Transport Layer Issue
in Wireless
Ad Hoc and Sensor
Network
1
Outline
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Introduction
TCP Operation
Problem Statement
TCP Feedback
Ad hoc TCP
Conclusion
References
Questions
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Transport Layer
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Transport Layer is the
fourth layer of OSI
reference model. It
provided transparent
transfer of data
between end system
using the service of
the network layer.
Two main protocols
are
◦ Transmission Control
Protocol (TCP)
◦ User Datagram Protocol
(UDP)
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TCP vs. UDP
TCP
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Connection oriented
service
Provides end-to-end
reliable
communication
Congestion control
Connection
management
Flow control
Wireless ad hoc and
wireless sensor
network
UDP



Is very simple
connectionless protocol
Does not guarantee
reliability and
correctness of the
sequence of the packet
IPTV, streaming media,
VoIP, and online games
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TCP vs. UDP
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TCP vs. UDP
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Mobile Ad hoc Network


Mobile Ad hoc network (MANET) is self-configured
network which consist of mobile devices within a
communication range of each other
Rapid topological change due to
◦ Mobility of the nodes

Tradition TCP design is not suitable
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Wireless Sensor Network

A wireless sensor network (WSN) is a
collection of sensor network that are
capable of sensing physical phenomena

Rapid topological change due to
◦ Mobility of the nodes

Tradition TCP design is not suitable
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TCP
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TCP Open Operation
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TCP Open Operation
Active participant
(client)
Passive participant
(server)
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TCP Data Transfer Operation
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TCP Termination Operation
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Active participant
(server)
Passive participant
(client)
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Problem Statement
TCP was originally designed and optimized
for a wired network
 In wired network route failure is not
common
 In mobile ad Hoc and sensor network route
failure is frequent and it is unpredictable
 Traditional TCP misinterpreted route failure
as congestion problem
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TCP misinterpretation

The sender TCP attempt to perform
the following:
◦
◦
◦
◦
Invoke congestion control mechanism
Retransmit unacknowledged packet
Enter a slow rate recovery phase
Waste the scarce power and BW of the sender
and intermediate nodes
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Solution
TCP-feedback (TCP-F)
 Ad hoc TCP or (ATCP)

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TCP-F

Network layer provide feedback to the
intermediate node and the source node’s
TCP agent by notification packet
◦ Route Failure Notification (RFN) packet
◦ Rout Re-establishment Notification (RFN) packet
◦ The point where the route is disconnected is
called failed point (FP)

The source node changes from active state
to snoozing state when it receives RFN
◦ The route failure time (RFT) ensures the sender
does not remain in the snoozing state forever
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TCP-F
S
A
RFN
RFN
N
B
C
Failed Point
D
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TCP-F
RFN
S
RRN
RFN
RFN
A
B
RRN
RRN
C
RRN
D
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TCP-F issue
It does not re-calculation the congestion
window upon establishing a new route
 Out-of- order packet is not optimized
 Bit error rate is not considered

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A TCP
ATCP is a thin layer that is inserted
between the IP and TCP
 It listen the network state information
provided by Explicit Congestion Notification
(ECN) and by the ICMP “Destination
Unreachable” message
 The Source node change from active state
to persist state when ICMP message is
detected
 ATCP change from connected to
disconnected mode

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ATCP
TCP generate probe packet while the
source is in persist mode
 Continuously probe the network until a
new route is established
 Destination node send ACK packet

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ATCP Advantage
Standard TCP/IP is not modified
 ATCP is invisible to TCP
 ATCP does not interfere when TCP is
delivering end-to-end message
between a mobile node to a wired
network
 Congestion window is calculated to
adapt with the new route BW
requirement

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ATCP Drawback
The source node can remain in the
persist mode forever
 The probing mechanism can generate
problem in case of high load
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TCP-F vs. ATCP
TCP-F
ATCP
High BER packet lost
Not handled
Handled
Route Failures detection
RFN packet freezes TCP
sender state
ICMP message freezes
TCP sender state
Route reconstruction
detection
RRN packet resumes
TCP to normal state
Probing mechanism
Packet reordering
Not handled
Handled
Congestion window and
RTO after RR
Old CW and RTO
Reset for each new route
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Conclusion
Traditional TCP misinterpret route
failure as a congestion problem
 It has to be optimized to work with
wireless ad hoc and sensor network

◦ TCP -F
◦ Ad hoc TCP
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References
[1] K. Chandran, S. Raghunathan, S. Venkatesan, and R. Prakash, “A Feedback based
scheme for improving TCP performance in ad hoc wireless networks,” in
Conference on Distributed Computing Systems, Amsterdam, Netherlands, May
1998, pp. 472–479.
[2] J. Liu and S. Singh, “ATCP: TCP for mobile ad hoc networks,” IEEE JSAC, vol. 19,
no. 7, pp. 1300–1315, Jul. 2001.
[3] H.AL.Ahmed,A.Eitan,and N.Philippe, “A Survey Of TCP over Ad Hoc Networks,”
June, 2005
[4] “Networking Technology Layer 4,” class notes for ELG 5369, Departemnt of
Electrical and computer Engineering, Univeristy of Ottawa, Ottawa, Fall 2010.
[5] R.Eric, “TCP vs. UDP” May,2004 http://www.skullbox.net/tcpudp.php
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Questions 1

Why is the traditional TCP is not suitable in
mobile ad hoc and sensor network
◦ Because route failure or topological change is misinterpreted as a
congestion problem
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Question 2

TCP three way handshaking open operation is
shown in the diagram below. What is the value of
x and y?

x=700, y=501
(client)
(server)
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Question 3

In TCP-F technique, the route failure notification
(RFN) packet changes the source node’s TCP
state from an active state to a snoozing state.
Before receiving the RFN packet, the source was
transmitting the packet at a rate of 100Kbit/sec.
Upon receiving the route retransmission notification
(RRN) packet, the sender node resumes
transmission. At what rate the source node
resume transmitting?
Answer: 100Kbit/sec
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