Explicit Routing Research Articles

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.

Multicasting in MPLS domains

Explicit routing in MPLS is utilized in traffic engineering to maximize the operational network performance and to provide Quality of Service (QoS). However, difficulties arise while integrating native IP multicasting with MPLS traffic engineering, such as point-to-multipoint or multipoint-to-multipoint LSPs layout design and traffic aggregation. In this paper, we have proposed an edge router multicasting (ERM) scheme by limiting branching point of multicast delivery tree to only the edges of MPLS domains. As a result, multicast LSP setups,multicast flow assignments, and multicast traffic aggregation are reduced to unicast problems. We have studied two types of ERM routing protocols in the paper. The first approach is based on modifications to the existing multicast protocols, while the second approach applies Steiner tree-based heuristic routing algorithm in the edge router multicasting environment. The simulation results demonstrate that the ERM scheme based on Steiner tree heuristic can provide near-optimal performance. The results also demonstrate that ERM provides a traffic engineering friendly approach without sacrificing the benefits of native IP multicasting.

Explicit multicasting for mobile ad hoc networks

In this paper we propose an explicit multicast routing protocol for mobile ad hoc networks (MANETs). Explicit multicasting differs from common approaches by listing destination addresses in data packet headers. Using the explicit destination information, the multicast routing protocol can avoid the overhead of employing its own route construction and maintenance mechanisms by taking advantage of unicast routing table. Our protocol - termed Differential Destination Multicast (DDM) - is an explicit multicast routing protocol specifically designed for MANET environment. Unlike other MANET multicasting protocols, instead of distributing membership control throughout the network, DDM concentrates this authority at the data sources (i.e. senders) thereby giving sources knowledge of group membership. In addition, differentially-encoded, variable-length destination headers are inserted in data packets which are used in combination with unicast routing tables to forward multicast packets towards multicast receivers. Instead of requiring that multicast forwarding state to be stored in all participating nodes, this approach also provides the option of stateless multicasting. Each node independently has the choice of caching forwarding state or having its upstream neighbor to insert this state into self-routed data packets, or some combination thereof. The protocol is best suited for use with small multicast groups operating in dynamic MANET environment.

MPLS 네트워크에서의 부하 분산 방안

MPLS(Multi-Protocol Label Switching)는 효율적인 명시적 라우팅(explicit routing)을 지원할 수 있어 트래픽 엔지니어링 가능성을 크게 향상시켰다. 본 논문에서는 이와 같은 MPLS를 이용하여, 좀 더 효율적으로 네트워크 자원을 활용하고 성능을 향상시키는 방안으로서 다중 경로 상에 부하를 분산시키는 방안을 제안하고 이를 LBM(Load Balancing in MPLS networks)이라 명명하였다. LBM은 하나의 진입-진출 라우터 쌍 간에 다중의 LSP(Label Switching Path)론 설정하고, 플로우 단위로 이들 다중의 LSP에 부하를 분산하되 경로의 길이와 부하를 함께 고려하여 부하를 분산한다. 또한, 링크의 효율적인 활용을 위하여 링크의 활용률이 커짐에 따라 더 짧은 경로에 의해서만 사용되도록 제한하고, 더 짧은 경로의 활용률이 커짐에 따라 더 길지만 활용률이 더 낮은 경로를 대체 경로(alternative path) 후보로 고려한다. 시뮬레이션을 통하여 최단 경로 방식 및 기존의 다중 경로를 사용하는 방식들과 성능을 비교한 결과 LBM의 성능이 우수하며, 특히 국부적으로 트래픽이 편중되는 경우 LBM이 효율적으로 대처할 수 있음을 알 수 있었다. MPLS enables efficient explicit routing, and thus provides great advantages in supporting traffic engineering. Exploiting this capability, we Propose a load balancing scheme which deploys a multipath routing. It is named LBM (Load Balancing in MPLS networks), and targets at efficient network utilization as well as performance enhancement. LBM establishes multiple LSP (Label Switched Path)s between a pair of ingress-egress routers, and distributes traffic over these LSPs at the new level. Its routing decision is based on both the length and the utilization of the paths. In order to enhance the efficiency of a link usage, a link is limited to be used by shorter paths as its utilization becomes higher Longer paths are considered to be candidate alternative paths as the utilization of shorter paths becomes higher. Simulation experiments are performed in order to compare the performance of LBM to that of static shortest path only scheme as well as the other representative dynamic multipath traffic distribution approaches. The simulation results show that LBM outperforms the compared approaches, and the performance gain is more significant when the traffic distribution among the ingress-egress pairs is non-uniform.

