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Volume 29 : Issue 11 : "text" Format

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 Re: AT&T asking FCC for "end date" of switched network..

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Date: Sun, 10 Jan 2010 10:55:38 -0800 (PST) From: "harold@hallikainen.com" <harold@hallikainen.com> To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org. Subject: Re: AT&T asking FCC for "end date" of switched network.. Message-ID: <0bd98547-b41c-43cc-beb7-f5a30f603fa4@s31g2000yqs.googlegroups.com> > In the old analog days, a group was not 12 circuits on undersea cable, > but 16 circuits (3 kHz bandwidth instead of 4 kHz) a few groups would > be assembled into a set for TASI.  The circuit gain was well above > 100%.   How is the circuit gain well over 100%? If it's a two way conversation with each person talking 50% of the time, it seems that you'd get a gain of 100% by dropping in other circuits during the idle times in each direction. There are, of course, other pauses, and people don't start talking right when the other person talks (though my wife says I start before she's finished, but that's another story). So, the circuit gain COULD go a bit above 100%. I was assuming they would leave some reserve circuits to handle the times when more than 100% of the people were talking in one direction, but your mention of dropping the encoding level in digital TASI makes sense. They could, I suppose, drop bandwidth per channel on analog TASI, but that seems complex. So, for analog TASI, did they leave some excess circuits to handle the peaks? This sort of multiplexing is interesting. The data stream is bursty (even in analog, since there are pauses with no speech). Without multiplexing, you're stuck with allocating a full circuit to the data. With multiplexing, though, the bursts of one stream can fill in the valleys of another stream, decreasing the required bandwidth. With real time streaming, though, there are times where the peaks coincide and you run out of bandwidth. Moving from real time to near real time by adding buffers, you can shift the peaks such that they do not coincide, then restore the timing at the receive end. I think this works very well for stuff like satellite television where a bunch of channels can be put in one datastream. A scene change in the video results in a spike in the data rate since the entire screen has to be redrawn, instead of just the changes. But, this spike can be time aligned with a static scene where no data is to be sent. With a large enough buffer, you can get real high usage of the available bandwidth. Any excess can, of course, be used for non - realtime data, such as program guide info, subscriber authorizations, etc. With voice, however, latency is really a problem since the speakers become confused. I often get confused on a digital cellphone and start talking over the person I'm talking to (especially my wife, but, again, that's another story). Moving away from TASI a bit, but still staying with statistical multiplexing, I've been giving more thought to network neutrality and traffic shaping. If indeed ISPs are suffering from network congestion, prioritizing of traffic may make sense. Email probably does not have to be delivered as quickly as interactive video. I believe IP has bits allocated to packet priority. ISPs could charge different rates based on the packet priority. They could also go to time of use metering to try to even out the load. Economics could provide a method of allocating limited resources. Anyway, thanks for the TASI discussion. It's been a long time since I saw that system at the AT&T underground building in San Luis Obispo. They had a pamphlet entitled "San Luis Obispo, Communications Center of the World" showing the various Pacific undersea cables. Harold
TELECOM Digest is an electronic journal devoted mostly to telecom- munications topics. It is circulated anywhere there is email, in addition to Usenet, where it appears as the moderated newsgroup 'comp.dcom.telecom'. TELECOM Digest is a not-for-profit, mostly non-commercial educational service offered to the Internet by Bill Horne. All the contents of the Digest are compilation-copyrighted. You may reprint articles in some other media on an occasional basis, but please attribute my work and that of the original author. The Telecom Digest is moderated by Bill Horne. Contact information: Bill Horne Telecom Digest 43 Deerfield Road Sharon MA 02067-2301 781-784-7287 bill at horne dot net Subscribe: telecom-request@telecom-digest.org?body=subscribe telecom Unsubscribe: telecom-request@telecom-digest.org?body=unsubscribe telecom This Digest is the oldest continuing e-journal about telecomm- unications on the Internet, having been founded in August, 1981 and published continuously since then. Our archives are available for your review/research. We believe we are the oldest e-zine/mailing list on the internet in any category! URL information: http://telecom-digest.org Copyright (C) 2009 TELECOM Digest. All rights reserved. Our attorney is Bill Levant, of Blue Bell, PA. --------------------------------------------------------------- Finally, the Digest is funded by gifts from generous readers such as yourself who provide funding in amounts deemed appropriate. Your help is important and appreciated. A suggested donation of fifty dollars per year per reader is considered appropriate. See our address above. Please make at least a single donation to cover the cost of processing your name to the mailing list. All opinions expressed herein are deemed to be those of the author. Any organizations listed are for identification purposes only and messages should not be considered any official expression by the organization.
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