On investigating overlay service topologies

Recently, a moderate amount of work has been reported on the use of overlay networks to support value-added network services, such as multicasting, Quality-of-Service (QoS), security, etc. To design an overlay network, the first step is to choose an overlay topology connecting all the overlay service nodes. When considering overlay topologies, several questions need to be answered first: How overlay topologies affect overlay routing performance? Which topologies can provide satisfactory performance? How can we construct efficient overlay topologies connecting all the overlay nodes?In this paper, we focus on the overlay network topology construction issue. First, we evaluate and compare the performance and overhead of the existing overlay topologies. Second, we formalize the overlay topology construction problem and propose two new heuristic methods to construct efficient overlay topologies. Simulation results have demonstrated the efficiency of the two proposed approaches. It is shown that overlay service performance varies significantly with respect to different overlay topologies. Thus, it is important to choose an appropriate overlay network topology. The knowledge of IP-layer topology information also benefits significantly in constructing efficient overlay topologies as inferred from the results.     

Toward Optimal Network Fault Correction in Externally Managed Overlay Networks

We consider an end-to-end approach of inferring probabilistic data forwarding failures in an externally managed overlay network, where overlay nodes are independently operated by various administrative domains. Our optimization goal is to minimize the expected cost of correcting (i.e., diagnosing and repairing) all faulty overlay nodes that cannot properly deliver data. Instead of first checking the most likely faulty nodes as in conventional fault localization problems, we prove that an optimal strategy should start with checking one of the candidate nodes, which are identified based on a potential function that we develop. We propose several efficient heuristics for inferring the best node to be checked in large-scale networks. By extensive simulation, we show that we can infer the best node in at least 95 percent of time, and that first checking the candidate nodes rather than the most likely faulty nodes can decrease the checking cost of correcting all faulty nodes.     

On basic properties of fault-tolerant multi-topology routing

Multi-topology routing has recently gained popularity as a simple yet efficient traffic engineering concept. Its basic purpose is to separate different classes of network traffic, which are then transported over disjoint logical topologies. Multi-topology routing is used as a basis for implementation of an IP fast reroute scheme called Multiple Routing Configurations (MRC).MRC has a range of attractive properties, but they do come at a cost. In order to guarantee recovery from any single link or node failure in the network, MRC has to maintain several logical topologies and thus an increased amount of routing information. The number of the logical topologies in MRC need not be large; even simple heuristic algorithms often yield good results in practice. However, why this is the case is not fully understood yet.In this paper, we introduce a theoretical framework for fault-tolerant multi-topology routing (FT-MTR). MRC is a practical implementation of FT-MTR in connectionless IP networks. We use FT-MTR to study how the internal topological structure of the communication network relates to two important problems. The first problem is minimizing the number of logical topologies and thus the routing state in FT-MTR. We show how to use the sets of nodes that separate the topology graph to devise an advanced heuristic for “intelligent” construction of the logical topologies. Finding the separating sets in a topology graph is computationally demanding; we present an algorithm that performs well in tested real network topologies. We evaluate the separation-set based heuristic for the logical topology construction and show that it outperforms the known MRC heuristics.The second problem is the FT-MTR load distribution after a failure. We use the separating sets to devise a novel algorithm for failure load distribution. This algorithm does not require knowledge of the traffic demand matrix, still, our tests indicate that it performs as good as, or better than, known MRC load-distribution algorithms that do require the demand matrix as input.     

A Two-Hop Solution to Solving Topology Mismatch

The efficiency of Peer-to-Peer (P2P) systems is largely dependent on the overlay constructions. Due to the random selection of logical neighbors, there is serious topology mismatch problem between the overlay and the physical topologies in many P2P systems. Such mismatching causes unnecessary query message duplications on both overlay and IP level, as well as increase query response time. In this research, we define the optimal overlay problem, and prove its NP-hardness. To address this issue, we propose a distributed overlay optimization algorithm, THANCS, and evaluate its effectiveness through trace driven simulations. The proposed THANCS has four major strengths. First, it does not need any global knowledge. Second, its optimization convergent speed is fast. Third, it is orthogonal to other types of advanced search approaches. Fourth, it reduces both the traffic cost and the search latency.     

