Multi-Resource/Multi-Dimension QoS Optimization

Q-RAM Overview

The QoS-based Resource Allocation Model (Q-RAM) is an analytical approach for satisfying multiple quality-of-service dimensions in a resource-constrained environment. Using this model, available system resources can be apportioned across multiple applications such that the net utility that accrues to the end-users of those applications is maximized.

Application Context

Multimedia systems using audio and video streams can provide better audio/video quality at higher resolution and/or very low end-to-end delays. Tracking applications can track objects at higher precision and accuracy if radar tracks are generated and processed at higher frequencies. In many cases, computationally intensive algorithms can provide better results than their less-demanding counterparts. Even interactive systems can provide excellent response times to users if more processing and I/O resources are made available. Conversely, many applications can still prove to be useful and acceptable in practice even though the resources needed for their maximal performance are not available. For instance, a 30 frames/second video rate would be ideal for human viewing, but a smooth 12 fps video rate suffices under many conditions. The QoS-based Resource Allocation Model (Q-RAM) addresses the following question: "how does one allocate available resources to multiple concurrent applications?".

Q-RAM Novelty

The novelty of Q-RAM is that it allows multiple Quality of Service requirements such as timeliness, cryptography and reliable data delivery to be addressed and traded off against each other. It also allows resources to be traded off against each other to obtain the same level of QoS along a particular dimension. For example, video at a certain frame rate can be transmitted in raw form, consuming minimal CPU cycles and high network bandwidth. Alternatively, the video can be compressed, consuming significant CPU cycles but consuming less network bandwidth. Q-RAM provides a framework to make such resource and QoS tradeoffs across multiple applications. Both discrete and continuous QoS dimensions have been studied.

Visual Q-RAM

Installing the Tcl Plugin and Amaranth Policy

In order to run Visual Q-RAM, you will need to download and install the tcl/tk plug-in from Scriptics. You will also need to create and enable an "amaranth" policy for the plugin. This will allow the plugin to create a connection to the QoS Optimization Server. Follow the steps bellow to enable the policy:

Locate and change directories to the policy configuration directory for the Tcl Plugin. On Unix systems this is typically "~/.netscape/tclplug/2.0/config", on Windows systems it is typically "C:\tclplug\2.0\config".
Copy the file "outside.cfg" to the file "amaranth.cfg".

Edit the file "amaranth.cfg", change the lines:

   section hosts ports
   disallow * *

to:

   section hosts ports
   allow "gadoid.ices.cmu.edu" *

To enable the Amaranth policy edit the file plugin.cfg, add the line:
```
          allow amaranth
```
somewhere after the "section policies" line, but before the next section.

Visual Q-RAM is a tcl/tk applet (tclet) for the visual presentation of multi-dimensional QoS optimization problems and their solutions. Problems can be entered manually through the interface, or loaded from a file. By communicating with the Q-RAM server, an optimial solution to the displayed problem can be obtained and displayed.

The interface is comprised of nine main sections. These sections and their functions are:

