The system, whose hardware is depicted in Figure 3.12 consists of an IBM personal computer clone with 128 MB of main memory, a 166 MHZ Intel Pentium processor, an Ethernet interface and two Fore PCA-200 PCI ATM interface cards running on a 33 MHz 32-bit wide PCI bus. The Intel i960 processor on the Fore cards allows to optimize OC3MON operation with custom firmware. Usually, Fore does not disclose the source code for this firmware, however NLANR made arrangements with Fore to obtain it and freely distribute the custom firmware executables along with the source code developed for the OC3MON system processor.
The OC3MON ATM NICs are attached to an OC3 fiber pair carrying IP traffic, connecting the receive port of each ATM card to the monitor port of an optical splitter, which carries 5% of the light from each fiber to the receive port of one NIC. Attached to an OC3 trunk terminated on a switching device (e.g., ATM switch or router), one of the OC3MON NICs sees all traffic received by the switching device and the other NIC sees all traffic transmitted by the switching device.
The system is currently used on the vBNS in between the wide area ATM backbone and the primary nodes at the supercomputer centers . Other sites using OC3MON include the National Center for Supercomputing Applications (NCSA) at the University of Illinois, Urbana-Champaign, Nokia (Finland), NTT (Japan), the University of Auckland (New Zealand) and MCI (USA).
The software for OC3MON is free. All source code files are available by FTP. However the source of OC3MON is relatively hard to reuse or extend, since it strongly depends on the Fore adapters that are used, and for which the programmers manuals are not available without special agreements with Fore.