Adaptive Resource Observation for Congestion Alleviation using Constrained Application Protocol

This paper presents an adaptive resource observation (ARO) for congestion alleviation using constrained application protocol (CoAP), which prevents buffer overflow of the client by adjusting observing period of the associated servers. The operation of ARO consists of two main phases; 1) buffer overflow estimation, 2) observing period adaptation. In the former, the client estimates whether buffer overflow will occur by comparing its service rate with packet arrival rate, then it determines the new observing period that can prevent buffer overflow of the client. The latter is used to adjust the observing period of servers considering the predefined the minimum and maximum queue threshold. ARO can significantly reduce the number of dropped packets caused by buffer overflow. The simulation results show that ARO achieves a higher network performance than legacy CoAP.

A Downlink and Uplink Alignment Scheme for Power Saving in IEEE 802.16 Protocol

This study shows the problem of power saving mechanism (PSM) that sleep intervals of uplink (UL) connections do not synchronize with sleep intervals of downlink (DL) connections. That is, the energy of a mobile station (MS) is notreallysaved if the DL connections are in the sleep mode while the UL connections are in normal mode, and vice versa. To avoid the asynchronism of power saving (PS) between UL and DL connections, we invent a mechanism of DL connections regulating UL connections, calledDL and UL Alignment(DUAL) scheme, to improve the energy efficiency for PS. Considering that the buffer size of MS is limited, DUAL uses the mean packet arrival rate of ULλuand a relatively safe threshold of buffer sizeQTas the parameters to estimate the maximum allowable waiting time to align the UL with the DL connections. To analyze the performance of DUAL, a system model of PS is proposed to evaluate the performance of DUAL under different conditions. The correctness of performance analysis of DUAL is validated by using simulation with realistic parameters. Numerical experiments show that DUAL improves the energy conservation significantly when UL traffic is greater than DL traffic.

A Reliable and Efficient Highway Multihop Vehicular Broadcast Model

A reliable and efficient highway broadcast model based on gain prediction is proposed to solve excessive information retransmission and channel conflict that often happen to flooding broadcast in vehicular ad hoc network. We take accountofthe relative speeds, the intervehicle distance, and the coverage difference of the neighboring vehicles into predicting the gain of every neighbor, and further select the neighbor with the maximum gain as the next hop on the every direction of road. Simulations show that the proposed model is clearly superior to the original flooding model and a recent variant based on mobility prediction in packet arrival rate, average delay, forwarding count, and throughput.

A Study on the Performance of IPv6-Based Mobility Protocols

The performance of IP mobility protocols is highly dependent on the change of mobile nodes’ (MNs’) mobility and traffic-related characteristics. Therefore, it is essential to investigate the effects of these characteristics and to conduct an in-depth performance study of these protocols. In this paper, we introduce a novel analytical approach using a continuous-time Markov chain model and hierarchical network model for the performance analysis of IPv6 mobility protocols: Mobile IPv6 (MIPv6) and Hierarchical Mobile IPv6 (HMIPv6). According to these analytical models, we derive the location update costs (i.e., binding update costs plus binding renewal costs), packet tunneling costs, and total signaling costs, which are generated by an MN during its average domain residence time, when MIPv6 or HMIPv6 is deployed under the same network architecture, respectively. In addition, based on these derived costs, we investigate the effects of various parameters, such as the average speed of an MN, binding lifetime period, the ratio of the network scale, and packet arrival rate, on the signaling costs generated by an MN under MIPv6 and HMIPv6. Moreover, we conduct the performance comparison between these two protocols by showing the relative total signaling costs under the various conditions. The analytical results show that as the average speed of an MN gets higher and the binding lifetime period is set to the larger value or as its packet arrival rate gets lower, the total signaling cost generated by an MN during its average domain residence time under HMIPv6 will get relatively lower than that under MIPv6, and that under the reverse conditions, the total signaling cost under MIPv6 will get relatively lower than that under HMIPv6.