Buriedcode
Joined: 06 May 2004
Posts: 316
Helped: 34
Location: London
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 01 Apr 2006 22:03 Re: WLAN bit rates |
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Hi,
I'm completely out of my depth here, with little or no experience in designing Wifi...or any wireless systems, but I'll give it a whirl.
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My question is what is bit rate at MAC level and why is it less
than at physical level |
When information is sent wirelessly, information is added to the 'useful' information to allow the reciever to syncronise, decrypt, and decode the 'useful data'/ So, say you want to send 400 bytes to another PC, with wifi. This 400 bytes can be anything, its user data, say, a small text file. There are many 'levels' at which a protocol works...you mentioned the two main ones, MAC and PHY. I believe 'MAC' refers to networking..(I'm not computer buff though) it carries information about the sender, the recipient, network topology, and the way it is being sent. This level of 'protocol' is used for wired communication as well. It doesn't care how the data gets to its destination...but it does control who gets it, and how the receiver interprets it.
PHY layer on the other hand, deals purely with the RF part (the 'physical connection in a link). This includes, channel coding, security, modulation, symbol rate, forward error correction, framing/syncronisation (and chip syncronisation in DSSS)..
So, what is sent over-the-air contains all this information as well as the data we wanted to send. Its added to our 'useful' information so it can be sent to a particular destination quickly, securely, and without error. So, if the maximum over-the-air bit rate (not symbol rate) is say, 2MB/s, we must send extra information for the MAC and PHY, it reduces the rate at which we send useful information.
I'm sorry if this is too simplified, or just plain wrong, but this is basically what I understand of wireless networking in 802.11x
Regards,
BuriedCode.
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