[ns] help with errormodule

[Rocío R]

Hi,
what's the difference between errormodel and errormodule?
I find an example with the code:
set emod [$lossylink_ errormodule]
set errmodel [new ErrorModel/Periodic]
$errmodel unit pkt
$errmodel set offset_ 10
$errmodel set period_ $interval
$ns at $changetime "$errmodel set period_ 10000"
$emod insert $errmodel
$emod bind $errmodel 0

but I can't find what means "insert" and "bind". 
Where can I look for those commands?

Thaks everyone.

Rocío