光网络中实现流量工程的负载均衡动态路由算法

提出了一种在光网络中实现流量工程的负载均衡动态路由算法(LBDRO).该算法通过新定义的链路关键度函数和链路当前可用带宽确定链路动态成本,并依据该动态成本运用最短路径优先算法为到达的LSP请求建立动态成本优化路径.该算法的计算复杂度低,仿真实验表明,与MHA、WSP、MIRA算法相比,在光传输网络中,该算法在降低LSP建立请求服务拒绝率、均衡网络负载以及链路失效后重路由等方面有很好的性能.     

基于IP/MPLS网络的动态业务流量矩阵测量模型

IP网络动态业务流量矩阵的测量是业务量工程研究中的一个难点,本文提出了一种面向IP/MPLS骨干网络的基于LSP级的动态业务流量矩阵测量模型。该模型能够获取网络边界处对应于每一条LSP的路径转发信息,并根据每一条LSP上的测量结果,计算得知全网的业务流量矩阵。文中证明该测量模型是可行的,并给出了相关的算法及其性能分析。模型的优点是测量只在网络边界处进行而不涉及网络核心,故引起的网络开销较小。另外模型所需的算法复杂度低,仿真结果显示测量模型是有效的。     

ASON中信令协议RSVP_TE建立LSP的研究

文章对自动交换光网络（ASON）信令协议——基于流量工程扩展的资源预留协议（RSVP_TE）的主要内容及工作机制进行了分析研究,它主要是在ASON网络中动态地完成建立、保持和删除标签交换路径（LSP）。LSP的建立时间与信息传输时延、信息处理时延和节点配置时间有关。在RSVP_TE信令基础上提出一种新的标签分组方式来减少LSP建立时延。从理论和仿真上都验证了采用这种标签分组方式会改善LSP建立时延性能。     

基于单程建路的高效快速双向标签交换路径生成算法

双向标签交换路径(LSP)是多协议标签传输应用(MPLS-TP)网络技术的重要组成部分,但现有的双向LSP生成算法因双程建路而在控制开销和用时方面导致冗余。为此,该文提出一种基于单程建路的高效双向LSP生成算法(EAEBL),在保障建路效果的前提下,通过控制消息的一次单程正向传递完成双向LSP的生成,从而减少建立双向LSP的控制开销和用时而且能够加快启动数据分组的传递。理论分析验证了EAEBL算法的有效性,仿真结果显示:与现有的4种双向LSP生成算法相比,EAEBL算法的建路控制开销和用时分别减少了14.7%和50%以上,数据分组在源LSR的等待时间则被减至趋近于0。     

一种基于GMPLS的双重恢复(P&R)方案

提出一种基于GMPLS的双重保护机制,在此方案中,LSPP&R是第一级的恢复,LSP的分段P&R是第二级的恢复。针对这种方案提出了一种LSP保护路径选择算法。     

基于梯度加速算法的LSP流量分配算法

本文在MPLS系统模型中提出了一种基于加速梯度算法的LSP流量分配算法。仿真结果表明,它可以减少由传统路由算法引起的网络拥塞和包丢失率;随着LSP请求数的增加减少了LSP的拒绝数,优化网络资源的利用率,降低了资源占用率,提高了系统的稳定性。     

一种自适应线谱对滤波器的终点误差LMS算法及其学习特性

本文提出了一种计算线谱对（LSP）系数的新算法．该算法以最小均方（LMS）误差型算法为基础，梯度计算使用系统终点误差。对接收到的语音观测样本在一个时序的基础进行迭代更新计算，直接产生LSP系数，形成一个LMS算法的自适应LSP滤波器。实验结果表明，该算法与其它自适应滤器的LMS算法比较，具有更高的收敛率和较低的失调。     

IP over WDM网中的综合选路算法

研究了IP over WDM网中,当节点不具备波长变换能力并且配备有限光收发器对时,如何利用综合选路(IR)算法为到达业务请求建立标签交换路径(LSP)。提出一种新颖的辅助图模型(AGM)表示网络的当前状态,基于AGM提出一种动态IR算法-最小光收发器对法(MTA)。MTA总是选择占用光收发器对最少的通路来建立LSP,仿真结果表明：与已有算法相比,MTA可以降低全网的阻塞率,从而提高业务通过率,并且有利于减少业务连接所经光／电变换的次数。     

一种新的基于可分配流量的MPLS网络流级负载均衡

提出了一种新的基于可分配流量的MPLS网络流级负载均衡机制,该机制考虑到实际网络中的背景业务,每个LSP模拟为M/G/1处理器共享队列.根据每个LSP上的延迟和丢包率,来计算成本函数,并对这个成本函数最小化.每个LSP上的可分配流量与最小化成本函数成反比.仿真结果表明该算法具有更好的公平性,能够在多径之间平衡地分配流量.网络中的吞吐率得到显著的提高,丢包率也有所下降.     

