Queries from a beginner

Hello all,
          I am new to research in the Header Compression field and I have
been trying to get my head around the RFC. If anyone can answer
the following queries, it would be much appreciated.
Just to set the scenario first, I am at the moment just looking into IP
header compression in Uni-directional Mode.
1.)The RFC says that in Uni-directional mode, the compression moves
between IR and normal packet mode.
             a.)So my question is what is the packet header size for these
packets?
             b.) Can IR-Dyn packets be used as well?
2.) The RFC also says that for each compression mode there are three
states (IR,FO,SO),so if I were to apply this for Uni-directional mode.
            c.) What is the SO mode packet that will be sent?i.e., if IR=
normal packet, FO = IR packet, does SO = IR-Dyn packet?
3.) What are the respective header sizes for all these packets?
Cheers
Nikhil