UNIVERSITY OF PENNSYLVANIA - AFRICAN STUDIES CENTER
AN OVERVIEW OF THE PUBLIC TELEMATIC
AND DATA TRANSMISSION SERVICES
AVAILABLE WITHIN SOUTH AFRICA
by Mr MJ VELLA
Some twenty five years ago the only non-voice telecommunications services in existence in South Africa were the telex service, and the data transmission service operating at speeds of 300 and 1200b/s. Ten years later the situation had changed inasmuch as data transmission speeds had increased - albeit in limited numbers -to 64kb/s. Today speeds as high as 2Mb/s are commonplace, and the non-voice product portfolio of Telkom includes more than a dozen services, with other offerings in the pipeline. The rapid growth which has been experienced in the telematic arena, both in terms of technological development and demand for service, can be expected to continue, driven by the demands of the business community and the emergence of new areas of application, such as the need to apply these technologies for developmental purposes.
The aim of this paper is to give a brief overview of the public telematic and data transmission services offered by Telkom, and the direction in which these can be expected to evolve.
2.0 Basic Telecommunications infrastructure
Given the dependency of data transmission and telematic services on the basic transmission infrastructure it is considered necessary, before focusing more specifically on Telkom's non- voice services, to briefly sketch the situation in so far as the basic telecommunications infrastructure in South Africa is concerned.
2.0.1 Telephony infrastructure
From a telephony viewpoint, the country is served by a total of approximately 1 600 exchanges, of which 60% are digital. The remaining electromechanical units are gradually being phased out and replaced by more modern electronic units. The electronic units are to be upgraded shortly in order to be able to support narrowband ISDN, a service which is not currently offered.
2.0.2 Transmission infrastructure
Telkom's transmission network has evolved over a number of years. It started off being completely analogue, with microwave being used to support the long distance routes, and FDM systems working over open-wire routes being used regionally. Starting in the early 1980's, the transmission network has been progressively digitised. Today 93% of the total transmission infrastructure, the total size of which is 100 million circuit -kilometres, is digital. Widespread use is made of optic fibre, which accounts for 63% of the installed capacity, with a current installed base of roughly 200 000 fibre- kilometres. Digital microwave accounts for 13% of the installed capacity, and the remaining 24% is accounted for by PCM systems, working over junction - or Z-screen cables, in the local and multi-exchange networks. The existing digital infrastructure is predominantly PDH and it is planned to continue to use this to support basic voice services with an SDH overlay being progressively established to support data transmission and similar high-profile services.
2.0.3 International Links
Telkom's International network comprises terrestrial -, satellite - and submarine cable links to 57 countries. Switching is achieved by means of two digital switches both situated in Johannesburg.
The terrestrial links are mainly in use to our neighbouring states. Both analogue - and digital microwave as well as optical fibre systems are used to provide these routes.
Satellite links are provided by means of three earth stations situated approximately 60 km west of Pretoria. The Intelsat satellites located at 60-, 335, 5- and 342 deg east are used and links are implemented by means of Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA) and Intermediate Data Rate (IDR) carriers. All of the services traditionally carried over telephone lines are supported and since the vast majority of circuits are digital (in excess of 90%), 64 - and n*64 kbps data lines can be (and are in fact being) provided to most destinations. All three earth stations are also equipped to transmit and receive analogue video material to and from International destinations. Two additional earth stations were built recently; one to restore the SAT 2 submarine cable when required and the other to act as a maintenance backup unit to the other earth stations. VSAT hubs were recently established, and both Personal Earth Station (PES) and Telephony Earth Station (TES) services can now be offered.
Submarine cable links are provided by means of the SAT 2 optical fibre cable. This runs from Cape Town in South Africa to Funchal in Madeira and El Medano in Spain. From these two landing points traffic is extended to various destinations in Europe, the United Kingdom and the United States of America by means of other submarine cables and terrestrial systems. SAT 2 is co-owned by 14 countries with South Africa being the major investor.
From South Africa direct routes presently exist to 15 African countries and during this year direct routes will be introduced to 5 more. An interesting development is that several of these are planned to either convert to or open up as digital carriers during this year.
Having taken a brief look at the national telecommunications infrastructure and links to the outside world, we will now move on and consider the non-voice services offered by Telkom.
3.0 Text Communication Services
Text communication has been an important telecommunications medium ever since the first telegraph line was installed in South Africa in 1860. Text services, however, only developed into a major source of revenue after the introduction of the automatically switched national and international telex and gentex services in 1969.
The telex service was enhanced by the replacement of the electromechanical exchanges with fully electronic units during the period from 1979 until 1983. This resulted in the country having one of the most advanced telex services in the world, and paved the way for the further enhancements to the service which took place during 1986 when additional features such as multi-address, message headers, delayed delivery, and call charge information were introduced.
