Simulating CSMA/CA Behavior for Performance Evaluation of Multi-hop Wireless Networks

Abstract—In this paper, we design an efficient method of simulating wireless networks that use CSMA/CA-based protocols in the MAC layer. In the method, a stochastic model to estimate the CSMA/CA frame transmission delay is naturally incorporated into the conventional fully event-based model. The stochastic model can simplify the interactions between a frame transmitter and its surrounding nodes, which alleviates the event scheduling overhead in simulation. The important feature is that the stochastic model can be applied in “per-node ” and “time” basis, i.e. we may simulate the behavior of some intended nodes precisely while the others are simplified by the stochastic mode to save computational resources. To the best of our knowledge, this is the first approach to coexistence of the stochastic and eventbased models in wireless multi-hop network simulation. We have implemented this scheme in a commercial network simulator and conducted several experiments. From the results, it is confirmed that the proposed method could perform simulation of frame transmission much faster than the fully event-based simulation achieving the same accuracy as the conventional model. Index Terms—Wireless Network Simulation, CSMA/CA I

An Autonomous and Decentralized Protocol for Delay Sensitive Overlay Multicast Tree

In this paper, we present a protocol for dynamically maintaining a degree-bounded delay sensitive spanning tree in a decentralized way on overlay networks. The protocol aims at repairing the spanning tree autonomously even if multiple nodes ’ leave operations or failures (disappearances) occur simultaneously or continuously in a specified period. It also aims at maintaining the diameter (maximum delay) of the tree as small as possible. The simulation results using ns-2 have shown that the protocol could keep reasonable diameters compared with the existing centralized static algorithm even if many nodes ’ participations and disappearances occur frequently.

Protocol Testing and Performance Evaluation for MANETs with Non-uniform Node Density Distribution

Part 6: New Testing MethodsInternational audienceIn this paper, we focus on Mobile Ad-hoc Networks (MANETs) with non-uniform node density distribution such as Vehicular Ad-hoc Networks (VANETs) and Delay Tolerant Networks (DTNs), and propose a technique for protocol testing and performance evaluation. In such MANETs, node density varies depending on locations and time, and it dynamically changes every moment. In the proposed method, we designate node density distributions and their dynamic variations in a target area. Then, we construct a graph called TestEnvGraph where all node density distributions are treated as its nodes and they are connected by edges whose weights denote differences of two node density distributions. We specify a set of edges to be tested in the graph, formulate a problem for efficiently reproducing all the given node density distributions and their dynamic variations as a rural postman problem, find its solution and use it as the order of reproduction of designated node density distributions and their variations. Protocol testing is carried out by reproducing node density distributions in the derived order. We have designed and developed a method and its tool for mobility generation on MANETs, which can reproduce any designated node density distribution and its dynamic variations in a target area. From our experiments for a VANET protocol, we have shown that our method can give a similar trend in network throughput and packet loss rates compared with realistic trace based protocol testing

Quality Requirement Coordination in Rate Adaptation of Multiple Layered Videos

for multiple layered video multicast distribution. Assuming that each user has his/her own quality requirement for the multiple videos, a "quality coordinator" determines the set of layers of videos to be dropped by those users who have detected network congestion on their common bottleneck link so that their requirements are satisfied as much as possible. Based on the proposal scheme, MPEG1 layered video distribution system has been designed and implemented. Through an experiment on an IP multicast network, we have confirmed that the recovery time from network congestion was less than half time and the satisfied requirements are higher than a simple layer adaptation where each user drops layers according to his/her requirement independently of the others