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Essay: Understanding the performance of the TCP variants in MANET and its behavior with respect to different protocols

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  • Published: 22 September 2015*
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Introduction –
1.1 Background-
To cope with multiple simultaneous data networks internet requires and efficient algorithmic techniques to supports data transmission successfully. Transmission control protocol/Internet Protocol (TCP/IP) has been very effective in data transmission delivery and have also developed variants to posses the possibility to increase performance and multiple packet loss recovery . An important aspect from-
‘ Define the data flow method that applications are responsible for the selection of the protocols and IP plays a central role all TCP and users datagram protocol (UDP) for data transmission.
TCP is reliable and connection oriented protocol developed in 1981. It’s based on simple sliding window flow control, during the early stages congestion collapses occurred because of lack of congestion control mechanism. With the advent of Jacobson congestion algorithms for TCP as a remedy, TCP is updated its new version known as TCP Tahoe. Now currently TCP Reno is widely used in internet. TCP Tahoe congestion control includes slow start, congestion avoidance and fast retransmission.
While in addition to these three algorithms, TCP Reno also adds the fast recovery algorithm.
TCP Reno also adds the fast recovery algorithm. TCP is design for wired network, but with the technology emerging towards wireless medium, the need to implement TCP is of great important but it faces many problem especially in an ad hoc networks. Mobile ad hoc network (MANET) is a famous ad hoc network can be utilized well for emergency situation and military applications. TCP has poor performance in MANET due to dynamic topology, shared medium, higher error ratio: channel connotation and multi hop architecture.
As an evident, ad hoc networks are growing dynamically and its true development fact lies in the problem associated with the seamless internet access and connectivity. With evolution in the hardware devices and software that offers wireless access to the internet by means of an intermediate connection through access point ad hoc tends to improve and increase gradually .mobile ad hoc network is sub field with enormous commercial, industrial and military growth and realistic practical approach for internet access. Most important things to know about the technology is the ability of autonomously establishing and managing the network-
‘ While an effective military consensus applications, data exchange based on mobility networks for commercial purpose i.e. business organization or it could be better utilized during emergency within and out of remote areas. This IP based dynamic wireless networks works effectively, reliable and robust data transmissions.
Problems are associated with in the MANET performance, an evaluation and optimization techniques are necessary to optianed here for the better execution of the transmission medium. data delivery is TCP utmost drawback in wireless network but possible solutions are available to recognize the data transmission effects. To measure the performance of different TCP variants, simulation study has been conducted. MANET utilizes TCP and UDP for data transmission and our study focus on different variants of the TCP i.e. Tahoe, Reno and New Reno explicitly using AODV,DSR and TORA protocols in focus.
Ad-hoc network basically communicate in peer to peer manner, and also work with multi hop communication. It’s never used fixed infrastructure or access point. Ad-hoc network work in decentralized manner. In short we can say that ‘art of networking without a network’ MANET used unlicensed frequency spectrum and send the quick distribution of information around senders. Ad-Hoc wireless network is a part of wireless communication network. This network does not require any infrastructure. It is a distributed Routing network, and it supports for reusing of frequency dynamically. Mobile ad hoc network routing protocols have been classified basically two different categories namely Reactive routing protocol and second one is Proactive routing protocol. In this paper I evaluate the performance of these protocols using different scenario with TCP variants. Here present a comprehensive TCP performance evaluation to understand the nature of the TCP performance in different scenarios likes ‘variable amount of payload and number of nodes. In three different routing protocols (AODV,DSR,TORA) are to be evaluated with three different TCP variants (Tahoe,Reno,New Reno) with three different scenarios having 3,5,8 nodes. Here majoring performance parameters named mainly throughput, congestion window and delay. Final results are based on the simulation results.
Here OPNET simulation tool is used because it provides easy graphical interface, possibility to Develop and run this simulation environment, validity of the simulation results and the tools is highly reliable, robust and efficient. Most important region of selecting OPNET is to its familiarity and trust over the tool.
Keywords: Mobile ad hoc network(MANET),TCP Variants (Tahoe, Reno, New Reno),Routing protocol-AODV,DSR& TORA, OPNET (Simulation Tool),Performance measurements, Delay and throughput by increasing number of nodes.
Fig: Ad hoc network
1.2 Objectives ‘
Thesis aims to understand the performance of the TCP variants in MANET and its behavior with respect to different protocols.
‘ Detail study for technology in TCP and MANET.
‘ Performance comparison in delay and throughput by increasing number of nodes.
‘ Performance comparison between the different protocols used in MANET through congestion window delay and throughput.
‘ Suggest better protocol and TCP variant for MANET.
1.3 Research Questions
Q1: What are different TCP variants and its need?
Q2: What are important routing protocols used in MANET?
Q3: What is the impact on TCP performance during different protocol selection/ implementation in MANET?
Q4: Which factors influence the TCP performance and why?
1.4 Thesis Structure
Chapter 2 defines wireless networks and an extension to ad hoc networks and its working, it also include the detail study about the TCP flavors and its limitations.
Chapter 3 is associated with the study of MANET routing protocols specific to ad hoc networks, their types, working and algorithms.
Chapter 4 depicts the overall project flow explicitly starting form problem definition and following it towards solution, implementation, simulation and results hierarchy.
Chapter 5 contains simulation environment description, list of figures and assumptions.
