ATM Virtual Path Research Articles

Prioritized traffic restoration in connection oriented QoS based networks

Connection oriented quality-of-service (QoS) based networks offer several service classes each designed to handle connections supporting various types of applications. A network failure will typically result in a large number of disrupted connections in each service class, all of which need to be restored simultaneously. In this paper we propose a distributed fault recovery priority scheme for dynamic restoration of connections. The proposed scheme exploits available network resources immediately after a failure together with properties of typical applications carried by the connections in order to give the applications sufficient network performance. The scheme is formulated within the context of switched virtual circuit routing in ATM networks, but it is applicable to ATM virtual path restoration as well and to other class based QoS networks like DiffServ MPLS based networks. The priority based restoration scheme is formulated as a centralized path flow integer programming optimization problem serving as a comparison benchmark for suboptimal distributed schemes. We propose a distributed heuristic scheme and give numerical results illustrating the quality of the proposed distributed scheme in comparison to the centralized optimal approach. Our numerical results show that the proposed distributed scheme can significantly improve utilization of network resources and enhance network performance after a failure.

BFRA: bounded flooding routing algorithm for provisioning the globally optimal route in a hierarchical ATM network

ATM virtual path (VP) contains bundles of virtual channels (VCs). A VP layer network can be used as a server layer network of VC layer networks and each VC layer network can be a client layer. Therefore, the effective provision of VC services can be achieved by the more optimal routing scheme of the VP layer network. However, the traditional hierarchical routing scheme of PNNI signaling protocol does not provide the globally optimal route in hierarchical transport network due to its successive network partitioning and topology abstraction. We propose a new VP routing scheme suitable for the national wide hierarchical transport network and a network model suitable for the scalable VP network management system. The routing algorithm can provide the globally optimal route in the hierarchical network environment from the perspectives of maximization of network resource utilization and satisfaction of the end user's QoS requirement. In addition, we describe the implementation model of the ATM virtual path network management system (VP-NMS). Lastly, we show the routing performance evaluated in the high speed information network (HSIN) of Korea Telecom.

A priority leaky-bucket regulator for virtual path traffic in ATM networks

In integrated services networks (B-ISDN/ATM) incoming traffic streams with different Quality of Service (QoS) requirements, sharing a single contract for use of a policed virtual path, may be jointly regulated on the basis of their type and QoS requirements to make the best use of available bandwidth in the path. The shaping/policing mechanism may use the information about the network policer located at the User-Network Interface (UNI) to perform policing with a form of priority service to ensure satisfactory levels of cell loss and delay for both real-time and non-real time traffic. This paper proposes and analyzes such a priority, buffered leaky-bucket mechanism for shaping/policing high-priority and low-priority sources, which share an ATM virtual path under a single, common user-network connection contract. The proposed priority traffic regulator maintains a dedicated cell buffer for each type of traffic to be able to trade off cell delay and loss (or tagging) on the basis of the QoS requirements for each priority class. The analysis adopts a Discrete Batch Markovian Arrival Process (D-BMAP) model for both high-priority and low-priority sources. It is shown that the system model has an M/G/1 type queuing structure, which is exploited for the computation of the joint buffer content distribution and cell loss probabilities of the high-priority and low-priority traffic streams. The obtained numerical results capture the effect of the shaper/policer and source parameters on the cell loss performance, and may be used for design optimization. A comparison of the priority leaky-bucket with the classical single buffer leaky-bucket regulator is carried out to quantify the improvement in terms of bandwidth utilization.

Failure protection methods for optical meshed-ring communications networks

We study the survivability of a meshed-ring communication network that employs cross-connect switches. For WDM networks, the cross-connect switches are implemented as wavelength routers. Nodes can also provide cross-connection at the ATM VP (virtual path) level. By meshing the ring, the nodal degree of connectivity is increased as compared to a ring topology, and thus more alternative (protection) paths are available. For routing purposes, wavelength subnetworks are embedded in the topology. Nodes communicate with each other across one of the subnetworks to which both belong. We consider two types of subnetwork topologies to simplify the routing in a normal (nonfailure) situation. For each type of subnetwork, different protection methods are proposed to protect against a single link and/or nodal failure. The throughput performance of such meshed-ring networks under failure conditions is clearly superior to that achieved by (SONET) ring networks. We show that certain protection methods even result in lower values of the protection capacity as well as the protection capacity ratio (i.e., the overall capacity used under a failure divided by the total capacity) as compared to ring networks. We also present methods for constructing wavelength subnetworks to achieve single-failure protection using the minimal number of wavelengths.

