Hi Karthik,
GSM MSCs and TAP 3 Generators work at different priority levels. Here are
some significant inputs to design your architecture and some pitfalls to be
aware of.
The MSCs will exhibit a sense of emergency while dumping the records and
will be more or less stateless,
Several nested records could be in indefinite lengths.So be wary of the
0x00 and 0x00 0x00 patterns.
The fillers and EOC (End Of Contents) indicators seem alarmingly alike when
occurring in series.
Most GSM MSCs use context-sensitive, IMPLICIT tagging, hence they reuse the
tags.
So, this will mean that you cannot tie a tag with a data type (decoding
logic). Your generic parser must consider this tricky situation.
Since fillers are used, the CDRs would mostly be filled up by blocks
(Ericsson uses 2k block techniques). An advantage, any given point of time,
you don't have to read more than 2k to memory to be treated as a document
to be parsed.
With regard to ASN.1 definitions, you have to contact the vendors or their
support team in your area. (Not sure if that will help, the vendors would
hold the documents with clenched fists, close to their heart. They cant
sell their mediation products otherwise)
TAP3 Generator will have all available data on hand and will generally have
Headers and Footers.
So you will practically not see any Indefinite length records.
While this may seem good, the length of certain records/segments would be
inordinately huge.
Reading a record to memory would be fatal in terms of performance.
Certain TAP 3 definitions and encodings are still following X.209, which
means that you probably might not see IMPLICIT tagging used.
So you may associate Tags with Data Types (decoding logic)
With regard to ASN.1 definitions, you can download the latest from GSMWorld
site. However, if you want to work with some older versions, you might have
to contact a Data Clearing House of the operator you are servicing.
Hope this is of any help to you.
regards,
Sathya Narayanan
LnT Infotech
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| | "Karthikeyan |
| | Ramnath" |
| | <[EMAIL PROTECTED]|
| | xgroup.com> |
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| | |
| | 11/20/2003 04:01 |
| | PM |
| | Please respond to |
| | asn1 |
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| To: <[EMAIL PROTECTED]>
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| Subject: [ASN.1] some doubts
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Dear Sir,
At work, I have to deal with parsing Call Detail Records generated by GSM
MSCs, TAP 3 applications, etc which are in ASN.1 format.
I wrote a generic parser/decoder which accepts the tags and the value
encodings in a tree structure as configuration, and ran into some doubts.
Presently, I'm unsure of how to handle 0x00 and 0xFF values between
records.
Also how are fillers/noise represented and handled?
Also, is there any place from which we can get the ASN.1 specification for
the different applications/enterprises? Just so that we can shift to using
generic compilers.
Thank you.
karthikeyan.r
---------------------------------
The will to do, the soul to dare
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