Wireshark-dev: [Wireshark-dev] p2p_dir
From: Richard van der Hoff <[email protected]>
Date: Mon, 06 Aug 2007 19:22:21 +0100
Hi all,

I'm looking at extending the H.223 dissector to work over ISDN. (ftr, H.223 is a circuit-based protocol which is supposed to work over the telephone network; currently wireshark will dissect it over IAX2, TCP or RTP, and I want to extend it to the one place it really really _ought_ to work...)
The isdn dissector currently sets pinfo->ctype = CT_ISDN, and 
pinfo->circuit_id to the ISDN channel number; however, it provides no 
means to distinguish the two directions on that channel, which the H.223 
dissector needs in order to perform conversation tracking.
One option would be to special-case for pinfo->ctype==CT_ISDN in the 
H.223 dissector, and then check pinfo->pseudo_header->isdn.uton for the 
direction bit - but that seems unnecessarily specific to ISDN.
It seems better to use pinfo->p2p_dir for this. I just wanted to check 
that this was the intended use of this field before modifying the isdn 
dissector. (It's also not entirely obvious how the user/network 
semantics of isdn should map onto the sent/received semantics of 
p2p_dir; however, I don't think that actually matters a great deal).