my AP is a linksys WRT54G and it supports client isolation (or AP isolation as linksys calls it) which prevents one wireless client communicating with another wireless client.
this is a nice feature but im not sure how it works and wether i could see traffic to and from stationA to the AP from stationB (for example) .
MTIA
I think that it blocks two messages which stops M$ networking from talking to each other.
Tony
Oh, it's really simple. Wireless access points work by bridging the wireless port to the wired switch ports and router port. Everything happens at the MAC address level and does not involve IP addresses, NETBIOS over TCP/IP (also known as MS Networking). Just MAC addresses.
The wireless bridge builds a bridging table consisting of a table of "heard" (or sniffed) MAC addresses that appear on various ports. There are really just 3 available ports[1]. Wireless, ethernet switch, and router port. If the destination MAC address of a port is shows up in the MAC address table as sitting on a specific port, only that port gets the traffic. Broadcasts, which have no destination MAC address are sent to all ports.
Well, it's simple enough to build a logical rule (or filter) for these MAC addresses and ports that says: "If the packet originates on the wireless port, it can only send and receive packets that are destined or originate from the router port or ethernet switch port." Not a very complex rule, but one which totally prevents wireless client to client traffic. Not even broadcasts will go from wireless client to client.
[1] Actually, that's not true as each port on the 4 port ethernet switch is considered a seperate port. However, let's make life simple and pretent the switch section is just one port.Thanks again Jeff
That makes perfect sense.
Presumbaly this must also improve performance slightly ?
Nope. Absolutely no improvement in performance which I guess means speed. Performance is exactly the same as if you were using one antenna. The difference is in "reliability" or ability to survive in a multipath environment. However, you'll get more reliability benifits out of OFDM modulation, which actually benifits somewhat from being able to use multiple delayed (reflected) transmissions, than out of diversity.
To make matters more complex, diversity has the benifit of reducing the number of speed changes the access point has to make to compensate for lousy signals. The access point has no way to know if the corrupted packets are comeing from reflections, poor signal strength, or interference. It only knows that the packets are arriving trashed. So, it has only two recourses. It can decrease the maximum packet size to smaller packets that have a higher probability of getting through interference or overlapping valid data with reflective collisions. However, this isn't done because the fragmentation threshold is normally defaulted to maximum for optimum performance. So, the only remaining option is to slow things down, which has the effect of improving the receiver sensitivity. Algorithms vary, but basically as soon as there's garbage packets, there will be a corresponding slow down, which of course affects performance. If diversity can be used to reduce the need to recover from corrupted packets, then overall performance will improve.
In case you haven't noticed, everything affects everything else, ad nausium. In my never humble opinion, it is better to go slow and error free, than fast with lots of retransmissions, speed changes, and corruption.
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