Efficient Routing in Intermittently Connected Mobile Networks: The Multiple-Copy Case

Intermittently connected mobile networks are wireless networks where most of the time there does not exist a complete path from the source to the destination. There are many real networks that follow this model, for example, wildlife tracking sensor networks, military networks, vehicular ad hoc networks, etc. In this context, conventional routing schemes fail, because they try to establish complete end-to-end paths, before any data is sent. To deal with such networks researchers have suggested to use flooding-based routing schemes. While flooding-based schemes have a high probability of delivery, they waste a lot of energy and suffer from severe contention which can significantly degrade their performance. Furthermore, proposed efforts to reduce the overhead of flooding-based schemes have often been plagued by large delays. With this in mind, we introduce a new family of routing schemes that "spray" a few message copies into the network, and then route each copy independently towards the destination. We show that, if carefully designed, spray routing not only performs significantly fewer transmissions per message, but also has lower average delivery delays than existing schemes; furthermore, it is highly scalable and retains good performance under a large range of scenarios. Finally, we use our theoretical framework proposed in our 2004 paper to analyze the performance of spray routing. We also use this theory to show how to choose the number of copies to be sprayed and how to optimally distribute these copies to relays.     

Efficient Routing in Intermittently Connected Mobile Networks: The Single-Copy Case

Intermittently connected mobile networks are wireless networks where most of the time there does not exist a complete path from the source to the destination. There are many real networks that follow this model, for example, wildlife tracking sensor networks, military networks, vehicular ad hoc networks (VANETs), etc. In this context, conventional routing schemes would fail, because they try to establish complete end-to-end paths, before any data is sent. To deal with such networks researchers have suggested to use flooding-based routing schemes. While flooding-based schemes have a high probability of delivery, they waste a lot of energy and suffer from severe contention which can significantly degrade their performance. With this in mind, we look into a number of ldquosingle-copyrdquo routing schemes that use only one copy per message, and hence significantly reduce the resource requirements of flooding-based algorithms. We perform a detailed exploration of the single-copy routing space in order to identify efficient single-copy solutions that (i) can be employed when low resource usage is critical, and (ii) can help improve the design of general routing schemes that use multiple copies. We also propose a theoretical framework that we use to analyze the performance of all single-copy schemes presented, and to derive upper and lower bounds on the delay of any scheme.     

Delay and capacity in MANETs under random walk mobility model

The closed-form results for delay and capacity in mobile ad hoc networks are important for the performance analysis of different transmission protocols. Most existing works focus on independent and identically distributed mobility model, which is always regarded as an idealized global model. In this paper, we extend the investigation to the random walk model, which characterizes practical situations more accurately. Some local movements cause a series of complicated probabilistic problem, we develop a method to calculate the meeting probability between two randomly selected nodes under random walk mobility model. Targeting at the most commonly used routing schemes which are modeled by 2HR-f algorithm, we obtain the closed-form solutions for delay and capacity, where the wireless interference and medium access contention among nodes are considered. Extensive simulations demonstrate the accuracy of our theoretical results.     

Opportunistic Routing in Wireless Ad Hoc Networks: Upper Bounds for the Packet Propagation Speed

Classical routing strategies for mobile ad hoc networks operate in a hop by hop ?push mode? basis: packets are forwarded on pre-determined relay nodes, according to previously and independently established link performance metrics (e.g., using hellos or route discovery messages). Conversely, recent research has highlighted the interest in developing opportunistic routing schemes, operating in "pull mode": the next relay can be selected dynamically for each packet and each hop, on the basis of the actual network performance. This allows each packet to take advantage of the local pattern of transmissions at any time. The objective of such opportunistic routing schemes is to minimize the end-to-end delay required to carry a packet from the source to the destination. In this paper, we provide upper bounds on the packet propagation speed for opportunistic routing, in a realistic network model where link conditions are variable. We analyze the performance of various opportunistic routing strategies and we compare them with classical routing schemes. The analysis and the simulations show that opportunistic routing performs significantly better. We also investigate the effects of mobility and of random fading. Finally, we present numerical simulations that confirm the accuracy of our bounds.     

Dynamic routing in translucent WDM optical networks: the intradomain case

Translucent wavelength-division multiplexing optical networks use sparse placement of regenerators to overcome physical impairments and wavelength contention introduced by fully transparent networks, and achieve a performance close to fully opaque networks at a much less cost. In previous studies, we addressed the placement of regenerators based on static schemes, allowing for only a limited number of regenerators at fixed locations. This paper furthers those studies by proposing a dynamic resource allocation and dynamic routing scheme to operate translucent networks. This scheme is realized through dynamically sharing regeneration resources, including transmitters, receivers, and electronic interfaces, between regeneration and access functions under a multidomain hierarchical translucent network model. An intradomain routing algorithm, which takes into consideration optical-layer constraints as well as dynamic allocation of regeneration resources, is developed to address the problem of translucent dynamic routing in a single routing domain. Network performance in terms of blocking probability, resource utilization, and running times under different resource allocation and routing schemes is measured through simulation experiments.     

