Provisioning QoS in inter-domain traffic engineering

This work describes an architectural framework that allows inter-domain Traffic Engineering Label Switched Paths (TE-LSPs) with guaranteed quality of service (QoS) to be setup. Such TE-LSPs, called EQ-links, are setup by coordinating path computation elements (PCEs) of neighboring autonomous systems (ASs) along a pre-determined inter-AS path, computed through cooperative interaction between pairs of neighboring ASs. After defining the architectural requirements for the framework, we describe and analyze the Inter-AS Path Computation Protocol (IA-PCP), which computes an interdomain path at the AS level, i.e., selecting a sequence of ASs to the destination, based on a loose source routing approach. The results of the IA-PCP computations are then fed to the PCEs for complete path computation. The proposed architecture has been actually implemented within the testbed of the EuQoS project, which is aimed at enabling end-to-end QoS in the Internet. We report results related to the setup time of EQ-links, measured in the pan-European testbed of the EuQoS project, showing that path computation and setup takes an affordable time overhead.     

On inferring autonomous system relationships in the Internet

The Internet consists of rapidly increasing number of hosts interconnected by constantly evolving networks of links and routers. Interdomain routing in the Internet is coordinated by the Border Gateway Protocol (BGP). The BGP allows each autonomous system (AS) to choose its own administrative policy in selecting routes and propagating reachability information to others. These routing policies are constrained by the contractual commercial agreements between administrative domains. For example, an AS sets its policy so that it does not provide transit services between its providers. Such policies imply that AS relationships are an important aspect of the Internet structure. We propose an augmented AS graph representation that classifies AS relationships into customer-provider, peering, and sibling relationships. We classify the types of routes that can appear in BGP routing tables based on the relationships between the ASs in the path and present heuristic algorithms that infer AS relationships from BGP routing tables. The algorithms are tested on publicly available BGP routing tables. We verify our inference results with AT&T internal information on its relationship with neighboring ASs. As much as 99.1% of our inference results are confirmed by the AT&T internal information. We also verify our inferred sibling relationships with the information acquired from the WHOIS lookup service. More than half of our inferred sibling-to-sibling relationships are confirmed by the WHOIS lookup service. To the best of our knowledge, there has been no publicly available information about AS relationships and this is the first attempt in understanding and inferring AS relationships in the Internet. We show evidence that some routing table entries stem from router misconfigurations     

Per-domain packet scale rate guarantee for expedited forwarding

The expedited forwarding per-hop behavior (EF PHB) was recently replaced by a new definition, called packet scale rate guarantee (PSRG), under the Differentiated Services (DiffServ) framework. This replacement raises two challenges. One is the implementation of a PSRG server. Another is the provision of per-domain PSRG. Specifically, for the former, an open issue is whether hierarchical schedulers can provide PSRG; for the latter, it is not clear whether and how per-domain PSRG can be provided in the presence of flow aggregation. Since, in DiffServ networks, flow aggregation is a natural phenomenon and hierarchical scheduling is high-likely desired, these two challenges become even more critical. To address the first challenge, we introduce a new concept called latency-rate worst-case service guarantee (LR-WSG). We prove that, if a server provides LR-WSG, it also provides PSRG. We show that many well-known schedulers support LR-WSG, which include not only one-level schedulers but also their hierarchical versions. To address the second challenge, we first prove that PSRG can be extended from per-node to per-domain if no flow aggregation is performed. The proof is notable in that it depends solely on the concept of PSRG itself. We then investigate the provision of per-domain PSRG in presence of flow aggregation. We propose to use packet scale fair aggregator (PSFA) to aggregate flows. We show that, with PSFA, per-domain PSRG can be provided in spite of flow aggregation. We finally provide a brief discuss on the viability of using PSFA in DiffServ networks and define an expedited forwarding per-domain behavior (EF PDB).     

The stable paths problem and interdomain routing

Dynamic routing protocols such as RIP and OSPF essentially implement distributed algorithms for solving the shortest paths problem. The border gateway protocol (BGP) is currently the only interdomain routing protocol deployed in the Internet. BGP does not solve a shortest paths problem since any interdomain protocol is required to allow policy-based metrics to override distance-based metrics and enable autonomous systems to independently define their routing policies with little or no global coordination. It is then natural to ask if BGP can be viewed as a distributed algorithm for solving some fundamental problem. We introduce the stable paths problem and show that BGP can be viewed as a distributed algorithm for solving this problem. Unlike a shortest path tree, such a solution does not represent a global optimum, but rather an equilibrium point in which each node is assigned its local optimum. We study the stable paths problem using a derived structure called a dispute wheel, representing conflicting routing policies at various nodes. We show that if no dispute wheel can be constructed, then there exists a unique solution for the stable paths problem. We define the simple path vector protocol (SPVP), a distributed algorithm for solving the stable paths problem. SPVP is intended to capture the dynamic behavior of BGP at an abstract level. If SPVP converges, then the resulting state corresponds to a stable paths solution. If there is no solution, then SPVP always diverges. In fact, SPVP can even diverge when a solution exists. We show that SPVP will converge to the unique solution of an instance of the stable paths problem if no dispute wheel exists     