s-t路径确定方法的研究

确定网络ｓ－ｔ间的路径是利用路径枚举法计算网络可靠性及确定ｓ－ｔ路由所必须的。本文在对以往确定网络ｓ－ｔ间路径算法的研究基础上,提出了一种新的确定路径的算法－邻接矩阵算法,该算法不仅节省计算机内存,减少了计算量,而且用节点序列表示的路径可方便地用于同时考虑节点和边失效情况下的网络可靠性计算。     

Routing bandwidth guaranteed paths with local restoration in label switched networks

The emerging multiprotocol label switching (MPLS) networks enable network service providers to route bandwidth guaranteed paths between customer sites. This basic label switched path (LSP) routing is often enhanced using restoration routing which sets up alternate LSPs to guarantee uninterrupted connectivity in case network links or nodes along primary path fail. We address the problem of distributed routing of restoration paths, which can be defined as follows: given a request for a bandwidth guaranteed LSP between two nodes, find a primary LSP, and a set of backup LSPs that protect the links along the primary LSP. A routing algorithm that computes these paths must optimize the restoration latency and the amount of bandwidth used. We introduce the concept of "backtracking" to bound the restoration latency. We consider three different cases characterized by a parameter called backtracking distance D: 1) no backtracking (D=0); 2) limited backtracking (D=k); and 3) unlimited backtracking (D=/spl infin/). We use a link cost model that captures bandwidth sharing among links using various types of aggregate link-state information. We first show that joint optimization of primary and backup paths is NP-hard in all cases. We then consider algorithms that compute primary and backup paths in two separate steps. Using link cost metrics that capture bandwidth sharing, we devise heuristics for each case. Our simulation study shows that these algorithms offer a way to tradeoff bandwidth to meet a range of restoration latency requirements.     

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     

Efficient Distributed Bandwidth Management for MPLS Fast Reroute

As service providers move more applications to their IP/MPLS (multiple protocol label switching ) backbone networks, rapid restoration upon failure becomes more and more crucial. Recently MPLS fast reroute has attracted lots of attention as it was designed to meet the needs of real-time applications, such as voice over IP. MPLS fast reroute achieves rapid restoration by computing and signaling backup label switched path (LSP) tunnels in advance and re-directing traffic as close to failure point as possible. To provide a guarantee of bandwidth protection, extra bandwidth has to be reserved on backup paths. Using path merging technique as described in IETF RFC 4090 only, the network is able to share some bandwidth on common links among backup paths of the same service LSP, i.e., so-called intra-sharing. But no solution is provided on how to share bandwidth among backup paths of different service LSPs, i.e., so-called inter-sharing. In this paper, we provide an efficient distributed bandwidth management solution. This solution allows bandwidth sharing among backup paths of the same and different service LSPs, i.e., both intra-sharing and inter-sharing, with a guarantee of bandwidth protection for any single node/link failure. We also propose an efficient algorithm for backup path selection with the associated signaling extensions for additional information distribution and collection. To evaluate our schemes, we compare them via simulation with the basic MPLS fast reroute proposal, IETF RFC 4090, on two networks. Our simulation results show that using our bandwidth management scheme can significantly reduce restoration overbuild from about 250% to about 100%, and our optimized backup path selection can further reduce restoration overbuild to about 60%.     

On Achieveing Bandwidth-Aware LSP//spl lambda/SP Multiplexing/Separation in Multi-layer Networks

We present a new traffic engineering (TE) model which is based on QoS rerouting and uses hybrid resilience to improve the recovery performance of multi-layer networks where an MPLS network is layered above an MPlambdaS network. We formulate the rerouting of the LSPs/lambdaSPs as a multi-constrained problem and use its polynomial reduction to find a heuristic solution that can be implemented by standardized constraint-based routing algorithms. This heuristic solution uses a cost-based routing optimization to achieve different network configurations which multiplex/separate bandwidth-aware LSPs/lambdaSPs on the network links. We formulate the resilience upon failure as a multi-objective problem consisting of finding a resilience strategy that minimizes recovery operation time and maximizes the LSP/lambdaSP restorability. A solution to this problem is proposed where a hybrid resilience framework is used to achieve restoration in the MPLS layer to complement path switching in the MPlambdaS layer. We evaluate the performance of the TE model when rerouting the tunnels carrying the traffic offered to a 23- and 31-node networks. Simulation reveals that the hybrid resilience model performs better than classical recovery mechanisms. In terms of restorability, quality of rerouting paths and rerouting stability     

A Bandwidth Guaranteed Integrated Routing Algorithm in IP over WDM Optical Networks