The effect of mobility-induced location errors on geographic routing in mobile ad hoc sensor networks: analysis and improvement using mobility prediction

Geographic routing has been introduced in mobile ad hoc networks and sensor networks. Under ideal settings, it has been proven to provide drastic performance improvement over strictly address centric routing schemes. While geographic routing has been shown to be correct and efficient when location information is accurate, its performance in the face of location errors is not well understood. We study the effect of inaccurate location information caused by node mobility under a rich set of scenarios and mobility models. We identify two main problems, named LLNK and LOOP, that are caused by mobility-induced location errors. Based on analysis via ns-2 simulations, we propose two mobility prediction schemes - neighbor location prediction (NLP) and destination location prediction (DLP) to mitigate these problems. Simulation results show noticeable improvement under all mobility models used in our study. Under the settings we examine, our schemes achieve up to 27 percent improvement in packet delivery and 37 percent reduction in network resource wastage, on average without incurring any additional communication or intense computation.     

Differentiated contention resolution for QoS in photonic packet-switched networks

Packet contention is a major challenge in photonic packet-switched networks due to the lack of random access buffers in the optical domain. Existing contention resolution approaches such as wavelength conversion and fiber-delay-line buffering may significantly increase the overall system cost and may be difficult to implement. To avoid such issues, this paper proposes a framework for providing label-based differentiated contention resolution by exploiting recirculation buffering and deflection routing. To accommodate more options for differentiation and to avoid the potential problem of forwarding packets in a network indefinitely, two classes of loopless deflection algorithms are provided. An analytical model is also developed to evaluate the packet loss probability and the end-to-end delay for different buffering and deflection routing schemes. The paper also investigates the effectiveness of the control schemes in providing differentiated loss and delay through simulation and analysis. The accuracy of the analytical model is confirmed by simulation.     

Hop ID: A Virtual Coordinate based Routing for Sparse Mobile Ad Hoc Networks

Routing in wireless communication systems such as ad hoc networks remains a challenging problem given the limited wireless bandwidth, users' mobility, and potentially large scale. Recently, a thrust of research has addressed these problems-the on- demand routing, geographical routing, and virtual coordinates. In this paper, we focus on geographical routing that has been shown to achieve good scalability without flooding; however, this usually requires the availability of location information and can suffer from poor routing performance and severe dead end problems, especially in sparse networks. Specifically, we propose a new Hop ID routing scheme, which is a virtual coordinate-based routing protocol and does not require any location information. This achieves excellent routing performance comparable with that obtained by the shortest path routing schemes. In addition, we design efficient algorithms for setting up the system and adapt to the node mobility quickly and can effectively route out of dead ends. Extensive analysis and simulation show that the Hop ID-based routing achieves efficient routing for mobile ad hoc networks with various density, irregular topologies, and obstacles.     

A Minimum Interference Cross-Layer Routing Protocol for Mobile Ad Hoc Networks

In mobile ad hoc networks (MANETs), channel contention and packet collision can seriously affect the performance of routing protocols, which will eventually affect the performance of the whole network. Besides, the arbitrary mobility of nodes makes contention and collision ever-changing and more complex. Thus, it is imperative to analyze the problem of contention and collision so as to build appropriate routes in MANETs. In this paper, by respectively predicting the durations of the contention and collision at every hop along the route, a minimum interference cross-layer routing protocol (MI-CLR) is proposed based on Random Waypoint (RWP) model. The new protocol classifies the interference in the network into two types; the first type of interference can only affect channel contention, while the other affects both channel contention and packet collision. Via taking the two types of interference together into account, we propose a new routing metric to build routes which guarantees that the established routes will not break frequently while having the minimum interference. Simulation results show that the MI-CLR protocol can significantly improve the network performance such as the average end-to-end delay, the packet loss ratio, the routing overhead and the throughput.     

Modeling throughput gain of network coding in multi-channel multi-radio wireless ad hoc networks

In this paper, we model the network throughput gains of two types of wireless network coding (NC) schemes, including the conventional NC and the analog NC schemes, over the traditional non-NC transmission scheduling schemes in multihop, multi-channel, and multi-radio wireless ad hoc networks. In particular, we first show that the network throughput gains of the conventional NC and analog NC are (2n)/(2n-1) and n/(n-1), respectively, for the n-way relay networks where n ges 2. Second, we propose an analytical framework for deriving the network throughput gain of the wireless NC schemes over general wireless network topologies. By solving the problem of maximizing the network throughput subject to the fairness requirements under our proposed framework, we quantitatively analyze the network throughput gains of these two types of wireless NC schemes for a variety of wireless ad hoc network topologies with different routing strategies. Finally, we develop a heuristic joint link scheduling, channel assignment, and routing algorithm that aims at approaching the optimal solution to the optimization problem under our proposed framework.     

