Label Switched Paths Research Articles

On the Analysis of Mobility Mechanisms in Micro Mobile MPLS Access Networks

One of the major challenges for the next generation mobile systems is related to efficient mobilitymanagement issue. In this paper, we propose a new micromobility management scheme, called Micro Mobile MPLS, that supports both mobility and quality-of-service (QoS) management in wireless networks. Our proposal includes two protocol variants. In the first variant, called FHMicroMobile MPLS, we consider the fast handoff (FH) mechanism, which anticipates the LSP (Label Switched Path) procedure setup with an adjacent neighbor subnet that an MN is likely to visit. This mechanism is proposed to reduce service disruption by using the link-layer (L2) functionalities. In the second variant, called FC-Micro Mobile MPLS, the forwarding chain (FC) concept is providedto track efficiently the host mobility within a domain. This concept is more suitable for MNs with high mobility rate. In order to assess the efficiency of our proposals, all underlying protocols are compared. To achieve this, we develop analytical models to evaluate the link usage cost, the registration updates cost, the handoff latency and the packet loss rate. Numerical and simulation results show that the proposed mechanisms can significantly reduce the registration updates cost and provide low handoff latency and packet loss rate under various scenarios.

Fast setup of end-to-end paths for bandwidth constrained applications in an IP/MPLS–ATM integrated environment

Transport networks are currently being moved towards a model of high performance Internet Protocol/Multiprotocol Label Switching (IP/MPLS) routers interconnected through intelligent core networks. Currently, Asynchronous Transfer Mode (ATM) technology has been widely deployed in several network backbones along with the Private Network-to-Network Interface (PNNI) protocols as the control plane. In order to cope with the increasing Internet traffic demands in the current context, fast setup of end-to-end paths with the required Quality of Service (QoS) is necessary. This paper analyzes the case of two IP/MPLS networks interconnected through an ATM core network, assuming MPLS as the mechanism to provide Traffic Engineering in the IP networks, and a PNNI-based control plane in the core network. This paper aims to define a mechanism needed to set up a fast end-to-end QoS Label Switched Path (LSP) between two Label Switched Routers (LSRs) belonging to different IP/MPLS domains. First, the fast end-to-end setup is achieved by modifying the network backbone control plane. Second, two different aggregation schemes are proposed to summarize the QoS network state information to be transported through the ATM core network. Therefore, both the efficient aggregation schemes and the fast mechanism allow source routing to set up a path faster than the existing methods and to reduce the blocking probability using a summary of the available resource information.

Path selection with preemption and re-routing control for multi-protocol label switching networks

Multi Protocol Label Switching (MPLS) networks enhance the services of conventional best-effort IP networks by providing end-to-end Quality of Service (QoS) guaranteed Label Switched Paths (LSP) between customer sites. The LSP has to be set up in advance before carrying the traffic. Contention for network resources may happen if many LSPs try to use a common network link with limited bandwidth. In this paper, we investigate the problem of providing services to high priority LSPs whereby existing LSPs with lower priority may be preempted. The consequent interruption of the services of preempted LSPs would detrimentally affect users’ perception on the QoS provided. Therefore, the preemption strategies may incorporate additional re-routing mechanisms to provide alternative paths for the LSPs which are to-be-preempted so that their services remain unaffected. A newly arrived high priority LSP in an MPLS network may find M possible paths between its source and destination. It may select the shortest path which may trigger preemption or choose a longer path which however utilizes more resources. We begin by formulating preemption strategies with global re-routing. Our investigations include the effects of routing of high priority LSPs on the shortest path and its alternative paths. We show that by persistently routing the high priority LSP on the shortest path, more preempted LSPs can be re-routed which would reduce the negative effects of preemption. However, as excessive re-routing may degrade the network performance as well, a re-routing control strategy is proposed to constrain the length of these re-routed paths. Finally, a decentralized preemption strategy with local re-routing is also presented to approximate the performance of the proposed strategy with significantly lower control overheads. Simulations show that with this approach, high priority LSPs can gain better access to network resources while simultaneously ensuring that, as compared to the existing preemption strategies, the network throughput and the ongoing connection services are not adversely affected.

