Overview
A wireless network interface
controller (WNIC) is a network card which connects to a radio-based
computer network, unlike a regular network interface controller (NIC) which
connects to a wire-based network such as token ring or Ethernet. A WNIC, just
like a NIC, 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.
Infrastructure
mode
In an infrastructure mode network
the WNIC needs an 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.
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.
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.
- 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.
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 a 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. 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.
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