SpeedScreen Technology

SpeedScreen Technology

SpeedScreen is a technology developed by Citrix to improve the responsiveness of published applications and desktops over slow communications links. Server-based computing, in general, is always hungry for more network bandwidth because it is essentially the mechanism that makes the concept possible. On local area networks (LANs) or wide area networks (WANs) that have enough network bandwidth, performance is never an issue, and to the end user , everything seems to run perfectly . However, when you deal with slow network connections, you need to take some additional measures. Even though Citrix has made many advances by tweaking the ICA protocol and compressing the data so that it can travel the communications link faster, the frequency of the client screen updates can consume a significant amount of bandwidth and slow down the session. Just imagine what the impact on bandwidth would be like if every pixel on the screen needed to be re-created and retransmitted every time you moved your mouse around or double-clicked an icon or used your keyboard.

To alleviate this frequent transmission of screen updates, Citrix designed a technology, known as SpeedScreen, that improves the performance of slow sessions by at least four times over sessions that do not use SpeedScreen. SpeedScreen works by transmitting only the part of the screen that has changed. For example, assume that you hovered your mouse in the lower-right corner of the screen over the clock. SpeedScreen then compares your mouse movements to the last screen refresh it sent you and determines that only the lower-right corner of the screen has changed and thus refreshes just that part of the screen instead of resending the entire screen.

SpeedScreen Latency Reduction

The robustness of SpeedScreen and its performance benefits have led Citrix to improve the technology further and add new features to the SpeedScreen family. SpeedScreen Latency Reduction is the name given to two SpeedScreen features: Local Text Echo and Mouse Click Feedback.

Local Text Echo

Local Text Echo works on slow communications links such that when the user is entering data or using the keyboard to interact with the application, the response to the user's input lags behind the keyboard strokes. For example, if Joe is using a word processing application and is typing a memo, the letters may not appear on the screen at the pace he is typing, but rather seconds or even minutes later depending on the lag. This lag frustrates the user, forcing him to wait for the text to update before he can continue typing.

Local Text Echo addresses this issue in particular. If Local Text Echo is enabled on the server, as soon as a session is established between the ICA client and the MetaFrame server, the server pushes a series of screen images and basic fonts. As the user Joe is typing, Local Text Echo uses these initial screen images and fonts to keep up with his pace. In most cases, the user will not know the difference as he is typing and before the server has time to process the data and send the correct font and images. Local Text Echo intercepts the keyboard strokes and populates the input using the fonts that were transferred at connection time.

In the background, this feature gives the server time to process the data and send the correct information back to the client. The data is then refreshed. All this is seamless to the user. In rare cases, if Local Text Echo cannot detect the font the user is using, it populates the screen with boxes or circles, basically informing the user "I acknowledge you are typing something, but I just don't know what it is yet." After the server receives and processes the data, it sends the data back to the client, and the boxes or circles are replaced with the proper fonts.

Mouse Click Feedback

Mouse Click Feedback is also enabled at the server level and is used to remedy the lag that occurs between the time a user double-clicks an icon and the time needed to process this action and reflect it on her screen. Many times, users double-click an icon, and if they don't get a response immediately as they are used to with applications running locally on their machines, they assume the command did not register and attempt to double-click again and again. Mouse Click Feedback intercepts the command before it gets to the server. It then changes the cursor to an hourglass, telling the user "I know you double-clicked the icon. Don't double-click again because I am processing your command." As soon as the command is processed and sent back, the application is launched and the mouse pointer is changed back to its original shape.

We discuss how to configure SpeedScreen latency reduction on the server side in Chapter 6, "Configuring and Administering MetaFrame Presentation Server," and on the client side in Chapter 13, "Citrix ICA Client Software."

SpeedScreen Browser Acceleration

SpeedScreen Browser Acceleration was designed specifically for web applications. It has a special compression algorithm that improves the performance of GIF and JPEG images in HTML pages. Applications such as Microsoft Internet Explorer, Microsoft Outlook, or Outlook Express can take advantage of this technology by presenting the user with the text on the page first and then gradually displaying the image as the packets arrive until the image is composed . We discuss how to configure this feature in greater detail in Chapter 6.

SpeedScreen Flash Acceleration

SpeedScreen Flash Acceleration addresses performance issues with Flash animations, which may run slow on a MetaFrame server. With the introduction of this technology, Citrix uses a technology known as Lossy Compression , which essentially reduces the size of the images in the animation, speeding up its delivery to the client. It does this by removing some of the image data reserved for advanced photo editing. Because this data is removed, the image size is reduced, and the flash animation is displayed quicker, improving performance. We discuss how to configure this feature in greater detail in Chapter 6.

SpeedScreen Multimedia Acceleration

SpeedScreen Multimedia Acceleration tackles streaming audio and video through an ICA session. When this feature is enabled, streaming media runs as smoothly as it does when run locally. SpeedScreen Multimedia Acceleration compresses the packets sent across the link and makes the client's CPU do all the processing instead of having the server CPU do it. This feature puts very little stress on the server CPU and does not require significant network bandwidth. We discuss how to configure this feature in greater detail in Chapter 6.