Ashok Jhunjhunwala
Bhaskar Ramamurthi
Timothy A. Gonsalves

Indian Institute of Technology Madras, India



in
IEEE Communications Magazine, December 1998


ashok@tenet.res.in
bhaskar@tenet.res.in
tag@tenet.res.in
Phone / FAX : + 91– 44 – 235 2120

It is not viable to expand the telecom network in India substantially at the prevalent level of per-line investment. However, systems based on new technologies, many developed in India, promise to more than halve the investment required. This article looks at the telecom scenario, the new technologies, the Indian products based on these technologies, and the cost reductions they promise. The provision of widespread Internet service with low access tariff is an important aspect of the new approach.

1 Introduction

India, along with other large developing countries, is currently engaged in rapid expansion of its telecommunications infrastructure. In an attempt to speed up the process, find private finance, and introduce competition, the government has licensed one private Basic Services Operator (BSO) in each state, to set up an independent telecom network in the state. The inter-state network and international links will be operated by the government-owned monopoly operator (DoT) for the time being. The DoT, of course, is already an operator in all the states, and is expanding its subscriber base every year.

Until now, the telecom network has been built along conventional lines, similar to networks in developed countries. The long-haul backbone network is mostly digital, and employs optical fibre, microwave and satellite links. The exchanges are largely electronic, with major cities (metros) having large 40,000-line switches. The local loop is copper-based, with extensive use of Remote Line Units to reduce copper length. The capital investment (hereafter referred to simply as cost) per line has also been more or less the same as in other countries.

Now that the BSOs are starting afresh to put new networks in place, they are looking at an array of technology choices that have become available over the last decade. These include new access technologies with a recently standardised interface to the main exchange, and with capability to provide inexpensive Internet service on a circuit-switched network. 

In this article, we will see how new technological developments are being leveraged to provide an elegant, service-rich, rapidly deployable, and cost-effective network. A persisting theme throughout the article is the cost of the solution. It will become clear that large-scale expansion will simply not occur unless a lower per-line revenue is sustainable, at least in the near term. This is feasible only if the cost per line is halved, to begin with, and goes down every year. It will be argued that products based on new technologies are making this a reality. Electronics will be seen to provide the solution for rapid expansion of telecommunications, as it has done with computing.

Section 2 gives a summary of some of the economic parameters that circumscribe our arguments. The current availability of telephones, the cost per line today, the income strata of the population, the urban/rural segmentation, and the realisable revenue targets, are discussed. Section 3 deals with the new paradigm in the telecom network. Attention is focused on the new access technologies, and their open interface to the switches, and on the provision of efficient Internet service. In Section 4, we describe some of the products developed in India to provide the new solutions outlined in Section 3. Innovations in the use of technology and standards, proposed originally in some cases for other applications, are shown to be the key in achieving low cost and richness of features. Section 5 concludes the article.

2 The Indian Telecom Scenario Today

India has barely 17.5 million telephones today. For a population of 970 million, this amounts to a teledensity of a little over 1.5 per 100. As shown in Table 1, about 25% of these telephones are in four metropolitan cities. Even though 74% of the population lives in rural areas, the number of village telephones is less than a few percent. The total number of Internet subscribers amounts to barely 1 per 10,000 population, mostly confined to the large cities. The number of long-distance circuits, even though now almost fully digitised (see Table 2 for details), crossed the 150,000 mark only in 1996.

The primary reasons for low teledensity are the high cost of providing a telephone and the limited revenue expected. The total investment required for each telephone today, assuming conventional technology, is more than $900 (see Table 3). This may not appear to be very large, but once one considers the 15% financing cost (interest rates for loans) prevalent in India and 15% operational, maintenance and obsolescence cost, a minimum yearly revenue of $270 per subscriber is required for the operator to break even. Once again, the amount does not appear to be very large. However, when viewed against the income levels prevailing in India, this amount is affordable only to a small number of people.

