Ethereal-dev: Re: [Ethereal-dev] Re: [Ethereal-users] Problem with h245 dissector
Ah thats it.
Thanks for digging this out.
We should then change it back to use a dissector for restricted character
strings and make that function recognize whether the
number of bits were reduced or not and check whether there are other
restricted strings where this might apply.
----- Original Message -----
From: "Martin Regner"
Sent: Sunday, November 23, 2003 10:03 AM
Subject: Re: [Ethereal-dev] Re: [Ethereal-users] Problem with h245 dissector
> Martin Regner wrote:
> > There is something on page 446 i Dubuissons book "ASN.1 Communication
> > Between Heterogeneous Systems" (chapter 20.6.10 Character Strings and
> Dates)
> > that I think could be an explanation to why the decoding with Ethereal
> > 0.9.16 fails for this scenario.
> >
> > Dubissons book can be downloaded from OSS Nakalva's homepage:
> > http://www.oss.com/asn1/dubuisson.html
> >
> > I'm not completely sure if I have understood the text correct, but my
> > preliminar interpretion of the text is that since there is 8 bits used
for
> > each character then every character of the string is encoded as its
> > associated number in the the interval (0..127) for IA5 characters (i.e.
> 0x32
> > for '2') instead of reindexing the characters as the index in
> > "!#*0123456789ABCD" (i.e. 0x05 for '2').
> >
>
>
> On page 305 in the "ASN.1 Complete" by Larmouth its written in a way that
I
> think is more easy to understand:
> "If remapping the original values to a compact range from zero to n-1 does
> not produce a reduction
> in number of bits per character in the PER encoding (for whichever variant
> is in use), then the remapping is
> not done, and the original associated value is used in the encoding."
>
> http://www.c7.com/ss7/books/ASN1_Complete.pdf
>
>
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