Your calculation is assuming that all of the traffic from those 4 million London-based users is travelling through LINX. While LINX is the IX for London, not al

Your calculation is assuming that all of the traffic from those 4 million London-based users is travelling through LINX. While LINX is the IX for London, not all traffic originating from London would have to travel through it; Tier 2 and Tier 3 networks would route some portion of the traffic as well. This diagram from wikipedia shows some of the sorts of alternate routes that might be used: http://en.wikipedia.org/wiki/File:Internet_Connectivity_Distribution_%26_Core.svg http://en.wikipedia.org/wiki/File:Internet_Connectivity_Dist... As an aside: does anyone know of a good resource that gives an example of the rough percentage of traffic that would be handled in each of the various ways?