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Andy White
Technology Officer
RNIB Education and Employment Network (South West)
10 Stillhouse Lane
Bristol BS3 4EB
United Kingdom
Tel: +44 (0)117 934 1717
Email: andy.white@rnib.org.uk


There has been much concern expressed recently around the growth of a new breed of networked computer technologies, known as "Terminal Servers." This paper is an attempt to shed some light on this sometimes confusing subject, using as little technical jargon as possible. Its aim is to draw attention to the incompatibility of access technology software with terminal server technology, and to inform how best to work around such incompatibility issues.

What is Citrix?

One of the foremost companies working in the field of terminal servers is called Citrix, who make a product known as Metaframe. Citrix produce software, which enables the administration of all network services from a centralised server. This includes not only the storage of data and programmes, but also centralised processing as well. Effectively this converts fully functioning desktop PCs into dumb terminals.

In recent years we have grown used to the notion of 'Fat Client' architecture, whereby the desktop computer sitting in front of the user is a fully functioning PC, with it's own hard drive, central processing unit, application software, operating system (usually Microsoft Windows) and connection to a network. Data is often stored on a central server, so that it can be shared amongst a number of computer users and backed up centrally for safekeeping. Terminal server technology however, removes all power from the desktop PC and places it onto a central server. This includes not only the data but also the application software, the central processing of data and importantly, the graphical output, which is sent to the client machines. This effectively means a return to the old style of thin-client network architecture, reminiscent of main frame computers serving a network of dumb terminals.

Essentially terminal server technology puts the entire computer's processing power onto the server.

According to Citrix;

"The architecture provided by Citrix Computing Architecture enables client devices to shift application processing from the individual device to the server, resulting in centralised application management."

Citrix is typically installed on top of Microsoft server applications. The equivalent Microsoft product is called 'Windows 2000 Terminal Server' or its NT equivalent, 'NT TSE'. As I understand it, Citrix invented the technology, and Microsoft wrote their own version. Most people install both (on the same "terminal server"), as NT/2000 Terminal Server on its own doesn't have all the bells and whistles that Citrix brings to the party.

Why are Terminal Servers a problem for visually impaired computer users?

Be afraid. All major access technology software relies on some flavour of the Microsoft Windows operating system ('95/'98/Me/NT/2000/XP). Serving applications and processing from a centralised server using terminal server technology such as Citrix, does away with all the nuts and bolts of the Windows operating system.

The result of this is that access technology software, such as screen readers and screen magnifiers, do not work under any circumstance within a terminal server environment.

A phone call to Freedom Scientific (JAWS), confirmed our worst suspicions. Terminal server software such as Citrix renders JAWS completely useless. There is nothing they can do until the manufacturers of Citrix technology make serious adaptations to their software. This is like going back to the dark ages when dumb terminals offered little or no accessibility potential.

To make JAWS or any other screen reader work within a terminal server environment is likely to be very difficult indeed. To do this, the screen reader will need to have far greater artificial intelligence to work out where the focus is and what windows are being used and still maintain speed and stability. Essentially we will need a screen reader that can literally "see". Currently this doesn't seem feasible, so Citrix Terminal Server, is a no go for the immediate future.

Screen magnifiers are also severely limited, if not useless, within terminal server architecture. Although there have been examples where Zoom Text or Lunar have nominally "worked" and magnified the image on screen, the functionality of these screen magnification packages is completely lost. It is as important as the magnification itself for the user to be able to track the focus and navigate using keyboard commands, all of which functionality is lost under terminal server architecture. Be very careful not to be fooled into thinking that a screen magnifier is "working" just because the screen is magnified.

Does all this mean that access technology can never be administered from a server?

No. The issue of incompatibility of access technology software with Terminal Server Architecture should not be confused with making screen readers and magnifiers available to client machines from a server. Access technology software can typically be administered from a server to a client machine under the following 3 conditions:

What are the technical reasons why access technology will not work with terminal servers?

The most basic reason that access technology software will not work with terminal servers such as Citrix is the same reason that such software currently does not work with Windows CE, Linux or any other operating system at present. All the major access technology software is currently written for Windows operating systems and therefore requires Windows to be present in order for it to work.

Jaws could theoretically run on a thin client machine that ran Windows but there are difficulties about getting Jaws etc. onto such machines and non-standard hardware type issues.

In response to an email enquiry, Dolphin Computer Access' helpdesk had this to say:

"Unfortunately the current version of Hal will not work successfully in a terminal server environment. In fact, at present, no screen reader on the market will work successfully in a terminal server environment."

