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【FAQ】Question and Answers for 802.11n Technology

Q: What is 802.11n?

A: 802.11n is a developing new-generation Wi-Fi standard for wide area wireless networks. Devices built to the 802.11n specification will provide significantly higher performance levels than is possible with legacy 802.11b, 802.11a and 802.11g technologies. 
 
Q: Why do I need 802.11n products?
A:  802.11n is a breakthrough technology that enables Wi-Fi networks to do more, faster, over a larger area. 802.11n Wi-Fi provides the very best connection available for computer networking and home entertainment applications alike – delivering the range, bandwidth, and performance today’s multimedia applications and products demand.
Key features of 802.11n products include:
? A strong Wi-Fi signal that can blanket the entire home
? The whole family sharing an internet connection on a wide array of devices without degradation
? Plenty of bandwidth to move high-definition video and audio streams from device to device, throughout the home
? The best user experience with voice calls, video games, and other multimedia applications
? Back up large files in a snap
? Confidence that devices from different manufacturers will work together
 
Q: What levels of performance can be expected from 802.11n?
A: Initial products using will operate at up to 300 Mbps physical data rates, this data rate translates into actual end-user throughput of more than 160 Mbps, nearly six times the rate of 802.11a and 802.11g.
 
Q: The highest internet download speed possible with Cable and DSL is 3 Mbps. Why do I need more than the 54 Mbps my 802.11g router provides to handle such traffic?
A: While the throughput of Cable and DSL connections is limited to a maximum of 3 Mbps, devices connected within a network have the throughput capacity of the devices themselves.
The 54 Mbps physical rate delivered by 802.11g and 802.11a devices is more than enough to support standard internet activities such as web browsing, email and average data transfers. However, 54 Mbps physical rate translates into 24 Mbps of actual end-user throughput. This throughput level is not capable of supporting simultaneous; high-bandwidth applications on a single network such as streaming of multiple HD video transmissions from a wireless media server to a set-top box. And, while many 802.11g and 802.11a networks offer good coverage, none can provide the robust connectivity and coverage required to operate high-bandwidth applications that extend to every room and corner of the home.
 
Q: Which applications require throughput levels not easily supported by legacy Wi-Fi networks?
A: The emergence of the 802.11n standard signals the wireless industry’s move beyond traditional PC networking into consumer electronics including high definition (HD) and standard definition (SD) video disc players, PVRs,, gaming systems, media servers and players. 
A greatly increased level of throughput is required by consumers and product manufacturers to support the growing number of consumer and business applications demanding much greater wireless bandwidth than currently available with legacy devices.  Higher throughput supports multiple applications on a single network.  These applications are multimedia transmissions including HD (high-definition) video streams and wireless gaming.
Many of the applications growing in popularity require steady, reliable bandwidth. So while voice over internet protocol (VoIP), for example, does not require extremely high throughput levels, it needs a constant supply of uninterrupted bandwidth to avoid jitters and frozen or dropped calls. This is also true of video or gaming transmissions.
Some of the bandwidth requirements of these applications:
·         MPEG 2 HDTV 1080i - 19 to 20 Mbps for a channel
·         WM 9* and MPEG 4 - 8 Mbps per single stream
·         Microsoft Media Center standard TV stream – 8 to 10 Mbps per stream
·         Video Gaming – 10 Mbps per console
·         VoIP calls – 1 Mbps
·         Audio files/MP3 – 2 Mbps
·         Digital photography – 1+ Mbps
*It should be noted that digital content delivered by cable and satellite operators is provided in MPEG 2 format. Also, broadcast ATSC HD standard and cable and satellite HD is encoded in MPEG 2. While WM 9 and MPEG 4 require lower bandwidth for effective operation, they are not yet widely deployed.
Given the relatively limited bandwidth of legacy devices, it is clear that high bandwidth multimedia applications and latency intolerant applications cannot operate effectively on legacy networks.
 
Q: Can I use 802.11n products with my old Wi-Fi gear?
A: Yes. 802.11n products are tested for backward compatibility with 802.11 a/b/g gear. Users should match the letters on the logo for the new product to the standard in their old product.
 
Q: If I have a mixed network of 802.11n and previous generation Wi-Fi gear (802.11 a/b/g), can I still get the benefits of 802.11n?
A: 802.11n gear is backward-compatible with 802.11 a/b/g gear that operates in the same frequency bands. When using an 802.11n router (access point), you will probably see some performance improvements on a mixed network, but the dramatic range and throughput improvements are only possible when both client and network devices are 802.11n.
 
Mix-Mode Scenarios:
 
Scenario One: The access point is based on 802.11n, the client is 802.11g.  
The access point will communicate with the client in 802.11g mode, and the devices will deliver 802.11g performance. 

Figure 1: 802.11g client on 802.11n network.
 
Scenario Two: The access point is based on 802.11n and there are one or more 802.11n clients, and one or more 802.11g clients. 
The access point will communicate in 802.11n to the 802.11n clients; the access point will speak 802.11g to the 802.11g clients. The devices should deliver the performance expected from 802.11n and 802.11g, respectively.

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Figure 2: 802.11n and 802.11g clients operating on an 802.11n network.
 
Scenario Three: The router/access point is 802.11a or 802.11g and it is connected to an 802.11n client.
Again, the negotiation of protocols will be completely seamless. The 802.11n client will communicate in either legacy 802.11a or 802.11g mode to the legacy AP.
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Figure 3: 802.11n client on an 802.11g network
 
Q: What is MIMO?
A: Multiple-input and multiple-output, or MIMO, (pronounced mee-moh or mai-moh) refers to the use of multiple antennas both at the transmitter and receiver to improve the performance of radio communication systems. It is one of several forms of smart antenna (SA) in a narrow sense or the state of the art of SA technology. The MIMO technology enlarges the scope and penetration of the wireless signal and eliminates dead zones.
It is similar to having two FM radios tuned to the same channel at the same time – the signal becomes louder and clearer. This multiplies the performance of the Wi-Fi signal, and is reflected in the two, three, or even more antennas found on some 802.11n routers.
 
Q: Why can’t my wireless device connect that 300 Mbps?
A: 1) If you are using encryption the router must be configured to use AES cipher. In some firmware versions/models, the only way to get the AES cipher is to run WPA2-PSK.

2) The channel width needs to be set to 20/40 Auto, if it is not, the adapter will report a connection speed of 130Mbps. This is a feature that was added for compatibility with Intel 802.11n adapters, as they only operate on a channel width of 20.