In this paper, we have developed an integrated online algorithm for dynamic routing of bandwidth guaranteed label switched paths (LSPs) in IP-over-WDM optical networks. Traditionally, routing at an upper layer (e.g., IP layer) is independent of wavelength routing at the optical layer. Wavelength routing at the optical layer sets up a quasi-static logical topology which is then used at the IP layer for IP routing. The coarse-grain wavelength channels and the pre-determined virtual topologies with respect to some a priori assumed traffic distribution are barriers to efficient resource use and inflexible to changing traffic. We take into account the combined knowledge of resource and topology information at both IP and optical layers. With this added knowledge, an integrated routing approach may extract better network efficiencies, be more robust to changing traffic patterns at the IP layer than schemes that either use dynamic routing information at the IP layer or use a static wavelength topology only. LSP set-up requests are represented in terms of a pair of ingress and egress routers as well as its bandwidth requirement, and arrive one-by-one. There is no a priori knowledge regarding the arrivals and characteristics of future LSP set-up requests. Our proposed algorithm considers not only the importance of critical links, but also their relative importance to routing potential future LSP set-up requests by characterizing their normalized bandwidth contribution to routing future LSP requests with bandwidth requirements. Moreover, link residual bandwidth information that captures the link's capability of routing future LSPs is also incorporated into route calculation. Extensive simulation was conducted to study the performance of our proposed algorithm and to compare it with some existing ones, such as the integrated minimum hop routing algorithm and the maximum open capacity routing algorithm. Simulation results show that our proposed algorithm performs better than both routing algorithms in terms of the number of LSP set-up requests rejected and the total available bandwidth between router pairs.     

A Preemption-Aware On-line Routing Algorithm for MPLS Networks

In the context of Multiprotocol Label Switching (MPLS), we look at the problem of organizing the mapping of Label Switched Paths (LSPs) in an optimal way throughout the network on the basis of a given objective function. This problem is highly combinatorial and makes dynamic and real-time features a difficult issue for any LSP routing scheme. For this reason, we propose a computationally efficient, though approximate, on-line scheme adapted to an incremental optimization of the network state. We also propose an integration of a computationally efficient preemption mechanism into this approximation. The efficiency of this algorithm is obtained through a very rigid but seemingly appropriate policy concerning which LSPs are appropriate for preemption. A feedback from preemption on the routing process is proposed, in order to regulate the rate of the reroutings and to tune the balance between stability and continuous reorganization in a network.     

Creating multipoint-to-point LSPs for traffic engineering

Traffic engineering enhances an ISP's capability to manage and utilize its resources effectively. MPLS has emerged as an efficient packet forwarding tool that gives a significant boost to the traffic engineering capabilities of an ISP. A fundamental problem in MPLS is to reduce label space usage by label switched paths while meeting the requirements of the flows traversing the network. Using multipoint-to-point LSP trees has been proposed as one of the techniques to reduce label space usage. We look at the problem of creating multipoint-to-point LSPs given a set of precomputed point-to-point LSPs. We propose a heuristic for multipoint-to-point LSP creation and show its effectiveness.     

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.     

Connection Establishment of Label Switched Paths in IP/MPLS over Optical Networks

We propose and investigate three connection admission control policies for the establishment of label switched paths (LSPs) in IP/MPLS over optical networks. We show that the policy of establishing LSPs first in the optical layer achieves a better blocking performance. We examine the effect of the number of add/drop ports of optical cross-connects (OXCs) on the LSP blocking performance. We show that there exists a lower bound for the number of add/drop ports of OXCs for the network to achieve almost the best LSP blocking performance.     

On the Maximum Protection Problem in IP-over-WDM Networks Using IP LSP Protection

In dynamic IP-over-WDM networks efficient fault-management techniques become more difficult since as demands change with time the optimal logical topology varies as well. Changes in the virtual topology should be done with care because working IP LSPs routed on top of a virtual topology should not be interrupted. Reconfiguration of the virtual topology may also affect precomputed backup IP LSPs to be activated in case of failure meaning that backup IP LSPs would need to be recomputed after any change in the virtual topology. A good sense solution can be the dimensioning of the virtual topology for a worst case traffic scenario, having as goal the minimization of the network cost, for example, and then route dynamic IP LSPs on this virtual topology. The virtual topology would remain unchanged as long as possible, that is, until changes in the virtual topology are considered to bring considerable benefits. Since data services over IP are essentially of a best-effort nature, protection could be provided, using IP LSP protection, only when bandwidth is available in the virtual topology. The computation of backup IP LSPs does not interfere with working IP LSPs meaning that no service interruption will exist. Such a strategy, considered in this paper, allows resources to be used efficiently, since free bandwidth is used for backup purposes, while the normal delivery of traffic is guaranteed in peak traffic situations although having no protection guarantees. Our main objective is to quantify the spare capacity, which can be used for restoration (backup) purposes, over a virtual topology designed and optimized to carry a traffic scenario with no survivability and QoS requirements. We analyse the maximum protection (MP) problem in such IP-over-WDM network environment. Protection is provided to IP LSP requests whenever possible through bandwidth reservation in a backup IP LSP on the virtual topology. Besides the mathematical formalization of the MP problem, an upper bound and heuristic algorithms are proposed and evaluated. The traffic considered includes IP LSPs of different granularities and is the worst case traffic scenario for which the network should be dimensioned.