The Pier Shareware 1/Pier Shareware 1.iso/020a/slick59.exe/COMTUTOR.TXT

Text File | 1992-09-17 | 38KB | 580 lines

    From Simple Software Company....................producers of SlickWare !

                     Telecommunications for the Beginner
                               by G.M. Raymond


      Welcome to the world of Slick Communications. This tutorial is
      intended for the new telecommunicator who is interested in
      learning about the world of modem and computer communications.
      Perhaps you have already heard about modem telecommunications and
      just want more information. This article will tend to serve the
      needs of either person.

      Your first question may be "Just what is a Modem good for?" The
      most common use is to access other computers. This could be to
      exchange data with other computers within a company or to access
      computers of other individuals or companies. This computer
      connection can be made via an ordinary telephone system or on a
      special leased line or network. Perhaps the most ordinary use
      today for individuals, is to use their modem to call other private
      or commercial systems, known as BBS's (short for Bulletin Board
      Systems). These BBS's provide a place for program writers to
      market their products (called ShareWare) and an electronic mail
      forum for messages, questions, and anything of interest to
      telecommunicators. Most people elect to download programs. We will
      talk more about that later.

      First, lets get a handle on terms and definitions. To communicate
      via voice, be it wire or radio, it is necessary to MOdulate our
      voice signal onto the electrical current carried by wire or radio
      wave. Then, on the receiving end, DEModulate the current back into
      intelligent audible sound waves. Essentially we do the same thing
      with a computer. We take data and send it out and reinterpret it
      on the received end. So, this is the job of the MODEM. The humble
      modem is actually a very sophisticated piece of electronics-. Just
      as standardization took hold of broadcasting, with AM and FM
      dominating the available channels today; there has been a slow but
      consistent push to standardize the methods of exchanging data
      between computer modems. First, you should understand that the
      modem, like the computer itself, is just a dumb machine. It too
      (the modem) need a soft-ware program to operate. These are
      generally referred to as Terminal programs or comm software.
      Naturally, we are partial to SLICK terminal because we sell it.
      Fortunately, most all modems still being manufactured today, use a
      set of instructions called Hayse commands which have more or less
      become the industry standard. Most all modems and software found
      on todays market will have the necessary configurability to adjust
      to each other as well as the computer. We need to talk about this
      more.

      Your modem will connect to your computer via a connection
      referenced as a serial port. It might be interesting at this point
      to state that any external peripherals (printers, modems,
      monitors) will usually attach to either a serial or parallel
      interconnection. The basic difference between the two methods lies
      in how the signal is moved through the cable. In a serial
      connection, each bit of data is sent sequentially (that is, one
      after another). It takes 8 bits of data to represent a single
      character of which there are 256 (including 0) characters in the
      IBM ASCII set, or, 7 bits for any character below ascii number
      128. The alphabet and most common punctuations are in the range of
      decimal 33 to decimal 127. So, with a serial connection, 7 or 8
      signals must pass to have one character arrive on the other end.
      By comparison, with a parallel connection, all 7 or 8 bits are
      sent together on eight separate wires in the cable. With this
      system, each character arrives intact and almost eight times
      faster. The parallel method is ideal for supplying devices like
      printers with input data because of its speed. The biggest
      drawback is signal attenuation when trying to use long cables
      (i.e.,stay under 12 feet) and finding accurate method of error
      checking the integrity of the data sent. (i.e. did a character Z
      actually arrive as a "Z"). Sending data serially has certain
      drawbacks when it comes to this error checking procedure. Several
      methods have been developed that have become standards. If you are
      only interested in sending the alphabet, you do not need the full
      byte or all eight bits, remember, seven will do nicely. This is
      because the dec value of 127 in binary form is 0111-1111,
      requiring only 7 bit positions. Starting from right to left, each
      of these bits represents a decimal value of 1,2,4,8,16,32, and 64.
      The sum of these bits equals 127. If the left most bit were to be
      used (1111-1111), its value alone equals 128 so by using 8 bits
      all 255 characters could be encoded and transmitted. That is, a
      range of values from zero (0) to 255. (Yes, zero has a value). The
      bottom line, 7 bit rate transfers are faster but useful only for
      text data. (sometimes referred to as low ascii- [under 128]). On
      the other hand, the eighth bit can be useful for parity checking
      which we will discuss later. If we were to actually use the 8th
      bit for character data this would eliminate parity verification.
      Hence a setting of 7E1 is useful for character (English text)
      only. This also precludes a setting of 8E1 or 8E2. Yes, the 7 is
      the number of data bits used, the E, O or N indicates the use of
      parity or NO parity. The one (1) is for the number stop & start
      bits. There are some technical exceptions to all this but it is
      not important to discuss it here in order for you to generalize
      the grits of the matter.

