About IEEE 802.3ab 1000Base-T TCM encoding

[cianfa72]

TL;DR Summary

About some clarification on Trellis Coded Modulation (TCM) employed in IEEE 802.3ab 1000BASE-T standard

Hi, I would like to discuss some details about the Trellis Coded Modulation (TCM) used on 1000BASE-T 802.3ab Gigabitethernet IEEE standard.

Is this the right place to do that ? Thanks.

 

[berkeman]

Is this the right place to do that ?

Yes, it's a good place to start. If needed later, we can move the thread elsewhere.

 

[cianfa72]

Starting from this link, it isn't clear to me whether IDLE is one of the symbol sent or is actually a state of the Convolutional encoder employed in 1000BASE-T.

The above picture from that link shows a 2-stage Trellis of the Convolutional encoder where the triplets in blue circles are the states and each of the arcs/edges represents an encoder's output symbol for a specific binary input (i.e. this encoder has 8 states and 2 binary inputs).

My question is: what is IDLE (000) ? Is it a state or is it a specific output symbol ? The doubt arises from the following statement:

When there is no data, IDLE (000) is sent. To make IDLE easily detectable, it has its own symbol, and the convolutional decoder is reset on IDLE.