Browsing by Subject "Routers (Computer networks)"

Now showing 1 - 13 of 13

Open Access
Analysis and mitigation of interference in multi-radio multi-channel wireless mesh networks
(2013) Uluçınar, Alper Rifat
Wireless mesh networking, which is basically forming a backbone network of mesh routers using wireless links, is becoming increasingly popular for a broad range of applications from last-mile broadband access to disaster networking or P2P communications, because of its easy deployment, self-forming, self-configuration, and self-healing properties. The multi-hop nature of wireless mesh networks (WMNs) aggravates inter-flow interference and causes intra-flow interference and severely limits the network capacity. One technique to mitigate interference and increase network capacity is to equip the mesh routers with multiple radios and use multiple channels. The radios of a mesh router can then simultaneously send or receive packets on different wireless channels. However, careful and intelligent radio resource planning, including flow-radio and channel assignment, is necessary to efficiently make use of multiple radios and channels. This first requires analyzing and modeling the nature of co-channel and adjacent channel interference in a WMN. Through real-world experiments and observations made in an indoor multihop multi-radio 802.11b/g mesh networking testbed we established, BilMesh, we first analyze and model the nature of co-channel and adjacent channel interference. We conduct extensive experiments on this testbed to understand the effects of using multi-radio, multi-channel relay nodes in terms of network and application layer performance metrics. We also report our results on using overlapping in addition to orthogonal channels for the radios of the mesh routers. We then turn our attention to modeling and quantifying adjacent channel interference. Extending BilMesh with IEEE 802.15.4 nodes, we propose computational methods to quantify interference between channels of a wireless communication standard and between channels of two different standards (such as Wi-Fi and ZigBee). Majority of the studies in the literature on channel assignment consider only orthogonal channels for the radios of a multi-radio WMN. Having developed quantitative models of interference, next we propose two optimization models, which use overlapping channels, for the joint flow-radio and channel assignment problems in WMNs. Then we propose efficient centralized and distributed heuristic algorithms for coupling flows and assigning channels to the radios of a WMN. The proposed centralized and distributed schemes make use of overlapping channels to increase spectrum utilization. Using solid interference and capacity metrics, we evaluate the performances of the proposed schemes via extensive simulation experiments, and we observe that our schemes can achieve substantial improvement over single-channel and random flow-radio and channel assignment schemes.
Open Access
Channel assignment and routing for multi-radio wireless mesh networks
(2008) Gülten, Sıtkı
In this study, we analyze the channel assignment and routing problem for multi-radio wireless mesh networks. We assume that each router has more than one radio, the system operates in a time-slotted mode, and channel assignments are static. In particular, within a time slot the channel assignments for radio connections have to obey the interference constraint. The union of all the connections established throughout the time horizon should result in a strongly connected network where each node can communicate with every other node within the given maximum hop-distance or the diameter value. The objective is to minimize the number of time slots used while respecting the interference and diameter restriction. An integer linear program is proposed as an exact methodology to solve the problem for small scale networks. For larger network sizes, three type of heuristic approaches are developed. In order to evaluate the quality of the heuristic solutions, the lower bound of the model is strengthened through the use of valid inequalities and lagrangian relaxation. The subgradient algorithm is used in lagrangian relaxation models to find optimal solutions or lower bounds. The heuristics are tested on a large set of varying network topology instances. The computational experiments illustrate that improvement heuristic based on local search is the most suitable approximation technique.
