Advanced Solutions For Distance Learning

Computer Communications 26 (2003) 423–429 www.elsevier.com/locate/comcom

Advanced solutions for distance learning via satellite Mario De Blasia,*, Carlo des Doridesb a

Universita` di Lecce, Via Monteroni, 73100 Lecce, Italy Alenia Spazio spa, Via G.V. Bona 85, 00156 Rome, Italy

b

Received 12 May 2002; accepted 13 May 2002

Abstract Distance learning has aroused more and more interest during the last few years due to the convergence of several factors, namely the growth of education as a key driver for socio-economic development, the remarkable step forward of telecommunication technology and the number of people involved in the education process itself (user basin). A major obstacle has resulted to be, in many cases, the cost factor induced by the telecom transmission cost which has often made the distance learning system non-viable. This consideration has directed people’s attention to satellite systems which, due to their intrinsic peculiarities, well answer the most important requisites: wide coverage area, high geographical penetration, low unit cost when operating in broadcasting mode, mature technology and so affordable terminal receiving cost. In this direction an interactive solution is offered by SkyplexNet,1 an advanced satellite telecommunication platform based on innovative space technology and integrated with versatile network management functions. SkyplexNet well answers distance learning service requirements, providing an asymmetrical connection to the user, namely a high rate on the forward (receiving) link via satellite and a low rate on the return (interactive) one via a terrestrial modem: this paper describes the main functions of the system highlighting its operational characteristics as well as the tele-education application which allows the creation of new pedagogical education models. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Skyplex; Distance learning; Satellite based telecommunication

1. Introduction SkyplexNet platform is based on a quite innovative technology, namely the Skyplex on-board multiplexer [1], designed and developed by Alenia Aerospazio and presently operational on Eutelsat Hot Bird 5, placed at 138E. The basic idea is to avoid any kind of centralisation regarding the management of the space resource, making available the direct access to the satellite transponder through relatively simple and inexpensive up-link stations. The key feature of the Skyplex system is then the possibility to avoid the cost of long and expensive terrestrial tails to reach the master up-link station. Although Skyplex was initially designed for TV broadcasting, it has revealed during the course of its development enormous advantages also regarding the IP based applications, due to the MPEG2-transport stream * Corresponding author. E-mail addresses: [email protected] (M. De Blasi), desdorid@ roma.alespazio.it (C. des Dorides). 1 SkyplexNet has been co-financed by ESA, the European Space Agency.

inherent capability to transport also IP packets. The SkyplexNet system specifically addresses such emerging potentialities, thus revealing its capacity to exploit several forms of WWW multimedia contents. The SkyplexNet system optimises separately the two basic links of a generic satellite broadcasting system: the first between the earth station and the satellite and the second between the satellite and the end-user receiving station. This is because Skyplex is capable of re-combining a number of up-streams into a single 55 Mbps down-link stream compatible with DVB-S standard; end-users do not perceive any difference between a Skyplex transmission and the one operated through a usual transparent transponder. Firstly operating on an experimental basis on Hot Bird 4, Skyplex technology is now operating on a commercial basis with Eutelsat Hot Bird 5 with three transponders while eight more transponders, with increased capabilities, will be embarked on Hot Bird 6. In the geographically distributed access to Skyplex repeater, the network management and control system have well distinct duties from those required in a usual

0140-3664/03/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 4 0 - 3 6 6 4 ( 0 2 ) 0 0 1 6 2 - 7

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satellite transparent transponder. More specifically, the overall network management maintains the functional control over the satellite access (co-ordination, spectrum management, etc.), but has many more responsibilities regarding the telecommunication transmission. 2. SkyplexNet system architecture The SkyplexNet system will be described on the basis of its major component elements2 involving service provision, namely the service centre, where the content is composed, and the client platforms, where the service is received. The overall functional view of the SkyplexNet system architecture is shown in Fig. 1 which follows. The picture also includes the network operation centre (NOC) whose primary mission is to offer a set of services to manage the Skyplex_Net system so that the appropriate transponder quota is guaranteed to each service provider. Major components of the NOC are: (i) (i) (i)

CMS is the customer management system NMS is the network management system NCS is the network control system

3. The SkyplexNet service centre architecture The overall functional view of a service centre architecture is shown in Fig. 2. A user of the service centre may be an end-user or a content provider. The nature of the interaction of enduser and content provider with the service centre is similar but the functions are complementary. The requests of the end-user are mainly receiving services whereas the requests of the content provider are meanly transmitting services. The service centre (SC) is composed of the following modules: Internet access server (IAS) that is the interface between the SC and Internet. Its aim is to manage relationships with end-users. Transaction service (TS) system that manages: † † † † † †

Information about the end-user Billing Tariffing Contract management User troubleshooting support Session logging and monitoring

Service scheduler (SS) that manages resources allocation and requests the NOC for bandwidth reservation IP gateway (IPG) that: 2

SkyplexNet project internal technical document.

