Private Network-to-network Interface Research Articles

Security and protection in the broadband ATM telecommunication networks

Security of communications over broadband ATM networks is analyzed in this paper. Attacks on ATM networks (faber tapping, SONET (Synchronous Optical network) drop/add multiplexor attacks, eavesdropping, spoofing, virtual channel stealing, service denial, traffic analysis, protocol weaknesses, ILMI (Integrated Local Management Interface) attacks, PNNI (Private Network to Network Interface) attacks), model of ATM and ATM security framework are described. Some problems occurring within security and protection realization in the communication over ATM networks are also specified. .

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.

Modeling and analyzing the performance of adaptive hierarchical networks

As networks become larger, scalability and QoS-awareness become important issues that have to be resolved. A large network can be effectively formed as a hierarchical structure, such as the inter/intra-domain routing hierarchy in the Internet and the Private Network-to-Network Interface (PNNI) standard, to resolve these critical issues. Methods of modeling and analyzing the performance of QoS-capable hierarchical networks become an open issue. Although the reduced load approximation technique has been extensively applied to flat networks, the feasibility of applying it to the hierarchical network model has seldom been investigated. Furthermore, most of the research in this area has focused on the performance evaluation with fixed routing. This work proposes an analytical model for evaluating the performance of adaptive hierarchical networks with multiple classes of traffic. We first study the reduced load approximation model for multirate loss networks, and then propose a novel performance evaluation model for networks with hierarchical routing. This model is based on a decomposition of a hierarchical route into several analytic hierarchical segments; therefore the blocking probability of the hierarchical path can be determined from the blocking probabilities of these segments. Numerical results demonstrate that the proposed model for adaptive hierarchical routing yields accurate blocking probabilities. We also investigate the convergence of the analysis model in both the originating–destination (O–D) pair and the alternative hierarchical path. Finally, the blocking probability of the adaptive hierarchical O–D pair is demonstrated to depend on the blocking of all hierarchical paths but not on the order of the hierarchical path of the same O–D pair.

Optimal PNNI complex node representations for restrictive costs

The Private Network-to-Network Interface (PNNI) is a scalable hierarchical protocol that allows ATM switches to be aggregated into clusters called peer groups. To provide good accuracy in choosing optimal paths in a PNNI network, the PNNI standard provides a way to represent a peer group with a structure called the complex node representation. It allows the cost of traversing the peer group between any ingress and egress to be advertised in a compact form. Complex node representations using a small number of links result in a correspondingly short path computation time and therefore in good performance. It is, accordingly, desirable that the complex node representation contains as few links as possible. In earlier work, a method was presented for constructing the set of the optimal complex node representations in the restrictive and symmetric cost case, under the assumption of a restricted set of optimal paths and a corresponding minimal path computation time. Here this method is extended to constructing the set of the optimal complex node representations appropriate for deployment in a heterogeneous environment where no uniform policy is used to derive them. These representations are not confined by a reduced optimal path constraint, and consequently use the absolute minimum possible number of links, resulting in a minimum path computation time.

Optimizing qos routing in hierarchical atm networks using computational intelligence techniques

In this paper, the use of a computational intelligence approach -a reinforcement learning algorithm (RLA)-for optimizing the routing in asynchronous transfer mode (ATM) networks based on the private network-to-network interface (PNNI) standard is proposed. This algorithm which is specially designed for the quality of service (QoS) routing problem, aims at maximizing the network revenue (allocating efficiently the network resources) while ensuring the QoS requirements for each connection. In this study, large-scale networks are considered where it becomes necessary to be organized hierarchically so that a scale in terms of computation, communication and storage requirements will be achieved. A comparative performance study of the proposed and other commonly used routing schemes is demonstrated by means of simulation on existing commercial networks. Simulation results over a wide range of uniform, time-varying and skewed loading conditions show the effectiveness of the proposed routing algorithm, and disclose the strength and weakness of the various schemes.

