Efstathios D. Sykas

Simulative analysis of optimal resource allocation and routing in IBCN's

The problem of resource allocation for future integrated broadband communication networks (IBCNs) is addressed. It mainly involves resource allocation at the connection level. The resource allocation problem is decomposed into the following interdependent tasks: given that a network can accommodate the bandwidth demand of a call request, determine a route for the corresponding asynchronous transfer mode (ATM) virtual connection; and allocate bandwidth, i.e. links inside the trunks of the chosen route, to this connection according to predefined limits on bandwidth use by various service calls. Various link allocation schemes combined with routing algorithms are examined. Their performance in terms of service call blocking is evaluated using a software package developed, for that purpose. It is shown that the traditional complete sharing (CS) and complete partitioning (CP) policies are not adequate for IBCNs. Movable boundary (MB) policies are more flexible and present near-optimal performance when access of broadband service to narrowband service resources is allowed and suitable routing algorithms are dynamically applied. >

Analysis, stability and optimization of Aloha-type protocols for multichannel networks

Abstract In this paper we propose a protocol appropriate for multiple access in a multichannel environment. All free stations contend in one channel, while the busy stations construct one queue belonging to all retransmission channels for collision resolution. Thus asymmetric access methods, such as pre-selection or sequential selection of retransission channels. A queueing model appropriate for the analysis and performance evaluation of the proposed protocol is derived. Analytic solutions are developed for a system with a finite number of stations using discrete time Markov chains. Numerical results indicate the dependence of normalized performance (normalized throughput and normalized delay) on the number of channels. The cases in which the multichannel system is superior to the single channel protocol are found. The stability of the multichannel system with infinite population is studied. Pakess Lemma criteria are applied to specify regions in which the multichannel system is stable. The control parameters are the retransmission probabilities. Optimization rules are derived which show that the optimal retransmission probabilities are a function of the number of busy stations.

Queueing Analysis of Some Buffered Random Multiple Access Schemes

A queueing model appropriate for the analysis of multipleaccess schemes with finite user buffer capacity is proposed. This model can be applied to several slotted random multiple-access schemes, such as the URN, ALOHA, random TDMA channels, etc. The examined system, in general, can be modeled as a multidimensional Markov chain. The enormous state space for its complete description makes numerical analysis intractable. Nevertheless, symmetry properties of the system can be exploited so that the state space will be reduced. In particular, the queue length at one station and the number of busy stations are used to characterize the behavior of the system. In this way, a two-dimensional Markov chain can be constructed and an approximate solution is obtained which is in excellent agreement with simulation results.

Congestion avoidance in ATM networks

The authors propose a new policy to prevent congestion phenomena in asynchronous transfer mode (ATM) networks. In particular, using a synthesis approach, they define and calculate the bandwidth which is assigned to every acceptable source from the ATM network. This bandwidth, which varies between the peak and the average bandwidth demands of the particular source, is called effective or virtual, and is mainly characterized from the burstiness of the source. In constant bit rate sources the effective bandwidth is equal to the peak rate. Based on the concept of effective bandwidth, a connection acceptance algorithm that leads to a very high utilization of network resources is formulated.<<ETX>>

The effect of platform instability on the system level performance of HAPS UMTS

High Altitude Platform Stations (HAPS) are a new, promising means of providing Third Generation (3G) mobile services. One of the potential problems of the system is the platform positional instability due to stratospheric winds. In this letter, we present a study of the effect of positional instability on the system level performance of a Universal Mobile Telecommunications System (UMTS) served by HAPS. A platform instability model obtained through measurements of stratospheric winds gives input into a UMTS system level dynamic simulator and the effect of instability on the system capacity and call blocking probability is examined. Finally, it is shown that the positional instability can be counterbalanced by a simple propulsion mechanism, thus reducing the performance degradation.

