The Online World, Odd de Presno [simple ebook reader txt] 📗

stop the process by pressing the ESC key. Procomm has another method called "file logging." You start this by pressing ALT-F1. Procomm requests the file name, and the storage process starts. (Read under "Strip" about the difference between these methods.) If you forget to tell Procomm to store incoming data, then you will most probably lose this data for ever. Do not waste time and money by forgetting to store what you receive!

The term "append"

When downloading text - or anything - it is important to know whether you are appending information to an existing file, or overwriting it (i.e., destroying the old text).

Most communication programs complain with an audible signal, when you try to overwrite an existing file. They will ask you if you really want to delete it, or append the current data.

The term "strip"

The purpose of 'strip' is to remove something from incoming data or to change it on the fly.

When you use ASCII downloading with Procomm, ALL incoming data are being stored. This includes so-called ESCape sequences. If you use File Logging, all control characters (except the line feed and new page characters) are being removed (filtered). If you download text from a computer that uses other ASCII characters for linefeed and return, save time by having the communications program convert them on the fly to their correct form for your computer. You define strip procedures through Procomm's SetUp menu (ALT- S). You can also request automatic conversion of characters to graphics values, or local language variants.

National characters

Special national characters cause problems in many countries. One reason is that they are represented by different internal codes on various hardware platforms, and that some networks are unable to transmit 8-bits data.

Some systems represent these special characters by a 7-bit code, others by an 8-bit code. Some depend on the computer having an internal national language ROM, or that it uses a special (resident) conversion program. What gives good results on an MS-DOS computer, may give rubbish on a Macintosh, Amiga, Atari, or a PC using MS Windows. Many communication programs have features that can help you solve at least some these problems. They let you make translation tables for automatic conversion of special incoming and outgoing characters. If you call a Scandinavian online service using 7 bits even parity, many transfer the national special characters using the ASCII code equivalents of number 91, 92, 93, 123, 124, and 125. Similar, more or less formal standards are in place in other countries.

Protocol transfers

If your purpose is to transfer digitized pictures, a computer program, a batch of invoices, a piece of music or an animated sequence of pictures, it's important that each character (bit) arrives correctly. We achieve this by using protocol transfers.

These files often contain control or binary characters. You cannot transfer binary files without the use of special methods. It is easy to understand why we need protocol transfers when retrieving plain text as tables of numbers, statistics, and financial reports. Transfer errors may have fatal consequences. Protocol transfers are also required when transferring word processor text files having imbedded control codes (like text made with WordPerfect), and compressed files. Here is an example:

Downloading public domain software

First, you need the names and features of the programs that can be downloaded from a service. On most bulletin boards, you must enter a command to navigate to the File Library. Here, they normally greet you with a menu listing available commands.

Try H (for Help!) or ? when you are stuck.

Public domain and shareware programs are stored in subdirectories on my bulletin board. The directories have numerical names. Utility programs for MS-DOS computers are stored in directory 10. Games are stored in directory 17.

Enter L for a list of available directories (other bulletin boards may use different commands). Enter "L 17" to list the files in directory 17. This will give file names, lengths in characters (to help you estimate download time), creation dates, and a short description of each file. You can search for files of interest. When looking for programs that can help you get more out of a printer, you may search using keywords like "printer." Some programs are made available in text form. This is the case with older BASIC programs. (The file name extensions .BAS, .ASC or .TXT suggest that the files contain plain text.) You can download these files using ASCII. Most programs are stored in their executable form, or as one executable file among several in a compressed transfer file (a library of files). On my board, most of these files have the file name extension .EXE or .COM. What transfer protocol to use, depends on what is available in your communications program.

The protocol transfer method explained

The protocol transfer algorithms use methods to check the transfer with automatic error correction. In principle, they work like this:

The sending program calculates a check sum based on the contents of the file. The receiving program does the same calculation and compares the result with the senders' check sum. If the figures match, the transfer was successful. If not, all or part of the file will be retransmitted. These are some popular protocols:

XMODEM

has automatic error detection and correction. Most modern programs have this feature. XMODEM exists in programs for MS-DOS computers, CP/M computers, Apple, TRS-80 Model 100, etc. It is the most commonly used transfer protocol.

