Due to the high population density in Hong Kong, a cable builder would pass a large number of households per kilometre of horizontal duct. The vertical component therefore dominates over the horizontal; we estimate that the ratio of cable length (vertical to horizontal) is approximately 10:1.
The above description is simplified. In practice there are many difficulties and additional costs which would be incurred by any cable operator. Where appropriate these differences have been described in the following analysis.
4.1.2 The use of HKT's duct network
For the fibre optic supertrunk and the coaxial trunk network, HKT has proposed using its existing duct network as a conduit. There are several factors which need to be addressed on this issue including the technical restrictions in using partially filled duct, the percentage of duct which can be used, the amount of duct which would need to be upgraded and the cost apportionment of duct cost to the cable operations. The legal issues of duct sharing would also have to be considered.
Technical restrictions
There is concern over whether using the existing ducts for a cable television service would disrupt the telecommunications service. BAH has examined this topic in detail and has concluded that there is no technical reason why coaxial cable needed for cable television could not share duct space with cable needed for telephone service without causing service degradation. This conclusion is based on several points:
i.
Cable operators in the United States do not as a rule share ducts with the local telephone companies. However in those instances where the local telephone company was required to allow a cable operator access to its ducts, the cable was installed without incident and has operated without any disruption to the telecommunications service.
ii. There is no operational difference between the installation of a
cable for the purpose of cable television in a partially filled duct and the installation of a cable for the purpose of telecommunications service. The practice of pulling cable in a duct which is partially filled is a long standing, proven procedure in Hong Kong, as the United States and Europe.
iii. The current level of shielding in the cables needed for
telecommunications and those needed for cable television service is adequate to prevent any "crosstalk" (interference) between the two services.
Owing to the relative fragility of fibre optic cable compared to coaxial cable, the above statements do not apply without reservation to the fibre optic supertrunk network. Fibre optic cable can be pulled over existing cable, but it requires considerably more care, and hence expense. This cost has been taken into account in BAH's calculations of the cost for the supertrunk network.
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