575 lines
20 KiB
C
575 lines
20 KiB
C
/* packet-lapdm.c
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* Routines for LAPDm frame disassembly
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* Duncan Salerno <duncan.salerno@googlemail.com>
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*
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* Wireshark - Network traffic analyzer
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* By Gerald Combs <gerald@wireshark.org>
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* Copyright 1998
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*
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* SPDX-License-Identifier: GPL-2.0-or-later
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*/
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/* LAPDm references:
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*
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* Mobile Station - Base Stations System (MS - BSS) Interface Data Link (DL) Layer Specification
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* Base Station Controller - Base Transceiver Station (BSC - BTS) interface; Layer 2 specification
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* http://www.3gpp.org/ftp/Specs/html-info/44006.htm
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*
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* From 3GPP TS 44.006:
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*
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* LAPDm is used for information sent on the control channels BCCH, AGCH, NCH,
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* PCH, FACCH, SACCH and SDCCH as defined in 3GPP TS 44.003.
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*
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* AGCH, NCH and PCH are sometimes referred to by the collective name CCCH.
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* FACCH, SACCH and SDCCH are, similarly, referred to by the collective name DCCH.
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*
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* Format A is used on DCCHs for frames where there is no information field.
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* Formats B, Bter and B4 are used on DCCHs for frames containing an information field:
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* Format Bter is used on request of higher layers if and only if short L2 header type 1 is
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* supported and a UI command is to be transmitted on SAPI 0;
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* Format B4 is used for UI frames transmitted by the network on SACCH;
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* Format B is applied in all other cases.
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* Format Bbis is used only on BCCH, PCH, NCH, and AGCH.
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* In addition there is a Format C for transmission of random access signals.
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*
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* This module currently supports A, B, B4
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* In the future will support Bter
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* Bbis and C should be supported elsewhere
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*/
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#include "config.h"
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#include "packet-lapdm.h"
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#include <epan/packet.h>
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#include <epan/prefs.h>
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#include <epan/xdlc.h>
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#include <epan/reassemble.h>
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#include <epan/conversation.h>
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void proto_register_lapdm(void);
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static dissector_handle_t b4_info_handle;
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static int proto_lapdm = -1;
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static int hf_lapdm_address = -1;
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static int hf_lapdm_ea = -1;
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static int hf_lapdm_cr = -1;
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static int hf_lapdm_sapi = -1;
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static int hf_lapdm_lpd = -1;
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static int hf_lapdm_control = -1;
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static int hf_lapdm_n_r = -1;
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static int hf_lapdm_n_s = -1;
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static int hf_lapdm_p = -1;
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static int hf_lapdm_f = -1;
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static int hf_lapdm_s_ftype = -1;
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static int hf_lapdm_u_modifier_cmd = -1;
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static int hf_lapdm_u_modifier_resp = -1;
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static int hf_lapdm_ftype_i = -1;
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static int hf_lapdm_ftype_s_u = -1;
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static int hf_lapdm_length = -1;
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static int hf_lapdm_el = -1;
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static int hf_lapdm_m = -1;
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static int hf_lapdm_len = -1;
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/*
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* LAPDm fragment handling
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*/
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static int hf_lapdm_fragment_data = -1;
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static int hf_lapdm_fragments = -1;
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static int hf_lapdm_fragment = -1;
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static int hf_lapdm_fragment_overlap = -1;
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static int hf_lapdm_fragment_overlap_conflicts = -1;
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static int hf_lapdm_fragment_multiple_tails = -1;
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static int hf_lapdm_fragment_too_long_fragment = -1;
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static int hf_lapdm_fragment_error = -1;
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static int hf_lapdm_fragment_count = -1;
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static int hf_lapdm_reassembled_in = -1;
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static int hf_lapdm_reassembled_length = -1;
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static gint ett_lapdm = -1;
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static gint ett_lapdm_address = -1;
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static gint ett_lapdm_control = -1;
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static gint ett_lapdm_length = -1;
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static gint ett_lapdm_fragment = -1;
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static gint ett_lapdm_fragments = -1;
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static reassembly_table lapdm_reassembly_table;
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static wmem_map_t *lapdm_last_n_s_map;
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static dissector_table_t lapdm_sapi_dissector_table;
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static gboolean reassemble_lapdm = TRUE;
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/*
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* Bits in the address field.