Table 4 provides the household income distribution in 1993–94. Even if the incomes are assumed to have increased in real terms by approximately 40% in the last five years, not more than 1 million households have annual incomes greater than $3,000. Therefore, spending $270 per year on a telephone is not possible for more than 1% of the population.

However, there is a broad middle class of 150 million people with a per-capita income of $400–700 in 1998. Such households would be willing to spend $50–200 per year on a telephone, plus perhaps $60 for Internet access. The middle class can be provided telephones and Internet connections either by large-scale subsidy, or by reducing the cost of telecom infrastructure by a factor of at least two. The question is: can technology be used in an innovative manner to reduce the per-line cost from $900 today to $400?

Before we delve into the role of technology in achieving such numbers, let us take a brief look at the expectation of the average Indian, keeping in view the 10–15 year lifetime of telecom equipment. Besides toll-quality Plain Old Telephone Service (POTS), Internet access at 28.8–64 kbps is essential. Video-conferencing at 64/128 kbps will grow in popularity as quality improves and cost drops. With the average population density in India being close to 400 persons per sq. km, the subscriber density ranges from 10,000 phones/sq.km in some urban areas to 5–10 telephones per sq.km in most rural areas [2]. Some sparsely populated pockets may initially require less than 0.5 telephones per sq. km.

The question posed in the previous paragraph can be rephrased now: can technology be harnessed to provide all these services and yet be low in cost?

3 The Role of Technology

We now examine the impact of changing technology on the major components of the telephone network, namely, the backbone, the switches, and the access network.

3.1 The Backbone Network

Until the eighties, the Indian long distance telephone network mostly used 4-wire or 6-wire analog trunks, along with FDM analog multiplexers. The total number of circuits available were barely 50,000 [3], and the quality of service provided by these links was considered unsatisfactory. The introduction of digital multiplexing, and later of optical fibre, changed this situation. While the quality dramatically improved, the cost to the operator also continuously went down.

Today, there are a number of manufacturers of optical fibre in the country. The cost of a 12-core burial-type optical fibre cable has come down from around $5,000 per km a few years ago, to barely $1,000 per km. SDH-1, SDH-4 and SDH-16 multiplexers and drop-and-insert equipment are being rapidly introduced in the network. Though WDM is not yet being used in a significant way, it is recognised that it can be introduced in future to multiply capacity.

Besides optical fibre, point-to-point digital microwave radio systems have played a significant role in expanding the Indian backbone network, and continue to do so. Useful where fast deployment is required, where the terrain is difficult, or to serve low-density or medium-density rural areas, these links are deployed with 8 Mbps, 34 Mbps, 140 Mbps, and now SDH-1, capacity. Several frequencies are used in the 2 GHz to 18 GHz band. Point-to-point radios are especially popular for short-haul feeder links. Much of the equipment is manufactured in India. The costs have again tumbled down over the years, with a 34 Mbps, 2 GHz, 30 km, link costing about $40,000 today including installation and tower costs.

To sum up, backbone technology is mature and the emphasis today, rightly enough, is on network expansion and the induction of a Q3-based Network Management System [4] for the network. The cost for providing a new high-capacity backbone network works out to barely $40 per subscriber line, assuming conventional traffic levels. All BSOs have planned the backbone network in the states along the lines described here.

3.2 Switch Technology

Until the early eighties, most of the exchanges in the Indian telecom network were electro-mechanical. The total number of lines in 1982 was about 2.4 million [3]. The exchanges were expensive, and the service could not be expanded to meet the demand primarily because of limited capital. It is here that the innovation of time switching [5] resulting in essentially non-blocking digital exchanges, came to the nation’s rescue. The size, power consumption, and per-line cost of the exchange, have come crashing down. The digital electronic exchange today consists of a switching matrix, processors (computers) with associated software, and subscriber and trunk line interfaces. The interface used on the trunk side today is the digital multiplexed 2.048 Mbps E1 stream. The introduction of Remote Line Units (as discussed in section 3.3) has lead to a bifurcation of the exchange into a switch core (also referred to as Main Exchange) and the Access Unit (AU). With this, the subscriber interface is also a digital multiplexed E1 line. Further, concentration of traffic at the AU reduces both the number of E1 interfaces required as well the size of the switch matrix at the Main Exchange. This, coupled with the revolution in IC technology, has reduced the hardware cost of the exchange significantly. 

