Subject: RE: [mobile-ip] Re: How to move forward in the HAO & ingress filt er discussion

From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Thu, 17 Jan 2002 11:48:38 +0100

> >Hesham 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,
  > > 
  > > Francis wrote in response:
  > > => 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.
  > 
  > Yes, but does that make any significant difference for real 
  > traffic and 
  > applications given than the traffic from CN to MN goes 
  > through the HA 
  > in the triangular case?
  > 
  > For instance assume that the CN and MN are next to each 
  > other (delay 1 ms) 
  > and the HA is 100 ms away from them (one way delay).
  > If you route optimize TCP will see a RTT of 2 ms.
  > If you do triangular the rtt will be 201 ms.
  > If you do bidirectional tunneling the rtt will be 400 ms.
  > You can look at these numbers differently depending what you want to
  > prove. "400/201 = 2" would make your argument.
  > But my argument is that "201/2 = 100".
  > Thus if you care about rtt when the CN/MN are close 
  > compared to the MN/HA
  > delay you should route optimize.

=> Exactly. So I don't see the improvement with triangular
routing over bidirectional tunnelling... for real time
or TCP connections.

Hesham
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