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Introduction

Contents

• Basic principles
• FaxChange Scheme
• Description *.CTL files
• Semaphore files in the FLAG folder
• Restarting the system : what is actually going on?

Basic principles

The FaxChange is modular. It includes the following components:

Gateway	Gateway transfers messages from the FaxChange to the e-mail system, in our case to the MS Exchange. To connect to another e-mail system simply change the gateway. FaxChange can also be connected to several e-mail systems simultaneously -- there are simply more gateways running. The MS Exchange gateway comprises two parts: gatewayitself which transmits messages such as FAX (i.e. sent and received faxes) and mailbox agentwhich facilitates the transport of other messages (receipt confirmations, fax viewing, error messages, etc.) In the following text, GATE-F (GW-F) stands for gateway and GATE-M (GW-M) for mailbox agent.
Server	The server is a "central shift". It distributes tasks to other components.
Convertor	The convertor transfers documents and messages into a fax format -- bitmap picture TIFF Class G4. The conversion of common MS Exchange (RTF text) messages is carried out by a special one-purpose application. The conversion of documents of a different format is carried out by executing the appropriate application from the command line or with the help of DDE (and a consequent printing by the "fax printer"). Of course, everything is fully automatic. Therefore, it is possible to convert all documents on the server, if their applications support printing from the command line or through DDE. The convertor for RTF is saved in the folder convert/small. "The big convertor" for all documents is in the folder as convert/big. MasterConvert, which is a service distributing work to both previously mentioned convertors, operates above the folder convert.
Line driver	The line driver sends prepared faxes and retrieves faxes from the net. Once again it is a self-contained module. Currently, we can use remote controls for the specialized fax cards Brooktrout. Remote control for fax modems Class 2 and Class 1 is in an early beta stage, and the development of drivers for cards Gammalink/GammaFAX has started. Of course, it is also possible to run several line drivers (even drivers of different types) in the framework of one system. Therefore, it is possible for a firm to start FaxChange on one common modem Class 1 and later, when the capacity of one port is no longer sufficient, it can buy another Brooktrout card, e.g. with four ports and use both at the same time.
System Attendant	System Attendant is an important tool to ensure reliable operation. It acts as a "watch dog". At regular intervals, it asks each module if it is functioning correctly. If any module does not reply within the required time, it is considered not functioning. System Attendant will try to stop this modul and restart. If repeated attempts to restart the module are not successful -- i.e. the module is still not replying or stops replying after a while, System Attendant will record all necessary information into eventlog and will also send an e-mail message to the network administrator to inform him about the problem. Currently, there are suggestions to develop a gateway that enables System Attendant to send an emergency message on administrators GMS mobil phone or pager via SMS messages. This way, the network administrator can be notified about the problem immediately.

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FaxChange Scheme

All FaxChange modules communicate with each other solely through the file system. The picture shows the folders through which each particular part "talks" to the other.

The communication is always facilitated in the same manner. A module records each of the binary files that it wants to transfer further to the appropriate folder and in the end it creates file *.CTL, which will include all necessary operating information -- where to send the fax, which files need to be converted, etc.

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Description of *.CTL files

All modules, with the exception of the convertor, use CTL files with the same structure as those of the INI files in Windows 3.1.

As a fax goes through all the components of FaxChange, its CTL file is not generated each time. Instead, new sections are added.

Description of individual items:

SYSTEM

Here one can find system information about the fax --e.g., for a fax that is to be sent one can find its subject, the time priority for which the fax is scheduled, the name of the file with the message, the list of attachments, etc.

FROM

Information about the sender

TO

Information about the addressee. If a fax has multiple addressees, this section is repeated.

FAX_TO

Information about the fax addressee. In this phase, the CTL file includes only one addressee and his phone number (ready to dial).

FAX

List of TIFF files received or ready to be sent.

ATTEMPT

Record of one attempt to send the fax. If a fax was not sent until the n-th attempt, there will be n-sections "attempt" in the CTL file.

All folders except fax/out includes CTL files in two stages. While they are being created (ie. one of the modules writes to them), they have different extension from CTL. As soon as they are closed, the program changes their extension to CTL and so indicates that another modul can take them.