Open Access
Channel assignment and routing for multi-radio wireless mesh networks
(2008) Özdemiray, Ahmet Murat
Wireless Mesh Network is a promising technology since it extends the range of wireless coverage by multi-hop transmission between routers. However, in multihop networks the total throughput decreases with increasing number of nodes and hops. To increase the total throughput, some mesh routers are equipped with multiple radios to use the available bandwidth of multiple non-overlapping channels. However, channel assignment should be done carefully to effectively use this available bandwidth. Moreover, the optimal channel assignment algorithm is NP-hard. In this thesis, we propose a joint channel assignment and routing solution to effectively use the available bandwidth for multi-radio wireless mesh networks with given network topology and traffic profile. Initially, we predict the final routes of the flows and estimate the loads on the links using these path predictions and given traffic profile. Then three different heuristics determine the assignment order of the links. Then the least busy channel among the available channels is assigned to the link. Finally, our routing algorithm routes the flows such that the selected path is the least busy path among the alternatives. We evaluated our channel assignment and routing algorithm using ns-2 simulator which supports multiple channels and multiple radios per node and we compared our results with single channel WMNs, and different algorithms for multi-radio multi-channel WMNs. The results show that our joint algorithm successfully achieves up to 5 times more throughput than single channel WMN with using just 2 radios and 3 channels. Our algorithms also out-performs other compared channel assignment algorithms for multi-radio multi-channel WMNs.
Open Access
A collaborative system for providing routes between locations
(2008) Uluğ, Kerem Ali
Many systems, such as in-car GPS devices and airline company web sites, provide route information between locations. Although such systems are used widely and can provide route information successfully, users of these systems cannot contribute to the data entry process. In these systems, data is entered by the administrators and these systems cannot take advantage of the route expertise of their users. In this work, we present a collaborative system, which provides routes between locations upon user queries. The data in the system is entered by the users of the system. We present a model which is containing locations, links between locations and relationships between locations (containment, neighborhood and intersection) in order to store the data. For the route finding purpose, we present a customized version of the A* search algorithm. This customized version, named A*CD (A* for Collaborative Data), uses heuristics for estimating the cost remaining to the target location while processing the nodes. A*CD can also provide alternative routes, exclude certain link types in the searches according to user preferences and handle the problems associated with multiple stop transportation lines. As the cost models, we use duration and financial cost. We also present the intuitive connections concept. Even if a route does not exist between the selected locations, the system can provide a route with missing links. The gap(s) between the disconnected locations are filled by the help of the relationships between locations. In order to evaluate the performance of the A*CD algorithm, we present automated tests. These tests show that the costs of the routes that are provided by the A*CD algorithm are close to the actual shortest routes. In order to demonstrate the intuitive connections concept, we also present manual test queries.
Open Access
GridRoute : a multi-layered grid based routing protocol for delay tolerant mobile networks
(2012) Köksal, Emin Yiğit
This work proposes a new routing protocol for delay-tolerant mobile networks (DTMNs) called GridRoute. The proposed protocol can be adopted considering network requirements such as low message delay or low resource usage. GridRoute is a probabilistic routing protocol that takes advantage of mobility and location information of nodes. It uses a multi-layered grid for contact probability maximization. It requires almost no memory storage of contact or location probabilities for intelligent routing decisions. GridRoute also minimizes the number of redundant messages throughout the network with feasible delay on message delivery, and provides some security advantages like identity secrecy. Our simulation results show that GridRoute outperforms existing routing protocols in terms of memory requirement. It also achieves high delivery ratio, reasonable end-to-end delay and significantly lower message overhead.
Open Access
Joint link
(2009) Kaybal, Fazlı
In this thesis, we study the joint scheduling and routing problem in spatial reuse Time Division Multiple Access (STDMA) based multi-channel/multiradio/multi-rate wireless mesh networks (WMNs). The main objective of the joint scheduling and routing problem addressed in thesis is to reduce the number of required TDMA time slots to deliver all packets to their destinations. Since the optimum solution to the problem is NP-hard, we propose a greedy iterative solution methodology. The problem is formulated as an integer linear program (ILP) under the physical interference model. We consider two versions of the problem in order to investigate the factors affecting the capacity of WMNs. In the first one, we perform scheduling and routing when the number of channels and number of radios are varied for multi-rate WMNs where nodes are equipped with omni-directional antennas. This analysis is done for both single-class (best-effort traffic) and two-class (best-effort and delay sensitive classes) traffic models. We then extend this analysis by adding the power control scheme which allows transmitters to change the transmitting powers slot-by-slot. Finally, joint scheduling and routing problem is extended for WMNs where nodes are equipped with multiple sectored antennas. We show that the network performance is improved with more radio resources, e.g., using multiple orthogonal channels, multiple radios per node, transmit power control scheme, and directional antennas in terms of delay and total dissipated energy. The network throughput when using 3 channels and 3 radios is increased by up to 67.2% compared to single channel WMNs and the total dissipated energy is reduced by up to 45.5% with transmit power control scheme. Finally, when directional antennas with 6 sectors are used at both transmitters and receivers, the network throughput increases by up to 72.6% compared to omni-directional antenna case.
