812 lines
42 KiB
Plaintext
812 lines
42 KiB
Plaintext
SUBJECT: HOW TO ACT ON A UFO FORMAT BBS FILE: UFO1598
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MUFONET-BBS NETWORK - MUTUAL UFO NETWORK
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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THE MUFON MEMBER'S GUIDE TO BBS-ING !
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Welcome to the exciting world of electronic bulletin boards, also know as BBS's!
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here you will find literally thousands of text files, program files, graphics,
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animation, messages from Users like yourself from all over the world, news-
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wires, games, and the list goes on and on! Before we continue into what you
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will find on-line, let's take a look at what is required in the way of hardware
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and software to enable you to access the vast knowledge available in the world
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of BBS's.
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I. COMPUTER REQUIREMENTS
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To be able to access a electronic bulletin board, the computer you are using
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must contain the following hardware and software:
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A. HARDWARE - First and foremost, in addition to the basic computer and
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keyboard, you must have the following items and their related capabilities;
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1. MODEM: Telephone lines are optimized for the transmission of voice
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signals, which are analog. In order to send computer data, which is
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digital, over long distances, it is necessary to convert the digital data
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into analog signals that can be carried over the telephone line. This is
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the function of the modem.
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The modem initially sends out a continuous high-pitched tone at a certain
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frequency - this is known as the carrier. (This is the screeching noise you
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hear thru the speaker on your modem.) The transmitting modem then receives
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information from the computer (low and high voltages), and transmits this
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information by modulating the carrier (changing the frequency up and down). At
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the receiving computer, the receiving modem demodulates the signal - it
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translates the changing frequency back into voltage changes that the computer
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can understand. (The word "modem" is derived from - MOdulate/DEModulate.)
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2. MONITOR: The monitor which you use should be capable of showing a screen
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with 80 columns (that is, 80 characters or spaces across, from left to
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right), since most BBS's provide graphics, menus and information in this
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format.
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B. SOFTWARE - For virtually every type of computer, there is a proliferation of
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communication programs available. These communication programs can fall into
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three categories:
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1. Commercial software - offered by companies which usually market their
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programs thru commercial advertising, and sell thru software stores,
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computer stores, department stores and thru mail order.
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2. Shareware - This is software which is distributed on-line thru BBS's, and
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sometimes in stores. The software is used on a trial basis, at no
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charge. If you are satisfied with the communications program and
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continue to use it, you are expected to register and pay for it.
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3. Freeware or Public Domain software. This is software which has been
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released into the public domain, and is distributed free of charge.
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Which communications program to use? The choice is usually based on what is
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compatible with the type of computer you are using, price, ease of use (user
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friendly), capability and, often, one just recommended by a friend. In the vast
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region of software, communication programs range from barebone to highly
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sophisticated. The following paragraph will give you some insight towards
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choosing a communications program you will be satisfied with.
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Do not base your choice of communications program solely on the cost of the
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software alone; price does not always guarantee a better product, nor does it
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ensure that the software will best suit your needs. Many of the shareware
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communication programs rival the commercial ones in performance and features.
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Your best choice is one that will fit your current and future needs. So,
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compare features.
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TERMINAL EMULATION
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~~~~~~~~~~~~~~~~~~~~
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There exists many different standards for communications between computers,
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whether or not the communication is between a mainframe or a privately run, home
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computer-based electronic bulletin board (BBS). Terminal emulation usually
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involves translating the commands that are sent to and from the host computer,
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to the functions that are defined by the terminal manufacturer.
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The communications program which you are using usually contains a number of
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terminal emulation files which can be used during computer communications.
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Generally, this should be a relatively easy setup, but what makes it
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difficult at times in choosing the correct emulation is the proliferation of
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available communication programs for virtually every computer manufacturer!
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Coupled with this is the way in which your communication program can be
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configured for each type of emulation; as some communication programs can change
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emulations by simply highlighting a emulation on a list, to having to type in a
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file name and turning on or off other functions.
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If the host computer you are connected to uses full screen applications such
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as menu system or editor, you may need to use the terminal emulation feature. A
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few of the mainframe databases such as Compu$erve, GEnie, The Source or Easylink
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display text line by line. These do not need terminal emulation. However, most
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BBS's do require the use of terminal emulation by your communication program.
