- Email: [email protected]
International review
Australia Teletext services After a long delay pending federal government agreement on tec.hnical standards, Australian television stations were recently given approval to operate broadcast teletext services. The approval came as the culmination of a strong lobbying campaign by some commercial (i.e. private enterprise) television stations. Nevertheless, not all stations see teletext as a major commercial opportunity. Whereas the Fairfax media organization has been strongly in favour of it, the Packer organization appears more inclined to wait for interactive videotex services. As the ownership of major commercial I V stations in Australia is dominated by newspaper groups, it is likely that electronic distribution of news and newspaper advertisements may be one of the stations' main goals for teletext. The commercial success of the venture is, however, by no means assured. Decoders to adapt existing TV sets for reception of teletext are coming onto the market at a cost of about $300, and buyers have no assurance that the equipment will be compatible with the more advanced interactive videotex systems which may be available in Australia within the next three years. Thus the rate of growth in number of sets equipped for teletext is likely to be slow. Some TV advertisers, whose fees provide the main source of revenue for commercial TV stations, are sceptical of the teletext development because of the potential delution of their viewing audience, attributable to the number of TV sets that may be switched to the teletext alternative at the time when their advertisement goes to air. The stations, on the other hand, are hoping to convince potential advertisers that a teletext page will provide an effective medium for con-
vol 3 no 4 august 1980
veying an advertising message, presumably with a sliding scale of fees according to the expected popularity of particular pages. Advertising space available on theweather forecast page will undoubtedly command a premium over that available on the futures market page. One possible application of teletext that is being considered with some enthusiasm is that ofwagering information dissemination. The proposal is that offcourse betting organisations could broadcast odds progressively via the teletext service for punters. This would be realised by means of TV sets installed for public viewing in the agencies where bets can be lodged. Similarly, punters who lodge bets from their homes by telephone could access the odds display through modified domestic TV receivers. The degree of success and acceptance of such a scheme would appear to be determined by the timeliness and level of accuracy of the odds display.
Prestel trials The British Post Office Prestel interactive videotex information system will be demonstrated in Australia during 1980. For the purposes of demonstrations, data-communications links will be established between Prestel TV sets and the British Post Office computer network in the U K. The success of the trail is likely to depend to a great extent on the willingness of Australian information providers to contribute local data to supplement the existing BPO information base during the trial period. The trials will be aimed mainly at commercial firms, suggesting that the Australian market is presently being perceived more in terms of closed mode use of the public videotex system, or in terms of in-
house systems. This apparent emphasis on the commercial market seems to be at odds with the reported findings of various European studies which indicated that the most promising market segment for videotex was home information retrieval.
Public packetswitched service The Telecom organization has now made a commitment to offer public packet-switched network facilities nationally by the end of 1982. Technical standards for interfacing equipment will conform to the CCI'H- X.25 Recommendation. The packet-switched service will be based on a digital data transmission network now being implemented by Telecom. This is expected to be available during 1981 for leased data circuits in the high traffic density area of the Sydney-CanberraMelbourne triangle extending to the rest of the country in 1982. The scale of charges for the packetswitched service has yet to be announced. Some observers interpret this recent Telecom decision to accelerate its implementation of a digital data network as a response to potential threats to its monopoly position in data communications arising from the government decision to proceed with a domestic satellite sys tem. Some media organizations which are planning to use satellite channels for distribution of television programmes would probably be in a position to offer capacity on their channels for data-communications services. This prospect may indeed be a spur to Telecom for improving the range of data-communications facilities that it offers. However, legislative changes would be required to permit any organization other than Telecom to operate as a common communications carrier.
Angus Richards 185
USA Transport layer protocol standardization In the ISO open systems architecture, the lower three levels of protocol lie clearly in the domain of communications, while the fourth or transport layer is at the interface between the communication and the distributed processing worlds 1-3. Several sets of protocols for communications services have been defined, and one, X.25, has become awidely used standard in the US and the rest of the world. These lower level protocols are tailored to the particular networkthey serve, and are primarily concerned with efficient and correct deliven/of dat bits across a transmission link Because they are so necessary to any offer of network service, their development has proceeded quite far compared to the higher level, host-host protocol layers. Now that the use of networks has increased and users are demanding more from the network protocol offerings, there is significant activity in developing standards for higher level protocols, at level four and above. The function of the transport protocol is to accomplish data transfer between two hosts, either across a single network or possibly across several connecting networks. Because of this host-host function, and because the lower level protocols effectively mask many of the physical characteristics of the network(s), the transport level protocols can be relatively network independent. However, the nature of the subnetworkwill have a considerable impact on the operation of the transport layer and therefore on its features. Since most of the wellunderstood network applications require reliable, sequenced delivery of data, this must be guaranteed by the transport layer. If the underlying network does not pro186
vide reliable service, then the transport layer must perform error checking to ensure intact delivery, duplicate detection and sequencing to ensure in-order delivery, and an acknowledgement mechanism to communicate the state of the data transfer. Some of these functions can be 'borrowed' from lower layers if they are available; however, care must be taken to maintain a clean protocol layering. Most of the major computer vendors have incorporated these transport services into their network architectures, although not always in a clearly defined transport protocol. Moreover, the standardization effort has not generally progressed to the point where transport level communications is possible between machines from different vendors.
