SATELLITE-ENHANCED PERSONAL COMMUNICATIONS EXPERIMENTS

Users of future generation wireless information services will have diverse needs for voice, data, and potentially even video communications in a wide variety of circumstances. For users in dense, inner-city areas, low power personal communications services (PCS) technology should be ideal. Vehicular-based users travelling at high speeds will need high-power cellular technology. For users in remote or inaccessible locations, or for applications that are broadcast over a wide geographic area, a satellite technology would be the best choice. Packet data networks provide an excellent solution for users requiring occasional small messages, whereas circuit switched networks provide more economical solutions for larger messages. To provide ubiquitous personal communications service, it is necessary to capitalize on the strength of each wireless technology and network to create one seamless internetwork including both current and future wired and wireless networks. As an initial step in exploring the opportunities afforded by the merging of satellite and terrestrial networks, Bellcore and JPL conducted several experiments. These experiments utilized Bellcore's experimental personal communications system (including several messaging applications with adaptations to wireless networks), NASA's advanced communications technology satellite (ACTS), JPL's ACTS mobile terminal, and various commercial data networks (such as the wireline Internet and the RAM wireless packet data network). Looking at loss of bits, packets and higher layer blocks (over the satellite-terrestrial internetworks with mobile and stationary users under various conditions) our initial results indicate that the communication channel can vary dramatically, even within a single network. We show that these conditions necessitate powerful and adaptive protocols if we are to achieve a seamless internetworking of satellite and terrestrial networks.     

The role of ISDN in data networking

The integrated services digital network (ISDN) offers on-demand switched end-to-end digital connectivity over the wide area, enabling the integration of both voice and data services over a common core network. This paper considers the role of ISDN in data networking, both as the core transport network and as a means of enhancing resilience in a mixed-technology data solution, complementing other data network technologies. The issues associated with data transport based on an ISDN solution are considered, and include security, bandwidth utilisation, scalability and the management of ISDN-attached devices. Optimising the use of ISDN networks for supporting the most prevalent routed and routeing protocols is also discussed.     

A Distributed Experimental Communications System

The packet experimental communications system (packet XCS) is a new experimental voice and data switch. It uses a local-area network (LAN) for digital voice transmission, with local intelligence for switching. The packet XCS also has highly distributed control. The individual sites cooperate to provide user services as well as internal data management. We have learned that several local networks, including CSMA/CD networks, can be made to work well for voice transmission and that highly distributed control is practical in such a system. A system has been constructed which is used as a testbed for distributed voice and data communications experiments. This system is purely for experimentation and does not indicate a direction for future Bell System product offerings.     

Resource allocation in broadband ISDNs

Broadband integrated services digital networks (BISDNs) have recently received significant attention among researchers in the field of telecommunications. These broadband telecommunication networks are being designed for handling, in their final form, a large variety of digital information, e.g., data, voice, video, facsimile, etc. Asynchronous transfer mode (ATM) has been recommended by the CCITT as a means of providing efficient and fast packet switched communication among BISDN users. It supports a large variety of services in a simple and unified fashion. An efficient and simple, yet effective, technique for resource allocation in broadband networks is presented. This technique was simulated for a network with three types of services and results are presented in terms of call blocking probabilities for several different cases.<>     

An Integrated Voice/Data Terminal with Simple Synchronization Circuits Using an 80 kbit/s Ping-Pong Method

With recent digital technique progress, digitalization is spreading to subscriber loop systems. In-house systems will be digitalized earlier than other systems. In in-house networks, a pingpong method, especially an 80 kbit/s ping-pong method, using an existing cable pair, is superior to other digital transmission methods due to the sample system structure. For office use, a digital subscriber terminal is required to offer integrated services. However, the already reported 80 kbit/s method is insufficient to provide simultaneous and independent integrated services. This paper presents an 80 kbit/s ping-pong method which has 72 kbit/s capacity for the voice and data communications, so as to provide such integrated services. Furthermore, an experimental integrated terminal, which has simple synchronization circuits, is described.     