Quantifying Path Exploration in the Internet

Previous measurement studies have shown the existence of path exploration and slow convergence in the global Internet routing system, and a number of protocol enhancements have been proposed to remedy the problem. However, existing measurements were conducted only over a small number of testing prefixes. There has been no systematic study to quantify the pervasiveness of Border Gateway Protocol (BGP) slow convergence in the operational Internet, nor any known effort to deploy any of the proposed solutions. In this paper, we present our measurement results that identify BGP slow convergence events across the entire global routing table. Our data shows that the severity of path exploration and slow convergence varies depending on where prefixes are originated and where the observations are made in the Internet routing hierarchy. In general, routers in tier-1 Internet service providers (ISPs) observe less path exploration, hence they experience shorter convergence delays than routers in edge ASs; prefixes originated from tier-1 ISPs also experience less path exploration than those originated from edge ASs. Furthermore, our data show that the convergence time of route fail-over events is similar to that of new route announcements and is significantly shorter than that of route failures. This observation is contrary to the widely held view from previous experiments but confirms our earlier analytical results. Our effort also led to the development of a path-preference inference method based on the path usage time, which can be used by future studies of BGP dynamics.     

Fast Routing Algorithms for Lightpath Establishment in Wavelength-Routed Optical Networks

In this paper, we study shortest-path routing in wavelength-routed optical networks with an objective to optimize the average-case running time for path computation. Four fast routing algorithms are proposed for dynamically computing the shortest lightpaths or semilightpaths in a network with or without wavelength converters. To reduce the average-case running time for path computation, sequential search, backward routing, and informed search are used in the algorithm design. Simulation results show that the proposed algorithms can significantly reduce the average-case computational overhead for path computation as compared with existing algorithms.      

Interdomain routing through QoS-class planes [Quality-of-Service-Based Routing Algorithms for Heterogeneous Networks]

This article presents an approach to delivering qualitative end-to-end quality of service (QoS) guarantees across the multiprovider Internet. We propose that bilateral agreements between a number of autonomous systems (ASs) result in the establishment of QoS-class planes that potentially extend across the global Internet. The deployment of a QoS-enhanced border gateway protocol (BGP) with different QoS-based route selection policies in each of the planes allows a range of interdomain QoS capabilities to coexist on the same network infrastructure. The article presents simulation results showing the benefits of the approach and discusses aspects of the performance of QoS-enhanced BGP     

分布式服务质量路由预计算算法

服务质量路由作为下一代IP互联网提供服务质量(QoS)控制的一种重要方案,如何提高其可扩展性和路由性能是有待解决的难题.本文提出了基于聚类的分布式预计算算法,以具有多种QoS参数的路由表预计算为目标,引入了支持QoS参数的扩展距离向量,通过网络中各个节点的分布式协同计算,大大降低了单个路由器的计算复杂度.文章分析了优势路径及其选取策略,给出了路由计算中优势路径聚集的聚类方法,实现了QoS路由表的高效聚集压缩.实验结果进一步验证了该算法具有计算量小和QoS路由性能高的优点,在QoS度量维数和网络规模方面均具有良好的可扩展性,并对域间算法研究提供了重要依据.     

Stable Internet routing without global coordination

The Border Gateway Protocol (BGP) allows an autonomous system (AS) to apply diverse local policies for selecting routes and propagating reachability information to other domains. However, the BGP permits ASs to have conflicting policies that can lead to routing instability. This paper proposes a set of guidelines for an AS to follow in setting its routing policies, without requiring coordination with other ASs. Our approach exploits the Internet's hierarchical structure and the commercial relationships between ASs to impose a partial order on the set of routes to each destination. The guidelines conform to conventional traffic-engineering practices of ISPs, and provide each AS with significant flexibility in selecting its local policies. Furthermore, the guidelines ensure route convergence even under changes in the topology and routing policies. Drawing on a formal model of BGP, we prove that following our proposed policy guidelines guarantees route convergence. We also describe how our methodology can be applied to new types of relationships between ASs, how to verify the hierarchical AS relationships, and how to realize our policy guidelines. Our approach has significant practical value since it preserves the ability of each AS to apply complex local policies without divulging its BGP configurations to others     