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*/
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#define LAPDM_SAPI 0x1c /* Service Access Point Identifier */
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#define LAPDM_SAPI_SHIFT 2
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#define LAPDM_CR 0x02 /* Command/Response bit */
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#define LAPDM_EA 0x01 /* First Address Extension bit */
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#define LAPDM_LPD 0x60 /* Link Protocol Discriminator */
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/*
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* Bits in the length field.
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*/
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#define LAPDM_EL 0x01 /* Extended Length = 1 */
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#define LAPDM_M 0x02 /* More fragments */
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#define LAPDM_M_SHIFT 1
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#define LAPDM_LEN 0xfc /* Length */
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#define LAPDM_LEN_SHIFT 2
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#define LAPDM_HEADER_LEN 3
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#define LAPDM_HEADER_LEN_B4 2
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#define LAPDM_SAPI_RR_CC_MM 0
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#define LAPDM_SAPI_SMS 3
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/* Used only for U frames */
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static const xdlc_cf_items lapdm_cf_items = {
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&hf_lapdm_n_r,
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&hf_lapdm_n_s,
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&hf_lapdm_p,
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&hf_lapdm_f,
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&hf_lapdm_s_ftype,
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&hf_lapdm_u_modifier_cmd,
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&hf_lapdm_u_modifier_resp,
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&hf_lapdm_ftype_i,
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&hf_lapdm_ftype_s_u
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};
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static const value_string lapdm_ea_vals[] = {
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{ 0, "More octets" },
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{ 1, "Final octet" },
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{ 0, NULL }
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};
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static const value_string lapdm_sapi_vals[] = {
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{ LAPDM_SAPI_RR_CC_MM, "RR/MM/CC" },
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{ LAPDM_SAPI_SMS, "SMS/SS" },
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{ 0, NULL }
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};
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static const value_string lapdm_lpd_vals[] = {
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{ 0, "Normal GSM" },
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{ 1, "Cell broadcast service" },
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{ 0, NULL }
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};
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static const value_string lapdm_m_vals[] = {
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{ 0, "Last segment" },
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{ 1, "More segments" },
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{ 0, NULL }
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};
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static const value_string lapdm_el_vals[] = {
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{ 0, "More octets" },
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{ 1, "Final octet" },
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{ 0, NULL }
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};
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static const fragment_items lapdm_frag_items = {
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/* Fragment subtrees */
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&ett_lapdm_fragment,
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&ett_lapdm_fragments,
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/* Fragment fields */
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&hf_lapdm_fragments,
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&hf_lapdm_fragment,
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&hf_lapdm_fragment_overlap,
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&hf_lapdm_fragment_overlap_conflicts,
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&hf_lapdm_fragment_multiple_tails,
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&hf_lapdm_fragment_too_long_fragment,
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&hf_lapdm_fragment_error,
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&hf_lapdm_fragment_count,
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/* Reassembled in field */
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&hf_lapdm_reassembled_in,
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/* Reassembled length field */
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&hf_lapdm_reassembled_length,
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/* Reassembled data field */
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NULL,
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/* Tag */
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"fragments"
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};
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static gboolean hdr_has_length(enum lapdm_hdr_type hdr_type)
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{
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switch (hdr_type) {
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case LAPDM_HDR_FMT_A:
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case LAPDM_HDR_FMT_B:
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return TRUE;
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default:
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return FALSE;
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}
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}
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static int
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dissect_lapdm(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data)
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{
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proto_tree *lapdm_tree, *addr_tree, *length_tree;
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proto_item *lapdm_ti, *addr_ti, *length_ti;
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guint8 addr, length, header_len, cr, sapi, len, n_s;
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int control;
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gboolean m;
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tvbuff_t *payload;
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int available_length;
