[Mp4-tech] [Video] SP slices on H.264

[Luca]

Dear Experts,
i would like to ask you something concerning coding and decoding of 
Switching P slices in H.264.
I'm using as reference both:
a) Karczewicz, Kurceren: "The SP and SI-Frames Design for H.264/AVC"
b) Richardson "H.264 and MPEG-4"
General Questions:
1) Why in a) and in the other works on the topic, two different 
quantization parameters (namely PQP and SPQP) are used? Could please 
someone explain me the advantage of using two rather than one?
Specific Questions (Reserved to the one owning both the two references 
and time):
2) The structure of the SP encoder showed in figure 7 in a) has to be 
modified for Secondary SP slices encoding? Since the explanation seems 
to require some modification to the decoder but no further figure are 
available.
3) The primary [in a)] or SP-A [in b)] and secondary [in a)] or SP-AB 
[in b)] encoding/decoding scheme seems to to me be swapped between a) 
and b). It is just my misunderstanding?
Thank you in advance for your constant help.
Greetings,
Luca.