Decoding signalling on the Abis interface with Wireshark

Posted February 25th 2012

Wireshark can decode the packets on GSM Abis links (and, probably also UMTS Iub). To do it, you need to first capture the data using a GTH, which is basically the same process as described in this entry about capturing data from the Gb interface, except for one difference: you want to capture LAPD, not Frame Relay:

  save_to_pcap:lapd("172.16.2.7", "3A", 1, "abis.pcap").

Wireshark can open the file 'as is', but it only decodes up to L2. To get wireshark to decode everything, go to Edit/Preferences/Protocols/LAPD and then tick the "Use GSM SAPI values" checkbox. Presto, you get the RSL (Radio Signalling Link) protocol decoded for you. Nice.

Standards

The signalling protocol on GSM Abis links is specified in ETSI TS 100 595. ETSI specs are freely available from ETSI, you just have to register with an email address.