TELEKOMUNIKACJA CYFROWA

Permanent URI for this communityhttps://repo.agh.edu.pl/handle/AGH/102769

Tytuł archiwalny!

Adres wydawniczy: Kraków : Wydawnictwa AGH, 2007-2011
ISSN: 1505-9405

Czasopismo Telekomunikacja Cyfrowa wydawane było w latach 2007-2011. ISSN czasopisma: 1505-9405.

Roczniki i numery

Browse

Now showing 1 - 20 of 29

Telekomunikacja Cyfrowa : technologie i usługi
T. 9 (2008/2009)
Access status: Open Access ,
Automatyczna ocena wielomodalnych zniekształceń w obrazach cyfrowych
(Wydawnictwa AGH, 2008/2009) Głowacz, Andrzej; Grega, Michał; Janowski, Lucjan; Leszczuk, Mikołaj; Romaniak, Piotr
This paper presents a new method of qualitative assessment of images affected by multi-modal distortions. The idea is to assess the image quality perceived by an end user in an automatic way in order to avoid the usual time-consuming, costly and non-repeatable method of collecting subjective scores during a psychophysical experiment. This is achieved by computing quantitative image distortions and mapping results on qualitative scores. Overall qualitative image distortion is computed based on partial quantitative distortions from component algorithms operating on specified image features. Seven such algorithms are applied to successfully analyze the seven image distortions in relation to the original image. Useful mapping models have been proposed and constructed using the Generalized Linear Model (GLZ). These models allow for mapping the results of quantitative assessments on the subjective scores in order to obtain an overall quality score of the image. For research and validate the models, a survey of over 12,000 subjective quality scores has been carried out.
Access status: Open Access ,
Otwarty system przechowywania i udostępniania zbiorów przez Internet - projekty OASIS Archive i GAMA w Katedrze Telekomunikacji AGH
(Wydawnictwa AGH, 2008/2009) Głowacz, Andrzej; Grega, Michał; Leszczuk, Mikołaj; Romaniak, Piotr
This paper presents OASIS Archive project (with its extension plans in the framework of the GAMA project), which goal was to develop a system for the universal presentation of art works independent of their location. The main focus was on establishing a user-friendly search system in order to ensure the preservation and availability (sustainability) of cultural heritage in the field of Media Art. Databases of several participating institutions were integrated on basis of interlinking metadata system. The archive can be easily accessed by individual users (both researchers and general public) through an on-line interface, by multimedia archive servers engaged in exchange within a distributed system and by various play-out media. Scalability of the archive has been addressed during the project as well.
Access status: Open Access ,
Analiza usługi telewizji internetowej w Polsce
(Wydawnictwa AGH, 2010/2011) Krempa, Agata
Article shows different streaming methods used by Polish Internet Televisions. Real-time data should be sent with use of RTP/UDP protocol suite with RTCP control protocol [10]. Research on polish Internet Televisions shows that use of those protocols is very rare. Streaming method that was seen the most often is the use of RSTP Interleaved option that uses RTP/RTSP/TCP protocol suite to send real-time data. It was proposed as a solution to firewalls filtering UDP traffic [12]. The main purpose of RTCP protocol is to send periodic reports on received data. In rare cases that RTCP datagrams were seen they were not periodic reports on received data but messages that triggered RTP retransmissions [5].
Access status: Open Access ,
Analiza schematów SH-GKDS
(Wydawnictwa AGH, 2010/2011) Rams, Tomasz; Pacyna, Piotr
The paper presents techniques for selective group key distribution over an unreliable broadcast channel. It provides introduction to Self-healing Group Key Distribution Schemes (SH-GKDS), including guidelines for scheme design and analysis. The most important mechanisms used in SH-GKDS are described and analysed in terms of security, scalability and system life-time.
Access status: Open Access ,
Analiza symulacyjna sieci IEEE 802.11e o topologii gwiazdy w przypadku występowania stacji ukrytych
(Wydawnictwa AGH, 2008/2009) Kosek, Katarzyna; Natkaniec, Marek; Pach, Andrzej R.
The article presents results derived from a simulation analysis of IEEE 802.11e networks in the presence of hidden nodes. In order to show how meaningful the degrading impact of hidden nodes on ad-hoc networks performance is, two different star topologies were analyzed. There were three- and four-node ones. Additionally, in the presence of hidden nodes, the inability of the EDCA mechanism to assure a desired quality of service for different services (most of all video and voice) was shown. Furthermore, the usefulness of the RTS/CTS mechanism was also verified.
