[e2e] A simple scenario. (Basically the reason for the sliding window thread ; -))

Joe Touch touch at ISI.EDU
Fri Jan 19 09:17:41 PST 2007

rick jones wrote:
>> In this scenario, the 1500 byte host may be only offering a window of,
>> say 16K.  The splitter offers a window to the 64K host of something
>> like 512K.  This allows the 64K MTU host to send multiple 64K sized
>> packets, which the splitter then sends out as ethernet size packets to
>> the remote host.  In other words, for a 16K vs. 512K scenario, for
>> each window of data transferred between the 64K host and the splitter,
>> there are 32 windows of data transferred out to the remote hosts.
>> Conversely, as 1500 byte packets arrive from the remote host, they are
>> acked and accumulated into larger packets that are then transferred
>> over the 64K MTU network in larger packets.
> Apart from calling it a splitter, superficially at least that resembles
> what some 10G NICs can do today, albeit with some explicit
> knowledge/assistance by the stack.  Large send has the stack(host)
> giving the NIC(splitter) a large "segment" which the NIC(splitter)
> resegments for the link.  Those flow across the ethernet to the other
> NIC(splitter) which if it has Large Receive Offload enabled will
> "upsegment" the ethernet-sized traffic and give larger segments to the
> receiving stack(host).

Right - this looks like a cooperative outboard processor, which makes a
lot of sense in some environments when both the outboard processor and
host are managed/controlled by the same entity, but still makes very
little sense (to me) when that's not the case.


Joe Touch
Sr. Network Engineer, USAF TSAT Space Segment

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