Decoding CDRs

Hello all,

I'd like to know how I can decode GGSN CDRs in wireshark. I have the version 1.8 installed. I see that the packets are recognized as GTP Data record transfer request and response but when I checked the contents, it says that it's malformed.

Do I need to add something to wireshark to decode it and how? I did not see much options for GTP in preferences

Thanks