To the end customer it's not priority, consider the two cases: customer: GET www.site.com/images/rounded_corner.gif first hop to ISP, then n hops to www.site

To the end customer it's not priority, consider the two cases: customer: GET www.site.com/images/rounded_corner.gif first hop to ISP, then n hops to www.site.com vs GET cdn001.site.com/images/rounded_corner.gif first hop to ISP, then second hop to cdn001 The overhead takes place in the routing mechanism, not in the prioritization mechanism. In both cases, it costs the ISP the same amount to send the data back to the customer. The data is not prioritized, it just happens to be available in fewer hops, which is often (but is not necessarily) faster. A CDN could exist that imposed greater latency in exchange for an improvement elsewhere, such as reliability.