generic network protocols parser ?

[Aziz KEZZOU]

Hi all,
I am wondering if any one knows  about a generic parser which takes a
packet (mbuf) of a certain protocol (e.g RSVP ) as input and generates
some data structre representing the packet ?

I've been searching for a while and found that ethereal and tcpdump
for example use specific data structres and functions to dissect each
protocol packets. Is this the only approach possible ?

My supervisor suggested using a TLV (Type/Length/Value) approach
instead. Any opinions about that?

If no such a parser exists is there any practical reason why ?

Thanks,
Aziz