Access status: Open Access ,
Analiza symulacyjna układów anten MIMO w systemach łączności ruchomej trzeciej generacji
(Wydawnictwa AGH, 2005) Mazik, Maciej; Ludwin, Wiesław; Giersz, Maciej
The third generation systems being a next step of evolution of mobile communication face still growing demand for throughput, coverage and quality of service. To fulfill this demand the newest data transmission technologies have to be used in 3G systems. The most promising solution are MIMO multiple antennas, described in present paper. The paper compares simulation and experimental results for MIMO antennas. Experimental results are taken from the literature. The increase of throughput for the third generation systems due to improvement of spectral efficiency factor is presented in this work.
Access status: Open Access ,
Architektura QoS integrująca sieci ad-hoc z sieciami stałymi
(Wydawnictwa AGH, 2008/2009) Natkaniec, Marek; Gozdecki, Janusz; Kosek, Katarzyna; Szott, Szymon; Pach, Andrzej R.
This paper proposes a complete QoS architecture for integration of ad-hoc networks with infrastructure networks. The technology, service differentiation mechanisms, and signalling protocols are discussed. The modules required in the network elements and its integration to provide end-to-end QoS in mobile ad-hoc networks are also presented. The proposed solution is based on the SWAN model with several extensions to provide L2 traffic differentiation for four classes and supports integration with infrastructure networks. The deployed hierarchical architecture guarantees scalability and allows per-flow resource management in wireless access where scarce radio resources should be managed effectively.
Access status: Open Access ,
PUMA-TCS - nowy protokół warstwy MAC ze wsparciem jakości świadczonych usług
(Wydawnictwa AGH, 2010/2011) Natkaniec, Marek; Kosek-Szott, Katarzyna; Szott, Szymon
There is a growing interest in QoS provisioning for wireless local area networks in recent years. Because of this, the IEEE 802.11e standard was introduced. Unfortunately, a few research papers show, that it has a number of serious flaws. The presented work describes a new protocol called PUMA-TCS (Priority Unavoidable Multiple Access with Traffic Category Support), that allows for better than IEEE 802.11e traffic differentiation and QoS guarantees. Research results and comparative analysis of protocols using selected simulators are also included in the paper. This allows to reveal a pros and cons of both channel access schemes.
Telekomunikacja Cyfrowa : technologie i usługi
T. 7 (2005)
Access status: Open Access ,
Problemy wdrażania szerokopasmowych usług multimedialnych w heterogenicznych sieciach IP
(Wydawnictwa AGH, 2010/2011) Chodorek, Robert; Krempa, Agata; Pach, Andrzej R.; Chodorek, Agnieszka
For over 30 years of its existence, the Internet has evolved from traditional data networks in the largest multiservice networks. Some Internet service has been created from scratch (like e-mail), some of them (eg. television, or Internet telephony) is the adaptation of services previously implemented in specialized networks (broadcast television network, Plain Old Telephone Service - POTS, etc.). Implementation of new services is a complex issue. New services may interact with existing applications. Problems can also occur with services adapted from specialized networks - for example, due to much lower transmission quality than required. In this paper an analysis of contemporary services and requirements is described. We show problems, which occur due to the heterogeneity of multiservice network, as well as how to solve these problems.
Telekomunikacja Cyfrowa : technologie i usługi
T. 8 (2006/2007)
Telekomunikacja Cyfrowa : technologie i usługi
Wydawnictwa AGH (2007-2011)
ISSN: 1505-9405
Access status: Open Access ,
Programowa implementacja konfigurowalnego i zarządzanego przez interfejs WWW punktu dostępu do sieci standardu IEEE 802.11
(Wydawnictwa AGH, 2006/2007) Łabędź, Maciej; Natkaniec, Marek