High-Speed Packet Switching Systems for Multimedia Communications

High-speed packet switching (HPS) systems can Provide flexible, economical, high-quaiity services for integrated voice, video, and data communications. To realize such HPS systems, methods have been developed to bring about high-speed protocol processing as well as a system architecture for facilitating high-throughput switching. Adopting the parallel processing algorithm into protocol processing allows us to achieve high-speed packet protocol processing of about 100 times faster than conventional processing. Furthermore, a fully distributed system architecture in addition to hierarchical interconnection networks can achieve high-capacity packet switching systems. The proposed HPS system is thus capable of accommodating lines of up to 10-50 Mbits/s, of providing high-throughput switching capability of 1 000 000 packets/s, and of having an average delay of less than 2 ms. Furthermore, an evaluation of network delay performances of video conferencing and voice communications indicate that HPS systems are quite suitable for handling such multimedia communications.     

Customer network management: a service provider's view

Experience in providing network management for the 1986 Pan American (Pan Am) Games in Indianapolis USA are described. The situation called for an integrated solution that could manage the 5000 voice, data, and video circuits residing within several different networks providing communications for 6500 data terminals and 143 computers spanning 40 locations. The scope of network management is examined, separating it into two parts: management of the specific local exchange carrier services and integrating that with the management of all other products and services. The driving forces behind the need for customer network control are discussed. A two-stage approach to achieving that control is presented     

Voice/data channel access integration in TDMA digital cellularnetworks

The integration of digital data capabilities in the soon to be widely deployed digital cellular networks, which were primarily designed for voice communications, offers a low-cost way to capture the large and ever growing market for mobile data services. The authors propose and evaluate a multiaccess protocol for integrating data traffic in the E(nhanced)-TDMA voice system with digital speech interpolation, which is an enhancement of the emerging North American digital cellular standard. The proposed, protocol combines random access with slot reservation mechanisms to statistically multiplex data packets with speech spurt packets over the shared terminal-to-base air channel. The integrated protocol requires no modification in the voice access protocol used in the E-TDMA system, and can attain performance close to that of an ideal voice/data multiplexer. Furthermore, the protocol may enable multislot assignment per TDMA frame to match the throughput needs of individual data terminals, and can accommodate application-dependent data transmission priorities     

Broadband PLC access systems and field deployment in European power line networks

Data communications over low voltage power distribution networks provide an alternative and cost-effective last mile access technology. It offers data and voice services to users in residential and business areas. Currently, many field trials with different broadband power line communications systems are running worldwide. This article describes one of these systems for the last mile application in European power line networks. It addresses major field deployment aspects, such as range, coverage, coupling, and intercell interference.     

The evolution of packet switching

Over the past decade data communications has been revolutionized by a radically new technology called packet switching. In 1968 virtually all interactive data communication networks were circuit switched, the same as the telephone network. Circuit switching networks preallocate transmission bandwidth for an entire call or session. However, since interactive data traffic occurs in short bursts 90 percent or more of this bandwidth is wasted. Thus, as digital electronics became inexpensive enough, it became dramatically more cost-effective to completely redesign communications networks, introducing the concept of packet switching where the transmission bandwidth is dynamically allocated, permitting many users to share the same transmission line previously required for one user. Packet switching has been so successful, not only in improving the economics of data communications but in enhancing reliability and functional flexibility as well, that in 1978 virtually all new data networks being built throughout the world are based on packet switching. An open question at this time is how long will it take for voice communications to be revolutionized as well by packet switching technology. In order to better understand both the past and future evolution of this fast moving technology, this paper examines in detail the history and trends of packet switching.     

