amdx said:
Jerry, I was thinking you would come back and say a bridge is the same as a
usb wifi adapter, but I guess not.
Mike,
If I may chime in here...
In somewhat-simplified Ethernet-networking terms, a "bridge" is a
device which joins two Ethernet segments together, by forwarding
Ethernet packets from one network to the other based on the Ethernet
MAC address of the system to which the packet is being sent. It makes
the decision to forward (or not) without changing (or even acting
upon) their contents at any higher protocol level (e.g. IP address).
An Ethernet switch is a form of bridge. In most respects, a bridge is
"invisible" to the systems whose packets it is forwarding - they don't
even know it's there.
This is distinguished from a router, which makes the forwarding
decision based on a higher-level protocol (e.g. IP address), and which
is "known" directly to the systems that are using it.
An 802.11 access point tends to behave like a bridge, from the point
of view of those devices which are connected to its wired-Ethernet
ports. The devices whose packets are being bridged (via radio) out
through the access point don't realize that this is occurring.
In most 802.11 applications, the wireless client systems *do* know
that they're talking to an access point - they do all of the 802.11
protocol stuff (e.g. access-point scanning, requesting association,
the client side of key negotiation, etc.) themselves, in the device
adapter or firmware or driver. The USB or PCI 802.11 interfaces in
these devices are *not* bridges.
However, it's possible to build a device which looks outwardly like an
802.11 access point, in that it has a radio and antenna(s) and an
Ethernet port, but which implements the _client_ side of 802.11 rather
than the access-point side. You can then connect this to a PC (via
wired Ethernet), and *it* will establish an 802.11 connection with an
existing access point, and then start bridging packets from the wired
Ethernet to the access point. The PC plays no direct part in the
wireless connection setup - it simply transmits packets to what it
"thinks" is a hub or switch, and the "wireless bridge" sends them to
the access point.
You'll sometimes see these devices referred to as a form of "gaming
adapter", because they often have higher performance than typical USB
or PCI 802.11 adapters and don't burden the host CPU as much... and
are thus popular with players of high-performance PC videogames.
Many of the newer all-in-one "802.11 access point, router,
firewall, and wired-Ethernet switch" products can be configured in
this way via software... they'll take the client role in an 802.11
network just as happily as the role of an access point. Most of them
cannot do both things at once - they can serve as an outbound bridge,
or as an access point for a local WLAN, but not both.
So, I think you have at least three basic alternatives for how you can
set up the remote/client end of a longer-distance wireless link:
- Run a big, heavy low-loss coaxial cable from your PC's 802.11
adapter antenna jack, up to your antenna (dish or biquad or helical
or waveguide-can). For really low loss over long distances, plan
on using something like 2" heliax (which is to say, you really
don't want to do this!)
- Run a USB cable (extended as necessary with 15' "active" USB
repeater cables) up to the antenna, and connect a USB/802.11
adapter there (e.g. stick the adapter at the focal point of a dish,
or at the feedpoint in a waveguide can). Google for "Wok-fi".
- Run a CAT-5 Ethernet cable and DC power up to the dish, install an
802.11 bridge right at the antenna, and connect the Ethernet cable
to your PC's wired-Ethernet port.
It's worth noting that most methods of attaching an external antenna
to a commercial 802.11 adapter are likely to void the adapter's Part
15 certification, and make the adapter techically illegal to use for
transmission. 802.11 radios and their associated antennas are
required to be tested and certificated as a complete system.
I've rarely heard of anyone being hassled by the FCC for doing this,
though.
