A new report by M-Lab concludes that "we observed sustained performance degradation experienced by customers of Access ISPs AT&T, Comcast, Centurylink, Time Warner Cable, and Verizon when their traffic passed over interconnections with Transit ISPs Cogent Communications, Level 3 Communications, and XO Communications.
In a large number of cases we observed similar patterns of performance degradation whenever and wherever specific pairs of Access/Transit ISPs interconnected. From this we conclude that ISP interconnection has a substantial impact on consumer internet performance -- sometimes a severely negative impact -- and that business relationships between ISPs, and not major technical problems, are at the root of the problems we observed.
Observed performance degradation was nearly always diurnal, such that performance for access ISP customers was significantly worse during peak use hours, defined by the Federal Communications Commission (FCC) as the hours between 7pm and 11pm local time. This allows us to conclude that congestion and under-provisioning were causal factors in the observed degradation symptoms.
It is important to note that while we can infer that performance degradation is interconnection-related, we do not have the contractual details and histories of individual interconnection agreements. As such, we cannot conclude whether parties apart from the two we identify are also involved (e.g. in the case that an Access ISP shares an interconnection point with another, etc.). We leave this non-technical question open for further study by others and focus here on the impact of what we can observe on consumer performance through measurement".
See "ISP Interconnection and its Impact on Consumer Internet Performance" - here.