What is the purpose of 802.11n Greenfield mode? Will it cause problems for existing wireless networks?
By submitting your email address, you agree to receive emails regarding relevant topic offers from TechTarget and its partners. You can withdraw your consent at any time. Contact TechTarget at 275 Grove Street, Newton, MA.
A device that uses 802.11n high throughput (HT) mode -- also known as Greenfield mode -- assumes that there are no 802.11a/b/g stations using the same channel. 802.11a/b/g devices cannot communicate with a Greenfield AP. Instead, their transmissions are likely to collide, causing errors and retransmissions for both parties.
Normally, 802.11 devices share channels by sensing when another device is transmitting, using a back-off timer to wait until the channel is free. However, because an 802.11a/b/g device cannot tell that a Greenfield device is transmitting, it will go right ahead and transmit. To avoid this, the 802.11n standard also defines an HT mixed mode.
A device using HT mixed mode prepares to transmit in both the old 802.11a/b/g fashion and the new 802.11n fashion. Specifically, HT mixed mode devices transmit a legacy format preamble, followed by an HT format preamble. An HT mixed mode device must also send legacy format CTS-to-Self or RTS/CTS (Request to Send/Clear to Send) frames before transmitting. These "protection mechanisms" let nearby 802.11a/b/g devices -- including those not connected to the HT mixed AP -- sense when the channel is busy.
Of course, these protection mechanisms significantly reduce an 802.11n WLAN's throughput. But they are a price that must be paid to coexist peacefully with 802.11a/b/g neighbors.
Dig Deeper on Wireless LAN Implementation
Related Q&A from Lisa Phifer
Need to send an email, check your flight's status or get ready for a presentation? You can do it all on your smartwatch, thanks to a slew of Apple ...continue reading
New and improved management features have made Android devices more suitable for enterprise use, and API and EMM tools can streamline the device ...continue reading
Whether you need a basic open source mobile device management tool for your company's Apple or Android devices, or something more customized, you ...continue reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.