A router-assisted session tree configuration mechanism for reliable multicast

A session tree based mechanism provides an efficient method to avoid well-known feedback implosion. However, it is not easy to configure an efficient session tree for IP multicast because it does not provide any explicit membership and routing topology information to the upper layer protocol. Incongruity between a session tree built on the transport layer and the corresponding routing tree on the network layer would incur large cost to handle control messages. This problem can be solved if a router that knows the information of routing topology can support the configuration of a session tree. Thus this letter proposed a router-assistant mechanism which minimizes the change of router functions and allows the routers to assist in providing a reliable multicast transport service.

Explicit routing with QoS constraints in IP over WDM

Generalised multiprotocol label switching (GMPLS) is being developed as a unified control architecture for the optical transport network and the layers above it. GMPLS supports traffic engineering (TE) by allowing explicit routing (ER) of data-bearing paths across networks, which will help to guarantee quality of service (QoS) for types of services in IP over WDM networks. Although there have been many approaches to allocate resources in optical data networks using constrained linear programs, these do not consider the delays at layer 3, which impacts QoS. In networks where it is not possible to create a virtual topology at layer 3 that is a full mesh, more than one lightpath will be required to route traffic between certain pairs of source and destination IP routers. The authors present a technique for traffic engineering in optical networks that support QoS considering the traffic flows with delay QoS requirements across optical networks. This technique provides real-time services with a specific optical label switched path and optimises an objective function including the queueing delay at layer 3.

A survey on position-based routing in mobile ad hoc networks

We present an overview of ad hoc routing protocols that make forwarding decisions based on the geographical position of a packet's destination. Other than the destination's position, each node need know only its own position and the position of its one-hop neighbors in order to forward packets. Since it is not necessary to maintain explicit routes, position-based routing does scale well even if the network is highly dynamic. This is a major advantage in a mobile ad hoc network where the topology may change frequently. The main prerequisite for position-based routing is that a sender can obtain the current position of the destination. Therefore, previously proposed location services are discussed in addition to position-based packet forwarding strategies. We provide a qualitative comparison of the approaches in both areas and investigate opportunities for future research.

Evaluating explicit and implicit routing for watershed hydro‐ecological models of forest hydrology at the small catchment scale

AbstractThis paper explores the behaviour and sensitivity of a watershed model used for simulating lateral soil water redistribution and runoff production. In applications such as modelling the effects of land‐use change in small headwater catchments, interactions between soil moisture, runoff and ecological processes are important. Because climate, soil and canopy characteristics are spatially variable, both the pattern of soil moisture and the associated outflow must be represented in modelling these processes. This study compares implicit and explicit routing approaches to modelling the evolution of soil moisture pattern and spatially variable runoff production. It also addresses the implications of using different landscape partitioning strategies. This study presents the results of calibration and application of these different routing and landscape partitioning approaches on a 60 ha forested watershed in Western Oregon. For comparison, the different approaches are incorporated into a physically based hydro‐ecological model, RHESSys, and the resulting simulated soil moisture, runoff production and sensitivity to unbiased error are examined. Results illustrate that both routing approaches can be calibrated to achieve a reasonable fit between observed and modelled outflow. Calibrated values for effective watershed hydraulic conductivity are higher for the explicit routing approach, which illustrates differences between the two routing approaches in their representation of internal watershed dynamics. The explicit approach illustrates a seasonal shift in drainage organization from watershed to more local control as climate goes from a winter wet to a summer dry period. Assumptions used in the implicit approach maintain the same pattern of drainage organization throughout the season. The implicit approach is also more sensitive to random error in soil and topographic input information, particularly during wetter periods. Comparison between the two routing approaches illustrates the advantage of the explicit routing approach, although the loss of computational efficiency associated with the explicit routing approach is noted. To compare different strategies for partitioning the landscape, the use of a non‐grid‐based method of partitioning is introduced and shown to be comparable to grid‐based partitioning in terms of simulated soil moisture and runoff production. Copyright © 2001 John Wiley & Sons, Ltd.