      EXE Files are made up of ascii characters throughout the entire
      ascii range of zero through 255. (yes, zero is a value to be
      counted....in fact the computer could not survive without it).
      Just to be safe then with only a small sacrifice in speed, 8 data
      bits is the way to go. The next consideration is also one of
      protocol. Do we use 1 or 2 extra bits to signal the start or
      stopping point of the group of 8. There is an argument that can be
      made that two are more reliable than one but it also can be said
      the loss in double the transmitting time isn't worth the extra
      margin of accuracy. By preference, most choose only 1 stopbit for
      their protocol. Now we have to talk about parity. This is nothing
      more than a simple way of testing each character for accuracy on
      the receiving end. There can be either EVEN, ODD or NO parity.
      Parity is simply a checking of the transmitted bits per byte
      (character) to determine if the seven positions make up an odd or
      even number. A zero is used as the eight bit if the other seven
      result in an ODD number of ones and a 1 (one) is used to indicate
      an even number. i.e. 01000001 (normal capitol A) becomes 11000001,
      when parity is set to ODD. The reverse is true for EVEN Parity. (0
      means even) Parity checking is not only time consuming but also
      inefficient. It is rarely used today on anything but older DEC
      mainframes. Finally, we arrive at 8-N-1. Eight bits, No parity,
      and 1 stopbit as the desired order of doing business.

      The IBM Personal Computer or clone has various internal addresses
      for its four normally available serial ports. We reference these
      as COM1,2,3 & 4 but this is not in-fact the actual location
      pointer required by the hardware. $3F8,$2F8,$3E8 and $2E8 are the
      correct locations for these ports as defined in their hexadecimal
      format. (a number system using a base of 16 to represent larger
      decimal values in smaller numbers of bytes, i.e. 65,535 is equal
      to FFFFh [a two byte value]). Next, you must determine what
      Interrupt Request line is to be used internally with each comm
      port. The usual arrangement for COM1 is address 3F8h and IRQ4;
      COM2/2F8h/IRQ3. Seldom will you use more than two comm ports on a
      system although it is not out of the realm of possibility. It
      really doesn't matter what port address you use on a modem until
      you begin to use other serial port devices like a mouse or null
      modem connection (to link up two CPU's by cable). With more than
      one serial connection, it is sometimes important what device goes
      on what port as well as having them properly addressed in order
      for everything to work together smoothly. A good modem will have
      either switches or jumper pins for you to tell it what comm
      address it is looking for and with what interrupt. There is also a
      redundant process here because you must also configure the
      software to operate with the same settings.

      Probably the biggest headache of all is setting the software to
      tell the modem via attention commands (AT), what it needs to know
      to perform the required tasks. In most cases, this is done all at
      once via something called a modem initialization string that
      begins with AT. All modems will initialize with a pre set factory
      designed default setting. Very often it happens that a good modem
      will default to all the correct settings on its own and you are
      just wasting your time re coding an initialization string that
      will only repeat for a second time the built in factory settings.
      Here, several of the more important registers to think about are
      the CD and DTR registers. Normally you want software control over
      these and NOT have them forced on by either dip switch or jumper
      settings. Most all troubles related to problems with hanging up or
      auto-answer can be traced to the MCR register. If your modem
      defaults to &C1 and &D2, great. If not, you need to set them. (via
      the hardware if able and or software modem initialization string.)

      Here are some other recommended settings and what they accomplish.

      M1 ..... Speaker On for Dial,Carrier Detect,HandShake and Result
               Code, then off as DATA begins.
      V1 ..... Verbal Result Codes (examp: CONNECT 2400 rather than a "3")
      X4 ..... Show All available Result Codes
      E0 ..... NO local modem Echo of characters. (The host does this)
      &C1 .... Software control of Carrier Detect Status
      &D2 .... Software control of Data Terminal Ready [MCR] register
      S7 ..... DTMF (touch tone) dialing speed (usually 70ms aprox is ok)
      S0=x.... set this to 0 to prevent your modem from answering your
               phone line or x to the number of rings before pickup.

