I have not investigated UDT in detail. My sense is that it is pretty much
like TCP but assumes that the bottleneck is actually a fixed rate link, rather
than one with significant variability in the capacity-per-flow available.
I don't think it uses the "biggest gun" that can improve things when the
end-to-end latency gets long: non-ordered delivery acknowledgement coupled with
Fountain Codes (or some other rateless erasure code).
For file transfer (where the only goal is complete delivery of the entire
file), sending every file block independently and using rateless erasure coding
to ensure that any sufficiently large subset of the packets will give the
contents of the file, one can allow the bottleneck link to use packet drops to
signal congestion, while not requiring sequential retransmission.
So if I were starting with fq_codel in the network, I would use a
rate-controlled UDP with Fountain Coding on the file contents, per-file-block
acknowledgment (using a run-length-coded bitstring for blocks correctly
received), and a rate-controller that uses the number of blocks received vs.
blocks sent to detect drops due to buffer overflow to set window size to limit
the number of blocks in transit.
That would maximize FTP, while still allowing "mice" and "ants" and other FTPs
to get great, low-latency, service.
-----Original Message-----
From: "Dave Taht" <[email protected]>
Sent: Friday, February 22, 2013 11:48am
To: [email protected], "bloat" <[email protected]>
Subject: [Cerowrt-devel] Fwd: High Speed WAN Rsync now possible via UDT
Since we are essentially observing "wan" latencies anyway I am curious as to
how the UDT protocol functions... has anyone tried it?
If useful (or scary) I'll try to find the time to package it up for cero.
I liked how mosh solved the terminal emulation problem over lousy links (in
fact, reflecting on it, had it existed in 1998 when I was mucking with the
strip protocol, I'd have not bothered with getting tcp to work at all. :) ) I
also get a kick out of people using ssh to "authenticate" and then dropping to
something else....
---------- Forwarded message ----------
From: Erich Weiler <[mailto:[email protected]] [email protected]>
Date: Fri, Feb 22, 2013 at 10:54 AM
Subject: High Speed WAN Rsync now possible!!!
To: [mailto:[email protected]] [email protected]
Folks-
Just wanted to plug a totally awesome software package from a group I know:
UDR (UDT Enabled Rsync).
For those not familiar with UDT, it is a low level network protocol based on
UDP that allows for high speed transfers over high latency WAN networks:
[http://udt.sourceforge.net/] http://udt.sourceforge.net/
For a while the UDT API was available, developed by the Laboratory for
Advanced Computing at the University of Chicago, but there were little
development around it for actually developing a software suite to allow for
high speed WAN transfers, such as can be achieved by Aspera, GridFTP, FDT, and
a couple others. The problem with those often is:
Aspera: Great but *crazy* expensive
GridFTP: Not bad but non-trivial to set up
FDT: Java (Eh...)
But the awesome thing here is that UDR is a lightweight wrapper for rsync that
allows for rsync functionality, but uses UDT as the underlying protocol for
transfer (no rsh or ssh). It authenticates over ssh and then transfers the
data over UDT streams. And supports encryption.
Right now it is kind of in beta but we've been using it for a while and it's
very stable. It has been tested on Linux, BSD and OSX. It may compile on
other platforms but not much testing has been done on those. Written in C++.
[https://github.com/LabAdvComp/UDR] https://github.com/LabAdvComp/ UDR
You can clone the repo with 'git clone' and build the code. It compiles very
easily and only requires the OpenSSL library as a dependency.
As an example: We have been trying to transfer data from California to our
servers in Germany for a while, and have only be getting 10Mb/s. With UDR we
get 700Mb/s. Not bad.
There are details on the GitHub page. Check it out!!
-erich
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Dave Täht
Fixing bufferbloat with cerowrt:
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