Modify ASN.1 BER encoded CDR file

Question

I am processing some CDRs (call detailed record). I dont know which exactly the file it is? But i supposed this to be 'ASN.1' format BER encoded files. Now my problem is that I want to modify some data in this files but I dont know which Editor or decorder I can use to modify this files. I searched a lot and found many ASN.1 Decorder as well as ASN.1 BSR viewer/editor but no one allows what i want to perform.

This CDR is supposed to contain Customer detail, phone number, telecom services(telephony, SMS, MMS) etc.

One of CDR name is - GGSN01_20120105000102_56641-09-12-01-09%3A30 and file type is - File

No other information is available. When I am opening this file in some text editor it show some rectangles and some text data.

Any telecom guy can definite help me. I am new to telecom domain.

Please ask if you need more information. Thanks

Answer 1

You would need to know something about ASN.1 and BER to be able to correctly edit your file. BER is a binary format, not ASCII text, thus what you see in your text editor. Even modifying any embedded plain text is only safe if you are not changing the length of the string; BER uses nested structures that encode lengths and so a change in the length of a string value requires adjustments to the encoded lengths of the enclosing structures. Additionally, in order to really know what your data is, you would need to know the ASN.1 that describes it (defines the types that describe your encoded data).

You could use a tool such as ASN.1 editor, but without the requisite background knowledge, I think it will not be very helpful to you. You can follow various links on this resources page to get more information about ASN.1. (full disclosure: I am currently an Obj-Sys employee).

Answer 2

Look for tools like enber and unber, they come as debugging tools with the fee asn.1-compiler of Lev Walkin. At least you get text-format from them.

The systemic solution is, of course to write a program that reads the BER-file, applies the schnages and then writes out the altered BER-file. To do so you need the ASN.1-Specification file of your CDR-Format (usually to be found in the specifications of the standard e.g. IMS, you are using) an asn1-compiler such as Lev's and some programming skills.