Open Access
Joint routing, gateway selection, scheduling and power management optimization in wireless mesh networks
(2011) Uzunlar, Onur
The third generation (3G) wireless communications technology delivers user traffic in a single step to the wired network via base station; therefore it requires all base stations to be connected to the wired network. On the other hand, in the fourth generation (4G) communication systems, it is planned to have the base stations set up so that they can deliver each other’s traffic to a small number of base stations equipped with wired connections. In order to improve system resiliency against failures, a mesh structure is preferred. The most important issue in Wireless Mesh Networks (WMN) is that the signals that are simultaneously transmitted on the same frequency channel can interfere with each other to become incomprehensible at the receiver end. It is possible to operate the links at different times or at different frequencies, but this also lowers capacity usage. In this thesis, we tackle the planning problems of WMN, using 802.16 (Wi-MAX) protocol, such as deploying a given number of gateway nodes along with operational problems such as routing, management of power used by nodes and scheduling while maximizing the minimum service level provided. The WMN under consideration has identical routers with fixed locations and the demand of each router is known. In order to be able to apply our results to real systems, we work with optimization models based on realistic assumptions such as physical interference and single path routing. We propose heuristic methods to obtain optimal or near optimal solutions in reasonable time. The models are applied to some cities in Istanbul and Ankara provinces.
Open Access
Power-source-aware adaptive routing in wireless sensor networks
(2013) Tekkalmaz, Metin
A wireless sensor network (WSN) is a collection of sensor nodes distributed over an area of interest to accomplish a certain task by monitoring environmental and physical conditions and sending the collected data to a special node called sink. Most studies on WSNs consider nodes to be powered with irreplaceable batteries, which limits network lifetime. There are, however, perpetual power source alternatives as well, including mains electricity and energy harvesting mechanisms, which can be utilized by at least some portion of the sensor nodes to further prolong the network lifetime. Our aim here is to increase the lifetime of such WSNs with heterogeneous power sources by centralized or distributed routing algorithms that distinguish battery- and mains-powered nodes in routing, so that energy consuming tasks are carried out mostly by mains-powered nodes. We first propose a framework for a class of routing algorithms, which forms and uses a backbone topology consisting of all mains-powered nodes, including the sinks, and possibly some battery-powered nodes, to route data packets. We propose and evaluate a set of centralized algorithms based on this framework, and our simulation results show that our algorithms can increase network lifetime by up to more than a factor of two. We also propose a fully distributed power-source-aware backbone-based routing algorithm (PSABR) that favors mains-powered nodes as relay nodes. We validate and evaluate our distributed algorithm with extensive ns-2 simulations and our results show that the proposed distributed algorithm can enhance network lifetime significantly with a low control messaging overhead. Besides wireless technology independent routing solutions, we also propose a technology specific power-source-aware routing solution (PSAR) for sensor and ad hoc networks which use 802.15.4/ZigBee as the wireless technology. Our solution is fully distributed, tree-based, and traffic-adaptive. It utilizes some protocol specific properties of ZigBee, such as distributed and hierarchical address assignment, to eliminate battery-powered nodes on the routing paths as much as possible. To validate and evaluate our ZigBee-specific algorithm, we first implemented ZigBee extensions to ns-2 simulator and then implemented and simulated our protocol in this extended ns-2 environment. Our results show that the proposed algorithm operates efficiently and can increase network lifetime without increasing the path lengths significantly, compared to the default ZigBee routing algorithm.
