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Usablenet Assistive User's Manual

Usablenet Inc.
101 Avenue of the Americas - Suite 1201, New York, NY 10013, USA
Ph: +1 (212) 965 5388
Fax: +1 (212) 965 5391
Email: tt.support@usablenet.com


Table of Contents


1. What's Usablenet Assistive and how does it work?

Usablenet Assistive (or transcoder) is a web application that converts a web page into its text-only version on-the-fly by eliminating all page layout that is present in the original page and by hiding many accessibility defects.
The transcoder is useful for the website visitor, since it removes some accessibility issues and small defects like missing image ALTs or forms that are not properly linearized or flash objects. It can be used also by the web developer to determine if the reading order of the information presented in the page makes sense when read in the order that would be followed by a screen reader or speech browser.

Usablenet Assistive is especially useful for people and situations where:



1.1. Layout and content processing

Usablenet Assistive yields pages that are more in compliance to Section 508 and WCAG AA guidelines than the original ones. To do so, it performs a number of transformations on the web page layout and content:

Usablenet Assistive adds new CSS rules to the output page to let the user change color theme and font size of the web page.
These settings are saved using cookies and therefore are available to a Usablenet Assistive user (if cookies are enabled by his/her browser).


1.2. Supported protocols

The transcoder is able to process any page on the Internet. It currently can transcode pages whose content is based on:

If a framed page contains two frames requiring HTTP Base Authentication, Usablenet Assistive will open a connection only to the first frame for security reasons.

See the Security section for more details about how Usablenet Assistive supports secure connections.


1.3. Performance aspects

While Usablenet Assistive is very efficient, to transcode a page it has to:

  1. receive a request from the visitor's browser,
  2. issue a request to the webserver hosting the site,
  3. wait for the webserver and the network to yield the data,
  4. transform the page, and finally
  5. send the transformed page to the user's browser.

Figure 1: Interaction between browser, transcoder and web server

Diagram showing the interaction among browser, transcoder and web server

The response time for getting a text-only page (i.e. the time the web visitor has to wait to see some results), compared to the time to get the original page, is affected by steps 2, 3 and 4.
Depending on whether the transcoder is installed in the same local network as the webserver or in a different network, the performance will differ (the latter case is the worst as steps 2 and 3 require more time).


2. Using Usablenet Assistive

Using Usablenet Assistive is straightforward: once you activate a "text-only" link that is based on Usablenet Assistive, or after you use the form in the Main page, your browser will display the transcoded page. Most of the links that you can select will activate again Usablenet Assistive: when you select any of them, your browser will display the transcoded page.

To achieve this effect the transcoder does what is called URL remapping. In fact Usablenet Assistive, besides performing a number of changes to the content of the page (as described in the Layout and content transformations subsection), changes also most of the URLs of the links and form actions in such a way that your browser sends the requests to Usablenet Assistive rather than the web server. Usablenet Assistive then relays the request to the web server, gets the answer, processes it and hands it to your browser.

The webmaster managing the web server hosting the "text-only" links or the Main page can decide where to stop this URL remapping. (Consider that if there are no such limits then you would be able to navigate through the entire Internet via Usablenet Assistive.) When the border is reached (and it depends on how Usablenet Assistive has been configured by the webmaster running it), Usablenet Assistive does not remap URLs any further. Typically a border is crossed when the webserver changes. For example, you might be able to use Usablenet Assistive on pages hosted by www.anycompany.com. If some of the pages contain links to news.anycompany.com, then Usablenet Assistive may refuse to remap these links because they exit from the server for which Usablenet Assistive has been configured. The webmaster can configure Usablenet Assistive so that any other link can be prevented from being remapped by Usablenet Assistive.

The webmaster can also customize Usablenet Assistive and change the default way for displaying a text-only page. Usually this is done for forms, for navigation bars and for special sections within pages for which the webmaster has some special requirement.

Usablenet Assistive can produce error messages. This happens when Usablenet Assistive encounters anomalous situations in talking with the web server that should supply the page (for example the requested page cannot be delivered by the web server). These errors are displayed as shown in figure.

Figure 2: File not found error message of Usablenet Assistive

Screenshot showing the file not found (404) error message

Very rarely Usablenet Assistive may face weird situations and generate an error, even when a proper communication with the web server and the browser was in place. These errors include "Internal error" and are displayed as shown in figure.

Figure 3: Internal error message of Usablenet Assistive

Screenshot showing the  internal error message

When you need to browse websites that are behind a password authentication based on HTTP, Usablenet Assistive simply acts as a web proxy. This means that the browser will ask you to enter your username and password (required to access the website) and it will send the data to Usablenet Assistive, which in turn will send them to the web server. Username and password are not stored by Usablenet Assistive. They are acquired from the browser and sent to the web server through a secure connection (SSL) only if your browser shows HTTPS as a protocol. See the Security aspects and the Privacy aspects sections for more details.


