hes@ecsvax.UUCP (Henry Schaffer) (11/08/85)
I got the glossy 4 page brochure from Digital Communications Associates,
Inc. (the IRMA people) about their FASTLINK (tm) 10,000 bps modem. It
also has 300 and 1200 compatibility, but I thought people might be
interested in some of the "fast" features.
"Data transmission at 10,000 bps or faster." N1
"Asynchronous dial-up connection."
"Automatic error detection and correction." N2
N1- inside it says "Poor quality lines may result in lower transmisssion
speeds."
N2- Correction is done by the sending modem adding a CRC to each packet,
and then, "If the receiving modem detects an error, it requests a
retransmission to insure error-free transmission."
This modem sends out a bunch ("hundreds") of tones, decides which ones
are acceptable for use, and uses these. When the S/N ratio is bad, fewer
bits are encoded on each tone, and this is varied incrementally every few
milliseconds. Also, while this modem is full duplex, it adaptively varies
how much of the transmission capacity is allocated to each direction. (So
I imagine that the "10,000 bps or faster" speed is reached with nearly all
the data going in one direction.)
They call this a "Packetized Ensemble Modem". It comes bundled with a
special version of Crosstalk (r) for IBM PC/clones. The modem has a
superset of Hayes commands, and gives access to its registers containing
"phone line characteristics such as signal-to-noise ratio, number of
retransmitted packets, bits per packet, and frequency offset." It is not
clear how big the packets are, two places say they vary, and one
place says they don't. No mention is made of performance in
a character echo environment. All this fancy stuff is done by "multi-
processor power, capable of handling over 7" MIPS.
The company is at 1000 Alderman Dr., Alpharetta, GA 30201 (404)442-4000
and the list price of the stand-alone version is $2395. (The PC card version
is $400 less.)
--henry schaffer n c state univ
Standard Disclaimer - and I've never even seen one of them (the modems).idallen@watmath.UUCP (11/14/85)
The recent InfoWorld review of the 10,000 bps FASTLINK modems said that a
modem would transmit a single character after a full-second delay. If
you're thinking of using one of these things for interactive typing,
and you're depending on remote echo of characters (as in using a
full-screen editor on UNIX), you'll have to wait *two* seconds for
each singly-typed character to echo.
Their conjecture was that the modems assemble packets, and if not
enough characters fill the packet, the modem will only send the current
partial packet after a time-out. With two modems between you and the
remote computer, this produces a sizeable delay. The company has "no
plans" to fix this.
Sigh. I was so hoping these modems wouldn't have such a tragic flaw.
--
-IAN! (Ian! D. Allen) University of Waterloobobh@pedsgd.UUCP (Bob Halloran) (11/14/85)
Organization : CONCURRENT Computer Corp, Tinton Falls NJ In article <720@ecsvax.UUCP> hes@ecsvax.UUCP (Henry Schaffer) writes: > I got the glossy 4 page brochure from Digital Communications Associates, >Inc. (the IRMA people) about their FASTLINK (tm) 10,000 bps modem. It >also has 300 and 1200 compatibility, but I thought people might be >interested in some of the "fast" features. PC Week reviewed this beastie this week (12 November). Excerpts and comments follow. > > "Data transmission at 10,000 bps or faster." N1 > "Asynchronous dial-up connection." > "Automatic error detection and correction." N2 > >N1- inside it says "Poor quality lines may result in lower transmisssion > speeds." 'In our tests, we achieved error-free transmission at speeds of more than 7000 bps on long-distance lines (between two small towns outside of Atlanta and Boston), and 8500 bps over local lines. Considering that the average throughput with a 1200 bps modem is something like 800 bps...' -- PC Week, 12 Nov 85 >... Also, while this modem is full duplex, it adaptively varies >how much of the transmission capacity is allocated to each direction. (So >I imagine that the "10,000 bps or faster" speed is reached with nearly all >the data going in one direction.) While most connections are in principle full-duplex, in practice the back-and-forth nature of most sessions, and the frequent occurance of a short entry from a user causing a large response from the host, lends itself to such a scheme. >..... No mention is made of performance in >a character echo environment. All this fancy stuff is done by "multi- >processor power, capable of handling over 7" MIPS. 'Neither DCA or Telebit, their partners, view it as a replacement for the ubiquitous Hayes-compatible 1200 or 2400 bps modem in the Source/ Dow Jones/MCI world. Fastlink and its near twin, the Telebit Trailblazer, are intended primarily as high-speed file-transfer devices for moving files to computer systems across the office or across the company.' -- PC Week. The smarts of this thing are apparently a 68000 and the newest TI signal processing chip set. (Any specifics, you analog types?) > The company is at 1000 Alderman Dr., Alpharetta, GA 30201 (404)442-4000 >and the list price of the stand-alone version is $2395. (The PC card version >is $400 less.) > >--henry schaffer n c state univ Bob Halloran Sr MTS, CONCURRENT Computer Corp (Formerly Perkin-Elmer DSG) ============================================================================= UUCP: {decvax, ucbvax, most Action Central}!vax135\ {pesnta, topaz, princeton}!petsd!pedsgd!bobh USPS: 106 Apple St M/S 305, Tinton Falls NJ 07724 DDD: (201) 758-7000 Disclaimer: I doubt that my employer wants anything to do with my opinions. Quote: "When the going gets weird, the weird turn pro..." -- Hunter Thompson
lauren@vortex.UUCP (Lauren Weinstein) (11/16/85)
It isn't really a "flaw." It's part of the basic design. The modems are HALF-DUPLEX 9600 bps modems (in effect). They have some buffering on both ends, but it takes a substantial period of time (something like a second) to do a turnaround. I have one of those modems here that I'm experimenting with--more details when I have more to report. --Lauren--
