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Understanding Residential Broadband Networks for Internet Connectivity

Learn about the key characteristics of deployed cable and DSL networks, including bandwidths, queueing delays, and loss rates. Explore the challenges in studying residential broadband networks and methods used to measure hosts without direct access.

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Understanding Residential Broadband Networks for Internet Connectivity

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  1. Characterizing Residential Broadband Networks Marcel Dischinger†, Andreas Haeberlen†‡, Krishna P. Gummadi†, Stefan Saroiu* †MPI-SWS, ‡Rice University, * University of Toronto

  2. 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

  3. 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?

  4. Finding broadband hosts to measure • Identified IP addresses of broadband hosts using reverse-DNS lookups • E.g., BellSouth’s DNS names follow the schemeadsl-*.bellsouth.net • Sent TCP ACK and ICMP PING probes to the broadband IPs • 1000s of hosts from 100s of DSL/cable ISPs responded

  5. We focused on 11 major ISPs from North America and Europe • DSL • Cable

  6. How do we measure the broadband hosts? Broadband link Measurement 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 host Last-hop router

  7. Broadband host Last-hop router Are broadband links the bottleneck? • Broadband links are the bandwidth bottlenecks along the measured path • More validation results in the paper

  8. Rest of the talk • Allocated link bandwidths • Packet latencies • Packet loss

  9. 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

  10. Do ISPs allocate advertised link bandwidths? • DSL ISPs allocate advertised bandwidths • Some Cable ISPs do not offer discrete bandwidths PacBell BellSouth Rogers Road Runner

  11. What is the ratio of downstream to upstream bandwidths? • Upstream bandwidths are significantly lower than downstream • Broadband networks are provisioned for client-server workloads Ameritech PacBell Road Runner Comcast

  12. 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)

  13. 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

  14. How large are downstream queueing delays? PacBell • Downstream queues are significantly larger than avg. path RTT BellSouth Comcast Road Runner US coast-to-coast delay Transatlantic delay

  15. How large are upstream queueing delays? PacBell BellSouth • Upstream queues are extremely large • Packets can experience latencies in the order of seconds BellSouth Comcast Road Runner

  16. 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

  17. 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?

  18. Do ISPs deploy active queue management? • 25% of DSL hosts have AQM deployed in the upstream Active queue management (probably RED) (SWBell) Threshold Tail-drop (PacBell)

  19. 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

  20. Thank you! For more information, please contact me at: marcel.dischinger@mpi-sws.mpg.de

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