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Abstract - This paper presents a technical overview of some of the underlying principles of the modern telecommunication technology and the evolution of microwave radio, satellite systems and various optical fiber based infrastructures. Based on the proven superiority of fiber optics combined with the shortfalls of and the complexities faced by the existing satellite systems due to particularly unfavorable regional climatic conditions in and around Bangladesh, the need to link that country to a global submarine optical fiber telecommunication system as the backbone of choice for bulk information transport is underscored. In addition, novel ways of realizing cost effective land based long haul fiber-optic communications networks which use existing electric power lines to suspend optical fiber cables instead of resorting to expensive trenching techniques for cable laying is cited as a viable option given that there are practical examples in both developed and developing countries. Various aspects of optical fiber based wide area and metropolitan area networks such as Optical Gigabit Ethernet are also considered in the context of a mega-city like Dhaka and other highly populated areas. Finally, the economic benefits of having a reliable telecommunication infrastructure is discussed.[[1]]

I - Introduction

It is said that the transistor has done for man’s brain in this Information Age what the steam engine did for his brawn in the Industrial Age. Hence, it comes as little surprise that we are faced with the technological ability to communicate conveniently with anyone, anywhere and at any time in many different ways - voice, data, facsimile, e-mail, image and video - and all this at an affordable cost judging by the mushrooming number of “internet cafes” at every corner. Thus modern society has effectively been reduced to a global village and information exchange has experienced an enormous explosion. However, it is also said that the biggest hurdle to the full deployment of this technology is posed by the world’s fragmented telecommunications networks – especially in developing countries. The colossal growth in this market has forced scientists and engineers to address the issue of the ever-increasing demand.

In Bangladesh the bulk of international telecommunication traffic still relies on the geo-stationary satellite and terrestrial microwave link system operated by the Bangladesh Telegraph and Telephone Board (BTTB). Unfortunately, Bangladesh is well known for its monsoon rains and the annual floods. As seen from

the satellite photograph in Figure 1, the flatness combined with the large number of rivers in Bangladesh makes it particularly prone to becoming water logged during the rainy seasons.

Figure 1: Satellite photograph of Bangladesh (obtained from material available through NASA in the public domain)

Despite system allowances for a large rain fade margin in this region, the handling capacity of the satellite links is reduced – especially under adverse conditions. Also, floods (or any other water surface) can cause signal interference due to multi-path propagation as it travels through the microwave radio links. However, these are only the minor problems for the country’s telecommunication system. The major natural disasters such as cyclones, high winds and tidal waves originating from the Bay of Bengal that cause substantial physical damage to the towers and other equipment are by far the most significant problems. The 1991 cyclones knocked over the microwave tower in Chittagong thereby effectively severing the country’s international link.

Thus, while appraising the country’s telecommunications system requirements, optical fiber technology makes a compelling case as a solution to Bangladesh’s pressing needs. Short distance optical fiber links to handle dense traffic in intra-city communication started being used in the mid 80’s in the digital telephone networks. With a view to establishing a fully optical ISDN system to link the capital with other major cities, the government has implemented several major inter-city fiber links.

II – Satellite and Microwave Technology

Since the introduction of modulated microwaves in the 1920’s for communication between two distant points, this technology has gone through a tremendous amount of development. However, these links were limited to distances within the ‘line of sight’ (roughly 30 kilometers). Thus, the need for orbiting satellites to relay information over long distances was realized; pilot concepts evolved in the early 1950’s and were followed by the successful deployment of communication satellites a decade later.

Today satellites of all shapes and capabilities have been launched to serve almost all the countries of the World. Most communication satellites are in geo-stationary orbits (some 35,800 km above the Earth’s surface) and are able to ‘see’ nearly one half of the Earth from this vantage point. To provide continuous coverage to any point on Earth, only three satellites in such an orbit are sufficient [1].

However, signals are weakened about a hundred times after traveling these large link distances, thus necessitating the usage of high gain antennas and powerful transmitters. A more pertinent problem, however, is the delay and echo often experienced in long distance phone calls that use these satellites. The accommodation of ever increasing traffic requires the usage of higher frequency bands for satellite communications. Commercial satellites have been allocated 6 GHz and 4 GHz frequencies for up-links and down-links respectively each with about 500 MHz bandwidth. Another band with 500 or 1000 MHz bandwidth has been allocated near 12GHz for down-links with corresponding up-links at 14 GHz. A third band, which has substantial potential, is the 20/30 GHz band where a 2.5 GHz bandwidth has also been allocated.