Achieving effective resilience for QoS-aware application mapping

Overlay mapping provides a flexible and effective means of application deployment by selecting a subset of nodes and links from the substrate-hosting network to meet, or even enhance, the requirements of the application. In order to take full advantage of the potential of overlay mapping given the features of the substrate network, such as topology and performance characteristics, it is critical to carefully choose the subset of hosting nodes. This is to balance the effectiveness of the overlay mapping with substrate network constraints and resource usage. In this paper, we investigate how to provide effective resilience for a QoS-aware overlay mapping so as to make the mapped applications resilient against substrate network failure(s) whilst providing enhanced QoS. We first formulate the problem as an Integer Linear Program (ILP). Using simulations with small networks, existing methods are shown to be capable of achieving enhanced QoS but lack effective resilience when compared against the optimal ILP solution. To address this issue, a novel heuristic is proposed which incorporates substrate topology information. Through simulations with synthetic and real networks, the effectiveness of the new heuristic is confirmed.     

Building a Scalable Bipartite P2P Overlay Network

The peer-to-peer (P2P) model, being widely adopted in today's Internet computing, suffers from the problem of topology mismatch between the overlay networks and the underlying physical network. Traditional topology optimization techniques identify physically closer nodes to connect as overlay neighbors, but could significantly shrink the search scope. Efforts have been made to address the mismatch problem without sacrificing the search scope, but they either need time synchronization among peers or have a low convergent speed. In this paper, we propose a scalable bipartite overlay (SBO) scheme to optimize the overlay topology by identifying and replacing the mismatched connections. In SBO, we employ an efficient strategy for distributing optimization tasks in peers with different colors. We conducted comprehensive simulations to evaluate this design. The results show that SBO achieves approximately 85 percent of reduction on traffic cost and about 60 percent of reduction on query response time. Our comparisons with previous approaches to address the topology mismatch problem have shown that SBO can achieve a fast convergent speed, without the need of time synchronization among peers.     

Spare capacity provisioning for quasi-static traffic

Resource provisioning has for long been an important area of research in network design. The traffic grooming problem in optical networks is a design problem of aggregating sub-wavelength traffic demands onto lightpaths and lightpaths onto fiber links such that the required electronic switching capability, hence network cost, can be minimized. Because of the reconfiguration cost in optical grooming networks, a reactive resource provisioning approach may become inefficient, and result in revenue loss. In this paper, we propose an over-provisioning scheme, which pre-allocates the spare capacity of lightpaths to dynamic sub-wavelength traffic demands such that the network can be more agile in responding to traffic increment requests. For the single-link case, we formulate the problem as a non-linear programming problem, and for under reasonable assumptions, we prove the objective function is convex. We provide an exact algorithm to find the optimal solution. The problem with general topologies is then studied. We prove the NP-hardness in this case, and propose heuristics. Numerical results show our heuristics perform well.     

Routing in sparse splitting optical networks with multicast traffic

In this paper, we investigate the problem of Multicast Routing in Sparse Splitting Networks (MR-SSN). Given a network topology with the multicast capable nodes distributed uniformly throughout the network, and a multicast session, the MR-SSN problem is to find a route from the source node of the multicast session to all destinations of the multicast session such that the total number of fibers used in establishing the session is minimized. In this paper, we develop a rerouting algorithm for a given Steiner tree, which makes it feasible to route a multicast session using a tree-based solution in sparse light splitting optical networks. In addition, we present a heuristic based on Tabu Search (TS) that requires only one transmitter for the source node and one wavelength for each multicast session. To evaluate the performance of heuristics, we formulate the MR-SSP problem as an integer linear program (ILP), and optimally solve small instances using the commercially available linear solver, CPLEX. We test our heuristic on a wide range of network topologies. Our experimental results show that: (1) The difference between our solution and ILP optimal solution, in terms of the number of fibers used for establishing a multicast session, is within 10% in almost all the instances and within 5% in about half of the instances. (2) The average delay, taken over all destination nodes, falls within three times the optimal value. (3) A sparse light splitting all-optical network with 30% of multicast capable cross-connects has an acceptable low cost and relatively good performance. (4) The improvement achieved by TS heuristic increases considerably when the session size is large, the number of Splitter-and-Delivery cross-connects is small, and the network connectivity is dense.     