"To work successfully in a terminal server environment current screen reading technology would have to be modified and also tightly integrated with the terminal server system that it's running on, i.e. Microsoft's Windows Terminal Server or Citrix's MetaFrame."

"Running Hal on a Winterm (i.e. a client machine) in a WTS environment won't work because the terminal client on the Winterm is just an application acting like a terminal emulator, except that it displays graphics. The WTS just sends bitmap images of the application's screens from the server to the client. Hal is therefore unable to 'see' anything on the screen of the client machine."

"Hal really needs to run on the WTS itself so that it can communicate directly with the applications running on the server, such as your database, in order to get window information, etc. Also, Hal would have to intercept all the screen drawing operations on the server before they got to WTS' virtual display driver which sends the rendered output as bitmaps over the network to the Winterms."

"Also, another issue to bear in mind is that Microsoft's current Windows Terminal Server implementation doesn't have support for stereo Windows Audio (system and user) without a third-party plug-in from NCD (Network Computing Devices), so re-directing speech output from Hal running on the WTS to the Winterm client machine may prove difficult. However, Citrix's MetaFrame implementation does support the re-direction of Windows audio from the terminal server to the Winterm, so theoretically Hal's speech output should successfully get re-directed to the client machine."

"However, on a more positive note, we've recently opened up a dialogue with Citrix, and with their help hope to investigate a little further the possibility of getting Hal running under MetaFrame 1.8. No time frame for this project has been estimated yet."

Why are Terminal Servers popular with large organisations?

The main answer to this is simple. Control. Where there was once a move to provide maximum control to the end user, this has proved unworkable for many large organisations. Windows NT suffered from being slow and at times unreliable. System administrators often end up locking out a lot of the functionality of Windows from their company's employees. For example, a call centre operator does not need any of the functionality of as they are simply expected to enter and retrieve data.

Other advantages include:

However, it seems that in their drive to maximise efficiency and security, such organisations have completely overlooked the specific needs of their visually impaired employees.

How can incompatibility problems be overcome?

The immediate technical solution is superficially quite simple. A visually impaired computer user needs to keep his or her PC operating outside of the terminal server regime. This means that the client machine needs to be kept running under Windows NT / 2000 / XP Pro. Under a terminal server environment such as Citrix, data, programmes and processing is dealt from a central server. Under Windows NT, the programmes and processing (including any access technology) are kept on the client machine.

The suggestion to keep PCs out of a Citrix regime can prompt organisations that have just invested a large amount of time and money in their new Citrix technology, to claim that it can't be done.

What they really mean is they don't want to. It is maybe difficult, it may require additional time and expense and it may contravene some of the original thinking behind investing in the Citrix technology in the first place. However, for a visually impaired person it is essential that this happens.

Consider this:

Firstly, if employers roll out Citrix technology without considering provisions for their visually impaired employees and refuse to make adaptations as described above, then they are effectively making their employees redundant. This is likely to contravene disability discrimination law.

Secondly, keeping individual PCs outside of the Citrix architecture is probably no more difficult or different to the PCs being used by system support and software development departments within the organisation. It is an unlikely scenario to imagine systems support staff and software developers sitting in front of dumb terminals, making adjustments to corporate software.

What examples are there of success?

At the time of writing, the widespread adoption of terminal server technology is limited but growing. However, a pattern seems to be emerging and there are examples of small pockets of success in overcoming the problems experienced with access technology using the method described above.

It would be inappropriate to give details of specific cases here. However, RNIB are compiling a small database (extremely small) of cases where the problem of incompatibility between Citrix and access technology has been overcome. RNIB hold information on either the client, an RNIB Technology Officer involved, the organisation's IT contact or simply the organisation involved. Complete case studies where total success has been achieved would be most welcomed.

Organisations in the UK include:

University of the West of England
NHS Direct
Nationwide Building Society
Admiral Insurance Group

Some of these organisations have had more success than others. Some seem to be taking one step forward and two steps backwards.

The future

This solution to keep PCs out of terminal server regimes may only be a short-term solution. Citrix software is largely being installed at present onto existing networks, which probably ran under NT or 2000. Problems may well arise when a completely new network infrastructure is being constructed based solely upon terminal server technology.

For instance, real time processing of data on a fat client network requires greater bandwidth than a thin client equivalent. Indeed, one of the advertised benefits of Citrix technology is to do away with the need for high bandwidth over large distances. If a new network is constructed with only low bandwidth in mind, it may become technically difficult to provide an NT/2000 solution for remote PCs.