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The "standard" used by BBS's is "ANSI". Here are a few examples of types of
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terminal emulations:
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ANSI for ANSI color/graphics
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VT100A for DEC VT100 with ANSI support
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VT100B for DEC VT100 with ANSI and VT52 support
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3101 for IBM 3101 emulation
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WYSE50 for WYES 50 emulation
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TVI920 for televideo 920 emulation
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TVI9XX for televideo 920 and 925 emulation
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The list goes on and on. However, for our purposes of communicating with a
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BBS, our concern is with ANSI terminal emulation.
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Following is a partial listing of communication programs which support ANSI
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emulation. [Note: it would be impossible to list all communications
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programs, since there are virtually hundreds available!]
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Bitcom Deluxe 4.08 SideTalk II 1.0
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Boyan Communications 4.01 MTEZ 1.0
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Qmodem 4.0 PC/InterComm 5.0
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Term Communications Software 6.1 MEX/Pack 1.65
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TermNet 6.1.1 Professional
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Sparkle 2.05 BackComm 1.4
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Crosstalk for Windows 1.0 SeaDoc 4.51b
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ProComm Plus 1.1B Quick Link II 2.0
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pcAnywhere 3.11A Mirror III 1.01
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Smartcom III 1.1 Softerm PC 3.1
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HyperAccess 51.0 MicroPhone II for Windows 1.0
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APE 1.1 ASCII Pro 4.24
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Telix
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This is not a recommendation for any of the mentioned communication
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programs. Rather, this list is provided as a sampling of what's available. You
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alone are responsible for determining the suitability of any program with the
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computer system you operate.
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II. TO SUM IT UP?
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Rather than to go into considerable detail here of the pros and cons of
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individual hardware and software, I'm going to present you with a few items and
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standards that the hardware and software should conform to:
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MODEM -
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Required Features:
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* should be "Hayes" compatible
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* must be designed for your computer
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* can be internal or external
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* baud rate should be a minimum of 300 baud. 1200 baud is acceptable, 2400
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baud is an ideal speed
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* should have "auto-dial capability (can be dialed from the computer) ("Smart
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modem)
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Desirable Features:
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* auto answer (for receiving calls)
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* built-in speaker
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* provision for telephone or voice/data
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* test mode with self-diagnostics
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COMMUNICATIONS SOFTWARE
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Required Features:
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* compatible with your computer
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* able to send proper commands to modem
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* instruct disk operating system to send or receive data
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* control peripheral devices (printer, etc.)
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* ability to up-load and down-load files using protocol to detect errors
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* ability to change communication parameters
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* provide ANSI terminal emulation
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* saves configuration settings for the modem
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Desirable features:
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* choice of speeds (baud rate)
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* dialing directory
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* ability to re-dial busy numbers
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* status line to show communications parameters
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* filtering of unwanted characters
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* ability to capture text in a buffer for storage
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* "Host" mode to receive calls
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* keyboard macros for frequently used commands
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* variety of terminal emulations (ANSI is a must!)
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* useful on-line help
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* saves configuration settings for the modem
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WHY DO WE WANT TO COMMUNICATE WITH OTHER COMPUTERS, ANYWAY?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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* Transfer data files between incompatible computers
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* Enhance your computer
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* Business
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* Personal
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- Obtain software
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- Get up-to-the-minute news and financial information
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- Make travel arrangments
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- Get technical advice
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- Financial transactions
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- Make Friends
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- Send and receive mail
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- Entertainment
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- Go shopping
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- Personal banking
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DATA REPRESENTATION IN A COMPUTER
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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For all their power, computers are very stupid. They only understand two
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numbers: 0 and 1, which are represented inside of the computer by low and high
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electrical voltages. All of the data that the computer deals with (including
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numbers, letters, and special commands) are represented by 0's and 1's; this is
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known as binary notation. In order to understand why computer communications
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works the way it does, it's necessary to take a closer look at how the data is
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represented internally.
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* Each 0 or 1 is known as a bit. Personal computers use combinations of eight
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1's or 0's to represent numbers up to 256.
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* Each combination of eight 1's and 0's is called a byte. The byte is also
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sometimes referred to in communications as a word.
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* The string of bits in a byte may look something like: 01000001. The bits in
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a byte are numbered from right to left, so the leftmost bit is sometimes
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referred to as the eighth bit or the high bit.