Modeling and Simulation of QoS-aware Web Service Selection for Provider Profit Maximization

Web Services (WSs) are a new breed of web application that is gaining momentum. One of the research challenges it brings along is the establishment of an interoperable semantic framework suitable to represent not only the functional, but also the non-functional features of WSs, i.e. their Quality-of-Service (QoS), which in most cases are not included in the WS description. Nevertheless, integrating QoS features in WS profiles is to the advantage of both users and providers, as it supports QoS-aware WS selection and composition addressing the users QoS requirements, while enabling WS providers to increase their profits. The purpose of this paper is twofold. On the one hand, it aims to present a QoS ontology framework adequate for WS provision. On the other hand, it studies the problem of providers that receive concurrent requests of numerous customers for WSs demonstrating different bandwidth and price properties. It introduces the “Selective Multiple Choice Knapsack Problem” that aims to identify the services that should be delivered to the customers in order to maximize the providers profit, subject to maximum bandwidth constraints on the server side. Thus, the QoS-awareness in this version of this problem is limited to the consideration of two QoS parameters: service bandwidth and cost. The problem is solved by a proposed algorithm that has been empirically evaluated via numerous experiments.

Numbering and addressing in IBCN for mobile communications

Numbering and addressing issues arising in the integrated broadband communication network (IBCN) for the support of the Universal Mobile Telecommunication System (UMTS) and Personal Telecommunication Service (PTS) are discussed. Mobile communications services will allow a user to roam within a network. Thus, there will be a need to identify several types of objects (terminals, network points of attachment, users, customers premises networks or CPN, etc.). The mobility properties of these objects will necessitate dynamic bindings between their addresses and names. The situation is further complicated because the mobility may be embedded. A mobile user may employ a mobile terminal in a mobile CPN. Therefore, in UMTS and PTS there is a need for dynamic binding of various identifiers with location information data. The exclusive use of personal telecommunication numbers (PTNs) as dialing numbers (DNs) is proposed in IBCN for UMTS and PTS. That is, PTNs will be used (during dialing) for making calls to mobile terminals, mobile users, and fixed subscribers. When the personal communication service is not provided, the DN corresponds to the terminal number of the equipment (fixed or mobile) of the called subscriber. >

Performance bounds of a multiple-step paging strategy in future universal mobile telecommunication systems

In future mobile telecommunications, due to the huge number of users and the specific functions that support mobility, a significant amount of signaling load will have to be carried by the finite capacity of the radio link. Hence, methods aiming at radio link signaling load reduction are welcome. In this paper we propose and analyze a method that saves paging signaling load by exploiting information related to the terminal location during the most recent interaction between the terminal and the network. The penalty paid is extra processing power and extra paging delays. An analytical model is developed so as to describe the performance versus traffic intensity and mobility conditions. The performance of the proposed paging scheme is investigated, and it is shown that the method operates well even in the worst case, which is the high user mobility conditions. Possible extensions of the method, which exploit information related to the mobility degree of each individual user or information characterizing the mobility conditions in a certain location area, are also proposed.

Designing a quality-aware discovery mechanism for acquiring context information

The alignment of the context information with the service objectives facilitates the successful provisioning of context-aware services. Moreover, the fact that context may come from transient and/or unreliable sources needs consideration. False or stale context can dramatically affect the decisions and the actions taken by context-aware services. This paper presents an approach for evaluating and selecting the information to be used by context-aware services that takes into account the quality of information, and automatically adapts to any source changes and failures. The proposed quality-aware discovery of context information sources allows services to be ported easily to environments with different sets of sources.

Optimized handover procedure based on mobile location in cellular systems

Future-generation mobile communications will provide broadband multimedia services to users, anywhere and anytime. On the other hand network performance should be guaranteed to support these applications and services. In existing cellular systems handover is one of the procedures that causes serious network shortcomings. This procedure is much more complicated in next generation systems (UMTS) and is of great interest for investigation and optimization. Both these systems and those of the second generation (GSM & GPRS) will require redefined handover algorithms of active connections as the mobility support is a vital issue for cellular systems. In this paper we present a set of location aided handover mechanisms that use the location information to assist safe handover decisions. The implemented algorithms are validated by means of a cellular network simulator that clearly shows the impact of these techniques to the handover performance. Finally, we briefly describe how this can be integrated in the cellular system architecture.