An Extensible Remote Graphical Interface
for an ATM Network Simulator ¹

The University of California, Santa Barbara, is developing a 40 gigabit per second ATM switch as part of its Thunder and Lightning network project. To use the high bandwidth efficiently, new network protocols are being developed and simulated on the Thunder and Lightning network protocol simulator. Due to the extreme memory and computational requirements of the simulator, the display, unlike most Tcl/Tk interfaces, must be implemented as a distinct process capable of running on a remote machine. This paper discusses some of the issues that arise with such a physical separation of application and interface, and describes the implementation of the simulator's display application, with an emphasis on the use of the Tcl language. One module of the GUI for the simulator is discussed in detail, demonstrating the use of XDR (external data representation) with Tcl sockets to provide for cross-platform binary data exchange between the simulator and its display application. We also discuss our experience in building the simulator GUI and propose ways in which XDR might be incorporated into Tcl. We discuss some shortcomings of the canvas widget and describe mechanisms to overcome them.