Some of the fundamental limitations on the performance of satellite communication systems at frequencies greater than 10 GHz result from a strong interaction of radio waves with rain and ice in the lower atmosphere. Thus, system reliability demands detailed knowledge of these interactions. Rain attenuation dominates the power margin for systems operating above 10 GHz; hence multiple sites are required to meet high availability objectives. Also, in satellite communication systems the capacity per beam is strongly affected by rain. For example, to provide the same quality of transmission during a rainy period, the capacity may have to be halved. Finally, a substantial number of terrestrial relays (microwave radio links that operate only within ‘line of sight’ distances) are required to transmit the information to the telecommunication network exchange that may be up to a few hundred kilometers away from the satellite ground station.

III – Optical Fiber Technology

Faced with the aforementioned fundamental shortfalls of a satellite-based system, real interest in optical communication was aroused with the invention of the laser in early 1960's. Proposals for using optical fibers to avoid degradation of the optical signal while propagating through the atmosphere were made almost simultaneously in 1966 [2]. Early systems exhibited high attenuation (1000 dB/km). Today, less than 40 years on, attenuation of less than 0.2 dB/km is easily achieved for a carrier wavelength of 1.55mm as shown in Figure 2.

Figure 2: Loss characteristics of a silica optical fiber showing the three wavelengths of interest. (After Miya et al [3])

Thus the majority of the transmission and receiver systems are geared for operation at this wavelength. Unlike some of its predecessors, fiber optics technology has many unrivaled advantages, some of which are listed below:

1. Enormous potential bandwidth: the optical carrier frequency in the range 10¹³ to 10¹⁴Hz offers the potential for a fiber information carrying capacity that is many orders of magnitude in excess of that obtained using copper cable or wideband radio systems. This enables fibers to simultaneously carry voice, data, image and video signals.

2. Small size and weight: an optical fiber is often no wider than the diameter of a human hair; thus even after applying protective layers, they are far smaller and much lighter than corresponding copper cables. This is a tremendous boon to alleviating duct congestion in cities.

3. Immunity to interference and cross talk: they form a dielectric and are therefore free from electromagnetic interference.

4. Signal security: as light from a fiber does not radiate significantly, a transmitted optical signal cannot be obtained non-invasively, thus ensuring a high degree of signal security.

5. Low transmission loss: with losses as low as 0.2 dB/km, this feature alone has become a major advantage of optical fiber as extremely wide repeater spacings (70 to 100km) may be used in long-haul communication links. This in turn reduces both system cost and complexity.

6. System reliability and ease of maintenance: due to the low loss property, system reliability is generally enhanced in comparison to conventional electrical conductor systems. Furthermore, reliability of optical components have predicted lifetimes of 20 to 30 years. Combined, these factors tend to reduce maintenance time and costs.

There are three major applications of fiber optic telecommunications - each one corresponding to the three low fiber-attenuation windows in Figure 2: long haul backbone networks (1.55mm); metro area networks (1.3mm) and local area optical networks (0.85mm). Domestic intercity systems based on optical fibers have now been widely implemented. These use digital transmission with pulse rates ranging from a few hundred Mbit/s to about 2Gbit/s. With the usage of single mode fibers since 1984, repeater spacing of up-to 40km or more is achieved. Furthermore, with rapid progress in time, the distinction between local, intra-city and intercity systems is blurring.

A. Sub-marine Optical Fiber Based Long Haul Backbones:

Underwater cables for communications have a relatively long history. The first transatlantic cable was laid as early as 1858. It was used for telegraphy and transmitted less than a few words per minute! About a hundred years later in 1956, the first analog transatlantic telephone cable (TAT-1) became operational. It carried 36 voice channels. The analog TAT family grew with further development in telecommunications systems and the last such cable, TAT-7, carrying 4200 channels per co-ax cable was fully operational by 1983. An increasing demand in the early 1980’s for reliable intercontinental telecommunication links resulted in many proposals to introduce fiber optic undersea cable systems.

By the end of that decade high capacity optical fiber cables using a carrier wavelength of 1.31mm (corresponding to the second lowest fiber attenuation window) were laid under the Atlantic Ocean (TAT-8) and the Pacific Ocean (TPC-3) respectively. TAT-8 and TPC-3 have the capacity to transmit data at a rate of 280 Mbit/s per fiber pair. Thus, these formed part of the so-called first generation digital lightwave systems [4]. The second-generation cables (TAT-9 to TAT-11 and TPC-4), with enhanced capabilities such as 560 Mbit/s per fiber pair and using a carrier wavelength of 1.55mm (corresponding to the lowest fiber attenuation window), are now in operation. The third generation cables (TAT-12 and 13 and TPC-6) are now in their installation/operation stages; these have a capacity of 5 Gbit/s transmission rate per fiber pair employing the first fully optical regeneration techniques in the repeaters. They also use dispersion shifted fibers and carriers with a 1.55mm wavelength.

Figure 3: The global route taken by SEA-ME-WE-3 (Optical fiber cable system-3 connecting South East Asia, Middle East and Western Europe)

The second and third generation cables have extended digital connectivity to the South Pacific, South East Asia and other points. Two of such global submarine cable networks that are in the vicinity of Bangladesh are the “South East Asia, Middle East and Western Europe (SEA-ME-WE)” and the “Fiber Link Around the Globe (FLAG)” long haul backbones respectively. For example, Figure 3 shows the 39,000 km long route taken by SEA-ME-WE-3 cable network that was started in early 1997 and took two and a half years to complete. It is an SONET cable system that uses the latest wavelength division multiplexing (WDM) technology and provides the platform to launch innovative wideband services.

B. Optical Metro Area Networks:

Sandwiched between optical local area networks and the long haul backbones, the optical Metropolitan Area Network (MAN) is evolving at a tremendous rate. It is rapidly becoming a highly competitive market driven by the rise in demand for a broad range of data communication services such as remote applications, high volume information storage, web-hosting, video on demand, and other IP-centric needs as well as bandwidth flexibility at a low cost. Each customer will have different capacity and quality of service requirements [5]. But the creation of new data services based on SONET infrastructure has suffered major impediments due to the inherent inefficiencies of the latter: SONET has large fixed bandwidth granularity (1.5Mb/s, 50 Mb/s, 150 Mb/s, 600 Mb/s etc.,) leading to stranded capacity. Gigabit Ethernet or Optical Ethernet, on the other hand offers bandwidth in small granular increments (1 Mb/s).

This highly attractive feature of Gigabit Ethernet has led to the formation of Metro Ethernet Forum (MEF) consisting of component and system vendors, new and established telecommunication carriers with the aim to accelerate the adoption of optical Ethernet and making it the technology of choice in the world’s metro area networks [6]. Another one of the key capabilities of this technology is that it is cost competitive in the 40-70 km range and therefore suited to MAN applications; it is eight times cheaper than either SONET or ATM. However, since Ethernet was not originally designed with carrier grade features in mind, one of its pitfalls is that it suffers from network reliability issues. Although optical Ethernet is now serving a niche market, it is continually improving thus making it a serious contender for the metro application.

Fiber Optic Cables Installed on Overhead Power Transmission Lines:

Historically regional and international power transmission lines have required modern network automation and remote control systems. To achieve this, power utilities started very early to equip their lines with reliable telecommunications connections. With deregulated telecommunications, opportunities have been opened up for these power utilities to lease dark fibers or data transmission capacity or indeed to become telecom operators themselves. Fiber optic cable links are the foundation of such communication systems. Given their capacity to transport high bandwidth information over long distances and being immune to electromagnetic interference makes them an ideal candidate for installation on overhead electrical power transmission lines.

Stringing fibers on poles along electric utilities has traditionally been the second or third choice for carriers looking to expand a network backbone, but that is starting to change. Even a decade ago, the carriers were generally deterred from using aerial rights of way due to lack of marketing by the utilities, shortcomings of the technology and an age old habit of burying cables. But between 1988 and 1995, MCI worked closely with various utilities to install more than 3,800 route km of aerial optical ground wire (OPT-GW). Similarly, OPT-GW has been used on a significant segment of 3,500 route km of Trans-Siberian Communication line passing over Russia’s four large power utilities. Examples exist in Britain with Energis, a subsidiary of Scottish power utility, as well as in sub-Saharan African countries.

Aerial construction can be as much as 40% less expensive than going the underground route. In addition, overhead fiber cable installation tends to be much quicker than buried construction. Unlike buried solutions along railroad or public highways, electric utility right of way includes the unique advantage of having substation facilities approximately every 40 to 50 miles [7]. In a water logged country like Bangladesh, these are the reasons which make this technology a candidate for serious consideration for expanding the existing optical fiber network along with the power distribution infrastructure.