      This will give you a good idea but please remember, when all else
      fails, read the modem manual. It might be a good point now to
      bring up another related subject. Most computers will not respond
      to the high order graphics and ANSI color signals without the ANSI
      device driver, (found in the DOS diskette) called ANSI.SYS. ANSI
      can be loaded via a statement in the computer CONFIG.SYS file. The
      added line to the SYS file is simply DEVICE=C:\PATH\ANSI.SYS. Of
      course substitute PATH for the actual directory path to the
      location of the ANSI.SYS file. This will allow monochrome systems
      to receive ANSI graphics and at least see the graphics if not the
      color, and color systems to come alive with ANSI color and
      animation. My hats off to the guys who can write good quality ansi
      graphics for they are truly artist as well as programmers.

      It might also be wise to mention that the only difference between
      an internal modem and an external one is the price. There is
      little advantage in my mind in using external modems. Aside from
      their cost increase due to the necessity of having a built in
      power supply plus an external case they are more apt to both
      receive interference (due to poorly shielded cables) as well as
      generate RFI. Since most PC have at least two or three expansion
      slots left over after over zealous purchasing, there is usually
      plenty of room inside the computer case to install the modem. This
      is usually nothing more than slipping the card snuggle into an
      available slot and using one screw to secure it in place. There
      are usually two modular jacks on the back, the upper one for
      cabling to the phone line source and the second for plugging in a
      regular phone for whatever use you may have of it.

      Assuming all has gone well at this point you are ready to boot up
      the computer and run the software. Most all terminal programs
      first clear all registers back to default status with the
      universal ATZ command, then send the required initialization
      string for the subject modem. Unfortunately a lot of programs
      either blank the screen during this process or simply don't allow
      the string to appear on screen in this phase. I am against this
      kind of design because you never know if the modem swallowed the
      string without rejecting it. Meaning, accepted it fully and set
      registers accordingly or returned an ERROR rather than a friendly
      "Ok" reply. The error always indicates that one or more of the
      commands in the modem string is incorrect for that modem. This
      means its hardware controllable only (Dip Switches,etc) or not an
      option of that brand of modem. If just ONE command is at fault,
      the entire string is rejected. Most modems will accept up to but
      not exceeding 40 bytes or characters in the command string.

      If you are preparing to buy a modem for the first time, be
      careful. Like any products, there are good ones and buggy one.
      Sticking with Brand names usually is best and although most modems
      are being made overseas, there are several US and Canadian
      companies making superb products. If you want the latest state of
      the art, look for a modem that supports the newest hardware error
      checking and compression technique called MNP-5 (for Micro Comm
      Network Protocol, level 5). Finally, if you can afford it, there
      are several high speed modems around that run at 9600 baud or
      better. The high speed models almost always work at all the lower
      standard speeds as well. But, in any case, don't buy anything
      below 2400 baud. I say this because the price may be tempting as
      there are companies selling older 300/1200 baud rigs for well
      under twenty bucks. So what DOES modem speed have to do with
      anything? Well, if your one of those folks fond of quoting "Time
      is Money" you can certainly save a lot with a faster modem. Let's
      see what happens here. First of all, what is a baud or baud rate?
      Its the number of BITS per second capable of being transmitted.
      Now, if an average sheet of paper is 80 columns across and 66
      lines deep this counts out to exactly 5280 characters per page if
      completely filled. Now remember, each character may require 7 or 8
      bits to construct. Then we need the extra stop bit, parity bits if
      any and framing bits. We might end up with as many as five
      additional bits per character by the time they are formatted for
      transmission. So, for argument sake, use the value 12 bits X 5280
      characters. This is 63,360 bits. If we send them at the rate of
      300 baud this will take (63360/300) seconds. Or about 210 seconds
      (3 and one half minutes). At 1200baud it's four times faster or
      only 52 seconds. At the 2400 baud rate we half this down to around
      25 seconds. Since an average text page is really only half the
      maximum characters available this means in one minute at 2400 baud
      you could transmit four normal business letters. Since AT&T is not
      free and they have both minimum and time based rates on toll
      calls, there is no question that under some situations a high
      speed modem could easily pay for itself. The average size programs
      today run between 30 and 70k. (each k equals 1024 bytes). Most
      good modems running at 2400 baud will average about 4 seconds per
      k. Why did I use the word average? Well first of all, I left out a
      lot of detail that might have technocrats pulling out their hair.
      In any case, its neither my ability or intention to get too
      technical here but since were into speed somewhat as a subject of
      exploration, let's talk about SLOWDOWNS. Remember earlier we
      discussed a parity check at the byte level for catching errors? We
      said that in most cases it was no longer used. Well, the reason
      for that is due in part to more elegant ways of catching errors.