The key element of the Main Exchange is therefore the software. Today, it is imperative that the exchange have Signalling System 7 (SS7) software, ISDN signalling software, advanced Operations and Management (including Network Management) software, and the ability to handle a fairly large number (say, 20 per line) of Busy Hour Call Attempts (BHCA). Further, it is also important to have provision for Intelligent Network (IN) services. But, most important, the core exchange should have V5.1 and V5.2 [6] protocol software to enable a third-party AU to be connected seamlessly to the exchange (see section 3.3.1).

With the Main Exchange technology becoming primarily software-intensive, the cost per line comes down when the usage base is high. It is expected that the Main Exchange without the Access Unit will cost less than $30 per line in the near future.

However, it is important to point out that in future the Main Exchange also needs to support Internet access, and provide Internet Telephony gateways and ATM interfaces for the backbone. These introductions could significantly change the functions and economics of an exchange. It is however not clear whether all these functionalities need to be designed into the Main Exchange, or could be provided by independent units co-deployed with the exchange, and interfaced to it using standard E1 interfaces with SS7/V5.2 signalling. The latter approach makes it possible to acquire these add-on units, specifically tailored to local requirements, from third-party vendors.

3.3 Access Technologies

Till the eighties, an exchange in an Indian urban area used to typically serve subscribers located upto 8 kms away. Consequently, the twisted pair copper used in the local loop would typically be 0.5 mm (SWG 24) gauge or higher. It was difficult to maintain such long loops and as the price of copper rose every year due to inflation, the cost of the local loop became a significant part of the total cost of the telephone network. The introduction of the Remote Line Unit (RLU) and Remote Switching Unit (RSU), therefore, came as a big boon. These units, connected to the Main Exchange using digital multiplexed E1 lines, often using optical fibre, would now serve subscribers located at most 3–4 kms away as shown in Fig.1. The RLU not only makes the local loop shorter, significantly reducing the cost, but also concentrates traffic, something hitherto done only at the exchange. At 0.1 Erlang per subscriber, a 1000-subscriber RLU would have a total traffic of 100 Erlangs and would only require 4 E1 links (120 lines) to the Main Exchange to provide 0.5% grade of service. This not only reduces the link capacity, but also reduces the size of the switching matrix in the Main Exchange.

3.3.1 V5.1 and V5.2 Access Protocols

The RLUs and RSUs, introduced from the late eighties onwards in India, reduced the cost of access to almost two-thirds of its earlier level. With the RLU–exchange link provided by a standard E1 interface, if the signalling protocol used (hereafter referred to as the Access Protocol) were also standard, one could marry third-party access units with the Main Exchange. However, with the subscriber line interface removed from the main exchange to the RLU, and with the switching matrix of the Main Exchange reducing in size, most of the cost shifted from the Main Exchange to the RLU. Switch manufacturers, fearing loss of revenue, preferred that the access protocol be proprietary, even though there was little technical justification for this.

Fortunately, ETSI, followed by ITU-T, took initiatives to standardise these protocols, referred to as V5.1 and V5.2 access protocols [6]. V5.1 is non-concentrating, whereas V5.2 is concentrating. Countries like India could now source/develop innovative access technologies, while obtaining the very best Main Exchange available. Further, it is now possible for small localised access sub-networks to be owned and operated by a host of franchisees. This business model has significant advantages in India from the financing and servicing angles, and has been very successful in the cable-TV business.