IV – Status of Telecommunications Network Infrastructures in Bangladesh

Satellite/Microwave Network:

Relying primarily upon the IO-Inmarsat synchronous orbit satellites located above the Indian Ocean, the geo-stationary satellite/terrestrial microwave link network in Bangladesh that is solely used for international telecommunication consists of four ground stations: the first two are standard "A" stations located in Betbunia, about 40 km from Chittagong on the Chittagong-Rangamati highway and in Mohakhali, in Dhaka City; the third one is a standard "B" station at Talibabad, about 30 km north of Dhaka on the Dhaka-Mymensigh highway while the fourth one, of standard "F", is in Sylhet.

The microwave links carry the intra-country portion of the traffic. For instance, the Betbunia station is connected to Chittagong by a 2 GHz 140 Mb/s PDH Microwave; the international channels are then transmitted through a STM-16 Optical Fiber transmission system to Dhaka, where the three international gateway switches (two at Moghbazar and one at Mahakhali adjacent to the satellite Earth Station) are installed. The Talibabad station is connected to the international switch at Moghbazar through a single hop 6 GHz microwave link. The Sylhet Earth Station is to cater for the international trunk service to Sylhet and adjoining areas. This satellite station is directly connected to the international gateway switch of British Telecom in UK.

In addition to these, there are two more international terrestrial links: the first is the microwave link from Chuadanga near Kushtia to Krishnanagar in India while the second is an UHF link from Attari near Dinajpur to Bhadrapur in Nepal.

Optical Fiber Network

Establishment of fiber optic links in Bangladesh began in 1986, along with the installation of new digital switches. Starting with the optical fiber link between Dhaka’s Maghbazar and Gulshan telephone exchanges, all intra-city inter-exchange connections are now established through short distance fiber optic links. The inter-city portions between the major cities started with the completion of the STM-16 fiber link between Dhaka to Chittagong in 2001 (“STM” is a standard of data transmission rate where STM-1 represents 155 Mb/s). Bogra to Joypurhat to Ragpur and Dinajpur in the north west of Bangladesh is already connected by STM-4 optical link while Dhaka to Bogra optical fiber link via the Jamuna Bridge is currently under construction. In addition, there is a plan to connect Dhaka to Sylhet and Dhaka to Khulna on the optical fiber network. These are summarized in Figure 4:

Figure 4: Map of the existing fiber-optic network in Bangladesh

Moreover, to cater for the increasing international traffic, Bangladesh, having missed out on a similar opportunity a decade ago, is finally joining the SEA-ME-WE-4 submarine cable network consortium. The 10Gbs bandwidth of this network is expected to serve Bangladesh’s needs for the next 10 years and significantly reduce costs of international calls. This link, costing approximately US$60 million [8] will use Chittagong as the landing station. This guarantees BTTB’s free landing access in Singapore, Indonesia, Malaysia, India, Sri Lanka, Pakistan, UAE, Saudi Arabia, Egypt, Italy and France.

C. VSATs Users

With the intention of accelerating the growth of internet, the government licensed the use of Very Small Aperture Terminal (VSAT) satellites for data-com use about a decade ago. There are now about 120 operators consisting mostly of foreign organizations such as gas companies, embassies and financial institutions and some internet service providers. These users are linked to internet hubs located in Singapore or Hong Kong via these links. The Bangladesh Telecom Regulatory Commission (BTRC) is contemplating legalizing the use of Voice Over IP on these lines as a way to further alleviate the existing acute voice channel log-jam.

D. Cellular Phone Networks

There are about half a dozen licensed private cellular-phone network operators in Bangladesh. Most of these were established in collaboration with foreign telecom companies. Due to the lack of availability of land-based networks in the country, they serve a major part of the total telephone traffic in rural and remote parts of Bangladesh as well as business users in large cities. One of these operators has leased dark fibers from the Bangladesh Railway to serve as the backbone for their domestic mobile phone communication network.

V – Economic Benefits of a

Better Communication System

The advantages and benefits that telecommunication can bring in education, commercial, medical and governmental activities are too numerous to mention, suffice it to say that its expansion plays an important role in the economic and social development of a country [9]. One important benefit of a penetrative telecom infrastructure is that it can enhance instant communication between Bangladeshis on the one hand and people in distant places around the globe on the other. In other words, increasing the number of phone lines per inhabitant, teledensity, can help put Bangladesh on the world map through enhanced domestic and global trade. This will pave the way for a stronger economy. Currently, Bangladesh is among the countries with the lowest teledensity. Improving the telecom infrastructure will reduce the cost of local and international phone calls to and from Bangladesh enabling Bangladeshis to join the international community.

