SDP DataChannels

I've just been able to generate an offer only with DataChannels (seems
the fact that audio m-lines where added on Chrome due a bug on the
mediaConstraints, and that was the reason why SDP strings were so
long) and I've been able to dump the generated SDP, being now more
confident that SDP is not the best format at least for this use case
(only DataChannels). Could be any body explain me why there are so
much (almost) duplicated lines? What are the essential ones? What are
just the essential bits of data required to create this DataChannels?

-- 
"Si quieres viajar alrededor del mundo y ser invitado a hablar en un
monton de sitios diferentes, simplemente escribe un sistema operativo
Unix."
– Linus Tordvals, creador del sistema operativo Linux