Sharif Digital Repository

The quality of service in Wireless Multimedia Sensor Networks (WMSNs) is related to packet loss rate. Recently dierent studies have been done on developing ecient protocols in the transport layer for controlling packet loss in WMSNs. However, all of these protocols are independent of the characteristics of the multimedia content. In this thesis, a novel transport layer protocol, called User Datagram Dispatcher Protocol (UDDP), is proposed to minimize the packet loss ratio in WMSNs by considering trac characteristics, the inter-arrival pattern of packets and packet priority. UDDP is a new cross-layer transport layer that uses information of MAC and application layers to distribute packet... 

Sensor networks is a set of sensors (nodes) which are communicating with each other, and gather information from different environments, and process them to give us valuable results. Sensors have a small energy source like a small battery which have to be used efficiently. Congestion detection and avoidance, together are of great importance in Wireless Sensor Networks (WSNs) in case of traffic load, data loss, and power consumption. In this work, we propose a new APS layer (application support sub-layer), which is another key standard component of Application layer, offering a well-defined interface and several control services. It functions as a bridge between the network layer and other... 

Vehicular Ad hoc Network (VANET) is a subclass of Mobile Ad hoc Network (MANET), which provides us ability to communicate between moving vehicles. VANET has been developed as a standard means of communication for Intelligent Transport Systems (ITS) to improve traffic safety and efficiency while providing internet access on the move. Congestion control is a challenging subject in VANETs primarily due to the shared nature of the wireless channel and frequent changes of the network topology. Inefficient congestion control causes periodical safety messages to be lost and introduces latency in threat modelling at the application layer. There are two methods to overcome this problem. First, based... 

Distinguishing characteristic of wireless sensor network is limited resources such as processing power, bandwidth, memory. Restrictions of sensor networks is impressive on the transfer of multimedia data such as video requiring high bandwidth and low latency. In wireless multimedia sensor networks, the probability of packet loss is high due to the high volume of multimedia data and limited bandwidth. Many congestion control protocols for wireless sensor networks have presented. Most of these protocols did not consider the multimedia content. Even some wireless sensor network congestion control protocols have worse result than a network which has no congestion control protocol in case of... 

Active queue management (AQM) is a key factor in congestion control and should provide appropriate feedback for flow control in traffic sources to overcome the congestion problem. Beside providing congestion control, achieving predictable queuing delay, maximizing link utilization, simplicity and robustness are also the main objectives of an AQM controller. We propose in this thesis an improved queue dynamic model while incorporating the packet drop probability as well. The proposed model is evaluated using ns2 platform. By applying the improved model, a new compensated proportionalintegral- derivative (PID) AQM controller is developed for TCP network. The time-varying nature of the network... 

Today, the use of data centers has drastically increased, and load balancing is one of the challenges of data centers. Generally, load balancing is the effective distribution of network traffic between service providers, and it has become more important due to the difference between the size of the network traffic and its unpredictable nature. Because of the difference between data center networks and wide area networks, special services have been provided to meet the needs of these networks. In this thesis, we intend to explain load balancing and characteristics of data centers, and then explore the particular methods of load balancing in data centers and divide them into two groups of... 

Many congestion control protocols proposed so far to alleviate the problems encountered by TCP protocol in high-speed networks and wireless links have to estimate the parameters of the network. For example, the TCP WESTWOOD congestion window is adjusted based on available bandwidth estimation, or TCP Vegas detects the congestion status based on RTT (Round Trip Time) estimation, and XCP protocol operates according to network traffic load. In this paper, we proposed a novel estimation algorithm that is based on burst identification techniques in router. we show through analysis and simulation that during burst periods this method can estimate the congestion window size of the specific flow... 

Congestion is an important issue in the network environment. To keep stable the perfor-mance of the network, congestion control algorithms have been extensively studied. Queue management method employed by the routers is one of the important issues in the congestion control study. Active Queue Management (AQM) has been proposed for early detection of congestion inside the network. AQM mechanisms control the queue length in a router by dropping arriving packets. The Random Early Detection (RED) is the most popular AQM mechanism used in routers on the Intenet to allow network users to simultaneously achieve high throughput and low average delay. The RED algorithm may cause heavy oscillation of... 

One of the basic characteristics of Wireless Sensor Networks is their resource limitations. As a result, it is essential to try to decrease costs in such networks. These limitations are more critical in transmitting multimedia data with larger data units. In addition, when transmitting real-time multimedia data, delay is an important factor to consider. According to these limitations, Wireless Multimedia Sensor Networks are congestion prone. In this thesis, a transport layer protocol has been proposed. This protocol consists of three three steps in handling congestion. First, it detects congestion according to the queue length in the node. If the lsength is greater than a minimum threshold,...