TCP over satellite links: Problems and solutions

Satellite communications are destined to play an important role in future telecommunications infrastructure. There is in particular an increasing interest in transporting Internet traffic over satellite links. Many studies have shown that TCP has a poor performance in the context of satellite communications. This is due to many factors inherent to satellite communications and for which TCP – originally designed for terrestrial networks – is inadequate. Our study is an overview of the many factors limiting TCP performance over a satellite link and the different solutions proposed to address the problem. This revised version was published online in June 2006 with corrections to the Cover Date.     

TCP/IP performance over satellite links

Achieving high data rates using TCP/IP over satellite networks can be difficult. This article explains some of the reasons TCP/IP has difficulty with satellite links. We present solutions to some problems, and describe the state of the research on some the unsolved problems     

Binary DPSK transmission over terrestrial and satellite links (Corresp.)

It has been observed previously that downlink noise correlation has no effect on the average error probability of a differentially phase shift keyed (DPSK) satellite system when the symbols are equiprobable. We show thai this observation holds for a satellite system exhibiting amplitude-modulation-to-amplitude-modulation (AM-AM) conversion effects and amplitude-modulation-to-phase-modulation (AM-PM) conversion effects. It is also shown thai noise correlation has no effect even when a constant phase error is caused by the delay line of the DPSK receiver in terrestrial and satellite links.     

基于SIP的多媒体会议分布式管理架构的设计

与会者及设备在地理上多处分布的大规模多媒体会议系统的一个重要设计思想就是要提高会议管理架构的可伸缩性.文章介绍了基于会话初始协议(SIP)的多媒体会议分布式管理架构的设计,并将策略管理技术引入到分布式管理架构中,从而为解决会议系统的缩放性、扩展性问题提供了一种新途径.     

Scalable processor architecture for Java with explicit threadsupport

A scalable processor architecture for multi-threaded Java^TM applications is presented. The proposed architecture consists of multiple application-specific processing elements, each able to execute a single thread at one time. The architecture is evaluated by implementing a portable and scalable Java machine on an FPGA board for demonstration     

One-parameter adoptive cancellation for satellite microwave links

For dual linearly polarised microwave links (especially to satellites), in situations where differential phase shift is the dominant cause of crosspolarisation, it is proposed to perform adaptive cancellation of crosspolarisation by means of a simplified network having only one variable parameter. A possible construction of the device is suggested and its performance in various situations assessed.     

Policy-based distributed management architecture for large-scale enterprise conferencing service using SIP

Recent advances in broadband communication and computing technology have accelerated the proliferation of Internet protocol-based multimedia conferencing services in large-scale enterprises. Most of the research on session initial protocol (SIP)-based multimedia conferencing, however, has been limited in scalability due to the centralized management of conference control by a single server. In order to overcome this limitation, we have designed policy-based distributed management architecture for a large-scale enterprise conferencing service by extending the Internet Engineering Task Force's (IETF's) approach. The salient feature of the proposed management architecture is that in addition to the distribution of media processing, both participant membership control and authorization functions are dynamically distributed in accordance with the management policy in order to improve scalability. In order to implement these distributed management functions, we have extended both SIP and conference policy control protocols of the IETF. We also show the procedures for the distributed conference management using the extended SIP signaling methods. Finally, we have evaluated by simulation the performances of the proposed architecture in comparison with the centralized architecture of the IETF. The simulation results show that the proposed architecture greatly improves scalability.     

High-speed fiber-optic links for distribution of satellite traffic

Low-loss fiber-optic links are designed for distribution of data and the frequency reference in large-aperture phased-array antennas based on the transmit/receive-level data mixing architecture. In particular, design aspects of a fiber-optic link satisfying the distribution requirements of satellite data traffic are presented. The design is addressed in terms of reactively matched optical transmitter and receiver modules. Analog and digital characterization of a 50-m fiber-optic link realized using these modules indicates the applicability of this architecture as the only viable alternative for distribution of data signals inside a satellite at present. It is demonstrated that the design of a reactive matching modules enhances the link performance. A dynamic range of 88 dB/MHz was measured for analog data over 500-1000-MHz bandwidth     

