Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!elroy!cit-vax!ucla-cs!casey From: casey@CS.UCLA.EDU Newsgroups: comp.dcom.modems Subject: BYTE high speed modem article and the Telcor Accelerator 2496MA Keywords: BYTE magazine article, high speed modems, wild compression results Message-ID: <12997@shemp.CS.UCLA.EDU> Date: 2 Jun 88 04:08:29 GMT Sender: news@CS.UCLA.EDU Reply-To: casey@COGNET.UCLA.EDU (Casey Leedom) Organization: none Lines: 107 For those who haven't seen it yet, the June 1988 issue of BYTE magazine has an absolutely incredible article on modems (volume 13, number 6, pages 102-113). The article is clear, comprehensive, and interesting. It covers the current state of modem protocol standards and describes how some of the most popular high speed modems achieve their performance. SUMMARY: V.32 is a CCITT full duplex 9600 protocol for two wire telephone lines. It was adopted in 1984. It uses echo cancellation to sort out the interference caused by two senders operating at the same time. Unfortunately V.32 was ahead of its time and difficult to implement because it required such sophisticated techniques (high speed signal processors). Many companies responded to consumer demand for an immediately available high speed modem by modifying another, older CCITT standard, V.29 (V.29 protocol engines were/are readily available). V.29 is a full duplex protocol for four wire lines. It was adopted in 1976. The high speed modems designed around the V.29 engines of course have to play games in order to operate over two wire lines. I won't go into the details here - read the article. Many of these modems also incorporate various data compression techniques and almost all of them have error correction of one form or another. Again, read the article for the details - your time will be well spent. The article goes on to describe 13 currently available high speed modems, describing their communication protocols, and compression and error correction schemes. It then goes on to reporting the results of a fairly extensive series of tests which measured the modems' performance over clean and noisy lines. At the risk of getting sued for copyright infringement, I'll include one of the summary tables here: Manufacturer/ Typical line Noisy line Modem MAX AVE MAX AVE Protocol ------------------------------------------------------------------------ Case 4696/VS 8429 6422 4925 3274 V.29/V.27 Concord 296 Trellis 8842 8448 8861 8237 V.32 * Data Race BMX-VM 4963 4704 4829 4339 V.29 Data Race VM I 5520 5136 0 0 V.27 Fastcomm Turbo 2496 3475 2486 3341 2102 V.29 Hayes V-Series Smart Modem 9600 5002 4742 4973 4435 V.32 HDX Microcom AX/9624c 8304 6115 3926 2592 V.29 Racal-Vadic 9600VP 6442 5798 6461 5002 V.29 Telcor Accelerator 2496MA 9091 8256 9082 8362 V.22bis * Telebit TrailBlazer Plus 7152 5568 7229 5078 PEP Telenetics 9600E/V.32 9283 8995 0 0 V.32 * USRobotics Courier HST 8678 8083 0 0 Asym. TCM QAM Ven-Tel EC18K-34 7066 5414 7190 4704 PEP All MIN/AVE figures are bits per second (bps). Test is transmission of 81920 bytes of pseudo random data. Modem/computer connections were fixed at 9600 baud (the lowest common denominator). Full duplex modems (those marked with `*') were tested with full duplex data streams, all others with data flowing in only one direction (the half duplex modems exhibited very poor performance when full data streams were running in both directions). (The Cermetek, NEC, and Universal Data Systems high speed speed modems were not available at the time of publishing for the BYTE article and will be reviewed in a later article.) COMMENTS: As I said above, this is an excellent article and well worth the time to read it. The testing results are valuable to anyone considering buying a high speed modem (though it must be remembered that since almost none of these modems will talk with each other - availability of other modems of the same brand to talk to should also be considered for general use purposes, eg. the Trailblazer for USENET sites). One of the most startling results of the review is the performance of the Telcor Accelerator 2496MA. Using only 2400 baud protocol technology, it was second only to the two true V.32 modems tested for average transfer rates on typical lines, and topped the entire field hands down on noisy lines. This to me is nothing short of astonishing. The Telcor also appears to be practically immune to noise. Finally, it had the cheapest list price ($895) of any of the tested modems. The authors of the BYTE article were also impressed with the Telcor's performance and used it to justify prophecies of 38Kbps modems in the near future. One disturbing aspect of the Telcor is the fact that it accomplishes its miracles of throughput via a proprietary data compression and error correction technique. This bodes ill for the survival of the company unless they want to drop the price of their modems down to $300. At the current price, one's thought is: ``I'll only *ever* be able to talk to other Telcors. I wonder how many other people are going to buy one?'' My advise to Telcor would be to copyright or patent their technique (whichever legalism is appropriate) and license it out to other modem manufacturers at the very least. And if Telcor is truly far sighted, to simply publish their technique and propose it as a standard. They'll win either way in the long run because the consumer will perceive that they won't be stuck with an expensive 2400 baud modem. Publishing their technique would obviously go a lot further along those lines. FINALLY, QUESTIONS: Has anyone gathered any data to support the figures given above, especially for the Telcor 2496MA? Has anyone had any experience with the Telcor? Would anyone at Telcor be willing to debate the benefits vs. liabilities of the proprietary nature of Telcor's data compression, error correction scheme? Casey