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Implementation and Evaluation of a Performance Enhancing Proxy for Wireless

TCP

Master Thesis Project (Sep 03 – April 04)

Dennis DungsTechnical University Munich, Germany

Aalborg University, Denmark

Januar 2004

Supervised byHans-Peter Schwefel

Aalborg University, Denmark

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Agenda

• Goal and steps of this project• Considered Scenarios

– Infrastructure– Mobility– Network traffic

• Implementation– Network setup– Proxy design

• Evaluation of some scenarios• Future Outline• Current Problems

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Goal of this project

• Goal:– Identify TCP performance lacks in wireless scenarios– Evaluate performance capabilites of a TCP Proxy

• Steps– Getting familiar with concepts of TCP– Research about common TCP implementations– Describing wireless scenarios– Analyzing TCP performance and Identifying TCP

performance lacks in wireless scenarios– Designing and Implementing a TCP Proxy– Evaluation of Scenarios using the TCP Proxy

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Considered Scenarios

• Definition:„A Scenario consists of the network infrastructure, mobility and network traffic.“

• Network Infrastructure:– Access Technology– Proxy Location– Sender / Receiver Location– Network configuration

Proxy

Server

Wired Network

MobileHost

Wirelesssupporting Network

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Considered Scenarios

• Mobility– Fixed position– Handover to same subnet– Handover to different subnet– Handover to new access technology

BT -> WLAN -> GPRS -> W-CDMA

• Network traffic– Size of transmitted data– Used bandwith– Single-/Multi-User– Cross-traffic

BSC

WLAN AP

Mobile Node

WLAN AP

WLAN AP

GPRSNetwork

Router

Switch

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Implementation

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Implementation of TCP Proxy - Idea

Application

Split TCP Idea:

Sender Receiver

Split TCP-Daemon

TCP

IP

LL / PHY

Application

TCP

IP

LL / PHY

TCP

IP

LL / PHY

TCP

IP

LL / PHY

TCP Proxy

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Implementation of TCP Proxy - Options

• IP-Header-Option-Solution– Add original IP-Destination-Adress to IP-Header Option– Send every IP packet to Proxy– Unpack IP-packets at Proxy and start a „normal“ TCP/IP-Connection– Disadvantage: Changes in TCP/IP-Stack of connection initiator necssary

• IP-Tunneling– Tunnel the IP-packets from connection initiator to Proxy– Unpack IP-packets at Proxy and start a „normal“ TCP/IP-Connection– Disadvantage: additional IP-Overhead

• Hardware - Solution– Proxy directly integrated in Sender-Receiver-Path– Disadvantage: Different Scenarios need different locations of proxy ->

Maintainance efforts

• ARP – Solution– „emulate“ IP Adresses by faking IP-MAC-Maps– Disadvantage: Difficult to maintain maps– Disadvantage: Timing problems

• Routing-Solution

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Implementation of TCP Proxy – Network setup

10.10.4.X

Tokyo Delft

Legend:Proxy

Aalborg

Fixed Host

Mobile Host

Spjald

Router

10.10.254.254

Mobile Node San Francisco

Toronto

Server

10.10.1.254

TorontoSwitch

WLAN Access Point

8 MBit/s 8 MBit/s

100 MBit/s100 MBit/s

100 MBit/s

100 MBit/s

Policy-Based Routing applied

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Implementation of TCP Proxy – Software Architecture

NIC

Packet-buffer

NIC

Packet-buffer

decode encode

ConnectionConnection

ConnectionConnection

Connection ConnectionSend data

establish connection

close connection

Process packet Create packet(s)

Send data

Data buffer

(Mirror)

Split TCP daemon

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Implementation of TCP Proxy – Current Features

• Mirroring• Split TCP:

– TCP Reno implementation– Slow start– Congestion avoidance– Retransmission timer (partially)– Fast retransmission– Delayed ACKs– Adjustable Maximum Segment Size– Adjustable data buffer– Asymetrical TCP setup

