characterizing residential broadband networks marcel dischinger †, andreas haeberlen †‡,...
TRANSCRIPT
Characterizing Residential Broadband Networks
Marcel Dischinger†, Andreas Haeberlen†‡, Krishna P. Gummadi†, Stefan Saroiu*
† MPI-SWS, ‡ Rice University, * University of Toronto
2Marcel Dischinger || IMC 2007
Why study residential broadband networks?
Used by millions of users to connect to the Internet
Rapidly growing user base
Used for many different workloads:
Music / movie downloads, VoIP, online games
Yet, researchers know little about the characteristics of
deployed cable and DSL networks
Such as provisioned bandwidths, queueing delays, or loss rates
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Why do we know so little?
Commercial ISPs have no incentives to reveal information about their network deployments
Researchers lack access to broadband networks
Testbeds composed of academic nodes
PlanetLab only has two DSL nodes
Prior studies were limited in scale
Largest study so far had 47 broadband nodes [PAM’04]
Prior studies depended on access to the broadband hosts
Challenge: Can we measure hosts without access to them?
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Finding broadband hosts to measure
Identified IP addresses of broadband hosts using reverse-DNS
lookups
E.g., BellSouth’s DNS names follow the scheme
adsl-*.bellsouth.net
Sent TCP ACK and ICMP PING probes to the broadband IPs
1000s of hosts from 100s of DSL/cable ISPs responded
5Marcel Dischinger || IMC 2007
We focused on 11 major ISPs from North America and Europe
DSL
ISP Ameritech BellSouth PacBell Qwest SWBell BT Broadband
Region S+SW USA SE USA S+SW USA W USA S+SW USA UK
HostsMeasured 113 155 158 97 397 173
ISP Charter Comcast Road Runner Rogers Chello
Region USA USA USA Canada Netherlands
HostsMeasured 114 118 301 148 120
Cable
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How do we measure the broadband hosts?
We measured from well-connected hosts in University networks TCP ACK / ICMP PING probes sent at 10Mbps for a short duration
Probes saturate the bottleneck, which is often the broadband link TCP ACK probes saturate just downstream direction
ICMP PING probes saturate both directions
We analyzed probe responses to infer various characteristics
Internet
Broadband link
Broadband host
Measurement hosts
Last-hop router
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Are broadband links the bottleneck?
Broadband host
Last-hop router
Broadband links are the bandwidth bottlenecks along the
measured path
More validation results in the paper
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Rest of the talk
Allocated link bandwidths
Packet latencies
Packet loss
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Outline
Allocated link bandwidths
Do broadband providers allocate advertised link bandwidths?
How do the downstream and upstream bandwidths compare?
Are broadband bandwidths stable over the short-term?
Are broadband bandwidths stable over diurnal time-scales?
Is there evidence for traffic shaping?
Packet latencies
Packet loss
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Do ISPs allocate advertised link bandwidths?
DSL ISPs allocate advertised bandwidths
Some Cable ISPs do not offer discrete bandwidths
PacBell
BellSouth Rogers
Road Runner
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What is the ratio of downstream to upstream bandwidths?
Upstream bandwidths are significantly lower than downstream
Broadband networks are provisioned for client-server workloads
PacBell
Comcast
Road Runner
Ameritech
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Are link bandwidths stable over the short-term?
DSL bandwidths are relatively stable, while cable are not
Hard for protocols like TCP to adapt to highly variable cable BWs
Unstable (Rogers cable host)
Stable (PacBell DSL host)
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Outline
Allocated link bandwidths
Packet latencies
How large are broadband queueing delays?
Queues should be proportional to the end-to-end RTT
Recent research recommends even shorter queues [SIGCOMM’04]
How do cable’s time-slotted policies affect transmission delays?
Do broadband links have large propagation delays?
Packet loss
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US coast-to-coast delay
How large are downstream queueing delays?
Downstream queues are significantly larger than avg. path RTT
PacBell
BellSouth
ComcastRoad Runner
Transatlantic delay
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How large are upstream queueing delays?
Upstream queues are extremely large
Packets can experience latencies in the order of seconds
BellSouthPacBell
BellSouth
Comcast
Road Runner
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Why are large queues worrisome?
Large queues avoid losses at the cost of latency
Good for web workloads
But, bad for popular emerging workloads
Interactive traffic like VoIP and online games
Multimedia downloads like music and movies
Low latency vs. maximum bandwidth
TCP does not fully drain large queues after a loss event
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Outline
Allocated link bandwidths
Packet latencies
Packet loss
Do ISPs deploy active queue management (AQM)?
Tail-drop queue
Active queue management techniques, such as Random Early Detect (RED)
Do broadband links see high packet loss?
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Do ISPs deploy active queue management?
25% of DSL hosts have AQM deployed in the upstream
Active queue management(probably RED) (SWBell)
Tail-drop(PacBell)
Threshold
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Conclusion
We presented the first large-scale study of broadband networks
Measured their bandwidth, latency, and loss characteristics
Broadband networks are very different from academic networks
Cable networks have unstable bandwidths
Large queues can cause latencies in the order of seconds
Broadband links have low loss rates, show deployment of AQM
Our findings have important implications for network operators
and systems designers
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Thank you!
For more information, please contact me at: