Optical satellite networks

Several nongeosynchronous satellite constellation networks providing broad-band access to end-users are currently under development. The use of multigigabit laser intersatellite links (ISLs) is the enabling factor for routing traffic through the spare segment and creating a global space-based optical backbone network. Optical networking techniques based on wavelength division multiplexing (WDM) ISLs and wavelength routing can allow by-pass of the transit traffic significantly simplifying routing decisions and minimizing processing delays. The paper examines the characteristics of these networks and investigates the applicability of various optical networking schemes based on single hop and multihop approaches. Single hop can be adopted in medium earth orbit (MEO) systems consisting of 10 to 15 satellites whereas double-hop schemes based on the matrix lightpath allocation approach are suited for constellations up to 100 satellites, covering the requirements of most of the proposed low earth orbit (LEO) systems. Multihop will be required for some of the very large in number of satellites constellations. Statistical multiplexing of the transported traffic over the ISLs appears to be a necessary condition to achieve an efficient utilization of the satellite resources. Traffic routing has to take into account the impact of the varying range of the interorbit ISLs on the propagation delays. Although maximum leverage of the technologies developed for fiber optic WDM networks should be made, the technologies to be employed on board the satellites have to be space-qualified that may limit the applicability of some otherwise high-efficiency components     

Telematic services via satellite in Europe

The word ‘telematics’ was used for the first time in France in 1978 by Simon Nora and Alain Minc; it is a contraction of the French words ‘tétécommunications’ and ‘informatique’, and defines a marriage between computers and data transmission networks. This paper describes the five systems which will be implemented to provide telematic services via satellite in Europe during the next few years: EUTELSAT, TELECOM 1, UNISAT, DFS and ITALSAT. The main characteristics of the ‘special service’ transponders are presented, showing that, in Europe, (a) 2 to 5 transponders per satellite will be devoted to the special (telematic) services; (b) 4 satellites out of the 5 use the 12.5–12.75 GHz down-link band for this purpose (only ITALSAT uses the 20 GHz down-link for the same purpose), and (c) e.i.r.p.s at 12 GHz are in the range 40–49 dBW. The ground and space segments corresponding to this new service are presented. The main peculiarity of the ground segment is the exclusive use of ‘small’ earth-stations equipped with fixed antennas and SCPC or 25–60 Mb/s TDMA multiple access equipment. Telematic services include videoconference at 2048 kb/s, voice services, computer-to-computer transfer of data, data distribution, remote printing, electronic mail, high-speed facsimile, offshore voice and data services, digital network overflow, transatlantic digital business etc… Customer bit rates start from 2.4, 4.8, 9.6 and 32 kb/s (for TELECOM 1) up to 2048 kb/s by 64 kb/s steps. Bit error rates are maintained below 10^?6 (standard) or 10^?10 (higher grade) during 99 per cent of the year using FEC. The five networks for telematics via satellite in Europe are independent. A large efficiency improvement of the different services should be obtained through a future interconnection of the various networks via intersatellite links.     

Commercial satellite broadcasting for Europe

A review is presented of the current television broadcasting situation in European countries, which involves a varied mix of terrestrial VHF or UHF systems and cable networks. A small market has emerged in Europe for receivers using the low-power telecommunications satellite transmission between the program providers and cable network companies. This is expected to change with the launch of medium-power pan-European telecommunication satellites (e.g. ASTRA, EUTELSAT II), which are now directly addressing the market of home reception. DBS (direct broadcast satellite) in the UK, using the D-MAC transmission standard, will offer three additional television channels, data broadcasting services, and a planned evolution to compatible forms of wide-screen, high-definition television. Comments are given on receiver and conditional access system standardization. Some views are expressed on satellite broadcasting as part of an overall broadcasting framework for the future     

MPLS-based satellite constellation networks

Nongeostationary satellite constellations with intersatellite links are a challenge for networking due to their continuously changing topology. In order to make maximal use of the network's capacities, special attention has to be paid to routing and traffic engineering. Multiprotocol label switching (MPLS) as underlying protocol is an interesting candidate for this task since it offers many possibilities to exert influence on traffic flows and supports today's dominating Internet protocol traffic very well. This paper describes a general MPLS-based networking concept for satellite networks and discusses different scenarios considering the particularities and constraints of the dynamic topology. Functional elements of MPLS like ingress, egress, or core routers have to be mapped onto the physical entities of the network and prerequisites for traffic engineering are discussed. Routing and rerouting of paths is of key interest since this affects route computation effort and routing performance. Thus, an analytical estimation of routing effort is deduced and numerical and simulation results are presented.     

Next-generation mobile satellite networks

Due to the increasing demands of multimedia services supporting high bit rates and mobility, ATM, TCP/IP, and satellite technology are going to be associated to form the internetwork infrastructure of future global systems. In this scenario, distinctions between terrestrial and satellite communications systems, as well as between fixed networks and 3G mobile networks, will cease to exist in a global coverage wireless system. The European Action COST252 actively participated in developing the satellite component of UMTS     

New data networks in Europe

This short paper, which serves as an introduction to the four papers that follow it, comments on the plans for international data communications in Europe. It points out that plans for public data networks, while understandably varying from country, to country, have a promising degree of compatibility and commonality.     

Hybrid satellite and terrestrial networks

The role of satellite communications in networks that provide new services, such as frame relay and multimedia, is investigated. Both passive and active (on-board switching/processing) satellite systems are considered. Novel techniques are developed for each system to demonstrate, via detailed analysis and simulation, how the communications bandwidth agility of multipoint/broadcast satellite channels, and the on-board switching/processing, makes it feasible to provide these new services via hybrid satellite and terrestrial networks in a resource-efficient manner.     

General purpose packet satellite networks

The use of satellite communication techniques to provide integrated data network and point-to-point and conference speech services is discussed. The concept of a General Purpose Packet Satellite Network (GPSN) is introduced in terms of its requirements, and consideration is given to techniques that satisfy these requirements. The class of Priority Oriented Demand Assignment (PODA) algorithms is defined and compared with other packet-oriented demand assignment algorithms. PODA is shown to be well suited to the GPSN application. Networking and access protocol issues are considered in the context of a GPSN. The Atlantic Packet Satellite Experiment, an ongoing experimental program which is developing packet satellite technology, is described in some detail.     

Propagation research in Europe using the OLYMPUS satellite

The launch of the European Space Agency's (ESA) large telecommunications satellite OLYMPUS in the summer of 1989 offered a unique opportunity to study the effects of the atmosphere on satellite communication links at Ku-band (14/12 GHz) and Ka-band (30/20 GHz). The community of OLYMPUS Propagation Experimenters (OPEX) operates experiments at more than 50 locations covering all of Western Europe with its different climatic regions. The authors introduce the European propagation research scenario, summarize the major features of the current OLYMPUS campaign, discuss the significance of the first results obtained, and give an outlook for new activities     

Capacity of two-layered satellite networks

Wireless Networks - Satellite networks have great potential in providing global ubiquitous broadband communication. In this paper, we explore the capacity of both single-layered and two-layered...     

Multiservice on-demand routing in LEO satellite networks

In this paper, a distributed on-demand routing protocol for Low Earth Orbit (LEO) satellite systems, named multiservice on-demand routing (MOR), is proposed and evaluated. The proposed protocol adjusts the routing procedure to the QoS requirements of different traffic classes. The performance of the MOR protocol is compared to the unique proposal for traffic class dependent routing in the literature and the good characteristics of the proposed scheme are corroborated by ample simulation experiments, where significant gains in performance are witnessed.     

Performance of packet networks in satellite clusters

The authors introduce an approximate performance model for a packet switched satellite cluster consisting of m satellites interconnected through intersatellite links. The satellite cluster performance is expressed in terms of mean delay, throughput, and overflow probability. These performance measures are obtained as a function of the system load, traffic distribution, and system configuration in terms of the number of uplinks, number of buffers, number of transponders, and the intersatellite link capacity. The results obtained from the analytical model were within the confidence intervals of the simulation results obtained with a 99% confidence level. The analysis can be used to investigate the sensitivity of the system performance as a function of the system configuration     

Digital speech networks

Digital techniques, already widely used for transmission of data, are now being introduced in the field of voice communications. By appreciating some of the long-range implications of this trend we can help point the way towards appropriate usage of this developing technology for improved customer service. This paper focuses on the voice problem and the possibilities offered by complete digitization of the voice signal immediately following the microphone. Included in the discussion are a summary of the properties of the speech signal and its potentialities for efficient transmission, a survey of the existing voice digitization algorithms, some examples of voice digitization implementations, and a brief treatment of voice packetization. There are some comments, near the end of the paper, on the possibility of digitized-voice inputting to, and outputting from, computers in an integrated telephone-computer network.     

