Transcript Presentation - Suraj @ LUMS

Improving TCP
Performance over
Wireless Networks
Project Proposal
Outline
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Wireless Network
TCP
Challenges
Design Issues
Existing Research Work
Research Focus and Directions
References
Wireless Network
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Architecture
Mobile Hosts are connected to Base stations through Wireless and Base
Stations are connected with Wireline Internet
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MH
FH
BS
Radio Tower
MH
MH
Wireline Internet
Satellite Dish
BS
FH
MH
Wireless Access Point
MH
BS
Wireless Network
FH
MH: Mobile Host
BS: Base Station
FH: Fixed Host
Wireless Network
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Issues
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High rate of Packet Loses
Handoff
Large RTT and RTT Variation
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Wireless Network
TCP
Challenges
Design Issues
Existing Research Work
Research Focus and Directions
References
TCP
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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…
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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
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Issues in Wireless
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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
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In short…
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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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Wireless Network
TCP
Challenges
Design Issues
Existing Research Work
Research Focus and Directions
References
Challenges
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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…
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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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Wireless Network
TCP
Challenges
Design Issues
Existing Research Work
Research Focus and Directions
References
Design Issues
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Which part of network to implement the
solution? It can be following…
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Sender
Receiver
Wired part of the Network
Wireless part of the Network
Hybrid Approach
Design Issues
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Which layer to implement the solution? It can
be following…
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Transport Layer
Network Layer
MAC Layer
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Wireless Network
TCP
Challenges
Design Issues
Existing Research Work
Research Focus and Directions
References
Existing Research Work
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TCP-Probing
Indirect TCP (I-TCP)
MTCP
Explicit Bad State Notification (EBSN)
WTCP
Snoop
Existing Research Work
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TCP-Probing
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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
Existing Research Work
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Indirect TCP (I-TCP)
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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.
Existing Research Work
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MTCP
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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.
Existing Research Work
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Explicit Bad State Notification (EBSN)
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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.
Existing Research Work
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WTCP
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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
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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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Wireless Network
TCP
Challenges
Design Issues
Existing Research Work
Research Focus and Directions
References
Research Focus and
Directions
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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.
Research Focus and
Directions
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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.
Research Focus and
Directions
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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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Wireless Network
TCP
Challenges
Design Issues
Existing Research Work
Research Focus and Directions
References
References
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“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