Phasing out of the older mechanical T100 telex terminals began in 1978 when the first electronic T1000 terminals were introduced. Since then the entire network has been equipped with these machines and an even more advanced terminal, the T1200, has also been introduced, providing the user with enhanced editing features and all the modern requirements such as delayed delivery and multi-address.
The teletex service was introduced in 1983. The service initially provided full access to the local teletex network and the international telex service. During 1984 it was also extended to provide international access to the USA and those European countries supporting the teletex service. The service is now linked to 13 major countries.
Due to the demand for cheaper services and the large number of personal computers in the field, telex and teletex interface units have been developed locally to enable a standard personal computer to access the telex and teletex services.
Although the telex service is sometimes considered to be out-dated, it still remains one of the most reliable communication mediums worldwide, particularly in sofar as communication to many less developed countries is concerned. With the advent of FAX the telex service has moved into decline, but for the above mentioned reason it is considered that it will continue to be used - albeit to a diminishing extent - for some years to come.
4.0 Data Transmission Services: Leased Lines
Data Transmission in South Africa began in the mid 1960's with the installation of dial-up and leased line modems operating at 1200 bits per second. The rapid development in data communications equipment was driven by the requirements of the business community for higher transmission speeds and more flexible methods of communication. Today analogue data services have developed to the stage where speeds of 9 600 bits per second and higher are commonplace.
The digitisation of the South African telecommunications infrastructure, both switching and transmission, led to the decision in 1985 to implement a dedicated digital data transmission network called DIGINET to support the requirement for data transmission at speeds up to and including 64 kilobits per second. This service has proven to be extremely popular and is still growing at 20% per annum, due primarily to the better performance that can be realised over the digital transmission network and its cost-effectiveness over long distances. Diginet was further enhanced in 1988 by the introduction of the Diginet-Plus service that provides transmission speeds up to and including 1984 kilobits per second, in multiples of 64 kilobits per second.
Diginet is a modern, fully digital data transmission service which, in contrast to the relatively static analogue leased line service, is growing very rapidly. There are currently 60 000 customer terminals connected to the Diginet network, which consists of 33 Digital crossconnects and 3 400 multiplexers spread over 475 exchange areas and several hundred customer sites.
In order to meet the need to provide Diginet services in remote parts of the country which have not yet been digitised, a "home grown" solution - the so called "long-line network terminating unit" was developed. This unit allows a Diginet circuit to be extended beyond the periphery of the Diginet infrastructure, via the analogue infrastructure feeding the particular remote sites. Although speeds are presently limited to 9 600 b/s, the major benefit gained is that the greater reliability and maintainability of the digital infrastructure can be exploited, with only the end section of the circuit being subject to analogue degradation.
In addition to the Diginet and Diginet-Plus offerings, which provide a managed leased line service at speeds up to 1984 Kb/s, an unmanaged leased line service, Megaline, offering speeds of 2 Mb/s, 34 Mb/s and higher is available.
5.0 The "Last mile" - the use of radio
It is generally true that the "last mile" represents the greatest challenge in feeding services to remote areas, particularly at the higher operating speeds. Telkom is increasingly making use of digital radio to address this difficulty.
A range of equipment has been acquired/developed which makes it possible to extend a 64 Kb/s Diginet circuit over any 64 Kb/s digital channel terminating in a standard G.703 interface, and digital radio offers a possible solution for providing such channels.
In order to feed a single 64 Kb/s diginet circuit to a remote location, a basic point-to-point digital radio link is used.
In order to be able to feed such circuits to multiple locations in a particular remote geographic area, time-division-multiple-access (TDMA) radio is used. This in fact represents a very useful solution, as TDMA systems are increasingly being deployed in remote areas in order to provide basic telephony services, and these same systems can then be used to additionally support 64 Kb/s data circuits as the need develops.
6.0 Data Transmission Services: X.25 and Frame Relay
The packet switching needs of the South African public are met by SAPONET-P, Telkom's X.25 service. The service is provided by means of a network of packet switches, interconnected by digital trunks, installed in 23 of the larger centres. Speeds of up to 48 Kb/s are supported. Access into the closest packet switch is provided by means of a leased line, either baseband, analogue, or (predominantly) Diginet. Saponet-P is connected to 130 packet networks in 59 countries worldwide.
A Frame Relay network has also recently been established, and is proving to be extremely popular as users exploit the advantages of this efficient protocol. Speeds of up to 2 Mb/s are offered.
