Communications Tools

Today, the term ‘communications’ usually refers to links created between computers by means of high-level protocols, such as Internetworking Protocol (IP), which forms the basis of the Internet. Although modern versions of the Mac OS also support such mechanisms, they also include software that provides communication at a much lower level, allowing information to be conveyed directly between computers, either by means of a serial port or a modem and a telephone line.

Normally, a communications application is required for such a data transfer, although some general-purpose Mac OS programs, such as ClarisWorks 5, can also be used. A typical application has a Settings menu that leads you into the following kinds of dialogue:-

The content of such dialogues is often provided by the Communications Toolbox (CTB), part of the Mac’s system software. The CTB uses communications tools, also known as basic connectivity tools, which are stored as individual files in the Extensions folder. These tools work with any suitable hardware, including a CTB-compatible serial port expansion card.

The following sections describe how to use an application that’s based on the CTB windows. The screen shots are from ClarisWorks 5, an application that uses the CTB throughout.

  Connection Settings

These settings match the software to the actual hardware used to create a link, informing the computer about the port that’s in use and what’s connected to it.

Depending on your version of the Mac OS, there can be restrictions on how you can use the Printer or Modem ports for other purposes whilst AppleTalk is active. For example, with Classic AppleTalk in operation the Printer port can’t be used for anything other than conveying LocalTalk data.

With the Open Transport version of AppleTalk you can use whichever port isn’t assigned to AppleTalk. However, if you need both the Printer and Modem ports for serial devices, you must ensure that the Remote Only extension is available and selected in the AppleTalk control panel.

The following connection tools are commonly used:-

  Apple Modem Tool

This tool is suitable for almost any modem and a telephone link, although it can be difficult to set up if you employ a non-standard modem or require to use some of its more advanced features.

The window is shown here:-

Providing you select the correct device under the Modem menu, most of the default settings should give reasonable results. Note, however, that the Port Settings area is particularly crucial.

The window’s settings are as follows:-

If you have an unusual telephone circuit or non-standard modem you should select Custom Modem in the Modem pop-up menu, which causes this window to appear:-

This contains the following:-

If you check the error correction boxes in the above, the Error Correction and Correction Type pop-up menus in the Menu options area of the main window cease to be greyed-out. However, this only happens when the appropriate type of modem is selected in the Modem menu.

  Serial Tool

This tool should be used if you want to sent data directly to another computer, terminal or personal organiser. It’s ideal for transferring data between a Mac OS machine and a PC.

Its simple window contains the following options:-

Terminal Settings

Traditionally, mainframe computers are reached via a dumb terminal, consisting of a screen, keyboard and serial port. Using the correct terminal settings, you can emulate such a terminal.

• See above for limitations concerning the Modem and Printer ports and AppleTalk.
• Most terminal emulation software employs standard control codes, such as Control-S for Stop and Control-Q for Continue. In some instances, Mac OS software uses the ⌘ key in place of the Ctrl key for the Control functions, although this isn’t always convenient.

The following terminal tools are commonly used:-

  TTY Tool

This emulates a simple teletype (TTY) link, also known as Telex, which is normally employed for conveying 7-bit data to a teleprinter.

• Telex systems normally operate on their own network, segregated from standard telephone circuits. Communication normally consists of only uppercase letters.

Here’s the window provided by this tool:-

which has the following settings:-

  VT102 Tool

This emulates a simple computer terminal of the VT52, VT100 or VT102 type, as used for conveying 7-bit data. The VT100 and VT102 systems are compatible, although the ANSI variation uses separate alphanumeric keys and cursor keys whilst the DEC variant employs escape sequences for the alphanumeric characters plus an alternative set of cursor codes.

The tool uses the four windows described below, which are selected by the scrolling icon list on the left of the main window.

General Window

Screen Window

Keyboard Window

Character Set Window

File Transfer Settings

File transfer software should transport a file over a link without damage and at the highest possible speed. It’s vitally important that the same settings are used at both ends of the link.

