🚀 go-pugleaf

>According to Annex B, there is no transition between states r2 and r3, p6
>and p7 and d2 and d3 resp.... But in Annex C it says the DCE should, when
>receiving some invalid packet, send a restart indication with "Local
>procedure error" and enter state r3.

You are confusing NORMAL conditions and ERROR conditions. The Annex B state
diagrams cover only normal operation; Annex C covers all states and condi-
tions (except for timeouts), and ERROR conditions in particular. So yes, r2
to r3, p6 to p7, and d2 to d3 transitions are all missing from Annex B, but
so are several other "error" transitions. 

Collision is a NORMAL condition, not an ERROR, and is covered by both Annex
B and C. Look at Table C-2/X.25, under the r3 column, first event (Restart
Request). This is the collision case, and the table specifies that you go to
state r1. 

An invalid packet is an ERROR condition, and is covered only by Annex C.

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