Dissector on top of CCSDS Space Packet

Question

Hello,

I have written a dissector that works on top of the Space Packet protocol (packet-ccsds) that at the same time works on top UDP in my application. My question is: As the protocol is not working neither on top of UDP nor on TCP how should I code the protocol registration in this case? More specifically, how should be the "proto_reg_handoff" routine?

This routine for CCSDS is the following:

proto_reg_handoff_ccsds(void){
dissector_add_handle ( "udp.port", find_dissector("ccsds") ); /* for 'decode as' */
data_handle = find_dissector("data");}

But as this protocol works on top of CCSDS I do not know how to modify it.

Thank you!

Accepted Answer

2

I have no idea how CCSDS works but how does the actual protocol stack find the next protocol to hand off to? You will have to add code to the CCSDS dissector to hand of to the next protocol either by a preferense or by adding a register table where sub dissector can register or some other method.(register_dissector_table())

answered 16 Jul '13, 01:26

Anders ♦
4.6k●9●52
accept rate: 17%

Thank you for the answer! I added a register table to ccsds:

ccsds_dissector_table = register_dissector_table("ccsds.apid", "CCSDS apid", FT_UINT16, BASE_DEC);

And also modify the proto_reg_handoff of my protocol this way:

void proto_reg_handoff_cfdp(void) { dissector_handle_t cfdp_handle; cfdp_handle = create_dissector_handle(dissect_cfdp, proto_cfdp);
dissector_add_uint("ccsds.apid", 2045, cfdp_handle); }

I can see it in the menu Internal-> Dissector tables but still does not work. By doing it this way the protocol is supposed to be dissected automatically or do I have to use the menu Decode as...?

(16 Jul '13, 05:00) Juan_Kash

1

In the CCDSDS dissector do you use the dissector table to call the "next" dissetor for the payload? Something like this from the GTP dissector: if (length > 2) { next_tvb = tvb_new_subset(tvb, offset, length-2, length-2); if(!dissector_try_uint(gtp_priv_ext_dissector_table, ext_id, next_tvb, pinfo, ext_tree_priv_ext)){ proto_tree_add_item(ext_tree_priv_ext, hf_gtp_ext_val, tvb, offset, length - 2, ENC_NA); } }

(16 Jul '13, 05:06) Anders ♦

Ok, now the protocol gets called from CCSDS. Thank you!

(16 Jul '13, 08:04) Juan_Kash

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(16 Jul '13, 08:06) grahamb ♦