On Tue, 15 Jan 2002, Francis Dupont wrote:
>    I haven't heard anyone answering my question as to why
>    reverse tunnelling by the MN thru the HA is so much 
>    worse than triangular routing,
> 
> => d(bidir tunnel) = 2 * d(MN,HA) + 2 * d(HA,CN)
>    d(triangular) = d(MN,HA) + d(HA,CN) + d(MN,CN)
>    d(optimization) = 2 * d(MN,CN)
> and we always have d(MN,CN) <= d(MN,HA) + d(HA,CN)
> so d(optimization) <= d(triangular) <= d(bidir tunnel)
> and even stronger 2 * d(triangular) = d(optimization) + d(bidir tunnel)
> i.e. in my poor English the cost/performance of triangular routing
> is at the middle of bidirectional tunneling and routing optimization.

In theory, yes.  But the question is, does it really make that much of a 
difference as long as at least one way is "unoptimized"?

Practise?  I don't think there's much difference in bidir
tunnel/triangular routing; I doubt e.g. TCP would be able to get much
better performance from triangular than from bi-dir (and there are goals
like hiding your origins that triangular cannot solve).

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords

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