Wolfgang Bziuk

Approximate state probabilities in large shared multirate loss systems with an application to trunk reservation

The saddle-point method of integration is used to derive a non-recursive approximation for the distribution of occupied bandwidth units of the multirate loss system with complete sharing, which achieves complexity O(1) per state. For the multirate finite sources model an asymptotic scaling is assumed in which the capacity and the number of sources are large and as an application the tail probability is approximated in the region 10 -4 -10 -10 . The limits for the infinite sources model are obtained as well and the approximate distribution is used to initialise a partial recursion, which transforms the state probabilities into an approximate distribution of the same system with trunk reservation. As a result the blockings are obtained with a low numerical complexity, which scales independent of the capacity. Numerical results show the accuracy and efficiency of the approximations. The estimate of the tail probability is shown to be superior if compared to the modified Chemoff bound.

High Performance Digital Media Network (HPDMnet): An advanced international research initiative and global experimental testbed

Currently, support for digital media is one of the fastest growing requirements of the Internet as demand transitions from services designed to support primarily text and images to those intended also to support rich, high quality streaming multi-media. In response to the need to address this important 21st century communications challenge, an international consortium of network research organizations has established an initiative, the High Performance Digital Media Network (HPDMnet), to investigate key underlying problems, to design potential solutions, to prototype those solutions on a global experimental testbed, and to create an initial set of production services. The HPDMnet service is being designed not only to support general types of digital media but also those based on extremely high resolution, high capacity data streams. These HPDMnet services, which are based on a wide range of advanced architectural concepts at all layers, provide a framework for network middleware that allows non-traditional resources to enable new network services, including those based on dynamically provisioned international lightpaths supported by flexible optical-fiber and optical switching technology. These HPDMnet services have been showcased at major national and international forums, and they are being implemented within several next generation communications exchanges.

Defragmentation-as-a-Service (DaaS): How beneficial is it?

We analyze Defragmentation-as-a-Service (DaaS) in elastic optical networks and show that the positive effect of defragmentation depends on the rate at which it is performed, load (or, call arrival rates) and the available resources.

A new topology-based algorithm for next cell prediction in cellular networks

In mobile communication systems of the 3/sup rd/ and 4/sup th/ generation the mobile users are expected to demand the same quality of service (QoS) available to fixed users. To investigate the performance of predictive schemes a new mobility model is derived that simulates human behavior in realistic environments. This paper also presents a new adaptive scheme for micro-cellular environments that combines stochastic information with topological information about the cell region to predict the next cell to be visited by the subscriber. The results show that the presented algorithm provides a high prediction accuracy in realistic environments.

A new framework for characterising the number of handovers in cellular networks

The handover process was widely studied in the literature in the past decade. While significant efforts addressed the mean handover rate, few attempted to characterise the distribution of the number of handovers under the assumption that the call and the cell residence times (CRTs) are generally distributed. Motivated by the increasing impact of handovers on the design and performance of the control and data planes in the emerging cellular networks, in this paper, we propose a new analytical framework to obtain the probability generating function (PGF) of the number of handovers. Our work covers three generic session behaviours, including new, roaming and location triggered calls, and thus facilitates the calculation of the mean number of handovers for such session types. When the distributions have rational Laplace transforms, we obtain closed form solutions that are simple-to-compute and hence provide cellular network designers and researchers with deeper insights into the performance of mobility aware wireless protocols for different application scenarios. Our results show that handover models for new sessions can reasonably approximate location triggered sessions while separate treatment for roaming sessions is generally required. The numerical examples based on the generic hyper-Erlang session durations show the practicability of our framework. Copyright

A Scalable Billing Architecture for Future Wireless Mesh Backhauls

The backhaul network, which connects base stations to the radio network controllers, poses a major challenge in cellular networks today due to the expensive maintenance, operation and poor scalability in response to traffic dynamicity. The majority of the present backhaul networks is composed of either leased lines, i.e., T1/E1 and/or microwave links. Recently, wireless mesh networks have been proposed as a possible backhaul transport media, not only for their significant cost savings but also for their scale, flexibility and resilience. At the same time, however, wireless mesh backhauls pose many technical challenges including timing synchronization for GSM networks, bandwidth reservation techniques, dynamic bandwidth control, and billing. To address some of these challenges, we propose the first ever billing architecture for wireless mesh networks and analyze its performance and scalability in response to a novel, threshold based bandwidth management algorithm. Using analysis based on a simple Markov process, we evaluate a highly unstable reservation mechanism and establish the corresponding upper bounds on the billing signaling performance over mesh backhauls. The analysis and simulation results show that our billing scheme scales well even for poor implementations of bandwidth reservations.

Replication of Virtual Network Functions: Optimizing link utilization and resource costs

Network Function Virtualization (NFV) is enabling the softwarization of traditional network services, commonly deployed in dedicated hardware, into generic hardware in form of Virtual Network Functions (VNFs), which can be located flexibly in the network. However, network load balancing can be critical for an ordered sequence of VNFs, also known as Service Function Chains (SFCs), a common cloud and network service approach today. The placement of these chained functions increases the ping-pong traffic between VNFs, directly affecting to the efficiency of bandwidth utilization. The optimization of the placement of these VNFs is a challenge as also other factors need to be considered, such as the resource utilization. To address this issue, we study the problem of VNF placement with replications, and especially the potential of VNFs replications to help load balance the network, while the server utilization is minimized. In this paper we present a Linear Programming (LP) model for the optimum placement of functions finding a trade-off between the minimization of two objectives: the link utilization and CPU resource usage. The results show how the model load balance the utilization of all links in the network using minimum resources.

SDN and NFV as Enabler for the Distributed Network Cloud

SDN and NFV gained significant momentum within the last years. Although widely used in research labs and cloud environments, SDN has not yet been deployed in mobile telecommunication networks. In this paper, we focus on use cases driving mobile network evolution towards cost-efficient IT-based solutions using standardized hardware and software-based concepts, such as SDN and NFV. Two SDN use cases for mobile networks are described. One deals with the disaggregation of mobile network gateways and the other with SDN-enabled security concepts and applications for mobile networks. Based on the SDN use cases, the paper highlights open issues and challenges for integrating IT concepts in future telecommunication networks.

A novel framework for handoff analysis under generalized session and mobility statistics

Recently, cellular networks have witnessed major developments pertaining to user mobility, rich multimedia service offering and a melange of network access options including 3G/4G, WiFi, WiMAX, etc. As a result, sessions are expected to last longer and users are more likely to roam between access technologies and to other networks. As architectural design is advancing in all-IP cellular systems such as the Long Term Evolution (LTE), the question we propose to address is whether the established results on handoff and roaming statistics used in cellular theory still apply. To this end, we revisit the theory for handoff statistics and take up the challenge on extending the current model under general assumptions for session distributions, user mobility, network coverage and access technology. We show that the derived model yields estimates of handoff frequency and roaming statistics which cannot be obtained otherwise. The key strength of the proposed analysis is offering closed form results, which are easy to use and can lead to more accurate conclusions about the signaling load and the observed QoS, as a direct function of handoff statistics.

Efficient computational technique for virtual partitioning

A numerically efficient approximation for virtual partitioning, a scheme for connection admission control, is considered. It shares the resource among several traffic classes in a fair and efficient manner using a state-dependent trunk reservation. In the absence of a product form, an approximation for the occupancy distribution for this multirate loss system was originally suggested by Borst and Mitra. Based on this approximation, a more numerically efficient approximation is developed here. It combines asymptotic approximation methods with recursive formulas in a way that the computational complexity is reduced by several orders of magnitude. Furthermore, a modified approximation is derived such that its complexity scales independent of the state space. It avoids recursive formulas and thus is well suited for real-time computations, but with reduced accuracy. Numerical results show the computational efficiency of the new approximations and their accuracy is compared with the simulation results. It is clearly shown that this accuracy is comparable to that of the existing approximation methods.