Chapter 6 holds the brief discussion about the simulation results and future work.
First here to discuss the concept of wireless networks such is infrastructure network and ad hoc (infrastructure less) network. Then before to discuss the different challenges transmission control protocol (TCP) is facing in wireless networks, it is better to give a look to the TCP working mechanism and its different variants.
2.1 Types of Wireless Networks ‘
One of the unique features of wireless networks is compare to wire network is that data is transmitted from one point to another through wireless link i.e. there is no need to wired link between the two nodes for transmission. They just need to be in the transmission range of each other. Wireless networks or divided into two categories.
1. Infrastructure wireless network
2. Infrastructure less or ad hoc wireless network.
2.1.1 Infrastructure Networks :
Infrastructure network have fixed network topology, wireless nodes connect through the fixed point known as base station or access point .In most cases the access point or base station or connected to the main network through wired link. The base station, or access point, is one of the important element in such types of network. all of the wireless connections must pass from the base station .whenever a node is in the range of several base station then it connect to any one of them on the bases of some criteria.
Infra structured wireless networks, the mobile node can move while communicating ,the base stations are fixed and as the node goes out of the range of a base station, it gets into the range of another base station.
2.1.2 Ad hoc Network :
The mobile node can move while communicating ,there are no fixed base stations and all the nodes in the network act as routers. the mobile nodes in the Ad hoc network dynamically establish routing among themselves to form their own network ‘on the fly’.
Fig: Infrastructure and Ad hoc network
2.2 TCP Working mechanism and Variants of TCP :
Transmission Control Protocol (TCP) is a Transport Layer Protocol and originally designed for wired network in 1981.The basic responsibility of TCP is to provide reliable transfer of data between the nodes i.e. to ensure that the data is reached the destination correctly without any loss or damage. The data is transmitted in the form of continuous stream of octets. The mechanism is adopted to assign a sequence number to each octet of data and receiver respond with positive acknowledgement to ensure that the data is received correctly.
Another aspect of TCP is the tree way handshakes mechanism to establish a connection between the end points (nodes). In case if there are two or more TCP connection between the end points for this TCP uses the port assignment mechanism to differentiate each connection from others.
Acknowledgments in TCP ‘
‘ Receiver sends ACK to sender
ACK is used for flow control, error control and congestion control.
‘ ACK number sent is the next sequence number expected.
‘ Delayed ACK : TCP receiver normally delays transmission of an ACK.
‘ ACKs are not delayed when packets are received out of sequence.
Fast Retransmit ‘
‘ If three or more duplicate ACKs are received in a row, the TCP sender believes that a segment has been lost.
‘ Then TCP performs a retransmission of what seems to be the missing segment, without waiting for a timeout to happen.
‘ When can duplicate ACKs occur.
– Loss
– Packet reordering
‘ Assume packet reordering is infrequent.
– Use receipt of 3 dup ACKs as indication of loss.
– Retransmit that segment before timeout.
Fast Recovery ‘
‘ Fast recovery avoids slow start after a fast retransmit.
‘ Intuition: Duplicate ACKs indicate that data is getting through.
2.2.2 Various Flavor of TCP :
After the introduction of first version of TCP several different flavor exist. Here we are discussing the most famous implementation of TCP called Tahoe, Reno, New Reno and Vegas. Tahoe – In the first version of TCP there was no congestion control mechanism. So after observing the congestion collapses 1988 Jacobson introduced several Congestion Control algorithms and this version is called TCP-Tahoe . The Congestion Control algorithms introduced in this version are:
A) Slow start
B) Congestion Avoidance
C) Fast Retransmit Reno ‘ The fast retransmit phase was first introduced in TCP-Tahoe followed by slow start. But TCP-Reno also added the algorithm of fast recovery. So that first Recovery dictates the sender to perform congestion avoidance directly after fast retransmission rather than immediately reducing the data flow using slow start mechanism.
‘ Duplicate ACKs :
– Fast retransmit
– Fast recovery
‘ Fast recovery avoids slow start .
‘ Time out :
– Retransmit
– Slow start
‘ TCP Reno improves upon TCP Tahoe where a single packet is dropped in a round trip time.
Problem with Reno ‘
1. Multiple packet losses with in a window of data.
‘ Terminates recovery prematurely.
‘ Detection of second loss relies on another fast retransmission.
– But with much less incoming dup ACKs.
– Much less new data packets being sending out.
– Lose self clocking. New Reno ‘
TCP Reno recovery only one lost packet during the recovery process. So TCP-New Reno is just adding the capability to TCP Reno to deals with multiple packets losses to recovery in a single transmission window.
‘ When multiple packets are dropped, Reno has problems.
‘ Partial ACK :
– Occurs when multiple packets are lost.
– A partial ACK acknowledgment some ,but not all packets that are outstanding at the start of a fast recovery, take sender out of fast recovery.
‘ Sender has to wait until timeout occurs.
‘ New Reno :
– Partial ACK does not take sender out of fast recovery.
– Partial ACK causes retransmission of the segment following the acknowledgment segment.
‘ New Reno can deal with multiple lost segments without going to slow start.
‘ Remember the outstanding packets at the start of fast recovery.
‘ If a new ACK is Partial ACK, immediately retransmit the following packet, and does not exit the recovery phase.
‘ Upon two dup ACKs, send out one new data packet; keep the ‘flywheel’ running.

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