Responsibility for making Terminal Server technologies accessible is a complex situation. The current state of affairs is that although Citrix and Microsoft are both aware of accessibility issues and are looking into the problems, there is no indication of when they may be made accessible.

Citrix have previously held the view that it is the responsibility of Microsoft to make their Terminal Server products (which Citrix typically runs on) compatible with access technology. However, this required Microsoft to co-operate with access technology vendors by releasing certain codes and protocols. Microsoft have been approached about this, and although appearing enthusiastic, they have been less than helpful and to date appear to have done nothing. Thus we appear to be at a stalemate.

Citrix are now pursuing an independent solution to making their product accessible (see appendix a). However, there are still many technical reasons why we should not be prematurely optimistic.

Microsoft appear to have achieved some success with their own Narrator and Magnifier facilities built in to the Windows operating system. However, neither of these products can offer blind or partially sighted computer users the same degree of control, flexibility or workability that third party access technology software offers.

The only sustainable, long-term solution is for Citrix and Microsoft to work alongside access technology companies to make their products compatible. This process has now begun, but there is still a great deal of work to be done.


The solution at present is to work around the problem rather than solve it. The simplest way to work around the problem is to keep the client PC running under Windows NT/2000/XP pro. This has been demonstrably achieved in several cases with minimal fuss.

Beyond that, there is much awareness-raising to be done, as well as lobbying of employers, organisations, political bodies as well as Microsoft and Citrix themselves.


Andy White
Technology Officer
RNIB Education and Employment Division

2nd August 2002

First Revision November 2002
Second Revision February 2003

Many thanks to those whose emails, correspondence and spoken words of wisdom this paper is largely based upon.

This paper is work in progress and any updates, suggestions, comments and corrections will be gratefully received.

Please email me at: andy.white@rnib.org.uk

Appendix A

An open letter from Bob Kruger;
CTO and SVP for Product Development. Citrix Systems, Inc.

Dear Valued Customer,

Citrix is committed to providing accessible products and solutions. We support the government's implementation of Section 508 of the Rehabilitation Act to provide greater access to technology solutions for all users. Citrix believes that the implementation of these standards aligns with our vision to provide accessible solutions for the Virtual Workplace.

Section 508 requires that when Federal agencies develop, procure, maintain, or use electronic and information technology, Federal employees with disabilities have access to and use of information and data that is comparable to the access and use by Federal employees who are not individuals with disabilities, unless an undue burden would be imposed on the agency. Section 508 also requires that individuals with disabilities, who are members of the public seeking information or services from a Federal agency, have access to and use of information and data that is comparable to that provided to the public who are not individuals with disabilities, unless an undue burden would be imposed on the agency.

Citrix is committed to supporting the regulations of Section 508 in our products. To that end, we have been working closely with accessibility tool vendors for some time. This year, we contracted AT&T Government Systems and Bartimaeus Group to perform a full assessment of MetaFrame XP Feature Release 2. We were very pleased to learn that, because of our adherence to Microsoft's coding standards, this release is nearly compliant. Remedies for the small number of outstanding 508 issues identified in the assessment will be incorporated into the next major MetaFrame XP product release, planned for the second half of 2003. That release will be fully compliant with the statute.

Whenever possible, Citrix products attempt to leverage enhanced accessibility solutions provided by the operating system software. Some examples of these solutions include extending accessibility features such as Narrator and Magnifier in the Windows 2000 Server Operating System through our MetaFrame Application Server. We have used our close partnership with Microsoft to emphasise the importance of their support for video drivers from accessibility vendors in the Terminal Services environment. Microsoft support would enable products such as Dolphin, JAWS, and so forth, to work with the Citrix MetaFrame XP family of products. Microsoft plans to provide accessibility vendors with the opportunity to join their Premier Partner program for the development tools they need. These vendors would then be able to have their drivers certified at Microsoft test labs. Microsoft has not yet published their timeframe for launching this two-part process.

In the interim, Citrix has begun investigating other solutions that would be completely within our control to implement. These solutions present a variety of business and technical challenges, which we are aggressively pursuing.

The Citrix Product Development Team is currently working to implement the standards defined in Section 508 into our product development process. In addition, our internal information systems team is working to ensure that our public web site and services follow the standards. Though our products and services already conform to a large percentage of the standards defined in Section 508, there are current areas that will require alterations in order to fully comply with the standards. We are committed to supporting these standards in our future product releases and services.


Bob Kruger
CTO and SVP for Product Development
Citrix Systems, Inc.

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