Other related technical changes in the surrounding infra structure

TV display technology - There is a noticeable convergence starting to appear between the display technology used for Personal Computers and that for TV. On the one hand, we have the rapid development o f dramatically improved computer graphics, extending to real-time video capability, for use in multi-media PCs such as the Apple or IBM ranges. This is increasingly linked to the very large digital storage abilities o f CD-ROM and the rapidly decreasing cost o f silicon RAM frame-stores. Its impact is seen in the wide spread growth of new video games as well as more serious education and other information systems products. In entertainment, we have the emergence of technologies such as CD-I

121 which again combine compressed video storage but utilise standard PAL or HD-TV display. The growth of digital signal processing capability with digital ffame-storage in advanced domestic TV receivers is further pointing to convergence into an all-digital processing system.

Office System Convergence - Compatibility between computer based systems in the office has been a notorious problem area ever since they started to become widespread and needed to converse! The UNIX operating system started a process whereby major applications software packages could be ported to many different machines. More recently, we have seen the growth of applications packages for PCs, such as MS-Word, which, whilst individually tailored to a given PC family, could at least accept files produced by their brothers running on other families. The recent announcement of the Power-PC range by Apple, to be followed by an IBM Power PC range, heralds a further convergence since it is claimed that these machine can run both Apple Finder and MS-Windows software packages simultaneously and patch results from one directly into the other. Then the introduction of Windows-NT by Microsoft appears to usher in an era when the application software becomes hardware independent on most machines and finally, the recent announcement of Microsoft-at-Work appears to open the way for a much broader level o f integration of oflSce type equipment, embracing not just easy interchange between PC families but also the integration o f telephones, FAXs, modems, personal assistants, OCRs, printers and copiers and o f course, their interaction remotely. It is tempting to believe that the "electronic office" may actually be arriving!

The common theme across all the applications is digital technology, from storage through transmission and processing to display and with the emergence of operating systems and standards designed to enable interworking. Furthermore, the barriers between the previously completely separate business sectors o f information systems and communications are fast disappearing with the interesting emergence for transmission purposes o f the ISDN 64 and 128 kBit/s levels and the T1 or CEPTl rates o f 1.5 and 2 MBit/s as prime carriers for many information services. The US and BT approach using ADSL over a local copper network is clearly targeted at exactly this scenario. What is unclear is the extent to which such a technology can be deployed; is it to 100% o f the existing Local Access Network or 50% or less, and if not 100%, then how does one identify which parts? It seems likely that even a compressed video offering will require fibre for a major part o f its travel towards the customer and that at best ADSL will provide a vehicle for launching unidirectional services at low penetration into the user community.

The digital storage o f video is driven by the existence and growing influence o f the Motion Picture Experts Group (MPEG) and the standards they are developing (Table 5.1

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below). These already pervade both home and office and it seems difficult to avoid the conclusion that they will also be influential in the development of a switched local broadband network. The H.261 standard forms the basis of the latest video-phone, draws upon the MPEG standards and allows heavily compressed moving pictures to be carried over an ISDN line. Furthermore, multi-media PCs operating to H.261 also allow the machines to view and interact with other application windows displayed on their screen in addition to the video phone window, a development of great potential for teleworkers.

Title Subject & typical bit rate.

MPEG-1 Digital video into CD-ROM format up to 1.5 Mbit/s MPEG-2 Higher rates, from 2 up to 20Mbit/s also embraces HDTV MPEG-4 Very low bit rate audio and image data

H261 Standard for video and multimedia phone

Table 5.1 - Compressed digital video rates

These parallel developments in consumer and office electronic technology seem to point very strongly to the widespread deployment o f MPEG standard video decoders in both markets, greatly enhancing the case for developing broadband access networks around digital rather than analogue standards.

The developments in compression technology point to another change in desired traffic characteristics. Telephony is seen as a steady information flow whereas a heavily compressed video signal generates little traffic when the picture is changing slowly but generates bursts o f data when the picture changes substantially. The variation in bit rate can only be smoothed out using buffer memory which introduces delay. This is o f little consequence for entertainment services but may critical in video phones and other interactive video services