A message could be a simple letter sent by mail. It could be a covering letter with an enclosure. Its enclosure could be a brochure, a printed report, an audio cassette, a diskette containing computer files or any other object you want to send. A message can also be sent by fax. It could be a simple letter, or a covering letter with an 'enclosed' follow-on document.
A message could be a letter sent as a text file to your contact's electronic mailbox which could be accessible either through the public telephone network or by direct point-to-point radio. Most electronic mail systems now accept binary files. A message could therefore be a covering 'letter' for any quantity or type of computer file - a text file, a word-processor or DTP file, a graphics image file, a program-specific data file, an executable file, a digital voice file and so on.
A message could be a telephone call to your contact. Its enclosures could be any number of computer files of any type sent by file transfer between your PC and his during the telephone call. Instead of a telephone call, the message medium could be a direct point-to-point radio call.
To originate a message you simply type it in on the main Message Library window and then save it. Note that here you write only the plain text of the message: no name & address or signatory information. The message is saved under a formal filename LetterNN.wri in the current Nexus database directory. The allocated filename then appears in the Library List box. You then fill in the corresponding Subject of Letter. This is a short description of the letter to help you identify it later.
If you now wish to write the text of another message, you simply press OK to get back to the main Message Library window. If you wish to delete this or any other existing message, Mark its entry in the list by double-clicking in its left margin. Then you click the Delete button.
If you wish to send to your contact this or any other existing message from the library, first mark its entry in the list as described above. Next check that the format you want the message to have is the one shown in the Format box at the bottom left of the library list.
If not, open the format window and select the one you want. The business letter format assumes headed stationery. The private letter format assumes plain paper and therefore puts your own address at the top right. Parliamentary style omits "Dear... " and "Yours ... " which it assumes you will put in by hand. Memo format is simply headed by "To: ", "From:" and "Subject:" plus phone/fax numbers. The invoice format is like a business letter, but omits the contact name, the "Dear... " and all signatory details.
Next check that the medium through which you want to send the message is the one shown in the Medium box at the bottom right of the library list. If not, open the box and select the medium you want. Then click the Send button. The ensuing action depends on which medium you chose.
With electronic mail, you receive files sent to you by all contacts who have left something in your mailbox since the last time you cleared it. However, during a file transfer session your contact can send files to you as well as you sending files to him.
File Transfer can be done automatically, but this requires your contact to have his PC on with his file transfer software in a state ready to receive at the time you choose to send. A file transfer is therefore usually done as an inset to a voice contact session. This allows both of you and your contact to monitor the transfer. It is of particular value when transferring files over an unreliable or intermittently open channel such as an HF radio path.
You will almost invariably use the Post button when doing File Transfers.
The Communication Window allows you to:
In the case of Radio, it calls the contact on the prescribed frequency, using the specified call sign, waits for the specified answer code, transmits in the required modulation mode and so on. In the case of the Public Telephone Network (PSTN) it dials the contact on the given telephone number and awaits connection. It follows corresponding procedures for the other types of common carrier service.
Once the Connect sequence has started, the Connect button becomes a Clear button. The progress of the connection sequence is shown by the 4 indicator 'lamps' on the right.
If you wish to expedite the connection procedure manually, you click the second button which in this example for Radio communication is labelled Tune. (For a PSTN connection it would be labelled Dial.) This will cause the manual Connection Window to be displayed:
This window allows you to define a set of virtual radio frequency bands to suit your particular communications requirements. The example shows some of the amateur radio bands. To mark one of these bands you click in the left margin of the little scroll window next to the name of the band you want to use or search. An analogue presentation of that band appears in the band display at the top left of the window.
You can then sweep the band manually using the direction buttons below the scale. You can scan for existing signals by pressing the Scan button. In this case, the band will be swept automatically until a signal is found. To continue past a signal you simply press the Scan button again.
Two frequencies can be set up simultaneously: one for outbound signals, and one for inbound signals. Thus different bands and different positions of the 'tuning needle' can appear according to whether you have just marked the Inbound box or the Outbound box.
Pressing the Hail button causes the current contact's hailing sequence to be transmitted a predefined number of times. The Acknowledged 'lamp' indicates when the contact's correct acknowledgement sequence has been received. The Connect button puts you on-line, and, for appropriate transmission modes, establishes link level.
If you now press OK then the current inbound and outbound frequencies and modes will be stored for the currently selected contact. If you press Cancel then the contact's details will not be updated, but the settings you have just entered will remain in effect until you select another contact.
This allows you to mark the files you wish to send to your remote contact and then send them, or select a directory into which you want to receive files from your remote contact and then receive them.
Pressing the Terminal button causes the Terminal window to appear:
When the File Transfer window or the Terminal window appears, the Identification window disappears and the Communications window relocates to top left of screen to allow the two windows to be displayed together as shown.
To send files, press Send, and then press the Start button. To receive files from your contact, select the directory into which you want the files to be placed, select Receive, then press the Start button.
A single click opens a Communications Window which allows you to:
When this is done, the main Communication Window accepts the details currently in this person's Communication Window as the context in which it will conduct a new communications interchange. That is, it is this person with whom the Communication Window will establish a communications link, and to whom all ensuing communications activity will be directed by the means and in the mode specified in the contact's Communication Window.
The Communication Window also uses the range and bearing information given by the Map Window to direct the servo which steers the appropriate dish or antenna in the direction of the other party's current location.
From the Identification Window you can also open the Account Window. This holds all the currently active transactions pertaining to this individual, plus creditworthiness information, a summary of all past business and targeted future business.
The full operation of the Account Window is dealt with elsewhere.
Communication between a client and server is by way of an industry standard set of query & command messages. This means that a Nexus installation's clients and servers can be installed at different nodes within the coterie network it is managing.
Refer to Scientific American Sept 1984: Software for Information Management. B Tree. The idea of extracting the top B Tree node into memory at switch-on or whenever an index item is added, deleted or modified.