I think Larry's description (below) about how STP works is pretty
much accurate modulo 'various levels of details / mechanisms' but
hey, thats what protocol spec's are for :-)
http://www.hippi.org/cST.html
The STP Long Message Transfer stuff is realized to be useful for
network enabled storage - may it be through higher performance
solutions in the upper layer - NFS/BDS etc., or via the lower layers
like SCSI over STP.
What I'd like to add is, that STP also specifies persistent (longer
duration - spanning multiple messages) mappings and pinning down of
memory which is useful for low latency communications a'la clustering
applications. Again, what STP offers here is an open, media-independent
and scalable protocol.
Are there any other applications that people can forsee?
thanks,
:a
> What it does do is give you a high bandwidth, low CPU cycle way of moving
> the data.
>
> The simplified view of STP is really just remote DMA. How it works, again
> greatly simplified, is sort of like this:
>
> client server
> request to send 1GB ->
>
> <- please wait while I set up some pages (optional)
>
> <- clear to send first 100MB of data, here's a cookie
>
> data on wire, prefixed with incrementing cookie ->
> data on wire, prefixed with incrementing cookie ->
> data on wire, prefixed with incrementing cookie ->
> data on wire, prefixed with incrementing cookie ->
> data on wire, prefixed with incrementing cookie ->
> data on wire, prefixed with incrementing cookie ->
> data on wire, prefixed with incrementing cookie ->
> data on wire, prefixed with incrementing cookie ->
> data on wire, prefixed with incrementing cookie ->
>
> -> data hits NIC, cockie is index into CAM, exactly
> like an ethernet switch indexes MAC addresses,
> except that the value here is a physical page
> address instead of an outgoing port
>
> -> data hits NIC ....
> -> data hits NIC ....
> -> data hits NIC ....
> -> data hits NIC ....
> -> data hits NIC ....
> -> data hits NIC .... we're at 75MB or so
>
> server goes off and locks down another 100MB
>
> <- CTS another 100MB (this happens well before the
> first 100MB is drained, so there are no bubbles,
> the pipe is 100% full at all times)
>
> I trust that the SGI guys, who know this stuff better than I, will correct
> and problems with this description. I'm sure there are some, but I'm also
> sure this is pretty close to how it works modulo flow control, security,
> and other important bits.
>
> What's important is that you notice two things:
>
> (a) this is what I call "polite networking". Normal networking is
> impolite, the packets show up on your doorstep uninvited. Here,
> the receiver is nicely asked if it is OK, and gets to set things
> up first. Just like in DMA.
>
> (b) There is some hardware on the NIC that translates from packets to
> physical page addresses, this happens inline, so the packet gets
> DMAed into memory as it is coming off the wire. Very low buffering
> requirements.
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This archive was generated by hypermail 2b29 : Tue Feb 15 2000 - 21:00:27 EST