XMODEM assumes 8-bit settings in your communications program. The file to be sent is split up into 128 bit sized blocks (or "packets") before transfer. The sender calculates the check sum and adds a check sum bit at the end of each packet. (Packing, sending and checking is done automatically by the software.) The receiving program calculates its own check sum and compares with the sender's. If an error is detected, XMODEM will request retransmission of the last block. XMODEM is reasonably good when there is little noise on the telephone line is low. When the line is bad, however, there is always a chance that the transfer will stop. You cannot use XMODEM on computer networks that use ASCII flow control or ESCape codes. The transfer commands must be given to both computers. You can only transfer one file per command. XMODEM's "packet size" (block length) is short. This has an impact on transfer speed, and especially when downloading from timesharing systems, packet switched networks, via satellites, and when using buffered (error correcting) modems. The control method (8-bit check sum) and unprotected transactions give a low level of safety against errors in the transmission. The transferred file may contain 127 bytes with noise characters (at the end). The creation date of the file is lost in the transfer. These weaknesses have given us better methods. Here are some of them:

XMODEM/CRC

CRC is an abbreviation for Cyclical Redundancy Check. The method guarantees 99.9969 percent free transfer. It still has the other weaknesses of ordinary XMODEM transfers.

YMODEM Batch

is faster than XMODEM and gives a high level of safety in the transfers. When used with some programs, YMODEM can transfer the files' creation time/date. You can transfer updated documents. This will replace documents with an older creation date. Only one party must enter the file name. YMODEM takes care of the rest.

Kermit

is used on many computer platforms, and especially where they use a terminal emulation mode (like VT-100) which makes the use of XMODEM impossible. Kermit is one of the few asynchronous error correction protocols that functions well when exchanging files having half duplex IBM front-end machines.

Kermit can transfer more than one file at the time.

Super-Kermit

is also called Kermit with Sliding Windows. It can transfer many packets before stopping to check the transfer. The protocol is much faster than XMODEM.

ZMODEM

is currently the fastest transfer protocol for many applications. All transactions are protected with a 16-bit or 32-bit CRC. ZMODEM is immune against most error conditions that prevent traditional protocols to achieve correct transfer.

ZMODEM transfers the creation date of the file and its exact contents. The file name is read once, and all transfer commands may be given by the sending program.

Decompression of files

If a file has name extensions like ZIP, LZH, ARC, PAK, LQR, LBR, ZOO, ARJ, or QQQ, you are facing a compressed file. We use such files to achieve faster transfers.

Files having the extension .EXE or .COM may be compressed files that have been converted into a self-extract format. To retrieve the files from a self-extract compressed file, just enter the file's name. To decompress files that have not been made self-extract, you need a utility program. These programs have many names and are available through most bulletin boards.

Transfer problems

Most transfer problems are caused by the communication programs and their (lack of) features.

Some Procomm users have problems with the Kermit protocol. Tip: use 8 bit world length and no parity in your program setup. 7 bits and even parity does not always work (on version 2.4.2).

Uploading

The transfer of data "the other way," i.e., from your disk to a remote computer, requires that you start by making some decisions. Is the file to be sent as plain ASCII? Should I compress it in a distribution file to reduce transfer time, and make it easier to handle for the recipient?

If you are transferring a text file containing special national characters, then these may have to be converted to another format. If your text contains blank lines (like blank lines between paragraphs), you may have to insert a space character at the start of all such lines. Some systems interpret a blank line as a signal telling that transmission is done. The invisible space character prevents this. Some hosts have limitations on line length. They may require that lines be shorter than 80 characters. If you send lines that are too long, the result may be fatal.

Sending electronic mail

If you send your mail too fast, some online services tend to get digestion problems. You must be very accurate with the format of your message. It has to agree with the host machine's rules about line length, and maximum number of lines per message.

Let's assume that you want to send the following message to an electronic mailbox: To: Datatid cc: Anne-Tove Vestfossen Sj: Merry Christmas! Text: Thanks for the box with herring. The taste was formidable. etc .. etc... etc... Greetings, Odd

If this is all you have to say, doing it manually may be as fast as doing it automatically. However, if the line containing "etc .. etc .." is two full pages of text, you may feel differently. Then, the best may be to upload a prewritten letter.

Many Procomm users prefer to split the job in two. They enter the first four lines manually, and upload the body of the text (when the remote computer is ready to receive). Press PgUp to get a menu of various uploading protocols. Select ASCII for transfer of plain text. Procomm will ask for the name of the