3.3.2 Digital Loop Carrier (DLC) System

Despite the use of RLUs, and the resulting shorter copper loops, the rising cost of copper has driven the total access cost upwards, reaching $350–450 per line today. At the same time, the cost of fibre was continuously going down. The Digital Loop Carrier System, shown in Fig.2, therefore became a cost-effective option. A typical DLC has a Central Office (CO) unit co-located with the exchange, interfacing typically to 500 subscriber lines. The CO unit digitises the signals on the subscriber interface, and multiplexes them on an optical fibre to a Remote Terminal (RT). The RT is a small battery-backed unit installed on the wayside, meant to serve subscribers within a radius of 500–800 m.

By reducing the copper loop to 500–800 m, the DLC results in lower cost than the RLU approach. The cost advantage is expected to increase over the years. In fact, the Indian government has contractually insisted that the private BSOs use copper only for the last 500 m, in an attempt to ensure that the most cost-effective access technologies are deployed.

3.3.3 Fibre Access Network (FAN)


 

The DLC, does not take advantage of the concept of the Remote Line Unit and the standardisation of the Access Protocol. In contrast, the Fibre Access Network (FAN) combines the advantage of DLCs and RLUs. As shown in Fig.3, the FAN (also sometimes referred to as Fibre in the Local Loop or FiLL) also has a CO unit. However, the interface between the main exchange and the CO unit of the FAN is now an E1 link with V5.1 or V5.2 protocol, and the CO unit is essentially a digital multiplexer. The subscriber line interfaces, both at the exchange as well as the CO unit in the DLC, are now avoided. Note that V5.2 provides a cost advantage over V5.1, since traffic concentration is now carried out at the RT, nearer to the subscribers.

A FAN can be deployed with multiple RTs in a star or a loop configuration as shown in Fig.3. The loop configuration has an advantage, since failure of an RT or a cable-cut can be healed by using the reverse link. Each RT serves typically 500 subscribers within a radius of 500–800 m, using copper, fibre or wireless, as shown in Fig.4.

Assuming that each subscriber offers a high load of 0.15 Erlang, a 500-subscriber RT generates a total load of 75 Erlang. This is easily served by 3 E1 links using the V5.2 protocol. Therefore, if an E3 signal at 34.368 Mbps consisting of 16 E1s is transmitted on the fibre, typically five RTs can be served by a FAN. On the other hand, using the SDH-1 signal that carries 63 E1s, many more RTs can be served.


 

3.3.4 Wireless Access Network

A wireless access network is advantageous in many situations. Firstly, wireless access promises quick deployment, an aspect particularly important to the new operator. Secondly, and perhaps more surprisingly, wireless access is proving to be more cost-effective than other access technologies as a permanent access network in mid-sized Indian towns and rural areas.

It is important to point out that Wireless in Local Loop (WiLL) should not be confused with mobile communications, which is meant for people on the move. Therefore, mobile systems do not have to cater to the exacting demands of high voice quality and high data rates placed on the home and office telephone. Further, the traffic is much lower than in the PSTN.

The requirements of Wireless in Local Loop are significantly different [7]. Not only must the voice be toll quality, it is also very important to provide high bit-rate Internet connectivity at 28.8 kbps or higher (see sections 2 and 3.4). Further, services like N-ISDN are also desirable. Besides, the WiLL system should cater to high traffic levels (0.1–0.15 Erlang per subscriber, in view of data communications) and should be able to serve a high density of upto 5,000 subscribers per sq.km in urban areas. It is also desirable that the system serve sparse rural areas where subscriber density is less than 1 per sq. km.

While doing all this, the cost must be low. The target for the total installed cost for wireless access in dense urban areas is $300 per subscriber and about $400 per subscriber for sparse rural areas. If multi-subscriber units are used, the cost target could be lower. It is also important that suitable back-up power be included in the subscriber unit to provide POTS service exceeding 16 hours, because long outages are quite common even in large towns. Further, it would be desirable to have a solar-powered subscriber unit with appropriate battery back-up for rural areas.