Large Scaling Unstructured Peer-to-Peer Networks with Heterogeneity-Aware Topology and Routing

Peer-to-peer (P2P) file sharing systems such as Gnutella have been widely acknowledged as the fastest-growing Internet applications ever. The P2P model has many potential advantages, including high flexibility and serverless management. However, these systems suffer from the well-known performance mismatch between the randomly constructed overlay network topology and the underlying IP-layer topology. This paper proposes to structure the P2P overlay topology using a heterogeneity-aware multitier topology to better balance the load at peers with heterogeneous capacities and to prevent low-capability nodes from throttling the performance of the system. An analytical model is developed to enable the construction and maintenance of heterogeneity-aware overlay topologies with good node connectivity and better load balance. We also develop an efficient routing scheme, called probabilistic selective routing, that further utilizes heterogeneity-awareness to enhance the routing performance. We evaluate our design through simulations. The results show that our multitier topologies alone can provide eight to 10 times improvement in the messaging cost, two to three orders of magnitude improvement in terms of load balancing, and seven to eight times lower topology construction and maintenance costs when compared to Gnutella's random power-law topology. Moreover, our heterogeneity-aware routing scheme provides further improvements on all evaluation metrics, when used with our heterogeneity-aware overlay topologies     

Traffic grooming, routing, and wavelength assignment in WDM transport networks with sparse grooming resources

While a single fiber strand in wavelength division multiplexing (WDM) has over a terabit-per-second bandwidth and a wavelength channel has over a gigabit-per-second transmission speed, the network may still be required to support traffic requests at rates that are lower than the full wavelength capacity. To avoid assigning an entire lightpath to a small request, many researchers have looked at adding traffic grooming to the routing and wavelength assignment (RWA) problem. In this work, we consider the RWA problem with traffic grooming (GRWA) for mesh networks under static and dynamic lightpath connection requests. The GRWA problem is NP-Complete since it is a generalization of the RWA problem which is known to be NP-Complete. We propose an integer linear programming (ILP) model that accurately depicts the GRWA problem. Because it is very hard to find a solution for large networks using ILP, we solve the GRWA problem by proposing two novel heuristics. The strength of the proposed heuristics stems from their simplicity, efficiency, and applicability to large-scale networks. Our simulation results demonstrate that deploying traffic grooming resources on the edge of optical networks is more cost effective and results in a similar blocking performance to that obtained when distributing the grooming resources throughout the optical network domain.     

Adding structure to unstructured peer-to-peer networks: the use of small-world graphs

The “small-world” graph structure is pervasive and is observed to arise “without-design” or “naturally” in many practical systems such as the World Wide Web. In contrast to natural systems, overlay networks provide an opportunity to design structure. We seek the advantages of designing overlay topologies with small-world properties to support file sharing in peer-to-peer networks. We focus on two metrics of performance: (a) search protocol performance, a local gain perceived directly by peer-to-peer network users and (b) network utilization, a global property that is of interest to network service providers. We propose a class of overlay topologies and show, by simulation, that a particular topology instance of this class where every node has many close neighbors and few random neighbors (i.e., a small-world graph) exhibits very good properties. In this overlay topology, the chances of locating files are high, and the nodes where these files are found are, on average, close to the query source. This improvement in search protocol performance is achieved while decreasing the traffic load on the links in the underlying network. We propose a simple greedy algorithm to construct such overlay topologies where each node operates independently and in a decentralized manner to select its neighbors.     

Routing and resource optimization in service overlay networks

Service Overlay Networks (SONs) create a virtual topology on top of the Internet and provide end-to-end quality of service guarantees without requiring support by the underlying network.The optimization of the resources utilized by an SON is a fundamental issue for an overlay operator owing to the costs involved and the need to satisfy user requirements. Careful decisions are necessary to provide enough capacity to overlay links, to route traffic, to assign users to access nodes and to deploy overlay nodes.In this paper, we propose two mathematical programming models for the user assignment problem, the traffic routing optimization and the dimensioning of the capacity reserved on overlay links in SONs. The first model minimizes the SON installation cost while providing full access to all users. The second model maximizes the SON profit by selecting which users to serve, based on the expected gain, and taking into consideration budget constraints of the SON operator. Moreover, we extend these models to include the optimization of the number and position of overlay nodes.We provide the optimal solutions of the proposed SON design formulations on a set of realistic-size instances and discuss the effect of different parameters on the characteristics of the planned networks. Numerical results show that the proposed approach is able to solve the problem to the optimum even for large-scale networks.     