† Constitutes the interface between service centre and uplink earth station † Packs data in DVB format and transmits them to the satellite transponder Content server (CS) that manages the acquisition of multimedia content from internal (hosting case) or external content providers Conditional access (CA) system that provides keys for scrambling of DVB transport stream Packages exchange information directly or across intermediary data storage, like the data buffer resident in the IPG. The data buffer temporary memorises flows of multimedia contents arriving from the content server and directed to the IP gateway server. The data buffer provides to the service scheduler the possibility to guarantee the continuity of the audio/video streaming.

4. The distance learning service The Distance learning service is provided by a video communication service centre (VCSC) and is based on the concept that knowledge flows from the information provider (teaching/training centre) in form of: † live training session † study material on demand and the students/trainees gain that knowledge through two complementary means: † synchronous learning † asynchronous learning In synchronous learning, the interaction between students and instructor takes places during the live training session, at a time previously scheduled by information provider (i.e. palimpsest): the instructor and the student are synchronised. In asynchronous learning the interaction takes place between the students and the multimedia study material from a database at any time between lessons or even in place of the lesson itself for individually paced learners. The teaching process must also allow the students interact among themselves, to exchange information and experience and to be able to work as a team. Another dimension in distance learning services is the symmetry/asymmetry of communication channels. Asymmetric communication is inherent in any teaching/training program: † During live lessons, a great amount of information (realtime images, video clips, slides) flows from the instructor to the students, while small amounts of information flow randomly from the students to the instructor (such as when a student asks or answers a question).

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425

Fig. 1. SkyplexNet system architecture.

† When students are involved in asynchronous learning, they need access to a great deal of information (multimedia tutorial module). The students create and provide less information than they receive. The students shall receive the information flowing from the information provider (live lessons, study material) through one-way satellite broadcast channel and interact with the instructor or multimedia tutorial module or each

other using the two way Internet connection as return / interactive channel. 5. The distance learning client platform Two kinds of client sites can be identified: † Single end-user † Collective user

Fig. 2. Service centre architecture.

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The scenario in Fig. 3 shows the client site when distance learning subscribers are single users (students/trainees at home). Every single end-user shall be equipped with: † † † † †

PC Satellite dish Dial-up modem Smart card Set-top-box and parallel cable/DVB receiver board

The picture shows the presence of two kinds of single end-user: † users with integrated receiver decoder (IRD) † users without IRD Users with IRD (that is the set-top-box ), shall connect the set-top-box to the PC parallel port using a parallel cable. Users without IRD shall plug into their PC a DVB receiver board. DVB has two basic approaches to the problem of conditional access internetworking: multiple receivers, each with a single conditional access system (the ‘Symulcrypt’ route), and receivers with a common interface (CI), allowing for the use of multiple conditional access systems (the ‘Multicrypt’ route). The choice of route is optional. The CI is an interface between a standard PCMCIA module and a DVB receiver. The DVB – CI provides interchangeable plug-in CA smart card readers for DVB receivers. This allows several different CA technologies to be used on the same receiver.

The scenario in Fig. 4 shows the client site when distance learning subscribers are collective users (students/trainees in a remote lecture-hall). The LAN servers receive transport streams from the broadband channel, route live sessions or study material to PC end-users and send questions/answers of PC end-users to VCSC (teaching/training centre) via return channel (the Internet). The students/trainees at their PC interact with the LAN server via a 10/100 BaseT Ethernet. The LAN server shall be equipped with: † † † † †

Satellite dish DVB receiver plug-in PC card Common interface (CI) for conditional access Dial-up modem Ethernet card Every end-user shall be equipped only with:

† PC † Ethernet card In both cases it has been supposed that client sites have their own local Internet service provider (ISP). Optionally, Internet services may be provided by video communication service centre. 5.1. Client SW Interaction, whether synchronous or asynchronous, is very important for every person involved in the training process. The Distance learning SW enables the trainees/

Fig. 3. Single user scenario.

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Fig. 4. Collective users scenario.

students to interact with the instructor and among themselves during live sessions and to access study material (e.g. written in HTML format) on the remote VCSC, when they need any information. The video communication service centre appears to end-users as a website. Distance learning functions will be covered by the following packages:

† display the current material on the instructor’s PC to all trainees’ video displays † play audio or video tapes to the trainee † prevent all participating trainees from ‘surfing the web’ † send an URL to all participating trainees

† † † †

5.1.2. Interaction management This package enables the trainees/students to contact the instructor to ask and answer questions, during a live session. The trainees will be able to:

Course browser Interaction management Communication Corporate DVB receiver (collective user option)

Distance learning SW allows the instructor to:

5.1.1. Course browser This package enables the trainees/students to attend a live session, to view course material and to access that material in-between sessions. The trainee will be able to:

† register to attend a live session † answer multiple-choice questions prepared by the instructor and shown in a window on all trainees PC screen † request to speak with the instructor † contact the VCSC help desk

† View instructor during a live session (i.e. for synchronous learning) in a window on the PC screen † Record a live session (store it on a local hard disk) for asynchronous learning † Access the study material at any time of the day and download the selected material for asynchronous learning † ‘surf the web’ to locate course-related material

In the registration phase, trainees type their name, ID and other related information which may be necessary to access the distance learning service. If VCSC provides a pure multicast service, registered end-users are able to receive the service without notifying any information (like in push services). Instead, if VCSC provides a conditional multicast service, registered end-user are able to receive the service only after successful access.

