Decode and parse a file encoded with BER(Basic encoding rules) to output relevant fields to csv without a .asn (ASN.1) schema?

Question

The files I have been given are sample CDR files(Call Detail Records)

SGSN / GGSN data format: ASN.1 Basic Encoding Rules (BER).

The files have no extensions and I do not have a schema to work with. How can I approach this?

Answer 1

To a certain extent it is possible to decode any valid BER encoded data without having the ASN.1 schema.

Try decoding the file using the unber tool from the asn1c project or this online decoder.

Answer 2

Vasil is correct that, to a degree, BER can be decoded without a schema. However, if the schema uses implicit tags, you won't get very far until you have blocks of data that you have no idea how to interpret. You will very likely need to either get the schema files or use a tool that has the appropriate schema definitions built-in.

If the files follow 3GPP 32.297 and 32.298, those specifications are freely available and you may be interested in https://www.3gpp.org/ftp/Specs/archive/32_series/32.298/ASN.1/

My company has a visual editor that can handle 32.297 CDR files. You can get a trial at: https://www.obj-sys.com/products/asn1ve/index.php. It comes with some CDR specs built in, so you might not need to get the schemas yourself.