The convolution technique is based on the convolution of the line's terminal variables with its impulse-responses.The impulse-responses characterise the behaviour of the line.
The simple lossy line has three basic impulse responses.
The char. imp. response is a generalization of a lossless line's char. impedance; an example is shown on the lower left. This response describes the voltage-current relationship at each end of the line.
The delay response is a generalization of the delay in a lossless line, and is shown on the lower right. This response describes signal transfer from one end of the line to the other.
A third response, the convolved response, is the convolution of these two responses.
Note that there are sharp discontinuities in the impulse responses.