3.4 Internet Access

Today, Internet access is becoming increasingly important. Those who have an Internet connection have rapid access to all kinds of information, and this could create another divide between the haves and the have-nots [2, 8]. A telecom network installed today must therefore provide widespread access to Internet.

Internet access on the existing telephone network appears to be very simple—just connect a modem to your telephone line, dial up a router of an Internet Service Provider (ISP), and get going. Unfortunately, there are several problems with this approach, particularly in India. Let us examine these problems.

The PSTN in India, as in many other parts of the world, has been designed to handle 0.1 Erlang traffic per subscriber. While this is largely sufficient for voice telephony, Internet access complicates the matter. While a voice call lasts only for a few minutes, an Internet call usually lasts much longer, resulting in a load as high as 0.3 Erlang during the peak hour [9]. As the ratio of Internet users to total users grows, the network gets increasingly congested and fails to complete many calls.

The second problem has to do with the analog modem connection between the subscriber and the ISP. The analog link, especially in India, is just not reliable, mainly due to the variable quality of the copper local loop. This is even more so when a subscriber is located in a small town, where the trunk could also be analog. The quality of the dial-up link varies, and while it does provide 28.8 kbps connectivity occasionally, it often provides only 9.6 kbps or 4.8 kbps. Sometimes the modem link also drops, requiring redialling and a new connection. 

The call charges are very high for Internet access: $0.70 per hour for a local call in the cities, and as much as $30 for subscribers in rural areas making a toll call to an ISP perhaps 250 km away. The charges paid to the ISP are extra. Further, for the ISP, the investment in telephone lines, modems and router ports increases rapidly and linearly with the number of customers served.

In India, the solution to this Internet tangle is emerging in the form of a low-cost Remote Access Switch (RAS). Here, one explicitly recognises that the telecom network is a circuit-switched network whereas the Internet is packet-switched. The traffic on an Internet connection is very bursty. When such traffic is sent through a circuit-switched PSTN connection, the link utilization is very low. Yet, the circuit-switched telephone network is the only available mode of access at homes and offices. The Internet cannot avoid this network, especially when millions of connections are to be made. 

The RAS solution is similar in principle to Remote Access Vehicles presented in [9]. The RAS is co-located with the local exchange (or even RLUs or RTs of a Fibre Access Network, as we will show later) and connected to it using standard E1 interfaces. A subscriber desiring an Internet connection dials the RAS, and sets up a circuit-switched local call, as shown in Fig. 5. The call uses only the local exchange part of the PSTN. These exchanges today have very little blocking and can therefore handle the much longer holding-times (and therefore, higher Erlang traffic) of an Internet call. The RAS multiplexes the bursty data from several subscribers, and routes the data to the ISP router, using one or more leased or dial-up 64 kbps channels. It is desirable that the RAS dynamically adjusts the number of channels to the ISP depending on the traffic volume.

 

Let us assume that each Internet subscriber has a 56 kbps connection to the RAS with an average traffic as high as 10% of 56 kbps. With 100 active subscribers, only about nine 64 kbps PSTN connections are required between the RAS and ISP. The Erlang load on the PSTN due to the data calls is thus not more than the 0.1 Erlang value for which the network is designed.

The connection between the subscribers and the RAS could use an analog modem, or it could be digital, wherever ISDN access or digital wireless access are available. The connection could even be on a leased line, especially when the RAS is used in conjunction with a Fibre Access Network and placed next to its RT (see Section 4.2). 

The call charges can now be low, since only intra-exchange calls are being made by the subscriber. The small number of connections between the RAS and ISP utilise only digital trunks. They are very reliable and do not require modems. Assuming that upto 10 Internet connections use one 64 kbps slot, a single E1 link (consisting of thirty 64 kbps slots) to the ISP could handle 300 Internet calls.

The RAS provides a very attractive solution for the Internet tangle. Further, the additional cost per line due to the RAS is marginal (see Section 4.3).