Location awareness in unstructured peer-to-peer systems

Peer-to-peer (P2P) computing has emerged as a popular model aiming at further utilizing Internet information and resources. However, the mechanism of peers randomly choosing logical neighbors without any knowledge about underlying physical topology can cause a serious topology mismatch between the P2P overlay network and the physical underlying network. The topology mismatch problem brings great stress in the Internet infrastructure. It greatly limits the performance gain from various search or routing techniques. Meanwhile, due to the inefficient overlay topology, the flooding-based search mechanisms cause a large volume of unnecessary traffic. Aiming at alleviating the mismatching problem and reducing the unnecessary traffic, we propose a location-aware topology matching (LTM) technique. LTM builds an efficient overlay by disconnecting slow connections and choosing physically closer nodes as logical neighbors while still retaining the search scope and reducing response time for queries. LTM is scalable and completely distributed in the sense that it does not require any global knowledge of the whole overlay network. The effectiveness of LTM is demonstrated through simulation studies.     

Energy-efficient topology control in wireless ad hoc networks with selfish nodes

In wireless ad hoc networks there is no fixed infrastructure or centralized controller to enforce cooperation between nodes. Therefore, nodes may act selfishly in running network protocols for conserving their own energy resources. In this paper, we consider the “topology control (TC) game” as the problem of creating an energy-efficient topology in wireless ad hoc networks in the presence of selfish nodes. We define a new TC game in which nodes are able to dynamically adjust their transmission power in a per-packet manner, and try to minimize their energy usage through considering both traffic load and transmission power parameters. After analyzing the problem, we propose several algorithms to find stable topologies in an environment composed of selfish nodes, using two types of global and local connectivity information. Finally, we evaluate the performance of the proposed algorithms by simulations. Our simulation results show that using appropriate local information can interestingly result in more efficient topologies than global information.     

Topology Design of Network-Coding-Based Multicast Networks

It is anticipated that a large amount of multicast traffic needs to be supported in future communication networks. The network coding technique proposed recently is promising for establishing multicast connections with a significantly lower bandwidth requirement than that of traditional Steiner-tree-based multicast connections. How to design multicast network topologies with the consideration of efficiently supporting multicast by the network coding technique becomes an important issue now. It is notable, however, that the conventional algorithms for network topology design are mainly unicast-oriented, and they cannot be adopted directly for the efficient topology design of network-coding-based multicast networks by simply treating each multicast as multiple unicasts. In this paper, we consider for the first time the novel topology design problem of network-coding-based multicast networks. Based on the characteristics of multicast and network coding, we first formulate this problem as a mixed-integer nonlinear programming problem, which is NP-hard, and then propose two heuristic algorithms for it. The effectiveness of our heuristics is verified through simulation and comparison with the exhaustive search method. We demonstrate in this paper that, in the topology design of multicast networks, adopting the network coding technique to support multicast transmissions can significantly reduce the overall topology cost as compared to conventional unicast-oriented design and the Steiner-tree-based design.     

Approaching neighbor proximity and load balance for range query in P2P networks

We present a platform for building a range-queriable system. A distinguishing characteristic of the platform is that objects are not bound to any particular node. Rather, they can be freely moved between neighboring nodes to balance load as long as some ordering between objects in different nodes is respected. Decoupling the link between nodes and objects allows the overlay network to be constructed independently of object placement, focusing only on its own concerns, e.g. proximity and balanced load in routing. The main focus then is to present several heuristics for proximity-aware node joining to reduce communication costs in the platform. These heuristics are based on a novel process called hierarchical neighborhood search, which utilizes the overlay links to provide incoming nodes an overview of the network topology, thereby to guide them to find their neighborhood in the overlay. The experimental results show that some of the heuristics are very effective; they can reduce as much as 80% of the communication costs for neighboring nodes, and 40% overall.     