Task List Box - Located in the upper left corner of the applet, the Task List Box contains a list of all tasks in the current optimization problem. Clicking on a task name in the list box will cause the user and application profiles for that task to be displayed on the right hand side of the display, and the task weight and utility to be displayed just under the task list. Tasks can be deleted, added or renamed by using the buttons and the task name entry box.
Problem Load/Save Box - Located just to the right of the Task List Box, the Problem Load/Save Box lists all of the QoS optimization problems that can be loaded. In addition to local files, there may also be several built-in problems. Double clicking on an problem name, or selecting a problem name and pressing the "Load" button will cause a problem to be loaded. Entering a name in the entry box below the problem list and pressing the "Save" button will cause the current problem to be save to a file. When Visual Q-RAM is run as an applet under a browser, files are saved to the "sandbox" area for the tcl/tk plugin. See documentation on the plugin to locate your sandbox. The "New" button can be used to delete all tasks and create a new problem from scratch.
Optimization Command Box - To run the optimizer on the current problem, use the Optimization Command Box located below the Problem Load/Save Box. There are three optimization algorithms: amrmd, an approximate QoS optimizer, amrmd1, an alternate approximate QoS optimizer, and mrmd an exact QoS optimizer. To optimize the current problem, first select and algorithm and then press the "Optimize" button. Press "Cancel" to cancel an optimization request. While amrmd and amrmd1 typically return a result in less than a second, mrmd can require ten or more seconds to complete. The result of the optimization is indicated by changing the current setpoints for all of the tasks in the problem. The Global Utility and Global Resource Allocation Boxes will indicate the optimized utility value and resource utilizations.
Task Utility Box - The Task Utility Box is located just below the Task List Box and includes a slider for setting the task weight, and a bar graph indicating the task utility. The task utility is defined as wt* ( w1*u1 + ... wn*un)/n where wt is the task weight, ui is the dimension-wise utility for QoS dimension i, wi is the dimension-wise weight for QoS dimension i, and n is the number of QoS dimensions for the task. The task weight is always between 0 and 1.
Resource Limits Box - The Resource Limits Box is located to the right of the Task Utility Box, and contains sliders for setting the maximum amount of resources available for each resource dimension. In addition, an entry box above each of the sliders can be used to set the names of the dimensions in the current problem.
Global Utility Box - The Global Utility Box is located below the Task Utility and Resource Limits Boxes and displays the global utility as a stacked bar graph. Each segment in the bar graph represents one task. The segments are stacked the same order as in the Task List Box with the current task being highlighted in red. It is also possible to select a task be clicking on a segment of the bar graph. This feature can be used to select a task which seems to be getting more or less utility than other tasks.
Global Resource Allocation Box - Located below the Global Utility Box, this box is used to display the current global resource allocation. There is one stacked bar graph for each resource. Each segment in the bar graphs represent one task. The segments are stacked in the same order as in the Task List Box with the current task being highlighted in red. It is also possible to select a task be clicking on a segment of one of the bar graphs. This feature can be used to select a task which seems to be using more or less of a resource than other tasks.
Each of the resource utilization graphs contains a dark vertical bar to indicate the position of the resource maximum set in the "Resource Limits Box". The position of this bar can be changed by dragging it with the mouse pointer to change the scale on the bar graph.
User Profile Box - The User Profile Box is located in the upper right corner of the applet and details the utility curves for the current task. Each of the graphs displayed in this box is the utility curve for a single QoS dimension. The vertical bars in each graph represent the quality indices of the QoS dimension. To change the dimensional utility value associated with a quality index, click on the appropriate point on the utility curve and drag it up or down the bar. As you move the selected point on the utility curve, the dimension-wise utility (without the weight factor) will be displayed near the y-axis at the same level as the point. The text entry box above each of the graphs indicates the name of the QoS dimension. QoS dimension names are unique to each task and can be change by modifying the contents of the box. A weight for each QoS dimension can be set using the slider below each of the graphs.
Application Profile Box - The Application Profile Box is located in the lower right corner of the applet and details the QoS to resource mapping as well as displaying the currently selected QoS setpoint for the current task. The mapping is presented as a matrix of graphs showing each QoS dimension (along the top) against each resource dimension (along the side). Within each graph is a set of vertical bars representing the quality index values for the QoS dimension of the column under which the graph is located. On each bar is the set of setpoints having the quality index for that bar and QoS dimension. The vertical position of the setpoints correspond to the resources consumed by the setpoint. Lines connecting setpoints accross quality index values are setpoints which differ only in the quality index for the QoS dimension corresponing the graph in which it is displayed.
The currently selected setpoint for a task is indicated by the enlarged black setpoint, and by the highlighted quality index bars for each QoS dimension. Within each graph, setpoints which vary only in the quality index value for the QoS dimension of the graph are highlighted in black but are not enlarged. All other setpoints and quality index bars are shown in gray.
There are two methods for selecting a QoS setpoint. The direct method is to click the mouse pointer on the setpoint you wish to select. When the pointer is near multiple setpoints, the current setpoint and setpoints differing only in the index for the graph in which the selection is made takes precedence. The second method for selecting a setpoint is to click on the quality index bars in a graph for each of the dimensions. This method can be used to select a setpoint for a specific QoS vector. In order to change the resource utilization associated with a setpoint, you must first unlock the setpoints. Do this by unselecting the "Lock Setpoints" check box in the upper right corner of the box.
A task may be excluded from by checking the "Task Excluded" box. An exculded task is a task which is granted no resources and obtains no utility. When a task is excluded, the setpoint is grayed out, the task utility goes to zero, and the task contributions to global utility and resource allocation go to zero.