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* Each character (the digits 0-9, alphabetical characters, or special
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characters) can be represented by a single byte.
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* Many characters (all printable characters) can be represented by only 7 of
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the 8 bits in a byte.
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* A standardized code for representing characters in binary notation has been
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established; this is known as ASCII (American
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Standard Code for Information Interchange).
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AN EXAMPLE OF ASCII REPRESENTATION
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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As an example of the ASCII code, the letter A (Capital A; this is different
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from lower case a!!) is represented by the decimal number 65. In binary
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notation, this translates to:
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01000001 So the translation goes something like this:
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Character ASCII Decimal Number Binary
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A -------------> 65 -------------------> 01000001
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Note that the first digit in the ASCII binary representation of A is a zero.
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This is true for all "printable" characters (the characters that can be printed
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on your screen). In a pure text file (similar to a printed page), all of the
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characters may be represented by ASCII characters that contain 7 bits. This
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type of file is sometimes called a text file. (Note: Many word processors use
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the high bit for inserting special codes into documents.) Program files and data
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files contain data in a special form, so they require all 8 bits. These are
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sometimes called binary files.
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The two different types of files are generally transmitted differently. The
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main difference to keep in mind is that any errors (wrong bits) in a binary file
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will be much more harmful than in a text file.
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SERIAL AND PARALLEL TRANSMISSION
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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In order for information to be transmitted from one computer to another, the
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series of 8 bits representing each character must be sent. There are 2 ways to
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do this:
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* Parallel Transmission: In parallel transmission, all 8 bits are
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transmitted simultaneously (i.e., in parellel). This obviously
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requires at least 8 wires from the transmitting unit to the
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sending unit. This type of transmission is capable of high
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speeds. Data transmission inside of a computer is in parallel.
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Parallel transmissin is also often used for connecting printers
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to PCs.
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* Serial Transmission: The 8 bits representing each character are
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transmitted one at a time. This slows the data down somewhat;
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however, it allows data to be transmitted using only a single
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wire.
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Serial transmission is used for modem communications.
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RS232C: THE "NON-STANDARD STANDARD"
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The function of the serial adapter is to change the parallel data (inside
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the computer) into serial data. The RS232C has been adapted as the "standard"
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serial interface for microcomputers. However, the standard only specifies the
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number of wires (25), the size and shape of the connectors, and the functions of
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certain wires. In practice, there are many different variations in use.
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Only 3 wires out of the 25 are absolutely necessary for modem
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communications:
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* Number 2: For data transmission
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* Number 3: For data reception
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* Number 7: Common ground
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(In practice, 9 of the wires are usually used for additional modem functions.)
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For the simplest communication connection between two computers, it is only
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necessary to run a cable from the RS232C port on one computer to a RS232C port
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on the second. (The connecting cable is sometime known as a "null modem".) This
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only works over short distances. For communications over longer distances, it
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is necessary to use the telephone lines.
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SYNCHRONICITY!
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~~~~~~~~~~~~~~~~
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Sometimes you may hear reference to "asynchronous", "synchronous" or
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"bisynchronous" transmission. The differences are as follows:
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Synchronous: Depends on precise timing signal from one computer to
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synchronize the sending and receiving computers.
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Bisynchronous: Similar to synchronous, but BOTH computers send timing
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signals.
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These methods allow very fast data transmission; however, they are beyond the
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capabilities of most PCs.
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Asynchronous: The simplest and cheapest method- no timing signals are
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required. Each character is "framed" by start and
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stop bits to designate the beginning and end of a byte.
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Asynchronous transmission is usually used for PC modems.
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START BITS, STOP BITS, AND PARITY
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Sending a continuous stream of bits from one computer to another would just
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be gibberish to the receiving computer- it would be similar to writing sentences
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without any punctuation marks or spaces between the words:
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thisobviouslyisverydifficulttoreadandunderstand
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In asynchronous transmission, it is necessary to separate the individual
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bytes of information. This is done with "start bits" and "stop bits". The
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start bit is an extra bit (usually a "0") that is sent to alert the receiving
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computer that more data is one the way. At the end of each byte, one or 2 stop
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bits are sent to designate the end.
