6.5.1 The SVMDNS daemon

Figure 6.5: Multiple layers for distributed simulation in SVM

SVMDNS (SVM Dynamic Naming Service) is another daemon built on top of the PVM library. It provides a higher level of interface to SVM processes. For example, in Figure 6.5 there are 4 SVM processes, each of which has a DCharts component running on it. Those DCharts components communicate with each other via ports. The SVM processes register themselves to a single SVMDNS daemon. The SVMDNS daemon invokes functions in the PVM library to create 4 PVM processes. Each of them corresponds to an SVM process. The location of those PVM processes depends on the configuration of the PVM daemon. In this case, PVM processes 1, 2 and 3 are located on machine 1, while PVM process 4 is located on machine 2. The PVM library hides details of this configuration, but provides a uniform API to SVMDNS.

SVMDNS provides the following functionality to each SVM process:

• Registration. Each SVM process that interacts with remote components must register itself to SVMDNS. By default, the SVM simulator attempts to register itself to SVMDNS if and only if a model with at least one port is running in it.

• Life-time. Each SVM process registered to SVMDNS must periodically sends a keep-alive message to the SVM daemon. If the daemon does not receive such a message from an SVM process within a certain period of time (known as life-time), information about the SVM process is removed from SVMDNS' registry. The life-time can be customized in PVMUtil.py. By default it is 30 seconds. Each SVM simulator, after it registers itself, sends the keep-alive message to the SVMDNS every half life-time period.

• Component lookup. SVM processes send the name patterns or types of required components to the SVMDNS. SVMDNS then locates the registered components with those name patterns and types. It establishes the connections between components.

• SVMDNS also maintains the connections between components. SVM processes are ignorant of this information. They simply use ports to identify groups of connected components in SVMDNS. SVMDNS acts as a router in this inter-component communication.

Detailed information about the setup of the SVM daemon and the PVM daemon can be found in [39].