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All trainees participating in the live session appear on an instructor attendance list. The instructor may be able to show the attendance list to all participating trainees. All trainees who request to speak will appear on an instructor booking list. The instructor may be able to view the booking list and select a trainee to contact or indicate to the trainees that no question will be answered at any given time. We have supposed above that VCSC provides a help desk to meet trainees’ difficulties, either related to the course material or to technical problems. 5.1.3. Communication This package enables the trainees/students to contact the instructor and other trainees. The trainees/students will be able to communicate by means of: † † † †

e-mail telephone chat audio-conference (i.e. voice over IP)

E-mail package will provide an asynchronous interaction: for example, instructor and trainees may subscribe to the same mailing list. Telephone, chat and audio-conferencing package will provide a synchronous interaction. If chat or audioconference services are provided by VCSC, it will be possible to route information from instructor to trainees/students maybe through the broadband satellite channel instead of the interactive ground channel (i.e. the Internet). 5.1.4. Collective user DVB receiver On the client site of a collective user LAN, distance learning SW provides each trainee/student with all the functions described above. The idea is to create a virtual classroom, with end-user PC located in the same room or in a campus. A corporate DVB receiver package, running on a LAN server, provides the following functions: † web-based interface for LAN clients † common live training sessions provisioning to participating end-users (synchronous learning) † live training session recording on its mass storage for asynchronous learning † multimedia study material caching for post access and/or download at any time by LAN end-users (proxy server like technologies)

6. Educational system A distinctive characteristic of SkyplexNet is its flexibility in accepting different didactic models. Completely

asynchronous, completely synchronous, or a mixture of these, allows training operators to add greater freedom to their educational system. The perspective is radically changed respect to some past and present distance learning systems, that ‘constrain’ people to be at distance, even when there is no need for this. In our opinion, the distance factor should be one further possibility that increases the value of an educational system. In the same manner, asynchronism should not be the characterising feature of an educational system, but it has to co-exist with synchronism and faceto-face dimensions. Another quality of an educational system is the independence from a single technology and from the owner of an infrastructure—a quality, this, that is desirable for any type of communication. SkyplexNet avoids any kind of centralisation regarding the management of the space resources, thus reducing the dependence on infrastructure owners. As far as the dependence on a single technology is concerned, integration is the solution. A technology is of value if it is easily integrated with complementary technologies. The cost trade-off also suggests resorting to integrated networks. Indeed, synchronism can be accompanied by multicasting, and, so, the use of satellites is economical. But asynchronism often is uni-casting and, in this case, satellites are more expensive than terrestrial systems. So, the best is to have both of them, terrestrial and satellite systems. The first implementation of a SkyplexNet-based distance learning system is the Telematic University, designed in the framework of the MODUS Project,3 that presents ‘a new dimension in multimedia distribution over satellite and terrestrial telecommunication systems’ [2]. It is worth considering that although cost-affordable, SkyplexNet-based educational systems require consistent investments, and their design has to be evolutionary with rapid changing technologies, able to incorporate them, as they are available and cost-competitive. To this regard, it should be noted that a remarkable step forward would be made through Skyplex on-board Eutelsat Hot-Bird-6, which will introduce new functional performance and induced market competitiveness such as: 1. Adoption of turbo-codes on the up-link, with a consistent reduction of earth station dimensioning and cost. 2. Increased granularity of the up-link carrier (up to 64 Kbps). 3. Ka frequency band adoption together with multi-spot technology (more spectrum available with induced reduction on capacity prices).

3

MODUS Project is run within ESA ARTES 3 program.

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7. Conclusion An innovative tele-education system, completely coherent with traditional face-to-face education, of which can be considered an enrichment, has been presented. It allows to transmit interactively, with good audio and video quality, in-campus lectures to homes and remote lecture-halls distributed in a wide area. In addition, there is a possibility of following the lectures on demand, in whichever moment after the in-campus lecture, and of integrating them with courseware, exercises via Web, chatting, access to databases and texts. This system uses SkyplexNet, an advanced affordablecost satellite telecommunication platform based on innovative space technology, namely the Skyplex on-board multiplexer, integrated with versatile network management functions. The SkyplexNet system has been described on the basis of its major component elements involving: service provision, namely the service centre, where the content is composed, and the client platforms, where the service is received.

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Cost considerations have been reported that suggested the adoption of integrated technologies, terrestrial and satellite system: argumentations for these choices as well as the remarkable further step forward that will be possible with Hot-Bird-6 have been presented.

Acknowledgments The work reported in the paper has been made possible thanks to the invaluable contribution of the partners involved in the team of SkyplexNet, namely: Skydata sp, GCS GmbH, ITS srl, University of Lecce.

References [1] F. Carducci, R. Novello, On board multiplexing: the Skyplex transponder and the multimedia highways, IAAA (1997). [2] A. Campa, M. De Blasi, F. Tommasi, A new dimension in multimedia distribution over satellite and terrestrial telecommunication systems, SoftCOM (2000).