Analysis of adaptive cost functions for dynamic update policies for QoS routing in hierarchical networks

QoS routing for hierarchical networks are adopted for achieving high scalability and efficiency, e.g., the Inter/Intra Internet and the ATM Private Network-to-Network Interface (PNNI) specification. In hierarchical routing, several nodes of lower level are aggregated as a logical node of the corresponding next higher level recursively. Moreover, in PNNI, each (logical) node bundles its state information in the structure of PNNI Topology StateElements (PTSE) and sends to its neighbors periodically. That results in hierarchical routing with inaccurate information. Since, aggregated routing information is exchanged based on a time-based update policy in PNNI. However, the dynamic nature of network status makes it very difficult to set an appropriate update interval. Therefore, in this paper, we propose two cost-based adaptive update policies: Dynamic Cost-based Update policy and Dynamic Cost-based Update policy with hysteresis, which update routing information only when the change of the cost of a link exceeds a threshold. Our numerical results show that the cost-based update policies not only reduce connection blocking probability, but also decrease the frequency of routing information updates. In this paper, we analyze three approaches to define link cost function and examine the performance of the cost-based update policies under these link cost functions. We find that the proposed cost-based adaptive update policies together with the Markov Decision Process-based link cost function yield the best performance.

QoS routing and performance in packet networks: A visual simulation platform and case study

One of the critical components in providing quality of service (QoS) in packet networks is routing. As a consequence, significant efforts in the areas of open system specifications and active research are leading to new routing and signaling protocols for asynchronous transfer mode (ATM) and Internet protocol (IP) networks. Such developments have created the need for a general-purpose platform to understand and evaluate the performance of these new protocols. In this paper, we describe the Routing Performance Simulator (RopeSIM), a visual simulator developed for studying routing performance issues in packet networks. RopeSIM is based on the visual discrete-event simulation platform Q+ developed by the Performance Analysis Department at Bell Labs. The Q+ platform provides basic event scheduling and handling, queuing, and simulation control, as well as the various visual input/output capabilities exploited in RopeSIM. In addition, RopeSIM includes algorithms developed for routing, signaling, link state updates, and resource reservation/allocations. Various statistics useful for QoS routing algorithm performance studies, such as call blocking, network revenue, selected call routes, and link-state update message loads are also available in RopeSIM. For purposes of concreteness, we present a case study of ATM private network-to-network interface (PNNI) routing performance using RopeSIM. By using RopeSIM to investigate a wide range of performance issues in the case study, we demonstrate its versatility as a general-purpose platform for studying routing in packet networks. Finally, we outline ongoing and future work.

On the planning of the S-PVC overlay in ATM networks

We tackle the planning problem of the soft-permanent virtual connections (S-PVCs) in asynchronous transfer mode (ATM) networks. The private network-to-network interface (PNNI) routing standard is used to route these connections. The planning problem consists of determining the PNNI link metrics and the capacity to reserve on each ATM link that ensure the successful rerouting of the S-PVCs for all failure scenarios of interest to the network planner. A mathematical programming model is proposed and a tabu search heuristic in order to find "good" solutions. Finally numerical results are presented and analyzed.

Adaptive crankback schemes for hierarchical QoS routing in ATM networks

To reduce routing information and achieve scalability in large ATM networks, ATM Private Network-to-Network Interface (PNNI) adopts hierarchical routing. For efficient routing, a large ATM network is decomposed into subnetworks called Peer Groups (PG), which advertise aggregated routing information only. Because of lack of precision in the aggregated information, a call set up message on a chosen route can be rejected. When an ATM node discovers that a call set up message cannot proceed due to insufficient resources, a back-tracking procedure called ‘crankback’ is initiated against call blocking. Although crankback reduces blocking probability, it also causes additional overhead, such as longer setup delay. Consequently, this study proposes two approaches to reduce crankback overhead. The first approach adds extra information to the setup message, referred to as Crankback Information Stack (CIS), to reduce crankback overhead. Meanwhile, the other approach, referred to as Cost Threshold (CT), uses the aggregated path cost and the cost information of previously rejected call setup message to determine whether call setup should be tried on the next alternate path. The simulation results herein demonstrate that both of the proposed approaches significantly reduce crankback overhead, while the combination of the CIS and CT approach achieves further improvement.