4 Telecom Technology Development in India

The Indian DoT set up the Centre for Development of Telematics (C-DOT) in the mid-eighties with two immediate goals: to develop a small, rugged switch that would work in a tropical, non-air-conditioned environment in small towns and rural areas and to develop an advanced, large switch of 40,000 lines.

The first task was achieved very successfully, and most of the deployment in small towns and rural areas in India over the last few years has been C-DOT small switches. Today, there are few comparable products available in the world in their cost range (less than $40 per line).

The development of a modern large exchange was in line with similar efforts elsewhere. The goal here was to acquire design capability and reduce cost, capitalising on the software expertise in India. Today, C-DOT has a 40,000-line Main Exchange with SS7 signalling, ISDN capability, IN services and a fairly high BHCA. A benefit of the indigenous effort is the ability to react quickly to changing requirements. This long-term vision has already paid-off: while switch manufacturers all over the world are delaying induction of V5.2 in their switches in view of the perceived loss of revenue, C-DOT today has the interface ready and tested for deployment. The cost of C-DOT’s Main Exchange with V5.2 access is close to the target of $30 per line mentioned in Section 3.2.

Similarly, there have been several efforts in India over the last five years towards development of digital microwave point-to-point and point-to-multipoint radio systems. Capitalising on the development of microwave monolithic ICs, these efforts have brought down the costs to the low value mentioned in Section 3.1. A number of companies have also indigenously developed Optical Line Terminating Equipment and Digital Multiplexers for the backbone network.

4.1 corDECT Wireless Access Network

As the cost of the backbone network and switch core reduced substantially in the mid-nineties, the emphasis shifted to access technologies, especially wireless. However, the key to the successful large-scale deployment of a Wireless in Local Loop System in India is the right choice of technology. This must provide services comparable to wireline, and support high subscriber densities at a low cost, as discussed in Section 3.3.4. A study of available international wireless standards reveals that the choice narrows down to PCS (personal communication system) standards such as DECT, PHS and PACS [7]. These standards meet all the requirements, but have small radio range when deployed conventionally using microcells. While microcellular solutions are suitable for dense urban areas, innovative deployment strategies based on line-of-sight links are needed in other cases.

PCS-based wireless solutions are also attractive for India because of their low power consumption at the subscriber terminal. It is imperative that the subscriber unit provides a standard two-wire telephone interface with a total power in the region of a watt or two. Otherwise, battery back-up for long outages and solar-powered solutions for rural areas become just too expensive.

The Telecommunications and Computer Networking (TeNeT) Group at the Indian Institute of Technology Madras (IITM), located at Chennai, has been playing a key role in defining and developing access technologies suitable for India. Along with Midas Communication Technologies (Pvt.) Ltd., Chennai, and in partnership with Analog Devices, USA, for IC development, IITM took up the development of a DECT-based [10] Wireless in Local Loop system. 

The system, referred to as corDECT [11], has an interesting architecture, especially for its fixed part. The fixed part consists of a DECT Interface Unit (DIU) acting as a 1000-line wireless switching unit providing a V5.2 interface towards the Main Exchange, and weather-proof Compact Base Stations (CBS). These are connected to the DIU either on three pairs of copper wire carrying signal as well as power, or on fibre/radio using E1 links through a Base Station Distributor (BSD). The subscriber terminal is a wallset (WS), with either a built-in antenna, or a roof-top antenna providing a line-of-sight link to a CBS. The WS has an interface for a standard telephone (or fax machine, modem or payphone) and an additional RS232 interface for a computer, enabling Internet connection at 28.8/64 kbps. No modem is required, as all links between the WS and DIU are digital. 

All subsystems are built primarily using Digital Signal Processors (DSP), with the DIU having nearly a hundred DSPs. This soft solution, while cutting down development time and affording design flexibility, also ensures that the cost of the fixed part is no more than 15% of the total per-line cost in a fully loaded corDECT system. This allows deployment flexibility for both dense urban areas and sparse rural areas.

