Mobile + Internet = Performance ?

Jack Y. B. Lee

Department of Information EngineeringThe Chinese University of Hong Kong

(CAHK Innovation Forum, 11 Nov 2011)

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MobileMobile

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Narrowband no more …

Emergence of 3.5G Networks3G/HSPA easily offers 10+ Mbps bandwidth

4G/LTE NetworksOffers bandwidth in excess of 100 Mbps

What do these promise?Mobile bandwidth will soon, if not already, become comparable to fixed broadband;The Internet experience should become as good as fixed network accesses.

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InternetInternet

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All IP NetworksNetwork-Level Compatibility

Mobile data networks support the Internet protocols TCP/IP;Full compatibility with all major Internet applications.

Transmission Control Protocol (TCP)Used in nearly all Internet applications

WWW – HTTP on top of TCPEmail – SMTP/POP3/IMAP on top of TCPFile download – FTP/HTTP on top of TCPMobile youtube – HTTP on top of TCPiPhone video streaming – HTTP on top of TCPCountless others …

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Mobile + InternetMobile + Internet

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Mobile Internet Performance

Experiment #1 – 3G NetworkTestbed Setup

Linux server w/ Apache HTTP Server

Desktop client:(with K4505 modem)OS: WinXP/Windows7

Receiving Throughput (Mbps) Sending Rate (Mbps) TCP

Cubic TCP

Westwood TCP Veno

0.8 0.80 0.80 0.79 1.6 1.56 1.55 1.60 2.4 1.50 1.45 1.60 3.2 1.48 1.49 1.55 4.0 1.56 1.45 1.60 4.8 1.58 1.49 1.48 5.6 1.63 1.65 1.58

Usable bandwidth merely 1.6/6 = 27%!

Desktop client:(w/ USB 3G modem,Microsoft Windows XP)

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Mobile Internet Performance

Experiment #2 – HSPA+ NetworkSignal quality is at average levelMeasured maximum network bandwidth ~8 MbpsUsable bandwidth via Internet TCP protocol:

1.792.021.611.691.84 1.77Over TCP

AverageExp 5Exp 4Exp 3Exp 2Exp 1 Usable Bandwidth (Mbps) 

Usable bandwidth is only 1.79/8 = 22%!

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Mobile Internet Performance

Experiment #3 – LTE NetworkTheoretical maximum bandwidth of 100 MbpsActual measurement results:

50558081Maximum UDP goodput (Mbps)

{RSRP, SINR} {-64, 27} {-81, 27} {-90, 27} {-110, 15}Usable TCP throughput (Mbps)

34 36 30 27

Bandwidth efficiency 42% 45% 55% 54%

Higher signal quality

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Performance ?Performance ?

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TCP over Mobile Networks

Bandwidth EfficiencyVaries from 20% to 50%

What happened to the unused bandwidth?Gone, varnished, lost, nada.

Implication to usersCan’t get all the bandwidth they paid for.

Implication to operatorsCan’t provide subscribers all the bandwidth availableLoss of bandwidth -> loss of network capacity

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Now what?Now what?

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TCP for Mobile Networks

Develop a new, better TCP optimized for mobile networks

Modify an existing TCP variant or develop a new TCP variant for mobile networks.Sender-based, receiver-based, sender-receiver-based.Replace the existing TCP implementation in the operating systems

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TCP for Mobile Networks

An example: TCP-QAOptimized for mobile data networksSender-based, compatible with existing TCP in the client deviceImplemented into the Linux kernelTransparent to Internet servers / applicationsBandwidth efficiency:

Over HSPA network: over 90%Over LTE network: over 90%

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What about existing TCP traffics?What about existing TCP traffics?

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Network-Centric Approach

Mobile Network AcceleratorDeploy inside the operator’s networkCompatible with existing TCPsNo change to client or server

Internet

Internet Servers(Web, Email, etc.)

Mobile Cellular Networks (2.5G/3G/4G)

Mobile NetworkAccelerator

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Network-Centric Approach

Mobile Network AcceleratorPerformance comparison over HSPA network:

5.766.695.675.365.675.41 Accelerated TCP 

1.792.021.611.691.84 1.77Normal TCP

AverageExp 5Exp 4Exp 3Exp 2Exp 1 Receiving Bandwidth (Mbps) 

A potential performance improvement of 3.2x.

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Network-Centric Approach

Mobile Network AcceleratorPerformance comparison over LTE network:

50558081Maximum UDP goodput (Mbps)

94%96%91%91%Accelerator’sbandwidth efficiency

{RSRP, SINR} {-64, 27} {-81, 27} {-90, 27} {-110, 15}Normal TCP throughput (Mbps)

34 36 30 27

Accelerated TCP throughput (Mbps)

74 73 53 47

Accelerator Improvement

2.17x 2.03x 1.77x 1.74x

Higher signal quality

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Mobile + Internet = Performance?Mobile + Internet = Performance?

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The Current State

Today’s mobile data networks really do deliver their bandwidth promisesInternet protocols do not automatically perform optimally over mobile networksThe gap leads to inefficient network utilization, wasting precious network capacity and limiting user experiences

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The Road Ahead

Long-Term SolutionA new TCP design that works well in both wired and mobile networks is needed;Internet-scale deployment will take time.

Near-Term SolutionDeployment of mobile-optimized TCP for Internet servers directly serving mobile users;Deployment of mobile acceleration devices to improve the performance of existing TCP flows.

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AcknowledgementThis work was funded in part by the Innovation and Technology Fund (ITS/014/10) provided by the Innovation and Technology Commission, HKSAR.

Any opinions, findings, conclusions or recommendations expressed in this material/event (or by members of the project team) do not reflect the views of the Government of the Hong Kong Special Administrative Region, the Innovation and Technology Commission or the assessment panel of the Innovation and Technology Support Programme of the Innovation and Technology Fund.

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Thank YouThank You