Constraint-based Routing Research Articles

A Learning-based Adaptive Routing Tree for Wireless Sensor Networks

One of the most common communication patterns in sensor networks is routing data to a base station, while the base station can be either static or mobile. Even in static cases, a static spanning tree may not survive for a long time due to failures of sensor nodes. In this paper, we present an adaptive spanning tree routing mechanism, using real-time reinforcement learning strategies. We demonstrate via simulation that without additional control packets for tree maintenance, adaptive spanning trees can maintain the best connectivity to the base station, in spite of node failures or mobility of the base station. And by using a general constraint-based routing specification, one can apply the same strategy to achieve load balancing and to control network congestion effectively in real time.

Fast analytical assessment of the signal quality in transparent optical networks

Constraint-based routing (CBR) requires a fast and accurate assessment of the different physical degradation effects in optical communications systems. This paper deals with fast analytical approximation formulas describing the induced system penalty due to the dominant nonlinear effects in 10-Gb/s nonreturn to zero (NRZ) transmission systems. This paper concentrates on the multichannel effects of cross-phase modulation (XPM) and four-wave mixing (FWM).

Parallel LSPs for constraint-based routing and load balancing in MPLS networks

Two features of multiprotocol label switching are very useful in network traffic engineering: the path-oriented nature, and the capability to support multiple paths between an ingress–egress node pair. The first feature makes it easy to adaptively route traffic through the network based on the load condition in different parts of the network, while the second feature is often used for load balancing. The role of parallel label-switched paths (LSP) in load balancing and constraint-based routing is investigated. An algorithm named parallel-path-based bandwidth scheme (PPBS) is proposed to make use of parallel LSPs in choosing a bandwidth constraint path. The improvement on flow blocking probability by using PPBS is given quantitatively with respect to the average traffic load on the link, the hops along the path, and the possible number of parallel paths. In conjunction with the PPBS scheme, a feedback-based load-balancing algorithm (FBLB) is proposed to properly distribute traffic onto the parallel LSPs determined by the PPBS. This FBLB algorithm relies on the signalling packets to convey network status information back to the source. Consequently the sources can adjust the traffic distribution into each LSP accurately and promptly. Simulation results show that the FBLB algorithm is simple and effective.

Path Selection Methods With Multiple Constraints in Service-Guaranteed WDM Networks

We propose a new approach to constraint-based path selection for dynamic routing and wavelength allocation in optical networks based on WDM. Our approach considers service-specific path quality attributes, such as physical layer impairments, reliability, policy, and traffic conditions, and uses a flooding-based transfer of path information messages from source to destination to find multiple feasible paths. It is fully decentralized, as it uses local network state information. To better understand how multiple constraints impact the efficiency of wavelength routing, and consequently provision the service guarantees, we specifically focus on electronic regenerators that, while being widely considered as the basic building blocks for optical switching nodes, are likely to impose conflicting constraints on routing. For example, electronic regenerators extend the optical reach and could perform wavelength shifting, but also induce impairments, such as delays and operational costs. The question for constraint-based routing is how to account for these conflicting effects. To validate the network modeling, a wide range of networking scenarios are simulated, such as ring, mesh and interconnections of all-optical networks with electronic gateways. For all these scenarios, our approach is shown to efficiently accommodate multiple, conflicting routing metrics related to different services and network architectures.

Enhanced pool sharing: a constraint-based routing algorithm for shared mesh restoration networks [Invited

Feature Issue on Next-Generation WDM Network Design and Routing (WDMN). We investigate the availability performance of networks with shared mesh restoration and demonstrate that these networks cannot provide highly available protection services. A major factor in the poor performance of shared mesh restoration is that the resources at backup links are shared among demands. If multiple service-affecting failures occur in the network a multitude of these demands will rush to utilize the spare resources on backup links. These resources are not adequate to serve all of these demands simultaneously. We propose a heuristic routing algorithm that attempts to improve the availability performance of shared mesh restoration. We measure the likelihood that a backup link will not be available to restore a newly arrived demand if or when more than one failure occurs in the network. We adjust the backup bandwidth on that link if the measured likelihood exceeds a preset threshold. As a typical representative, we show that the downtime improves by 7%, 11%, and 18% when the total backup bandwidth in the network is increased by 5%, 10%, and 20%, respectively. These values are obtained through a series of fitting experiments.