网络功能虚拟化网络功能虚拟化:基于虚拟化的中间件盒子

基于虚拟化的中间件盒子的模型,采用x86架构的电脑硬件设备,依托虚拟化平台构建了一种集成了路由器、语音服务器、虚拟桌面等服务的虚拟中间件盒子。该虚拟中间件盒子采用了中间件盒子的概念,即在标准的服务器上运行开源的虚拟化平台,如XEN、KVM等,并运用网络功能虚拟化(NFV)的理念和软件定义网络(SDN)的理念进行控制管理,最终实现为每个组织、企业、个人提供虚拟通信网络服务(网络功能虚拟化)和虚拟运营服务。     

Design and performance analysis of an advanced, narrowbandintegrated voice/data mobile radio system

Private land mobile communications have experienced significant demand for increased capacity and for new services, but congestion within the currently allocated 450 and 800 MHz bands has severely limited the capability of present generation systems to meet this demand. This paper proposes a narrowband integrated voice/data mobile radio system which triples current voice traffic capacity and simultaneously provides capacity for mobile data communications such as mobile data terminals, automatic vehicle location, and mobile facsimile by utilizing the silence gaps inherent in speech. The system is designed to fit within the narrowband 25 kHz channels in the 450 and 800 MHz frequency bands, and thus the system can replace existing private land mobile radio systems with minimum impact. The centerpiece of the system design is an evolutionary multiplexing and access control technique known as Packetized Data, Voice Dedicated (PDVD) Burst Switching which allows transmission of data within the silence gaps inherent in speech. Simulation results for various voice and data traffic loads show the flexibility and efficiency of the proposed narrowband integrated voice/data mobile radio system     

The ultimate intelligent network?

An `intelligent' telecommunications network is a network that is capable of providing flexible control of its services and capabilities to both network operator and network user. The evolution to intelligent telecommunications networks began some thirty years ago with the introduction of stored programme control exchanges into the public switched network. Since then the introduction of digital switching technology, common channel signalling and network databases have advanced the concept. The evolutionary path now being followed by many network operators will lead from the universal voice telephone service to a universal information service in which the public switched network will be able to provide any combination of voice, data and image with maximum convenience and economy. Truly the ultimate intelligent network?     

A Data Modem for GSM Voice Channel

This paper introduces a novel approach to data communication over the global system for mobile communications (GSM) voice channel. It is based on the concept of ldquosymbolsrdquo-a set of predefined signals with finite bandwidths. Data are encoded into the symbols, and the symbols are voice coded as they were speech, modulated into the GSM signal, sent over the air, GSM demodulated, voice decoded, and converted back to data. The symbols are synthesized by a genetic algorithm with the aim of maintaining separability after passing them through the voice codec. This method enables data transfer over communication networks that do not have dedicated data channels and could also be used in conjunction with other data services to balance the system load between data and voice channels, allowing optimization of system resources. We present the full algorithmic structure of the system, which performs data communications over the GSM voice channel, and we also give the results of the performance tests.     

A reservation random-access protocol for voice/data integratedspread-spectrum multiple-access systems

Most code-division multiple-access (CDMA) systems described in the literature provide only one single service (voice or data) and employ the strategy of “one-code-for-one-terminal” for code-assignment. This assignment, though simple, fails to efficiently exploit the limited code resource encountered in practical situations. We present a new protocol called reservation-code multiple-access (RCMA), which allows all terminals to share a group of spreading codes on a contention basis and facilitates introducing voice/data integrated services into spread-spectrum systems. The RCMA protocol can be applied to short-range radio networks, and microcell mobile communications, and can be easily extended to wide area networks if the code-reuse technique is employed. In RCMA, a voice terminal can reserve a spreading code to transmit a multipacket talkspurt while a data terminal has to contend for a code for each packet transmission. The voice terminal will drop a long delayed packet while the data terminal just keeps it in the buffer. Therefore, two performance measures used to assess the proposed protocol are the voice packet dropping probability and the data packet average delay. Theoretical performance is derived by means of equilibrium point analysis (EPA) and is examined by extensive computer simulation     

