A hybrid multilayer error control technique for multihop ATM networks

There has been a great interest lately in the utilization of the ATM technology for networks. Especially in recent years, wireless ATM has emerged. The wireless links are characterized by higher, time-varying error rates and burstier error patterns in comparison with the fiber-based links from which ATM was designed. The mean time error checking and correction get more and more important and necessary. In this work, a new multilayer error control technique is presented and analyzed for ATM networks. While standard Go-Back-N ARQ technique is applied end to end, a new lost-cell concealment technique cooperates below as a forward error correction mechanism that also operates end to end. As the cell travels the inter-network enroute to the destination ATM user node interface (UNI), the CRC is checked and the cell is dropped or passed to the next ATM hop accordingly. The error detection and correction techniques above are applicable to connection oriented traffic, however in this work we deal with the connectionless case. The choice of one of these alternatives has its implication on the CRC regeneration at each ATM Network Node Interface (NNI). In this work we present the hierarchy of the error control technique above, and analyze the end to end user performance in terms of net throughput and reliability. In the process we investigate the interactive effects of the channel and ATM signaling parameters on the system performance, with particular emphasis on the design of the error control scheme

Advancing the Standards for Unmanned Air System Communications, Navigation and Surveillance

Under NASA program NNA16BD84C, new architectures were identified and developed for supporting reliable and secure Communications, Navigation and Surveillance (CNS) needs for Unmanned Air Systems (UAS) operating in both controlled and uncontrolled airspace. An analysis of architectures for the two categories of airspace and an implementation technology readiness analysis were performed. These studies produced NASA reports that have been made available in the public domain and have been briefed in previous conferences. We now consider how the products of the study are influencing emerging directions in the aviation standards communities. The International Civil Aviation Organization (ICAO) Communications Panel (CP), Working Group I (WG-I) is currently developing a communications network architecture known as the Aeronautical Telecommunications Network with Internet Protocol Services (ATN/IPS). The target use case for this service is secure and reliable Air Traffic Management (ATM) for manned aircraft operating in controlled airspace. However, the work is more and more also considering the emerging class of airspace users known as Remotely Piloted Aircraft Systems (RPAS), which refers to certain UAS classes. In addition, two Special Committees (SCs) in the Radio Technical Commission for Aeronautics (RTCA) are developing Minimum Aviation System Performance Standards (MASPS) and Minimum Operational Performance Standards (MOPS) for UAS. RTCA SC-223 is investigating an Internet Protocol Suite (IPS) and AeroMACS aviation data link for interoperable (INTEROP) UAS communications. Meanwhile, RTCA SC-228 is working to develop Detect And Avoid (DAA) equipment and a Command and Control (C2) Data Link MOPS establishing LBand and C-Band solutions. These RTCA Special Committees along with ICAO CP WG/I are therefore overlapping in terms of the Communication, Navigation and Surveillance (CNS) alternatives they are seeking to provide for an integrated manned- and unmanned air traffic management service as well as remote pilot command and control. This paper presents UAS CNS architecture concepts developed under the NASA program that apply to all three of the aforementioned committees. It discusses the similarities and differences in the problem spaces under consideration in each committee, and considers the application of a common set of CNS alternatives that can be widely applied. As the works of these committees progress, it is clear that the overlap will need to be addressed to ensure a consistent and safe framework for worldwide aviation. In this study, we discuss similarities and differences in the various operational models and show how the CNS architectures developed under the NASA program apply

Buffer management and cell switching management in wireless packet communications

The buffer management and the cell switching (e.g., packet handoff) management using buffer management scheme are studied in Wireless Packet Communications. First, a throughput improvement method for multi-class services is proposed in Wireless Packet System. Efficient traffic management schemes should be developed to provide seamless access to the wireless network. Specially, it is proposed to regulate the buffer by the Selective- Delay Push-In (SDPI) scheme, which is applicable to scheduling delay-tolerant non-real time traffic and delay-sensitive real time traffic. Simulation results show that the performance observed by real time traffics are improved as compared to existing buffer priority scheme in term of packet loss probability. Second, the performance of the proposed SDPI scheme is analyzed in a single CBR server. The arrival process is derived from the superposition of two types of traffics, each in turn results from the superposition of homogeneous ON-OFF sources that can be approximated by means of a two-state Markov Modulated Poisson Process (MMPP). The buffer mechanism enables the ATM layer to adapt the quality of the cell transfer to the QoS requirements and to improve the utilization of network resources. This is achieved by selective-delaying and pushing-in cells according to the class they belong to. Analytical expressions for various performance parameters and numerical results are obtained. Simulation results in term of cell loss probability conform with our numerical analysis. Finally, a novel cell-switching scheme based on TDMA protocol is proposed to support QoS guarantee for the downlink. The new packets and handoff packets for each type of traffic are defined and a new cutoff prioritization scheme is devised at the buffer of the base station. A procedure to find the optimal thresholds satisfying the QoS requirements is presented. Using the ON-OFF approximation for aggregate traffic, the packet loss probability and the average packet delay are computed. The performance of the proposed scheme is evaluated by simulation and numerical analysis in terms of packet loss probability and average packet delay