Benefits of traffic engineering using QoS routing schemes and network controls

We demonstrate the benefits of traffic engineering by studying three realistic network models derived from an actual service provider network. We evaluate traffic engineering in the presence of QoS-based routing schemes compared with Destination-Based Routing, the default routing behavior for the Internet. We also simulate prioritization of important traffic flows by implementing priority in one or more of the path caching, path ordering, and actual route selection phases of the constraint-based routing framework. We observe that traffic engineering can provide 20–50% network capacity savings. We also observe that prioritization in more than one phase of constraint-based routing can provide even more significant benefits.

QoS evaluation of diffserv-aware constraint-based routing schemes for multi-protocol label switching networks

Differentiated Services (DiffServ) and Multi-Protocol Label Switching (MPLS) are attracting attention as Quality of Service (QoS) technologies for the large-scale Internet. DiffServ cannot offer end-to-end QoS by itself, because it controls per-hop packet forwarding order with relative priority according to its class. Achieving end-to-end QoS requires traffic engineering support by using MPLS and Constraint-Based Routing (CBR) schemes in addition to DiffServ. CBR schemes compute explicit routes for Label-Switched Paths (LSPs), which specify packet forwarding routes in MPLS networks. In this paper, we assume two DiffServ classes: Expedited Forwarding (EF) class which corresponds to voice traffic requiring small path delay, and Best Effort (BE) class which corresponds to data traffic requiring high throughput. Four DiffServ-aware CBR schemes are constructed, based on a combination of route computation algorithms and LSP-types depending on whether or not DiffServ classes are considered. In addition to the schemes, we propose a DiffServ-aware CBR scheme that uses a different route computation algorithm for each class. By simulating path accommodations for two-class traffic between every node pair, we evaluate QoS achieved by the five DiffServ-aware CBR schemes. The results show that the proposed scheme can offer better QoS for each class.

Constraint-based routing in the internet: Basic principles and recent research

Novel routing paradigms based on policies, quality of service (QoS) requirements, and packet content have been proposed for the Internet over the last decade. Constraint-based routing algorithms select a routing path satisfying constraints that are either administrative-oriented (policy routing) or service-oriented (QoS routing). The routes, in addition to satisfying constraints, are selected to reduce costs, balance network load, or increase security. In this article, we discuss several constraint-based routing approaches and explain their requirements, complexity, and recent research proposals. In addition, we illustrate how these approaches can be integrated with Internet label switching and QoS architectures. We also discuss examples of application-level routing techniques used in today's Internet.

Demonstration of the highly reliable Hikari router network based on a newly developed disjoint path selection scheme

Integration of multiprotocol label switching functions and multiprotocol lambda switching functions can enhance the throughput of IP networks and remove bottlenecks that are derived from electrical packet processing. To enhance the packet forwarding capability, NTT proposed a photonic MPLS concept that includes MP/spl lambda/S, and demonstrated IP, MPLS, and photonic MPLS integrated router systems called the photonic MPLS router. This router system is now called the Hikari router. The word Hikari is Japanese meaning beam, light, lightwave, optical, photonic, and sunshine. The amount of IP data traffic has grown remarkably. Massive IP routers and flexible route control mechanisms are now required to cope with the increased amount of traffic. The Hikari router can offer two solutions utilizing photonic switching technologies, and photonic network operation and management technologies. The first solution is utilizing photonic switching technologies realized using optical-switch-based crossconnect systems. The other solution is realized using the MPLS and MP/spl lambda/S signaling protocol and photonic network protection functions. In this article we report on the implementation of the Hikari router systems, propose a newly developed disjoint path selection scheme for generalized MPLS networks with shared risk link group constraints, and demonstrate the signaling protocol and network protection functions. The demonstration system achieves a distributed optical path set-up/tear-down protocol with an extended constraint-based routing label distribution protocol. Fast self-healing through automatic protection switching and a new restoration scheme are also implemented. These functions are successfully implemented, and the performance is verified on a demonstration network. The protection switching scheme achieves protection in less than 20 ms, and the optical path restoration scheme achieves restoration in less than 500 ms.

