Hello, it's me again. (I used to think that ASN.1 was simple
... until I noticed that UMTS's RRC's designers were wise enough
to use only a very, very, very small subset of it ;) )
I am not completely clear on this ... and I can't seem to find
anything in X.680 nor in Olivier's Book that covers it (well, had
I found it I wouldn't have asked):
Consider the following type:
Toto ::= SEQUENCE {
tata INTEGER (0..10),
...,
[[tete BIT STRING (SIZE(5..6)),
tutu INTEGER (0..5)]], -- version 2
titi BOOLEAN -- version 3
}
It has two ExtensionAddition(s). X.691 says that PER encoding
needs (among other things) a bitmap of 2 bits (in this case)
coding the presence of each extension addition.
Does that imply that a value of type Toto could well have it's
component titi (corresponding to v3) filled, but tete and tutu
(v2) left non-present, even without being DEFAULT or OPTIONAL?
Or is the presence of each addition compulsory (baring DEFAULT
or OPTIONAL components) if a later addition is present? Here for
instance the first addition corresponds to v2, should it be
present if the next addition (v3) is present?
The last option seems to make more sense, but I still wonder.
Any help? Thanks a lot anyway.
Benoit.
