We have developed an IP-over-Ethernet-based ultra high-speed multimedia wireless LAN prototype operating in the 60-GHz band. It employs a media-access-control (MAC) protocol based on reservation-based slotted idle signal multiple access (RS-ISMA), which was implemented in the former prototype, for supporting various IP traffic such as real-time AV traffic and best-effort web traffic. The protocol also has a new function called NACK sensing for the efficient retransmission of wireless multicast packets. It was demonstrated that the prototype can provide the world's fastest radio transmission speed of 128 Mbps for two-way communications. We have measured the throughput and latency of the prototype LAN for Ethernet-frame transmission in a point-to-point baseband-connected environment. The measurement showed that the prototype LAN provides a maximum throughput of 30 Mbps, and that the measured throughput agrees with the theoretically predicted throughput. It also showed that the maximum latency, which includes switching and routing latency in the wired part, is below 1 msec.