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125 High Speed Mode

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125 High Speed Mode (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.

Contents

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.

Vendors

Other vendors have marketed 125HSM products under a variety of names:

  • g+ SuperSpeed (ZyXEL) (This one uses the G++ Technology solution from Texas Instruments, which uses 125 Mbit/s as well but may or may not be compatible to Broadcom's solution)
  • G Plus or HSM (Belkin)
  • 125* High Speed or Turbo G (Buffalo)
  • SpeedBooster (Linksys)
  • 125M or 125 High Speed or 125* High Speed (Asus)
  • 125 Mbit/s 802.11g

    • Manufacturers that have licensed 125HSM technology from Broadcom include Belkin, Buffalo Technology, Dell, Gateway, Hewlett-Packard, Asus, Linksys (now part of Belkin), Motorola, U.S. Robotics and Netcomm. In general, 125HSM products from different vendors are all interoperable in 125HSM mode.

    Interoperability

  • These (and similar) proprietary extensions are incompatible across different wi-fi chips vendors. So to make wi-fi links work in 125 HSM mode, both sides should use chips from same vendor (e.g. Broadcom). In most real-world scenarios such modes are simply useless due to different chips used by different devices.
  • Existence of several similar technologies with different branding and incompatible with each other causes massive consumer confusion.
  • These technologies are marketed in such a way it is possible to see them as cheating and tricking consumers through technology branding. This type of network will never be able to reach 125 Mbit/s as real data throughput; 125 Mbit/s is the maximum data rate before accounting for overhead. This causes consumer frustration due to failed expectations. For instance, the average consumer would expect a 125 Mbit/s wireless link to outperform a standard 100 Mbit/s wired link while, in fact, 100 Mbit/s wired link will be much faster; a standard wired 100Mbit/s 100BaseT link is approximately three times faster than 125HSM in simplex mode (i.e. transmitting or receiving only) and six times faster than 125HSM in full-duplex mode (i.e. both transmitting and receiving data—which is typical during file transfers between 2 computer connected to the same hub). In other words, even under ideal conditions, 125 HSM mode may only deliver anywhere from a third to one sixth the data transfer speed of a standard 100 Mbit/s wired LAN link.

    • Alternatives

    125HSM is one of several competing incompatible proprietary extension approaches that were developed to increase performance of 802.11g wireless devices, such as Super G (or "108 Mbit/s" technology) from Atheros, MIMO-based extensions from Airgo Networks, and Nitro from Conexant

    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).

    References

    125 High Speed Mode Wikipedia
    (Text) CC BY-SA