Fixed point approximation for multirate multihop loss networks with state-dependent routing

In this paper we consider a class of loss networks that have arbitrary topologies and routes of arbitrary length. Multiple traffic classes are present, each with different bandwidth requirement, and each routed according to a state-dependent routing scheme. In particular, we consider the least loaded routing method generalized to routes of arbitrary number of hops. The connection level performance metric of interest is the end-to-end blocking probability. We are interested in developing fast evaluation methods to provide reasonably accurate estimates of the blocking probability, especially under heavy traffic load. Our algorithms are based on the fixed-point method framework, also known as the reduced load approximation. In addition to what commonly examined by previous work, two more factors contribute to the complexity of the computation in the scenario under consideration in this paper. One is the state-dependent nature of the routing mechanism, the other is the possible overlapping between routes due to the general multihop topology of the network. We present two fast approximation algorithms to evaluate the blocking probability with state-dependent routing by simplifying the route overlapping computation. We discuss the computational complexity of our algorithms as well as sources of approximation error. We then compare the numerical results with that of simulation and show that our algorithms provide fairly accurate blocking probability estimates especially under heavy traffic load.     

Performance analysis of circuit-switched networks withstate-dependent routing

A novel nonhierarchical dynamic routing technique called state-dependent routing (SDR) is studied. SDR uses traffic measurements and statistics to produce its call by call routing decisions. The SDR scheme has a two-level, two-time scale structure. The algorithm for evaluating the performance of networks using SDR, is based on analytical models for the fast and slow stages that capture the behavior of the network at the link level and the node-pair level, respectively. Very good results were obtained for both small and large networks, especially in the performance range that is useful for design purposes     

Performance analysis for hierarchical multirate loss networks

The reduced load approximation technique has been extensively applied to flat networks, but the feasibility of applying it to hierarchical network model has seldom been described. Hierarchical routing is essential for large networks such as the Internet inter/intra-domain routing hierarchy and the Private Network to Node Interface (PNNI) standard. Therefore, this paper proposes an efficient and accurate analytical model for evaluating the performance of hierarchical networks with multiple classes of traffic. A performance analysis model with considering multiple classes of traffic, the complexity of analytical and explosion of computation will be extremely increased, and hence, result in inaccurate analytical. The issue of multiple classes of traffic has to be addressed in performance analysis model. In this paper, we first study the reduced load approximation model for loss networks, and then propose a novel performance evaluation model for large networks with multirate hierarchical routing. The hierarchical evaluation model is based on decomposing a hierarchical route into several analytic hierarchical segments. Once the blockings of these hierarchical segments are accurately determined, the blocking of the hierarchical path can be estimated accurately from these segments blocking. Numerical results indicate that the proposed hierarchical reduced load approximation yields quite accurate blocking probabilities as compared to that of simulation results. Furthermore, the accuracy of the proposed hierarchical reduced load approximation heuristic is independent of the blocking or the offered traffic load. Finally, we also draw some remarks on the convergence of the reduced load based approximation analysis model.     

Static and dynamic approaches to modeling end-to-end routing in circuit-switched networks

We present two routing strategies, identified herein as static least loaded routing (SLLR) and dynamic least loaded routing (DLLR). Dynamic routing in circuit-switched networks has been an active research topic. The literature to date in this area has focused on how to choose the "best" alternate route for overflow traffic from a direct route, within a network setting referred to as the backbone network. The traffic type considered in the literature has typically been one with a single destination. Least loaded routing (LLR) is an example of a state-dependent routing that selects the least loaded two-link alternate route when traffic overflows from the direct route. Motivated by the development of an emerging traffic type, called multidestination traffic, whose destination is not necessarily limited to a single location, we provide two routing strategies that deal with both the routing of the multiple-destination traffic to the extended network dimension, which is referred to as the destination network, and the routing of the backbone network traffic via LLR. In selecting the destination for multidestination traffic, SLLR employs static information, whereas DLLR employs real-time load status information concerning the destination links. We develop fixed-point models for both DLLR and SLLR. We also validate and compare the models through simulation. The results suggest that DLLR outperforms SLLR in all the scenarios, demonstrating the benefit of state-dependent routing in an end-to-end network. Further, the DLLR scheme improves if an "incident preference" rule is adopted; the rule allows a multidestination call to first choose the incident destination link, if any.     

