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

2 Marcel 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

3 Marcel Dischinger || IMC 2007 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 Marcel Dischinger || IMC 2007 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

5 Marcel Dischinger || IMC 2007 We focused on 11 major ISPs from North America and Europe  DSL ISPAmeritechBellSouthPacBellQwestSWBell BT Broadban d RegionS+SW USASE USAS+SW USAW USA S+SW USA UK Hosts Measured ISPCharterComcastRoad RunnerRogersChello RegionUSA Canada Netherland s Hosts Measure d  Cable

6 Marcel Dischinger || IMC 2007 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

7 Marcel Dischinger || IMC 2007 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

8 Marcel Dischinger || IMC 2007 Rest of the talk  Allocated link bandwidths  Packet latencies  Packet loss

9 Marcel Dischinger || IMC 2007 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 Marcel Dischinger || IMC 2007 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 Marcel Dischinger || IMC 2007 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

12 Marcel Dischinger || IMC 2007 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 Marcel Dischinger || IMC 2007 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 Marcel Dischinger || IMC 2007 US coast-to-coast delay How large are downstream queueing delays?  Downstream queues are significantly larger than avg. path RTT PacBell BellSouth Comcast Road Runner Transatlantic delay

15 Marcel Dischinger || IMC 2007 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

16 Marcel Dischinger || IMC 2007 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 Marcel Dischinger || IMC 2007 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 Marcel Dischinger || IMC 2007 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

19 Marcel Dischinger || IMC 2007 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 Marcel Dischinger || IMC 2007 Thank you! For more information, please contact me at: