Issue editor: Mariusz Głąbowski
During the last years telecommunications techniques made a revolutionary step forward. Such a progress was stimulated by growing requirements from traffic being served in modern networks. Broadband service platforms offer a significant leap in types of information available to end users, offering a multitude of new services. Video on demand, multimedia, unlimited Internet access become also possible in wireless systems. There are many questions that need to be answered including: how to interwork existing services with future wired and wireless networks, how to manage and optimise the transmission of growing traffic volumes, how to enhance network’s performance.
Villy B. Iversen, King-Tim Ko
In this paper we present a new algorithm for
evaluating queueing networks with multi-rate traffic. The detailed
state space of a node is evaluated by explicit formulæ. We
consider reversible nodes with multi-rate traffic and find the
state probabilities by taking advantage of local balance. Theory
of queueing networks in general, presumes that we have product
form between the nodes. Otherwise, we have the state space explosion.
Even so, the detailed state space of each node may become
very large because there is no product form between chains
inside a node. A prerequisite for product form is reversibility
which implies that the arrival process and departure process
are identical processes, for example state-dependent Poisson
processes. This property is equivalent to reversibility. Due to
product form, an open network with multi-rate traffic is easy to
evaluate by convolution algorithms because the nodes behave as
independent nodes. For closed queueing networks with multiple
servers in every node and multi-rate services we may apply multidimensional
convolution algorithm to aggregate the nodes so that
we end up with two nodes, the aggregated node and a single node,
for which we can calculate the detailed performance measures.
I. D. Moscholios, V. G. Vassilakis, J. S. Vardakas and M. D. Logothetis
We consider a single-link loss system of fixed capacity, which accommodates K service-classes of Poisson traffic with elastic bandwidth-per-call requirements. When a new call cannot be accepted in the system with its peak-bandwidth requirement, it can retry one or more times (single and multi-retry loss model, respectively) to be connected in the system with reduced bandwidth requirement and increased service time, exponentially distributed. Furthermore, if its last bandwidth requirement is still higher than the available link bandwidth, it can be accepted in the system by compressing not only the bandwidth of all in-service calls (of all service-classes) but also its last bandwidth requirement. The proposed model does not have a product form solution and therefore we propose an approximate recursive formula for the calculation of the link occupancy distribution and consequently call blocking probabilities. The accuracy of the proposed formula is verified by simulation and is found to be quite satisfactory.
Philipp M. Eittenberger, Seungbae Kim, and Udo R. Krieger
Mobile peer-to-peer (P2P) traffic is rapidly
growing, but present P2P applications are not specifically
designed to operate under mobile conditions. To assess
the performance of the prevalent file sharing application
BitTorrent in a mobile WiMAX network, we performed
a measurement and analysis campaign. In this study, we
use the obtained measurement traces to further investigate
specific characteristics of this P2P network. In particular,
we analyze the distribution of its peer population under
mobile conditions and present a general classification
scheme for peer populations in BitTorrent-like P2P networks.
Further, we propose a simple heuristic to bound the
out-degree of BitTorrent-like P2P systems when operating
in mobile environments.
Tomasz Holynski, Muhammad Faisal Hayat
Ongoing research in Optical Burst Switching (OBS) requires more in-depth studies both in theory and in practice before the technology is realized. In OBS paradigm, traffic from access networks is groomed at edge OBS nodes in the forms of large chunks called bursts. This grooming called assembly is crucial in analyzing the overall
performance of OBS networks as it affects the design of almost all major functions of OBS nodes. The characteristics of assembled traffic and its effects on OBS performance have been already extensively studied in literature. In this work, the assembled traffic is studied using a transformbased approach, since it is a natural way of analyzing such processes where random variables are summed. The main
contribution of this paper is formulation of distributions of burst length and burst inter-departure time in form of Laplace transforms, which are valid for general independent lengths and inter-arrival times of assembled packets. The results can be subsequently inverted analytically or numerically to give full densities or serve as moment generating functions for partial characteristics. A simple method for the distribution of the number of packets in a burst based on discrete Markov chain is provided. Detailed analytical derivations with numerical results are presented for Erlangian traffic and verified by simulations to show good exactness of this approach.
Due to the variation of radio condition in LTE the obtainable bitrate for active users will vary. The two most important factors for the radio conditions are fading and pathloss. By considering analytical analysis of the LTE conditions including both fast fading and shadowing and attenuation due to distance we have developed a model to investigate obtainable bitrates for customers randomly located in a cell. In addition we estimate the total cell throughput/capacity by taking the scheduling into account. The cell throughput is investigated for three types of scheduling algorithms; Max SINR, Round Robin and Proportional Fair where also fairness among users is part of the analysis. In addition models for cell throughput/capacity for a mix of Guaranteed Bit Rate (GBR) and Non-GBR greedy users are derived.
Numerical examples show that multi-user gain is large for the Max-SINR algorithm, but also the Proportional Fair algorithm gives relative large gain relative to plain Round Robin. The Max-SINR has the weakness that it is highly unfair when it comes to capacity distribution among users. Further, the model visualize that use of GBR for high rates will cause problems in LTE due to the high demand for radio resources for users with low SINR, at cell edge. Persistent GBR allocation will be a waste of capacity unless for very thin streams like VoIP. For non-persistent GBR allocation the allowed guaranteed rate should be limited.
