802.11b true bandwidth

[sonnierr]

I have been using APs and bridges for over a year now. I still can not uncover the details of the true bandwidth. The standard claims a theoretical 11 Mbps. But actual bandwidth from reviews and our own internel testing have shown that maximum bandwidtrh is only about 5.5 Mbps half duplex. That is, you can only move a total of 5.5 Mbps (in the aggregate) across the wireless AP or bridge.

Does anyone undestand why the standard and vendors claim 11 Mbps?

[MoleStrangler]

Just like all vendors claim that 10mbps & 100mbps actually do get that fast, which is also wrong. The reason is the CSMA/CD encoding using on in Ethernet. It allows more than one host to get access to the network.

In real terms you can only utilise 45%-50% of the available bandwidth with Ethernet. Any more then something is broken. Token-Ring can get up to 98% because it uses a token system and does not let all the NICs fight for network bandwidth.

You can switch this CSMA/CD off and only have one host connected to its own port on the switch. ha! Full duplex Ethernet. You tell both ends that they are the only two NICs that are on this cable so you do not need the CSMA/CD algorithm to detect for collisions and have back off algorithms etc...

The host use one pair in the Cat to TX with is connected to the RS side of the switch. And the TX side of the switch is connected to the RX side of the host.

The problem with 802.11 is that it uses a radio instead of a cable. There are standards to make sure that Ethernet cables are built to specific electrical properties hence CAT 5,6,7. This gives the Ethernet card a known medium to transmit its information over. But even with this Ethernet cannot react its 10 or 100mbps speed because of the CSMA/CD algorithm it uses to allow more that two hosts on any one segment.

So the radio network has a medium it uses that has unknown properties and a radio systems must be take into account a medium that it know nothing about. So the physical layer of 802.11b is just wow! just so complex. Ethernet 10mbps is very simple and easily understood (look for Manchester encoding).

[ktwebb]

Mole is right on the money. CSMA. Heavy overhead. The Wi-Fi devices do communicate at 11 Mbps, but the data itself is bogged down by overhead.

Edit: Found a link that discusses the issue in detail.

http://www.networkcomputing.com/1113/1113f2.html

[MoleStrangler]

Thanks for that:)