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Inevitably, some data errors will occur during transmission due to "noisy"
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telephone lines or other causes. There are a number of ways to detect any
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errors- the simplest method is by "parity checking". Parity checking uses the
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number of "1" digits transmitted in each byte as a method to check the accuracy
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of the transmission. It requires one additional bit to be transmitted with each
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byte of data - this is known as the parity bit. Parity may be either Even,
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Odd, or None. With even parity, the number of 1's in each byte added to the
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parity bit must be an even number. If the actual data byte contains an odd
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number, then the parity bit is "1"; if the data byte contains an even number,
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then the parity bit is "0". At the receiving end, the number of 1's are again
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summed up...if the number does not agree with the parity setting, the receiving
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modem asks the sender to retransmit the bad byte.
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The type of parity, number of data bits, and number of stop bits are
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commonly represented in a "shorthand" language in communications. The 2 most
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common settings are as follows:
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E-7-1 Even parity, 7 data bits, 1 stop bit after each byte
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N-8-1 No parity, 8 data bits, 1 stop bit after each byte
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If these settings are incorrect when communicating, it is still possible to
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make a connection...However, your screen will be filled with nonsense
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characters.
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MORE TERMINOLOGY: DIRECTION OF COMMUNICATION
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Different terms are used to refer to the direction of communication.
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Simplex: One-way transmission only. (e.g., television)
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Half-duplex: Two-way communication over a single channel, but not at
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the same time.
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Full duplex: Simultaneous 2 way communication- uses 2 frequencies on
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1 wire (e.g., standard telephone communication)
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Echoplex: Same as full duplex, but transmitted character is echoed
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back to the sender. (This acts as a form of error checking.) Most
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systems that you will be communicating with will use echoplex;
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However, a few do not.
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THE FUNCTION OF THE MODEM
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The type of modulation used can affect the number of bits that can be
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transmitted with each frequency change. In the simplest form, one bit is
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transmitted with each frequency change. With more advanced techniques, 2 or 4
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bits can be transmitted with each frequency change. The speed at which the
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modem can change the frequency (modulate) also controls the speed at which it
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can transmit data. Early modems modulated the signal 300 times per second,
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meaning they transmitted 300 bits of data per second.
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To summarize:
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The sending modem receives the computer-generated data and converts it into
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a telephone signal by MODULATING the carrier wave. The receiving modem receives
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this signal and DEMODULATES it, or translates it back into a signal the computer
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can understand.
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THE EFFECT OF CHANGING SPEEDS
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The term baud rate (or baud) is frequently used to designate the speeds of
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modems. Technically speaking, baud rate refers to the speed at which a modem
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modulates the signal. If only one bit is transmitted with each modulation, then
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the baud rate is equal to the number of bits per second (bps) that are
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transmitted. In a 300 baud modem, 300 bits per second are transmitted. However,
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in higher speed modems, the number of bits per second transmitted is higher than
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the modulation speed. A 1200 bps modem actually only modulates the signal 600
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times per second. However, baud rate is usually used interchangeably with bits
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per second. Thus, modems are usually referred to as 1200 baud or 1200 bits per
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second, for example.
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300 baud modems are rarely used any more. The most typical transmission
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speed is 1200 bps, with 2400 bps becoming more common. (The higher speed modems
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are almost always compatible with the lower speed ones.) Note: Faster speeds
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are possible, but they often require complex error-correcting techniques to
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transmit over standard phone lines.
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The effect of varying the transmission speed can be seen by comparing the
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length of time it takes to transmit text documents at various speeds. There are
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about 5.5 characters in the typical word (text word, NOT computer word!), so we
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can make the following comparison:
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Bits Second Characters/second Words/second Words/min.
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300 27 5 300
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1200 109 20 1200
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2400 218 40 2400
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Thus, if you have a 50 line document with 10 words per line, it would take
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over 1 1/2 minutes to transmit at 300 bps. It would take only about 15 seconds
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at 2400 bps.
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MODEM STANDARDS
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~~~~~~~~~~~~~~~~~
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A number of standards for designating just how modems send their signals
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have evolved over the years. The current standard is the Bell 212A standard,
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which covers operation at 300 and 1200 bps. The V.22Bis standard is almost
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universal for 2400 bps operation. For higher speeds (9600 bps) V.32 is being
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adopted as the standard. However, these standards only specify the form of the
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data as it's being transmitted, and factors such as what frequencies are used by
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the modems.
