NSS Group White Paper: Enterprise Faxing

If your company is typical of the vast majority at the moment, the paperless office is far from a reality.

In fact, the reverse is the case in many organisations thanks to that bane of the rain forest - the fax machine. Paper spews seemingly endlessly from the office fax, and whilst some of it is undoubtedly urgent, the fax has sadly become the latest tool in the armoury of the "junk mailer", resulting in unwanted material which actually costs you money and simply ends up in the bin.

In recent years, most businesses (and even home users) have turned to the fax machine as a means of rapid and reliable transmission of anything from a brief two line memo to a huge document. Irregular service and the occasional strike have led to the postal service being dubbed "snail mail", and the problem is even worse with international deliveries. But if you get your time differences right, you can have a contract delivered from London to New York, signed and returned to your desk in less than 10 minutes using the fax. With a communications medium that efficient - who needs a computer?

In many ways, therefore, the fax machine has done for the "paperless office" concept what DOS has done for personal computers - held up the whole process of technological development. But people don't care. Paper is familiar, and so are telephones - so what could be easier and more friendly than simply sticking a piece of A4 in a sheet feeder and dialling a number?

But the problems start when half of the 30 staff in the sales office all want to use the fax simultaneously, with a resulting queue of very annoyed impatient people, or an overburdened secretary who sends faxes 40 hours, or more, a week.

Either way, the situation is unworkable, so the usual answer is to buy another fax machine, and then another. But there is an alternative - a means of sending faxes without even leaving your desk, and without being told to "come back in ten minutes when the machine might be free" - in the form of a standalone PC or LAN-based computerised fax system.

Given the popularity of the modem as a means to transmit and receive computer data, the transfer of the fax facility to a computer based system was inevitable. Low cost fax modems - with few facilities and relatively slow data transmission rates - have been available for some time now, and in many organisations they have been utilised as stand alone computer based fax solutions for individuals.

But whilst that may be convenient for the individual who has the fax modem initially, the situation can soon turn into a nightmare. The point is that there is still the queue for the stand alone fax machines, and once our hero’s colleagues see how easy it is to send faxes straight from his PC, they soon catch on that all they have to do is save their document to the network and ask him to "fax it to Fred when you have a spare minute".

Therefore, despite the advantages on offer from purely computer-based communications - made available through the proliferation of Local and Wide Area Networks (LAN/WAN) - fax remains popular. The natural requirement is for a link between the enterprise fax and computer systems. This can be achieved either by making a particular user’s fax modem available to everyone (through peer to peer services), or by installing one on (or in) the file server.

This makes use of the currently fashionable - and highly cost effective - notion of a client/server architecture, whereby anyone with access to the network can now send a fax, but the jobs are submitted to, queued at, and processed by the PC acting as the fax server.

With the client/server approach, you gain the benefit of a high performance, high quality central fax machine, yet retain the convenience of being able to fax from your desk. This provides a much more efficient, better managed and controlled fax service for users, which may well pay for the system in itself. There is also the saving on not having to buy reams of expensive fax paper, and more importantly, the ease and relatively low cost of adding extra users to the system, as required, compared to purchasing extra facsimile machines.

A network fax system opens up new application areas too. For example, imagine doing a fax mail-shot to 1000 recipients manually, compared to a few keystrokes on the computer. Or perhaps you could arrange for an overnight report from the head office database to be automatically faxed to all the branch offices before business opens the next day.

The key to the flexibility of the network fax solution - apart from the fact that it is available to everyone without them having to leave their desk, of course - is the superior functionality afforded by the software approach. Building extra functions into a purely hardware device such as a stand alone fax machine can be an expensive proposition. But sophisticated software allows the network fax solution to shine, providing options such as automatic OCR (Optical Character Recognition) of incoming faxes, and auto-routing of incoming faxes directly to the intended recipient’s electronic mail box.

