Greenfield mode, an 802.11n AP can communicate only with 802.11n devices. All pre-802.11n communications are perceived as noise. While Greenfield mode does optimize the performance of 802.11n devices, its inability to play nicely with legacy devices is a major downfall to this mode.
2.4Ghz vs 5GHz
Users can take advantage of the reduced noise available in the 5GHz spectrum. This will provide faster data rates, fewer disconnects, and a more enjoyable experience.
Bluetooth and other wireless peripherals aren’t going to bother you in the 5GHz spectrum so there’s less interference. Microwaves don’t operate up here (not even newer ones), so that source of noise is eliminated, too.
There are many more reasons why 802.11ac is better than others, but this article is about switching to the 5GHz spectrum, rather than about 802.11ac specifically. With a compatible router or WAP, your 802.11n 0r 802.11ac smartphone or tablet will work much, much better. With a stronger the signal and faster the throughput, less power is required to get your signal above the noise floor, which should result in better battery life in addition to better network performance.
Lastly, there are some potential disadvantages. Given the same power, the higher the frequency, the shorter the distance a signal can travel. That means your signal may not travel as far as it would have on a 2.4GHz network.
Which smartphones support 5GHz?
Here is a small (not complete) list of smartphones that support 5GHz:
Apple iPhone 5, 5c, 5S
BlackBerry Q10, Z10, Z30, Bold 9790
Google Nexus 4 and 5
HTC One, One X, One Mini, One SV, Windows Phone 8x, DROID DNA
LG G2, LG Optimus L5 II, LG Optimus G Pro, LG Optimus G
Motorola Razr 1, Razr HD, DROID Razr M, Droid Razr HD
Nokia Lumia 925, 520, 620, 810, 820, 822, 920, 928
Samsung Galaxy S4, SIII, SIII mini, Activ S, Galaxy Note, Galaxy Note II, Galaxy Nexus
Sony Xperia Z, Z1, SP, T
Which Tablets support 5 GHz?
Here is a small current selection:
Amazon Kindle Fire HD, HDX 8.9
Apple iPad Mini, iPad 2, 3, 4
Asus Google Nexus 7, Fonepad 7
Google Nexus 10
Microsoft Surface Pro, Surface Pro 2, Surface RT
Samsung Galaxy Tab 3 10.1, Galaxy Note 8, Galaxy Note 10.1
Sony Xperia Tablet Z
Wi-Fi Multimedia (WMM), previously known as Wireless Multimedia Extensions (WME), is a subset of the 802.11e wireless LAN (WLAN) specification that enhances quality of service (QoS) on a network by prioritizing data packets according to four categories. Network administrators can change priority levels as they see fit.
Ranging from highest priority to lowest, these categories are:
1. Voice: Giving voice packets the highest priority enables concurrent Voice over IP (VoIP) calls with minimal latency and the highest quality possible.
2. Video: By placing video packets in the second tier, WMM prioritizes it over all other data traffic and enables support for three to four standard definition TV (SDTV) streams or one high definition TV (HDTV) stream on a WLAN.
3. Best effort: Best effort data packets consist of those originating from legacy devices or from applications or devices that lack QoS standards.
4. Background: Background priority encompasses file downloads, print jobs and other traffic that does not suffer from increased latency.
WMM also features a Power Save certification that helps small devices on a network conserve battery life. Power Save allows small devices, such as phones and PDAs, to transmit data while in a low-power “dozing” status. The certification gives software developers and hardware manufacturers a way to fine-tune battery use in the ever-increasing number of small devices that have Wi-Fi capabilities.
Wireless Protected Setup
WPS is a rather troubled wireless networking standard. While it can make your life easier, it is also vulnerable to attacks and it may be hard to use with some devices.
The WPS standard mandates the use of a PIN on your router. Even if you never use that PIN, the router will generate it. The WPS PIN is highly vulnerable to brute force attacks. You can read a paper detailing his findings, here. It is a very interesting read even if you are not a technical person.
The eight-digit PIN is stored by routers in two blocks of four digits each. The router checks the first four digits separately from the last four digits. A hacker can brute-force the first block of four digits and move on to the second block. A smart hacker with the right tools can brute-force the pin in as little as 4 to 10 hours. Most hackers should pull this off in about a day.
802.11n Frame Aggregation
802.11n can send multiple frames per single access to the medium by combining frames together into one larger frame.
There are two forms of frame aggregation: Aggregated Mac Service Data Unit (A-MSDU) and Aggregated Mac Protocol Data Unit (A-MPDU).
A-MSDU increases the maximum frame transmission size from 2,304 bytes to almost 8k bytes (7935 to be exact) while A-MPDU allows up to 64k bytes.
A-MSDU creates the larger frame by combining smaller frames with the same physical source and destination end points and traffic class (i.e. QoS) into one large frame with a common MAC header. One way to visualize this is an access point receiving frames from the wired side at a rate faster than it can transmit them on the wireless side. Ethernet frames headed for the same wireless client can be queued then combined into one larger frame for single transmission, cutting down the overhead dramatically.
One caveat, and it’s a big one, is that like any wireless transmission, the larger the frame the less likely it will be received with no errors. I’ve observed that 802.11n senders tend to learn the maximum data rates possible for given frame sizes.
Thus for instance, you may see a frame containing a TCP ACK send at 270 Mbps (or 300 Mbps if a short guard interval is in use) because it’s very small (typical 78 bytes including the 802.11 overhead). Frames containing FTP data may be sent at 121.5 Mbps simply because previous attempts at a higher data rate proved futile.
Thus it’s not clear how much we will gain in efficiency using the A-MSDU. With its frame size up to 7935 bytes, with one MAC header and payload protected by one CRC like any other single frame, it will most likely be transmitted at a lower data rate for reliable reception.
Contrast this to the A-MPDU which is essentially a chain of individual 802.11 frames sent back-to-back with one access to the medium (i.e. one preamble). The destination must still be one address and the traffic class (QoS) must be the same for each. Clearly, there is more overhead with the A-MPDU because we still have individual PDU frame headers vs. one in the A-MSDU.
Unlike the A-MSDU however, individual PDU frames also have their own CRC; an error in one PDU will not affect the others in the group.
The bottom line is this: Reliability has its overhead.
The A-MPDU allows a much larger “burst” of frame data to be sent compared the the A-MSDU. In fact, many 802.11n access points conservatively option for the 1/2 A-MSDU frame size (3839 bytes) by default to play it safe.