Efficient hierarchical QoS routing in ATM networks

For reducing network information to achieve scalability in large ATM networks, ATM Private Network-to-Network Interface (PNNI) adopts hierarchical routing. Consequently, although routing complexity is significantly reduced, numerous issues in PNNI routing require further study to achieve more efficient, accurate, scalable, and QoS-aware routing. Several methods are adopted herein to achieve efficient, scalable, and QoS-aware ATM PNNI routing. First, an efficient aggregation scheme, referred to as Asymmetric Simple, is proposed. The aggregated routing information includes available bandwidth, delay and cost. Second, two approaches for defining link costs are investigated, namely, the Markov Decision Process (MDP) approach and the Competitive On-Line (COL) routing approach, and these are compared with the Widest Path (WP) approach. Finally, a dynamic update policy, referred to as the dynamic cost-based update (DCU) policy, is proposed to improve the accuracy of the aggregated information and the performance of hierarchical routing, while decreasing the frequency of re-aggregation and information distribution. Simulation results demonstrate that the proposed Asymmetric Simple aggregation scheme yields very good network utilization while significantly reducing the amount of advertised information. Between these two link cost functions, the MDP approach provides a systematic method of defining call admission function and yields better network utilization than the COL approach. The proposed DCU policy also yields an enhanced network utilization while significantly reducing the frequency of re-aggregation and the amount of distributed aggregation information.

An Efficient Location Management Protocol for Wireless ATM Customer Premises Networks

In this paper we present a new location management protocol for wireless ATM networks, called LMCP (Location Management and Control Protocol). This protocol is based on the PNNI (Private Network-to-Network Interface) routing functionality to advertise the movement of mobile terminals within pre-defined areas. Moreover, LMCP uses specialized entities to store and retrieve the current location area of mobile terminals. These entities are located in mobility enhanced switches that control the execution of other mobility procedures (e.g. handovers). The main benefit from the application of LMCP is the establishment of connections that do not contain any misrouted segments. Furthermore, it requires minor modifications to the PNNI and enables its inter-working with other location management mechanisms. The protocol is compared with other similar mechanisms, and its efficiency is demonstrated by the results of an analytical model.

Analysis of link cost functions for PNNI routing

The emerging environment of ATM networks with unpredictable traffic patterns and ever-changing network configurations create the need for using dynamic routing methods. Dynamic routing basically means that path selection continuously adapts to the state of the network. The routing framework of the Private Network-to-Network Interface (PNNI) specification achieves this by using link-state information gathered from the network. One possible approach for selecting paths is to use a shortest path algorithm (e.g., Dijkstra's) with link costs generated from the link load information. This mapping is realised by the so-called link cost function. We investigated a number of such link cost functions with simulation. We developed two novel link cost functions and compared them with those found in the literature. The primary basis of comparison was the total throughput of the networks. Besides this, we also investigated such issues as imposed signalling load and robustness.

Optimal PNNI complex node representations for restrictive costs and minimal path computation time

The private network-to-network interface (PNNI) protocol, which specifies how topology information is to be distributed in an ATM network, allows ATM switches to be aggregated into clusters called peer groups. Outside of a peer group its topology is aggregated into a single logical node. This method can be applied recursively so that PNNI can hierarchically aggregate network topology state information. To provide good accuracy in choosing optimal paths in a PNNI network, the PNNI standard provides a way to represent a peer group with a structure called the complex node representation. It allows the cost of traversing the peer group between any ingress and egress to be advertised in a compact form. Complex node representations using a small number of links result in a correspondingly short path computation time and therefore in good performance. It is, therefore, desirable that the complex node representation contains as few links as possible. This paper considers the class of complex node representations for which the path computation time is minimal. It assumes that the path selection is based on restrictive costs, such as bandwidth, and considers the symmetric case. It presents a method for constructing the set of the optimal complex node representations in the sense that they use the minimum possible number of links. Central to the development of this method is the establishment of the optimal substructure property of the optimal complex node representations.

