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3. Broadband Internet connections to homes and offices
Internet usage in offices and homes is generally believed to be asymmetrical in terms of bandwidth: the data leaving the customer site will be much less than the data entering it. This belief affects the architecture of HFC, ADSL and other systems - in a way that may prevent an expansion of upstream bandwidth in the future. The belief is based on an assumption of usage resembling the 'passive viewer' pattern of mass media: that there are centralized sources of 'content' and that customers primarily receive this 'content' and so require little upstream bandwidth to control the servers of that material. To the extent that customers are accessing large volumes of centralized material, this assumption is valid - since large servers will be connected very closely to the fiber Internet backbones, rather than via a more expensive 'last mile' technology in a home or office.

The danger is that broadband telecommunications will be assumed to follow the asymmetrical 'consumption of mass media' model of television, rather than the symmetrical customer-to-customer model of telephony and much of the postal system. In contrast, Internet telephony, interactive games, video conferencing and sharing of audio and video recordings are 'customer-to-customer' applications involving symmetrical bandwidth.

Most current Internet activities would run perfectly well with several hundred thousand bits per second of bandwidth in both directions. However CD-quality digital audio is 1.6 Mb/s - and lossless compression (which does not degrade the sound quality at all) can only reduce this by 20%-30%. (However, many listeners are happy with MP3 lossy audio compression at data rates of 128 to 256 kb/s.) Video conferencing ideally involves 500 kb/s, and MPEG-2 movies with surround-sound for standard television display require around 3 Mb/s. Fast action sports requires 6 to 8 Mb/s, and HDTV requires at least 20 Mb/s.

Future demand scenarios are a matter of ongoing debate, as is the question of the best 'last mile' technologies and how all this traffic - including telephony, Internet and HDTV VOD - can best be switched and transmitted globally in a unified fashion. In 2001, there was an awkward mixture of local access technologies, with a variety of methods of data carriage, carrying a variety of types of communication. The engineering dream of all types of communication being carried by a single set of low-level data protocols, which operate equally well over everything from GSM to FTTH is likely to remain a dream for the foreseeable future.

While each access technology may be developed, become stable and be widely deployed in a 7 to 10 year time span, and remain in widespread use for ten or twenty years, there is a continuing evolution in applications and demand. In 2001, residential and small business customers communicate via circuit switched and TCP/IP packet-switched data protocols, but these are inadequate for broadband communications with QoS (Quality of Service) bandwidth guarantees. . There are fundamental problems of commercial complexity in providing QoS for communications carried over multiple networks, as must be the case for global communications. This problem remains whether the data is carried by either ATM or TCP/IP with QoS extensions.

So while xDSL and HFC local access technologies are mature and are being widely deployed, and a glut of long distance and intercontinental fiber capacity is predicted, it seems that broadband Internet with QoS on a global basis will not be achieved for many years to come. The long-predicted mass-market application of VOD awaits the development of suitable servers, and like DVD discs, is commercially threatened to some extent by the prospect of widespread user copying, both via broadband Internet and with writable DVD discs.

Competing Technologies
Because of uncertainty about future demand, and because telecommunications infrastructure is intended to remain productive for decades, a new installation should be flexible and easily expanded. If cost were no object, then each customer would be served with their own bi-directional optical fiber. Alternative approaches include making the most of existing twisted pair copper telephone cabling - which can also supply power to customer equipment and so provide highly dependable telephone services.

While the installation of one of these technologies may make others redundant in that area, all the following technologies are expected to remain in widespread use in early decades of the twenty-first century.

Several technologies, which are beyond the scope of this discussion, may compete with or complement these 'last-mile' bi-directional approaches:

• Geostationary satellites for broadcast and one-way data transmission, including video and the downstream path of an Internet link.
• Low Earth Orbit (LEO) satellites for mobile and fixed telephony and data services.
• Digital Terrestrial Television Broadcasting (DTTB) and Digital Audio/Sound Broadcasting (DAB/DSB), which may be delivered from terrestrial transmitters and/or satellites.
• Bi-directional and broadcast microwave communications from a permanently stationed stratospheric airship at an altitude of about 22 km.
• Unidirectional data and video transmissions from MDS microwave stations.
• Systems which purportedly provide high-speed Internet and other communications via power lines. Such systems are fundamentally incapable of providing high speed communications because to do so using power wires would cause them to radiate interference in the street and probably in the home at levels which would interfere with services such as AM radio reception.