In TCP-Reno, when the packet loss occurs, a TCP receiver sends a duplicate ACK immediately while a TCP sender utilizes a fast retransmit mechanism, where the arrival of 3 duplicate ACKs indicates that a packet has been lost and recovers the missing packet without waiting for a retransmission timer to expire. A fast recovery algorithm, in turn, governs the transmission of new data packets until a non-duplicate ACK arrives.
TCP-Vegas introduces a proactive congestion avoidance technique which does not violate the congestion avoidance paradigm of TCP. It is able to utilize extra bandwidth without the network congestion and oscillation in window size, whereas TCP Reno always updates its window size to guarantee full bandwidth utilization, which leads to packet losses constantly.
There are numerous applications of sensor networks. Here it is used for monitoring at an enterprise data center to reduce energy consumption and monitor various aspects of a data center.
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Posted by Mazliza -
September 26, 2011 at 11:05 am
The following are factors that must be considered to achieve efficient communications between nodes in a wireless sensor networks.
Node deployment may be manual/deterministic or random. In the former, nodes are manually placed and data is routed via pre-determined paths. In the latter case, nodes are scattered randomly, forming an ad hoc infrastructure. If the nodes are not uniformly distributed, it may be necessary to cluster the nodes to support connectivity and enable energy-efficient operations.
Sensor nodes are very dependent on battery lifetime because they are often left unattended for long periods of time, thus, it is imperative that communications and computations take an energy-conserving approach.
Data reporting method is either time-driven, even-driven, query-driven or a hybrid of these methods, depending on the criticality of the data. The time-driven method allows sensor nodes to periodically turn off their transmitters to conserve power. The event- and query-driven methods require sensors to react immediately to sudden and drastic changes in the environment, and are therefore, suitable for time-critical applications. The routing protocol is very influenced by the data reporting method in terms of energy consumption and route calculations.
Needless to say, routing in wireless sensor networks (WSNs) is different from routing in conventional wired networks. It is also different from routing in WLANs and MANETs due to several unique characteristics of WSNs. This post focuses on the unique characteristics of WSN that affects the design of routing protocols.
Sensor nodes are inherently constrained in terms of processing power, power supply, memory and storage capacity, all of which require careful planning and management.
It is impossible to use a global addressing scheme for mobile nodes because WSN may involve the deployment of a large number of nodes — the overhead cost of maintaining the ID would be very high. Therefore, the traditional IP-based protocols do not apply to WSNs.
Unlike typical communication networks, most sensor applications require the forwarding and aggregation of sensed data from multiple sources to a base station or a central coordinator.
