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Gnet 802.11 Architecture
[DRAFT]
February 1st, 2001
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There are a few ways two ways to approach this. The first is to roll our
own infrastructure, the second, is to use the infrastructure that is being
built around us. We'll address building our own infrastructure first,
and the second approach will be discussed further into this document.
802.11 wireless ethernet devices have finally proliferated the market and
are now in a price range within many people's grasp. Many support
1Mbit/sec and 2Mbit/sec data rates at a cost of under $100USD. Even
802.11b (11mbit/sec) NIC's can be purchased at prices under $150 US
dollars. However this is changing every day and we are starting to see
802.11 Access Points that are under the 802.11 mark.
One should not alienate non-802.11 wireless ethernet devices, as they can
still be employed as point-to-point links, especially crossing a large
distance, and Proxim ISA/PCI cards generally fit the bill. A very well
written and maintained [Low-Cost Wireless How-to] describes how to modify
Proxim cards to work over a greater distance inexpensively. Another non-
802.11 solution are the old wavelan 900Mhz and 2.4Ghz Wireless NIC (wNIC),
which can be commonly purchased on ebay and other auction sites for around
$80 US dollars.
First some general descriptions of 802.11 hardware is in order. The major
component is the Wireless STAtion (STA). These generally come in a PCMCIA
(PCCARD) form factor however, I have heard of USB STA's entering the market.
STA's are somewhat versatile in that they can be configured to operate in
STA mode or Access Point(AP) mode. In STA mode the act as a client. In
AP mode they act as a centeral server mode, allowing STAs to connect to
them.
Access Points can be a STA installed in a PC running specialized software,
or
can be a stand-alone unit with a wireless interface on one end, and an
ethernet port on the other. STAs in the surrounding area connect to APs
and APs connect to a backend Distribution Service(DS). The DS in Gnets
case SHOULD be a wireless link as well. In traditional 802.11 networks the
DS is the wired LAN.
802.11 can operate in two distinct modes. The first is Infrastructure mode,
where there are STAs and APs, and STAs must communicate through an AP
in order to participate in the network. The second is Ad Hoc mode, where
STAs can talk to each other, and APs can act as relay points. Depending
on the terrain and local situation Gnet may support either of these modes.
We will mostly be using Infrastructure mode until custom software is written
to handle automatic routing in dense areas.
On to the generally network diagram.
The basic 802.11 g.net installation of three nodes would be as follows:
Cell 1 Cell 2
| |
| directional directional | <- omni
omni -> | | | |
= | | =
| V | <- omni V |
|--------| / | \ |--------|
| site 1 |--[ - - - - - - - | - - - - - - - -]-- | site 2 |
|--------| \ | / |--------|
=