János Harmatos

Mobile broadband backhaul network migration from TDM to carrier ethernet

With the rollout of Long Term Evolution the capacity of the radio access network backhaul needs to be upgraded to 100-150 Mb/s. Nextgeneration mobile networks, such as LTE Release 10, will increase the requirement for backhaul capacity to gigabits per second. In order to increase network utilization and decrease operating expenses, carrier Ethernet transport infrastructure (MPLS and carrier grade Ethernet) will be deployed and maintained at a lower total cost of ownership than legacy TDM transport infrastructure. This article discusses different migration scenarios from the circuit-switched legacy backhaul networks toward packet-based networks.

Planning reliable UMTS terrestrial access networks

The Universal Mobile Telecommunication System (UMTS) will play a very important role in the telecommunication market of the near future. Due to the wide range of services and the increased transmission capacity, UMTS will become one of the most important access network types. The proposed topology of the UMTS terrestrial access network is tree-like, but the high amount of carried traffic requires a more reliable network structure. We introduce two types of heuristic algorithms to solve this problem, and we plan network topologies having a low magnitude of traffic loss in case of failures. One of our algorithms solves the problem by modifying the tree-topology, while others expand the network by inserting additional links. We show how to find a good compromise between topology refinement and network expansion in the case of realistic network scenarios, and we confirm our results by detailed tests.

Planning of UMTS core networks

Building new UMTS (Universal Mobile Telecommunication Systems) based networks, seems to be on time. Nowadays the UMTS network design related problems are moving to the interconnection of radio network controllers (RNC), placement of media gateways (MGw) and planning of the core network topology. This new area of UMTS network design is studied in the paper. A new algorithm is proposed for the above tasks, which based on efficient meta-heuristics, but applies some problem related features to obtain as good a solution as possible. The paper overviews the UMTS core network structure, a possible abstraction of the real network and equipment from the viewpoint of network planning are proposed, furthermore the design algorithm is outlined and a detailed performance analysis is proposed using some network scenarios. It is important to note that the abstract model enables the application of the proposed algorithm for the same type of design task, but in different technology background.

Planning of tree-topology UMTS terrestrial access networks

In this paper we propose a heuristic planning algorithm for optimizing tree-topology access networks. Our suggested method is able to plan a multi-constrained and capacitated subnetwork tree with a previously dedicated root node. The algorithm is a combination of an adaptive version of the simulated annealing meta-heuristic and a local improvement strategy. We use the proposed method to solve the optimization problem of UMTS (universal mobile telecommunications system) access networks. Beside the description of the model and the algorithm we present a detailed performance analysis of our proposed method using different network configurations and traffic demands. Tests show that our proposed algorithm provides solutions very close to the global optimum and because of its computational efficiency it is usable for planning practical size networks. It is also important to note that our method can be easily adapted for similar planning tasks in case of many other technological backgrounds.

Dynamic Routing and Wavelength Assignment in Survivable WDM Networks

Dense wavelength division multiplexing (DWDM) networks are very attractive candidates for next generation optical Internet and intelligent long-haul core networks. In this paper we consider DWDM networks with wavelength routing switches enabling the dynamic establishment of lightpaths between each pair of nodes. The dynamic routing and wavelength assignment (RWA) problem is studied in multifiber networks, assuming both protection strategies: dedicated and shared. We solve the two subproblems of RWA simultaneously, in a combined way using joint methods for the wavelength selection (WS) and wavelength routing (WR) tasks. For the WS problem in contrast to existing strategies we propose a new, network state based selection method, which tries to route the demand on each wavelength, and selects the best one according to different network metrics (such as available channels, wavelengths per fiber and network load). For the WR problem we propose several weight functions for using in routing algorithms (Dijkstra or Suurballe), adapting dynamically to the load of the links and to the length of the path. The combination of different wavelength selection and routing (WS&WR) methods enables wide configuration opportunities of our proposed algorithm allowing good adaptation to any network state. We also propose the extension of the RWA algorithm for dedicated and shared protection and a new method for applying shared protection in dynamic WDM environment. The detailed analysis of the strategies demonstrate that our RWA algorithm provides significantly better performance than previous methods in terms of blocking probability whether with or without protection methods.

A heuristic algorithm for solving the static weight optimisation problem in OSPF networks

This paper deals with the problem of OSPF weight system adjustment. It is one of the fundamental optimisation tasks in IP/OSPF networks, because the OSPF weight system determines the routes for traffic flows. If the OSPF weights are set in a proper way, significantly better network throughput and performance can be achieved compared with the simple weight setting heuristics used nowadays. Because this kind of weight configuration is typically set in the network planning phase, the overall quality of the weight setting algorithm results will determine the long-term network utilisation. In the paper we formulate a relevant optimisation problem and on the basis of the experiences of our previous research work we propose a deterministic, heuristic algorithm for solving the problem. In addition to the network model, formulation of the problem and description of the proposed algorithm, its performance is illustrated with numerical results.

Inverse shortest path algorithms in protected UMTS access networks

In this paper, the application questions of Open Shortest Path First (OSPF) routing protocols in the all-IP based protected Universal Mobile Telecommunications System (UMTS) access networks is investigated. The basic problem here is how the OSPF administrative weights should be adjusted in an adequate way, resulting near-optimal overall network performance both in nominal network operation and in case of single link failures. Currently, there are known algorithms which are able to solve the topology planning and dimensioning related problems of UMTS access networks, but they do not consider the special properties of the OSPF protocol. We formulate the problem as an Integer Linear Programming (ILP) task. Furthermore, we propose an advanced heuristic algorithm and compare its results with the ILP solution and other existing algorithms.

A cluster-based resource provisioning model in virtual private networks

This paper presents a novel resource provisioning method for virtual private networks. Trunk and hose models are well known bandwidth provisioning models for VPNs but both have significant disadvantages if applied to large scale networks. The management complexity of the trunk model highly increases with the size of the network, while bandwidth efficiency of the hose model is often excessively low. The authors proposed an intermediate solution between hose and trunk models. By dividing the network into clusters and using cluster-based traffic description an appropriate equilibrium between management complexity and over provisioning could be found. A method for computing the necessary links capacities for a traffic given by cluster-based description is also presented, which makes it possible to design congestion free networks. Routing strategies were also suggested to further improve the performance of the new provisioning method. The applicability and limitations of the method and the effect of different routing strategies and fault tolerance are examined by simulating several test scenarios.

Cluster-based resource provisioning for optical backbone networks

Feature Issue on High Availability in Optical NetworksA resource provisioning method for optical backbone networks running IP or multiprotocol label switching (MPLS) is presented. Trunk and hose models are well-known bandwidth provisioning models, but both have significant disadvantages if applied to large-scale networks. The management complexity of the trunk model highly increases with the size of the network, and the bandwidth efficiency of the hose model is often excessively low. We propose an intermediate solution between the hose and trunk models. By dividing the network into clusters and using a cluster-based traffic description, an appropriate equilibrium can be found between management complexity and overprovisioning.