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An analytical model to study the performance of wireless local area networks (WLANs) supporting asymmetric nonpersistent traffic using the IEEE 802.11 distributed coordination function mode for medium access control (MAC) is developed. Given the parameters of the MAC protocol and voice codecs, the voice capacity of an infrastructure-based WLAN, in terms of the maximum number of voice connections that can be supported with satisfactory user-perceived quality, is obtained. In addition, voice capacity analysis reveals how the overheads from different layers, codec rate, and voice packetization interval affect voice traffic performance in WLANs, which provides an important guideline for network planning and management. The analytical results can be used for effective call admission control to guarantee the quality of voice connections. Extensive simulations have been performed to validate the analytical results. Index Terms--IEEE 802.11 DCF, unbalanced traffic, voice capacity.

The service broker, a function introduced into next-generation networks to manage interactions among applications, to reuse existing applications in a combined fashion, or to enable existing applications with capabilities is discussed. A lightweight, programmable, Session Initiation protocol (SIP)-centric service broker architecture and the concept of the 'steplet', which is central to this architecture, is introduced.

The problem of global information flows via computer networks raises issues of competition, interoperability, and standard-setting parallel to those in the analysis of technical standards. Uniform standards, whether technical or [...]

The Bell Labs security framework and model was used in order to define the value of security strategy, to minimize the vulnerabilities and to identify the mitigation strategies for both civilian and non-civilian networks. The term civilian networks and non-civilian networks refer to communications networks that are used by private corporations and government agencies, respectively.

Byline: Ji-An Zhao (1), Bo Li (2), Chi-Wah Kok (3), Ishfaq Ahmad (4) Keywords: DBMAP with marked transitions; HMM channel; PH-type distribution; DBMAP/PH/1 priority queue Abstract: With the scalability and flexibility of the MPEG-4 and the emergence of the broadband wireless network, wireless multimedia services are foreseen to become deployed in the near future. Transporting MPEG-4 video over the broadband wireless network is expected to be an important component of many emerging multimedia applications. One of the critical issues for multimedia applications is to ensure that the quality-of-service (QoS) requirement to be maintained at an acceptable level. This is further challenged in that such a service guarantee must be achieved under unreliable and time-varying wireless channels. In this paper we study the link level performance of MPEG-4 video transmission over the uplink of an unreliable wireless channel. We introduce the discrete time batch Markovian arrival process (DBMAP) with two types of arrivals to model the MPEG-4 video source, which takes into account the inherent nature of the adaptiveness of the video traffic. We prove that in a hidden Markov modeled (HMM) wireless channel with probabilistic transmission, the service time for an arbitrary radio link control (RLC) burst follows phase type (PH-type) distribution. We show that the link level performance of a wireless video transmission system can be modeled by a DBMAP/PH/1 priority queue, and present computation algorithm and numerical results for the queueing model. Extensive simulations are carried out on the queueing behavior of the video transmission buffer, as well as on the packet level error behavior of the video data. The results demonstrate that video quality can be substantially improved by preserving the high priority video data during the transmission. Author Affiliation: (1) Department of Computer Science, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China (2) Department of Computer Science, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China (3) Department of Electrical and Electronic Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China (4) Department of Computer Science and Engineering, University of Texas at Arlington, Arlington, TX, 76019-0015, USA Article History: Registration Date: 03/10/2004

The sixth Dublin Core Metadata Workshop held on Nov 2-4, 1998, focused on unresolved issues such as standardization, HTML encoding and qualification mechanisms. Despite the intense debates that marked the workshop, important strides were noted in the fields of standardization and syntax alternatives.

The new global information infrastructure will prove effective only if it can guarantee high-speed transmission of all kinds of data - text, images, sound or film - without hiccups or [...]