characterizing residential broadband networks marcel dischinger †, andreas haeberlen †‡,...

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

3Marcel 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?

4Marcel 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

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

6Marcel 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

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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

8Marcel Dischinger || IMC 2007

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

12Marcel 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)

13Marcel 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

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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

17Marcel 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?

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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

20Marcel Dischinger || IMC 2007

Thank you!

For more information, please contact me at:

marcel.dischinger@mpi-sws.mpg.de