July 15, 1992 -- CURRENT STATUS OF THE V.FAST MODEM STANDARD An interview with Donald O'Connor. Chairman of TIA TR 30.1, the American committee of approximately 35 persons representing about 25 companies developing U.S.A. positions on core modem data pump issues for CCITT Study Group XVII. CCITT (Consultative Committee International for Telegraphy and Telephony) is the Geneva-based advisory committee established by the United Nations to recommend worldwide transmission standards within the International Telecommunications Union. CCITT Study Group XVII consists of about 50-60 scientific and industrial organizations (such as manufacturers) and user groups such as national telephone administrations. Study Group XVII is developing the "V.Fast" Recommendation for two-wire duplex modems with data rates above 14,400 bits per second (bps). O'Connor is Fellow of Engineering, Racal-Datacom, Central Engineering Division. QUESTION: There is growing interest in what has been nicknamed the "V.Fast" standard for modem speeds to reach and surpass 19,200 bits per second. How close are we to obtaining the "V.Fast" standard during the Summer of 1992? O'CONNOR: It's more than a year in the future. "V.Fast" is just a nickname. There is no standard V.Fast modem. When the CCITT adopts a V series standard, a number is assigned, such as the V.32 standard for modems with a data rate of 9,600 bits per second or V.32bis for modems capable of operating as fast as 14,400 bits per second. Since we are still using the nickname of "V.Fast" for the standard now being studied, you can tell it is still in the discussion stage. In fact, very little has been decided about the V.Fast standard. What has been accomplished so far is that the new standard will use single carrier modulation for data rates between 9,600 to 24,000 bps in 2,400 bps increments. There may be data rates of 26,400 and 28,800 bps, but performance at these speeds need to be substantiated. Data rates below 9,600 bps are also possible. V.Fast is the most complicated of the V standards to date. Issues still to be decided include the modulation scheme, how to achieve fractional bits per symbol, the channel probing strategy, the startup handshake sequence, automode capability with the installed base of modems, issues such as transmit power control, constellation pre-warping, transmit shaping and many other technical issues. Almost all of the technical issues are still to be decided. Even symbol rates and carrier frequencies are not yet decided. QUESTION: How are these issues decided? O'CONNOR: Manufacturing companies have positions on each of these issues and they prepare engineering papers advocating their positions. Then the Rapporteur Group (a study group which is assigned to a specific issue such as V.Fast) comprised of persons from a number of manufacturers and administrations (national PTTs) come together to evaluate these positions. The competitors thrash out conflicting opinions to reach recommendations that will best serve the needs of customers. Then we make our recommendations to Study Group XVII. When the Study Group tackles the issue, there are further discussions that involve additional users (PTTs). When there is consensus by all those concerned, then a standard can be issued. QUESTION: When can we expect to have the V.Fast standard? O'CONNOR: There's a Rapporteur's meeting scheduled for September 1992, possibly another one in late 1992, a Study Group XVII meeting in January 1993 and another Rapporteur's meeting in the Spring. Then there will be a Study Group XVII meeting in September 1993. The earliest that V.Fast can be approved is at this September 1993 meeting. But considering the significant number of open issues, the first quarter of 1994 is much more likely. QUESTION: Some companies. such as Racal-Datacom, have already announced plans to ship V.Fast modems this year. Will we have to wait until sometime in 1994 to obtain CCITT standard V.Fast modems? O'CONNOR: Yes. There are no standard V.Fast modems today. There can't be a true standard V.Fast modem until agreement is reached in CCITT which may take place in early 1994. Any announced V.Fast modem today is really a proprietary two-wire duplex unit with data rates greater than the V.32bis standard. Most of the details and alternatives for the eventual V.Fast standard are already on the discussion table. The menu is there with major choices before us. I don't expect any new significant technical details will be added to the discussion. Although there are many characteristics before us, the menu has been presented for our selecting. The Study Group has to sort out the best technology. There may also be testing of existing proposals. Meanwhile vendors may produce new modems with speeds greater than V.32bis and the user should consider whether these proprietary modems are flexible enough to meet the eventual V.Fast standard. Since there are still so many outstanding issues, users need to protect their investment via the modem's flexibility to meet the standard. In conclusion, V.Fast today is only a nickname and there are no standard V.Fast modems. Most of the technical details are on the discussion table in CCITT, but it will be a long time before a standard is finalized (September 1993 best case, Spring 1994 more realistic). With regard to proprietary "pre-standard" V.Fast modems, the user, in order to protect his investment, should consider the "pre-standard" modem's flexibility to meet the ultimate standard. +---------------------------------------------------------------+ | From the America Online New Product Information Services | +===============================================================+ | This information was processed with OmniPage Professional OCR | | software (from Caere Corp) & a Canon IX-30 scanner from data | | provided by the above mentioned company. For additional info, | | contact the company at the address or phone# indicated above. | | All submissions for this service should be addressed to | | BAKER ENTERPRISES, 20 Ferro Drive, Sewell, NJ 08080 U.S.A. | +---------------------------------------------------------------+