Computing approximate blocking probabilities for a class ofall-optical networks

We study a class of all-optical networks using wavelength-division multiplexing (WDM) and wavelength routing, in which a connection between a pair of nodes in the network is assigned a path and a wavelength on that path. Moreover, on the links of that path no other connection can share the assigned wavelength. Using a generalized reduced load approximation scheme we calculate the blocking probabilities for the optical network model for two routing schemes: fixed routing and least loaded routing     

Blocking in all-optical networks

We present an analytical technique of very low complexity, using the inclusion-exclusion principle of combinatorics, for the performance evaluation of all-optical, wavelength-division multiplexed networks with no wavelength conversion. The technique is a generalized reduced-load approximation scheme which is applicable to arbitrary topologies and traffic patterns. One of the main issues in computing blocking probabilities in all-optical networks is the significant link load correlation introduced by the wavelength continuity constraint. One of the models we propose takes this into account and gives good results even under conditions with high link load correlation. Through numerous experiments we show that our models can be used to obtain fast and accurate estimates of blocking probabilities in all-optical networks and scale well with the path length and capacity of the network. We also extend one of our models to take into account alternate routing, in the form of Fixed Alternate Routing and Least Loaded Routing.     

Analysis of automatic network management controls

The performance response of circuit-switched networks with stored program control exchanges is analyzed under nonstationary traffic conditions. Models of real time traffic measurements and dynamic flows in such networks are developed. A framework for analysis and design of state-dependent routing and flow control algorithms is provided based on concepts of various traffic measurements and different patterns of traffic nonhomogeneity. It is indicated that global performance objectives can be obtained by means of the state-dependent shortest route algorithms. Issues relevant to an implementation of different traffic control techniques are discussed. An example routing scheme is introduced and compared with known procedures     

A resource-efficient and scalable wireless mesh routing protocol

By binding logic addresses to the network topology, routing can be carried out without going through route discovery. This eliminates the initial route discovery latency, saves storage space otherwise needed for routing table, and reduces the communication overhead and energy consumption. In this paper, an adaptive block addressing (ABA) scheme is first introduced for logic address assignment as well as network auto-configuration purpose. The scheme takes into account the actual network topology and thus is fully topology-adaptive. Then a distributed link state (DLS) scheme is further proposed and put on top of the block addressing scheme to improve the quality of routes, in terms of hop count or other routing cost metrics used, robustness, and load balancing. The network topology reflected in logic addresses is used as a guideline to tell towards which direction (rather than next hop) a packet should be relayed. The next hop is derived from each relaying node’s local link state table. The routing scheme, named as topology-guided DLS (TDLS) as a whole, scales well with regard to various performance metrics. The ability of TDLS to provide multiple paths also precludes the need for explicit route repair, which is the most complicated part in many wireless routing protocols. While this paper targets low rate wireless mesh personal area networks (LR-WMPANs), including wireless mesh sensor networks (WMSNs), the TDLS itself is a general scheme and can be applied to other non-mobile wireless mesh networks.     

Polynomial cost approximations in Markov decision theory based calladmission control

The problem of call admission control and routing in a multiservice circuit-switched loss network can be solved optimally under certain assumptions by the tools of Markov decision theory. However, in networks of practical size a number of simplifying approximations are needed to make the solution feasible. Assuming link independence, we propose a new method for approximating the state-dependent link costs accurately and relatively efficiently, even on links with extremely large state spaces. The proposed polynomial approximations are optimal in the sense of minimizing the residual in the continuous-time Howard equations of the Markov decision processes associated with the links. Numerical results are presented, and the proposed approximations are found superior to some earlier link-cost approximation methods     

多光纤波分复用网的一种新的备用路由算法

基于经典的LLR算法,研究了波分复用光网络的路由问题,提出了一种用于多光纤网的新算法—LLHR,该算法综合考虑了链路负载和路由跳数两个因素。文章深入研究了网络光纤数、备用路由数和网络负载对算法性能的影响。计算机仿真结果表明,与LLR算法相比,该算法能有效降低网络的阻塞率,提高网络的性能。     

Computing approximate blocking probabilities for transparent waveband switching based WDM networks using hierarchical cross-connects

An analytical model is presented to study the dynamics of wavelength division multiplexing (WDM) networks with waveband switching (WBS). The reduced load approximation method is considered to compute approximated network blocking probabilities in WBS-based WDM networks. The analytical model considers the link blocking probability due to insufficient link capacity and an impact of the waveband granularity (G). The analytical model also considers the node blocking probability due to unavailability of a switch port at the wavelength cross connect (WXC) layer of an Hierarchical cross connect (HXC) switch node. The set of nonlinear equations is obtained with the link independence assumption and solved using repeated substitutions. The accuracy of the analytical model is examined by comparing with simulation results considering the random-fit algorithm for waveband and wavelength assignments in different network scenarios. Lightpaths are routed between source and destination (s-d) HXC switch nodes using shortest path first (SPF) routing. An impact of the switch parameter to limit the input and the output WXC switch ports of an HXC switching node is also being investigated using the analytical model as well as through simulation results.     

