cable has been its length and hence the unit cost of capacity falls dramatically with increased traffic volumes. But if you only have a small demand, then cables designed for large capacities produce a prohibitively expensive solution. Thus there has been a move designed to produce less expensive cables suited to smaller demands (or so-called “thin routes”).
Submarine Cables for Smaller Communities This year at the PTC conference in Hawaii, the theme of the Submarine Cable Workshop will be the development of submarine cable solutions for smaller communities. The following paper is intended to give an overview of this topic as a prelude to the detailed presentations at the conference. Submarine cables are one measure of the global standing of a country. For other than land-locked countries, they represent the Rolls-Royce form of international connectivity. Having a cable suggests that this country has made it and has joined or will shortly join the developed world. As a consequence, smaller and less developed countries aspire to acquire a cable as a pathway to their development primarily through the superior access to the internet and e-commerce. Hitherto it has been very difficult for smaller communities to justify the expense of a submarine cable. The Caribbean countries have been fortunate, because of the large number and
by John Hibbard
their close proximity, to be able to share the high costs and gain reasonably cost effective capacity. Countries like Papua New Guinea have been able to take advantage of nearby retired cables and to re-use them resulting in a lower cost. But for smaller communities, there are the issues of isolation and hence distance, and the obligation to acquire new cables with basic capacities far beyond the long term needs of the country. The industry has seen this emerging need of these communities and solutions are being developed to address them. Technical Solutions Historically submarine cables have been designed to maximise their circuit capacity. Consequently we have seen capacity of optical fibre cable rise from less than one Gigabit per sec to many Terabits per sec. While this is attractive for large streams, it has major disadvantages for smaller streams. The principal determinant of the cost of a
The capacity of the cable is determined by the dispersion degradation and the signal to noise ratio, which dictate the spacing of repeaters in long-haul cables (over 500 kms or so). Typically on large capacity repeatered cables, the spacing is around 75 kms. However if we are looking for capacities less than 100 Gigabits, spacings can go beyond 100kms, and for those smaller communities looking at a few tens of Gbps, then 150kms may be possible. With repeaters costing around $500K this can produce a significant saving. Repeaters take power, and the number of repeaters determines the voltage that must be fed to the cable. The higher the voltage, the greater the amount of dielectric needed to provide the insulation between the high voltage and the outer casing. With fewer repeaters, and hence lower voltage, less dielectric is needed allowing thinner cables. Thus instead of typically 23 or 17 mm cables, we might see 14 mm cables. This represents a significant saving in manufacturing costs. Other developments involve direct Ethernet access avoiding some SDH multiplex costs and reduced cost of PFE due the lower voltages. There are other techniques being developed which in combination might see the capital cost of a repeatered submarine cable reduce by 30 to 40%, and with fewer repeaters, the operating cost reduces due to lower power bills.
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