Aeronautical Mobile Airport Communications System (AeroMACS)

To help increase the capacity and efficiency of the nation s airports, a secure wideband wireless communications system is proposed for use on the airport surface. This paper provides an overview of the research and development process for the Aeronautical Mobile Airport Communications System (AeroMACS). AeroMACS is based on a specific commercial profile of the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard known as Wireless Worldwide Interoperability for Microwave Access or WiMAX (WiMax Forum). The paper includes background on the need for global interoperability in air/ground data communications, describes potential AeroMACS applications, addresses allocated frequency spectrum constraints, summarizes the international standardization process, and provides findings and recommendations from the world s first AeroMACS prototype implemented in Cleveland, Ohio, USA

Effects of Voice Compression on the Operation of aN-ISDN/B-ISDN IWF

The significant widespread of N-ISD , which has recently gained momentum, will make it hard for the emerging B-ISD whether to ignore its presence or to phase it out and replace it in the near foreseen future. Consequently, the ATM of the interoperability specification CES-IS V2.0 (af-vtoa-0078.000), which defines emulation standards for circuit characteristics of constant bit-rate (CBR) traffic within ATM. A critical attribute of a circuit emulation service (CES) is to achieve a performance comparable to that are still pending will be addressed. Special interest will be given to devising methods that will enable voice, which is a size able component of the current N-ISD traffic, to be carried efficiently over ATM network. First, a multiplexing technique for voice sources will be presented. Then, assuming that speech silence detection is being used, a technique for dealing with the partially filled cells wil be suggested, analyzed, and then simulated. The results will be then presented and analyzed, followed by conclusions and suggestions

Call Admission Control in Mobile Wireless

Some problems related to wireless network access are discussed in the article. Special attention is paid to Medium Access Control and Call Admission Control. Both have direct impact on communication link accession. While the first one dictates how to, the second one decides who can access the link. The problems with wireless medium access are mentioned and requirements on MAC protocols are named. Also need for CAC algorithms is illustrated and simple functional example is proposed. Finally, the reasons for future enhancements are shortly discovered

The rise and demise of Lucent Technologies

We analyze the rise and demise of Lucent Technologies from the time that it was spun off from AT&T in April 1996 to its merger with Alcatel in December 2006. The analysis, contained in the three sections that form the body of this paper, considers three questions concerning Lucent’s performance over the decade of its existence. 1.How was Lucent, with over $20 billion in sales in 1995 as a division of AT&T, able to almost double its size by achieving a compound growth rate of over 17 percent per year from 1995 to 1999? 2.What was the relationship between Lucent’s growth strategy during the Internet boom and the company’s financial difficulties in the Internet crash of 2001-2003 when the Lucent was on the brink of bankruptcy? 3.After extensive restructuring during the telecommunications industry downturn of 2001-2003, why was Lucent unable to re-emerge as an innovative competitor in the communications equipment industry when the industry recovered?Communications equipment; innovation; global competition; financialization

Managing Shared Access to a Spectrum Commons

The open access, unlicensed or spectrum commons approach to managing shared access to RF spectrum offers many attractive benefits, especially when implemented in conjunction with and as a complement to a regime of marketbased, flexible use, tradable licensed spectrum ([Benkler02], [Lehr04], [Werbach03]). However, as a number of critics have pointed out, implementing the unlicensed model poses difficult challenges that have not been well-addressed yet by commons advocates ([Benjam03], [Faulhab05], [Goodman04], [Hazlett01]). A successful spectrum commons will not be unregulated, but it also need not be command & control by another name. This paper seeks to address some of the implementation challenges associated with managing a spectrum commons. We focus on the minimal set of features that we believe a suitable management protocol, etiquette, or framework for a spectrum commons will need to incorporate. This includes: (1) No transmit only devices; (2) Power restrictions; (3) Common channel signaling; (4) Mechanism for handling congestion and allocating resources among users/uses in times of congestion; (5) Mechanism to support enforcement (e.g., established procedures to verify protocol is in conformance); (6) Mechanism to support reversibility of policy; and (7) Protection for privacy and security. We explain why each is necessary, examine their implications for current policy, and suggest ways in which they might be implemented. We present a framework that suggests a set of design principles for the protocols that will govern a successful commons management regime. Our design rules lead us to conclude that the appropriate Protocols for a Commons will need to be more liquid ([Reed05]) than in the past: (1) Marketbased instead of C&C; (2) Decentralized/distributed; and, (3) Adaptive and flexible (Anonymous, distributed, decentralized, and locally responsive)