ATM Routing Algorithms for Multimedia Trafficin Private ATM Networks

The goal of this paper is to recommend a good Private Network-to-Network Interface (PNNI) routing algorithm for private ATM networks. A good routing algorithm has to work well with multimedia traffic with several quality of service (QoS) requirements (such as cell loss ratio, cell delay and its variation etc.) in different networks under various traffic conditions. The multiplicity of QoS requirements makes the routing problem NP-complete, so our approach to the problem is based on large scale simulations involving several empirical algorithms (compliant with the PNNI routing specification) which have been tested for different network topologies and traffic scenarios. Based on analysis of tradeoffs involving performance metrics (such as blocking rate, complexity, load distribution) we recommend a consistently good routing algorithm for single domain ATM networks.

On the distribution of routing computation in hierarchical ATM networks

ATM private network-to-network interface (PNNI) is a hierarchical and dynamic link-state routing protocol, designed to scale to the largest possible ATM networks, encompassing thousands of nodes. This paper investigates the route computation load imposed by the PNNI routing scheme, and shows that this load is unevenly distributed among the network nodes. More specifically, the routing computation load associated with the setup of a single virtual path grows exponentially with the hierarchy level. As a result, some of the network nodes-mainly those that function as border nodes of high levels-may be overloaded with route computation, while other nodes are rarely involved in this process. This paper also proposes a possible scheme for spreading the route computation burden more evenly. According to this scheme, heavily loaded nodes transfer route computation tasks to lightly loaded nodes.

A route optimization algorithm and its application to mobile location management in ATM networks

In this paper, we propose an algorithm for optimizing the route of a connection that becomes suboptimal due to operations such as handoffs and location-based reroutes, for mobile ATM (asynchronous transfer mode) networks based on the PNNI (private network-to-network interface) standard. This algorithm uses hierarchical route information of the connection and summarized topology and loading information of the network to determine a such that adjusting the connection from that crossover node results in an optimally routed connection. We then apply this algorithm to the mobile location management problem. Location management schemes have been proposed in which an incoming call to a mobile is routed to its home switch (based on summarized reachability data) and then rerouted to the mobile's current location. If we consider such rerouting a first phase of mobile connection setup, a second phase is required to optimize the paths of such rerouted connections. Such an approach is considered a two-phase mobile location/connection setup scheme. Alternatively, an incoming call to a mobile can be routed to its home switch based on summarized reachability data, and then cranked back to an optimal crossover node before rerouting the connection to the mobile's current location. Such a scheme is a one-phase mobile location/connection setup scheme since it directly results in an optimal path. A comparative performance analysis of the one- and two-phase connection setup schemes is presented. Measures of comparison are call setup delay and the amount of network resources allocated to a connection. The maximum call setup delay (worst case call setup delay) is lower in the two-phase scheme, but the average call setup delay is lower in the one-phase scheme. The amount of resources required for a connection in the two-phase scheme (prior to route optimization) is significantly greater than that in the one-phase scheme.

Mobile location management in ATM networks

This paper presents two mobile location management algorithms for ATM (asynchronous transfer mode) networks based on the PNNI (private network-to-network interface) standard. The first solution is called the mobile PNNI scheme because it builds on the PNNI routing protocol. It uses limited-scope (characterized by a parameter S) reachability updates, forwarding pointers, and a route optimization procedure. The second solution is called the LR (location registers) scheme because it introduces location registers (such as the cellular home and visitor location registers) into the PNNI standards-based hierarchical networks. This scheme uses a hierarchical arrangement of location registers with the hierarchy limited to a certain level S. Analytical models are set up to compare the average move, search, and total costs per move of these two schemes for different values of the CMR (call-to-mobility ratio), and to provide guidelines for selecting parameters of the algorithms. Results show that at low CMRs (CMR<0.025), the LR scheme performs better than the mobile PNNI scheme. We also observe that the two schemes show a contrasting behavior in terms of the value to be used for the parameter S to achieve the least average total cost. At low CMRs, the parameter S should be high for the mobile PNNI scheme, but low for the LR scheme, and vice versa for high CMRs.