Abstract

DuPont commissioned The Tolly Group to evaluate FDDI network performance over 25-pair Category 5 UTP cable insulated with DuPont Teflon fluoropolymer resin, with the main focus on validating signal integrity, bit-error performance, and multi-topology LAN operation over extended copper distances. The project examined whether a single 25-pair cable could reliably carry FDDI while also supporting simultaneous Ethernet and Token Ring traffic, making it suitable for backbone-style structured cabling installations.  

The December 1994 report tested 90 meters of 25-pair Category 5 UTP cable terminated with a Category 5 S110 jack panel from The Siemon Company, with end stations and hubs connected by additional Category 5 4-pair cables for a total end-to-end distance of 100 meters. Tolly evaluated two scenarios: first, a single FDDI link operating alone across the cable, and second, a mixed multi-topology configuration in which two FDDI, two Ethernet, and two 802.5 Token Ring connections operated simultaneously through the same 25-pair cable bundle. This second configuration was intended to simulate a loaded backbone environment carrying multiple LAN types at once.  

Tolly measured FDDI link stability by collecting Link Error Monitor counts and Reportable Frame Errors over at least 30,000 seconds in each scenario. According to the bar chart on page 1, the measured bit-error-rate multiple relative to the 10^-12 standard was 0.29 for the FDDI-only configuration and 0.33 for the multi-topology configuration, both well below the Category 5 threshold. The report states that in both cases the cable successfully supported FDDI links up to 100 meters within acceptable bit-error limits. Tolly also notes that because the cable under test was evaluated while still on the spool, real-world installed performance could be even better.  

The methodology used 3Com FDDILink UTP adapters and a 3Com FDDI hub, plus Ethernet concentrators, Thomas-Conrad Token Ring MAUs, a Hewlett-Packard FDDI Network Advisor, and a Wandel & Goltermann DA-30 analyzer. In the multi-topology test, Ethernet LANs were flooded at 14,000 68-byte frames per second and Token Ring LANs at 1,800 1,024-byte frames per second to create heavy load conditions. Even with this concurrent traffic, Tolly calculated that bit-error-related retransmissions would add no more than about 1/100,000 of 1% additional network traffic, which translates to less than 1/1,000 of a second for a 1GB transfer. Overall, the report presents DuPont-insulated 25-pair Category 5 UTP as a viable copper medium for carrying FDDI, Ethernet, and Token Ring together over 100-meter runs with very low error overhead.