Integration with existing e-mail systems provides an additional level of functionality, allowing all messages to be dealt with from the same utility, and allowing received faxes to be mailed on to other users in the organisation, e-mail messages to be faxed to offices with no e-mail functionality, and so on.

Whereas many of the computer-based fax software packages currently available are network aware, we are beginning to see a whole new breed appearing which are specifically designed to be used on a network. For those sites who are running Novell NetWare, new developments include the ability to run fax server software as a NetWare Loadable Module (NLM).

In making the move to a client-server architecture for faxing, however, many organisations have made the mistake of attempting to use existing modems - previously purchased for personal fax applications - at the server.

Undoubtedly this approach does work, yet unless the faxing requirements are in the order of a few pages per day, bottlenecks rapidly occur. Assuming - quite rightly in most cases - that the modem itself is the cause of the bottleneck, the hapless network administrator adds more modems to the server. Once all the server’s COM ports are in use, an intelligent serial port processor card is added to the server and the modems attached to that.

What is not usually taken into account is the effect this has on the server itself. Communications via the serial port - even when using intelligent I/O cards - can place a severe load on the host server, and thus have a detrimental effect on the network as a whole.

In addition to which, none of the Class 1 and Class 2 modems currently on the market support advanced features like MMR or ECM, which can certainly have a detrimental effect on your telephone bill!

This is where intelligent fax co-processor cards come in, and the subject of intelligent fax card vs external Class 2 modems is the main focus of this mini-report.

The world of facsimile communications is still one filled with arcane terminology and mystery as far as many users are concerned. Let’s face it, as long as we can stick the paper in one end and a copy of the contents appear at the remote destination then everything is OK - right? Wrong!

It is important to have at least a basic understanding of fax technology in order to best understand and take advantage of the advanced features available on many of today’s high-end fax machines and computer-based fax cards.

Believe it or not, the first successful fax device was patented way back in 1843, with the first commercial fax service being introduced in France over 20 years later in 1865.

Through the 1930’s and 40’s fax evolved into more or less the form we recognise today, and as it became more widely used, standards were developed to enable communication between fax devices of different manufacture.

In 1966, the Group 1 standard made possible the more generalised use of fax, although transmission times were slow (up to six minutes for a page of text) and the resolution was poor. 1978 saw the release of the Group 2 recommendation by the CCITT (now the Telecommunications Standardisation Sector (TSS)), which was adopted by all fax machine manufacturers. Finally, in 1980 the Group 3 digital fax standard was implemented (based on the ITU-T Recommendation T.4), offering higher speeds (about 30 seconds for a page of text) and better resolution.

The next stage is Group 4, which will take transmission speeds to a new high (less than 5 seconds per page) and introduce new features such as colour. It is an all-digital standard, however, requiring an ISDN or leased line connection to operate. In the meantime, the Group 3 standard is continuing to evolve to provide many of the features of Group 4 over standard telephone lines.

Since many computer users were already using data modems, the addition of fax capability seemed a logical step forward. Since scanning a document - necessary with a standard fax device - naturally introduces image degradation, computer-based faxing (CBF) provides a marked improvement in image quality at the receiving end. Text and graphics produced on a PC and faxed directly from that PC are far superior in quality to anything coming from a regular fax device.

The origin of the fax modem is directly traceable to computer data modems. Standard fax modem technology today is known as V.29, and is based on the four wire, full duplex, leased line modem originally used to connect IBM mainframe terminals over polled networks. It is apparent, therefore, that V.29 was not originally devised for fax, though that is now its most popular use. The fax standards committee applied the V.29 specifications, modulation scheme and encoding methodology to fax because it correctly assumed they would work effectively on dial-up lines.

The structure of a modern fax machine’s call is governed by the T.30 specification, which defines the handshaking protocols and procedures for establishing and managing communications between two fax devices.

Phase A - The two units connect over the telephone line and recognise each other as fax machines. Handshaking is accomplished via the piercing tones we all know so well!