UMTS architecture for integrating terrestrial and satellite systems

This architecture proposal for the Universal Mobile Telecommunication System harmonizes several approaches to the evolving European Union mobile-systems standard. The architecture accommodates both satellite and terrestrial networks and allows a smooth transition from existing systems to UMTS     

A code-division switch architecture for satellite applications

This paper introduces a code-division methodology into switching applications. The proposed method is applied in satellite-switched code-division multiple-access (SS/CDMA) systems for routing CDMA traffic channels on board the multibeam satellites. We present code-division switch (CDS) architectures, analyze the CDS performance, and assess its complexity. The CDS has been shown to route CDMA user channels without introducing interference. The proposed CDS architecture is nonblocking, and its hardware complexity and speed are proportional to the size of the switch. We also examine the amplitude distribution of the combined signal in the CDS bus and the interference evaluation of the end-to-end link in the proposed applications. Then we consider the problem of switch control under an optimum or a random algorithm and compare its complexity with the equivalent problem in time-multiplexed switching methods     

Human perception-based distributed architecture for scalable video conferencing services: theoretical models and performance

This research work proposes a human perception-based distributed architecture for the multiparty video conferencing services. The new architecture can effectively reduce the unnecessary traffic of the multilayer video streams on the overlay network. Rich theoretical models of the three different architectures: the proposed perception-based distributed architecture, the conventional centralized architecture, and perception-based centralized architecture have been constructed by using queuing theory to reflect the traffic generated, transmitted, and processed by the three architectures. The performance has been considered in different aspects from the total waiting time to the required service rates. Together, the modeling tools, the analysis, and the numerical results help to answer the common concern about advantages and disadvantages of the centralized and distributed architectures. Overall, the proposed human perception-based distributed architecture can maintain a smaller total waiting time with a much smaller requirement of service rate in comparison with the conventional centralized architecture and perception-based centralized architecture.     

Simple rain attenuation prediction method for satellite radio links

The desirable features of a rain attenuation prediction method to be used in satellite radio link engineering are established, and a method satisfying such features is proposed. The method is tested over 77 satellite links situated in Europe, the USA, Japan, and Australia. Comparisons are made with the International Radio Consultative Committee (CCIR) method (CCIR, vol.V, Report 564, XVI Plenary Assembly, Dubrovnik, 1986). Using the worldwide coefficients for the links located in Australia there results a marked overestimation and a poor accuracy. This situation does not occur for the links located in Europe, the USA, and Japan, which are in temperate climates. The method's limitation is related to low rain intensities in satellite links having low elevation angle     

A network architecture for a geostationary communication satellite

An M-VSAT communication system envisioned by NASA would provide low data rate, direct-to-the-user communications services for interactive data, voice, facsimile, and video conferencing. Such a system would enhance current communications services and enable new services     

Voice over ATM: an evaluation of network architecture alternatives

This article describes eight application scenarios in which there is a business case for voice over ATM. It then evaluates alternative network architectures for implementing the required network functionality. The article incorporates much of the ongoing work of the ATM Forum and the ITU, but does not restrict itself to standards and implementation agreements. In addition, it evaluates nonstandardized alternatives for ATM transport of voice traffic. There are two main areas: N×64 kb/s structured data transfer, also known as composite cell transport-a network operator may aggregate individual voice calls into N×64 kb/s blocks for transport to an intermediate point in the network. At that point the individual calls need to be remapped into new M×64 kb/s blocks for the next stage of their transport. Architectural alternatives and advantages of remapping are investigated. Interworking of signalling is of two types: network interworking, in which the end users are connected to non-ATM networks and an ATM network is used for backbone transport; and service interworking, in which an ATM user is connected to a non-ATM user. Functionality and architectural alternatives for network and service interworking are evaluated     

多媒体会议目录服务体系结构标准-ITU-T H.350简介

简要介绍了H.350标准的设计目标、基本原理、优势和市场前景.随着Intemet上多媒体信息流的急剧增加,如何提供一种统一的在视频端点目录中存储和查找这些信息的方法,已经成为一个非常突出的问题.多媒体会议目录服务体系结构标准-ITU-T H.350解决了这个问题.     