All-Optical WDM Cross-Connect Meshed-Ring Communications Networks

We introduce a meshed ring communications network which employs cross-connect switches. The crossconnect switches can be implemented as wavelength routers resulting in WDM networks, or as ATM Virtual Path (VP) switches leading to ATM compatible network systems. We show in the paper that this network architecture results in a significant increase in throughput performance in comparison with (SDHISONET) ring networks. For a certain class of meshed rings, under a uniform traffic matrix, we derive the optimal topology which achieves maximum throughput efficiency. Using such a topology, we obtain upper and lower bounds on the number of wavelengths required to achieve that efficiency level. The network is divided into (overlapping) communities of nodes. Each community is assigned a wavelength and a subnetwork (identified as a wavelength graph). Each pair of nodes in a community can communicate across the associated wavelength graph. Wavelength graphs (subnets) are constructed to demonstrate the implementation of the routing scheme using the number of wavelengths that is equal to the derived upper bound. For practical implementation reasons, we investigate the performance of networks which employ a reduced number of wavelengths. We show that by modifying the topological layout of the meshed ring network, we can reduce substantially the number of required wavelengths, while incurring just a modest reduction in throughput efficiency.

A new synchronous digital hierarchical Bi-directional ring capacity design algorithm based on the shortest-route traffic matrix

In this paper, the concept of the Shortest-Route Traffic Matrix(SRTM) was first presented, and the generalized formula for computing ring capacity requirement in use of SRTM is given. Then, a new capacity design algorithm which is based on SRTM was presented for Synchronous Digital Hierarchical(SDH) Bi-directional Self-Healing Ring (BSHR). The algorithm simulation results demonstrate that this algorithm is very efficient for SDH BSHR capacity design and can make less project investment and make high utilization of lines and equipment. By means of the algorithm in this paper, capacity optimization assignment for SDH Hierarchical Self-Healing Ring (HSHR) and for ATM Virtual Path (VP)-based Self-Healing Ring (SHR) is also discussed.

Inter-operator OSS Interface for Delivering Pan-European ATM VP Service

The provision of ATM virtual paths across multiple network domains requires interaction between the operational support systems (OSS) used by the different network operators to manage those networks. This paper describes the interfaces needed between such OSS to support performance and accounting management. It also describes an approach to ensuring those interfaces are secure. The results may be suitable for operational deployment and applicable with further development for other ATM services such as virtual circuits and switched services.

Performance analysis of an adaptive bandwidth reservation scheme for ATM virtual path traffic

Adaptive, in-call, bandwidth reservation may be used to enhance bandwidth utilization in a policed ATM virtual path shared by traffic streams originated by many bursty sources. The mechanism is found to be effective when large changes in the aggregate traffic rate are slow in comparison to the feedback delay with which a requested change in the reserved rate is obtained. We present a model, based on Markov-modulated sources and stochastic fluid methods, for performance analysis of the proposed mechanism. The model, corroborated by simulations, is used to study achievable bandwidth gain and the effects of feedback delay and competing reservation processes.

Control protocol and its performance analysis for distributed ATM virtual path self-healing network

A restorable network comprised of a mesh of ATM virtual paths (AVPs) is expected to be superior to distributed SONET digital cross-connect self-healing networks in terms of restoration time. The paper presents a reliable protocol and evaluation of its performance for control information transfer in distributed AVP self-healing networks. Two error-recovery technologies for the data-link level (selective retransmission and go-back-N) in AVP networks are reviewed, and a model for evaluating the delay of the go-back-N method that has been used in existing terrestrial systems is derived analytically. The proposed analytic model is combined with a self-healing simulator for AVP mesh networks to evaluate the restoration time characteristics. Case study results for the worst-case scenario show that the total restoration time, including link-by-link error control for self-healing control messages, is expected to be less than 2 s, which is the time objective for complete restoration for a metropolitan LATA network. The results also show that the estimated average delay penalty for adding the link-by-link error recovery process is 7.5 ms for complete service restoration. >