125 High Speed Mode (or 125HSM) is Broadcom's proprietary frame-bursting and compression technology to improve 802.11g wireless LAN performance. The throughput transmission speed limit when using 125HSM is claimed to be up to 35%-40% higher than standard 802.11g.
The "125" in "125 High Speed Mode" refers to performance at a theoretical signaling rate of 125 Mbit/s: a 125HSM device can achieve a maximum throughput of 34.1 Mbit/s, which is the equivalent throughput of a system strictly following all 802.11g protocols and operating at a signaling rate of 125 Mbit/s.
When 125HSM was originally announced in 2004, it was called Afterburner. It is currently marketed as a proprietary extension of Broadcom's Xpress technology, their standards-based frame-bursting approach that is supported by their 54g Wi-Fi chipsets. Other vendors have marketed 125HSM products under a variety of names:
(It is not the same as "Super-G" or "108 Mbit/s" technology.)[1]
Manufacturers that have licensed 125HSM technology from Broadcom include Belkin, Buffalo Technology, Dell, Gateway, Hewlett-Packard, Asus, Linksys (now part of Cisco Systems), Motorola, U.S. Robotics and Netcomm. In general, 125HSM products from different vendors are all interoperable in 125HSM mode.
125HSM is one of several competing proprietary approaches that were developed to increase 802.11g performance of wireless devices, such as MIMO-based extensions from Airgo Networks, Nitro from Conexant, and Super G from Atheros. 125HSM can be more successful in radio-dense environments than non-standard channel bonding approaches to enhance 802.11g performance. Broadcom claims that in the real-world, 125HSM provides up to 17% better performance over channel bonding approaches such as Super G because other ISM band devices—such as neighboring wireless networks, cordless telephones, baby monitors, and Bluetooth devices—can interfere with channel bonding at distances of up to 150 feet (46 m).