Global mobility management by replicated databases in personalcommunication networks

This paper explores the use of replicated databases for management of customer data (e.g., mobility data, call routing logic) in global, intelligent, and wireless networks. We propose and analyze two, full and partial, data replication schemes-which are compatible with industry protocol standards-and compare them with the traditional, centralized database scheme. By identifying a set of key teletraffic and mobility parameters, we develop a modeling framework based on queueing models and apply it to assess the relative performance and merits of these schemes. The paper also addresses some implementation issues. Numerical results reveal that the full replication scheme outperforms the centralized one over a wide range of the parameters considered in this study. Furthermore, if some customer data-such as location data for highly mobile customers in wireless networks-change frequently, and if each call launches multiple queries into the databases, the partial replication scheme offers further performance improvement. In general, however, the choice of the database design would depend on the specific characteristics of the service and user behavior under consideration     

Routing in Delay-Tolerant Networks Comprising Heterogeneous Node Populations

Communication networks are traditionally assumed to be connected. However, emerging wireless applications such as vehicular networks, pocket-switched networks, etc., coupled with volatile links, node mobility, and power outages, will require the network to operate despite frequent disconnections. To this end, opportunistic routing techniques have been proposed, where a node may store-and-carry a message for some time, until a new forwarding opportunity arises. Although a number of such algorithms exist, most focus on relatively homogeneous settings of nodes. However, in many envisioned applications, participating nodes might include handhelds, vehicles, sensors, etc. These various "classes” have diverse characteristics and mobility patterns, and will contribute quite differently to the routing process. In this paper, we address the problem of routing in intermittently connected wireless networks comprising multiple classes of nodes. We show that proposed solutions, which perform well in homogeneous scenarios, are not as competent in this setting. To this end, we propose a class of routing schemes that can identify the nodes of "highest utility” for routing, improving the delay and delivery ratio by four to five times. Additionally, we propose an analytical framework based on fluid models that can be used to analyze the performance of various opportunistic routing strategies, in heterogeneous settings.     

The Mathematical Theory of Dynamic Load Balancing in Cellular Networks

While many interesting dynamic load balancing schemes have been proposed for efficient use of limited bandwidth and to increase the capacity of congested or hot spots (or cells) in wireless networks, to date, a comprehensive mathematical framework which encompasses all of these schemes does not exist. In this paper, we provide a unified mathematical framework for dynamic load balancing, which leads to closed-form performance expressions for evaluating the performance of some of the most important dynamic load balancing strategies proposed in the literature. To the best of our knowledge, this is the first generic theoretical framework that can be used to evaluate the performance of many different dynamic load balancing schemes with simple closed-form results. The accuracy of the results predicted by these analytical expressions derived from the theoretical framework is checked by comparing these results with simulation results provided in the literature for well-known schemes.     

Data-flow in mobile edge computing networks: end-to-end performance analysis using stochastic network calculus

Mobile edge computing (MEC) networks can provide a variety of services for different applications. End-to-end performance analysis of these services serves as a benchmark for the efficient planning of network resource allocation and routing strategies. In this paper, a performance analysis framework is proposed for the end-to-end data-flows in MEC networks based on stochastic network calculus (SNC). Due to the random nature of routing in MEC networks, probability parameters are introduced in the proposed analysis model to characterize this randomness into the derived expressions. Taking actual communication scenarios into consideration, the end-to-end performance of three network data-flows is analyzed, namely, voice over Internet protocol (VoIP), video, and file transfer protocol (FTP). These network data-flows adopt the preemptive priority scheduling scheme. Based on the arrival processes of these three data-flows, the effect of interference on their performances and the service capacity of each node in the MEC networks, closed-form expressions are derived for showing the relationship between delay, backlog upper bounds, and violation probability of the data-flows. Analytical and simulation results show that delay and backlog performances of the data-flows are influenced by the number of hops in the network and the random probability parameters of interference-flow (IF).     

The Peril of Evaluating Location Management Proposals through Simulations

The challenge of supporting rapidly growing numbers of mobile users, while constrained by limited radio spectrum, is being faced by cellular network operators worldwide. Several location management schemes have been proposed to improve the performance of such networks, but a fair assessment and comparison of their performance is difficult without an accurate mobility model. The performance of location management schemes depends considerably on subscriber mobility patterns. Some of the recent methods proposed in the literature are reviewed and selected that concentrate on the location updating and paging overhead. To analyze the performance of the selected proposals, two mobility models, namely activity-based mobility model and random mobility model, were used. From the results it is clear that the mobility model has a significant impact and the results described in various proposals using a random mobility model may not reflect the relative performance when deploying schemes in actual systems.     

