[j-nsp] CSPF computation and traceoption file

[jjsyed at aol.com]

Hi,
 
Why does a typical configuration of cspf at the mpls protocol level include all three flags; cspf, cspf-link, and cspf-mode?
I am not able to find any difference b/w follwings: 
 
cspf-link—Trace links visited during CSPF computations. 
cspf-node—Trace nodes visited during CSPF computations. 
What is the difference between 'links' and 'nodes', and what does it mean 'visited? 
 
Thanks in advance
 
JS