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THE HAYES "UNOFFICIAL" STANDARD
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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There is no official standard covering how modems interface with computers.
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However, the Hayes standard has become almost universal for microcomputers.
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Generally, Hayes (or Hayes-compatible) modems have two significant features:
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* A set of indicator lights on the front panel (external modems.)
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* The modem responds to a standard instruction set and contains
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internal memory registers for various parameters.
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The indicator lights are labeled, and indicate whether or not the modem is
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turned on, the transmission speed, whether the modem is detecting a carrier
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signal and whether the modem is sending or receiving data.
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HAYES MODEM COMMANDS
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~~~~~~~~~~~~~~~~~~~~~~
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The standard commands control the actual functions of the modem. All
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commands are started with "AT". A few of the more common commands are:
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AT "Attention"- tells the modem that a command is coming
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D Tells the modem to dial a number
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P Selects pulse dial (Rotary telephone lines)
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T Tone dial (touch-tone phones)
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A Puts the modem in "answer" mode
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H0 Hang up
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For example, to dial the number 555-1212 on a touch-tone line, the following
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command would be sent to the modem:
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ATDT555-1212
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The modem can also send response messages back to the computer indicating
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when a connection has been made or other conditions. In practice, you usually
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don't have to worry about issuing the commands directly to the modem; the
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communications software will do that. However, occasionally it is necessary to
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modify the commands that the software issues, so it is good to be at least aware
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of the Hayes command set! The documentation for your modem will contain the
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commands set.
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TYPES OF MODEMS
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~~~~~~~~~~~~~~~~~
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Acoustic couplers: Use telephone handset Limited to low speeds
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Rarely used
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Direct connect modems: Connect directly into phone lines using
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RJ-11 jack or other connector. Direct connection eliminates much
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|
noise and allows much faster transmission speeds.
|
|
|
|
Modems may be further broken down into two categories:
|
|
|
|
Internal modems: Mount internally inside computer, Powered from
|
|
computer, Contain the equivalent of RS232
|
|
interface, Must be designed for specific
|
|
computer
|
|
|
|
External modems: "Stand alone" devices, External power supply
|
|
(AC or battery), Connect to RS232 interface
|
|
with cable
|
|
Can be used with any computer
|
|
|
|
Of course, there are other options available. The proliferation of portable
|
|
(or laptop) computers has led to the development of small, battery powered
|
|
modems for use while travelling. There are even cellular modems that totally
|
|
free you from having to find a telephone.
|
|
|
|
CONNECTING YOUR MODEM
|
|
~~~~~~~~~~~~~~~~~~~~~~~
|
|
Internal
|
|
1) Install compatible modem according to instructions. (Modem
|
|
must be designed for specific computer.)
|
|
2) Connect telephone line to modem.
|
|
|
|
External
|
|
1) Need computer with RS232 (serial) port; modem; RS232 cable (if
|
|
not supplied with modem)
|
|
2) Plug one end of cable into RS232 port on computer; other end
|
|
into modem.
|
|
3) Connect telephone line to modem
|
|
|
|
Both
|
|
(optional) Connect telephone to modem
|
|
Note
|
|
-Turn off power before connecting ANYTHING.
|
|
-Check all connections (mounting of internal board, or connectors of
|
|
cable for external) for tightness.
|
|
-Check phone lines for good connection, no broken wires.
|
|
-Adapters may be needed for older "4-prong" phone lines.
|
|
-Use of a modem surge protector is HIGHLY recommended.
|
|
|
|
If an RJ-11 connector is not available (a frequent problem for travellers
|
|
who use their portable computers to go online), there are other options. It is
|
|
relatively easy to connect to a pay phones or "hardwired" hotel phones by
|
|
conducting some minor surgery on the phone handset or cable. This is generally
|
|
harmless, but it should be noted that, strictly speaking, it is also illegal.
|
|
(Instructions are widely available if you want to know exactly what not to do!)
|
|
|
|
|
|
TROUBLESHOOTING
|
|
External only ~~~~~~~~~~~~~~~~~
|
|
Problem Check
|
|
|
|
No lights. Power connection; is switch on?
|
|
|
|
Power to modem, but
|
|
no response from Cable -proper type and connections are tight?
|
|
modem when dialing Software is set for proper comm port?
