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
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•
•
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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