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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: BigISP<-->SmallISP peerings
On Saturday, Oct 26, 1996, Jon Zeeff writes: > >> all the Real Big ISPs use a technique of routing called 'closest exit'. > >They do, and the effect is that they then wash their hands of the >congestion problems that occur. Congestion where? Closest Exit routing has the effect of getting the packets onto the destination's providers backbone as soon as possible; where the hops from backbone to backbone take place is all that it changes, not the number of hops there are. Which means that with the current dialup customer's typical small-outbound-big-inbound traffic patters, it is the dialup customer's provider (or their provider's provider perhaps) whos backbone is the most congested. >Furthest exit would give a provider >the most control over quality of service but would be expensive*. >* - but many might be willing to pay for it I disagree; if everyone were to do 'furthest exit' (in which you transit outgoing packets across your backbone to the point closest to the destination and then pass them off to the destination's provider's backbone) , routing would still exhibit the asymmetry (and therefore would have the exact same amount of 'control over QoS) it does today. In fact, I believe that the loading would be the same as we have now, but with the labels 'Inbound Load' and 'Outbound Load' reversed. And it's only expensive because everyone is doing closest exit, and so the 'odd man out' trying to do 'closest-exit-to-destination' loses because he then bears the cost of transporting not only his incoming load across his backbone, but his outgoing load as well, when everyone else is mostly bearing the cost of just their incoming load. So in the current internet, yes, if an ISP was to do 'shortest external path' routing, their backbone would carry both their inbound and outbound traffic loads, and hence it its possible that they would have more control over the quality of service, as you pointed out. But let me point out that that situation only lasts as long as everyone else is doing closest exit routing; when they switch to 'shortest external path' then you no longer carry the brunt of the load of your inbound traffic across your backbone. >Best exit (perhaps closest unless there is congestion, then furthest) >doesn't seem possible with current routing technology. What *is* best exit? It's unclear to me which one is better; they're flip sides of the same coin. --Zachary - - - - - - - - - - - - - - - - -
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