John L
Bruno.Konik wrote:
Ed, I think you're right on the point that size constraint must be respected but this doesn't mean that the encoding (the bits that are effectively transmitted) respects it in the case of BIT STRING with named bits. Actually, the decoder must give a 'respecting constraint' value to the application. So, in the case of Ulrich, the sender who has removed trailing '0' bits is rigth and the decoder who issues an error because size is not respected in the encoding is wrong. It is my understanding of ITU-T X.690 § 8.6.2.4 and § 11.2.2. In BER nothing prevents the encoder to send a number of bits respecting the constraint but in DER it is clearly forbidden. In both cases, the decoder has to decode with no error and give a correct value to the application.
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-----Message d'origine----- De : [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] la part de Ed Day Envoyé : vendredi 28 février 2003 18:26 À : [EMAIL PROTECTED] Objet : Re: [ASN.1] Question on BER
It is my opinion that the size constraint in this case must be
respected; otherwise, it has no meaning. Clearly, the person who
wrote this definition wanted the bit string to be between 15 and 32
bits in length, otherwise the size constraint would not have been
added. As to precise language in the standards stating this, I
could not find any.
Regards,
Ed Day
Objective Systems, Inc.
REAL WORLD ASN.1 AND XML SOLUTIONS
Tel: +1 (484) 875-3020
Fax: +1 (484) 875-2913
Toll-free: (877) 307-6855 (USA only)
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----- Original Message ----- From: Wiehe Ulrich <mailto:[EMAIL PROTECTED]> To: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> Sent: Friday, February 28, 2003 4:27 AM Subject: [ASN.1] Question on BER
Dear ASN.1 experts
In order to solve an interoperability problem resulting from different interpretations of ITU-T X.690, your help on the following question is very much appreciated:
A BER encoded message contains a data type for which the abstract syntax is defined as
DataType ::= BIT STRING {
bitOne (0),
bitTwo (1),
bitThree (2),
bitSeven (6),
bitEight (7),
bitNine (8),
bitFour (3),
bitFive (4),
bitSix (5),
bitTen (9),
bitEleven (10),
bitTwelve (11),
bitThirteen (12),
bitFourteen (13),
bitFifteen (14),
bitNineteen (18),
bitTwenty (19),
bitTwentyone (20),
bitTwentytwo (21),
bitTwentythree (22),
bitTwentyfour (23),
bitTwentyfive (24),
bitTwentysix (25),
bitTwentyseven (26),
bitTwentyeight (27),
bitTwentynine (28)} (SIZE (15..32))
The entity sending the message encodes this data type as:
03 TAG
02 length
00 no unused bits
80 bitOne set to 1, bitTwo to bitSeven set to 0
The entity receiving the message does not accept it due to the SIZE constraint not being respected and performs the appropriate error handling.
Now designers of the sending entity argue that ITU-T X.690 § 8.6.2.4 and § 11.2.2 allow the encoder to encode the data type as shown above whereas designers of the receiving entity do not share this view and insist on the SIZE constraint being respected.
Dear Experts,
please let me know which of the above interpretations of ITU-T X.690 is correct and whether or not X.690 is incompatible to X.209 in this respect.
Thank you in advance
Ulrich Wiehe
GKS AG
Gesellschaft für
Kommunikations Software Tel:+496621 169139
MMC2 Fax:+49 6621 169 122
Breitenstr. 57 Mobil: +49 151 14016088
D-36251 Bad Hersfeld e-mail: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
-- Prof John Larmouth Larmouth T&PDS Ltd (Training and Protocol Development Services) 1 Blueberry Road Bowdon [EMAIL PROTECTED] Cheshire WA14 3LS Tel: +44 161 928 1605 England Fax: +44 161 928 8069