The following file transfer tools are used:-

  Text Tool

A very simple mechanism for transferring a plain text file over a link. Note that any resources in a text file, such as the styl (styled text) resource in a SimpleText document, are lost during transfer.

• This tool isn’t usually suitable for transferring other types of file.

  XMODEM Tool

A standard protocol for transferring files over telephone lines using 8 data bits and no software handshaking. It employs CRC or checksums in blocks of 128 or 1024 bytes.

The tool‘s single window has settings for:-

  Claris Kermit Tool

This is an alternative to XMODEM that uses its own transfer process. It’s supplied with ClarisWorks 5, requiring 8 data bits and no software handshaking.

The tool‘s single window has settings for:-

Other Transfer Tools

Other methods of transfer, some of which require special software, include XMODEM-1K, which gives a faster transfer since it always uses 1024-byte blocks. The more advanced ZMODEM provides a wide range of options including 16-bit or 32-bit CRCs. It can send files in batches and can resume the transfer should a crash occur in the middle of the process.

YMODEM, also known as YMODEM-Batch since it allows files to be sent in batches, is a variation of XMODEM that sends information about a file in its first block, including its file name, size and modification date. YMODEM-128, with 128-byte blocks, is rarely used, although the aforementioned YMODEM-1K is sometimes encountered. YMODEM-G is a further development of YMODEM, in which ACK signals are not used and instead reliance is placed on the error correction built into the modem. This makes it particularly suitable for direct connections between computers.

Communicating via a Modem

Most people use a modem to gain access to the Internet. This requires you to dial up an Internet service provider (ISP), giving you access to several different servers, each supporting the protocol required for a specific service, such as the World Wide Web (WWW), email or news.

Testing a Modem

Having set up a communications application, you should be ready to make a connection. Whatever you type or whatever text that you receive normally appears in the connection window of your application: you can usually adjust the size of font and font style to taste.

The link between modem and computer can be tested in this window by typing AT and Return. As you type each character the modem’s status lights should flash. And when you finally press Return an OK should appear in the application’s window.

You can test the dialling in this mode by typing ATDT followed by the phone number and Return. You should hear any conversation on the modem’s speaker (if it has one). When you’ve finished enter a ; (semi-colon) to take the modem off-line.

Establishing Communication

The following information applies to a the ClarisWorks 5 application. Assuming you have the correct Connection Setting, you can try to communicate with another modem. Before doing so, you may need to make entries in the Phone Book, which appears under the Session menu.To establish a link, you must choose Session ➡ Open Connection. As the application dials the number something similar to this appears on the screen:-

where 888-3456 is the number you’re dialling. After a while, you should hear the modems happily screaming at each other: just press Return and hopefully the noise will stop.

Once you’ve made a connection you may find you can’t see what you’re typing. If so, you should check the Local Echo box in the Connection Settings window. Conversely, if everything you type appears twice you should deselect it. Similarly, you should turn Local Echo off for peer-to-peer communication, although you should enable it when communicating with a BBS.

• If you have a tricky problem, try choosing Session ➡ Reset Connection or Session ➡ Reset Terminal and try again.
• Differences in hardware between various telephone networks can cause difficulties. For example, the US telephone system employs an answer tone of 2225 Hz, whilst Europe uses a frequency of 2100 Hz. This can cause problems when calling the USA from Europe.

Transferring Files

Having established keyboard communication you may wish to send or receive an entire file. Many protocols and terminals can handle a binary file, containing all possible digital values, whilst other services, such as email, can only use an ASCII text file, containing values between 0 and 127.

• Variations in files can cause confusion. For example, you should be aware that an ASCII text file can’t contain all the key combinations on your keyboard.

To send a file in ClarisWorks 5, simply select Session ➡ Send File, although if you want to send several files you should select Session ➡ Send Batch. To receive a file you must choose Session ➡ Receive File, and then you must wait.

©Ray White 2004.