George I. Stassinopoulos

Efficient modeling of VBR MPEG-1 coded video sources

The performance evaluation of broadband networks requires statistical analysis and modeling of the actual network traffic. Since multimedia services, and especially variable bit rate (VBR) MPEG-coded video streams are expected to be a major traffic component carried by these networks, modeling of such services and accurate estimation of network resources are crucial for proper network design and congestion-control mechanisms that can guarantee the negotiated quality of service at a minimum cost. The layer modeling of MPEG-1 coded video streams and statistical analysis of their traffic characteristics at each layer is proposed, along with traffic models capable of estimating the network resources over asynchronous transfer mode (ATM) links. First, based on the properties of the entire MPEG-1 sequence (frame layer signal), a model (Model A) is presented by correlating three stochastic processes in discrete time (autoregressive models), each of which corresponds to the three types of frames of the MPEG encoder (I, P, and B frames). To simplify the traffic Model A and to reduce the required number of parameters, we study the MPEG stream at a higher layer by considering a signal, which expresses the average properties of I, P, and B frames over a group of picture (GOP) period. However, models on this layer cannot accurately estimate the network resources, especially in multiplexing schemes. For this reason, an intermediate layer is introduced, which exploits and efficiently combines information of both the aforementioned layers, producing a model (Model B), which requires much smaller number of parameters than Model A and simultaneously provides satisfactory results as far as the network resources are concerned. Evaluation of the validity of the proposed models is performed through experimental studies and computer simulations, using several long duration VBR MPEG-1 coded sequences, different from that used in modeling. The results indicate that both Models A and B are good estimators of video traffic behavior over ATM links at a wide range of utilization.

Local and remote management integration for flexible service provisioning to the home

Giving the operator the ability to manage in- home devices greatly increases the potential of the cost-efficient provision of new profitable services. In this spirit, standardization undertaken by the DSL forum not only addresses remote management of the residential gateway but recently, also extends to in-house devices. We propose a solution that bridges remote management specified by CWMP with UPnP, already established inside the home environment. This approach will enable providers to remotely configure and manage in-house UPnP-enabled equipment, thus accelerating the deployment of new services. We investigate the nature of the two protocols and specify the bridging functionality, taking into consideration scalability and transparency. Experimental results support the applicability of the proposed approach, highlight the importance of message filtering, and provide general insight into the interplay intricacies of the particular protocol functions.

A computer vision approach for textile quality control

Textile manufacturers have to monitor the quality of their products in order to maintain the high-quality standards established for the clothing industry. Thus, textile quality control is a key factor for the increase of competitiveness of their companies. Textile faults have traditionally been detected by human visual inspection. However, human inspection is time consuming and does not achieve a high level of accuracy. Therefore, industrial vision units are of strategic interest for the textile industry as they could form the basis of a system achieving a high degree of accuracy on textile inspection. This work describes the software core of a system designed for fabric inspection on the basis of simple image-processing operations as well as its efficiency on detection of usual textile defects. The prerequisites of the overall system are then discussed analytically, as well as the limitations and the restrictions imposed due to the nature of the problem. The software algorithm and the evaluation of the first results are also presented in details. Copyright

A TDMA based access control scheme for APON's

The cost of a dedicated fiber access to the broad-band integrated services digital network (B-ISDN) is too high for small business and sesidential customers necessitating some form of sesource sharing. Combining the asynchronous transfer mode (ATM) over a passive optical network (APON) with a suitable medium access control (MAC) protocol can provide significant cost savings and a seasonable bandwidth. In this way the customer line section can support broad-band services at an early stage. The MAC protocol presented in this paper places emphasis on service transpasency aspects with an aim to incur minimal changes to the Local Exchange for APON connections. Sharing is effected through a reservation based time division multiple access method

Management traffic in emerging remote configuration mechanisms for residential gateways and home devices

XML technology is penetrating the network management in the IETF, UPnP, and DSL forum suite of standards and protocols. The advantages of XML are offered at the cost of long byte streams due to XMLs inherently verbose nature. The increase in packet size for remote configuration and management can pose problems, if executed in a point-to-multipoint arrangement comprising one automatic configuration server and thousands of home gateways and multimedia devices. We investigate and exploit the repetitive nature of text patterns in typical XML documents as produced by the configuration and management tasks and as coded in SOAP RPCs. The solution mainly comes from application of the Lempel-Ziv compression algorithm, with minimal additions in the proposed DSL Forum standard. Numerical and experimental results support the applicability and advantages of the proposed approach and provide insight on how these are attributable to different layers of the employed protocol stack.

