100BASE-T2: a new standard for 100 Mb/s Ethernet transmission over voice-grade cables

100BASE-T2 is a new physical-layer specification for IEEE 802.3 LANs operating at 100 Mb/s ("Fast Ethernet"). It enables users of the prevailing 10BASE-T Ethernet LAN technology to upgrade their networks from 10 to 100 Mb/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), as minimally required 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 duplex 100 Mb/s transmission over two pairs. 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 signaling directions. In the receivers, adaptive digital filters are required for echo and NEXT cancellation, equalization, and interference suppression.