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Evaluation

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Evaluation - Parameters

• Throughput over time

• Round-Trip-Times (RTT)– Average– Jitter

• Transmission time

• Nr. of packets

• Nr. of retransmitted bytes

• Nr. of timeouts– Transmission timeouts

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Evaluation – Measurement Procedure

• IPerf – Setup a TCP connection from sender to receiver– Send data from sender to receiver at maximum

bandwith

• Ethereal – Trace packets at sender and receiver in real-time into

a file

• TCPTrace – Generate TCP Statistics offline

• GNUPlot– Visualizing TCP Statistics (RTT Graphs, Throughput

Graphs)

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Evaluation – RTTs in WLAN

• Comparison of RTTs in WLAN– AP transmission power: 30 mW– Distance to AP: 20 cm– Transmission period: 10 s– TCP Proxy configuration:

• Delayed ACKs off• No Buffer Thresholding• MSS: 1460 Bytes

Samples Average Max Min Std. Dev.

No Proxy 2494 16 ms 57 ms 3 ms 3 ms

Mirror 2500 21 ms 60 ms 3 ms 5 ms

Split TCP Proxy

4455 22 ms 70 ms 3 ms 5 ms

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Evaluation – Distances in WLAN

Room 4

Room 3

Room 2

Room 1 Position #1

Position #2

Position #3

Position #4

Legend:

Mobile Host

WLAN Access Point

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Evaluation – Distances in WLAN

Measurement Options:•AP transmission power: 30mW•Transmission time: 10s•Proxy turned off

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Evaluation – Delayed ACKs in WLAN

Measurement Options:•AP transmission power: 30mW•Distance to AP: 20cm•Transmission amount: 30MB•Symmetrical TCP setup

•Delay Timer: 500ms•MSS: 1460 bytes•No Buffer Thresholding

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Evaluation – Delayed ACKs in WLAN

Measurement Options:•AP transmission power: 30mW•Distance to AP: 20cm•Transmission amount: 30MB•Symmetrical TCP setup:

•Delayed ACKs: 3•MSS: 1460 bytes•No Buffer Thresholding

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Evaluation - WLAN

• More Results (not shown here):– Test-setup (Ethereal) results in bursty captures– Impact of TCP Proxy on Wired->Wired scenario

comparable to WLAN– Sender correlates to Receiver in WLAN– Upstream correlates to Downstream in WLAN – No TCP Retransmissions over WLAN

• Conclusions:– L2-Retransmissions efficient in tested WLAN

scenarios– Standard TCP efficient in tested WLAN scenarios

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Future Outline

• Implementation:– Developing TCP-Mechanism for Handover-Detection– FreezeTCP

• Freeze Sender by advertising a zero Window• Recover sender by:

– 3 Duplicate ACKs (slow-start)– 1 Non-Zero Window ACK (fast recovery)

• Evaluation:– Impact of Buffer-Thresholding– Multi-User WLAN Scenarios– GPRS– Bluetooth– W-CDMA– MobileIP / Handover Scenarios

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Current Problems

• Ethereal not working with PPP in Windows NT/2000/XP (-> BT LAN, GPRS)

• No globally routable IP-Address available in GPRS

• Handover to same subnet: switching table• MobileIP not running• MobileIP-Setup over GPRS• No Bluetooth Equipment available• No W-CDMA Equipment available• Bugs,....

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References

• Project WebSite: http://kom.auc.dk/~dennis/

• IPLab WebSite:

http://kom.auc.dk/iplab/

• WLAN Evaluation Project:

http://kom.auc.dk/~ruipt/

• RFCs : RFC791 (IP), RFC793 (TCP)

• eMail: dennis@kom.auc.dk

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Thanks for listening!

Any Questions?

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Backup

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Current IPLab network architectureIP LAB: Current Architecture

Delft

Internet

Toronto

Frankfurt

Shanghai

Sydney Dhaka

Tokyo

San Francisco 130.225.51.6

10.10.1.210.10.2.2

10.10.2.1 10.10.1.1

Aalborg

10.10.2.254

Spjald10.10.4.2

10.10.1.254

Shanghai

10.10.3.254

10.10.254.254

Toronto10.10.3.1

GPRS Network