|
|
|
|
Both types
|
|
Modem responds when Busy line(monitor with speaker or phone),
|
|
poor phone connection (check with phone),
|
|
dialing, but no Noisy phone line
|
|
connection.
|
|
|
|
Connection is made, Change communications parameters (parity and
|
|
stop bits)
|
|
but "nonsense"
|
|
characters appear.
|
|
|
|
Garbled character "High bit" garbling - file contains control
|
|
characters - "Strip the high bit appears
|
|
periodically
|
|
|
|
Double spacing Both computers are adding CR/LF after each
|
|
line - change software configuration.
|
|
|
|
No spacing Neither computer is adding CR/LF after each
|
|
line - change software configuration.
|
|
|
|
Connection OK, but Change to half-duplex (Local echo)
|
|
characters you type
|
|
do not appear on
|
|
screen
|
|
|
|
Connection OK, but Change to full-duplex (No local echo)
|
|
double characters
|
|
appear
|
|
|
|
Occasional garbled Noisy phone line- hang up and try again.
|
|
character
|
|
|
|
Sudden disconnection "Call Waiting", phone answering machine. A
|
|
tip: dialing *70 before the phone number will
|
|
disable call waiting temporarily.
|
|
|
|
FILE TRANSFER TERMINOLOGY
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
One of the biggest advantages to adding a modem to your personal computer is
|
|
the ability to transfer files and programs from your computer to another (and
|
|
vice versa). A few of the more important terms that you encounter in this area
|
|
are:
|
|
|
|
ERROR CHECKING: A method by which files are checked for errors
|
|
caused by "noise" during transmission.
|
|
|
|
FILE TRANSFER PROTOCOL: An agreed upon convention for
|
|
transmitting files between two computers. Usually incorporates
|
|
some form of error checking.
|
|
|
|
UPLOADING: Sending a file from your computer "up" to another
|
|
computer.
|
|
|
|
DOWNLOADING: Sending a file from a remote computer "down" to
|
|
your computer.
|
|
|
|
FILE COMPRESSION: A technique to "squeeze" a file into a smaller
|
|
package to reduce transmission time.
|
|
|
|
BLOCK: A piece or unit of a file that the computer transmits.
|
|
|
|
WHAT KINDS OF FILES CAN I TRANSFER?
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
Two computers can transfer digital data to each other. However, the data
|
|
sent from one computer may not be usable by the other. Generally speaking,
|
|
ASCII text files are the "lowest common denominator" and can be understood by
|
|
all computers. For example, you can send a text file from your IBM to another
|
|
IBM, an Apple, or a mainframe computer and it will probably be understood.
|
|
|
|
Binary files are usually understood by only one type of computer. For
|
|
instance, you can download an Apple program to your IBM successfully and store
|
|
it on disk; but the program won't run on your computer. In a few cases, where
|
|
different computers use the same software, it is possible to send binary files.
|
|
A good example of this is the files created by word processing software. In
|
|
addition, programs written in some special languages are "portable"; that is,
|
|
they can be understood by different computers.
|
|
|
|
FILE TRANSFERS AND ERROR CHECKING
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
When communicating over telephone lines, some errors are bound to occur as a
|
|
result of "noise" in the telephone system. This can lead to characters being
|
|
altered, or the loss of some characters altogether. During the transmission of
|
|
ASCII text files, an occasional error like this is generally not catastrophic.
|
|
Therefore, only simple error checking techniques (such as parity checking)
|
|
can be used in the transfer of text files.
|
|
|
|
During the transmission of programs or important data (generally in "binary"
|
|
files), occasional errors can be important. The loss or changing of a single
|
|
bit may result in a program being unable to run, or may ruin vital data. (Think
|
|
of the result of a single misplaced decimal point in a multi-million dollar
|
|
financial transaction!)
|
|
|
|
For this reason, more-sophisticated error-checking techniques have been
|
|
developed for transferring files. These file transfer protocols monitor the
|
|
quality of the data being transferred, and try to re-transmit any data that has
|
|
had errors introduced. You will often see the terms cyclical redundancy check
|
|
(CRC check) or checksum. These refer to the type of error checking that is
|
|
being performed during a file transfer.
|
|
|
|
FILE TRANSFER PROTOCOLS
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
A file transfer protocol is an agreed-upon method for two computers to be
|
|
able to communicate and check the quality of the data being transmitted. The
|
|
rules governing file transfer protocols establish the amount of data sent per
|
|
unit (known as a data block), how long each side will wait before giving up on a
|
|
file transfer, what character will be used to signal receipt of information, and
|
|
how data will be checked for errors.
