802.1N verses 100BaseT Advertised Throughput

Posted on 2009-12-24
Medium Priority
Last Modified: 2012-05-08
   So from what I have been able to put together so far the advertised throughput is directly related to the type of network you are talking about. Wired vs Wireless. 100BaseT vs 802.11N

   The 100BaseT spec advertises 100Mbps but that is a half duplex advertisement. If you run Full Duplex then it becomes 100Mbps in both directions at the same time for a total throughput of 200Mb in one second correct?

   What I am being told is that 802.11N does it completely different. The manufacturers advertising of 150Mbps is a Full Duplex advertisment. 75Mbps in both directions at the same time (Full Duplex). A total of 150Mb in one second. FYI it is low because it is in the 5Ghz band over a really long distance.

   You can carry this 802.11N "advertising" to what most wireless manufactures advertise as 300Mbps. It is really 150Mbps in each direction at the same time for a total throughput of 300Mb in one second.

   So the long and short of it is 100BaseT is advertised in Half Duplex numbers and 802.11N is advertised in Full Duplex numbers. Can anyone confirm of deny my understanding?
Question by:jimbecher
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GuruChiu earned 2000 total points
ID: 26121019
Bit rate by itself does not tell the full story.

For a wired 100Mbps connection, full duplex you can have up to 100Mbps up and down at the same time. However, in many cases, traffic is mainly traveling in one direction. e.g. on a 100Mbps network, if I can transfer a file at more than 10M byte/s, it is already very efficient.

For wireless it is even worse. Even at the best situation (perfect sign strength, no interference), you may be hard press to get the advertised rate. All devices are sharing the same radio spectum and it use time division to share it. Not only you have no such things are full duplex, you also need to contend with other 802.11a/b/g/n devices for the spectum.
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Author Comment

ID: 26121038
  Thanks GuruChiu. We are talking theory here only. Everyone know about collisions, dropped packets, acks, nacks so on and so forth. It is interesting you say no full duplex in wireless. All done via time division? I wasn't aware of that. Sounds like back in the good old days of serail communication and time division multiplexers :)
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Expert Comment

ID: 26121073
Yes, it is a lot like good old days. Do you still remember alohanet in the 70s? It is a network over radio and the basis of all CSMA/CD network protocol, including Ethernet.

Multiple device using the same frequency will have collision. 802.11a/b/g/n uses CSMA/CA to share the spectum.

Wiki have a good explaination of the technology behind:
Not all 802.11n are created equal. Depends on what you have, you can have 54Mbps to a theoratical maximum of 600Mbps.
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ID: 26121638
300 up, 300 down... total 600 mbps.....

that is also split saying you are using the full 150 mbps on each 2.5 & 5 Ghz channels...

150 mbit up 2.5 Ghz
150 mbit down 2.5 Ghz
150 mbit up 5 Ghz
150 mbit down 5 Ghz

obviously we all know you will never get that but that should answer the question you asking....

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