On Thu, 18 Jul 2002, tong wrote:
> HI all
>
> again GSM-MAP
> example:
> UpdateLocationArg ::= SEQUENCE {
> msi MSI,
> msc-Number [1] ISDN-AddressString,
> vlr-Number ISDN-AddressString,
> lmsi [10] LMSI OPTIONAL,
> extensionContainer ExtensionContainer OPTIONAL,
> ... ,
> vlr-Capability [6] VLR-Capability OPTIONAL }
>
> 1 why encode 1,6,10,not continuously?
I don't follow the question. Please rephrase.
> 2 the order of context why not from small to big ? in this example is 1,10,6.
I don't know (but see my guess below). Perhaps someone who was involved
in the writing of GSM-MAP can give you some insight.
> 3 why some subtype(vlr-Number) not have context tag?
Some components are not taged because tags are required only when the type
would be ambiguously defined without it. A better question would be, "Why
does msc-Number have a tag, for it is not required by ASN.1?". I suspect
that whomever wrote the ASN.1 module thought that by adding tags where
they aren't required by ASN.1 it would somehow help them in manually
writing an encoder/decoder. Another possibility is that somewhere else in
GSM-MAP these components are tagged as you see above, and the person who
defined UpdateLocationArg thought that it would make the definition more
consistent if they were tagged the same here.
> 4 msc-Number not have OPTIONAL,so must presence,and so use context tag is absolutely
>unneeded ?
Correct. As far as ASN.1 goes, there is no need for the tag on
msc-Number. Note that it is required by encoders/decoders since it was
specified in the definition of the UpdateLocationArg type.
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