bobh@pedsgd.UUCP (Bob Halloran) (11/18/85)
In article <720@ecsvax.UUCP> hes@ecsvax.UUCP (Henry Schaffer) writes: > > I got the glossy 4 page brochure from Digital Communications Associates, >Inc. (the IRMA people) about their FASTLINK (tm) 10,000 bps modem. It >also has 300 and 1200 compatibility, but I thought people might be >interested in some of the "fast" features. > > "Data transmission at 10,000 bps or faster." N1 > "Asynchronous dial-up connection." > "Automatic error detection and correction." N2 > >N1- inside it says "Poor quality lines may result in lower transmisssion > speeds." Latest Mini-Micro Systems (Nov 85) has an item on it. Article has test being performed with 'Telebit Trailblazer' (Telebit being the actual developer, DCA is a marketeer licensing it as Fastlink). Test had PC-card version in a Compaq in Washington DC talking to a stand-alone version at Telebit's office in California. "Telephone circuits were established through three long-distance carriers, AT&T, GTE Sprint, and Western Union. The TrailBlazer modem in Washington transmitted files through each carrier, respectively, at 14,819, 11,023 and 9198 bps." -- Stephen J. Shaw, Mini-Micro Systems, Nov 85, p.45 As stated in previous follow-up, they don't intend it for use as an interactive modem, but chiefly for bulk-transfer applications. Seems to me some of the high-volume net sites ought to look into these beasties. Bob Halloran Sr MTS, CONCURRENT Computer Corp (Formerly Perkin-Elmer DSG) ============================================================================= UUCP: {decvax, ucbvax, most Action Central}!vax135\ {pesnta, topaz, princeton}!petsd!pedsgd!bobh USPS: 106 Apple St M/S 305, Tinton Falls NJ 07724 DDD: (201) 758-7000 Disclaimer: I doubt that my employer wants anything to do with my opinions. Quote: "When the going gets weird, the weird turn pro..." -- Hunter Thompson
romain@pyrnj.uucp (Romain Kang) (11/20/85)
> As stated in previous follow-up, they don't intend it for use as an > interactive modem, but chiefly for bulk-transfer applications. Seems > to me some of the high-volume net sites ought to look into these beasties. uucp "g" protocol wouldn't work too well, since the packets are 64 bytes apiece. I remember a few horror stories about the uucp in 2.9 bsd: there is a one second-per-packet sleep in the 2.9 uucp code that everyone comments out. The packet timeout on Fastlink would have a similar effect. Just think of telling your boss that your $2000 modems are putting out 22 bytes per second... However, pyramid!csg has pointed out that one could use a different protocol; also, 'g' is supposed to support 4096-byte packets, though I've never heard of anyone actually using packets larger than 64 bytes. Then again, maybe this is our big chance to break away from uucp altogether... -- Romain Kang, Pyramid Technology Corporation US Mail: 900 Route 9, Woodbridge, NJ 07095 Ma Bell: (201) 750-2626 UUCPnet: {allegra,cmcl2,pyramid,topaz}!pyrnj!romain "Eggheads unite! You have nothing to lose but your yolks!" -Adlai Stevenson
chris@umcp-cs.UUCP (Chris Torek) (11/20/85)
If I understand correctly, FASTLINK has error correction built in; if that is so, one would not want to use the `g' protocol. I think either the `f' protocol (for X.25) or a new `h'ardwired protocol would be in order. -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 4251) UUCP: seismo!umcp-cs!chris CSNet: chris@umcp-cs ARPA: chris@mimsy.umd.edu
lauren@vortex.UUCP (Lauren Weinstein) (11/21/85)
I (and a couple of other sites with these modems on loan) are planning to conduct some experiments. It is very clear that conventional file transfer programs will not function properly "as-is" with a half duplex modem that "simulates" full duplex in this manner. There are also some issues regarding transparency. To operate at high speeds, the modem requires ^S^Q flow control to operate in a particular manner to/from the hosts, or to have full RTS/CTS functions built into the drivers. As has been reported previously, the modem is basically unusable for most interactive applications. True throughput over typical dialup lines has also yet to be determined. Large block sizes on suboptimal circuits could potentially result in massive amounts of time being spent on retries--this is one of the reasons that "smallish" block sizes are usually preferable on dialup circuits, but this modem won't function very well with smallish blocks. One problem that has been reported is that the modems may crash on power glitches and require manually power cycling to recover. Also, right now the modem does not do automatic speed hunting for command input, though that is promised in a future firmware release. More details later. Experiments are really only getting under way. --Lauren--
lauren@vortex.UUCP (Lauren Weinstein) (11/21/85)
Unfortunately, the fact that the modems have error correction built in does not mean you don't need end to end error correction. Loss of data, particularly on busy Unix systems, is very common at even moderate speeds on serial input lines. So the fact that the data got between the modems intact does NOT mean that the data got from the modem to the computer, or from the computer to the modem without loss (particularly if the modems are busy doing retries and are unable to accept new data at full speed). Early indications are that these sorts of flow problems are so common that per packet error checking is still the most efficient way to go, with the issue of packet size being a yet to be determined variable. Overall flow control issues are also still not fully worked out. Right now, we're planning to work with standard file transfer programs and test different flow control techniques and block sizes to see how the modems perform in real life. However, we've all agreed that per block error checking should be maintained over dialup lines, just as it is at lower speeds. These modems may have some uses, but they are definitely not the ultimate. Their lack of true full duplex capability is a very significant factor. --Lauren--