Transcript ppt
An Empirical Evaluation of Wide-Area Internet Bottlenecks Aditya Akella (CMU), Srinivasan Seshan (CMU) and Anees Shaikh (IBM Research) • Conventional Wisdom: network edges limit performance –Last mile, acess links of stubs • What if these edges are upgraded? 3 Key Challenges –Where will bottlenecks shift to? • Non-access Bottlenecks What sources to pick? –Prevalence? Location? Characteristics? A. Location • Must have fast access links • Must be geographically disperse • Diverse connectivity Planet Lab Left bar – relative prevalance of bottlenecks • Must probe typical Internet paths • Public exchanges? –Considered congested hotspots Measure paths from sources leading into various ISPs; paths from sources to tier-4 customers of public exchanges How to probe? –Must be able to probe arbitrary destination • Single-ended mode Right bar – relative prevalance in paths • Low tier intra-ISP links are bottlenecks more often than their occurrence suggests What to probe? Dest –Must correctly identify bottleneck link • Report available bandwidth, ASes at either end, latency • Existing tools do not have this functionality BFind • Identifies bottlenecks reliably Rate controlled UDP • Reports available bandwidth Left bar – relative prevalance of bottlenecks Src Traceroute • Identifies bottleneck link, location and ASes at either end Incr/Decr the rate • Monitors each hop for increase in delay • Rate controls UDP if delay builds on a hop Right bar – relative prevalance in paths C. Public Exchanges • Tier-1 to tier-1 links are bottlenecks less often than their occurrence • Opposite is true for links to or from other tiers • Bottlenecks are equally split between intra and inter-ISP links –Equal probability of a bottleneck being a peering link or intra-ISP link –Since number of peering links on a path is smaller, likelihood of the bottleneck actually being at the peering link is higher. B. Latency • High-latency peering links are often bottlenecks, but not high-latency intra-ISP links • Of the 466 paths through public exchanges, 170 (37%) had bottlenecks; 70 of these (15%) were at the exchange –If path through an exchange has a bottleneck, then it is at the exchange itself nearly half the time. D. Bottleneck Bandwidth • • • • Tier-1 and tier-3 internal links have better available bandwidth than tier-2 Tier-4 links typically have low available bandwidth Tier-1 to tier-1 peering links are least constrained Again, tiers 2 and 3 show very similar characteristics E. Summary • Results mostly add weight to conventional wisdom – A few surprises: bottleneck is equally likely to be at a peering link or within ISP – Peering links are not bottlenecks as often as conventional wisdom suggests • Relative performance of ISPs: negligible difference between tiers 2, 3 – Tier-1 is the best and tier-4 the worst for available bandwidth • More than 50% of the paths had bottlenecks – Network is heavily under-utilized