|
|
|
|
For the transmission of a file, the computers will first exchange signals
|
|
indicating that each is ready for the start of transmission. The sending
|
|
computer will then break the file into appropriately sized blocks, and send one
|
|
block at a time, followed by error checking data and a signal that the block has
|
|
ended. The receiving computer checks the block for errors that were introduced
|
|
during transmission. If no errors are detected, it signals the sending computer
|
|
to send the next block. If errors are found, then a signal is sent telling the
|
|
sender to repeat the last block. It generally isn't necessary to know the
|
|
details of how the file transfer protocols work. However, it is important to
|
|
know what protocols your software supports. In order to tranfer a file, both
|
|
the sending and receiving computers must use the same protocol.
|
|
|
|
COMMON FILE TRANSFER PROTOCOLS
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
Some common file transfer protocols are:
|
|
|
|
XMODEM
|
|
YMODEM (XMODEM- 1K)
|
|
ZMODEM
|
|
YMODEM-Batch
|
|
KERMIT
|
|
|
|
Probably the most common protocol in use is XMODEM (in several different
|
|
forms). Often, you will also see an ASCII protocol available, too. This
|
|
generally does not employ error checking, and can be only used for the transfer
|
|
of ASCII files. Any of the other protocols may also be used to transfer an
|
|
ASCII text file, and will generally do it faster and with fewer errors than
|
|
ASCII transfer.
|
|
|
|
FILE COMPRESSION
|
|
~~~~~~~~~~~~~~~~~~
|
|
Most systems use some form of file compression. This "squeezes" the files
|
|
into smaller forms, which minimizes storage requirements and transfer time.
|
|
However, the files must be returned to their original forms before they can be
|
|
used.
|
|
|
|
On IBM compatible systems (MS-DOS), the most common forms of file
|
|
compression are ARC and ZIP. Compressed files may be recognized by their file
|
|
extension of .ARC or .ZIP, respectively. In order to use compressed files, they
|
|
must be de-archived using a separate program. This is often called ARC, PKARC,
|
|
PKZIP, or similar names.
|
|
|
|
Apple computers use similar file compression routines. The most common ones
|
|
in use are BLU and ACU. For the Mac, Stuffit is generally used. Specific
|
|
details on these programs and how to use them can be found in the documentation
|
|
for each program.
|
|
|
|
BULLETIN BOARD SYSTEMS (BBS)
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
One type of system that you may frequently want to contact is a computer
|
|
bulletin board system (abbreviated bbs). Typically, on a bulletin board there
|
|
is some sort of electronic mail or messaging system, an area for the exchange of
|
|
files and programs, and other functions such as games. The bbs is run by a
|
|
system operator, or sysop.
|
|
|
|
BBSs are run by a wide variety of people. Most are established on home
|
|
computers by hobbyists or computer clubs; many people run them just for the fun
|
|
of it. They range in size from small home systems to sophisticated, mult-line
|
|
systems. The bulletin boards are generally free, or charge only a nominal fee
|
|
or request donations. Some specialize in certain types of computers or
|
|
operating systems, while others welcome all brands.
|
|
|
|
The message or E-mail area of a BBS is often an excellent place to get help
|
|
from knowledgeable users. Also, want ads for equipment as well as messages
|
|
regarding non-computer subjects can be found. The files area on a BBS is a
|
|
place for the exchange of shareware and public-domain software, as well as other
|
|
files. In addition to local messages, some BBS connect to larger networks
|
|
periodically. In this way, messages are exchanged between local BBS, and in
|
|
some cases can be distributed nationwide.
|
|
|
|
SIGNING ONTO A BBS
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
When you sign onto a BBS for the first time, you will usually be asked for
|
|
information such as your name, address and phone number. This information is
|
|
not given out to the general public; the sysop uses it to verify users and keep
|
|
users from signing on under multiple names. (It's necessary to keep track of
|
|
users, as most BBS have daily time limits for each user. Also, it helps to
|
|
identify destructive users.) You will then be asked to choose a password that
|
|
you will use for future calls. Some systems then do not allow you access for a
|
|
day or 2 until your name and address are verified by a voice telephone call.
