Beware, this image is wrong and lead to misinformation!
From P1 to P2 there are 2.0µs. From P2 to P5 (inside P6) are 2.75µs. P5 is at 1.25µs from P6, so:
(P1 to P2) + (P2 to P5) - (P6 to P5) = 3.5µs
Preamble isn't 30.5µs long! It is 3.5µs!!!
See http://www.radartutorial.eu/13.ssr/pic/mode_s2.print.png as a clarification. P1 to P6 its clearly impossible to be 30.5µs!
Please, see page 3-82 from ICAO, Annex 10, Volume IV, Surveillance and Collision Avoidance Systems. I don't know if images from that document could be reproduced here without permission.