Phase B - This is the "pre-message" procedure, and it is here that the receiving unit identifies itself and describes its capabilities, whilst the calling machine responds with information about its own capabilities. Information regarding modem speed, image width, image encoding and page length is exchanged, before the two machines perform a "training sequence" to establish the maximum transmission speed.

Phase C - This is the fax transmission itself, along with the various synchronisation, line monitoring and problem detection functions necessary to ensure error-free transmission.

Phase D - The is the "post message" procedure which is performed at the end of each page, and determines whether the fax is to continue (back to Phase C for the next page) or terminate (on to Phase E). Signalling and retraining between pages is one of the biggest causes of errors, failures and long transmission times between fax machines from different vendors.

Despite the proliferation of low-cost fax modems which are capable of transmission at 14400 bps, there is still a huge installed base of fax devices which are limited to 9600bps.

Those which are compliant with the TSS V.17 extension to the Group 3 standard can transmit data at 14400bps (50 per cent faster than 9600bps modems), but are still restricted to the same 300bps handshaking and retraining of the slower machines.

It is worth pointing out here that if two devices of different speeds are communicating, then data transmission takes place at the speed of the slowest device.

It is also worth pointing out that although 14400bps devices are often said to transmit business letter faxes at about 6 seconds per page, this sort of speed actually requires MMR compression (see next section), a feature rarely supported by low cost fax modems and fax machines.

Work is currently underway to define a Group 3 fax standard for 28800bps transmission, though commercially available 28.8 fax devices are unlikely to be available at a reasonable cost for some time.

With any form of digital data transmission, compression techniques can improve performance by removing items of redundant data before transmission.

The TSS specifies that Group 3 machines incorporate Modified Huffman (MH) run-length encoding of scan lines - this is the lowest common denominator for fax data compression. In any given scan line, a white picture element (pixel) is likely to be followed by a long string of the same before reaching a black pixel. In typed or printed material, these long runs of a single colour can often continue across the entire page.

Rather than transmit 1728 bits of information for every white line, MH encoding produces a 9 bit code word representing the white run, thus compressing the data 192 times. Obviously we cannot expect this level of compression all the time, but by searching for transitions from black to white and vice versa, and reporting the number of pixels in each run, a significant saving is always achieved.

Whilst MH encoding compresses only one scan line at a time, Modified Relative Element Address Differentiation - also known as Modified READ, or simply MR - uses the previous line as a reference. This assumes that most information on a page has a continuity up and down, as well as from side to side, and can result in 35 per cent higher compression than with MH.

Because MR works vertically as well as horizontally, it is called a "two- dimensional compression encoding technique". The next step - Modified Modified READ - MMR) - can provide as much as twice the compression of one-dimensional encoding.

The following table (Source: FaxIS/Davidson Consulting, 1995) illustrates the impact of fax compression on transmission throughput for a single page of a "business letter" document.

Compression Method	Estimated KB per page (4% density)	9600bps	14400bps	28800bps
MH	18 KB	30 secs per page	20 secs per page	10 secs per page
MR	12 KB	20 secs per page	13.7 secs per page	6.7 secs per page
MMR	6 KB	10 secs per page	6.7 secs per page	3.3 secs per page

Because MR and MMR are processor intensive applications, most fax modems and low cost fax machines only support MH. Since the late 1980’s, however, an increasing number of business fax machines have included support for MR, whilst MMR support is still restricted to high-end machines.

The net result of this is that even those fax modems which are advertised as "high speed" - i.e. support 14400bps transmission - really only transmit as fast as "low end" 9600bps MR business fax machines (i.e. 20 seconds per page) - and they only do that well when transmitting to other 14400 devices! When sending to 9600bps fax machines using just MH, they send at the slowest possible Group 3 speed (i.e. 30 seconds per page).