A family of simple distributed minimum connected dominating set-based topology construction algorithms

This paper considers the problem of topology construction to save energy in wireless sensor networks. The proposed topology construction mechanisms build reduced topologies using the Connected Dominating Set approach in a distributed, efficient, and simple manner. This problem is very challenging because the solution must provide a connected network with complete coverage of the area of interest using the minimum number of nodes possible. Further, the algorithms need to be computationally inexpensive and the protocols simple enough in terms of their message and computation complexity, so they do not consume more energy creating the reduced topology than the energy that they are supposed to save. In addition, it is desirable to reduce or completely eliminate the need of localization mechanisms since they introduce additional costs and energy consumption. To this end, we present the family of A3 distributed topology construction algorithms, four simple algorithms that build reduced topologies with very low computational and message complexity without the need of localization information: A3, A3Cov, A3Lite and A3CovLite. The algorithms are compared in sparse and dense networks versus optimal theoretical bounds for connected-coverage topologies and two distributed heuristics found in the literature using the number of active nodes and the ratio of coverage as the main performance metrics. The results demonstrate that there is no clear winner, and rather, trade offs exist. If coverage is not as critical as energy (network lifetime), it would be better to use A3Lite, as it needs fewer number of nodes and messages. If coverage is very important for the application, then the A3CovLite is the best option mostly because of the lower message complexity.     

Topology-Aware Multiple Routing Configurations for Fault Tolerant Networking

Real-time services require reliable and fault tolerant communication networks to support their stringent Quality of Service requirements. Multi Topology Routing based IP Fast Re-route (MT-IPFRR) technologies provide seamless forwarding of IP packets during network failures by constructing virtual topologies (VTs) to re-route the disrupted traffic. Multiple Routing Configurations (MRC) is a widely studied MT-IPFRR technique. In this paper, we propose two heuristics, namely mMRC-1 and mMRC-2, to reduce the number of VTs required by the MRC to provide full coverage for single link/node failures, and hence, to decrease its operational complexity. Both heuristics are designed to construct more robust VTs against network partitioning by taking their topological characteristics into consideration. We perform extensive experiments on 3200 topologies with diverse structural properties using our automated topology generation and analysis tool. Numerical results show that the amount of reductions in VT requirements get higher up to 31.84 %, as the networks tend to have more hub nodes whose degree is much higher than the rest of the network.     

Optimal Clustering of Hierarchical Hyper-Ring Multicomputers

The Hyper-Ring (HR) is presented as a hierarchical and scalable ring-based topology for small-scale to massively parallel systems which eliminates the major disadvantages of large-scale rings. With a fixed node degree, a low cost, symmetric properties, and a simple routing scheme, the HR topology is very suitable for small-scale to large-scale multicomputer systems. Assuming pipelined communication, the performance of 4- and 5-dimensional HR multicomputers is modeled, the performance model is evaluated, and the results of the performance model evaluation are analyzed. Moreover, the impact of the traffic load and message length on the system performance is analyzed. The major objective of this work is to shed light on how to cluster HRs in order to optimize the system efficiency. Assuming a uniform message arrival rate into the nodes of the HR, the results show that the efficiency of HR topologies with an equal number of nodes is best when the topologies are perfectly balanced. The next best-performing HRs are those with larger rings at the lower (outer) levels and smaller rings at the higher levels (near the root ring). The results confirm that the HR topology is suitable for massively parallel and scalable multicomputer systems as well as for networks of workstations.     

根据IP地址奇偶性优化P2P对等网的方法

针对对等网(P2P)中因抽象的覆盖网与底层物理网不匹配而在网络上产生了大量多余的传送开销的问题,提出了一种基于IP地址奇偶性的方案来优化对等网的拓扑结构。该方法根据IP地址的奇偶性将对等网中的结点分成两组完成不同的工作。模拟实验证明了这种方法没有缩减查询范围,同时减小了网络中的传输负载和结点的工作负载,缩短了查询的响应时间,有效地解决了覆盖网与底层物理网拓扑不匹配现象。