit design for voice frequencies.
	Nothing prevents voice frequency use if the loop is short and within
	the same central office.

(2)	TELEGRAPH GRADE lines provide neutral or polar signalling for tty's,
	and are available up to 150 baud.  Voice transmission is not possible
	because all you get are signalling leads from a telco interface.

(3)	VOICE GRADE lines give you a bandwidth of 300 to 3,000 Hz with DC
	continuity if within the same central office.  E&M signalling is
	available if more than one central office is involved, but you
	won't get actual DC continuity any more.

(4)	OFF-PREMISES EXTENSION lines giving you voice frequency range with
	DC and ringing transmission *specifically* intended for use with
	PBX's.

(5)	RINGDOWN TIE LINES like taxicabs, hotels, etc. use.  You pick up a
	non-dial telephone at one end and a similar telephone rings at the
	other end.

(6)	DATA GRADE lines still give you only 300 to 3,000 Hz frequency response
	with *no* DC signalling; however, the lines are carefully designed for
	flat frequency response (i.e., equalized), low noise, low envelope
	delay, low phase jitter, etc.  There are various categories of
	the above parameters called 'conditioning', with typical grades of
	C1, C2, and C3 conditioning.  The higher numbers give better quality
	for more $$$.  Conditioning becomes critical when data circuits must
	run through carrier equipment.

(7)	WIDEBAND DATA lines available in typical bandwidths of 48 kHz and
	256 kHz.  These lines are so expensive it's unreal.

(8)	RADIO PROGRAM lines typically provide *one-way* service for radio
	stations, and are available equalized for 5 Khz and 15 kHz bandwidth.

(9)	VIDEO CIRCUITS where available are gen-u-wine coaxial cable or telco
	microwave link with a 6 MHz bandwidth.  These lines are *so* expensive
	you don't even want to ask...

(10)	DIGITAL DATA SERVICE is pretty much an AT&T offering where you can
	get data circuits with data sets for speeds from 2,400 baud to 1.5
	Mbits/sec.

	There are all sorts of variations of the above, like multi-point lines,
special burglar alarm lines (series circuits), telex/twx lines, etc.

	And then if you want a *real* laugh, ask your telephone company for
Picturephone (tm) service...        :-) to AT&T

	Larry Lippman
	Recognition Research Corp.
	Clarence, New York
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