Manual and Documentation

Installation Procedure for the Beta Version:

You should have Mathematica 5 installed in your PC to run QNAT. The software is being distributed as a beta release in compressed format. Please create a folder C:\qnat32 in your PC and decompress the files and folders in that folder.

This beta release of QNAT is done under the license conditions included in the license file. You should read and agree to that before installing or using this software.

Running QNAT:

This section gives a brief overview of the way QNAT can be run once it has been properly installed. The user may also find it convenient to consult the on-line help that has been provided. All the commands may be found by clicking on the items in the menu bar displayed at the top. Commands which cannot be executed at a particular time (possibly because it would not make sense to run the command at that time), are greyed out and cannot be executed.

Choosing Network Mode on Launch: When it is launched, QNAT asks the user to choose between a Blocking or a Non-Blocking mode. (We plan to add another option of Discrete-Time in the final version.) This selected mode cannot be changed except by exiting QNAT and relaunching it once again. It should also be noted that most of the Blocking Networks supported by QNAT may be run with some or all nodes of infinite capacity.

Saving and Loading Networks Through Files: QNAT may be used to create a new queueing network of a particular type that is supported by the package. This network may be saved and reloaded later. The network description is saved as an ASCII file using a storage convention internal to QNAT. Though it is possible to edit such a file directly using an ASCII text editor, we strongly recommend that this should not be done. We recommend that the following convention be used for the file extension -

However, this naming convention is not mandatory. The user is free to select his/her own naming convention. This convention has, however, been followed in the examples supplied with QNAT. These example networks may be directly loaded and run. The File Load and File Save options are to be found in the File item in the menu bar. (The Run command is there in the Tools item in the menu bar.)

Choice of Default Parameters: QNAT has also been set up such that, as far as possible, for any network that it is asked to create, it chooses default parameter values of a type which will allow the program to be run directly. This has been provided as a feature to quickly test whether QNAT and its connection to Mathematica are functioning properly or not. A network run with this set of default values will generally run all right without errors. One can, of course, also do such a test by loading and running any of the examples provided with the distribution.
For Open Networks, the user should not directly run the network using the default parameters by themselves. The following addiitional points must be ensured to allow QNAT to function properly -

Setting Up a New Network: After the initial choice of blocking/non-blocking mode, QNAT displays a menu bar. The Start command of the menu bar may then be used to start entering a new network. One can remove the current network, if any, on the screen by using the New option in the File item of the menu bar. This needs to be followed by the Start command once again to begin entering a new network.

On selecting the Start option, the user is guided through the following set of choices which help in defining the network. These choices also allow QNAT to decide internally the solution algorithm that it will use for this network.

After the network has been defined as above, the user is required to actually create the network before proceeding further. This is done by the Create option of the Tools item of the menu bar. Functionally, this command will draw the nodes on the screen so that the user may subsequently select the node to define the node type and its other parameters. Please note that at this point in time, the network interconnections have still not been defined so the network cannot really be drawn. However, internally the default routing chain followed is for a cyclic network. Under some combinations of input choices, this may actually get drawn. This, however should not worry the user because as he/she defines the actual routing chain, the routes drawn will get properly modified.

Once the nodes have been drawn as above (regardless of the interconnections shown, if any), the user is required to enter the parameters for each of them. This is done by clicking on the selected node with the left-mouse button. A special choice required for the case of Non-Blocking Open Networks is to declare whether the node is a Normal node or a Fork-Join node - the Fork-Join queue in this case is limited to being one with no synchronizing queue. The user will be asked to make this choice whenever he/she clicks on a node for the first time. Similarly, for the case of Non-Blocking Closed Networks, the user will be asked to choose between a Normal queue, a Fork-Join Queue with a Synchronizing Queue, or a Fork-Join Queue with no Synchronizing Queue; only after this is done can the user enter the parameters of the individual nodes by clicking on the node itself. If a node is declared as a Fork-Join node, then it is redrawn automatically as a cascaded set of two nodes - one of them is a normal queue while the other represents the combination of all the sibling queues of the Fork-Join combination - parameters for these two nodes need to be entered separately. Some more details on Fork-Join nodes and their parameters are presented later.

On clicking on a node, appropriate dialog boxes are opened to prompt the user to enter the node parameters. (Note that for a new network, the dialog boxes will show default values which may be changed if desired. If a network saved earlier is reloaded, then the dialog boxes will contain the old values which may once again be changed.) The node parameters required to be entered depend on the type of network being analyzed (ie. open/closed/mixed, number of classes and blocking/non-blocking). The dialog boxes will have appropriate entries corresponding to these choices and what can be analyzed in the current version of QNAT. Typical entries would be for parameters like -

The Probability Matrix entered for a node essentially specifies the routing for a customer leaving the current node. The following additional considerations apply for this - Fork-Join Nodes: Some special considerations apply to networks with Fork-Join nodes. These are summarized here. Since the equivalent flow server computation for a Fork-Join node is a lengthy computation that takes time, QNAT tries to minimize this by trying to intelligently decide whether recomputation is required at a particular node and doing this for the affected nodes when analyis for the network is finally run. In case of doubt, the user can play it safe by clicking the Run button in that node's input dialog box after the service time parameters have been entered.

Running the Analysis for a Network: Once the network has been properly set up (i.e. either a new network is created or a previously stored network is reloaded) and its parameters have been entered, the user can run the analysis by choosing the Run option in the Tools item in the Menu Bar. This processes the network and launches Mathematica appropriately. An "Evaluation" message is displayed while calculations are being carried out. This message disappears when the calculations are over. The user can then obtain the results of the analysis for each node by clicking at the selected node and then clicking the Output button. Network level results are shown by adding another item Network in the Menu Bar. The network can then be modified and run again. It may be stored and reloaded for analysis once again - note that storing a network stores only the network configuration and the input parameters.
For Open Networks, the user should additionally take care that the following requirements are satisfied -

Printing Run Results: Once the analysis for a network has been run, the user can use the Print Run Results option in the Tools item on the Menu Bar. This saves a text file with the user-specified name containing a description of the network and the results of the analysis. This file may be examined and printed under any standard editor such as "Notepad". The installation process creates a subdirectory "results" as a convenient place to store these files.

Quitting QNAT: This can be done by selecting the Quit item on the Menu Bar. The user is then asked to verify this before QNAT is terminated.

On-line Help: Online help is provided with QNAT. This help is not extensive but provides some clarification in places where some additional information or assistance was considered necessary.