Rapid advances made in the telecom world, specially in the last two decades, shock conventional minds. With different technologies and services converging these shocks are but inevitable.

Technologies and services like telecommunication, data transfers, television and related information, were earlier handled by different media using diverse technologies. But the Internet and development of access technologies, has led to these services being offered via one media. A telephone line could start offering TV services even as a cable connection enables the user to transfer data and make phone calls. It's a wild world out there.

Here then are frequently asked queries about some of the key technologies and systems that currently dominate the telecom service providers' arena. They represent the front-end telecom services. Details concerning the network and equipment manufacturers and the vendors who support these services will appear in a later issue.

PSTN
The PSTN or the switched networks have been the basic structure supporting telecom growth. In the nineteenth century when telephones caught the consumer fancy, they were merely direct lines connecting one place with another.

It was Almon B Strowger in New York who visualised the concept of circuits, switching and telephones with dialing facility. This instantly caught commercial fancy and telephone networks expanded all over the world. This metamorphosed into the telephone exchanges of today. The technology has evolved through the years even as cabling systems, materials and computers are changing the rules of the game.

A conventional PSTN system is quite like the one being operated by the Department of Telecommunications (DoT) and MTNL in India. In this system, voice from a terminal equipment or the telephone instrument is connected to a switching system by a cable, by a circuit or a line. A trunk circuit connects two switching systems.

Switching is required to interconnect central offices through inter-office trunks and tandem trunks. Central offices are also connected via trunks. In populated areas, a tandem office is used to minimise the number of trunks that a call must be routed through to reach its destination. Toll trunks are used to connect the central office with all the centres.

Also termed as basic services, the telephone service is fixed in nature. Off-late various value-added services are also being offered by the PSTNs.

Internet protocol
Circuit switching continues to be a driving force in the communications business. But then the concept of packet switching has revolutionised the way we communicate. The Internet protocol or IP networks took off in the late ‘60s launched by the US Department of Defence to allow the computers to talk with each other. Data was crunched into packets, sent over networks and re-assembled. It was in the late ‘80s that the commercial potential of the world wide web was realised and brisk developments thereafter is history.

One of the reasons for the popularity of the Net was that it was an open system. Computers' speaking with computers was not a new phenomenon when the protocol was first established. Data transfers were being made over proprietary networks. But then as mentioned earlier, the Net is an open system. Just about anybody adhering to the protocol, can latch on to the system and work.

Transparent technology and developments in compression techniques have resulted in newer advantages. Voice, data and multimedia can now be transferred over the Net. Development in access technologies has seen an unprecedented demand for cheap, high-speed Internet access. TV cables, electric utility wires and weather balloons are being used to provide high-speed Net access. This is thanks to the development of asymmetrical transfer methods which facilitate enhanced overall access speed - downstream or source to consumer data is faster than the upstream speed.

All these factors have then made cheap real-time multimedia transfers over distances a reality. And, Net telephony or Voice over IP (VoIP) is a very potent threat to traditional circuit switching businesses.

Wireless
Wireless radio or sending voice signals was an invention of the late eighties. The first 'walkie-talkie' or mobile communication system was developed in the ‘30s and was considered to be a practical application. The first commercial wireless telephone service became operational in 1946. But, systems then were bulky in size and difficult to use.

Repeated innovations by companies like Bell Laboratories saw the industry blossom. The major products apart from cellular services included the paging services and radio trunking services which allows for long distance wireless access. The latter service is still in the nascent stages in India. As digital technology evolves and permeates into the radio trunking services, it's utility will grow.

But the technology that demands attention today is the wireless in local loop or WLL. Often known as fixed wireless access or fixed mobile access, this technology is being accepted globally. This technology allows the users to be mobile using a wireless in short distances. Cables connect long distance trunk circuits and then transmitters relay them over short distances. The WLL technology is cheap and popular and can be implemented at great speeds if a long distance network exists. But then the quality of service, add experts, does not compare well with other cellular technologies.

Mobile/ Cellular
Mobile or cellular services gathered momentum in the late 80s. But the basic technology was in place in the forties itself when Bell Laboratories developed a 'cell' system to handle multiple calls. Each city was divided into small cell sites with equipment that could hand over voice signals to another as the user moved from one location to another. The development of the transistor and then the micro-chip saw instruments becoming lighter and capable of delivering quality sound.

Cellular technology then branched out into two main sub-sets - code division multiple access (CDMA) and the global standard for mobile (GSM). In India, we have the popular GSM900 standard.

While this was the first generation in mobile communications, the second generation was where signals could be digitised (zero and one). Digitisation of signals saw a slew of services like call waiting, forwarding and, line identification.

Currently, the third generation or 3G is evolving. 3G technologies will see the mobile handsets mimicking a PC. Besides sound, there could be data and multimedia transfers via the Internet. Users could surf the Net at relatively high-speeds using their mobiles. Experts say that a full fledged 3G would be a reality in the next three to four years.

Satellites
Satellites for communications have been in use since the mid-60s. For a decade or so, satellites carried the bulk of international telephone calls, which they still do on small routes and in developing countries. VSAT (very small aperture terminals) networks also provide communication pathways for big companies, ships, and for disaster relief.

Meanwhile, VSATs have been gaining popularity, especially in developing countries. In some countries, the existing telephone network just need to be expanded slightly. VSAT networks are being implemented to interface transparently with the existing analog network. Ethiopia, Kazakhstan and Russia have commissioned such networks thereby allowing for prompt provision of new and improved lines in their urban and semi-urban regions. Subscribers include local factories and shop owners, mining operations and international organisations.

At the high-tech end of the satellite market is the global mobile personal communication systems (GMPCS). The technology, boasts of enabling users to have one number that could be reached anywhere in the world. Mind you anywhere!

Currently, there are doubts being expressed over the commercial viability of these systems. This is especially so after the debacle of Iridium, a consortium led by Motorola. However, once the technical and commercial snags get ironed out, satellite communications could be a force to reckon with. The driver in this case would be the huge demand for high-speed broadband services that these satellites could deliver.