Wireless Local Area Networks are one of the fastest growing areas of data transmission networks. Today we have a broad family of IEEE 802.11 WLAN standards. IEEE 802.11b has recently become the de facto standard for WLANs. It provides 11 Mb/s in the ISM 2.4 GHz band. IEEE 802.11e extends the MAC layer to improve QoS capabilities. Unfortunately this standard up to now was not implemented in real WLAN network devices. The possibility of software access point implementation is presented in this article. The Linux OS with the WLAN interface which is based on the Prism chipset let one create developed cheap access point devices with good radio parameters for IEEE 802.11b network. This study contains also problems related to servicing QoS mechanism in the network layer. These mechanisms are discussed on the basis of Linux OS, which provides advanced service of traffic policing and traffic shaping.
Access status: Open Access ,
Implementacja punktu dostępu do sieci standardu IEEE 802.11 ze wsparciem jakości świadczonych usług
(Wydawnictwa AGH, 2010/2011) Natkaniec, Marek; Kosek-Szott, Katarzyna; Pach, Andrzej R.; Staniszewski, Andrzej; Witosz, Mariusz
The paper is related to the implementation of mechanisms for providing QoS in access point based on IEEE 802.11 standard. Three different methods for providing QoS are showed: for the data link layer (using IEEE 802.11 function), for the network layer (using queuing disciplines), and for the both mentioned layers (using hybrid solution). These mechanisms allow for improving and proper control of services provisioning in IEEE 802.11 wireless local area networks.
Access status: Open Access ,
Naliczanie opłat w sieciach telekomunikacyjnych
(Wydawnictwa AGH, 2005) Kantor, Mirosław; Wajda, Krzysztof
This paper presents Basic issues for billing system dedicated to support services in telecommunication networks. Main economic conditions and functionalities of the system are described. Fundamental terms and definitions are explained. Impact of billing system on service users' behavior is characterized. In concluding section main criteria for assessment of billing schemes are given.
Access status: Open Access ,
Wykorzystanie informacji pomiarowych pochodzących z protokołu BGP do oceny struktury sieci Internet
(Wydawnictwa AGH, 2008/2009) Malinowski, Marcin; Pacyna, Piotr; Nowak, Jacek
The paper presents methods for investigating topology of the contemporary Internet which jointly allow to learn its structure, discover operators and interconnections. The focus is on methods based on information available in BGP protocol which allows to learn dynamic properties of the Internet. Usability of the methods is presented in a case study of ACK CYFRONET AGH network.
Access status: Open Access ,
Analiza zagadnienia sprawiedliwego dostępu do kanału radiowego realizowanego za pomocą modyfikacji parametrów okna współzawodnictwa w sieciach ad-hoc standardu IEEE 802.11e
(Wydawnictwa AGH, 2008/2009) Natkaniec, Marek; Szott, Szymon; Pach, Andrzej R.
This paper is related to the problem of node misbehaviour. The presented work determines how contention window cheating can influence the performance of ad-hoc networks based on the new IEEE 802.11e standard. It is explained why such networks are more prone to misbehaviour than previous 802.11 (other WiFi) standards. A simulation analysis has been carried out for several distinct scenarios. The presented results show that a misbehaving node can significantly decrease the network performance. Therefore, countermeasures to this problem need to be developed.
Access status: Open Access ,
Zliczanie danych TCP w przypadku odbioru przemieszanych segmentów
(Wydawnictwa AGH, 2006/2007) Głowacz, Andrzej
Correct TCP data counting allows for efficient bandwidth estimation and congestion control. This paper presents an analysis of the data counting algorithm applied in TCP Westwood. Considering particular scenarios, where out-of-order data is received, we show that TCP Westwood data counting procedure can lead to following errors: negative bandwidth estimation, 100% momentary sampling error, and bandwidth underestimation. We propose a modified data counting algorithm for TCP Cracow. New method allows for-significantly improved bandwidth sampling and improving TCP performance in out-of-orderegments scenarios.
Access status: Open Access ,
Analiza działania strumieniujących systemów nakładkowych stosujących rozwiązania ISO Isolated Channel oraz View Upload Decoupling
(Wydawnictwa AGH, 2010/2011) Włodarczyk, Agnieszka; Wajda, Krzysztof; Staniszewski, Andrzej
The paper presents an analysis of two important overlay (peer-to-peer) streaming applications used for distribu¬tion of video streams: basic ISO Isolated Channel and enhanced - View Upload Decoupling. Theoretical investigations and illustration of efficiencies for both solutions are shown for different uplink and downlink transmission speeds. Additionally, the results using available statistical data for Polish Internet access are presented.