QoS routing granularity in MPLS networks

This study investigates how constraint-based routing decision granularity significantly affects the scalability and blocking performance of QoS routing in an MPLS network. Coarse granularity, such as per-destination, has lower storage and computational overheads but is only suitable for best effort traffic. On the other hand, fine granularity, such as per-flow, provides lower blocking probability for bandwidth requests, but requires a huge number of states and high computational cost. To achieve cost-effective scalability, this study proposes using hybrid granularity schemes. The overflowed cache of the per-pair/flow scheme adds a per-pair cache and a per-flow cache as the routing cache, and performs well in blocking probability. The per-pair/class scheme groups the flows into several paths using routing marks, thus allowing packets to be label-forwarded with a bounded cache.

Minimizing re-routing in MPLS networks with preemption-aware constraint-based routing

In this paper, we study the effect of distributed constrained shortest path first (CSPF)-based path selection on the dynamics of label switched path (LSP) preemption. We propose new CSPF algorithms for minimizing preemption of lower priority LSPs without requiring any enhancements to the recently proposed link-state parameters. The difference between priority-based path selection methods and previously proposed CSPF methods lies in the way the selection is done among equal cost shortest paths. Our priority-aware CSPF algorithms decrease the number of preempted lower priority LSPs while the LSP setup success ratio is basically the same for all methods.

Integrated Routing Algorithms for Provisioning “Sub-Wavelength” Connections in IP-Over-WDM Networks

This work focuses on developing and implementing comprehensive unified constraint-based routing algorithms within the generalized multi-protocol label switching framework (GMPLS) to provision “sub-wavelength” circuits (low-rate traffic streams). Constraint-based routing is further augmented in this work by dynamically routing both an active and another alternate link/node-disjoint backup path at the same time in order to provision a given connection request. This new integrated approach combines both IP routing and optical resource allocation to setup end-to-end connections.

Traffic engineering with MPLS in the Internet

This article discusses traffic engineering with multiprotocol label switching (MPLS) in an Internet service provider's network. We first review MPLS, constraint-based routing, and enhanced link state interior gateway protocols to provide a background for traffic engineering. We then discuss the general issues of designing an MPLS system for traffic engineering. The design of GlobalCenter's MPLS system is presented. Based on our experiences, a generic procedure for deploying an MPLS system is proposed. We also discuss how to provide QoS in a network with MPLS. Putting these together, we present to readers the practical issues of traffic engineering and a working solution for traffic engineering with MPLS in the Internet.

Internet QoS: a big picture

We present a framework for the emerging Internet quality of service (QoS). All the important components of this framework-integrated services, RSVP, differentiated services, multiprotocol label switching (MPLS), and constraint-based routing-are covered. We describe what integrated services and differentiated services are, how they can be implemented, and the problems they have. We then describe why MPLS and constraint-based routing have been introduced into this framework, how they differ from and relate to each other, and where they fit into the differentiated services architecture. Two likely service architectures are presented, and the end-to-end service deliveries in these two architectures are illustrated. We also compare ATM networks to router networks with differentiated services and MPLS. Putting all these together, we give the readers a grasp of the big picture of the emerging Internet QoS.

MPLS advantages for traffic engineering

This article discusses the architectural aspects of MPLS which enable it to address IP traffic management. Specific MPLS architectural features discussed are separation of control and forwarding, the label stack, multiple control planes, and integrated IP and constraint-based routing. The article then discusses how these features address network scalability, simplify network service integration, offer integrated recovery, and simplify network management. Scalability is addressed through integrated routing enabling a natural assignment of traffic to the appropriate traffic engineering tunnels without requiring special mechanisms for loop prevention. Change is greatly reduced. The label stack enables an effective means for local tunnel repair providing fast restoration. Feedback through the routing system permits fast and intelligent reaction to topology changes. Service integration is simplified through a unified QoS paradigm which makes it simple for services to request QoS and have it mapped through to traffic engineering.

Intradomain QoS routing in IP networks: a feasibility and cost/benefit analysis

Constraint-based routing gradually becomes an essential enabling mechanism for a variety of emerging network services such as virtual private networking and QoS support. A number of previous works have recognized its significance and investigated many aspects of the operation of constraint-based routing and in particular its variant concerned with determining paths for requests with specific QoS requirements, known as QoS routing. In this work we build on previous results on the cost of QoS routing and investigate the performance/cost trade-offs involved in the operation of a representative QoS routing architecture, elaborate on the constituents of this cost, and identify the main methods for containing the cost that QoS routing incurs on routers. Our results show that the cost of QoS routing is not excessive and that there indeed exist operational configurations, which can achieve reasonable performance gains with only a minimal increase in processing cost when compared to conventional best-effort routing.