      Probably the first and simplest of all methods is the CHECKSUM.
      Remember, the setting of each one of the eight bits of a byte
      (zeros or ones) determine its decimal (and character) value up to
      255. So, every byte has a decimal value as well as a character
      value. (i.e. capital A is decimal 65). With two bytes we can carry
      a decimal value up to 65k. This means we could sum the value of
      255 characters and send the total in two bytes of data. If the sum
      on the received end is not the same as the previously sent
      checksum value, the packet is rejected with a NAK and a request
      for re transmitting is made. By limiting the packet size to 128
      bytes, shorter transitions of interference (line noise, etc) wont
      cause bigger delays due to re transmitting of large packets. This
      gives rise to a common mistaken idea that while monitoring a
      download, and errors are reported by the protocol software, that
      the file is corrupted. No, it only means that for every error it
      cost you more time to receive the same packet without error by re
      transmitting. In any case, CHECKSUM was how it began and IT'S
      STILL HERE. I guess that speaks for its staying power. But, like
      everything, it has been greatly improved upon. Now Cyclic
      Redundant Checking, or simply CRC protocols are the rage. Its more
      difficult to explain in simple terms but the bottom line is a CRC
      value is calculated for each packet transmitted and compared with
      what is calculated on the received end. Again the two must agree.
      The accuracy derived from CRC methods lies in its ability to pass
      every bit through a 16 (or 32) bit shift register that does an
      Exclusive OR with the 6th,8th,11th and 15th bit of the 16 bit
      register. Each bit causes the value of the register (which can be
      expressed in four hex numbers) to change to a new value. By the
      time the last bit is processed a number is derived that represents
      a CRC value for the ordered group. This method is almost
      infallible. The method was originally developed to test the
      accuracy of the bit content (program) stored in the ROM's of the
      PC. Programmers specializing in writing transfer protocols soon
      began to incorporate it into their creations. Now, its used almost
      exclusively.

      There are several ways to ask a modem to dial a number for you.
      You can do it manually or call a number from a previously created
      dialing directory that is accessed by the software. To do it by
      hand simply type ATDT followed by the number if you have Touch
      Tone Service. Or ATDP for pulse dial. The string will look like
      this: ATDT288-6550 (note, the modem  ignores  the  hyphen). Or, if
      it's  long distance....ATDT1-504-288-6550. Suppose you wish to
      defeat Call Waiting for this call only (if left on, it can cause
      trouble), the string is ATDT*70,288-6550. *70 is the AT&T
      temporary disable wait instruction, the comma is a modem 3 second
      delay command before continuing with the dial. (this allows time
      for the command to be received and for AT&T to give back a dial
      tone). After entering your dial string you should hear the modem
      taking the line off hook (signaled by the appearance of the dial
      tone in the speaker), the DTMF dial pulses going out, the ring or
      busy tone at the destination number followed by the host modem
      answer tone and handshake, followed by a CONNECT message on your
      screen. The standard for a plain CONNECT is a 300 baud logon.
      CONNECT 1200 and CONNECT 2400 are self explanatory. Some host
      systems require a few carriage returns before you will see
      anything on the screen but most will automatically begin
      displaying after the connect message. Most of the people who
      operate BBS's are hobbyist. Running a BBS represents a form of
      hobby and social activity all rolled into one, similar in a lot of
      ways, to ham radio. Few Boards will give you total, immediate
      access to everything, but there are some exceptions. Most will
      request your real first and last name, a local phone and address,
      (or out of state,if that be the case). Some SysOp's or SYStem
      OPerators, (the guy who owns or manages the Board) will even phone
      you to verify your existence. Other sysop's have even more
      stringent requirements, but, most will simply give you access next
      time they sit at the console and get caught up with their duties.
      (usually within 24 to 48 hours). When BBS's first cranked up in
      the late seventies, Sysop's were sort of groping along trying new
      and innovative ideas. The first BBS'es were, in fact, nothing more
      than message (hence Bulletin) boards. The BBS concept was so new,
      the use of phoney names and cloaked identity was very common. The
      misuse of BBS's for a while even threatened their legality, as so
      called hackers exchanged ideas and information they gathered. Most
      of this was in the form of either passwords to big mainframes,
      private telephone access code numbers and pirated software.
      Fortunately, BBS's have grown up and matured into very legitimate
      forums of information exchange. To this day I still do not have a
      clear understanding of the word Hacker. It seems to mean many
      things depending on who you are talking to. Few Sysop's run
      Bulletin Boards that they authored. They usually use a favorite
      commercial product that seems to best fit their own idea of what a
      Board should do. Sometimes new SysOps fall victim to the advice of
      a so called master sysop or seasoned user. If nothing else, one
      thing you will learn quickly in this business is that there are a
      great deal of self proclaimed computer consultants. What's really
      funny is the true complicity of the machines vrs the real depth of
      knowledge of most of these so called consultants. I think the old
      saying "A little knowledge is dangerous..." is most appropriate.

