Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!usc!sdd.hp.com!spool2.mu.edu!uunet!hayes!tnixon From: tnixon@hayes.uucp Newsgroups: comp.dcom.modems Subject: Re: Abstracts of papers for upcoming V.fast Meeting Message-ID: <3740.279dc38c@hayes.uucp> Date: 23 Jan 91 17:10:35 GMT References: <3736.2796d6db@hayes.uucp> <89753@lll-winken.LLNL.GOV> Organization: Hayes Microcomputer Products, Norcross, GA Lines: 69 In article <89753@lll-winken.LLNL.GOV>, casey@gauss.llnl.gov (Casey Leedom) writes: > 1. My [naive] guess would be that multi-carrier technology would > be a lot better than single-carrier because of multi-carrier's > ability to adapt around bad spots in the frequency response > spectrum. > > Since Hayes is arguing in favor of single-carrier technology > can you give us a brief on what the arguments are in favor > of each? First of all, it's pretty rare to have single tone or other impairment that affects a narrow range of frequencies. Very rare, in fact. Most impairments affect a wide range of frequencies. In a multicarrier modem, it makes sense to be able to adaptively "turn off" (or adjust the number of bits sent on) individual frequencies. In a single-carrier modem, narrow-band impairments don't have much impact, and are generally handled by the equalizer. > 2. With 24Kbps, V.42bis could offer up to 96Kbps and may typically > deliver 48Kbps. Obviously we'll want to run our interfaces > near that 96Kbps in order to give V.42bis a chance to deliver > all that it can. > > What kind of interfaces are we going to use that will operate at > that rate? I don't think that we can expect to push that old > war hound EIA-232 that far. Perhaps this will provide the > impetuous for EIA-422 (or is it 423?) to start appearing as > standard equipment in personal computers, terminals, etc. > Are there interface chips that can operate at this speed and > take most of the load off of the CPU? (DMA output and SILOed > input.) There are two EIA standard interfaces that are likely to be considered the choice for these higher speeds. First is EIA-562, which is "compatible" with EIA-232 (is an entirely unbalanced interface). Two connectors are defined for 562 now: a 9-pin connector (identical to the PC AT), EIA-574, and an 8-pin modular connectors, EIA-561. EIA-562 has the advantage of operating with only +5 volt supply, at up to 64000bps (but can be pushed higher). The best choice will probably be EIA-530. This uses the same 25- or 26-pin connector as EIA-232, but uses EIA-422 (balanced) circuits for signals that change quickly (data, clocks) and EIA-423 (unbalanced) circuits for signals that don't change as often (DTR, DCD, etc.) There are companies that have driver and receiver chips available which can be switched between 232 and 530 on the fly. 530 was designed so that drivers and receivers are in the same place as the most commonly-used 232 circuits. One example of a device which can take the load off the CPU for high-speed transfer is the Hayes Enhanced Serial Port (ESP). It has two 16550AFNs on it, plus an 8031 microcontroller. Both transmit and receive have 1K-byte FIFOs, and the 8031 supports direct DMA transfers to/from main memory. ESP current supports only up to 38400 bps, but I suspect Hayes will come up with a new version that supports higher speeds in the future [this is NOT a product announcement, folks!]. There are similar buffered devices from other companies, but most of them don't preserve backward compatibility with existing comm software (which ESP does). -- Toby -- Toby Nixon, Principal Engineer | Voice +1-404-449-8791 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net