> > Section 4.5.3:
> > 
> >    If an older Request message (with smaller
> >    Sequence Number modulo 32) is received, it MUST be ignored.
> >   
> >    Smaller is not super obvious here. I would interpret it as
> > (Last_nr-15)%32 to (Last_nr-1)%32. Saying something like that might 
> > be clearer on which sequence numbers that are okay.
> 


Got it. How about the following:

<modified text>
   Implementations MUST keep track of the Sequence Number of the last
   received Request message, and MUST cache the corresponding Response
   message.  If a retransmission with the same Sequence Number is
   received, the cached Response message MUST be retransmitted without
   re-processing the Request.  If an older Request message is received,
   meaning one where the sequence number is smaller, it MUST be ignored.
   A newer Request message, meaning one whose sequence number is larger,
   is processed as usual.

   Note: A sequence number is considered "smaller" when s1 is smaller
   than s2 modulo 256 if and only if (s1<s2 and (s2-s1)<128) or (s1>s2
   and (s1-s2)>128)
</modified text>