Throughput Enhancement Technologies
Updated December 9, 2003
The ink had hardly dried on the 802.11g standard when wireless chip manufacturers started to roll out non-standard throughput "enhancement" technologies. Intersil (>GlobespanVirata>Conexant) introduced Nitro and Atheros announced Super-G at the Networld+Interop Las Vegas show in late April 2003.
Broadcom was notably absent from this first round of announcements, opting instead (in a surprisingly conservative move) to wait until the ratification of 802.11g on June 13 to introduce its Xpress technology.
The differences boil down to these basic points:
- Nitro and Xpress are primarily focused on enhancing the total throughput of multiple devices that use them in mixed 802.11b / g networks. (You may see slight throughput improvement for a single AP / client pair, depending on drivers, OSes and other factors.)
- Nitro and Xpress primarily use "packet (or frame) bursting" to provide throughput enhancement
- Super-G enhances the throughput of even a single AP / client pair (i.e. measured improvement doesn't depend on calculating the total throughput of multiple devices in a WLAN)
- Super-G uses packet-bursting, "fast frames", on-the-fly data compression / decompression, and dual-channel bonding to provide throughput enhancement
Tip: Atheros has not released its own Super-G White paper. But if you can wade through the marketing happy-talk, the "How it Works" section of NETGEAR's NETGEAR 108 Mbps Wireless Solution: Technology Overview (PDF) paper contains some helpful info.
As you can see, Nitro, Xpress and Super-G all use some form of packet-bursting, which speeds things up by removing the pause (to check for other stations that may want to send data) that normally occurs between packets. Since this feature is part of the 802.11e draft standard for Quality of Service (QoS), it's not at issue.
Neither is Super-G's "fast frames" feature - which inserts multiple data packets into a single data frame - since it's also part of the 802.11e draft. Broadcom could argue that the on-the-fly data compression / decompression is a problem, but the main objection is to Super-G's dual-channel bonding feature.
Broadcom alleges that Super-G's channel bonding feature can significantly degrade the performance of neighboring 2.4GHz WLANs that don't use Super-G. Broadcom's Comdex demos focused on showing two Super-G behaviors that Broadcom says are the root of the problem:
- There isn't enough room in the 2.4GHz wireless LAN spectrum for the increased spectrum used by channel bonding
- Super-G doesn't check to see if 11b or 11g standards-compliant devices are in range before using its non-standard techniques
This NTK will explore both of these points, but let's first look at the spectrum-use issue.