In the folder fax/out , the transfer of CTL files is more complicated:

• The name of the file here is X*.c* where X indicates the priority of the fax (h, n, l). Extension can be either *.ctl (such a fax can be sent by any of the line drivers) or *.c52 (such a fax can be sent only by line nr. 52).
• When some of the lines take the fax in order to send it, the CTL file is renamed to *.NOW (or possibly *.Nxx where XX is the line number). This name stays with the file for the duration of the transmission.
• If the fax was sent without any complications (or was not sent but the maximum number of attempts was made), the line driver renames it to*.STS (or *.Sxx). These files are taken by the server which sends to the user a confirmaton that it has or has not received the message.
• If a fax for any particular reason was not sent and did not exceed the maximum number of trials (attempts to send it will still be made), its CTL is renamed to *.WTL (or *.Wxx). The server renames such files to *.CTL (*.Cxx) after a pause between attempts to send them.
• The viewer of the line of faxes (fxQueue) reviews the CTL files to find out who is the addressee, etc. While they are being reviewed, they are renamed to *.C007.
• The viewer of the line of the faxes is able to temporarily stop the fax -- to delay transmission until the manager gives a new permission to send it. For this time period, the CTL file is renamed to *.CWait.

Convertor receives in the convert/in folder all CTL files much more simply. They include a list of documents to be converted -- each line contains one file name. After the conversion, the *.CTL file is deleted -- that is how the convertor informs the server that the conversion is done. If conversion is not successful, convert/out creates an *.ERR file with the description of the error (or creates no file at all) instead of a *.TIFF file.

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Semaphore files in the FLAG folder

Semaphore files are created in the folder flag . They describe the conditions of the individual modules of the FaxChange and facilitate their communication.

log-?.fxs	Describes how many entries will be made in the eventlog. This flag can be set using fxCfg.
run.fxs	This file is created by the server to order all other programs to run. A longer description can be found in section about restarting the system . The user is not allowed to change this file.
pause.fxs	This file is created by the server as a signal for the line drivers to pause after sending the processed fax -- i.e. to stop sending and only receive. Gateway’s reaction to this flag is to stop receiving messages and send them away from the server. Flag pause.fxs is used while starting the system to facilitate "clean out" in the folder fax/out. More details can be found in section about restarting the system . The user is not allowed to change this file.
down.fxs	This file is created by the server to inform all other programs that they must shut down immediately. The user is not allowed to change this file.
run.l??	The line driver informs the server that it is running. It is the reaction to the flag server run.fxs. More details can be found in section about restarting the system . The user is not allowed to change this file.
pause.l??	The line driver informs the server that it finished sending the fax and now it is not sending any for sure (as a reaction to the flag pause.fxs). More details can be found in section about restarting the system . The user is not allowed to change this file.
down.l??	The line driver finished with a critical error or reacted to the flag server down.fxs. The user is not allowed to change this file.
tst-????.fxs	These files are created by System Attendant. They are created to test the existence of other components of the system. If the destination modul does not delete these files on time, it is considered non-functional. Identification of individual modules: FXSV = server, GWFX = gateway, GWML = mailbox agent, BKTR = driver of Brooktrout cards. The user is not allowed to change these files.
cmd-????.dwn	These files create individual components of FaxChange, if they need to be restarted for some reason. System Attendant deletes them and this way verifies the reception. Identification of individual modules: FXSV = server, GWFX = gateway, GWML = mailbox agent, BKTR = driver of Brooktrout cards. The user is not allowed to change these files.

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Restarting of the system : what is actually going on?

• The server creates the file pause.fxs which orders all line drivers to finish sending an urgent fax and to start to only receive faxes.
• The server waits for answers from all lines (pause.l??).
• If it does not receive an answer within a certain time frame, it will make an entry in the eventlog and stop. System Attendant will try to restart line drivers as well as the server. If this fails, mail will be sent to the network administrator.

  If nothing is happening and the file pause.fxs is in the folder flag, some line driver probably does not answer or is looking for a faxserver.

• After shuting down all lines, the server deletes the fax/out folder -- all files *.NOW (*.N*) are transferred to *.CTL (*.C??) which "saves" faxes that were in process when the power or the system shut down.
• Finally, the server runs flag run.fxs which orders to all other components to start working.

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