Digital signal processing in communications satellite payloads

Satellite on-board digital signal processing (DSP) offers the potential for significantly improved performance in certain satellite communications system scenarios in terms of system capacity and link quality. On-board DSP functions include digital beamforming, frequency multiplexing and demultiplexing, interference suppression, signal level control and, in a regenerative system, modems. The authors review the status of DSP in communications satellite payloads, focusing on the system advantages, some basic algorithms, and application specific IC implementation issues. As a specific illustrative example an advanced land mobile system is described which features digital beamforming and associated digital signal processing to achieve significant gains in power efficiency (and hence capacity), frequency reuse and flexibility to response to changing traffic scenarios     

Interactive channel for multimedia satellite networks

Multimedia, including Internet traffic, can currently be multiplexed within the DVB/MPEG-2 formats and delivered direct to home users. Traditionally a slow terrestrial telephone link between the user and Internet service provider is used to request data. A direct return channel system will facilitate users' high-bit-rate bidirectional communication via satellite. The return link could be used for the fast Internet access or large data exchanges that will be necessary in a multimedia world. The satellite system not only removes the need for wires but also increases transfer speeds. Satellite interactive terminals can establish network connections via satellite and a ground-based hub. The DVB/MPEG-2 format carries up to 45 Mb/s in the forward link, and a multifrequency time-division multiple access scheme allows up to 2 Mbit/s in the return direction. The return channel of the interactive channel for multimedia satellite networks underwent final standardization by ETSI in early 2000. This article reviews the system concept of a typical implementation. The key features of the return channel air interface, from transmission parameter to login procedure, are explained. In general, Internet packets are expected to be carried via DVB/MPEG-2 in the forward direction and via ATM in the return direction. The IP transportation techniques are described     

Transport protocols for Internet-compatible satellite networks

We address the question of how well end-to-end transport connections perform in a satellite environment composed of one or more satellites in geostationary orbit (GEO) or low-altitude Earth orbit (LEO), in which the connection may traverse a portion of the wired Internet. We first summarize the various ways in which latency and asymmetry can impair the performance of the Internet's transmission control protocol (TCP), and discuss extensions to standard TCP that alleviate some of these performance problems. Through analysis, simulation, and experiments, we quantify the performance of state-of-the-art TCP implementations in a satellite environment. A key part of the experimental method is the use of traffic models empirically derived from Internet traffic traces. We identify those TCP implementations that can be expected to perform reasonably well, and those that can suffer serious performance degradation. An important result is that, even with the best satellite-optimized TCP implementations, moderate levels of congestion in the wide-area Internet can seriously degrade performance for satellite connections. For scenarios in which TCP performance is poor, we investigate the potential improvement of using a satellite gateway, proxy, or Web cache to “split” transport connections in a manner transparent to end users. Finally, we describe a new transport protocol for use internally within a satellite network or as part of a split connection. This protocol, which we call the satellite transport protocol (STP), is optimized for challenging network impairments such as high latency, asymmetry, and high error rates. Among its chief benefits are up to an order of magnitude reduction in the bandwidth used in the reverse path, as compared to standard TCP, when conducting large file transfers. This is a particularly important attribute for the kind of asymmetric connectivity likely to dominate satellite-based Internet access     

Towards SDN/NFV-enabled satellite networks

The telecom community is during the last years witnessing a paradigm shift towards the virtualisation/ “softwarisation” of the network infrastructure, mostly driven by the concepts of software defined networking (SDN) and network functions virtualisation (NFV). At the same time, satellite telecommunication technologies, although rapidly advancing in various fields, have not so far adequately followed this trend. The paper investigates the applicability of SDN and NFV technologies to satcom platforms and determines the benefits and the challenges associated with the integration of satellite infrastructures into future software-based networks. To that end, it identifies specific use cases which clearly benefit from the softwarisation of the satcom network and proposes a functional architecture for federated satellite-terrestrial software-based networks. The architecture is implemented in a lab environment which is used to validate some of the proposed use cases. Furthermore, a techno-economic analysis is conducted, which presents clear economic benefits via the introduction of SDN and NFV in the satcom ecosystem.