Design and Performance of Wireless Data Gathering Networks Based on Unicast Random Walk Routing

Wireless environment monitoring applications with significantly relaxed quality-of-service constraints are emerging. Hence, the possibility to use rough low knowledge routing in sensor networks to reduce hardware resource and software complexity is questionable. Moreover, low knowledge handling allows better genericity, which is of interest, for instance, for basic operation enabling system set-up. In this framework, this paper revisits stateless unicast random walk routing in wireless sensor networks. Based on random walk theory, original closed-form expressions of the delay, the power consumption and related spatial behaviors are provided according to the scale of the system. Basic properties of such a random routing are discussed. Exploiting its properties, data gathering schemes that fulfill the requirements of the application with rather good energy efficiency are then identified.      

Egocentric network focused community aware multicast routing for DTNs

Multicasting for delay-tolerant networks (DTNs) in sparse social network scenarios is a challenge due to the deficiency of end-to-end paths. In social network scenarios, the behaviors of their nodes are controlled by human beings, and node mobility is the same as that of humans. To design the multicasting algorithms for DTNs, therefore, it would be promising to capture the intrinsic characteristics of relationships among these nodes. In this paper, multicasting in DTNs is regarded as a message dissemination issue in social networks, and an egocentric network focused community aware multicast routing algorithm (ENCAR) is proposed. As distinct from some social-based routing algorithms which only focus on centrality analysis, ENCAR is an utility based and hierarchical routing algorithm, its utility function is constructed on the basis of centrality analysis and destination-oriented contact probability. We take notice of clustering phenomenon in social networks, and present the community aware forwarding schemes. In addition, to simulate the mobility of individuals in social networks, a novel community based random way point mobility model is also presented. In this paper, the performance of ENCAR is theoretically analyzed and further evaluated on simulator ONE. Simulation results show that ENCAR outperforms most of the existing multicast routing algorithms in routing overhead, on condition that delivery ratio is relatively high, with other significant parameters guaranteed to perform well.     

Provisioning of adaptability to variable topologies for routing schemes in MANETs

Frequent changes in network topologies caused by mobility in mobile ad hoc networks (MANETs) impose great challenges to designing routing schemes for such networks. Various routing schemes each aiming at particular type of MANET (e.g., flat or clustered MANETs) with different mobility degrees (e.g., low, medium, and high mobility) have been proposed in the literature. However, since a mobile node should not be limited to operate in a particular MANET assumed by a routing scheme, an important issue is how to enable a mobile node to achieve routing performance as high as possible when it roams across different types of MANETs. To handle this issue, a quantity that can predict the link status for a time period in the future with the consideration of mobility is required. In this paper, we discuss such a quantity and investigate how well this quantity can be used by the link caching scheme in the dynamic source routing protocol to provide the adaptability to variable topologies caused by mobility through computer simulation in NS-2.     

基于不同移动模型的移动自组网多播路由协议性能研究

为了研究移动自组网中多播路由协议在不同移动模型下的性能,选取随机路点移动模型、高斯马尔科夫移动模型和参考点组移动模型,将三种移动模型的移动场景加入到NS2中,对基于部分网络编码的实时多播协议PNCRM进行仿真.结果表明,PNCRM协议在随机路点移动模型和高斯马尔科夫移动模型中的数据包投递率明显高于参考点组移动模型,但是参考点组移动模型的总开销和端到端延时是最优的.这样我们就可以根据不同的性能指标要求选择合适的移动模型.     

Generic prediction assisted single-copy routing in underwater delay tolerant sensor networks

One challenge in delay tolerant networks (DTNs) is efficient routing, as the lack of contemporaneous end-to-end paths makes conventional routing schemes inapplicable. Although many DTN routing protocols have been proposed, they often have two limitations: many protocols are not mobility cognizant, so they only suit specific mobility models and become inefficient when the environment changes; some protocols employ multi-copy replication to accommodate mobility diversity for increased delivery probability or reduced delay, but they usually do not perform well in resource constrained networks. Due to the unique characteristics of underwater sensor networks (UWSNs), efficient DTN routing becomes even more challenging. In this paper, we propose a generic prediction assisted single-copy routing (PASR) scheme that can be instantiated for different mobility models. PASR first collects a short-duration trace with network connectivity information and employs an effective off-line greedy algorithm to characterize the underlying network mobility patterns, depict the features of best routing paths and provide guidance on how to use historical information. Then it instantiates prediction assisted single-copy online routing protocols based on the guidance. As a result, the instantiated protocols are energy efficient and cognizant of the underlying mobility patterns. We demonstrate the advantages of PASR in underwater sensor networks with various mobility models.