Research

Ad-Hoc Networks

Mobile ad hoc networks are typically characterized by high mobility and frequent link failures that result in low throughput and high end-to-end delay. In order to facilitate communication within the network, a routing protocol is used to discover routes between nodes. The primary goal of such an ad hoc network routing protocol is correct and efficient route establishment between a pair of nodes so that messages may be delivered in a timely manner. Though a large number of routing protocols have been developed for this kind of networks, most of them suffer from implementation difficulties and some inherent incapabilities to cope with highly dynamic scenarios as well as support for Quality of Services (QoS).

The aim of my research is to provide a generic solution to the implementation difficulties of Ad hoc routing protocols in general. We propose to introduce a new layer in between network layer and IEEE 802.11 MAC sub layer. This layer will interact with the underlying MAC layer and provide link connectivity information as well as various other valuable parameters (e.g. received signal strength, network resource usage etc.), which can be used for further enhancement of the routing algorithms.

TCP in Wired cum Wireless Scenarios

Internet access using wireless LANs and cellular links is growing quickly in particular. This has also led to the increase in hybrid (wired cumwireless) networks. The well-known challenge in providing congestion control in a mixed (wired cum wireless) environment is that it relies on packet loss as an indicator of network congestion. In the wired portion of the network a congested router is invariably the likely reason of packet loss (as the probability of a packet loss due to error in a wired network is negligibly small). In the wireless portion, on the other hand, a noisy, fading radio channel is the more likely cause of loss. This creates problem in TCP Reno since it does not possess the capability to distinguish and isolate congestion loss from wireless loss. As a consequence, TCP Reno reacts to wireless loss with a drastic reduction of the congestion window, hence of the sender transmission rate, when the best strategy in fact would be not to decrease the transmission rate. As a result of this its performance, in terms of throughput or goodput achieved by the connection, degrades and in most cases leads to the under utilization of the links.

We proposes a sender-side modification in the TCP congestion control algorithm that improves upon the performance of TCP Reno in wired, wireless as well as wired cum wireless networks. The improvement is most significant in wireless networks which have an inherent loss – prone nature. In fact, the modified TCP performance is not very sensitive to random errors, while TCP Reno is equally sensitive to random loss and congestion loss and cannot discriminate between the two kinds of errors and takes any packet loss as an indication for congestion thereby modifying its sending rate accordingly.The key idea behind the modified sender is to determine the fair share of the connection in a given scenario, compute the congestion window accordingly and keep the congestion window a constant for the rest of the connection.