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Text File | 1992-05-13 | 9.8 KB | 180 lines

------------------------------------------------------------------------------- The following is one of my bulletins. I thought others might find it helpful for their systems so... ------------------------------------------------------------------------------- HSLINK, by Sam Smith, is a fast, easy to use protocol capable of uploading files during downloads. This can make uploading all but free-of-cost, BEST ACCURATE SPEED OBTAINED HERE WITH HSLINK TO DATE: (12/91) BAUD ERROR COR SPEED 2400 No 236 2400 Yes 279 9600 Yes 1,128 9600 No ??? no valid ones yet--should be around 930 14400 Yes 1,708 OVERVIEW: Simultaneous transfers are often referred to as bi-directional transfers; it is the ability of the protocol to use both the transmit and receive channels (built-in to every modem) at the same time. "Normal" protocols use the one channel for transfer and the other typically goes all but unused-- being used for short acknowledgment of the blocks being transferred. HSLINK allows two files to be sent at once--one upload; one download. The overhead associated with acknowledging a good block of data received are built-in to the protocols other channel along with the data packet that is being transferred to allow taking active advantage of both channels. WHO CAN TAKE ADVANTAGE OF SIMULTANEOUS TRANSFERS? Any modem that is NOT a HST. HST modems have a single high-speed channel. Its back channel operates at a much lower speed and the modem WILL switch back-and-forth--giving the fast channel to the direction in greatest need. For typical bbs operation that places the high speed channel in the hands of bbs transmission and the user side which is typically much slower (keyboarding commands) at the user's disposal. Switching channels is time consuming and any advantage in simultaneous transfers is lost to its user. Now that we know who can't; <grin> let's try to answer the question properly. Any 2400 baud modem--both error correcting and non-correcting Any V.32 or V.32bis modem--with or without MNP or V.42 (EC) Telebit Trailblazers These modems have symmetrical channels--both transmit and receive operate at the same speed. The protocol works just fine with error correcting modem, although error correction is not a requirement. WHAT KIND OF SPEEDS SHOULD I SEE? If you don't have an error correcting modem, you should see speeds exceeding 98% of the rated speed. This means that a 2400 baud modem will be able to get 235 plus cps. Error correcting modems will add to that maximum speed. The reason for this is that they don't require the all of the overhead of start and stop bits. A standard modem has, beside the 8-bits of data, 2-bits of overhead. That is how we got to the 235 above by taking the baud rate and dividing it by the bits per word: 2400/10=240 : 240*98%=235.2 The error correcting modem doesn't always need the overhead (not when transmitting blocks) and the best speed for a 2400-baud error correcting modem is typically 270 rather than 240. A rule of thumb is that we should see an efficiency over 110% if our MNP/V.42 modem is downloading using a clean line and has been set to maximize its capability. Many modems quote a much higher speed; this applies only to the tranfer of text or uncompressed files. Compressed files like ZIP/ARJ/LZH file found on BBS's aren't capable of further compression. If your modem is MNP, disable compression when calling a bbs. If it is V.42, it will do intellegent selection of when to allow/use data compression. That's about the only difference you'll see/need between the two, common correcting methods. WHY AREN'T I SEEING THOSE SPEEDS? (Primarily Error Correcting Modems) There can be as many good guesses as good reasons. The real problem invariably boils down to just one--hardware. Our CPU may be a bit slow when it comes to handling the data stream to/from the modem. The baud rate you set the uart to may not be the optimum selection. You may not have enabled or selected the use/honoring of the CTS signal. A slow hard disk may not be able to write fast enough to also allow the modem to pass all characters without loss during disk writes. Hardware handshaking is a must with EC Modems. If your handshaking is incorrect you will see errors when you are transferring files; it's most evident when uploading a file. If your lost blocks occur at a fairly regularly spaced intervals (every n-kbytes or so) then it's probably the Hard Disk. You can tell the protocol about this problem by adding -HS to the command line that loads HSLINK. If you are running a multi-tasker like DesqView or using EXTENDED memory for a disk