Question about protocols

Hi all,
I'm sorry if my question isn't specific to Kannel, but it's in testing
it!

When you have a stack of protocols, can a lower protocol, DOWN, adress
the upper one, UP, without having UP asking for information, as in the
bind function of the socket lib?
I would say no, because DOWN can never know who asked for data.
Otherwise it would violate the principles of layering.

This is because I have to do some protocol testing framework, and I have
to have some uniform interface: (Very) generic get/put Vs. specific
protocol implementation.

Thanks in advance,
Reda
-- 
GCE/E/IT/M/SS !d---(+) s+:+(++:++) a-- C++ ULS++ P+? L+++ E+(++)
W++(+++) N++ o? K? w--- O! M! V! PS+ PE-() Y+(++) PGP! 5! t! R!* b+
DI(+) D!(+++) G e++ h++() r y+(+++++)