4.1.1 corDECT Deployment Scenarios

A new operator who wishes to initially deploy 5,000 lines in a mid-sized town/city in the very first year, would use the deployment scenario shown in Fig.6. All the DIUs are co-located with the Main Exchange and connected to it using the V5.2/E1 interface. Each DIU is connected to a BSD located on a roof-top at a suitable part of the town using a point-to-point 8 Mbps microwave link. At the BSD site, a cluster of about 12–15 CBS (each serving 50–70 subscribers at 0.1 Erlangs each), along with the microwave equipment, are mounted on a 15 m roof-top tower to serve an area of 2–3 kms.

This deployment uses no cables and can be made operational in 2–3 months at a total deployed cost of $350 per subscriber.

 

Later, the operator could increase the number of lines by using an optical fibre grid to connect BSDs to the DIUs. A CBS cluster now serves 1000 subscribers within a 700 m to 1 km radius. Here, many subscriber installations may not need line-of-sight links to the CBS. Once again, the total deployed cost of the access solution is under $350, including the cost of optical fibre cable and cable-laying charges.

The corDECT system also offers an excellent deployment opportunity for a small town and its surrounding rural areas at a similar cost. The mode of deployment is similar to Fig.6, except that the DIU itself is at the tower base and there is no BSD. To serve about 1,000 subscribers, an operator needs a tower (about 35 m high) in the town centre. The microwave link connects the DIU to the nearest trunk exchange. The base-stations now serve subscribers within a radius of 10 kms (see below, for enhanced range with DECT) using wallsets with roof-top antennas providing line-of-sight links.

Deployment in sparse rural areas is possible using the corDECT Relay Base Station (RBS). This provides a subscriber density as low as 0.5 subscriber per sq. km [11] at a total cost of $450 per line. A two-hop DECT link is used to provide connection to the subscriber. One link is from the WS to the RBS, which is mounted on a tower of typically 25 m height. The other DECT link is from the RBS to the CBS, which is also mounted on a tall tower (say 40 m). Both RBS and CBS use high-gain directional antennas, making a 25 km link possible. The 5 km maximum link distance due to the guard-time limitation of DECT is overcome by the use of auto-ranging and timing adjustment [12]. This technique is used in the RBS to support a 25 km link, and to enhance the CBS range to 10 km.

 

Finally, efficient transmission of packet-switched Internet data on a circuit-switched network is achieved by combining a RAS with the corDECT system, as shown in Fig.7. Here, the connection is digital all the way from subscriber to ISP. This approach differs subtly from the more generic one discussed in Section 3.4 in that an Internet call from a WS to RAS does not enter the exchange at all, but terminates in the Access Network itself. Only the concentrated IP traffic from RAS to ISP traverses through the exchange and PSTN.

4.2 Fibre Access Network

The TeNeT Group of IITM has also taken up the development of a cost-effective Fibre Access Network. Designed in accordance with the scheme discussed in Section 3.3.3, the Fibre Access Network again uses a new approach with an aim to provide, apart from the conventional POTS service, large-scale Internet connectivity at a cost affordable in India. 

 

As shown in Fig.8, low bit-rate digital subscriber link (LDSL) and high bit-rate digital subscriber link (HDSL) technologies are exploited in the short copper loop between the RT and subscribers. These relatively high-speed digital links carry both circuit-switched voice and packet-switched data. The digitised voice signals are directed by the Integrated Access Node (IAN) towards the RT and then to the Main Exchange. However, the Internet data is separated and passed on to a built-in RAS. After concentrating the Internet data from multiple subscribers, the RAS feeds it to the ISP via the FAN but bypassing the exchange. The subscriber terminal provides multiple telephone sockets and an Ethernet interface. This approach resembles the one described in the previous section in that Internet calls from the subscribers terminate in the IAN itself. The result is one of the most cost-effective means of providing medium and high-speed permanent Internet connections on a wide scale.

