Informatics Publishing Limited

J. Govindarajan ¹, N. Vibhurani ¹, G. Kousalya ²

Affiliations
1 Department of CSE, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Coimbatore – 641112, Tamil Nadu, IN
2 Coimbatore Institute of Technology, Coimbatore – 641014, Tamil Nadu, IN

Abstract

In Ad-hoc network, Packet reorder is effect of many causes like congestion loss, packet loss due to corruption, multi-path routing and node’s mobility. Transmission Control Protocol (TCP) performs poorly over wireless links which misinterprets the reordered packets as lost packets due to congestion. This has motivated researchers on developing TCP variants towards packet reordering problem for enhancing TCP performance. Some researchers have found the opportunity to use existing TCP variants like SACK, TCP-Westwood to address the reordering problem. TCP-DCR (TCP-Delayed Congestion Response) and RR-TCP (Reordering Robust TCP) are the TCP variants to acknowledge the packet reordering at the end level. In the existing investigations, the protocols were tested in a simulation environment with one or two causes (congestion or error) at a time over a simple topology. In our experiments, the simulation study of TCP variants has been done with all reordering causes simultaneously, over a large ad-hoc environment including mobility and multi-path routing. A performance analysis had been done using reordering metric (percentage of reordering) which accounts for earlier and lately arriving reordered packets and estimated using throughput and goodput metrics. From our analysis, it is observed that the Selective acknowledgement option of SACK-TCP and the delayed congestion response of DCR help to achieve better performance than other variants in presence of low reordering due to high congestion and low error. However, these variants were failed to meet up their performance in case of high reordering (reordering greater than 50%) due to high congestion loss and high channel error losses. This observation has given the research opportunity to incorporate a discrimination algorithm in the existing reordering solutions to classify the packet error from packet reordering.

Keywords

Analysis, End-to-End Performance MANET, Packet Reordering, TCP

Full Text

   

R. Bala ¹, V. Janani ¹, G. Kousalya ¹

Affiliations
1 Department of Software Engineering & IT [PG], A.V.C. College of Engineering, Mayiladuthurai, Mannampandal – 609 305, Nagapattinam District, Tamil Nadu, IN
2 Department of Software Engineering & IT [PG], A.V.C. College of Engineering, Mayiladuthurai, Mannampandal – 609 305, Nagapattinam District, Tamil NadU, IN

Abstract

Traditionally, mobile communication system is must be designed to cope with data transmission errors that may be introduced due to attenuation, noise and fading. Network protocols have been designed around the conventional metrics of throughput and latency. However, a proper design of these protocols offers many opportunities for optimising the design metric that is more relevant to battery operated devices: the amount of energy consumed per useful user level bit transmitted across the wireless link. Since high error rates are inevitable to the wireless environment, energy efficient error-control is an important issue for mobile computing systems. This includes energy spent in the physical radio transmission process, as well as energy spent in computation, such as signal processing and error control at the transmitter and the receiver.

Since high error rates are inevitable in the wireless environment, energy efficient error control is an important issue for mobile computing systems. When error-correction mechanisms are implemented on general-purpose processors the power consumption that is required to perform the error correction mechanism can be significant. These two methods, Parity code and Reed Solomon code, error correction mechanisms with different characteristics and capabilities will be used.

Keywords

Parity Code, Reed Solomon Code.

Full Text

     

J. Govindarajan ¹, G. Anusuya Devi ¹, G. Kousalya ²

Affiliations
1 Department of CSE, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Coimbatore - 641112, Tamil Nadu, IN
2 Coimbatore Institute of Technology, Coimbatore - 641014, Tamil Nadu, IN

Abstract

In Ad-hoc networks every single node or station takes the responsibility to forward the data packets from the nodes that lie in the range with them. This additional routing responsibility might lead to performance degradation in some cases. Moreover, it is also reported that TCP which is designed for wired networks exhibit poor performance in terms of throughput and fairness in ad-hoc networks. Attempts to alleviate this issue included solutions from both TCP and MAC layer protocol modifications. This work aims at in-depth analysis of MAC level solutions (basic 802.11, 802.11 with RTS/CTS and Collision Detection Mechanism Based-MAC) to address TCP unfairness problem in 802.11-based multi-hop networks. A set of simulation based experiments are conducted and their observations are analyzed using metrics like throughput, goodput and loss probability. The metric loss probability is taken to investigate the protocols both from the perspective of congestion and collision i.e. the impact of congestion window and contention procedure on the end-to-end performance. The results obtained from the simulation revealed the inefficiency of the CDMB-MAC in the scenarios where hidden and exposed terminals do not exist. Further when TCP congestion window is set to 1 the basic 802.11 MAC is found sufficient to provide higher throughput with better fairness among the TCP connections but when TCP congestion window size is increased to 32 the 802.11 MAC with RTS/CTS scheme gives better performance. Added to this all the three MAC protocols fail in the scenario where the source and destination of a connection lie in the transmission ranges of destination and source of other connections. Therefore it can be concluded that it is indispensable to design an adaptive MAC protocol that could provide Fairness among TCP connections in all scenarios.

Keywords

Ad-hoc, Analysis, Fairness, MAC, TCP

Full Text