      Many of the silly dumb questions that come fourth when attempting
      registration on a BBS are a the creative genus (or madness) of
      the Sysop or the author of the BBS program. One of my personal
      gripes is the Sex and Age questions; why not race too, and make it
      a total violation of first amendments rights. Anyway, like it or
      not, you have to comply with the SysOps rules if you expect to
      gain access to his system.

      Most Boards allow some limited ability on first Logon, like
      reading the Bulletins and E-Mail (Electronic Mail). A Menu will
      appear giving you the choices available. It is well known among
      seasoned Sysop's that 99% of all registered users only check in to
      see what's new in the Files Directories. Some BBS automatically
      advise what new files have arrived at time of initial Logon. Some
      Sysop's have the mistaken notion that running a BBS can be a neat
      way to accumulate a lot of good software. It really works in the
      other direction. A good Sysop will have access to files long
      before his local users will. He quickly realizes it is he who will
      ALWAYS be providing the latest files and not his users. For this
      reason I suggest steering away from any Boards that demand certain
      Upload/Down load ratios (what you contribute vrs what you take).

      In any case, most contributors cause more problems than they cure.
      They will repackage (re archive or compress a file under an
      altered name) in order to re transmit it for credit. Sometimes
      they leave important things out that could be grounds for license
      violations of the software. Then there is the Virus thing.
      Although at this point I see NO PROBLEMS AT ALL in this area, the
      potential is there. Perhaps for curiosity sake a few definitions
      might be in order. There are usually three adjectives tossed
      about; Virus, Worm & Trojan. Each has a separate but similar
      meaning with some crossover effects. Basically, a Virus is a
      segment of code that is capable of altering your operating system
      code (like COMMAND.COM) in such a way as to cause the virus
      code to be written into any files you transfer to floppy either
      via the operating system or the executable files themselves. This
      replicates the code (like a virus multiplying) onto disks that may
      ultimately infect other machines. The code theoretically could be
      constructed to remain dormant until a certain system date comes up
      or after the machine is booted so many times. Then it could pop
      its ugly head and cause all kinds of trouble. Possibilities are a
      reformat of your hard drives, a crippling slowing down of the CPU
      clock cycle, altering Interrupt vectors causing system crashes,
      locking the CPU into a constant reboot cycle....the list is
      endless. A Worm is identical to a Virus in damage possibilities
      but its not intended to be passed on or replicate itself.

