Date: Sun, 17 Mar 1996 01:25:56 -0500 From: "Louis A. Mamakos" <louie@TransSys.COM> To: Tony Kimball <alk@Think.COM> Cc: hackers@freefall.freebsd.org Subject: Re: hackers-digest V1 #986 Message-ID: <199603170625.BAA11556@wa3ymh.transsys.com> In-Reply-To: Your message of "Sat, 16 Mar 1996 23:10:48 CST." <199603170510.XAA16862@compound>
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> From: <hasty@rah.star-gate.com> > > BTW: I am looking around for ADSL modems anyone knows where I can > get two cheap ones! > > PairGain claims their 2d generation models will be out in June/July > "between $600 and $1000". This is the "Etherphone" model. With two > of these and a dry pair, I should get 4Mb/s downloads and 640Kb/s > uploads through my ISP. This presumes that you can get dry pair betwixt you and your "ISP", which is going to be a pretty good trick more and more. When the T1 circuits are delivered muxed up on a T3 bearer, it becomes an interesting problem. It's never really been clear to me how the ADSL stuff gets deployed on the public network, rather than on private facilities. It's getting more and more common that the major telecom facilities in a office building are on fiber systems, either async 150Mbs systems, or OC-3/OC-12 SONET systems. The copper you see is for POTS lines, and it some cases, it pops out of a T1 channel bank at the site. The larger Internet Backbone Operators (like UUNET, who I work for) are looking really, really hard at technologies to aggregate and multiplex customer connections. In the "bad old days", we'd have an seperate external box with a CSU/DSU, V.35 (or EIA 530 cable), and high speed serial port on a router for each circuit. Just working the power, space and cable managment problems for a rack of 16 T1 CSU/DSUs, 16 DSX-1/T-1 cables, and 16 V.35/RS-530 cables is quite a signifcant resource. All that stuff is just there to be broken and take up space, power, and HVAC. The technology in use today has equipment with integral T1 CSU/DSUs. This is solely because of the space and labor (that is operational expense) required to terminate all these T1 connections. When you elimate all those components, the capital costs go down, as do the maintenance costs. The stuff we're looking for tomorrow has DS3 bearers, each carrying a bundle of 28 T1 circuits. That is, a pair of coax right into the termination equipment, and the T1 circuits never see twisted pair cable; they're demuxed in the hardware.. The challange is to figure how how to terminate hundreds of customer T1 circuits per site, and this stuff just has to be compact (or even better, not even there in the first place). The tough part is figuring out where you put random ADSL hardware into this picture. It will be interesting to see what the pentration of ADSL hardware will be into the market. Much of the stuff that I've seen from the local RBOC has been ADSL capacity installed to support video trails, which they're trying to figure out how to use. With more and more customer premise equipment being manufactured with integral T1 CSU/DSUs, it will be interesting to see what they can do with it. From the RBOC's perspective, they'll need a critical mass to want to support this stuff in their infrastructure. The other interesting hardware you may see more commonly is HDSL, which can deliver standard T1 transmission over lesser quality twisted pair facilities. It has the advantage of popping out at a standard DSX-1 signal level, which can be DACS/MUXed easily as required in the Central office, since it's compatible with existing vast infrastructure of T1 transmission gear that they have. > ISDN is obsolete. Hey, the technology works pretty well. It's a tariff/rate problem that needs to be solved.. Louis Mamakos
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