Protection Schemes for IP-over-WDM Networks: Throughput and Recovery Time Comparison

This article presents a novel protection approach using Generalized Multi-Protocol Label Switching (GMPLS). This strategy provides protection at the Wavelength Division Multiplexing (WDM) layer, meaning that all Internet Protocol Label-Switched Path (IP LSPs) nested inside a lightpath are protected in an aggregated way. It uses resources efficiently since spare capacity of working primary lightpaths can be used for backup purposes whenever necessary. The IP and WDM layers are treated together as a single integrated network from a control plane point of view, so that network state information from both layers can be used. Besides discussing the strategy proposed and the key features of GMPLS that will allow its implementation, we mathematically formulate the maximum throughput problem. Thereafter, we propose and compare heuristic algorithms for IP-over-WDM networks using three protection approaches: WDM lightpath protection, IP LSP protection, and the proposed protection scheme. Their throughputs and recovery times are analyzed and compared. Our results show that, for a representative mesh network, the proposed aggregated protection scheme presents better protection efficiency and good scalability properties when compared with the other two schemes.

Optimum Arrangement of Reliable Label-Switched Paths in MPLS Over Optical Networks

In MPLS (Multi-Protocol Label Switching) over optical networks, both the optical level and the MPLS level fault recovery can be considered. Generally, a more flexible path arrangement can be realized by the MPLS level recovery, while fast recovery can be achieved by the optical level recovery. When the optical level recovery is adopted, only normal traffic is carried through the working lightpaths and only recovered traffic is carried through the backup lightpaths. In contrast, the working LSPs (Label-Switched Paths) and the backup LSPs corresponding to other working LSPs can be accommodated into an identical lightpath when the MPLS level recovery is adopted. By such sophisticated accommodation of LSPs into the lightpaths, lightpath bandwidth can be utilized efficiently under the condition that the bandwidth utilization is restricted to attain the given objective of transfer quality for the MPLS packets in the normal state and unrestricted in a short time a failure occurs somewhere in the network. This paper proposes a simple mathematical programming model to obtain the optimum arrangement of the working and backup LSPs assuming the MPLS level recovery and a practical LSPs provisioning mode. By comparing the minimized network cost obtained from the optimum arrangement of the working and backup LSPs with the network cost resulting from the optical level recovery, this paper quantitatively evaluates the effectiveness of such bandwidth utilization improvement obtained from the MPLS level recovery and reveals that the MPLS level recovery can actually reduce the network cost due to its flexible arrangement of LSPs on the lightpaths.

Architecture design and performance evaluation of multigranularity optical networks based on optical code division multiplexing

Feature Issue on Waveband Switching, Routing, and GroomingIn traditional lambda-based multigranularity optical networks, a lambda is always treated as the basic routing unit, resulting in low wavelength utilization. On the basis of optical code division multiplexing (OCDM) technology, a novel OCDM-based multigranularity optical cross-connect (MG-OXC) is proposed. Compared with the traditional lambda-based MG-OXC, its switching capability has been extended to support fiber switching, waveband switching, lambda switching, and OCDM switching. In a network composed of OCDM-based MG-OXCs, a single wavelength can be shared by distinct label switched paths (LSPs) called OCDM-LSPs, and OCDM-LSP switching can be implemented in the optical domain. To improve the network flexibility for an OCDM-LSP provisioning, two kinds of switches enabling hybrid optical code (OC)-wavelength conversion are designed. Simulation results indicate that a blocking probability reduction of 2 orders can be obtained by deploying only five OCs to a single wavelength. Furthermore, compared with time-division-multiplexing LSP (TDM-LSP), owing to the asynchronous accessibility and the OC conversion, OCDM-LSPs have been shown to permit a simpler switch architecture and achieve better blocking performance than TDM-LSPs.

