gnu@hoptoad.UUCP.UUCP (11/20/87)
> ...Bell today has > the capability to deliver optical fiber to every house in America, with > a bandwidth of 500 gigabits per second. I was wrong. The figure is > actually half a gigabit per second. (500 megabits/sec) I was only off > by a factor of 1000. This figure is given on page 68 of Brand's book. I doubt that Bell intends to provide switched 500MB/sec cross-country bandwidth; you and everybody else can probably get 500MB/sec through your local central office, perhaps 50MB/sec through your local city, and maybe 5MB/sec cross-country. (Though you could carry on more than one conversation at the lower rates.) If it takes a whole fiber to carry 500MB/sec, and ten thousand people want to talk at that rate from California to New York, they'd have to run 10,000 fibers each 3000 miles long. More likely they run 100 fibers and give you a fraction of the bandwidth. Also note that equipment that runs at 500MHz will not be cheap enough to put into every home, or every phone, "today". Even the lowly 100MHz video in Sun-3's gets its final shifting done in ECL chips, because the TTL/MOS technologies that are easy to build gate arrays & VLSI with don't run quickly enough. (This could've changed somewhat in the last 2 years.) Has anybody designed a "modular telephone jack" for optical fiber? Note that it has to provide a "T" connection, not just an end. Probably it would be more like a contention based bus for around-the-house use, with a full speed gateway at the telco service point. But today's fastest existing and contemplated LANs (FDDI, Hyperchannel, etc) run ~100MBit/sec, and get nowhere near that thruput, due to processing bottlenecks in host interfaces and gateways. Most main memory subsystems can't handle 100MBits/sec -- Ethernet at 10MBits/sec gives them trouble! John
djo@pbhyc.UUCP (11/21/87)
In article <8711201132.AA03014@hop.toad.com> gnu@hoptoad.UUCP (John Gilmore) writes: >I doubt that Bell intends to provide switched 500MB/sec cross-country >bandwidth; you and everybody else can probably get 500MB/sec through >your local central office, perhaps 50MB/sec through your local city, >and maybe 5MB/sec cross-country. I don't know about this. Various versions of TPC have been offering "switched" (i.e., very fast set-up) broadcast-quality video for some time now...broadcast quality video is (equivalent to) 90-135 MB/s. I don't know if it's ever done digitally (I *do* know it's been done digitally with more setup time, as the massive set-ups of fiber installed for the Democratic Convention and the '84 Summer Olympics by my own company, and probably similar setups by other RBOCs.), but the bandwidth is certainly there... ...and if *that* kinda bandwidth's been there for so long, then 500 MB/s can't be too unlikely these days. But note, it's expensive: it's been offered to networks and the like. miru mir, dan'l danehy-oakes Not Officially Speaking For Pacific Bell.
netnews@erc3bb.UUCP (11/22/87)
In article <8711201132.AA03014@hop.toad.com> gnu@hoptoad.UUCP (John Gilmore) writes: >I doubt that Bell intends to provide switched 500MB/sec cross-country >bandwidth; you and everybody else can probably get 500MB/sec through >your local central office, perhaps 50MB/sec through your local city, >and maybe 5MB/sec cross-country. There are various fiber-to-the-home experiments going on, one is in Hunters Creek, somewhere in Fla. Depending on coding, digital full-motion video (i.e. cable TV) requires on the order of 100Mb/s. This is the driving force behind offering services of 100-500Mb/s to the individual user. In such a situation you may have a video front-end at a central office that is then routed to the home's thata want to receive it. In this kind of situation you do not have to worry about transmitting 1000's of individual 500Mb/s data streams over the long-haul portion of the network. It is feasable to have 500Mb/s (and much higher) switched data connections. The question is how much of a demand is there for it, for the RBOCS and long distance carriers to support it. The concept of bandwidth on demand is however one of the ideas behind ISDN. The main question there is how long it takes for ISDN to begin propogating through the network. There are currently many ISDN network trials going on as the major switch manufacturers prove in their ISDN-compatible products. Avi Feldblum AT&T <- given for identification purposes only Disclaimer: The above in no way represents the official position of AT&T
rms@gubba.SPDCC.COM (Rich Sands) (11/23/87)
In article <282@erc3bb.UUCP> Avi Feldblum writes: >The concept of bandwidth on >demand is however one of the ideas behind ISDN. The main question >there is how long it takes for ISDN to begin propogating through the >network. There are currently many ISDN network trials going on as >the major switch manufacturers prove in their ISDN-compatible >products. What newsgroup(s) if any discuss ISDN? Please email rather than post, thanks! -- rms Internet: rms@gubba.spdcc.com, rms@gubba.UUCP UUCP: ...!harvard!spdcc!gubba!rms
fay@encore.UUCP (Peter Fay) (11/23/87)
In article <282@erc3bb.UUCP> netnews@erc3bb.UUCP (Network_News) writes: >In article <8711201132.AA03014@hop.toad.com> gnu@hoptoad.UUCP (John Gilmore) writes: >>I doubt that Bell intends to provide switched 500MB/sec cross-country >>bandwidth; you and everybody else can probably get 500MB/sec through >>your local central office, perhaps 50MB/sec through your local city, >>and maybe 5MB/sec cross-country. > >There are various fiber-to-the-home experiments going on, one is in >Hunters Creek, somewhere in Fla. Depending on coding, digital >full-motion video (i.e. cable TV) requires on the order of 100Mb/s. >This is the driving force behind offering services of 100-500Mb/s to >the individual user. In such a situation you may have a video >front-end at a central office that is then routed to the home's >thata want to receive it. [...] > >Avi Feldblum >AT&T <- given for identification purposes only > >Disclaimer: The above in no way represents the official position of AT&T This whole discussion assumes: 1. A "home" computer can (or will soon) receive data at this rate (as opposed to a TV). 2. A "home" computer can (or will soon) be able to put data on it's bus or store data at this rate. 3. A "home" computer can (or will soon) have enough secondary storage to store, say a few seconds of data (5 secs = 2.5 Gbytes). I have enough contact with fibre-optic data transmission in computers to know that the problem isn't the fibre-optic bandwidth at all. The problem is high-speed transceivers, high-speed buffering, and high memory and bus bandwidth, not to mention secondary storage. It can be done with ECL and high- speed static ram today, but the cost in implementing this and huge memory and secondary storage is daunting to a supercomputer, not to mention a home computer. If one wants to do this hypertext stuff (forgive me, but I'm still not really informed on this) without secondary storage, i.e., just download into memory, then the problem _still_ isn't fibre-optic bandwidth, but latency. Probably 10 Kbytes/sec. would be enough - how fast can you read (or look at graphics), anyway? All one needs is a display latency short enough not to be bothersome to the human reader. -- peter fay fay@multimax.arpa {allegra|compass|decvax|ihnp4|linus|necis|pur-ee|talcott}!encore!fay
kent@DECWRL.DEC.COM (11/24/87)
how fast can you read (or look at graphics), anyway? All one needs is a display latency short enough not to be bothersome to the human reader. Um I want to be able to retrieve real-time video in my documents. That takes bandwidth. chris