We propose the asynchronous receiver-initiated MAC protocol with the stair-like sleep mode; each node reduces its own sleep time by the sleep-change-rate depending on the number of hops from the source to the sink in wireless sensor networks (WSNs). Using the stair-like sleep approach, our protocol achieves high delivery ratio, low packet delay, and high energy efficiency due to the reduction in idle listening time. Our protocol can formulate the upper bound of the idle listening time because of the feature that the sleep time decreases in a geometric progression, and the reduction of the idle listening time is obtained by using the stair-like sleep approach. In our proposed scheme, the sink calculates the sleep change rate based on the number of hops from the source to the sink. By using the control packets which have the role of the acknowledgment (ACK), our proposed protocol can achieve the stair-like sleep with no additional control packets. In addition, even in the network condition that multi-targets are detected, and the number of hops to the sink are changed frequently, our proposed protocol can change the sleep change rate adaptively because the sink can always obtain the number of hops from the source to the sink. Simulation results show that the proposed protocol can improve the performance in terms of the packet delivery ratio, the packet delay, and the energy efficiency compared to the conventional receiver-initiated MAC (RI-MAC) protocol.

In optical burst switching (OBS) networks, burst with different numbers of hops experience unfairness in terms of the burst loss probability. In this paper, we propose a preemptive scheme based on the number of transit hops in OBS networks. In our proposed scheme, preemption is performed with two thresholds; one is for the total number of hops of a burst and the other is for the number of transit hops the burst has passed through. We evaluate the performance of the scheme by simulation, and numerical examples show that the proposed scheme improves the fairness among the bursts with different numbers of hops, keeping the overall burst loss probability the same as that for the conventional OBS transmission without preemption.

This paper proposes a distributed adaptive routing algorithm that may be applied to inter-domain calls passing over any type of network topology, traffic management and switching techniques on the path, while carrying bidirectional traffic with multiple QoS requirements. The path is searched within a contour area restricted by the number of hops between source and destination while the end-to-end admission of calls is controlled at source node and each hop's admission at each node, reflecting the latest resources availability and network conditions for the given QoS requirements. Performance analysis in various conditions shows good applicability in real networks.

Optical WDM (Wavelength Division Multiplexing) technology is a method of exploiting the huge bandwidth of optical fibers. Local lightwave networks which use fixed wavelength transmitters and receivers can be built in a multihop fashion. In multihop local lightwave networks, packets arrive at their destination by hopping a number of intermediate nodes. The channel sharing schemes for multihop lightwave networks have been proposed for efficient channel utilization, but those schemes result in the degradation of network capacity and the user throughput. In this paper, we propose an improved WDM channel sharing scheme using the logically bidirectional perfect shuffle interconnection pattern, achieving smaller number of average hops for transmission and better channel utilization efficiency. Better channel utilization efficiency is obtained without much deteriorating the network capacity and the user throughput. TDMA (Time Division Multiple Access) protocol can be used to control the sharing of channels, and time delay and lost packet probability analysis based on TDMA is performed.