Communication technology also serves as a “Market maker”. Given the often intense economic competition among nations, missed opportunities due to lack of communications access will have more dire consequences in the future [10]. To be successful, Bangladesh as a developing country must be prepared to compete in a global economy in which production takes place around the world on a decentralized and flexible basis. For example, a small business that serves a single niche market in a developing country can increase its size by using communication technologies like the internet to identify similar niche markets in other countries. This means that if developing countries deploy advanced communication technologies in tandem with developed countries, they can also compete in the expanding global services market on a more equal basis. Deployment of a better communication system encourages catalytic social, economic and political interaction, which in turn stimulates further network development and deployment.

VI - Conclusion

This paper has taken a detailed look at the technological advantages of a fiber optic telecommunication network in the context of Bangladesh’s unique geographical, social and economic needs. The cost advantages of hanging optical fiber cables for deploying inter-city networks was briefly discussed. This was followed by a status review of Bangladesh’s existing telecommunication networks. Finally, the vast economic benefits of having a reliable telecommunication infrastructure capable of adequately catering to the immediate and long term information technology needs of a developing nation on the brink of industrialization and looking to tap into the global IT markets was reiterated.

Acknowledgements

The author would like to acknowledge the help of Shaukat Osman of Sheba Telecom, Shahabuddin Khan and Nurul Basher of BETELCO for their help on gathering current information on the telecommunication infrastructure in Bangladesh. Anita Brady and Tanvir Bashar are thanked for proof reading the manuscript.

References:

[1] D. Reudink, ‘Advanced Concepts and Technologies for Communications Satellites’ in Advanced Digital Communications (Editor: K. Feher; Publisher: Prentice Hall, NJ, USA), 1987, Chapter 11.

[2] J. M. Senior, Optical Fiber Communications, Principles and Practice, (Publisher: Prentice Hall International, Hertfordshire, UK), 1992; 2nd Edition

[3] T. Miya, Y. Terunuma, T. Hosaka and T. Miyashita, “Ultimate Low Loss Single Mode Fiber at 1.55mm”, Electronic Letters, Vol. 15, pp. 106-108, 1979

[4] P. K. Runge, ‘Undersea Lightwave Systems’, AT&T Technical Journal, Vol. 71, No. 1, pp. 5-13, 1992

[5] L. G. Kazovsky, K. Shrikhande, I. M. White, M. Rogge and D. Wonglumson, “Optical Metropolitan Area Networks”, IEEE Optical Fiber Communication Conference, pp. WU1-1 – WU1-3, Mar. 2001

[6] R. A. Skoog, “Gigabit Ethernet: Is it a Disruptive Technology?” IEEE/LEOS Annual Meeting Conference Proceedings, Vol. 1, pp. 287-288, Nov. 2001

[7] K. Brown, “Advantages of Aerial Network Construction”, Xchange Mag, Sept., 2000.

[8] A. S. Khan, “Sub-marine Cable Debate: Govt’s Belated But Correct Decision”, The Daily Star, 2 September 2002.

[9] Y. Utsami, “The Rise of the Information Society”, speech at the UN General Assembly, New York, 17-18 June, 2002.

[10] D. L. Garcia, “Opportunities for Developing Countries in the Global Information Economy”, Georgetown University, Washington DC, 2002

Shabbir A. Bashar was born in Dhaka, Bangladesh in October, 1969. He received his B.Eng. (Hons.) and Ph.D. degrees in Electronic & Electrical Engineering from King’s College, University of London in 1991 and 1998 respectively. His doctoral thesis was on the study of components for fiber-optic telecoms.

From 1995 to 1997 he worked as a Post Doctoral Research Fellow on an Engineering and Physical Sciences Research Council (EPSRC) project in collaboration with the UK Defense Evaluation Research Agency (DERA). From 1999 to 2000 he worked on the technology development of 850nm lasers for optical local area networks as a Visiting Scientist at Cornell University, Ithaca, USA in collaboration with Nova Crystals, Inc. He has also worked in the Stanford Nano-Fabrication Facility (SNF) at Stanford University, California. He is currently a Member of Technical Staff at Nova - a Silicon Valley based communications company focused on manufacturing products for the Optical Gigabit Ethernet metro area and wide area networks.

Dr. Bashar has authored or co-authored more than 20 peer reviewed international journal and conference publications in the field of fiber-optic telecommunications devices and he jointly holds a number of US patents on optical telecommunications lasers and other light emitters.