When fax calls are made over telephone lines which are subject to static or other types of interference, it is frequently impossible for the fax devices involved to maintain the highest transmission rate. In such cases, they will "fall back" to slower speeds at which they are less likely to suffer errors which will impair image quality (i.e. a 14400 device may fall back to 9600, 7200, 4800 or even 2400bps).

When calculating the cost of your fax operations, this fact should be borne in mind - fax machines don’t always transmit at the maximum speed, even when both devices support it.

Even with normal line conditions, however, it is still possible for faxes to arrive "garbled" or for transmissions to fail completely due to various communications errors.

High-end fax devices support a feature known as Error Correcting Mode (ECM), the ITU-T world-wide standard error-correction method for fax. When both devices involved in a fax transmission support ECM (and have it enabled), the receiving fax device can error-check each data frame or packet which is faxed. When it detects errors, it will then request that just the incorrect frames are re-transmitted.

Obviously, ECM can cause lengthier phone calls if many errors are detected, but the overall effect is to lower fax bills since without it, the entire fax would have to be re-transmitted - possibly numerous times.

The final mechanism for ensuring trouble-free calls is known as "bit stuffing". Because many newer machines are so efficient at compression, they can actually send scan lines too quickly for older machines to keep up. To get around this problem, "fill bits" have to be re-introduced into the data to ensure that the older machine keeps pace without continually aborting the call.

Obviously - as with ECM - this can result on longer calls, but is preferable to continually aborting a fax transmission for no apparent reason. Unfortunately, many low-cost fax devices do not support fill-bit stuffing or do not handle the processor-intensive operation well at high speeds.

Fax modems are often designated by a "Class", and the use of such terms can be the cause of great confusion amongst the fax-buying public.

One of the first specifications for fax communication - approved by the EIA/TIA in 1990 - Class 1 defines a series of basic Hayes AT commands to control the fax modem device.

A Class 1 device has a certain amount of on-board processing - albeit at a low level - and can be thought of as a small, very basic computer in its own right. It can perform basic data link operations, such as dialling a telephone, answering a call, sending and receiving HDLC (High Level Data-Link Control) information and data, checking for errors, etc. These are very primitive operations which the modem itself can perform, and have nothing to do with the T.4 or T.30 protocols.

All the modem can do is send or receive data, and all the higher-level communication is done via the host computer’s serial port. For this reason, the T.30 protocol actually resides in the host PC, resulting in a heavy load on the host processor which must handle the T.30 requirements as well as all the RS-232 communications. This leaves very little spare processing capacity for anything other than fax processing.

Here there is even more confusion. Back in 1991, Class 2 was published as a "ballot standard", which later failed due to a number of technical an political issues.

Unfortunately, as is often the case, a number of manufacturers jumped the gun and began production of devices based on the unapproved Class 2 specification. The result was a huge installed base of Class 2 devices, and an unofficial de facto standard.

Meanwhile, the TIA continued with the real specification, eventually producing the official Class 2 standard - which was named Class 2.0 to differentiate it from the unofficial version. Unfortunately, by the time the Class 2.0 specification was published, it was already out of date in terms of new features in T.30 which should have been included.

The result, then, is a huge installed base of Class 2 devices which are based on an officially "unsupported" standard which is unlikely to be developed further due to a lack of official documentation. On the other hand, we have a relatively small number of "official" Class 2.0 devices, which are likely to remain in the minority as the fax world awaits the Class 2.1 specification which includes the new T.30 developments.

The reason that the standards issue is slightly more thorny here, is that a Class 2/2.0 modem has the T.30 protocol on board. This means that all the call set-up, HDLC transfer, handshaking and synchronisation is performed by the modem, leaving the host PC simply to transfer the data.

Unfortunately, this more efficient architecture has its down side, in that the T.30 code is locked into the hardware. Certain areas of the T.30 specification are open to interpretation, which has led to incompatibilities between fax devices. For developers, it is easier to change the T.30 code in software than hardware, resulting in a preference for host-based T.30 software driving a modem in Class 1 mode. All the performance advantages of Class 2/2.0 devices are thus lost.

