A Category 5 (UTP-5 "data grade") cable from a LAN switch or hub is connected to the twisted-pair Ethernet (TPE) connector on the back panel of the Sun Blade 150 platform (location 4 in the diagram below).
For information about signals at the TPE connector, see the "Twisted-Pair Ethernet Connector" section in the "Signal Descriptions" chapter of the Sun Blade 150 Service Manual.