Wireless network interface controller
A wireless network interface controller (WNIC) is a network interface controller which connects to a radio-based computer network rather than a wire-based network such as Token Ring or Ethernet. A WNIC, just like other NICs, works on the Layer 1 and Layer 2 of the OSI Model. A WNIC is an essential component for wireless desktop computer. This card uses an antenna to communicate through microwaves. A WNIC in a desktop computer usually is connected using the PCI bus. Other connectivity options are USB and PC card. Integrated WNICs are also available, (typically in Mini PCI/PCI Express Mini Card form).
The term may also apply to a card using protocols other than Wi-Fi, such as one implementing Bluetooth connections.
Contents |
[edit] Modes of operation
- A1 A2 IEEE 802.11y-2008 extended operation of 802.11a to the licensed 3.7 GHz band. Increased power limits allow a range up to 5,000 m. As of 2009[update], it is only being licensed in the United States by the FCC.
- B1 B2 Assumes short guard interval (SGI) enabled, otherwise reduce each data rate by 10%.
| 802.11 network standards | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 802.11 protocol |
Release[1] | Freq. (GHz) |
Bandwidth (MHz) |
Data rate per stream (Mbit/s)[2] |
Allowable MIMO streams |
Modulation | Approximate indoor range[citation needed] | Approximate outdoor range[citation needed] | ||
| (m) | (ft) | (m) | (ft) | |||||||
| — | Jun 1997 | 2.4 | 20 | 1, 2 | 1 | DSSS, FHSS | 20 | 66 | 100 | 330 |
| a | Sep 1999 | 5 | 20 | 6, 9, 12, 18, 24, 36, 48, 54 | 1 | OFDM | 35 | 115 | 120 | 390 |
| 3.7[A] | — | — | 5,000 | 16,000[A] | ||||||
| b | Sep 1999 | 2.4 | 20 | 5.5, 11 | 1 | DSSS | 38 | 125 | 140 | 460 |
| g | Jun 2003 | 2.4 | 20 | 6, 9, 12, 18, 24, 36, 48, 54 | 1 | OFDM, DSSS | 38 | 125 | 140 | 460 |
| n | Oct 2009 | 2.4/5 | 20 | 7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2[B] | 4 | OFDM | 70 | 230 | 250 | 820[3] |
| 40 | 15, 30, 45, 60, 90, 120, 135, 150[B] | 70 | 230 | 250 | 820[3] | |||||
| ac (DRAFT) | Nov. 2011 | 5 | 80 | 433, 867 | 8 | |||||
| 160 | 867, 1.73 Gbit/s, 3.47 Gbit/s, 6.93 Gbit/s | |||||||||
A WNIC can operate in two modes known as infrastructure mode and ad hoc mode.
[edit] Infrastructure mode
In an infrastructure mode network the WNIC needs a wireless access point: all data is transferred using the access point as the central hub. All wireless nodes in an infrastructure mode network connect to an access point. All nodes connecting to the access point must have the same service set identifier (SSID) as the access point, and if the access point is enabled with WEP they must have the same WEP key or other authentication parameters.
[edit] Ad-hoc mode
In an ad-hoc mode network the WNIC does not require an access point, but rather can directly interface with all other wireless nodes directly. All the nodes in an ad-hoc network must have the same channel and SSID.
[edit] Specifications
WNICs are designed around the IEEE 802.11 standard which sets out low-level specifications for how all wireless networks operate. Earlier interface controllers are usually only compatible with earlier variants of the standard, while newer cards support both current and old standards.
Specifications commonly used in marketing materials for WNICs include:
- Wireless data transfer rates (measured in Mbit/s); these range from 2 Mbit/s to 54 Mbit/s.[4]
- Wireless transmit power (measured in dBm)
- Wireless network standards (may include standards such as 802.11b, 802.11g, 802.11n, etc.) 802.11g offers data transfer speeds equivalent to 802.11a – up to 54 Mbit/s – and the wider 300-foot (91 m) range of 802.11b, and is backward compatible with 802.11b.
Most Bluetooth cards do not implement any form of the 802.11 standard.
[edit] Range
Wireless range may be substantially affected by objects in the way of the signal and by the quality of the antenna. Large electrical appliances, such as refrigerators, fuse boxes, metal plumbing, and air conditioning units can impede a wireless network signal. The theoretical maximum range of Wi-Fi is only reached under ideal circumstances and true effective range is typically about half of the theoretical range.[4] Specifically, the maximum throughput speed is only achieved at extremely close range (less than 25 feet (7.6 m) or so); at the outer reaches of a device's effective range, speed may decrease to around 1 Mbit/s before it drops out altogether. The reason is that wireless devices dynamically negotiate the top speed at which they can communicate without dropping too many data packets.
[edit] References
- ^ "Official IEEE 802.11 working group project timelines". Sept. 19, 2009. http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm. Retrieved 2009-10-09.
- ^ "Wi-Fi CERTIFIED n: Longer-Range, Faster-Throughput, Multimedia-Grade Wi-Fi® Networks" (registration required). Wi-Fi Alliance. September 2009. http://www.wi-fi.org/register.php?file=wp_Wi-Fi_CERTIFIED_n_Industry.pdf.
- ^ a b "802.11n Delivers Better Range". Wi-Fi Planet. 2007-05-31. http://www.wi-fiplanet.com/tutorials/article.php/3680781.
- ^ a b Meyers, Mike: Network+ Certification All-in-One Exam Guide, McGraw-Hill, 2004, p. 230.
