[e2e] TCP to exhibit MTU unfairness?

Anoop Ghanwani anoop at brocade.com
Mon Nov 19 13:48:20 PST 2007

> -----Original Message-----
> From: end2end-interest-bounces at postel.org 
> [mailto:end2end-interest-bounces at postel.org] On Behalf Of Tze-Ven Poh
> Sent: Monday, November 19, 2007 11:43 AM
> To: l.andrew at ieee.org; Detlef Bosau; e2e
> Subject: Re: [e2e] TCP to exhibit MTU unfairness?
> Greetings,
> ----- Original Message -----
> From: "Lachlan Andrew" <lachlan.andrew at gmail.com>
> To: "Detlef Bosau" <detlef.bosau at web.de>; "e2e" 
> <end2end-interest at postel.org>
> Sent: Tuesday, November 13, 2007 10:10 PM
> Subject: Re: [e2e] TCP to exhibit MTU unfairness?
> > Fairness between heterogeneous flows is complicated.  If a flow
> > traverses multiple congested links, it is sensible to give 
> it a lower
> > rate than others using only one of those links.  However, I haven't
> > seen any compelling reason that the rates should depend on RTT or
> > packet size.
> If a few users are on a parking-lot type of network and are 
> all paying the 
> same (monetarily) for the access service, is it fair for the 
> fellow who has 
> to go through multiple congestion links to get lower rate?
> [just a question] 

This can be argued either way.  If a connection is going
through multiple hops, it is already consuming more 
resources in the network (regardless of whether or not
those hops are congested); so the argument for this
case would be that it is probably OK for it to get
a lower rate.  However, routing policy is often dictated 
by someone other than the user, possibly forcing the
user through more hops than may be needed; in this
case, it could be argued that a connection should receive
a rate independent of the number of congested links.

At this point, I don't think it makes a difference.
You get what you get with TCP and it's probably
not going to change any time soon. :-)


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