3. Setting your preferences

Usablenet Assistive allows you to choose your display preference. These preferences are handled via cookies so that Usablenet Assistive can remember your choices. You must enable cookies in your browser.

Display preferences can be selected in a section entitled Text Only Options located at the bottom of any transcoded page.
Hold down ALT key and press T to jump to the Text Only Options section.
If you are using Internet Explorer, you must hold down ALT key, press T and then press enter key to obtain the same result.
If your browser has a menu with T as shortcut (for example 'Tools' in Internet Explorer) you can still open it using the keyboard by pressing ALT key and T separately.

The last part of Text Only Options section can be used to view the original version of the transcoded page, to launch Usablenet Assistive on any other public web page and to view the Usablenet Assistive Main Page.

Figure 4: Preferences affecting the behaviour of Usablenet Assistive

Screenshot showing the Usablenet Assistive options.

Within the Text Only Options section you can select the following preferences.

Figure 5: Display of links for motor-disabled persons and with a yellow on black color mode

Screenshot showing how Usablenet Assistive displays links for motor-disabled persons.

4. Privacy aspects

Usablenet Assistive has to acquire from the web server the pages it processes, transform them, and deliver the transformed version to your browser. And you might be concerned about who can see and what can be done with that information.
Usablenet Assistive has been designed so that privacy and security issues are minimized.

When you use the text-only pages produced by the transcoder, you submit forms or your browser uses cookies, the information about the pages being visited, the data sent when submitting the form, and the cookies required by the pages are sent first to the transcoder server (i.e. the machine on which Usablenet Assistive runs) and then sent again to the web server that is the proper recipient.

By design, most of this information is not stored in any permanent form within Usablenet Assistive files. It lives in volatile memory only within the processes implementing the transcoder service and only for a very limited time (a fraction of a second). The only information that is permanently stored is the log of the HTTP/HTTPS requests, which does not include cookies nor form values.

However consider that Usablenet does not necessarily host the transcoder you are using. (It is easy to check: if the URL of a transcoded page starts with http://assistive.usablenet.com:... then it is hosted by Usablenet.) If Usablenet is not hosting Usablenet Assistive (i.e. Usablenet Assistive has been licensed to another party) then Usablenet cannot give any guarantee in terms of privacy and security. You should contact the webmaster of the organization that is hosting Usablenet Assistive (whose domain name appears at the beginning of the transcoded URLs).

If you are using a transcoder hosted by Usablenet then the only information that is permanently stored is the log of the HTTP/HTTPS requests, which does not include cookies nor form values.

Usablenet, according to its privacy policy, does not and will not release to third parties such an information. In addition, Usablenet does not and will not manipulate nor change the submitted information (other than for the purposes of implementing the functions required by the transcoder itself).

Please contact us at tt.support@usablenet.com for additional information.


5. Security aspects

Usablenet Assistive works as a web proxy, and when it transcodes a page it has to transform all the URLs of the links and form buttons that are contained in the page. Each URL is transformed (remapping of URLs) so that the request is first filtered by Usablenet Assistive and then it is Usablenet Assistive that issues another request to the original web server.

However when the URLs specify the HTTPS protocol, things become more complex. Usablenet Assistive has to remap URLs so that both the Internet connections (the one between the user browser and Usablenet Assistive and the one between Usablenet Assistive and the web server) are secure (i.e. on a Secure Socket Layer, SSL). Therefore Usablenet Assistive remaps each HTTPS link into an HTTPS link pointing to Usablenet Assistive and specified so that the Usablenet Assistive connects to the web server through HTTPS.
For example the link


is transformed into


(the actual server name for Usablenet Assistive may be different in your case). Notice the two occurrences of "HTTPS".

Security warning: if in your browser you notice that a link contains only one instance of HTTPS (instead of two), it means that the connection between your browser and Usablenet Assistive or the connection between Usablenet Assistive and the web server is not secure. In this case, if you are concerned about security of information exchanged between your browser and the web server, you should not continue your activity. Contact the webmaster responsible for the transcoder.

HTTPS is based on certificates, special files that contain all the information that allow the two parties in a connection to verify the identity of each party and to make sure that transit information is encrypted so that it cannot be tampered.
When you use the browser to open a page with the HTTPS protocol, your browser and the web server exchange also certificates. When a browser receives a certificate from a web server, unless the certificate is signed by an official Certificate Authority (i.e. unless the certificate has been issued by such an authority, usually called public certificates), the browser will tell you that with an appropriate pop-up window.

Usablenet Assistive properly processes secure pages (i.e. it remaps secure pages into secure transcoded pages) only if the webserver uses public certificates. If the webserver requires HTTPS to access a page, but the webserver does not have public certificates, Usablenet Assistive would not transcode the page.

Figure 6: Generic HTTPS error of Usablenet Assistive

Screenshot showing the Usablenet Assistive generic HTTPS error

In this way Usablenet Assistive behaves as a very conservative browser, refusing to continue a transaction when it is insecure but the Usablenet Assistive user expects it to be carried out securely.