      A Trojan file is, in my opinion, the worst possible threat. This
      is a program that sells itself as a game or utility while in fact
      is purely intended to cause harm to your system. Why is it so
      dangerous as compared to a Virus or Worm? It has to do with
      Intelligence itself. The kind of PhD education, experience and
      training it would take to write an effective Virus or Worm
      generally would ethically and morally preclude the creator from
      doing it in the first place. He would in reality have to be off
      balance and suffering severe mental and emotional distress to
      conceive of this as entertainment. In any case there are perhaps
      less than a few dozen minds in the country who are even capable.
      BUT, the Trojan is a different story. First, almost any self
      taught programmer could, via the readily available high speed
      compilers available today in any software store, write a simple
      trojan. It might start by playing music, let's say, while using
      that to mask the sound of your hard drive reformatting! It would
      not take much creativity to come up with an idea and write the
      code for it. Anyone familiar with Pascal or "C" could do it. For
      that matter it could be done in BASIC.

      Well, "What can be done?" you ask. Actually a lot if you are
      willing to take the effort. Keep a virgin copy of COMMAND.COM
      locked away on a diskette with a known good copy of the two hidden
      system files. Use a CRC checking Utility to determine the CRC
      value of the original copies, including their exact byte length.
      The man who could alter a file, imbed a Virus, and do it in such a
      way as not to effect the CRC and byte length of the file just
      doesn't exist because that'd almost impossible. (yea, I did say
      almost). Also, just as every criminal act must have a motive, no
      hacker would take the time unless he could get some kind of ego
      trip going. Once he bit your hand it would be meaningless unless
      he got to inform you that you were a sucker and have been had! To
      do this he would probably have an ASCII message in the code to
      that effect. There are many utilities capable of scanning an
      executable file for hidden messages. There are also a number of
      utilities that are capable of searching through an executable file
      for calls to certain DOS Interrupts that would be necessary to
      play havoc with the central processor or mass storage devices
      (hard drives, tapes, etc).

      Right now, in my opinion, this whole business of Virus etc. is
      more a question of knowledge and preparation rather than a current
      reality. Cuba could send a strike force up the Mississippi to
      invade the US via New Orleans. There are even occasional reports
      of vessels at the mouth of the river. What does reason and logic
      say about this? One real tragedy of human nature involving
      personal computers is the user who either unknowingly or while
      engaged in experimentation, trashes his hard drive or corrupts his
      files; and, rather than accept personal responsibility, claims
      foul Viruses did him in. Sort of like a modern version of "Crying
      Wolf". Its been done so often, will we believe it if it ever
      actually does begin to happen?

      Now lets talk about archived files. An archived file is rather
      like a suitcase. A repository or collection of a number of
      separate items, organized or placed in such a matter as to make
      retrieval quick and easy. There is one special difference however.
      Archived files are compressed to their minimum possible size
      before being stored in the archive or suitcase. This compression
      technique can be based on a number of possible algorithms or
      compression formulas. The first clue is the extension of a file.
      Here are several very common ones: .ARC, .PAK, .ZIP, .LIB, .ZOO.
      Generally these are not compatible methods and each requires its
      own special utility (work program) to compress and un-compress.

      There is another method, gaining popularity, called suitcase files
      which have the .EXE extension. When executed, they immediately
      begin spawning many additional files that come from within the
      main suitcase file itself. They are automatically uncompressed as
      they are re-written back to disk by instruction or programming
      from within the suitcase. Since they look like any other
      executable file it is sometimes difficult for the inexperienced to
      tell them apart from ordinary run time programs. There is a trend
      developing, due mostly to the influence of BBS's, to standardize
      the algorithm's (formulas) used to archive. There is to this day
      no clear cut winner. However, ZIP files (for being Zippered up)
      are showing up everywhere, perhaps becoming the dominate method.
      Time will tell. In the meanwhile, it can't hurt to begin
      collecting the top four or five Compression utilities. Then, no
      matter what you encounter, you will be prepared. Most all good
      BBS's carry them all in the Archive/ Compression directory of
      their Files department. Aside from going with the flow, things to
      consider if you have a lot of personal need for storing files are:
      The speed of both compressing and un-compressing, (remember, time
      is money); the degree or % of compression (how much space are you
      really saving); ease of use; extra utilities (i.e. the ability to
      password protect, etc etc); registration cost; support if you need
      it; and suit-casing ability. I like features I find in each of the
      popular methods but, again, due to BBS impact, find myself working
      most often with Zippered files.

