Re: Tor speed

[Scott Bennett <bennett@xxxxxxxxxx>]

     On Fri, 13 Feb 2009 05:56:44 -0600 Drake Wilson <drake@xxxxxxxxxxxx>
wrote:
>Quoth slush <slush@xxxxxxxx>, on 2009-02-13 09:55:45 +0100:
>> But what in the case of short-time overloading? My tip is, that in
>> this case, node is working for somebody faster than for else. I
>> think so, because it can be the reason, why I often have ZERO
>> throughput thru Tor for tens seconds.
>
>One case that has probably been discussed before (but not in this
>thread) is that TCP isn't really good for overlay networks that pass
>many concurrent streams.  TCP enforces in-order delivery of all the
>packets on a connection between two onion routers, when in fact in the
>ideal case, this ordering is not required, and only ordering within
>streams is necessary.  Enforcing full in-order delivery across streams
>magnifies the effects of latency and packet loss, and can cause data

     True enough, but isn't SCTP supposed to handle many streams inside
a connection at once?  And it looks like it would also provide an
equivalent of RDP, which could be used for various kinds of signalling
between the two instances of tor that were connected, all within the
same connection.

>rate allocation between streams to be suboptimal; it's literally true
>that while one stream is tying up the TCP connection, another cannot
>use it at all, even though the streams are effectively preempted after
>transferring a certain number of bits in a slice/cell so that the
>delay does not become unbounded.  (It's rather like pre-emptive
>scheduling of multiple tasks on a uniprocessor computer, in fact.)

     It's also true that network interfaces can only read/write one
packet at a time.  Your point is?
>
>(Theoretically there's going to be enforced-ordering lossage somewhere
>anyway, because the physical world forces this to some extent, but a

     Exactly.

>TCP connection has much more of this than would be present if one were
>using the underlying packet network more directly, I think.)

     But I don't think reimplementing all of that over UDP is necessarily
the optimal way to go about it.
>
>Using a protocol like SCTP might help with this, but that brings up
>various other annoying practical problems that are particularly
>annoying because there's no good reason for them to exist.
>
     Such as?  A list of pros and cons is the kind of elaboration I've
been hoping to get.


                                  Scott Bennett, Comm. ASMELG, CFIAG
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