Wireshark-bugs: [Wireshark-bugs] [Bug 3166] Support for GSM Um and LAPDm

Date: Mon, 5 Jan 2009 12:33:27 -0800 (PST)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=3166





--- Comment #9 from Duncan Salerno <duncan.salerno@xxxxxxxxxxxxxx>  2009-01-05 12:33:25 PDT ---
I did consider enhancing the LAPD dissector, but:

* LAPDm has a length byte, LAPD doesnt
* LAPD has a checksum, LAPDm doesnt
* They both have the same control byte (but that uses the common xdlc decode)
* SAPI's mean different things eg. SAPI 3 is SMS in LAPDm but undefined in LAPD
* LAPD supports GSM SAPI's, however this is for Abis, whereas Um uses LAPDm
(Abis uses RSL to multiplex the GSM signalling of many users, Um is single user
and carries the signalling directly)

so their based on the same ideas, but I'd say the implementation is fairly
different.

Additionally I don't have any decent samples of LAPD to test the modifications
on, but there are plenty of LAPDm samples on the THC wiki.


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