Wireless
media carry electromagnetic signals at radio and microwave frequencies that
represent the binary digits of data communications. As a networking medium,
wireless is not restricted to conductors
or pathways, as are copper and fiber media.
Wireless
data communication technologies work well in open environments. However,
certain construction materials used in buildings and structures, and the local
terrain, will limit the effective coverage. In addition, wireless is
susceptible to interference and can be disrupted by such common devices as
household cordless phones, some types of fluorescent lights, microwave ovens,
and other wireless communications.
Further,
because wireless communication coverage requires no access to a physical strand
of media, devices and users who are not authorized for access to the network
can gain access to the transmission. Therefore, network security is a major
component of wireless network administration.
Types of
Wireless Networks
The IEEE and
telecommunications industry standards for wireless data communications cover
both the Data Link and Physical layers. Four common data communications
standards that apply to wireless media are:
Standard
IEEE 802.11 - Commonly referred to as Wi-Fi, is a Wireless LAN (WLAN)
technology that uses a contention or non-deterministic system with a Carrier
Sense Multiple Access/Collision Avoidance (CSMA/CA) media access process.
Standard
IEEE 802.15 - Wireless Personal Area Network (WPAN) standard, commonly known as
"Bluetooth", uses a device pairing process to communicate over
distances from 1 to 100 meters.
Standard
IEEE 802.16 - Commonly known as WiMAX (Worldwide Interoperability for Microwave
Access), uses a point-to-multipoint topology to provide wireless broadband
access.
Global
System for Mobile Communications (GSM) - Includes Physical layer specifications
that enable the implementation of the Layer 2 General Packet Radio Service
(GPRS) protocol to provide data transfer over mobile cellular telephony
networks.
Other wireless
technologies such as satellite communications provide data network connectivity
for locations without another means of connection. Protocols including GPRS
enable data to be transferred between earth stations and satellite links.
In each of
the above examples, Physical layer specifications are applied to areas that
include: data to radio signal encoding, frequency and power of transmission,
signal reception and decoding requirements, and antenna design and
construction.
The
Wireless LAN
A common
wireless data implementation is enabling devices to wirelessly connect via a
LAN. In general, a wireless LAN requires the following network devices:
Wireless
Access Point (AP) - Concentrates the wireless signals from users and connects,
usually through a copper cable, to the existing copper-based network
infrastructure such as Ethernet.
Wireless NIC
adapters - Provides wireless communication capability to each network host.
As the
technology has developed, a number of WLAN Ethernet-based standards have emerged.
Care needs to be taken in purchasing wireless devices to ensure compatibility
and interoperability.
Standards
include:
IEEE 802.11a
- Operates in the 5 GHz frequency band and offers speeds of up to 54 Mbps.
Because this standard operates at higher frequencies, it has a smaller coverage
area and is less effective at penetrating building structures. Devices
operating under this standard are not interoperable with the 802.11b and
802.11g standards described below.
IEEE 802.11b
- Operates in the 2.4 GHz frequency band and offers speeds of up to 11 Mbps.
Devices implementing this standard have a longer range and are better able to
penetrate building structures than devices based on 802.11a.
IEEE 802.11g
- Operates in the 2.4 GHz frequency band and offers speeds of up to 54 Mbps.
Devices implementing this standard therefore operate at the same radio
frequency and range as 802.11b but with the bandwidth of 802.11a.
IEEE 802.11n
The IEEE
802.11n standard is currently in draft form. The proposed standard defines
frequency of 2.4 Ghz or 5 GHz. The typical expected data rates are 100 Mbps to
210 Mbps with a distance range of up to 70 meters.
The benefits
of wireless data communications technologies are evident, especially the
savings on costly premises wiring and the convenience of host mobility.
However, network administrators need to develop and apply stringent security
policies and processes to protect wireless LANs from unauthorized access and
damage.
These
wireless standards and Wireless LAN implementations will be covered in more
detail in the LAN Switching and Wireless course.