Transport control The US Government has begun looking for standards for its federal networks. While no federal or Ansi standard exists yet for a transport level protocol, the US Department of Defence (DoD) has adopted as its official standard the transport control protocol, TCP. TCP, which has been under development by the DoD Advanced Projects Research Agency (Darpa) since 1974), provides for reliable, sequenced, flow-controlled interprocess communication. It is designed to work over unreliable networks or concatenations of networks, although initial implementations were used over the reliable Arpanet. It has now been implemented on a variety of host processors, which are linked to each other through an internet of packet-switching nets, satellite networks, packet radio networks and
local networks. The lower level services are provided by the protocols indigenous to these individual nets and by the internet protocol, a datagram mechanism for internetwork transmission, which is used by gateways between the networks. TCP and the internet protocol were formerly integrated into a single protocol; their separation allows the development of internet services which do not have the requirement for reliable transport, butwhich may have, for example, delay requirements which are difficult to meet with a protocol like TCP. Recently, TCP has been introduced into the Ansi arena as a candidate for a transport level protocol standard. So far this has been done on a fairly informal basis, with a spokesman explaining TCP at Ansi task group meetings. There are some more formal efforts underway to propose a standard transport level protocol.
N BS study The US National Bureau of Standards is sponsoring a study of higher level protocols, at levels four and above of the ISO open systems architecture. As part of this study, Bolt Beranek and Newman (BBN), USA, is studying transport protocols. The ultimate goal is to produce a draft Federal information processing standard (FIPS), which will then be publicized, commented on, and changed as necessary before being adopted. The effort is being done in cooperation with the Ansi standards groups to avoid duplication of effort and to provide a standard which will be useful to the largest possible community. If the draft standard, which is currently being developed, is compatible with TCP, this will enhance the chances of interoperability between the DoD and other Federal systems. In fact, one probable goal is for the new standard to be an extension of TCP, and for TCP users to be able to interoperate with users of the FIPS standard. The NBS has produced several computer communications
===~ interesting insights in an analysis of featu res oftransport layer protocols. First, there is the observation that most such protocols are connection-oriented rather than transaction-oriented. The exception, the Delta-t protocol developed by Dick Watson at Livermore Laboratories, offers a reliable transaction service rather than connections. No protocol studied offered broadcast service, probably because reliable broadcast service has not yet been defined or understood. The authors of the NBS report make the interesting observation that a reasonably efficient transaction mechanism can be added to TCP by modifying only the user interface. This mechanism allows a reliable transaction in a total of three TCP segments, and so compares reasonably well with the Delta-t requirement of two transmissions plus the maintenance of internal state information. In addition, TCP's retransmission facility
would allow an implementation which included a transaction interface to communicate with an implementation which did not include this feature. The authors reached a conclusion that transaction service could be added to a connectionbased protocol much more easily than connection service could be added to a transaction-based protocol, and recommended that connection service be made a basic feature of the transport level. It is interesting to consider the position of the internet datagram protocol in the protocol architecture. This was also examined in the course of the BBN studyfor NBS. It is clear that the bottom two levels of the architecture, which deal with physical and logical links, are below the internet level; it is also clear that the transport level is directly above it. The BBN researchers have recommended that internet be placed as the top part of level three. Part of the reason for this positioning is to per-
mit the standardization of the interface between the transport level and lower levels, and to insulate this level from concerns of whether the transmission travelled over a local network, a packet-switched network, or an internet. Ruth Nelson
REFERENCES 1
Taylor, F 'Open system stan-
2
Comput. system standards' Commun. Vol 1 No 4 (August 1978) pp 210-217 Taylor, F 'Open system standards for open network operation' Comput. Commun. Vol 2 No 5 (October 1979) pp
244-248 3
Houldsworth, J 'Standards for open network operation' Comput. Commun. Vol 1 No 1 (February 1978) pp 5-12
inlomation 4ipnWty
an international journal covering the technical, legal and social issues of computer-based information systems and their use The journal is of interest to engineers, designers, analysts, data processing management, legal advisers, security managers, government officials and top management.