Lightpath routing for intelligent optical networks

An overview of current issues and challenges in lightpath routing for optical networks is given. An architecture is presented in which optical switches are deployed, usually in the core, to interconnect IP routers at the edges. Lightpath routing within this architecture follows the framework of generalized multiprotocol label switching. Our discussion pays particular attention to the aspects of optical routing that differ from routing in irrational IP networks. Such aspects include physical layer constraints, wavelength continuity, the decoupling of the control network topology from the data network topology, explicit routing with wavelength assignment, and diversity routing for fast protection. We also present an algorithmic framework for lightpath computation, highlighting the issue of wavelength continuity and the differences between lightpath computation and traditional IP route computation.

RATES: a server for MPLS traffic engineering

It has been suggested that one of the most significant reasons for multiprotocol label switching (MPLS) network deployment is network traffic engineering. The goal of traffic engineering is to make the best use of the network infrastructure, and this is facilitates by the explicit routing feature of MPLS, which allows many of the shortcomings associated with current IP routing schemes to be addressed. This article describes a software system called Routing and Traffic Engineering Server (RATES) developed for MPLS traffic engineering. It also describes some new routing ideas incorporated in RATES for MPLS explicit path selection. The RATES implementation consists of a policy and flow database, a browser-based interface for policy definition and entering resource provisioning requests, and a Common Open Policy Service protocol server-client implementation for communicating paths and resource information to edge routers. RATES also uses the OSPF topology database for dynamically obtaining link state information. RATES can set up bandwidth-guaranteed label-switched (LSPs) between specified ingress-egress pairs. The path selection for LSPs is on a new minimum-interference routing algorithm aimed at making the best use of network infrastructure in an online environment where LSP requests arrive one by one with no a priori information about future requests. Although developed for an MPLS application, the RATES implementation has many similarities in components to an intradomain differentiated services bandwidth broker.

Optimization and design of network routing using refined asymptotic approximations

The problems of route optimization, and the sizing of virtual paths and explicit routes in wide-area multi-service broadband networks are considered. The problems are formulated at the call-level in the framework of multi-rate, circuit-switched, loss networks, with effective bandwidth encapsulating cell and packet-level behavior. Broadband networks are characterized by links with very large capacities in circuits, and are expected to support many services each having a characteristic bandwidth or rate. Various asymptotic results based on Uniform Asymptotic Approximations (UAA) have previously been obtained to reduce the complexity of the numerical calculations. This paper offers refinements (RUAA) to UAA to the loss probabilities for a single link, as well as their sensitivities to the offered traffic. Network loss probabilities are obtained by solving fixed-point equations. Another system of equations determines the implied costs for services and links, which are used to guide the network optimization. Refined asymptotic approximations to the network's loss probabilities as well as to the implied costs are proposed based on the RUAA. The refinements are crucial for the accurate evaluations of the implied costs. The complexity of these calculations remains bounded as the link capacities and traffic intensities become increasingly large, and the complexity for the implied costs is independent of the number of services. A network design tool TALISMAN has been extended to implement the refined approximations. Numerical examples illustrate the accuracy of the RUAA.

Carotenoids in photosynthesis: structure and photochemistry

Abstract