Study of Minimum Interference Routing Algorithm for MPLS Traffic Engineering

Multiprotocol Label Switching (MPLS) enables the deployment of Internet traffic engineering to be sim- ple and efficient by using explicit routing of Label Switching Path (LSP). Hence, the LSP routing algorithm becomes the core and hot topic of traffic engineering. This paper analyzes the key ideas of Minimum Interference Routing Algorithm (MIRA) for LSP routing and then surveys the current improved schemes of MIRA. According to their technical methods, they are classified as reconfirming critical links class, utilizing traffic profile information class, adding admission control class, and solving multiple Quality of Service constraints class. After the key idea is analyzed for each class, their typical algorithms are presented and their advantages, suitable environments and shortcomings with a detailed comprehensive comparison are discussed. The end of the paper points out the future

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 constraintbased 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.

LSP protection for delay-differentiated dynamic traffic in IP-over-WDM networks with port constraints

We consider the problem of label switched path (LSP) protection for dynamic traffic with differentiated delay requirements in IP-over-WDM networks with limited port resources. A pair of link-disjoint primary LSP and backup LSP is provided for each connection to enable guaranteed and timely recovery in the event of a single link failure. To support delay sensitive traffic such as voice, the primary and backup LSPs must traverse a limited number of optical–electrical–optical (OEO) conversions (equivalently, to traverse limited number of electronic routers and hence reduced electrical processing), besides the bandwidth requirement. This OEO constraint can be specified by users in service level agreement (SLA) or determined by service providers based on the end-to-end delay requirement. We propose two integrated routing algorithms to route traffic with or with no OEO conversion requirements, respectively. These two algorithms can compute primary LSPs and backup LSPs in polynomial time. We consider the case where limited ports are provided at each node in the network and develop two routing approaches called port-independent routing and port-dependent routing. In the port-independent routing, paths are selected first and then port availabilities are checked to setup the path. While this approach is simple to implement, it leads to connection blocking if ports required on the chosen path are not available. In the port-dependent routing, port information is incorporated in the path selection process. It guarantees that a path can be setup once it is found. We evaluate the effectiveness of LSP protection using the proposed algorithms on the NSFNET network.

An efficient traffic engineering approach based on flow distribution and splitting in MPLS networks

This paper develops an efficient method based on traffic flow distribution and splitting for traffic engineering in the MPLS networks. We define flow distribution as selecting one of the available label switch paths (LSPs) to carry one aggregated traffic flow. Flow splitting is, however, the mechanism designed for multiple parallel LSPs to share one single aggregated flow. Our studies show that flow distribution and flow splitting approaches readily solve the routing problems such as bottleneck and mismatch problems. An algorithm based on network bandwidth utilization is also proposed to integrate both approaches. The simulation results presented at the end of the paper demonstrate the effectiveness of the proposed approaches.

Study of LSP arrangement schemes in label switch networks

Label switch paths (LSP) are regarded as the routing components of an end-to-end connection in label switching network from the traffic engineering point of view. Thus, an end-to-end connection may travel more than one LSP. The QoS of this end-to-end connection relies on the performance of each LSP it travels. Therefore, to carefully arrange LSP is an essential step towards QoS networks. Generally speaking, the capacity of a specific link is not allocated for high-priority LSP because it will cause inflexibility in the scheduling process. In this paper, the best-fit shortest path (BSP) assignment and the worst shortest path (WSP) assignment schemes are proposed for the arrangement of label switch paths. In order to provide flexibility in packet scheduling, we propose that the BSP scheme to be applied for allocation of low-priority LSP and the WSP scheme is used for the arrangement of LSP with high priority. Based on these two schemes, we extend them with elastic bandwidth allocation to prevent the bandwidth of the link from being occupied by the higher priority LSP. The experimental results indicate that, compared to the BSP-only scheme, the proposed hybrid scheme demonstrates a more efficient way of arranging prioritized LSP. Moreover, the proposed elastic constrained bandwidth allocation scheme also illustrates a rather good performance in smoothing the link utilization of high-priority LSP.

Generalized Traffic Engineering Protocol for Multi-Layer GMPLS Networks

This paper proposes a Generalized Traffic Engineering Protocol (GTEP). GTEP is a protocol that permits communication between a Path Computation Element (PCE) and a Generalized Multi-Protocol Label Switching (GMPLS) controller (CNTL). The latter is hosted by each GMPLS node: it handles GMPLS and MPLS protocols such as routing and signaling protocols as well as controlling the GMPLS node host. The PCE provides multi-layer traffic engineering; it calculates Label Switched Path (LSP) routes and judges whether a new lower-layer LSP should be established. GTEP functions are implemented in both the PCE and GMPLS router. We demonstrate a multi-layer traffic engineering experiment conducted with GTEP.