Scalable architecture for word HMM-based speech recognition and VLSI implementation in complete system

This paper describes a scalable architecture for real-time speech recognizers based on word hidden Markov models (HMMs) that provide high recognition accuracy for word recognition tasks. However, the size of their recognition vocabulary is small because its extremely high computational costs cause long processing times. To achieve high-speed operations, we developed a VLSI system that has a scalable architecture. The architecture effectively uses parallel computations on the word HMM structure. It can reduce processing time and/or extend the word vocabulary. To explore the practicality of our architecture, we designed and evaluated a complete system recognizer, including speech analysis and noise robustness parts, on a 0.18-/spl mu/m CMOS standard cell library and field-programmable gate array. In the CMOS standard-cell implementation, the total processing time is 56.9 /spl mu/s/word at an operating frequency of 80 MHz in a single system. The recognizer gives a real-time response using an 800-word vocabulary.     

A recommended error control architecture for ATM networks withwireless links

This paper provides performance results through analysis and simulation for key error control problems encountered in using wireless links to transport asynchronous transfer mode (ATM) cells. Problems considered include the forward-error correction (FEC) and interleaving at the physical layer, the impact of wireless links on the ATM cell header-error control (HEC) sand cell delineation (CD) functions, the application of data link automatic repeat-request (ARQ) for traffic requiring reliable transport, and the impact of the choice of end-to-end ARQ protocol for reliable service. We conclude that it is very important to make the physical layer as SONET-like as possible through the use of powerful FEC, interleaving, and ARQ. These additional error control measures are especially necessary for disturbed channels because of the degrading effects of the channel on higher-layer functions. A recommended error control architecture is given with tradeoffs     

A codec for HDTV signal transmission through terrestrial and satellite digital links

A codec for digital transmission of HDTV is described. The bit-rate compression algorithm is based on advanced techniques such as spatial discrete cosine transform (DCT), temporal differential PCM (DPCM), variable length coding. The codec is designed to operate with both the interlaced studio systems 1125/60 and 1250/50, and, thanks to the inherent flexibility of the packet structure, a wide range of line bit-rates can be used as a compromise between video quality and bit-rate constraints of the digital transmission link. The flexibility of the HDTV codec is highlightened through examples of applications over satellite digital links in practical situations.     

Scalable video coding and transport over broadband wirelessnetworks

With the emergence of broadband wireless networks and increasing demand of multimedia information on the Internet, wireless multimedia services are foreseen to become widely deployed in the next decade. Real-time video transmission typically has requirements on quality of service (QoS). However, wireless channels are unreliable and the channel bandwidth varies with time, which may cause severe degradation in video quality. In addition, for video multicast, the heterogeneity of receivers makes it difficult to achieve efficiency and flexibility. To address these issues, three techniques, namely, scalable video coding, network-aware adaptation of end systems, and adaptive QoS support from networks, have been developed. This paper unifies the three techniques and presents an adaptive framework, which specifically addresses video transport over wireless networks. The adaptive framework consists of three basic components: (1) scalable video representations; (2) network-aware end systems; and (3) adaptive services. Under this framework, as wireless channel conditions change, mobile terminals and network elements can scale the video streams and transport the scaled video streams to receivers with a smooth change of perceptual quality. The key advantages of the adaptive framework are: (1) perceptual quality is changed gracefully during periods of QoS fluctuations and hand-offs; and (2) the resources are shared in a fair manner     

Packetized radiographic image transfers over local area networksfor diagnosis and conferencing

The authors present a multimedia medical communications system based on packet local area networks. This system is intended to facilitate the communications between radiologists and physicians within a hospital. Radiographs are taken, digitized, and then stored in the database. Radiologists retrieve radiographic images from the database for diagnosis, and make diagnostic reports to be stored in the database. Physicians can then consult these radiographic images and diagnostic reports. A real-time conference can be set up between a radiologist and a physician who are in different locations, for discussing a particular case or radiographic images can be retrieved from the database for diagnosis and conferencing. Simulations indicate the delay for displaying an image of 1 Mb from the local storage (hard disk) at a workstation is approximately 6.5 s