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SS7 BSSAP Protocol

0

I wonder how does Wireshark know that there is BSSAP underlying the SCCP protocol ?

asked 29 Jan '13, 04:06

ahmediukas's gravatar image

ahmediukas
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One Answer:

1

By the sub system number, SSN 98 is tied to BSSAP, changable by a protocol preference.

answered 29 Jan '13, 05:58

Anders's gravatar image

Anders ♦
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Isnt SSN specified as 250 (BSC) and 251 (MSC) ? And further, it is in the SCCP DataForm1 message, so no SSN's provided (as in UDT) Example: http://cloudshark.org/captures/ea49319c49ca

(29 Jan '13, 11:09) ahmediukas
1

BSSAP is also detected heuristically, SCCP has a heuristic table where dissectors can register to have a peek a the packet and claim it if it's determined to be the protocol in question - might not be correct.

(29 Jan '13, 11:19) Anders ♦

I am pretty sure, GSM machines knows its BSSAP somehow, they doesn't heuristically dissector packet. Even if MTP/SCTP addresses are for them.

(30 Jan '13, 01:13) ahmediukas

Sure, but the question was how Wireshark detects them.

(30 Jan '13, 03:40) Anders ♦