Optimal Congestion Control in Single Destination Networks

We present an algorithm for optimal routing in communication networks, resulting in minimum time and minimum total delay clearing of congested traffic towards a single destination. The algorithm is suitable for on-line implementation and can also be applied in the presence of time constant external arrival rates. In the case where several optimal solutions exist, the solution given is of the simplest form. The results are discussed and compared to existing ones, in particular to optimal feedback solutions found in the literature. The simplicity of approach and results allows us to give necessary and sufficient conditions for arrival rates, so that the minimal value for the maximal delay encountered by any packet in the network does not increase when these external arrivals are present. This suggests a flow control policy which, together with optimal routing, gives a guaranteed upper limit for traffic delay, while inhibiting incoming traffic as little as necessary. A thorough geometric interpretation is given and examples illustrate the applicability of results.

Efficient use of protocol stacks for LAN/MAN-ATM interworking

Connectionless (CL) services as already developed in LANs, have to interwork with emerging asynchronous transfer mode (ATM) connection-oriented (CO) networks. MANs are a significant evolutionary step and CO MANs, in particular, constitute a technically appealing method to integrate both environments and provide shared medium access for all services. The functions required for enhancing distributed-queue dual-bus (DQDB) MANs with CO services in a way compatible with ATM are described. Within the integrating framework of B-ISDN, the practically useful scenarios for interworking LANs, CO and CL MANs, and ATM are investigated and classified in order to exploit the advantages of an efficient protocol relay utilizing the resources of the lowest possible layer. This is aimed at assisting interworking unit (IWU) designers and implementors to decide on key options in this versatile and evolving environment. The CO DQDB case emerges as the most advantageous development in terms of interworking simplicity and robustness. >

ATM adaptation layer protocols for signalling

Abstract The paper examines newly proposed Layer 2 protocols for signalling and packet data to be employed in broadband integrated networks based on the Asynchronous Transfer Mode (ATM) principle. Assuming that signalling and information traffic will be multiplexed across a 150 Mbit/s user network interface, it models and analyses the processing and transmission delay encountered by signalling messages. Performance issues are contrapositioned to architectural ones, which call for a specific sublayering within Layer 2. This results in efficient grouping of subfunctions so that the protocols find the widest possible use in an integrated services environment.

High performance computing algorithms for textile quality control

At the present time, industries like textile are in constant need of modernisation. Thus, their presence in the high technology area of high performance computing (HPC) based inspection is of strategic interest. Textile manufacturers have to monitor the quality of their products in order to maintain the high quality standards established for the textile industry. The scope of this paper is to present a HPC architecture which can be implemented at each step of the quality control process in fabrics. The prerequisites or the overall system are then discussed analytically, as well as the limitations and the restrictions imposed due to the nature of the problem. The software algorithm and the evaluation of the first results are also presented in detail.

Automating remote configuration mechanisms for home devices

We examine the automatic configuration of consumer electronics devices delivering remote services to the home network. This environment has two particular aspects; it addresses a mass market, hence any automated approach for streamlined deployment, operation and scalability is of prime importance; it also relies on standardization due to its high dependency on communication protocols and services. Modern standards in this domain, along with the invocation of state of the art technologies around XML, give a totally new look at old management problems. More importantly, these standards directly and primarily address configuration issues in a structured and comprehensive way. This paper promotes the view that these standardizations work, pursued and presented in text form by the relevant standardization bodies. It also suggests standard-based methodologies and tools for remote configuration, management, life-cycle support and testing of devices. This inherently ensures compliance to the standards and enables a streamlined design, thus facilitating the provisioning and management of services offered to subscribers. Our contribution concerns relevant tool suites covering to some variable extend all of these aspects. We emphasize the logical succession of each consecutive step/tool and draw attention to the fact that the resulting interrelationships originate from a common source (i.e. the TR-069 standard) and reflect generic needs of the user/player in question.