100BASE-T2: 100 Mbit/s Ethernet over two pairs of category-3 cabling
Abstract
100BASE-T2 is a new physical layer specification for IEEE 802.3 LANs operating at 100 Mbit/s (`Fast Ethernet'). It enables users of the 10BASE-T Ethernet LAN technology to upgrade their networks from 10 Mbit/s to 100 Mbit/s performance while retaining an existing voice-grade cabling infrastructure. 100BASE-T2 transceivers will operate over two pairs in unshielded twisted-pair cables corresponding to EIA/TIA category 3 (UTP-3), which is the minimum requirement for 10BASE-T. In a four-pair UTP-3 cable, simultaneous operation of two 100BASE-T2 links, or one 100BASE-T2 and one 10BASE-T link, is permitted. Since voice-grade cables exhibit more signal attenuation and significantly higher crosstalk coupling between adjacent pairs than data-grade cables, sophisticated digital signal processing techniques are needed to achieve reliable 100 Mbit/s transmission. The 100BASE-T2 standard defines dual-duplex baseband transmission at a modulation rate of 25 MBaud. During each modulation interval, a four-bit data nibble or Ethernet specific control information is encoded into a pair of quinary signals. These signals are transmitted simultaneously on the two wire pairs in both signalling directions. In the receivers, adaptive digital filters are required for echo and NEXT cancellation, equalization, and interference suppression.