      Now its time to talk about how to get the files to your end of the
      computer, (down loading), then we will discuss the opposite
      situation, contributing a file to someone else's system (up
      loading). As with most situations there is sort of a convention of
      thought when it comes to the keys used to manipulate a terminal
      communications program. Normally, PgUp and PgDn bring the upload
      or download menu into view. Lets start first with down loading.
      Assuming you found your way into the Files section of a BBS and
      had opportunity to request a display of all (N)ew files since your
      last visit (or perhaps you used the BBS searching utility to
      determine if what you want is present) your next step is to
      request a (D)ownload. Some BBS require that you be within the
      specific file directory that the file is located before starting,
      some will allow a download from any location within the files
      section. As soon as you request a download, the BBS will usually
      first ask for the protocol name (method of sending the file which
      must be the same on both ends). Some BBS have your preference
      protocol as a default. (a protocol you requested on initial
      registration). Then, the name of the file is requested. If you
      type it in wrong or its really not there, the BBS usually informs
      you. Otherwise you get a message to continue on your end. You
      don't have all-day to reply to prompts, usually 60 seconds or
      less. Here is where you hit PgDn on your end. Depending on the
      protocol selected you may or may not have to retype the file name
      on your end BUT you must pick the SAME protocol. From here on, the
      process is rather automatic and you can usually go about some
      other duties in the room until it beeps that its finished. The
      file will either be deposited into your default directory or if
      the comm program allows, wherever you instructed it to go.

      Let's talk about protocols for a moment. The common ones are
      Ascii, Xmodem, Ymodem and Zmodem. Most everything else is
      variations of these such as Clink, Mlink, Jmodem, Lynx, etc etc.
      Its true that a few protocols are inter-compatible but if you go
      by the rule of sameness for BOTH ends, you can't go wrong. Some
      protocols allow the selection of multiple filename's for transfer
      such as Ymodem/Batch and Zmodem. My own preference is
      Ymodem/Zmodem when available. Zmodem has a few intelligent
      features, that under some trying circumstances, could be handy. It
      has the ability to reduce or increase packet size depending on
      quality of transmission conditions. It also has a crash recovery
      mode. Meaning, if you lost connection halfway through a file
      transfer, you could reconnect and pick up where you left off
      (without repeating the entire file). On the other side of the coin
      there are still a large number of systems using only Xmodem and
      Kermit. Kermit is a protocol used when a personal computer has to
      exchange data with a big main frame. Its seldom ever used PC to
      PC. Because of computer design, storage design etc. packet sizes
      can vary from 128 bytes of data too several k. Sizes of 1k
      (1024bytes) are the more common. The only real reason for limiting
      size is quality of transmission medium. If a transmission medium
      is 100% capable, there really be no need to limit packet sizes. On
      clean systems, Jmodem is popular because of its ability to run up
      to 8k packets. This saves a small amount of time but in my opinion
      not worth the risk of some corrupted bytes getting through. (a
      byte whose value has been altered from its original value by a
      change in one or more of its 8 bits)

      If you desire, you can obtain services on Telephone Network
      systems that are, on average, cheeper than regular long distance
      services. US Sprint has PcPursuit on the Telenet System that cost
      $1.00 per hour for the first 30 hours of time. Yes, there are a
      few hooks. You pay a 30 buck monthly fee regardless of the minimum
      time used and are limited to perhaps only 40 or less cities. Still,
      considering AT&T at $6+ per hour this can save money. Slick has a
      special set of built in Macros to make logging on to Telenet's
      PcPursuit service an easy process.

      Lets talk now about some simple rules of BBS etiquette. First,
      never drop carrier (hang up) when you are finished. Take the time
      to leave via the proper exit (Goodby or Off key). Dropping carrier
      is the equivalent of having a guest suddenly leave your home and
      SLAM the door on the way out. Second, don't POST (leave messages)
      in ALL Capitol Letters. This is the equivalent to shouting in
      someone's face. Third, if you are going to use someone's else's
      BBS, operate according to his rules. If you don't like the rules,
      go some-where else where the rules are more to your liking.
      Finally, be cautious. If you are intent on pranks you should be
      aware that most ALL forms of communication are supervised and
      protected by federal laws. Its easy to get caught when on a phone
      system today as everything is a matter of record. With ESS
      offices, the system can log/trace anything, anytime it's
      necessary.

                                  EOF