|
|
|
|
BBS ETOQUETTE
|
|
~~~~~~~~~~~~~~~
|
|
When you're on-line to a BBS, it's important to remember that you're a guest
|
|
in someone else's computer! Please be sure to follow their rules. In general,
|
|
remember the following:
|
|
|
|
1) Use your real and name and address when it is requested...and don't
|
|
try to use multiple names.
|
|
2) Due to their popularity, most BBS have established daily time limits
|
|
for users. Don't hog too much time!
|
|
3) If you download a lot of files, try to upload some occasionally. If
|
|
you've gotten some interesting software, upload it so others can
|
|
enjoy it, too.
|
|
4) With regards to (3), don't upload any software that you know is
|
|
hacked or pirated commercial software. Most sysops will
|
|
delete it anyway.
|
|
5) See (4) The same goes for any destructive software (containing bombs,
|
|
viruses, etc)!
|
|
6) When uploading, use file compression whenever possible-it leaves more
|
|
room on the BBS for more files, and saves you time.
|
|
|
|
A WORD ABOUT PASSWORDS
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
In order to sign on to virtually any online service (including bulletin
|
|
boards), it is usually necessary to give both your name (or an identification
|
|
number) and a password. On free BBS, this is usually only to control the access
|
|
and ensure that people adhere to the daily time limit.
|
|
|
|
If someone calls up with your name and password, as far as he computer is
|
|
concerned, it's YOU that's online! This is usually not a crisis on a free BBS;
|
|
however, if someone causes destruction while using your name, you'll have some
|
|
explaining to do to the sysop. When you start calling services that cost money,
|
|
though, a dishonest person with your identification can cost you a lot of money.
|
|
Some services can cost well over $100/hour; you could easily end up being
|
|
charged several thousand dollars for someone else's fun!
|
|
|
|
In general, BE PARANOID when it comes to your password!
|
|
1) Don't use anything that is TOO obvious for a password (your
|
|
initials, etc.)
|
|
2) Don't write it down anywhere where it might be found easily
|
|
(documentation books, etc.)
|
|
3) Change your passwords frequently (every month or so)
|
|
4) Don't leave it on disks that you loan to others (i.e., in an
|
|
automatic log-on file).
|
|
5) Never give it to anyone who asks you for it on-line. NO SYSOP
|
|
will ever ask for it like this.
|
|
|
|
NOTE: The same precautions apply when running your computer in "host"
|
|
mode. You don't want just any casual caller logging on to your
|
|
computer and getting access to your files!
|
|
|
|
BOMBS AND VIRUSES
|
|
~~~~~~~~~~~~~~~~~~~
|
|
One of the more unpleasant aspects of downloading software from sources such
|
|
as BBS is the potential presence of bombs, trojans, and viruses. These programs
|
|
may be relatively benign, or can cause serious destruction. They are generally
|
|
disguised as, or even incorporated into, innocent looking programs. Sometimes
|
|
the program may just display an innocent message on the screen; other programs
|
|
may delete data or format disks.
|
|
|
|
Bombs or Trojans: Generally cause destruction by deleting files or
|
|
formatting disks when the program is run. The program may wait for a certain
|
|
time period before doing this.
|
|
|
|
Viruses: Viruses are generally more dangerous than simple bombs. Software
|
|
viruses can "multiply" by copying themselves onto floppy discs, and can be
|
|
spread throughout a collection of discs, or from computer to computer. After
|
|
it has copied itself a certain number of times, the virus may then cause mayhem
|
|
by formatting discs, etc.
|
|
|
|
While the problem of bombs and viruses is not a crisis at this point, you
|
|
should be aware of them, and take some simple precautions:
|
|
|
|
1) Most BBS post an updated list of programs known to contain bombs
|
|
or viruses. Check it occasionally.
|
|
|
|
2) There are a number of programs available (commercial and public
|
|
domain) that protect your system against destructive programs.
|
|
|
|
3) ALWAYS back up your important data in case your disk is formatted.
|
|
(This is especially important for hard disk users,
|
|
and should be done routinely anyway!)
|
|
|
|
Regards, John Komar
|
|
Administrator - MUFONET - BBS NETWORK
|
|
*******************************************
|
|
*THE U.F.O. BBS http://www.ufobbs.com/ufo *
|
|
*******************************************
|