The telephone network of the 1960s

In 1960 the transmission technology of the public switched telephone network was ordinary cable pairs, carrier systems on both paired and coaxial cable, and point-to-point microwave radio systems. Voice signals were frequency multiplexed for efficient transmission, but remained in analog form from end to end of a connection. Electromechanical switching systems provided circuit-switched connections, and about half of the customers could directly dial long distance calls. The following decade saw the beginnings of electronic switching and direct distance dialing on a global basis. Meanwhile, applying digital technology to achieve lower costs and better quality for voice transport began in earnest, and the interconnection of data terminals and computer centers became an increasingly important communications need. The initial data communications approach, still used with ever increasing sophistication and speed, was to convert data to speech-like form with data modems. Later, the direct connection of digital data to digital network facilities became the method of choice for building computer communications networks and the backbone of the Internet. It now appears likely that one day all signals, including voice, will be transported by unified high-speed digital networks with a common set of protocols     

A Transmission Scheme for Integrated Services on Broad-Band Internal Private Business Networks

Internal business networks are expected to present an economic area of application for broad-band communications. A star network with switches optimized for various services is envisaged. An asynchronous switch for video in square wave frequency modulation (SWFM) format can provide a practical solution for full bandwidth switched video services. A transmission scheme is described which combines a SWFM video service together with synchronous PCM data and voice services, asynchronous data up to 9.6 kbauds and network clocks at both 2 MHz and 160 kHz for ISDN, so that all services destined for one terminal site may be transmitted in binary format on cable or fiber. An experimental link is described which provides up to 10 Mbit/s data capacity together with the video service. The hardware is constructed with 74HC family CMOS. An analysis of the effects of data modulation on video quality is given. Measurements of video S/N and distortion are reported. Measured bit-error rate in a 64 kbit/s data channel is reported. The measurements relate to a coaxial cable link with link lengths from 200 to 400 meters.     

Trunking of TDM and narrowband services over IP Networks

The recent interest in IP as the vehicle for transporting TDM and narrowband services stems from the possibility of using a common transport network for voice, video, and data, and the flexibility with which new services can be introduced. A key step in the evolution of networks towards a ‘broadband’ IP‐based environment is the ‘graceful’ interworking of the IP networks with the existing networks and services, particularly with the circuit switched telephone network. A ‘graceful’ interworking approach is one whose complexity is minimal and preserves the user's perceived quality of service (QoS). To interwork with a circuit switched network whose services are pre‐dominantly time‐sensitive, the IP network must essentially behave as a transparent ‘link’ in the end‐to‐end connection. This paper presents an overview of the main technical problems to be addressed when trunking TDM and narrowband services over IP networks. Copyright © 2002 John Wiley & Sons, Ltd.     

La commutation de paquets dans le RNIS: de (l’experimentation à I’intégration dans les systèmes*

Integrated service digital networks concepts are currently well established and a number of administrations or network operators are expecting to offer some isdn services soon on a commercial basis: most of these services currently under consideration are based on 64 kbit/s circuit switched bearer capabilities which are inherent to the integrated digital networks from which the isdns are emerging. However network evolution strategies are still under elaboration for the integration of packet switching capabilities. This paper focusses on the steps that, in the view of the French PTT Administration, are necessary to allow a smooth integration of packet switching features in the isdn while preserving a valuable coexistence with existing and well established public switched packet data networks, such as the Transpac network in France. Whilst the commercial opening of the circuit switched based isdn services is planned by 1988, following the Renan pilot, the PTT research center is carrying out the evaluation of the packet feature integration strategy in the isdn, with the Cérame experiment presented here after. Finally the Alcatel developments in relation to the support of isdn packet switched services are presented together with indications on systems impacts.     

Voice over IP service and performance in satellite networks

Voice over IP services have emerged as a low-cost alternative to PSTN voice service, and an attractive solution for voice/data integration in public and private networks. Satellite systems, as an integral part of the global communications infrastructure, already have an increasing portion of their capacities used to carry data packets, and with their global coverage and reach to remote areas are well positioned to enable growth of VoIP services. For VoIP over satellite, several issues need to be addressed. These include transmission and quality of service issues, as well as service-related issues such as service creation and customization, support of IN and supplementary services, and seamless integration with the PSTN. While the service-related aspects of VoIP are common to both terrestrial and satellite networks, transport-related issues are different. This article reports performance results of laboratory experiments for evaluating VoIP over satellite under different link and traffic conditions