VM-based gateway to Grid computing: "Grid middleware is enabling resource sharing between computing centres across the world and sites with existing clusters are eager to connect to the Grid. However, the hardware requirements for access to the Grid remain high: a standard Grid-Ireland gateway requires four separate servers. We propose the use of Virtual Machine (VM) technology to run multiple OS instances, allowing a full Grid gateway to be hosted on a single computer. ..
We evaluate implementations of this architecture on two popular open-source VM solutions: Xen and User-Mode Linux (UML). Our results show that Xen outperforms UML for installation tasks and standard gateway operations. Performance is close to that of standard Linux, and more than acceptable for everyday use.
The Grid gateways support remote installation and management to facilitate integration with a national Grid infrastructure. Configuration is similar to that of sites running multi-computer gateways, making it easy to keep site installation profiles synchronised. Our VM gateway architecture provides a low-cost entry path to the Grid and will be of interest to many institutions.. " 11:49:46 PM
Understanding Citrix's SpeedScreen Latency Reduction (SLR): Description of how Citrix improves upon terminal server on high-latency links. Reminds me of mainframe terminals and the "local echo" and "keyboard lock" buttons! "Citrix has long talked up as a benefit of MetaFrame Presentation Server.. imagine a situation without SLR where a user is typing a document via an ICA session with 400ms of latency. .. To the user, it would appear that there is a half-second “lag” when typing.
To address this, SLR’s Local Text Echo causes the ICA client to behave a bit differently. When enabled, a user pressing a key on their keyboard causes that key code to be sent to the server. However, at the same instant, the local ICA client software also draws the appropriate character on the user’s screen even though the actual screen drawing instructions from the server are bogged down in the 400ms latency between the client and server. Then, once the ICA client finally receives the actual updated screen from the server, it doesn’t have to update that character on the local screen .. [It] works really well. It works with all different fonts and font sizes. .. complex things such as highlighting and deleting large chunks of text exhibit the lag associated with the actual latency...
The other major SLR feature is something called “Mouse Click Feedback.” This addresses another common problem in Citrix environments with high latency, namely, the fact that users click on a button, become impatient, and click on a button again before the first click registered. Then, when the application’s response finally makes its way to the user, whatever the user clicked on comes up twice. Mouse Click Feedback works by adding the hourglass symbol to the arrow cursor the instant the user clicks the mouse anywhere within the boundaries of the remote ICA application. [The mouse isn't locked, but users generally respond to the hourglass by waiting] ..
SpeedScreen is automatically used on a MetaFrame server whenever a user connects to a session that has between 150 and 500ms of latency. As long as the client supports it, it's used." In another article, the author notes that SLR consumes more bandwidth, sometimes as much as 20% more; thus it's a tradeoff of more bandwidth for less latency. 12:21:22 AM