[LARTC] Question - duplication of packets for reliability

[Peter Lister Peter Lister <P.Lister@sychron.com>]

<PRE>We have offices in the UK and the US, both with DSL connections. Linux
routers at both ends. We frequently get high packet loss (&gt;10%) and
have had occasional ISP router outages. Yes, we can spend more money
on a leased line, but even so, the transatlantic / continental
carriers on the leased line have had routing problems when the DSL has
been OK. TCP traffic becomes very slow with any appreciable packet
loss - terminal traffic is very slow indeed. End-to-end service
providers cost a fortune - and we don't need very high bandwidth. The
speed of light dictates that we'll always have fairly high latency, so
any retransmissions will be noticeable.

So - it occurs to me that we could use multiple cheap DSLs at both
ends from different telcos/ISPs to guarantee that office-office comms
work. My thought is that something like eql (I'll call it &quot;dup&quot;) can
be adapted to duplicate all packets down several links rather than
distributing packets down each link.

             UK              US

         uk-dsl0 ---------  us-dsl0
                 \___  ___/
      /              \/              \
  uk-dup0         ___/\___            us-dup0
      \          /        \          /
         uk-dsl1 ---------  us-dsl1


Every packet into dup0 generates 4 packets out (eth0-eth0, eth0-eth1,
eth1-eth0, eth1-eth1). The exact mechanism isn't the point (I imagine
4 VPNs of some sort, enslaved by dup in the same way as eql) - we just
make multiple packets end up at the destination router somehow.

Q 1: Does mass duplication cause problems to e.g. TCP, which probably
expects a small amount of duplication in the same way that it expects
a small amount of packet loss?

Q 2: Are there any alternative / better (Linux) solutions to provide
this sort of resilience over high latency connections?

Q 3: Has anyone written &quot;dup&quot; ? :-)

-- 
Peter Lister         <A HREF="mailto:P.Lister@sychron.com">P.Lister@sychron.com</A>    PGP (RSA): 0xE4D85541
Sychron Ltd          <A HREF="http://www.sychron.com">http://www.sychron.com</A>  PGP (DSS): 0xBC1D7258
1 Cambridge Terrace  Voice: +44 1865 200211
Oxford OX1 1UR  UK   FAX:   +44 1865 249666




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