Open Access
Routing and scheduling decisions in the hierarchical hub location problem
(2013) Dükkancı, Okan
Hubs are facilities that consolidate and disseminate flow in many-to-many distribution systems. The hub location problem considers decisions including the locations of hubs on a network and also the allocations of the demand (non-hub) nodes to these hubs. In this study, a hierarchical multimodal hub network is proposed. Based on this network, a hub covering problem with a service time bound is defined. The hierarchical network consists of three layers. In this study, two different structures, which are ring(s)-star-star (R-S-S) and ring(s)-ring(s)-star (R-R-S), are considered. The multimodal network has three different types of vehicles at each layer, which are airplanes, big trucks and pickup trucks. For the proposed problems (R-S-S and R-R-S), two mathematical models are presented and strengthened with some valid inequalities. The computational analysis is conducted over Turkish and CAB data sets. Finally, we propose a heuristic algorithm in order to solve large-sized problems and also test the performance of this heuristic approach on Turkish network data set.
Open Access
Routing in delay tolerant networks with periodic connections
(2010) Mergenci, Cem
In delay tolerant networks (DTNs), the network may not be fully connected at any instance of time, but connections occurring between nodes at di erent times make the network connected through the entire time continuum. In such a case, traditional routing methods fail to operate as there are no contemporaneous end-to-end paths between sources and destinations. This study examines the routing in DTNs where connections arise in a periodic nature. Various levels of periodicity are analyzed to meet requirements of di erent network models. We propose various routing algorithms for periodic connections. Our proposed methods can nd routes that can guarantee earliest delivery and minimum hop count. We evaluate our routing schemes via extensive simulation experiments and also compare them to some other popular routing approaches proposed for delay tolerant networks. Our evaluations show the feasibility and e ectivenes of our schemes as alternative routing methods for delay tolerant networks.
Open Access
Shortest path problem with re-routing en-route
(2008) Karakaya, Banu
In this study, we examine the shortest path problem under the possibility of “re-routing” when an arc that is being traversed is blocked due to reasons such as road and weather conditions, congestion, accidents etc. If an incident occurs along the arc being traversed, the vehicle either waits until all effects of the incident are cleared and then follows the same path thereafter, or returns to the starting node of that arc and follows an escape route to the destination node, the latter course of action is called as “re-routing”. Also, we consider that this arc is not visited again throughout the travel along the network when an incident occurs and the alternative of not following this arc after the event is chosen. We propose a labeling algorithm to solve this specific problem. Then, a real case problem is analyzed by the proposed algorithm and several numerical studies are conducted in order to assess the sensitivity of the probability and travel time parameters.
Open Access
Solution methods for planning problems in wireless mesh networks
(2012) Özdemir, Görkem
Wireless Mesh Networks (WMNs) consist of a finite number of radio nodes. A subset of these nodes, called gateways, has wired connection to the Internet and the non-gateway nodes transmit their traffic to a gateway node through the wireless media in a multi-hop fashion. Wireless communication signals that propagate simultaneously within the same frequency band may interfere with one another at a receiving node and may therefore prevent successful transmission of data. In order to circumvent this problem, nodes on the network can be configured to receive and send signals in different time slots and through different frequency bands. Therefore, a transmission slot can be defined as a pair of a certain frequency band and a specific time slot. In addition, by adjusting the power level of a radio node, its transmission range can be modified. Given a wireless mesh network with fixed node locations, demand rate at each node, and maximum power level for each node, we study the problem of carrying the traffic of each node to the Internet through the network. Our goal is to allocate capacities in proportion to the demand of each node in such a way that the minimum ratio is maximized. We propose a mixed integer linear programming (MILP) formulation to select a given number of gateway locations among the nodes in the network, to determine the routing of the traffic of each node through the gateway nodes, to assign transmission slots to each node in order to ensure no interference among wireless signals, and to determine the transmission power levels. In our study, we adopt the physical interference model, instead of the protocol interference, since this is more realistic. Since MILP formulation becomes computationally inefficient for larger instances; we developed several different approaches. Then, we proposed a combinatorial optimization model which successfully solves most of the instances. We tested our models and methods in several data sets, and results are presented.
Open Access
Traffic engineering and regenerator placement in MPLS and GMPLS networks with restoration
(2002) Yetginer, Emre