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    SubjectRe: XTP: A better TCP than TCP
    On Thu, Jun 03, 1999 at 01:49:30PM -0400, Greg Lindahl wrote:
    > > I think a much more interesting protocol to have in the kernel would
    > > be Bell Labs' IL. It's implemented in Plan 9, and they say they are
    > > very happy with its performance. It's a sequenced packet protocol,
    > > ideal for NFS, CORBA messages and pretty much anything which currently
    > > either implements its own out-of-order + retransmit strategy over UDP
    > > or puts packet boundaries into TCP.
    > Note that IL has no flow control. You may not think you need flow
    > control, but the minute you have several people talking to 1 at high
    > speed, life gets interesting. A group I used to work for (Legion) had
    > its own IL-like protocol, and we finally decided that TCP's flow
    > control was a huge win locally (our Legion-MPI programs were
    > overrunning the 64k OS buffers), and TCP's adaptive stuff was far
    > superior over WANs.

    As I understand it, the idea behind not requiring flow-control in IL
    was that the higher level protocols would take care of this; in 9P
    (which is the main user of IL), there's a reply to each request, so if
    the server is replying slowly, the client will slow down to compensate.
    I don't think IL is suitable for simply sending packets to hosts, it
    must have a request-response protocol layered on top of it.

    Yes, this requires the higher level protocol knows about doing
    flow-control stuff like nagle, but the idea is that the TCP layer doesn't
    _really_ know what the application requires and setting options such as
    TCP_NODELAY is a crude way of telling it.

    Matthew Wilcox <>
    "Windows and MacOS are products, contrived by engineers in the service of
    specific companies. Unix, by contrast, is not so much a product as it is a
    painstakingly compiled oral history of the hacker subculture." - N Stephenson

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