Wireshark · Wireshark-dev: Re: [Wireshark-dev] [Wireshark-commits] rev 39384: /trunk/epan/dissectors/ /trunk/epan/dissectors/:

[Martin Mathieson <martin.r.mathieson@xxxxxxxxxxxxxx>]

On Wed, Oct 12, 2011 at 6:42 PM, Guy Harris <guy@xxxxxxxxxxxx> wrote:

(Paging LTE experts here....)

On Oct 12, 2011, at 8:02 AM, wmeier@xxxxxxxxxxxxx wrote:

> http://anonsvn.wireshark.org/viewvc/viewvc.cgi?view=rev&revision=39384
>
> User: wmeier
> Date: 2011/10/12 08:02 AM
>
> Log:
> Fix a benign bug: Use correct proto_tree_add_item() encoding arg.

At least as I read RFC 3095:

  UOR-2-TS

    0   1   2   3   4   5   6   7
  +---+---+---+---+---+---+---+---+
  | 1   1   0 |        TS         |
  +===+===+===+===+===+===+===+===+
  |T=1| M |          SN           |
  +---+---+---+---+---+---+---+---+
  | X |            CRC            |
  +---+---+---+---+---+---+---+---+

neither the old code nor the new code are correct - the "M" bit is in the octet after the TS field.

I don't see anything obvious in 3GPP TS 36.323 itself that says the format is different; does something in a later RFC specify something different?

Guy, I'm sure to be missing something, but I don't see what is wrong with the current code, pasted here:

    if (T) {
        /* UOR-2-TS format */

        /* TS */
        guint8 ts = tvb_get_guint8(tvb, offset) & 0x1f;
        proto_tree_add_uint(tree, hf_pdcp_lte_rohc_ts, tvb, offset, 1, ts);
        offset++;

        /* Large CID */
        if (p_pdcp_info->large_cid_present) {
            offset = dissect_large_cid(tree, tvb, offset);
        }

        /* m */
        proto_tree_add_item(tree, hf_pdcp_lte_rohc_m, tvb, offset, 1, ENC_BIG_ENDIAN);

        /* TODO: */
    }
 

'offset' is incremented after TS is dissected.  The strange +====+=====+ notation indicates that if we have a large CID, thats where it appears.
hf_pdcp_lte_rohc_m has the bitmask 0x40, which is OK.

Note that the ROHC support in this file has been superceded by packet-rohc.c.  Its been on my TODO list for a long time that I rip out  this implementation and call the one in packet-rohc.c instead (after carefully checking that everything here was already there or merge it across).  As far as I know, RFC 3095 is used as-is in PDCP (note that there are corrections/clarifications for this RFC, don't remember where)

Regards,
Martin