BT is also the only PTO able to provide ISDN on a national basis. New services such as Switched Multi-megabit Data Service (SMDS), Frame relay and ATM are becoming available, using the installed national optical fibre network as the common carrier. BT were chosen to provide the network for the SuperJANET pilot. Initially this was based on their 34 Mbps Plesiochronous Digital Hierarchy, but is moving to the 155 Mbps Synchronous Digital Hierarchy [Janet93 ; Clyne94]. BT are also providing Internet and video conferencing services. At present government policy prevents BT from offering video services to the home, but much of the technical work being undertaken by BT such as Asymmetric Digital Subscriber Lines (ADSL) technology anticipates the lifting of this regulation.
With the liberalisation of telecommunications in the UK a number of other alternatives to BT are available. Mercury, Energis, Water companies and others are hoping to tap regional and national market niches. The basic technologies available from these operators is very similar to those of BT. One such market niche may be the linking of educational sites, schools etc. for the distribution of multimedia learning material.
However a number of providers are offering analogue telephony service, with ISDN as a possibility in some cases. Potential exists for the glass fibre infrastructure to support Metropolitan Area Networks (MANs) linking educational institutions and related organisations.
The cable industry's broadband integrated services network architecture is based on a hierarchical deployment of network elements interconnected by broadband fibre optics and coaxial cable links. Starting at the home, a coaxial cable tree-and-branch plant provides broadband two-way access to the network. The local access coaxial cable plant is connected at a fibre node, which marks the point in the network where fibre optics becomes the broadband transmission medium. The multiple links from the fibre nodes reach the head end, which is where existing cable systems have installed equipment for origination, reception and distribution of television programming. The head ends are in buildings that can accommodate weather protection and powering facilities, and hence represent the first natural place into the network where complex switching, routing and processing equipment can be conveniently located. Cable networks will continue to be asymmetric, and they will continue to deliver analogue video. But digital capabilities are being installed and a significant upstream bandwidth is rapidly being activated. The deployment of optical fibre deeper into the network is making the shared coaxial plant more effective in carrying broadband traffic in both directions. The recent announcement in the USA by Continental Cablevision and PSI to provide Internet access services is one example of the many uses that these two-way broadband capabilities can provide.
If compressed digital video is the way to deliver future video programs (including interactive video, video on demand, and a whole menu of other applications like computer supported collaborative work, multi-party remote games, home shopping, customised advertisement, multimedia information services, etc.) will be made available.
In this sense the Cable TV providers will play a role in the provision of an infrastructure for multimedia capable networks.
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