A Cross-Layer Routing Scheme Using Adaptive Retransmission Strategy for Wireless Mesh Networks

In this paper, we develop a link quality-based adaptive adjustment mechanism of the MAC maximum retransmission count to reduce collision probability of wireless Mesh networks. Based on statistics acquired in the link layer and the retransmission strategy, a multi-metric cross-layer on-demand routing scheme is proposed for wireless Mesh networks. The proposed scheme uses information such as available link bandwidth, node residual load rate and transmission efficiency of a path adequately to cross-layer routing. The network layer can adaptively select an optimal path to deliver packets based on the acquired statistics of the MAC layer. Extensive simulation results demonstrate that the proposed scheme can reduce link failure probability, improve network throughput, and decrease the end-to-end delay effectively.     

Adaptive alternate routing in WDM networks and its performance tradeoffs in the presence of wavelength converters

Routing in wavelength-routed all-optical WDM networks has received much attention in the past decade, for which fixed and dynamic routing methods have been proposed. Taking into account the observation that wavelength-routed all-optical WDM networks are similar to circuit-switched voice networks, except with regard to wavelength conversion, we propose an adaptive alternate routing (AAR) scheme for wavelength-routed all-optical WDM networks. A major benefit of AAR is that it can operate and adapt without requiring an exchange of network status, i.e., it is an information-less adaptive routing scheme. The scope of this work is to understand this scheme in its own right since no other dynamic routing schemes are known to have the information-less property. In this paper, we conduct a systematic study of AAR with regard to factors such as the number of converters, load conditions, traffic patterns, network topologies, and the number of alternate paths considered. We observe that the routing scheme with multiple alternate routes provides more gain at a lower load instead of requiring any nodes to be equipped with wavelength converters. On the other hand, the availability of wavelength converters at some nodes, along with adaptive routing, is beneficial at a moderate to high load without requiring all nodes to be equipped with wavelength converters. We also observed that a small number of alternate routes considered in a network without wavelength converters gives a much better performance than a network with full wavelength converters and fewer alternate routes. Throughout this study, we observed that the proposed adaptive alternate routing scheme adapts well to the network traffic condition.     

Performance evaluation of dynamic routing based on the use of satellites and intelligent networks

A dynamic routing scheme for public switched telephone networks is introduced which employs satellite broadcast to distribute network load data. The proposed network architecture closely resembles the IN (Intelligent Network) architecture, whereby the IN SCPs (Service Control Points) serve as so‐called Routing Control Points (RCPs). The key functions of an RCP are (i) to execute the routing algorithm and issue routing instructions in response to routing queries it receives from its associated switches for calls which overflow from the default network links, and (ii) to monitor and evaluate the pattern of received routing queries to obtain an estimate for the traffic loads present in each RCP's domain of associated switches. Satellite broadcast is used to distribute the load information among all RCPs in the network in a periodic fashion. This paper also reports on the results of extensive call‐by‐call simulations. The objective of the simulations was to validate this new routing scheme and compare its performance with well‐known existing schemes. Real traffic and network data as measured in the Austrian PSTN were used in the simulations. The main results are that, under all realistic network and traffic conditions including link and node failures, the proposed scheme yields lower blocking rates and significantly less routing and crankback attempts than the existing dynamic routing schemes. Note that this is achieved in the absence of any load measurements within the switches. As regards the periodic satellite based RCP‐RCP broadcast for the PSTN studied, it was shown that an update period of 10 seconds yields an excellent routing performance which is close to the limit of a vanishing update period. This revised version was published online in June 2006 with corrections to the Cover Date.     

Locally Restorable Routing of Highly Variable Traffic

Two-phase routing, where traffic is first distributed to intermediate nodes before being routed to the final destination, has been recently proposed for handling widely fluctuating traffic without the need to adapt network routing to changing traffic. Preconfiguring the network in a traffic independent manner using two-phase routing simplifies network operation considerably. In this paper, we extend this routing scheme by providing resiliency against link failures through fast restoration along link backup detours. We view this as important progress towards adding carrier-class reliability to the robustness of the scheme so as to facilitate its future deployment in Internet Service Provider (ISP) networks. On the theoretical side, the main contribution of the paper is the development of linear programming based and fast combinatorial algorithms for two-phase routing with link restoration so as to minimize the maximum utilization of any link in the network, or equivalently, maximize the throughput. The algorithms developed are fully polynomial time approximation schemes (FPTAS)-for any given isin > 0, an FPTAS guarantees a solution that is within a (1 + isin)-factor of the optimum and runs in time polynomial in the input size and 1/isin. To the best of our knowledge, this is the first work in the literature that considers making the scheme resilient to link failures through preprovisioned fast restoration mechanisms. We evaluate the performance of link restoration (in terms of throughput) and compare it with that of unprotected routing. For our experiments, we use actual ISP network topologies collected for the Rocketfuel project and three research network topologies.     

