Wavelan
Wavelan is a wireless local network tecnology defined by the IEEE 802.11
standard. It uses the ISM band frequecy, operating from 902 Mhz to 5.85
Ghz.
The 802.11 standard defines two different network types protocols:
- Ad-Hoc: A simple network where the communications are established
between multiple hosts without the use of a server access point.
- Managed: Uses an access point that alocates the transmission time for
all the hosts and enables mobile stations to roam.
Difference from Ethernet
The most obvious difference with Ethernet cards is that there are more
parameters to configure. In order to communicate, all nodes of the network
must have those parameters configured the same. Some examples of these
parameters are : frequency or hopping pattern, network id, domain,
encryption key (for security)...
Radio Frequency
Wavelan devices can operate in types of transmission frequencies:
- Frequency Hopping Spread Spectrum: The data signal is modulated
in a narrow carrier signal, that jumps in a random (but predictable)
sequence. This tecnique reduces interference because the signal in a
narrow band system will only affect the signal spectrum if both signals
are operating in the same frequency at the same time.
- Direct Sequence Spread Spectrum In this transmission
tecnology the signal is combined in a larger rate of bit sequencing
(chipping code).
The MAC Controller
The Wavelan device is controlled by a MAC controller, responsible to run
the MAC protocol. This is implemented
mainly in an ASIC and/or a microcontroler on the card, but some
functionalities of the MAC may be as well in the driver on the PC. The
card also includes some memory for the MAC controller to store incoming
and outgoing packets (buffers) and other data (configuration, statistics).
Links:
2001.2
Implementation Group
iPaq Implementation Group
Anatomy
of a Radio Lan