One advantage that Class 2/2.0 modems do have over Class 1 is the ability to buffer small amounts of data at the modem. This - together with the on-board processing power - removes some of the load from the host PC, making it better able to support the multiple modem applications which are more common in enterprise faxing situations.

However, because of the processing power required to drive the host fax software (even with Class 2/2.0 modems) and handle the load imposed by multiple interrupt-driven serial ports, a fax server based on external fax modem devices will only work well if its host is dedicated to it, requiring all other tasks to be suspended or receive secondary CPU attention. This is clearly unsatisfactory if the host machine is a central server which is also expected to provide adequate file and print services to its clients. In our tests, we found that even the use of intelligent multi-port serial adapters did little to alleviate the load on the host fax server.

Because of the timing dependencies and the bottlenecks they create in multiple serial ports, manufacturers of intelligent fax processor cards - such as GammaLink and Brooktrout - decided against the Class 1/2 approach in order to maintain reliability.

Such cards will use a polled I/O architecture rather than rely on interrupts, and will perform all fax-related tasks such as :

on the board itself, thus freeing the host computer for other tasks. Whereas the relationship between a host computer and an external modem is one of master and slave, intelligent fax co-processors communicate in more of a peer-to-peer fashion with the computer in which they reside.

Because of the on-board processing power (which is much greater than that available in Class 2/2.0 modems) and the elimination of reliance on the host computer’s serial ports, the intelligent fax board is eminently suitable for the high channel density installations which characterise enterprise faxing applications. With multiple ports available on a single card, the limit to most installations is the number of free expansion slots in the host computer!

The aim of the tests was to simulate an enterprise faxing environment using faxes of varying lengths, thus enabling a performance comparison between a GammaFax CP4i intelligent fax processor and standard external Class 2.0 fax modems.

6 page fax - The cover sheet with 5 additional pages each full of plain text

The host server was a Compaq ProLiant with a DX2/66 processor and 32MB of RAM running Novell NetWare 3.12 and Tobit FaxWare 3.01. In order to provide a realistic scenario, four standard high-end fax machines with ECM, MMR and 14400bps transmission capabilities were used to receive all the test transmissions.

Comparison tests were run using a single line followed by four lines simultaneously in order to observe the load on the file server, and all tests were carried out on each of the following hardware configurations:

To ensure consistency, all test suites were repeated ten times and the average times were recorded. All fax transmissions were timed and verified using a Gray Fax Analyser on each line.

The figures for the "six page" tests in the above table have been isolated and represented graphically on the following pages to make comparisons easier. The larger tests were selected in order to provide the most meaningful graphical results over the longest time span.

Note that we were unable to obtain consistent results from the US Robotics modem.

The conclusion of the Gray Analyser makes interesting reading here, since it lends weight to the arguments against the use of Class 2/2.0 modems in enterprise faxing applications. Since in our test environment the communications lines were devoid of all noise and interference (we used PSTN line simulators), it is apparent that the errors were due to the inability of the modem/host combination to handle the high data rates generated by our test scenario. For more information on the Gray Fax Analyser, contact Gray Associates on +1 916 582 8623 (fax +1 916 582 8622).

The graph below (Figure 2) compares the average time taken (in seconds) to transmit the six page test fax using each of the hardware configurations. The following points should be noted :

There is a negligible difference in performance terms between a single-line transmission and four simultaneous transmissions

Standard modems - whether attached to standard or intelligent serial ports - take over twice as long to transmit the fax, despite that fact that all fax devices are transmitting at 14,400bps

Figure 3 Compares the average time taken (in seconds) to transmit the single-page test fax using each of the hardware configurations.

The graph shape is very similar to the six page graph above, indicating the repeatable nature of the tests, and the same conclusions apply.