不确定型模糊Kripke结构的计算树逻辑模型检测

本文研究了不确定型模糊Kripke结构的计算树逻辑的模型检测问题,并说明了该问题可以在对数多形式时间内解决.首先给出了不确定型模糊Kripke结构的定义,引入了模糊计算树逻辑的语法和语义.为了刻画存在量词∃和任意量词∀在不确定型模糊Kripke结构中的两种语义解释,在模糊计算树逻辑语法中引入了路径量词∃_sup,∃_inf和∀_sup,∀_inf,分别用于替换存在量词∃和任意量词∀.其次讨论了基于不确定型模糊Kripke结构的计算树逻辑模型检测算法,特别地对于模糊计算树逻辑公式∃_suppUq,∀_suppUq,∃_infpUq和∀_infpUq分别给出时间复杂度为对数多项式时间的改进算法.     

Faster Algorithms for Construction of Recovery Trees Enhancing QoP and QoS

Medard et al. proposed an elegant recovery scheme (known as the MFBG scheme) using red/blue recovery trees for multicast path protection against single link or node failures. Xue et al. extended the MFBG scheme and introduced the concept of quality of protection (QoP) as a metric for multifailure recovery capabilities of single failure recovery schemes. They also presented polynomial time algorithms to construct recovery trees with good QoP and quality of service (QoS). In this paper, we present faster algorithms for constructing recovery trees with good QoP and QoS performance. For QoP enhancement, our O(n + m) time algorithm has comparable performance with the previously best O(n²(n + m)) time algorithm, where n and m denote the number of nodes and the number of links in the network, respectively. For cost reduction, our O(n + m) time algorithms have comparable performance with the previously best O(n²(n + m)) time algorithms. For bottleneck bandwidth maximization, our O(m log n) time algorithms improve the previously best O(nm) time algorithms. Simulation results show that our algorithms significantly outperform previously known algorithms in terms of running time, with comparable QoP or QoS performance.     

Policies for allocating performance impairment budgets among multiple IP providers

An important technical aspect of achieving end-to-end quality of service (QoS) in next generation networks refers to allocation of the total performance impairment budget (delay, jitter, packet loss) among multiple providers. In this article, we first propose a generic policy for allocating per-domain impairment budgets, relying on the set of performance metrics from service request and the rules for their composition on the multi-domain path. The objective is to provide end-to-end QoS through the set of heterogeneous domains, with different QoS models and definitions of service classes. The allocation of impairment budgets among multiple domains is then closely related to mapping of service classes between providers and selection of the most appropriate class for particular service in each domain. Based on the generic policy, we further derive examples of specific policies and evaluate them with respect to fulfillment of QoS objectives, fairness, adaptability and scalability. Evaluation tool implements a policy-based conformance matching scheme, which enforces selection of the domain class that most tightly matches with the required QoS.     

M_CSPF: A Scalable CSPF Routing Scheme with Multiple QoS Constraints for MPLS Traffic Engineering

In the context of multi‐protocol label switching (MPLS) traffic engineering, this paper proposes a scalable constraint‐based shortest path first (CSPF) routing algorithm with multiple QoS metrics. This algorithm, called the multiple constraint‐based shortest path first (M_CSPF) algorithm, provides an optimal route for setting up a label switched path (LSP) that meets bandwidth and end‐to‐end delay constraints. In order to maximize the LSP accommodation probability, we propose a link weight computation algorithm to assign the link weight while taking into account the future traffic load and link interference and adopting the concept of a critical link from the minimum interference routing algorithm. In addition, we propose a bounded order assignment algorithm (BOAA) that assigns the appropriate order to the node and link, taking into account the delay constraint and hop count. In particular, BOAA is designed to achieve fast LSP route computation by pruning any portion of the network topology that exceeds the end‐to‐end delay constraint in the process of traversing the network topology. To clarify the M_CSPF and the existing CSPF routing algorithms, this paper evaluates them from the perspectives of network resource utilization efficiency, end‐to‐end quality, LSP rejection probability, and LSP route computation performance under various network topologies and conditions.     