SLEA: a novel scheme for routing in overlay IP/WDM networks

This paper studies the routing problems in Internet protocol/wavelength-division-multiplexing (IP/WDM) networks based on the overlay routing algorithm (ORA) and the integrated routing algorithm (IRA), respectively. Although IRA usually outperforms ORA in terms of blocking performance, IRA exhibits disadvantages in control information exchange, network privacy issue, and wavelength port efficiency. In this paper, a new mechanism called the short lightpath establishment approach (SLEA) is proposed for ORA in order to tackle the problems in IRA and achieve similar (or even better) network performance at the same time. The main idea of SLEA is to ensure that each new lightpath created by ORA is restricted by an optical hop constraint when a subwavelength-granularity connection is routed in the optical layer. It follows that SLEA essentially avoids per-connection-based greedy treatment and improves network wide resource utilization by eliminating inefficient long optical bypasses. To implement SLEA in ORA, the Dijsktra's algorithm has been modified based on an extended layered graph model. SLEA does not introduce any additional signaling and computational complexity. The analysis and simulation in this paper show that there exists an optimal optical hop constraint for each particular network configuration such that SLEA-based ORA (SLEA-ORA) can efficiently utilize the network resource of concern. As a result, with the optimal optical hop constraint, SLEA-ORA could outperform ORA and IRA in terms of the bandwidth-blocking ratio (BBR) and the average number of IP hops of label-switched paths (LSPs).

New MPLS Network Management Techniques Based on Adaptive Learning

The combined use of the differentiated services (DiffServ) and multiprotocol label switching (MPLS) technologies is envisioned to provide guaranteed quality of service (QoS) for multimedia traffic in IP networks, while effectively using network resources. These networks need to be managed adaptively to cope with the changing network conditions and provide satisfactory QoS. An efficient strategy is to map the traffic from different DiffServ classes of service on separate label switched paths (LSPs), which leads to distinct layers of MPLS networks corresponding to each DiffServ class. In this paper, three aspects of the management of such a layered MPLS network are discussed. In particular, an optimal technique for the setup of LSPs, capacity allocation of the LSPs and LSP routing are presented. The presented techniques are based on measurement of the network state to adapt the network configuration to changing traffic conditions.

A minimum interference routing algorithm with reduced computational complexity

Minimum interference routing algorithms are designed to reduce rejections of future requests for the establishment of Label Switched Paths (LSPs) but make no assumption about specific patterns of arrival request. This paper introduces a novel minimum interference routing algorithm, Light Minimum Interference Routing (LMIR), which is based on a new approach to the identification of critical links. This approach reduces the computational complexity involved in finding a path for the establishment of an LSP. The LMIR is shown to have the same precision as existing algorithms but with less computational complexity.

Network design and cost optimization for label switched multilayer photonic IP networks

Dealing with the explosive increase in the amount of Internet traffic requires high-speed and huge capacity Internet protocol (IP) backbone networks. Existing IP backbone networks are constructed using point-to-point wavelength-division-multiplexing (WDM) transmission systems, where all the wavelengths are terminated link-by-link, so that rather expensive optical/electrical conversions are necessary at every node. In these systems, since every IP packet is routed at each intermediate node based on the header information, a header processing bottleneck will occur when the node input traffic exceeds several hundreds of gigabits per second. In order to mitigate these problems, an optical cross-connect (OXC) function that employs wavelength routing of the optical paths (OPs) will provide an effective solution. This paper proposes a network design method where electrical and photonic multiprotocol label switching (MPLS) technologies are used; the network is referred to as a photonic IP network. We first propose new algorithms that minimize the network cost in a multilayered network comprising electrical label switched paths (LSPs) and optical LSPs (optical paths that are controlled using the MPLS mechanism). The particular point of the proposed algorithms is that they include different cost minimization scenarios appropriate for the different OLSP provisioning conditions that are chosen as the first step in the design stage. The effectiveness of the proposed algorithms and the benefits of the OLSPs are quantitatively evaluated through various simulations.