-------------------Further details and sample copy from:
Christine Mullins, IPC Science and Technology Press Ltd., PO Box 63, Westbury House, Bury St., Guildford, Surrey GU2 5BH, England Telephone: 0483-31261. Please send me further details of INFORMATION PRIVACY Name
.
Organization and address ..
Annual subscription £48.00 ($124.80)
'---------------------------.... vol 3 no 4 august 1980
_-----------------187
vol 3 no 4 august 1980
veying an advertising message, presumably with a sliding scale of fees according to the expected popularity of particular pages. Advertising space available on theweather forecast page will undoubtedly command a premium over that available on the futures market page. One possible application of teletext that is being considered with some enthusiasm is that ofwagering information dissemination. The proposal is that offcourse betting organisations could broadcast odds progressively via the teletext service for punters. This would be realised by means of TV sets installed for public viewing in the agencies where bets can be lodged. Similarly, punters who lodge bets from their homes by telephone could access the odds display through modified domestic TV receivers. The degree of success and acceptance of such a scheme would appear to be determined by the timeliness and level of accuracy of the odds display.
Prestel trials The British Post Office Prestel interactive videotex information system will be demonstrated in Australia during 1980. For the purposes of demonstrations, data-communications links will be established between Prestel TV sets and the British Post Office computer network in the U K. The success of the trail is likely to depend to a great extent on the willingness of Australian information providers to contribute local data to supplement the existing BPO information base during the trial period. The trials will be aimed mainly at commercial firms, suggesting that the Australian market is presently being perceived more in terms of closed mode use of the public videotex system, or in terms of in-
house systems. This apparent emphasis on the commercial market seems to be at odds with the reported findings of various European studies which indicated that the most promising market segment for videotex was home information retrieval.
Public packetswitched service The Telecom organization has now made a commitment to offer public packet-switched network facilities nationally by the end of 1982. Technical standards for interfacing equipment will conform to the CCI'H- X.25 Recommendation. The packet-switched service will be based on a digital data transmission network now being implemented by Telecom. This is expected to be available during 1981 for leased data circuits in the high traffic density area of the Sydney-CanberraMelbourne triangle extending to the rest of the country in 1982. The scale of charges for the packetswitched service has yet to be announced. Some observers interpret this recent Telecom decision to accelerate its implementation of a digital data network as a response to potential threats to its monopoly position in data communications arising from the government decision to proceed with a domestic satellite sys tem. Some media organizations which are planning to use satellite channels for distribution of television programmes would probably be in a position to offer capacity on their channels for data-communications services. This prospect may indeed be a spur to Telecom for improving the range of data-communications facilities that it offers. However, legislative changes would be required to permit any organization other than Telecom to operate as a common communications carrier.
Angus Richards 185
USA Transport layer protocol standardization In the ISO open systems architecture, the lower three levels of protocol lie clearly in the domain of communications, while the fourth or transport layer is at the interface between the communication and the distributed processing worlds 1-3. Several sets of protocols for communications services have been defined, and one, X.25, has become awidely used standard in the US and the rest of the world. These lower level protocols are tailored to the particular networkthey serve, and are primarily concerned with efficient and correct deliven/of dat bits across a transmission link Because they are so necessary to any offer of network service, their development has proceeded quite far compared to the higher level, host-host protocol layers. Now that the use of networks has increased and users are demanding more from the network protocol offerings, there is significant activity in developing standards for higher level protocols, at level four and above. The function of the transport protocol is to accomplish data transfer between two hosts, either across a single network or possibly across several connecting networks. Because of this host-host function, and because the lower level protocols effectively mask many of the physical characteristics of the network(s), the transport level protocols can be relatively network independent. However, the nature of the subnetworkwill have a considerable impact on the operation of the transport layer and therefore on its features. Since most of the wellunderstood network applications require reliable, sequenced delivery of data, this must be guaranteed by the transport layer. If the underlying network does not pro186
vide reliable service, then the transport layer must perform error checking to ensure intact delivery, duplicate detection and sequencing to ensure in-order delivery, and an acknowledgement mechanism to communicate the state of the data transfer. Some of these functions can be 'borrowed' from lower layers if they are available; however, care must be taken to maintain a clean protocol layering. Most of the major computer vendors have incorporated these transport services into their network architectures, although not always in a clearly defined transport protocol. Moreover, the standardization effort has not generally progressed to the point where transport level communications is possible between machines from different vendors.