7.0 Asynchronous access to X.25 and other services
The rapidly increasing number of asynchronous terminals and personal computers necessitated the introduction in 1983 of public packetising and depacketising facilities. The so-called "Triple-X" service was therefore introduced.
The service complies with the X.3, X.28 and X.29 recommendations, and routinely supports low-speed (up to 2 400 b/s) access into the Saponet-P environment, by means of leased access circuits. 9 600b/s access can be provided on request.
Telkom's home-grown "Easy Access" service provides asynchronous dial-in access and dial- out connections at data transmission speeds up to and including 2400b/s. The dial-in facility allows customers to access a selection of Value Added Services offered by the network whilst the dial-out facility enables users to economically perform data transfer nationally using dial-up facilities. The network was made available to the public in January 1990, providing access to two Value Added Services, namely Triple-X and Beltel. In addition to these two services, access is currently available to Videotex, Teletel and X.29 gateways.
The network currently consists of 65 nodes at 60 sites countrywide, each having its own access group of telephone numbers, arranged in hunt groups. The service is currently being upgraded to support speeds up to 14,4 Kb/s.
8.0 Switched Multimegabit Data Service (SMDS)
The rapid proliferation of local area networks (LANS), as well as the ongoing development of bandwidth-intensive computer applications, has resulted in a growing demand for a high speed bandwidth-on-demand service. In order to meet this demand, a pilot Metropolitan Area Network (MAN) based on the DQDB protocol, has been installed in Cape Town, and is being used to support an SMDS service.
The field trials on the system have been highly successful, and a full commercial service is to be launched within the next few months. A second MAN is presently being installed in the Pretoria-Johannesburg area, in order to provide SMDS service to the industrial hub of the country.
It is also worth mentioning that Telkom is presently engaged in installing a pilot ATM network - ATM being the basis of a future broadband ISDN. This pilot system will initially be used to support telematic services, and to link up the Metropolitan Area Networks supporting the SMDS service, and at a later stage, once various technical issues have been resolved, the technology will be used to carry telephony traffic.
9.0 Beltel - Telkom's public videotex service
Beltel is a Public videotex system which is accessed by dialup into the Easy Access system, or directly into the Beltel system itself. The network currently supports 4 information transfer standards namely, ASCII, Prestel, CEPT and Teletel, with Prestel being the most popular standard. Information on Beltel can be accessed either by means of a Minitel terminal, or by means of specialised software packages (such as PC-BEL) running on conventional PCs.
Various other locally developed software packages are also available to the public; IPBEL is a software package for Beltel Information Providers to allow off-line editing, and automatic uploading and reading of their databases. TSBEL is file transfer software which allows Information Providers to store standard PC files on Beltel. These files can be downloaded by any Beltel user accessing the system with the PCBEL software. ECBEL was developed to assist Services Providers in providing gateway services on Beltel.
Beltel currently has a user base of 45 000, a figure which is growing at 25% per annum.
10.0 Electronic Messaging: Telkom 400 and TelkomEDI
Telkom 400 is Telkom's X.400-compliant electronic messaging system, which was introduced in 1992.
The system provides both a public inter-personal messaging service (IPMS) and a store and forward message relay function between private management domains. Access to the system is via Saponet-P, either via X.25 links, or via Easy Access.
In addition to providing IPMS facilities and acting as a hub linking PRMDs and providing access to ADMD's in other countries in the world, the system additionally provides interworking with Telkom's other telematic services. Direct interworking is provided with the Beltel system, and telematic access units provide for bi-directional access between the Telkom 400 service and the telex and teletex services, and outgoing access to group 3 facsimile terminals. Any electronic messaging client, be it an Easy Access, private management domain or Beltel client, can submit messages to any Telex, Teletex or facsimile terminal for direct delivery of messages. Telex and teletex clients can also address messages to any terminal accessible from the Telkom 400 service.
Incoming FAX access, as well as FAX store and forward facilities, are to be provided shortly.
Basic X.500 facilities are already available on Telkom 400, and these will be enhanced as the standards evolve.
Apart from the above mentioned applications, it is Telkom's view that X.400 will rapidly become a major carrier of both national and international Electronic Data Interchange (EDI) traffic. It is for this reason that TelkomEDI was introduced, with EDIFACT support, dedicated EDI mailboxes, longterm archiving, and a host of other facilities.
This paper has attempted to sketch the situation within South Africa in so far as non-voice telecommunications services are concerned. Telkom believes that it has a strong base of technological expertise and a solid, established core infrastructure - an infrastructure which is being progressively expanded into the most remote areas of the country. With the rapid development of suitable applications, it is our view that this infrastructure and technological know-how can and will be increasingly used to the benefit of all the peoples of our country. It is our intention that Telkom should play its full part in this regard.
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