100Base TX Idle Symbols

[John Pye]

Could someone clear this up for me?

I've read that in 100BaseTX ethernet, the line is never "idle", meaning that if no nodes on the network have data to send, then idle symbols are sent to keep things alive and synchronized.

I am guessing this is how it works:

1) that in Full Duplex mode, where there are only two nodes on the network, each node is always sending either data or idle symbols on its transmit line.

and...
2) that in Half Duplex mode, idle symbols are sent by only one node- in particular, the node that sent the most recent data frame. When another node wants to transmit, it waits for the network traffic to be idle symbols, and then starts sending to collide with the idle symbols. The node that is sending the idle symbols then stops transmitting, allowing the new node to take over the physical layer.

I was hoping someone in the know could either confirm or correct my thinking.
Thanks.

[Brian Hackley]

John,

Check out Charles Spurgeon's website at http://wwwhost.ots.utexas.edu/ethernet/ethernet-home.html which will has an excellent set of references and a nice search capability.

Hope that helps,

-> Brian Hackley