Multi‐topology routing based egress selection approach to achieve hybrid intra‐AS and inter‐AS traffic engineering

Hot‐potato routing is a border gateway protocol policy that selects the ‘closest’ egress router in terms of interior gateway protocol cost. This policy imposes inherent interactions between intra‐AS (Autonomous System) and inter‐AS traffic engineering. In light of this observation, we present a hybrid intra‐AS and inter‐AS traffic engineering scheme named egress selection based upon hot potato routing. This scheme involves link weight optimization, which can not only minimize the time that IP (Internet Protocol) packets travel across the network by assigning specified egress router but also balance the load among the internal links of the transit network. Egress selection based upon hot potato routing also incorporates multi‐topology routing technique to address the problem that one set of link weights might not guarantee specified egress routers. Accordingly, we formulate the link weights optimization problem using multi‐topology routing as a mixed integer linear programming model. And we present a new heuristic algorithm to make the problem tractable. Numerical results show that only a few topologies are needed to guarantee specified egress router, and maximum link utilization is also reduced. Copyright © 2014 John Wiley & Sons, Ltd.     

Guaranteed Performance Routing of Unpredictable Traffic With Fast Path Restoration

Two-phase routing, where traffic is first distributed to intermediate nodes before being routed to the final destination, has been recently proposed for handling widely fluctuating traffic without the need to adapt network routing to changing traffic. Preconfiguring the network in a traffic-independent manner using two-phase routing simplifies network operation considerably. In this paper, we extend this routing scheme by providing resiliency against link failures through fast path restoration along disjoint end-to-end backup paths. We view this as important progress toward adding carrier-class reliability to the robustness of the scheme so as to facilitate its future deployment in Internet service provider (ISP) networks. On the theoretical side, the main contribution of the paper is the development of linear-programming-based and fast combinatorial algorithms for two-phase routing with fast path restoration so as to minimize the maximum utilization of any link in the network, or equivalently, maximize the throughput. The algorithms developed are fully polynomial time approximation schemes (FPTAS)-for any given epsiv > 0, an FPTAS guarantees a solution that is within a (1+epsiv)-factor of the optimum and runs in time polynomial in the input size and [ 1/(relax epsiv)]. To the best of our knowledge, this is the first work in the literature that considers making the scheme resilient to link failures through preprovisioned fast restoration mechanisms. We evaluate the performance of fast path restoration (in terms of throughput) and compare it to that of unprotected routing. For our experiments, we use actual ISP network topologies collected for the Rocketfuel project and three research network topologies.     

Supporting network management with real-time traffic models

Real-time routing and flow control in circuit-switched networks is investigated. An algorithm which updates routing tables and flow-control parameters according to changing load conditions is derived. The network is described by means of stochastic difference equations. A control structure imposed by hardware requirements and realistic network status information patterns is considered. It is shown that the global objectives can be achieved by means of shortest-route algorithms with state-dependent route lengths. Implementation issues which are related to traffic estimation and prediction are discussed. The performance of a particular algorithm implementation is investigated by simulation     

Call admission control and routing in integrated services networksusing neuro-dynamic programming

We consider the problem of call admission control (CAC) and routing in an integrated services network that handles several classes of calls of different value and with different resource requirements. The problem of maximizing the average value of admitted calls per unit time (or of revenue maximization) is naturally formulated as a dynamic programming problem, but is too complex to allow for an exact solution. We use methods of neuro-dynamic programming (NDP) [reinforcement learning (RL)], together with a decomposition approach, to construct dynamic (state-dependent) call admission control and routing policies. These policies are based on state-dependent link costs, and a simulation-based learning method is employed to tune the parameters that define these link costs. A broad set of experiments shows the robustness of our policy and compares its performance with a commonly used heuristic     

Multicast routing, load balancing, and wavelength assignment ontree of rings

There are two steps to establish a multicast connection in WDM networks: routing and wavelength assignment. The shortest path tree (SPT) and minimum spanning tree (MST) are the two widely used multicast routing methods. The SPT method minimizes the delay from the source to every destination along a routing tree, and the MST method is often used to minimize the network cost of the tree. Load balancing is an important objective in multicast routing, which minimizes the maximal link load in the system. The objective of wavelength assignment is to minimize the number of wavelengths used in the system. This paper analyzes the performance of the shortest path tree (SPT) and minimum spanning tree (MST) methods in the tree of ring networks, regarding the performance criteria such as the delay and network cost of the generated routing trees, load balancing, and the number of wavelengths required in the system. We prove that SPT and MST methods can not only produce routing trees with low network costs and short delays, but also have good competitive ratios for the load balancing problem (LBP) and wavelength assignment problem (WAP), respectively