Dutta, Banibrata (STSD) wrote:
Are we absolutely sure that we can claim this, i.e. V3 parser will be
able to understand V1 request, if encoding is BER ?
To me, the sore-point appears to be the fact that V3 is missing an
element with tag [2]. If the received PDU has a field with tag=2, then,
it'd be "ignored" at best, IMHO. It would be "ignored" by virtue of the
fact that the "..." (extension-markers) are there, and have nothing to
do with the presence of the Extension-Container field, per-se.
the good thing about this specification is that mwd-Set in V1
and extensionContainer in V3 are marked as OPTIONAL. if decoder
does not see the expected tag, it'll treat the encoded element
as part of extension (the ellipsis). in case of V3 decoder,
the decoder won't see the [4] tag and will move to processing
the (zero-or-more) elements of extension (ellipsis mark),
treating the mwd-Set as one of them.
and yes, I am pretty sure.
Being an ASN.1 newbie, I'd love to be corrected. Waiting to hear.
-banibrata
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of
Lev Walkin
Sent: Tuesday, March 06, 2007 1:00 AM
To: Marcelo Nahum (QA/EMC)
Cc: [email protected]
Subject: Re: [Asn1] Question on MAP extension containers
The V3 parser will be able to understand V1 request, if BER (CER, DER)
is used. It won't be able to understand it if XER is used.
Marcelo Nahum (QA/EMC) wrote:
Hi Ramaswamy,
Thanks for your quick response. I copied the example again since the
V3 version is a bit different. As you can see the entry mwd-set was
removed, and there is an extension container instead. Will in this
case a V3 parser understand a V1 request if the entry mwd-Set is
present in the request ?
V1:
RoutingInfoForSM-Res::= SEQUENCE {
imsi IMSI,
locationInfoWithLMSI [0] LocationInfoWithLMSI,
mwd-Set [2] BOOLEAN OPTIONAL,
...}
V3:
RoutingInfoForSM-Res ::= SEQUENCE {
imsi IMSI,
locationInfoWithLMSI [0] LocationInfoWithLMSI,
extensionContainer [4] ExtensionContainer OPTIONAL,
...}
Thanks again,
Marcelo
________________________________
From: Ramaswamy R [mailto:[EMAIL PROTECTED]
Sent: March 5, 2007 12:53 PM
To: Marcelo Nahum (QA/EMC)
Cc: [email protected]
Subject: Re: [Asn1] Question on MAP extension containers
Hi,
Extension are used to say that future version may contain more
data
than what is there at present. I.e. V3 will have the data from V1,
V2 and it additions more from V3. I believe that the definition must
have been as follows -
V1: RoutingInfoForSM-Res::= SEQUENCE {
imsi IMSI,
locationInfoWithLMSI [0]
LocationInfoWithLMSI,
mwd-Set [2] BOOLEAN OPTIONAL,
...}
V3: RoutingInfoForSM-Res ::= SEQUENCE {
imsi IMSI,
locationInfoWithLMSI [0] LocationInfoWithLMSI,
mwd-Set [2] BOOLEAN OPTIONAL,
...
extensionContainer [4] ExtensionContainer
OPTIONAL,
}
The extension marker helps ensure backward compatibility as
follows.
Since RoutingInfoForSM-Res in V3 has the fields of V1 when a V1 based
encoder / decoder intercepts a message from V3 it only interprets the
fields that it understands and skips the rest. Thus this does not
break the way older versions interpret the data from newer versions.
On 3/5/07, Marcelo Nahum (QA/EMC) <[EMAIL PROTECTED]>
wrote:
I'm quite new to ASN.1 and have a question related to
extension
containers.
Are extension containers used also for backward
compatibility ?
For example, regarding the different versions of the GSM
MAP
standard (29.002), extension containers seem to be there where an old
version of the standard had a deprecated entry.
V1:
RoutingInfoForSM-Res::= SEQUENCE {
imsi IMSI,
locationInfoWithLMSI [0]
LocationInfoWithLMSI,
mwd-Set [2] BOOLEAN OPTIONAL,
...}
V3:
RoutingInfoForSM-Res ::= SEQUENCE {
imsi IMSI,
locationInfoWithLMSI [0]
LocationInfoWithLMSI,
extensionContainer [4] ExtensionContainer
OPTIONAL,
...}
If I parse a V1 request using a V3 parser, will the
extension
container contain the mwd-Set value ?
IMHO this ain't a valid usage of extension marker across
versions of
an asn.1 spec. If you actually intended the one I mentioned above,
then YES.
In my understanding, a V3 encoder / decoder receiving a V1 data
will
fail saying that expected field (with tag [4]) was not there unless
the field in the extension was OPTIONAL. This is where you can use the
ExtensionAndException notation to raise exceptions when the fields
past the extension marker are not found.
Hope this throws some clarity to the problem you stated.
Cheerios
Ramaswamy
Thank you in advance,
Marcelo
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