Evaluation of multicast routing algorithms for real-timecommunication on high-speed networks

Multicast (MC) routing algorithms capable of satisfying the quality of service (QoS) requirements of real-time applications will be essential for future high-speed networks. We compare the performance of all of the important MC routing algorithms when applied to networks with asymmetric link loads. Each algorithm is judged based on the quality of the MC trees it generates and its efficiency in managing the network resources. Simulation results over random networks show that unconstrained algorithms are not capable of fulfilling the QoS requirements of real-time applications in wide-area networks. Simulations also reveal that one of the unconstrained algorithms, reverse path multicasting (RPM), is quite inefficient when applied to asymmetric networks. We study how combining routing with resource reservation and admission control improves the RPM's efficiency in managing the network resources. The performance of one semiconstrained heuristic, MSC, three constrained Steiner tree (CST) heuristics, Kompella, Pasquale, and Polyzos (1992), constrained adaptive ordering (CAO), and bounded shortest multicast algorithm (BSMA), and one constrained shortest path tree (CSPT) heuristic, the constrained Dijkstra heuristic (CDKS) are also studied. Simulations show that the semiconstrained and constrained heuristics are capable of successfully constructing MC trees which satisfy the QoS requirements of real-time traffic. However, the cost performance of the heuristics varies. The BSMA's MC trees are lower in cost than all other constrained heuristics. Finally, we compare the execution times of all algorithms, unconstrained, semiconstrained, and constrained     

Tabu search based algorithms for bandwidth-delay-constrained least-cost multicast routing

The advent of various real-time multimedia applications in high-speed networks creates a need for quality of service (QoS) based multicast routing. The Steiner tree problem, is a well-known NP-complete problem, provides the mathematical structure behind multicast communications. Two important QoS constraints are the bandwidth constraint and the end-to-end delay constraint. In this paper, we propose various algorithms to solve the bandwidth-delay-constrained least-cost multicast routing problem based on Tabu Search (TS), addressing issues of the selected initial solution and move type as two major building blocks in short-term memory version of Tabu Search and longer-term memory with associated intensification and diversification strategies as advanced Tabu Search techniques. We evaluate the performance and efficiency of the proposed TS-based algorithms in comparison with other existing TS-based algorithms and heuristics on a variety of random generated networks with regard to total tree cost. Finally we identify the most efficient algorithm uncovered by our testing.     

Performance evaluation of constraint-based path selection algorithms

Constraint-based path selection is an invaluable part of a full-fledged quality of service (QoS) architecture. Internet service providers want to be able to select paths for QoS flows that optimize network utilization and satisfy user requirements and as such increase revenues. Unfortunately, finding a path subject to multiple constraints is known to be an NP-complete problem. Hence, accurate constraint-based path selection algorithms with a fast running time are scarce. Numerous heuristics and a few exact algorithms have been proposed. In this article we compare most of these algorithms. We focus on the restricted shortest path algorithms and multi-constrained path algorithms. The performance evaluation of these two classes of algorithms is presented based on complexity analysis and simulation results and may shed some light on the difficult task of selecting the proper algorithm for a QoS-capable network.     

基于节点搜索的可变形块运动补偿

本文讨论可变形块匹配(DBMA)的运动补偿和预测方法,提出基于节点搜索的可变形块匹配算法(NS-DBMA),并在此基础上提出分数像素精度预测和双模式混合预测方法.实验结果表明,NS-DBMA比全搜索方块匹配法(EBMA)平均改善约2dB;其运算量仅为基于梯度的可变形块匹配算法(GB-DBMA)的一半,但能得到更好的主客观预测质量,且更易于VLSI硬件实现.     

TSB:一种多阶段IPv6路由表查找算法

充分分析IPv6地址结构、IPv6地址分配策略和IPv6骨干网路由表的特点后,将二叉树、段表和路由桶技术相结合,提出一种多阶段IPv6路由表查找算法.和已有算法相比,提出的算法查找速度快、占用内存少、扩展性好、支持增量更新.实验结果表明算法的软件参考实现在装有P4 2.4GHz CPU,512M DDR333 内存和Linux 操作系统的普通PC 机上的查找能力可以到达16MPPS(Million Packet per Second),这可以满足10Gbps 80 字节IPv6最小包的线速转发.对于当前IPv6骨干网BGP 路由表,算法的参考实现只占用几百K 字节的内存.     

低能耗的隐私数据安全融合方法

为解决物联网安全数据融合过程中,数据隐私保护与节点计算能力及能量受限之间的矛盾,在对现有方法优缺点分析的基础上,提出一种低能耗的隐私数据安全融合方法(LCSDA, low energy-consuming secure data aggregation),该方法根据最短路径原则选择邻居节点,并且采用Prim最小生成树算法建立簇内数据融合路径。仿真结果表明,该方法可以有效降低节点能耗和簇头节点被捕获的概率,同时保证节点数据的隐私性。