If support filter BSSAP+ protocol in Wireshark?

I checked on Wirshark support protocols for BSSAP+ protocol and got below information: http://wiki.wireshark.org/GsmProtocolFamily This is an optional interface for PS/CS interoperability. Using the Gs interface it is possible to perform combined GPRS/IMSI attaches, combined location updates and paging the subscriber using PS facilities. The protocol is BSSAP+ specified in 3GPP TS 29.016 ( supported by Wireshark on ssn 98)

And I checked http://www.wireshark.org/docs/dfref/b/bssap.html I saw two elements include bssap_plus, so does it means BSSAP+ message decode and filter support is embedded in BSSAP protocol??

Can you give a sample for how to filter BSSAP+?

Thanks, Justin