Tuesday, November 22, 2011

U.S. Robotics 802.11g Wireless Turbo Multi-function Access Point reviewed

| Wireless Driver & Software

Features, Continued

You get a pretty complete set of controls, including three not shown on the screenshot above:

  • Antenna Selection (Left, Right, Diversity)
  • SSID Broadcast (Enable / Disable)
  • 4X Mode (Enable / Disable)

Although the wireless controls actually have understandable names, I did a little digging to find out specifically what some of them do:

Dot11Mode – The selections of B only, B+ only, G only, and Mixed work by allowing AP association with clients that advertise rates specific to each particular standard in their Beacon frames.Note that the G only selection does not disable the 802.11b protection mechanism that’s part of the 802.11g spec. In response to my query as to whether the 5450 had any controls to disable 802.11b protection, I received the following reply from USR:

“… the TI TNET chipset does not use the same “802.11b protection” mechanism Broadcom and others use, in that the chipset was designed to be relatively agnostic when allowing mixed clients to associate to the AP or router. In essence … there is no protection mode necessary on the TI devices since they treat the 802.11b / 802.11g clients on a case by case basis.”

This is a new one on me, since I thought that the 802.11b protection mechanism was part of the 802.11g spec!

4X Mode – This mode enables TI”s throughput enhancement technology, which of course is unlike anyone else’s! Here’s how TI and USR pitches their throughput-boosting “secret sauce”:

Today, 802.11g+ consists of a technology called packet aggregation or use of larger packets. Traditional IEEE 802.11 implements have used a maximum packet length of approximately 1500 Bytes which was borrowed from Ethernet. The TI physical layer is capable of sending packets that are up to 4000 Bytes long. These longer packets help reduce protocol overhead and thereby increase throughput. There will be additional enhancements to 802.11g+ that include 802.11e and other mechanisms.

• 802.11g+ disables once the rate goes below 11Mbps since the larger packets when sent at slower data rates would result in excessively long transmissions.

• This improvement equates to up to 30-33 Mbps throughput versus 20-23 Mbps average in 802.11g devices on the market.

• An AP using this technique will still talk to any 802.11b, b+ or 802.11g product from TI or any other vendor.

One point of note for TI’s method is that it claims throughput enhancement only when both client and AP use the technology. Both Intersil’s Nitro and Broadcom’s Xpress use a similar stuff-more-bits-into-the-allowed-transmit-slot technique called “frame bursting”, but they both claim at least partial network throughput enhancement even if only APs employing either technology are used. We’ll see later in the Performance section whether any of this actually boosts throughput.

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