Today, the cost of providing POTS service using this FAN is around $225 per line. The LDSL permanent Internet connection adds $200.

4.3 Internet Access Devices

The TeNeT Group of IITM along with Banyan Networks (Pvt.) Ltd., Chennai, is developing a whole range of Remote Access Switches and Servers, including those tailor-made for the corDECT Wireless Access System and the Fibre Access Network, as described above. It is also developing a RAS with built-in digital modems to provide Internet connectivity to existing POTS subscribers. In all the products, emphasis is on low cost while maintaining high functionality. The additional cost of the RAS, for example, amounts to no more than $15 per Internet subscriber.

5 Conclusions

If a hundred million or more telephones are to be installed in India, and the service is to be economically viable, the investment per line has to be less than half of what it has been until recently. A key service that will be sought, and that will add to the viability, is inexpensive Internet access. Recent technological advances in wireless and fibre-based access technology, open interface standards, high-speed digital transmission on the copper loop, and Internet remote access switches, have made this cost reduction feasible. A new network with significant rural penetration can be installed today at under $450 per line. Many of the systems required to make this a reality have been developed in India. Expertise for Network Management System (NMS) software and customer care/billing software, which are key to the operation of a complex network with dispersed intelligent modes, is also available in India today. Electronics will do for telecommunications in India what it has already done to make personal computing less elitist and more broad-based. In this lies the hope of countries like India to provide universal telecommunications service. 

References

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3. Annual Report, 1992-93, Department of Telecommunications (Ministry of Communications), Govt. of India.
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10. DECT Reference Document, ETSI Technical Report ETR015, European Telecommunications Standard Institute, March 1991.
11. corDECT Wireless in Local Loop, Internal Product Description Report, IIT Madras, Chennai, July 1997.
12. "A Long Range Relay Base DECT System", Patent Application Number 332/MAS/97, 19 Feb. 1997, Chennai, India.

Dr.Ashok Jhunjhunwala

Ashok Jhunjhunwala (M '84) received his B.Tech. from IIT Kanpur, India, in 1975, and M.S. and Ph.D. from University of Maine, USA, in 1977 and 1979 respectively, all in Electrical Engineering. During 1979-81, he was on the faculty at Washington State University, and from 1981 he has been at IIT Madras. He is a Professor and currently the Chairperson of the Electrical Engineering Department.

He is a co-founder of the TeNeT Group at IIT Madras. His research interests are communication systems, computer networks, fibre optics, and surface acoustic wave devices.

Dr. Timothy A. Gonsalves

Timothy A.Gonsalves (S '78, M '86) received a B.Tech. from IIT Madras India, in 1976, M.S. from Rice University, USA, in 1979, and a Ph.D. from Stanford University, USA, in 1986, all in Electrical Engineering. From 1986–1988 he was an Assistant Professor in the Department of Computer Science at WPI, Massachusetts. In 1989, he joined the Department of Computer Science and Engineering, IIT Madras, where he is currently a Professor.

A co-founder of the TeNeT Group at IIT Madras, he focuses on the development of technologies and products in computer networks and telecommunications. His research interests are in voice/data networks, distributed operating systems, and network management.

Dr. Bhaskar Ramamurthi

Bhaskar Ramamurthi (M '85) received his B.Tech. from IIT Madras, India, in 1980, and an M.S. and Ph.D. from the University of California, Santa Barbara, USA, in 1982 and 1985 respectively, all in Electrical Engineering. During 1984–1986, he was a Post-Doctoral Fellow at AT&T Bell Laboratories, Crawford Hill, New Jersey, USA. In 1986, he joined the Electrical Engineering of IIT (Madras), Chennai, where he is currently an Associate Professor.

A co-founder of the TeNeT Group at IIT Madras, his research interests are in signal processing, digital communications, speech and video coding, and voice/data networks.