improving tcp performance over wireless networks project proposal

Improving TCP Performance over

Wireless Networks

Project Proposal

Outline

Wireless Network TCP Challenges Design Issues Existing Research Work Research Focus and Directions References

Wireless Network Architecture

Mobile Hosts are connected to Base stations through Wireless and Base Stations are connected with Wireline Internet

MH

MH

MH

MH

Wireless Access Point

MH

Radio Tower

Satellite Dish

BS

BS

BS

Wireline Internet

FH

FH

FH

Wireless Network

MH: Mobile HostBS: Base StationFH: Fixed Host

Wireless Network

Issues High rate of Packet Loses Handoff Large RTT and RTT Variation

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TCP

Today, Majority of Application Protocols use Internet’s reliable Transmission Control Protocol (TCP).

TCP aims at providing a reliable service with aiming to provide following features… Fairness to other flows that potentially share a channel’s

bandwidth Dynamic Discovery of current availability of bandwidth Congestion Avoidance and Control Optimization of Error Recovery Process

TCP

Issues in Wireless TCP only assume that Packet loss is due to Congestion But in wireless environment Packet loss can be due to

following reasons… High bit Error Rates Handoffs Disconnections

TCP Only resolve the packet Loss issue by decreasing the sending rate

TCP resolution strategy degrades TCP Performance and throughput

TCP

In short… Not Capable of detecting the nature of Error but only the

result of the error Error recovery mechanism is not efficient specially in

Wireless environment Very important need of TCP features for wireless devices

similar to TCP features for wireline devices

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Challenges

Propose TCP must be able perform in wireless environment similar to as current TCP in Wireline network.

Also able to deal with following characteristics of Wireless environment… High bit Error Rate Handoff Disconnections Large RTT and RTT Variation

It should be simple to implement and easy to deploy

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Design Issues

Which part of network to implement the solution? It can be following… Sender Receiver Wired part of the Network Wireless part of the Network Hybrid Approach

Design Issues

Which layer to implement the solution? It can be following… Transport Layer Network Layer MAC Layer

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Existing Research Work

TCP-Probing Indirect TCP (I-TCP) MTCP Explicit Bad State Notification (EBSN) WTCP Snoop


TCP-Probing Monitor the Network status on time out event or

due to three Duplicate Acknowledgements A structured probe segment, is initiated by sender

and sender also suspends all data transmission until probe acknowledgement


Indirect TCP (I-TCP) Splits the transport link at the wireline-wireless

boundary Attempt to hide the effect of wireless losses from

TCP. Loses the TCP’s end-to-end semantics Also causes the high overhead of two

connections at boundary of wireline-wireless.


MTCP Similar to I-TCP except that the last byte of data is

to acknowledged to the source only it is received by the mobile host.


Explicit Bad State Notification (EBSN) If the wireless link is in erroneous state then the

base station sends EBSN message to source for every retransmission of a segment to mobile host. It will require changes at source to incorporate EBSN messages.


WTCP Congestion is detected by inter-packet separation

at the receiver side. Receiver does most of the computations for

congestion control. It requires modifications in both Mobile host and

as well as Fixed host.

Existing Research Work Snoop

Implemented at Data Link Layer Base station, boundary of wireline-wireless network, monitor

packets in both directions. Base Station cache the packets and if detect the duplicate

acknowledgements then it retransmit the packet from cache to mobile host.

Sack is used when traffic is send from mobile host to fixed server.

No change required in fixed host. End-to-End mechanisms will also be preserved. But the Link layer needs to aware that that the segment is of TCP

packet. It can also not be implemented for encrypted headers.

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Research Focus and Directions

As transport layer seems to be most appropriate place for Error Control so my research will focus for the implementation at transport layer.

There may also include lower layers for optimization based on more precise information that could be gathered from lower layers.

My design goals will focus to cover above mentioned challenges maximally.


My intention will be to design the mechanisms which will able to identify the nature of the error due to which packet is dropped. And design of error recovery techniques based on different nature of error.

My initial focus of implementation will be wireless part of the network.


My initial though is that the Wieleline network will provide an interface to wireless network at connection management time to communicate its network characteristics so that during further communication my mechanism will consider these characteristics to detect the nature of the error.

To analyze the performance of identified techniques I will work on Network Simulator named as REAL.

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References “Open Issues on TCP for Mobile Computing” by Vassilis

Tsaoussidis and Ibrahim Matta “Improving Reliable Transport and Handoff Performance in Cellular

Wireless Networks” by Hari Balakrishnan, Srinivasan Seshan and Randy H. Katz

“Congestion Control for High Bandwidth-Delay Product Networks” by Dina Katabi, Mark Handley, Charlie Rohrs

“Comparative Study of Various TCP Versions Over a Wireless Link with Correlated Losses

Presentation on “Introduction to TCP in Wireless Networks by Wan Gang Zeng at Simon Fraser University on July 2003

15th lecture of Topics in Internet Research on Wireless TCP by Satyam Sharma on February 2003

improving tcp performance over wireless networks project proposal

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