Jie Xu, Yuming Jiang, Andrew Perkis, and Elissar Khloussy
In this paper we investigate multi-service load balancing mechanisms in an overlay heterogeneous WiMAX/WLAN network through vertical handover. Considering the service characteristics of the overlay heterogeneous network together with the service requirements of different applications, all streaming applications are served in WiMAX while elastic applications are distributed to WiMAX and WLAN. Two load balancing mechanisms are compared which switch the elastic application with maximum (MAX) and minimum (MIN) remaining size respectively to WLAN. Simulation results indicate that MIN outperforms MAX at the cost of significantly increased number of load balancing actions. Furthermore, it is discovered that both load balancing granularity and proper integration of streaming and elastic applications in WiMAX determine the whole system performance.
Paweł Swiatek, Piotr Rygielski, Adam Grzech
The aim of this paper is to introduce a problem of e-health services quality management. The process of delivering e-health services to users consists of two major tasks: service personalization and resources allocation. In this paper we introduce a use-cases of e-health system and distinguish services that can be offered. In order to satisfy user requirements one have to manage resources properly especially when communication conditions change ie. in an ambulance. An exemplary solution has been presented and conclusions for further work have been formulated.
Cezary Żukowski, Artur Tomaszewski , Michał Pióro, David Hock, Matthias Hartmann, Michael Menth
This paper discusses compact node-link formula-
tions for MPLS fast reroute optimal single path layout. We
propose mathematical formulations for MPLS fast reroute local
protection mechanisms. In fact, we compare one-to-one (also
called detour) local protection and many-to-one (also called
facility backup) local protection mechanisms with respect to min-
imized maximum link utilization. The optimal results provided by
the node-links are compared with the suboptimal results provided
by algorithms based on non-compact linear programming (path
generation) approach and IP-based approach.
Matin Bagherpour, Mehrdad Alipour, and Øivind Kure
In this paper, multipath routing is utilized for data transmission in a packet-switched network to improve the reliability of data delivery to multicast destinations and to reduce network congestion. A multi-objective optimization model is presented that utilizes FEC (Forward error Correction) across multiple multicast trees for transmitting packets toward the destinations. This model assigns the transmission rates over multicast trees so that the probability of irrecoverable loss for each destination and also the link congestion are minimized. We propose a genetic algorithm based on SPEA (Strength Pareto Evolutionary Algorithm) in order to approximate Pareto optimal solutions of this rate allocation problem with a non-dominated solution set. Numerical results show that splitting data packets between multiple trees increases reliability and decreases network congestion when compared with the results obtained for transmitting data packets over a single tree.
Piotr Krawiec, Andrzej Bęben and Jarosław Śliwiński
In this paper, we propose analytical model of Virtual Link used in the Service Overlay Networks. The Virtual Link exploits Selective Repeat ARQ scheme with time constrained number of retransmission and the playout buffer mechanism. Our model allows deriving equations that express trade-off between loss and delay characteristics experienced by packets transferred through VL. The main innovation of our model is the ability to cope with variable delay experienced by packets transferred by underlying network. Following the analytical model, we propose a method for Virtual Link dimensioning. The accuracy of the proposed model and dimensioning method is illustrated by simulation results.
Charlott Lorentzen, Markus Fiedler, Peter Lorentzen
When using the web, large response times are bones of contention for users, i.e. they damp the Quality of Experience (QoE). Though, if one knew the cause of a large response time, one can examine what can be done about this obstacle. In this paper, we determine the weak point of the Extensible Authentication Protocol Method for GSM Subscriber Identity Modules (EAP-SIM) with the OpenID service with regards to excessive authentication times, which determine the response times. In order to provoke controlled increases of the latter, we emulate bad network performance by introducing bi-directional delay between the supplicant (client) and the authentication server. The same procedure is also applied to several other EAP methods. Based on a recent, exponential relationship between QoE and response time, we then identify, quantify and compare the decisive factors for QoE reduction as functions of the components of the authentication times. The results we obtain clearly show that one task of the EAP-SIM authentication contributes significantly more to the total response times than the other tasks, which points out the direction for future optimisation of user perception of authentication times.
Grzegorz Oryńczak, Zbigniew Kotulski
In this paper we introduce our new VoIP model which aim is to meet the challenges of modern telephony. We present project concepts, details of implementation and our testing environment which was designed for testing many aspects of VoIP based systems. Our system combine mechanisms for ensuring best possible connection quality (QoS), load balance of servers in infrastructure, providing security mechanisms and giving control over the packet routing decisions. System is based on Peer-to-Peer (P2P) model and data between users is routed over a overlay network, consisting of all participating peers as network nodes. In the logging process, each user is assigned to a specific node (based on his geographic location and nodes load). Every node also has a built-in mechanism allowing to mediate between the user and the main server (e.g. in logging process). Besides that, because nodes are participating in data transmission, we have control over the data flow route. It is possible to specify the desired route, so, regardless of the external routing protocol, we can avoid paths that are susceptible to eavesdropping. Another feature of presented system is usage of agents. Each agent acts within the single node. Its main task is to constantly control the quality of transmission. It analyzes such parameters like link bandwidth use, number of lost packets, time interval between each packets etc. The information collected by the agents from all nodes allows to built dynamic routing table. Every node uses Dijkstra’s algorithm to find the best at the moment route to all other nodes. The routes are constantly modified as a consequence of changes found by agents or updates sent by other nodes. To ensure greater security and high reliability of the system, we have provide a reputation mechanism. It is used during actualization of the information about possible routes and their quality, given by other nodes. Owing to this solution nodes and routes which are more reliable get higher priority.