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Initiation responsibility: Head of IT Section, IT Security Management
Implementation responsibility: Head of IT Section
A fax server generally consists of the following components: the IT system itself, the operating system, the communications component (e.g. fax modem, active or passive ISDN card or dedicated fax card) and the actual fax server application. In addition the workstations may require a corresponding fax client.
Before a fax server is procured, the essential factors which will affect its usage must be ascertained. These are:
IT-System
The choice of IT system is generally determined by the performance characteristics required by the software and the operating system. In addition, the IT system must be compatible with the operating system selected. Depending on the requirements for fax server availability, the use of additional protection mechanisms can be considered. Options for ensuring and/or increasing availability include:
Operating system
Fax server applications are available for all common network operating systems such as Unix, Microsoft Windows NT and Novell Netware. When choosing the operating system, the extent to which integration into the existing network is possible and the requirements of the fax server application should be the decisive factors. Where only one network operating system has previously been in use in an organisation, e.g. only servers which run under Unix are used, then if possible that network operating system should be selected and an appropriate fax server application should be purchased. Nevertheless, if a particular software application is the only one to offer a user facility which is urgently required but which will only run on a different operating system platform from that used up to now, then that operating system should be chosen. A change of network operating system brings with it a significant increase in administrative effort. If different network operating systems are already in use on the network, then the one which offers the easiest path to integration should be chosen, provided that the desired fax server application supports it.
Communications component
The communications components establish the connection between the server and the public switched telephone network. Communications are processed using the T.30 protocol. This protocol determines amongst other things the connection setup, the exchange of originator fax numbers and transmission and acknowledgement of the document. Transmissions using the Group 3 standard are generally effected at 9,600 bps and 14,400 bps. In addition, the Modified Huffmann, Modified Read and Modified Modified compression techniques are also in use. The Group 3 standard is the most widely used. There is also a Group 4 standard; however, this requires ISDN. Transmission speeds of 64 KB per second are possible with this standard. The Group 4 standard has not succeeded in becoming as well established in the last few years, as appropriate stand-alone devices are relatively expensive. Moreover, the Group 3 and Group 4 standards are mutually incompatible.
At the start of communication, both the transmission speed and the compression method are negotiated between the devices. The highest speed and the best possible compression procedure which are supported by both devices are selected.
The following communications components can be considered when using a fax server:
a) Fax modem
Fax modems are available very cheaply. However, they are not always sufficiently tamper-resistant and moreover are not supported by all fax server applications when operated continuously. Therefore they should be confined to private usage and to individual workstations.
b) Passive ISDN cards
Passive ISDN cards are simple to build and hence inexpensive. The main communication load is borne by the computer. This can be a problem where heavy use is made of the fax server (e.g. when it is used for serial fax transmissions). With passive ISDN cards, assuming that the recipient has an appropriate device, transmission using the Group 4 standard is generally also possible. If fax data has to be transmitted using the Group 3 standard, then the data has to be converted accordingly. As in the case of fax modems, passive ISDN cards should be used only on a single workstation or in the private domain.
c) Active ISDN cards
Active ISDN cards, also known as ISDN controllers, have a processor of their own. This means they can handle the ISDN protocol largely independently. According to the specification of the Common ISDN API (CAPI), the fax data must be transmitted to the ISDN card in Structured Fax File (SFF) format. Conversion must take place on the fax server. Like modems, active ISDN cards in the Group 3 standard only support transmission rates of 9,600 and 14,400 bps, using the Modified Huffmann compression code. A major disadvantage both of fax modems and also of active and passive ISDN cards is the fact that these can also be used for other purposes than fax transmission, e.g. in modem operation or as a remote access component. However, for reasons of network security this is precisely what one does not want with a fax server. Active ISDN cards can make up to 30 ISDN channels available. When active ISDN cards are used, the ISDN signalling possibilities are also available for automatic fax routing. Despite the fact that they can be used for non-fax operations, active ISDN cards are still positively recommended for use in fax service.
d) Fax cards (if necessary, with ISDN interface)
Special fax cards are optimised for handling the T.30 protocol. They assume the tasks of connection setup and "negotiation" of communications parameters. Data conversion and compression can be performed on the card, thus considerably reducing the load on the fax server. Fax cards which offer fax data transmission rates of at 9,600 and 14,400 bps and use of all three compression techniques are available. These cards also have the advantage that they generally can only handle the T.30 protocol and therefore cannot be used either for modem operation or as a remote access component. Some fax cards are enhanced to include an ISDN interface. The advantage of this is that ISDN signalling can be used for fax routing.
To conclude, therefore, as a rule only active ISDN cards or fax cards should be used on fax servers. The card must be compatible with the application software as not every card is supported by all fax server applications. The number of cards that are necessary depends on utilisation of the fax server. Each channel can transmit approx. 40-50 pages of fax data per hour and per line.
Fax server application
When selecting the applications software, both the volume of faxes which will have to be processed over the fax server and the number of users need to be considered.
If an E mail or workflow system already exists in the organisation, then it should be possible to integrate the application software with these systems. It may then be desirable for incoming and outgoing faxes to be exchanged between the user's personal computer and the fax server using the existing workflow or E mail system. In this connection it is also of interest whether and how any existing address books and distribution lists can be synchronised with the fax server's address books. Moreover, archiving of incoming and outgoing fax transmissions should be possible in existing workflow systems.