Fast network re-optimization schemes for MPLS and optical networks

This paper presents algorithms for re-optimizing network routing in connection-oriented networks such as Multi-Protocol Label Switched (MPLS) networks. The objective in re-optimization is to allow the network to carry more traffic without adding capacity. The need for re-optimization arises because of dynamic connection routing where connections, such as bandwidth guaranteed Label Switched Paths (LSPs) in MPLS networks, are routed as they arrive one-by-one to the network. Continual dynamic routing leads to network inefficiencies due to the limited information available for routing and due to simple path selection algorithms often used to satisfy connection set-up time constraints. We present a re-optimization scheme, where the re-optimizer constantly monitors the network to determine if re-optimization will lead to sufficient network efficiency benefits. When sufficient benefits can be obtained, the re-optimizer computes the least cost set of connections which must be re-routed to attain the necessary network efficiency and then computes the routes for the connections to be re-routed. We develop efficient re-optimization algorithms and demonstrate by simulations that several network performance metrics are significantly improved by re-optimization.

Multi-layer protection in IP-over-WDM networks with and with no backup lightpath sharing

We consider the problem of multi-layer protection in IP-over-WDM networks. In our multi-layer protection schemes, traffic is protected either at the lightpath level or at the label switched path (LSP) level based on the restoration time requirements. In lightpath-level protection, traffic on a path (LSP) is protected by routing it over primary lightpaths which are protected at the optical layer by their respective backup lightpaths. In LSP-level protection, the traffic on a primary LSP is protected at the IP- multi-protocol label switching (MPLS) layer by a backup LSP. In this case, both primary and backup LSPs traverse unprotected lightpaths. We allow two backup LSPs to share bandwidth resource on these unprotected lightpaths if their primary LSPs are link-disjoint. In lightpath-level protection, whether backup resources can be shared or not depends on the protection mechanisms used. In 1:1 dedicated protection where the backup lightpath is pre-configured at the time of setting up of the corresponding primary lightpath, sharing is not possible. However, sharing is allowed in shared protection where the backup lightpaths are configured only after failure. We consider these two schemes and refer them as multi-layer protection with no backup lightpath sharing (MLP-NLS) and multi-layer protection with backup lightpath sharing (MLP-LS). An inter-level sharing (ILS) method is proposed to improve resource utilization in MLP-NLS, by allowing dedicated backup lightpaths to be used by backup LSPs. Two integrated-routing algorithms are developed to select paths in lightpath-level protection and LSP-level protection with the objective to utilize the network resources efficiently. We verify the effectiveness of the proposed multi-layer protection schemes through simulation results on the NSFNET and Pan-European networks.

Flow-Level Multipath Load Balancing in MPLS Network

Multi-Protocol Label Switching (MPLS) can efficiently support the explicit routes setup by the use of Label Switched Paths (LSPs) between an ingress Label Switched Router (LSR) and an egress LSR. Hence it is possible to distribute the network traffic among several paths to achieve load balancing, thus improving the network utilization, and minimizing the congestion. The packet-level traffic characteristics in the Internet is so complex that it is natural to do traffic engineering (TE) and control at the flow level. The emerging Multi-Protocol Label Switching (MPLS) has introduced an attractive solution to TE in IP networks. The main objective of this paper is to balance traffic at the flow level among the parallel Label Switched Paths (LSPs) in MPLS networks. We introduce a multipath load-balancing model at the flow level. In this model, each LSP is modeled as an M/G/1 processor-sharing queue. The load-balancing problem is then considered as an optimization problem. Based on the analysis of the model, we propose a heuristic but efficient mechanism that can make good use of the traffic characteristics at the flow level. Packet disorder is avoided effectively by dispatching packets belonging to one flow to the same path. This mechanism only need to be implemented in the ingress LSRs and the egress LSRs, while the intermediate LSRs only forward the packets. Apart from discussing the traffic allocation granularity, and the implementation issues in details, we have also performed extensive simulations using NS-2 with MPLS modules. The simulation results show that the load through the network is well balanced so that the network throughput is improved and the delay is decreased efficiently.

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.