cache, the modem can also have more random overrun problems. Often you can solve this problem with an UART (The chip that provides/is the serial port services.) upgrade. Switching to a 16550 gives you a uart capable of holding more than one byte in its receive buffer. This prevents the loss of characters that some experience. If you don't experience a loss of characters, having a 16550 will be of NO advantage to you--it won't speed or make better anything to do with your modem connections. WHAT CAN I DO WHEN IT ABORTS/CRAPS/LOCKS-UP/DIES/ETC? Yeah, well, sooner-or-later it happens to all of us. Equipment is less than perfect and software even more so. At some point, the gods will conspire and the transmission goes south. If you are lucky, you abort the transfer and go at it again. If you are not, you reboot. However, if you have selected the options that retain partial files and also the one that allows recovery (-K -R) you will be able to pick up from the point that your download aborted. If it was an upload that died, you're probably out-of-luck as most BBS software will not retain such uploads in the upload directory. (Nobody wants to be the next caller and spend time downloading a bum file.) OK, I KNOW MORE ABOUT HARDWARE THAN I EVER WANTED TO... JUST HOW DO I USE HSLINK, ANYWAY? Sorry, I get carried away sometimes. HSLINK from the user standpoint is simplicity itself. On the BBS you just select the files you want to download and then... SELECT UPLOAD FROM/IN YOUR TERMINAL PROGRAM Yes, I said to upload! You enter the filename(s) that you are uploading and start the terminal program's upload. HSLINK will handle everything from there and you see files being both sent and received on the HSLINK screen. I said it was easy, didn't I? Well, I meant to... NOTE: Because the BBS doesn't know about the upload until it is returned to after its download process... And, because the bbs will probably be testing the upload for viruses or whatever.. BE SURE TO WAIT AND THEN DESCRIBE THE FILE(S) UPLOADED. IF YOU DON'T WAIT YOU WON'T RECEIVE CREDIT. IF YOU UPLOADED A NUMBER OF LARGE FILES, THIS TESTING CAN RUN SEVERAL MINUTES. REMEMBER, YOU'VE SAVED A BUNCH OF TIME/$$$ ALREADY--SO THE WAIT ISN'T REALLY THAT BAD/COSTLY--JUST ANNOYING. A file is also available to assist you in using HSLINK. HS-INST.ZIP has the necessary files and configuration instructions for installing it in just about every terminal/bbs program out there. If you are familiar with how your terminal program shells to a protocol, you might not even need it. OK, A WHILE BACK YOU MENTIONED SPEED, MY SPEEDS MOVE AROUND LIKE A CHINESE FIREDRILL, THEY ARE ALL OVER THE PLACE. Well, speeds are affected by the overhead involved in finding and opening a file along with then sending info to the other side so that it can create/open a file of that name on its side. This affects the reported speeds on short files. As filesize goes up this affect is minimized. I use 50k as a rule of thumb--anything smaller will be obviously distorted somewhat downward. And by the time we reach 80k or so, the speed should hold pretty steady and only move the speed around by a CPS or two. Error correcting modems throw another variable into the pot. They are buffered. My US Robotics modem has a 4-k transmit buffer. When it fills it on starting up a file send, the baud rate is alarmingly high. It then creeps down to something more believable. No modem program is able to read how full the modem buffer is--so there is no way to tell/compute a 100% accurate value on such a modem. CONCLUSION: HSLINK is as good or better than any other protocol. If you have a modem that can take advantage of simultaneous transfers, it will save you LOTS and LOTS of MONEY!!!. If you can't, its is still as efficient as any other protocol and just as easy or easier to use. All serious modem users-- especially when calling Long-distance--should install and use this protocol. ORDERING: HSLINK may be ordered from Sam Smith using a credit card on his bbs. The bbs numbers are: (818) 891-6780 US Robotics 2400 (818) 891-3772 US Robotics HST 9600 (818) 891-1344 Supra v.32bis/v.42bis It can also be mail ordered from: SAMUEL H. SMITH P. O. BOX 4808 PANORAMA CITY, CA 91412-4808 The voice number for credit card orders is (818) 891-4228. Current price is $20 making it quite a bargain. COPYRIGHT 1991 by Ken Prevo, The Toolkit BBS -- ALL RIGHTS RESERVED Permission for reproduction as a bulletin on public bbs systems is granted as is reproduction by any not-for-profit computer club for the use of or presentation to its members. The above copyright notice must be retained in all reproductions. Lines following the above copyright are optional.