The next graph (Figure 4) compares the maximum CPU utilisation figure noted at the host fax server during transmission of the six page test fax using each of the hardware configurations.

There is now a more marked difference in impact on the server between the single-line and four-line transmissions.

What is unusual is that the Digiboard - despite being an intelligent serial card with on-board processing power - has a particularly heavy impact on the CPU. Although the number of standard serial ports on our Compaq file server restricted us to two-line tests only, it is obvious from comparing the single-line figures that CPU usage was heavier with the Digiboard.

Figure 5 compares the average CPU utilisation figure noted at the host fax server during transmission of the 6 page test fax using each of the hardware configurations.

We can now see that - particularly as the number of lines increase - the effect of the GammaFax card on the host server remains slight compared with standard modems attached to serial ports. This is of particular interest in enterprise environments where heavy fax activity could have an adverse effect on the host server and thus on other end user applications.

Figure 6 and Figure 7 highlight the difference in CPU utilisation throughout the transmission of the six page test fax.

Note that although the GammaFax card peaks at 30 per cent, it is quite "bursty" in nature, and has an average loading of just 8 per cent.

In contrast, the Digiboard/Interdial combination exhibits a maximum loading of 80 per cent, and a much higher constant loading throughout the transmission of 33 per cent.

It is apparent that the server under the sort of load exhibited in Figure 7 would be unable to provide effective file and print services to its clients whilst performing fax transmissions.

Even if the server were dedicated to fax operations, it is clear that the host computer would be capable of only a single task at a time, thus preventing it, say, from converting one document form ASCII to fax whilst transmitting another.

In such an environment, overall transmission time of a large "fax shot" would be increased to an unacceptable level compared with a host computer equipped with intelligent fax cards.

There is much confusion regarding the capabilities of the current crop of Class 1 and Class 2 data/fax modems.

The T.30 recommendation - the handshaking protocol describing the overall procedure for establishing and managing communications between two fax devices - is open to interpretation in some areas.

In the early days of Group 3 fax this did not matter too much since the majority of fax device manufacturers were using the same ROM with a single version of the T.30 code.

The proliferation of shrink wrap data modems which are also offering fax capabilities has changed things, however. Data/fax modem manufacturers have implemented their individual interpretations of T.30, and these devices can encounter serious problems when attempting to fax to other devices. Also, because much of the T.30 - and other - processing must take place on the host computer itself instead of within the fax device, these modems place great demands on the host computer’s processing time, making it difficult for it to perform other tasks effectively whilst faxing.

This obviously gives rise to some concern as to the suitability of Class 1 or Class 2 modems for enterprise-level mission critical faxing, and these concerns were certainly highlighted during our tests.

In our stringent test environment we found that one of the Class 2 modems consistently failed to transmit the longest of our test faxes. We also noticed problems in connecting to remote fax devices when the system was under load, unusually high CPU utilisation levels on the host server during fax transmission, high error rates and poor transmission times.

None of these problems were encountered during tests on the GammaFax internal fax card, leading us to draw the following conclusions :

Class 1 and Class 2 modems should be kept for personal/desktop use. Such devices are not capable of working in a busy fax server environment where enterprise-level mission critical faxing is taking place

Dedicated fax processor cards should be used for enterprise faxing applications from both a reliability and cost savings point of view. When using such cards in our tests, identical faxes were transmitted in half the time taken by Class 2 modems, even though all devices were transmitting at 14,400bps.

The use of serial ports for faxing places an unacceptably high load on the host CPU when more than one fax line is in use simultaneously. Intelligent fax processing cards reduce this load considerably.

MMR capability provides the prospect of reducing fax costs even further. In our tests we saw an improvement of 10 per cent. As with all forms of compression, however, the "right" data can provide even greater gains, and we have seen improvements of up to 40 per cent when using MMR.

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Copyright � 1991-2006 The NSS Group Ltd.
All rights reserved.