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Transport Layer Issue Transport Layer Issue in Wireless in Wireless

Ad Hoc and Sensor Ad Hoc and Sensor Network Network

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OutlineOutline Introduction TCP Operation Problem Statement TCP Feedback Ad hoc TCP Conclusion References Questions

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Transport LayerTransport LayerTransport 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. UDPTCP vs. UDP

TCPConnection

oriented service Provides end-to-end

reliable communication

Congestion controlConnection

managementFlow controlWireless 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. UDPTCP vs. UDP

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TCP vs. UDPTCP vs. UDP

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Mobile Ad hoc NetworkMobile Ad hoc NetworkMobile 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 NetworkWireless Sensor NetworkA 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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TCPTCP

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TCP Open OperationTCP Open Operation

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TCP Open OperationTCP Open Operation

Active participant(client)

Passive participant(server)

SYN, SequenceNum = x

SYN + ACK, SequenceNum = y,

ACK, Acknowledgment = y + 1

Acknowledgment = x + 1

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TCP Data Transfer TCP Data Transfer OperationOperation

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TCP Termination OperationTCP Termination Operation

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Active participant(server)

Passive participant(client)

FIN, SequenceNum = x

Acknowledgment = y + 1

Acknowledgment = x + 1

FIN, SequenceNum= y

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Problem Statement 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 misinterpretationTCP misinterpretationThe 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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SolutionSolutionTCP-feedback (TCP-F)Ad hoc TCP or (ATCP)

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TCP-FTCP-FNetwork 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-FTCP-F

N

S B D

G

A

F

E

D

C

RFNRFN

Failed Point

New Route

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TCP-FTCP-F

S B DA C

Faile

d Po

intRFNRFNRFNSnoozing State

C

RRN RRNRRNRRN

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TCP-F issueTCP-F issueIt does not re-calculation the

congestion window upon establishing a new route

Out-of- order packet is not optimizedBit error rate is not considered

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A TCPA TCPATCP 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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ATCPATCPTCP generate probe packet while

the source is in persist modeContinuously probe the network

until a new route is establishedDestination node send ACK

packet

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ATCP AdvantageATCP AdvantageStandard TCP/IP is not modifiedATCP 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 DrawbackATCP DrawbackThe 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. ATCPTCP-F vs. ATCP

TCP-F ATCPHigh 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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ConclusionConclusionTraditional TCP misinterpret route

failure as a congestion problemIt 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 1Why 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 2TCP three way handshaking open operation

is shown in the diagram below. What is the value of x and y?

x=700, y=501

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(client) (server)

SYN, SequenceNum = 500

SYN + ACK, SequenceNum = x

ACK, Acknowledgment = 701

Acknowledgment = y

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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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