drake@drake.almaden.ibm.com (02/23/91)
In article <39096@muvms3.bitnet> crp002@muvms3.bitnet writes: > >I came up with a transmition rate of roughly 1221 megabytes/second [...] >Is this a practical tranmission >speed? I don't think it is, but if what I think works, we are being really >screwed by the computer industry. Gigabit links are coming (experimentally) but do not exist today. There's nothing in the 10Gbit/sec range as you suggest. You can get several different 100 Mbit/sec systems commercially today. What would be the computer industry's motivation in holding back high speed communications systems? If they existed and worked, why wouldn't they be on the market? High speed links would sell lots of fast CPUs, huge disk drives, and other gear, and would let everyone make gobs of money. I'm certain there's no conspiracy holding such wonders back! :-) Sam Drake / IBM Almaden Research Center Internet: drake@ibm.com BITNET: DRAKE at ALMADEN Usenet: ...!uunet!ibmarc!drake Phone: (408) 927-1861
longc@cs.fau.edu (Courtney Long) (02/23/91)
In article <546@rufus.UUCP> drake@drake.almaden.ibm.com writes: >In article <39096@muvms3.bitnet> crp002@muvms3.bitnet writes: >> >>I came up with a transmition rate of roughly 1221 megabytes/second [...] >>Is this a practical tranmission >>speed? I don't think it is, but if what I think works, we are being really >>screwed by the computer industry. > >What would be the computer industry's motivation in holding back high >speed communications systems? If they existed and worked, why wouldn't >they be on the market? High speed links would sell lots of fast CPUs, >huge disk drives, and other gear, and would let everyone make gobs of >money. I'm certain there's no conspiracy holding such wonders back! :-) > I don't believe that the computer industry is holding back gigabit data communications technology. I do believe that gigabit datacom is possible, although I don't know how to do it myself. As far as the motivation for holding back technology, I postulate the following. Suppose a company is currently at market with product X. X represents the state-of-the art. Naturally the company wants to earn maximum profits on X for the ususal reasons. All of a sudden the same company develops product Y. Y represents a significant improvement over X. Naturally one would expect product Y to be introduced to the market as the latest and greatest and expect the company to gain market share as a result. The only thing is, X is still selling. X is very profitable. The company has an inventory of X. Y is then saved for when X is nearing the end of its business cycle. By the way, I'm much more interested in technical matters than business matters, but thought I'd share my idea! CL > >Sam Drake / IBM Almaden Research Center >Internet: drake@ibm.com BITNET: DRAKE at ALMADEN >Usenet: ...!uunet!ibmarc!drake Phone: (408) 927-1861
john@IASTATE.EDU (Hascall John Paul) (02/25/91)
In article <39096@muvms3.bitnet>, crp002@muvms3.bitnet writes: > > I came up with a transmition rate of roughly 1221 megabytes/second based on > the 100 ns memory of an XT. How, pray tell, do you propose to get 1221 MB/sec from a memory capable of delivering no more than 10M memory cycles/sec? Transfer 122.1 bytes/cycle? I didn't know the XT had such a wide bus! Never mind how you are going transmit 10 Gb/sec (that's well into the microwave spectrum) -- of course, you said expensive, so 1000 ethernets ought to do the job! John -- John Hascall An ill-chosen word is the fool's messenger. Project Vincent Iowa State University Computation Center john@iastate.edu Ames, IA 50011 (515) 294-9551
jrg@otter.hpl.hp.com (John Grinham) (02/26/91)
>>What would be the computer industry's motivation in holding back high >>speed communications systems? If they existed and worked, why wouldn't >>they be on the market? longc@cs.fau.edu writes: >I don't believe that the computer industry is holding back gigabit >data communications technology. I do believe that gigabit datacom is >possible, although I don't know how to do it myself. HP has published papers on a gigabit/second network which has been developed in this lab. There is no conspiracy to hold back gigabit networking, it's just a little bit too expensive for most people .... we'll gladly sell you one if you've got the money though :-) regards, John Grinham. High Speed Networks Dept. ----------------------------------------------------------------------------- John Grinham. HP Labs ISC, Filton Road, Stoke Gifford, Bristol BS12 6QZ, UK. Tel: (0)272 799910 Fax: (0)272 790554 Telex: 449206 jrg@hplb.hpl.hp.com jrg@hplb.hp.co.uk jrg@hplb.uucp -----------------------------------------------------------------------------
dcf@tpc..bellcore.com (Dave Feldmeier) (02/26/91)
When discussing gigabit transmission, one must define where the rate is measured and over what period. For example, multi-gigabit digital transmission lines already carry telephone conversations among major cities. However, a file transfer of 1 gigabit that takes one second from the user's point of view is an entirely different thing. Sending bits down a fiber at multi-gigabit rates is not the hard part. The hard part is controlling the gigabit transmission. The reason that a telephone network can use gigabit lines is that few devices in the network must operate at high speed because the system is circuit switched. The only control that occurs is when a telephone call is set up or shut down. Otherwise, every nth bit in the wire is yours. Packet switching is much more difficult because each packet of data must be interpretted in the period that it takes to transmit one packet. So why do we use packet switching? Packet switching is a more efficient method of resource allocation than circuit switching for traffic sources that are bursty, such as computers. Thus it is cheaper. What do we have to do besides send the bits? The efficiency of packet switching is achieved with dynamic resource allocation. This means that we now need congestion control and flow control to assure that the transmission rate of our data does not exceed the processing rate in the network and receiver, respectively. This is a difficult control problem, particularly on fast and large networks. Another problem is retransmission. If our data must be perfectly replicated at the receiver, then we must retransmit any data that was corrupted or lost in transit. Whether a packet has been lost or is just delayed is a difficult problem in packet-switching network. Once again, the network dynamics make it difficult. If we are slow to respond to loss, the transfer time increases because we let the network go idle even though we could be retransmitting data. If we retransmit too quickly, then we may congest the network with redundant packets. Determining when to retransmit is another tricky control problem. Even if we get the control right, there are few computers that exist today that could use a gigabit network. Most buses are slower than this and the buses aren't faster because the CPU doesn't need a faster bus. As CPU speed increases, bus speed will increase also. The point is that few people need a gigabit data rate now, and so the appropriate machines are rare. Another problem is that if protocol processing is done with a conventional CPU, the CPU may be unable to process data at a gigabit. In summary, packet-switching networks are cheaper because they are more efficient, and they are more efficient because because they allocate resources dynamically. The network dynamics make high-speed transfer difficult because we our control systems are not good enough. If one were willing to spend the money so that a circuit-switched network could be used, then these control problems are simplified. Even if you have a gigabit network, then you will probably need a supercomputer to accept and process data at that rate. The other possibility is to design a system with custom VLSI protocol processors and a high-speed bus. This approach is not cheap either. As has been noted previously, running an application at a gigabit today is possible, but expensive. -Dave Feldmeier P.S. I am exploring multimedia transport protocol design (layer 4) for the AURORA gigabit network.