Another factor to be considered is how fax transmissions should pass from the user's workstation to the fax server and at what point the data should be converted into a data format which the fax server can accept. Conversion of the outgoing fax data at the workstation is normally effected using a printer driver or a special fax client application. The converted data can then be passed to the fax server either via E mail or else using the fax client application. One option is that the user copies the converted data to a special directory on the fax server. Finally there are fax servers for which a print queue is configured on the network. Fax data is written to this queue by the application software, e.g. a word processing program. It is also possible for full data conversion to be performed on the fax server. In this case, the user creates the file which is to be sent as a fax using appropriate application software, e.g. a word processing program, and this file then has to be sent to the fax server. This can be done using E mail, an appropriate fax client application or by copying to a shared directory on the fax server. It should be borne in mind that conversion of the fax data at the workstation uses up resources there. This is not generally a problem if only a few faxes are sent per day. However, where serial faxes need to be sent, this can mean that the workstation is tied up for a considerable time. On the other hand, if demand is great at the fax server, conversion there will require appropriately high-performance hardware and software.
A final consideration when selecting suitable application software is the logging facilities which are available on the fax server. As well as error reports, transmission reports are also of interest. As a first step the transmission protocols for the relevant fax transmissions should be made available to the users through the fax server. This is the only way to ensure that users respond promptly, e.g. to connection errors. Furthermore it should be possible to calculate the charges incurred from the transmission reports and to distribute these to the relevant cost centres.
Another factor to be considered when selecting the application software is the question of how incoming faxes reach recipients. Digital forwarding of incoming faxes over the network is also referred to as fax routing.
The option that is simplest to implement from the technical point of view is of course to print out incoming faxes at a central location (fax mail centre) and to forward the printout to the recipient. The advantage of this solution is that the incoming faxes are printed out centrally for the files. Moreover, the incoming fax transmissions can be archived both digitally and manually. Furthermore, existing procedures for dealing with staff absences can be accommodated without problem. One disadvantage, however, is the workload at the fax mail centre which it can induce. Again, this approach means that the faxed data is not then available in electronic form at workstations.
Another option is for the fax mail centre to send the incoming faxes to recipients by E mail. Once again, this solution has the disadvantage of creating extra work for the fax mail centre. Nor is every incoming fax automatically printed out. If such a printout is desired for organisational or other reasons, appropriate procedures must be adopted.
The following options are available for the automatic routing of incoming fax transmissions to recipients over the network:
a) Line routing
Under this method, a fixed recipient is assigned to each line. The number of recipients who are directly accessible is limited to the number of lines which are available.
b) Processing and interpretation of originator identifier
A second approach involves assigning faxes on the basis of the transmitted originator identifier (CSID - Call Subscriber ID) of an incoming fax. The fax server is instructed that incoming faxes from certain originators should be routed to a particular recipient. The disadvantage of this approach is that only incoming faxes from originators already known to the system can be automatically routed. All other incoming faxes have to be manually redirected to the recipients. Another problem is that there are no constraints on the choice of originator identification by senders of faxes, so that sometimes these are not a reliable form of identification.
c) Signalling using ISDN
Where ISDN is used, additional possibilities for automatic fax routing are available. A distinction must be made here between "point-to-multipoint connections" and the system connection.
With a point-to-multipoint connection, 2 lines and up to 10 call numbers are available per connection. The call numbers are issued by the relevant telephone company. As long as the fax server is equipped with an ISDN card or a fax card with ISDN interface, the recipient can be determined on the basis of the call number used by the sender. Due to the upper limit of 10 call numbers, it is only possible to distribute incoming faxes to a maximum of 10 recipients.
With an ISDN system connection, a private branch exchange is switched between the public telephone network and the organisation's internal telephone network. With this type of connection the fax server can detect the call number used by the sender and route an incoming fax automatically to the appropriate recipient on the basis of this number. The maximum possible number of recipients is considerably higher with this solution. It is implemented by giving every person expected to receive incoming faxes from the fax server a second direct dial number. The PBX forwards incoming faxes which arrive on this second number directly to the fax server. The only disadvantage of this approach is that the organisation requires a larger pool of call numbers, so that the private branch exchange needs to have a high capacity.
d) Processing and interpretation of the recipient using optical character recognition
Another, but little used method of automatically routing incoming faxes is to use optical character recognition (OCR). An attempt is made here to recognise names or numbers contained in the incoming fax, e.g. in the address field. This solution requires powerful OCR software and appropriate computing power as well as relying on maximum use of standard address fields in the incoming faxes.
e) Other procedures
There are two other procedures for automatic routing of incoming faxes, the Dual Tone Multi-Frequency procedure and the Direct Inward Dialling procedure However, as neither method is usable in Germany, they are simply mentioned here for the sake of completeness.
Automatic routing of incoming fax transmissions has the advantage of reducing the workload of staff in the fax mail centre. It also means that incoming fax transmissions reach the intended recipient more quickly. The main disadvantage when ISDN signalling is used is that heavy demands are placed on the pool of call numbers. On the other hand this is the most effective way of implementing automatic routing of incoming fax transmissions. When the volume of incoming faxes is high, preference should be given to this solution. Where incoming fax transmissions are only sent to a few workstations or groups and generally they are received from the same originators, processing and interpretation of the originator identification is also a practicable solution. If the volume of incoming fax transmissions is only low, then manual distribution may be a viable alternative.
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by Bundesamt für Sicherheit in der Informationstechnik |
last update: Januar 2000 |