Transport control The US Government has begun looking for standards for its federal networks. While no federal or Ansi standard exists yet for a transport level protocol, the US Department of Defence (DoD) has adopted as its official standard the transport control protocol, TCP. TCP, which has been under development by the DoD Advanced Projects Research Agency (Darpa) since 1974), provides for reliable, sequenced, flow-controlled interprocess communication. It is designed to work over unreliable networks or concatenations of networks, although initial implementations were used over the reliable Arpanet. It has now been implemented on a variety of host processors, which are linked to each other through an internet of packet-switching nets, satellite networks, packet radio networks and
local networks. The lower level services are provided by the protocols indigenous to these individual nets and by the internet protocol, a datagram mechanism for internetwork transmission, which is used by gateways between the networks. TCP and the internet protocol were formerly integrated into a single protocol; their separation allows the development of internet services which do not have the requirement for reliable transport, butwhich may have, for example, delay requirements which are difficult to meet with a protocol like TCP. Recently, TCP has been introduced into the Ansi arena as a candidate for a transport level protocol standard. So far this has been done on a fairly informal basis, with a spokesman explaining TCP at Ansi task group meetings. There are some more formal efforts underway to propose a standard transport level protocol.
N BS study The US National Bureau of Standards is sponsoring a study of higher level protocols, at levels four and above of the ISO open systems architecture. As part of this study, Bolt Beranek and Newman (BBN), USA, is studying transport protocols. The ultimate goal is to produce a draft Federal information processing standard (FIPS), which will then be publicized, commented on, and changed as necessary before being adopted. The effort is being done in cooperation with the Ansi standards groups to avoid duplication of effort and to provide a standard which will be useful to the largest possible community. If the draft standard, which is currently being developed, is compatible with TCP, this will enhance the chances of interoperability between the DoD and other Federal systems. In fact, one probable goal is for the new standard to be an extension of TCP, and for TCP users to be able to interoperate with users of the FIPS standard. The NBS has produced several computer communications
===~ interesting insights in an analysis of featu res oftransport layer protocols. First, there is the observation that most such protocols are connection-oriented rather than transaction-oriented. The exception, the Delta-t protocol developed by Dick Watson at Livermore Laboratories, offers a reliable transaction service rather than connections. No protocol studied offered broadcast service, probably because reliable broadcast service has not yet been defined or understood. The authors of the NBS report make the interesting observation that a reasonably efficient transaction mechanism can be added to TCP by modifying only the user interface. This mechanism allows a reliable transaction in a total of three TCP segments, and so compares reasonably well with the Delta-t requirement of two transmissions plus the maintenance of internal state information. In addition, TCP's retransmission facility
would allow an implementation which included a transaction interface to communicate with an implementation which did not include this feature. The authors reached a conclusion that transaction service could be added to a connectionbased protocol much more easily than connection service could be added to a transaction-based protocol, and recommended that connection service be made a basic feature of the transport level. It is interesting to consider the position of the internet datagram protocol in the protocol architecture. This was also examined in the course of the BBN studyfor NBS. It is clear that the bottom two levels of the architecture, which deal with physical and logical links, are below the internet level; it is also clear that the transport level is directly above it. The BBN researchers have recommended that internet be placed as the top part of level three. Part of the reason for this positioning is to per-
mit the standardization of the interface between the transport level and lower levels, and to insulate this level from concerns of whether the transmission travelled over a local network, a packet-switched network, or an internet. Ruth Nelson
REFERENCES 1
Taylor, F 'Open system stan-
2
Comput. system standards' Commun. Vol 1 No 4 (August 1978) pp 210-217 Taylor, F 'Open system standards for open network operation' Comput. Commun. Vol 2 No 5 (October 1979) pp
244-248 3
Houldsworth, J 'Standards for open network operation' Comput. Commun. Vol 1 No 1 (February 1978) pp 5-12
inlomation 4ipnWty
an international journal covering the technical, legal and social issues of computer-based information systems and their use The journal is of interest to engineers, designers, analysts, data processing management, legal advisers, security managers, government officials and top management.
-------------------Further details and sample copy from:
Christine Mullins, IPC Science and Technology Press Ltd., PO Box 63, Westbury House, Bury St., Guildford, Surrey GU2 5BH, England Telephone: 0483-31261. Please send me further details of INFORMATION PRIVACY Name
.
Organization and address ..
Annual subscription £48.00 ($124.80)
'---------------------------.... vol 3 no 4 august 1980
_-----------------187