Measurements of in motion 802 11 networking
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Measurements of In-Motion 802.11 Networking. Richard Gass and James Scott Intel Research Cambridge Christophe Diot Thomson. Outline. Motivation Experimental Setup Results Conclusions. Motivation. 802.11 Access Points are everywhere Predominant usage model is stationary

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Measurements of In-Motion 802.11 Networking

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Measurements of in motion 802 11 networking

Measurements of In-Motion 802.11 Networking

Richard Gass and James Scott

Intel Research Cambridge

Christophe Diot

Thomson


Outline

Outline

  • Motivation

  • Experimental Setup

  • Results

  • Conclusions

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Motivation

Motivation

  • 802.11 Access Points are everywhere

  • Predominant usage model is stationary

    • Periods of use measured in minutes or hours

    • User stationary or slow-moving during use

    • Device in standby between uses

  • New and future devices are “always on” and have 802.11

    • PDAs or push-email devices

    • Smart phones with WiFi e.g. Imate SP5

    • Low-power long-life trend in notebook computers

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Our research study in motion use of 802 11 aps

Our research: Study in-motion use of 802.11 APs

  • How does off-the-shelf equipment perform

    • Without using additional antennae or other hardware

    • Without tweaking the link layer parameters

  • Is the wireless channel well behaved?

    • Is it resilient to relative speed of device and AP?

    • How does a channel perform over the course of a drive-by?

  • What should in-motion users expect?

    • Study backhaul network effects as well as WiFi

    • Study performance of current applications in this scenario

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Measurements of in motion 802 11 networking

Experiment location

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Measurements of in motion 802 11 networking

  • Straight

  • Flat

  • Nobody around

  • Can test a range of speeds

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Experimental setup

Experimental setup

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Measurements of in motion 802 11 networking

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Measurements of in motion 802 11 networking

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Hardware software used

AP

Linksys WAP55AG

Out of the box configuration

Laptops – IBM Thinkpads

T30 : Backhaul Simulator

T41 : Mobile Client

T42 : Stationary Server

Operating system

Linux Fedora Core 3

Wireless Cards

Intel 2915ABG (In-Motion)

Netgear WAG511 (monitoring)

DHCP not used

Traffic Generation

TCP - iperf

HTTP - wget and apache

UDP – bash /dev/udp interface

Traffic Collection

Tcpdump (layer 3)

Kismet (layer 2)

Hardware/Software used

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Experimental procedure

Experimental procedure

Start scripts

Get to target speed

Hit “enter” as first marker passed

Deassociate

Out of range

Hit “enter” as last marker passed

Association happens and data transfer starts

Set experimental parameters

Confirm experimental parameters

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Experimental parameters

Experimental parameters

  • Various speeds from city speeds to highway speeds

    • 5, 15, 25, 35, 55, 75 mph target speeds

    • Actual speed measured by noting the time over the 1000m range

  • Various traffic types

    • TCP – 1500 byte packets

    • UDP – Cycling packet sizes 50, 100, 200, 400, 800, 1500

    • HTTP – Downloaded local caches of 6 popular webpages

  • Backhaul network

    • Direct link (100Mbit/s Ethernet)

    • 1 Mbit/s bandwidth limit

    • 100 ms added latency each way

    • Both bandwidth limit and added latency

  • 2 repetitions of each run

    • Total number of runs : 108

    • Four 12-hour days for 4 people

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Distance in range

Distance in range

  • Speed reduces usable range

  • But not to zero!

392 Meters

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Association time

Association time

  • Transfer opportunity decreases with speed

  • Association time effectively levels out while time associated continues to fall with speed

  • Significant transfer opportunities still exist

13.7 sec

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Total data transferred

Total data transferred

  • Data transferred follows expected behaviour (1/x)

    • In-motion channel not crippling transfers

  • Useful amounts of data transfer possible

    • 25mph : 27 MB

    • 55mph: 8 MB

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Instantaneous throughput

Instantaneous throughput

  • We saw the same channel “phases” as Ott/Kutscher

    • Entry phase where bandwidth ramps up

    • Production phase with full, constant bandwidth

    • Exit phase with bandwidth ramping down

Entry

Production

Exit

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Measurements of in motion 802 11 networking

5 mph

35 mph

75 mph

5.5Mbit/s

TCP

3.5Mbit/s

UDP

HTTP does not utilize channel

1.8Mbit/s

HTTP

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Packet loss udp

Packet loss (UDP)

Does the size of the packet have an effect?

  • < 1% loss (for all traces)

  • Packet size has little effect at network layer

  • Link-layer examination shows:

    • Virtually no loss in production phase

    • Majority of losses at link layer occur at edge of wireless range

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Backhaul effects on tcp

Backhaul effects on TCP

  • Bandwidth limit has obvious effect

  • Latency is coped with by TCP

  • Transfer sizes drop by ~4x

Delay

BW limit

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Backhaul effects on http

Backhaul effects on HTTP

  • Opposite effects to TCP:

    • Bandwidth limit has little effect

    • Latency is deadly

  • Due to high number of round-trips to download webpages

    • Get index, here is index, get image 1, here is image 1, etc

    • Each using slow start (pipelining does not help across servers)

  • Transfer size drops ~15x

  • With backhaul, http wastes >90% of bandwidth

BW Limit

Delay

WMCSA-06

April 6-7, 2006Semiahmoo Resort, Washington, USA


Implications

Implications

  • 802.11b provides useful transfer sizes while in-motion

    • Even using off-the-shelf equipment without modifying link layer

    • Without adding external antennae

    • Periodic in-motion opportunities could support user needs

  • Must make transfers asynchronous with human activity

    • No time for manual authentications e.g. for AP, VPN or email

  • Start-of-day protocols (DHCP, VPN, etc) execute during entry phase

    • Must cope with varying channel conditions which might cause loss etc

    • Cannot afford many round trips, or long timeouts to retransmit

  • Application layer protocols (HTTP, IMAP, SMTP, etc) need to reduce round-trip reliances to make better use of short connections

    • E.g. by adding a “bulk” mode to the protocol

  • WMCSA-06

    April 6-7, 2006Semiahmoo Resort, Washington, USA


    Our future work

    Our future work

    • Haggle – networking framework for mobile devices allowing applications to make use of all connectivity opportunities, including neighbourhood, in-motion, infrastructure, device mobility, etc

    • YAAP (Yet Another Access Point)

      • Personal, always-on device acting as network proxy for notebook, etc

      • Can opportunistically utilize in-motion connections and later provide the data to laptop when it comes out of standby

    • We are running a demo now: try it out!

      • Connect to access point “yaap-01” with 802.11

    WMCSA-06

    April 6-7, 2006Semiahmoo Resort, Washington, USA


    Measurements of in motion 802 11 networking

    Thanks

    Questions/Comments

    More info:

    http://www.cambridge.intel-research.net/haggle/research.php

    Traces available online

    WMCSA-06

    April 6-7, 2006Semiahmoo Resort, Washington, USA


    Backup

    BACKUP

    WMCSA-06

    April 6-7, 2006Semiahmoo Resort, Washington, USA


    Measurements of in motion 802 11 networking

    WMCSA-06

    April 6-7, 2006Semiahmoo Resort, Washington, USA


    Measurements of in motion 802 11 networking

    WMCSA-06

    April 6-7, 2006Semiahmoo Resort, Washington, USA


    Measurements of in motion 802 11 networking

    WMCSA-06

    April 6-7, 2006Semiahmoo Resort, Washington, USA


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