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gboolean is_response = FALSE;
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enum lapdm_hdr_type hdr_type = LAPDM_HDR_FMT_B;
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if (data) {
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lapdm_data_t *ld = (lapdm_data_t *) data;
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hdr_type = ld->hdr_type;
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}
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switch (hdr_type) {
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case LAPDM_HDR_FMT_A:
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case LAPDM_HDR_FMT_B:
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length = tvb_get_guint8(tvb, 2);
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header_len = LAPDM_HEADER_LEN;
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break;
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case LAPDM_HDR_FMT_B4:
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length = 0;
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header_len = LAPDM_HEADER_LEN_B4;
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break;
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default:
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return 0;
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}
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/* Check that there's enough data */
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if (tvb_captured_length(tvb) < header_len)
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return 0;
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col_set_str(pinfo->cinfo, COL_PROTOCOL, "LAPDm");
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addr = tvb_get_guint8(tvb, 0);
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cr = addr & LAPDM_CR;
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if (pinfo->p2p_dir == P2P_DIR_RECV) {
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is_response = cr ? FALSE : TRUE;
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}
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else if (pinfo->p2p_dir == P2P_DIR_SENT) {
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is_response = cr ? TRUE : FALSE;
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}
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if (tree) {
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lapdm_ti = proto_tree_add_item(tree, proto_lapdm, tvb, 0, header_len, ENC_NA);
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lapdm_tree = proto_item_add_subtree(lapdm_ti, ett_lapdm);
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addr_ti = proto_tree_add_uint(lapdm_tree, hf_lapdm_address, tvb, 0, 1, addr);
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addr_tree = proto_item_add_subtree(addr_ti, ett_lapdm_address);
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proto_tree_add_uint(addr_tree, hf_lapdm_lpd, tvb, 0, 1, addr);
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proto_tree_add_uint(addr_tree, hf_lapdm_sapi, tvb, 0, 1, addr);
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proto_tree_add_uint(addr_tree, hf_lapdm_cr, tvb, 0, 1, addr);
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proto_tree_add_uint(addr_tree, hf_lapdm_ea, tvb, 0, 1, addr);
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}
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else {
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lapdm_ti = NULL;
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lapdm_tree = NULL;
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}
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control = dissect_xdlc_control(tvb, 1, pinfo, lapdm_tree, hf_lapdm_control,
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ett_lapdm_control, &lapdm_cf_items, NULL /* LAPDm doesn't support extended */, NULL, NULL,
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is_response, FALSE, FALSE);
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/* dissect length field (if present) */
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if (tree && hdr_has_length(hdr_type)) {
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length_ti = proto_tree_add_uint(lapdm_tree, hf_lapdm_length, tvb,
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2, 1, length);
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length_tree = proto_item_add_subtree(length_ti, ett_lapdm_length);
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proto_tree_add_uint(length_tree, hf_lapdm_len, tvb, 2, 1, length);
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proto_tree_add_uint(length_tree, hf_lapdm_m, tvb, 2, 1, length);
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proto_tree_add_uint(length_tree, hf_lapdm_el, tvb, 2, 1, length);
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}
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if (hdr_has_length(hdr_type)) {
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len = (length & LAPDM_LEN) >> LAPDM_LEN_SHIFT;
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m = (length & LAPDM_M) >> LAPDM_M_SHIFT;
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} else {
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len = tvb_captured_length(tvb) - header_len;
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m = 0;
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}
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sapi = (addr & LAPDM_SAPI) >> LAPDM_SAPI_SHIFT;
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n_s = (control & XDLC_N_S_MASK) >> XDLC_N_S_SHIFT;
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available_length = tvb_captured_length(tvb) - header_len;
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/* No point in doing anything if no payload
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*/
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if( !MIN(len, available_length) )
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return 2;
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payload = tvb_new_subset_length_caplen(tvb, header_len, MIN(len,available_length), len);
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/* Potentially segmented I frame
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*/
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if( (control & XDLC_I_MASK) == XDLC_I && reassemble_lapdm && !pinfo->flags.in_error_pkt )
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{
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fragment_head *fd_m = NULL;
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tvbuff_t *reassembled = NULL;
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guint32 fragment_id;
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gboolean save_fragmented = pinfo->fragmented, add_frag;
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pinfo->fragmented = m;
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/* Rely on caller to provide a way to group fragments */
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fragment_id = (conversation_get_id_from_elements(pinfo, CONVERSATION_GSMTAP, USE_LAST_ENDPOINT) << 4) | (sapi << 1) | pinfo->p2p_dir;
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if (!PINFO_FD_VISITED(pinfo)) {
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/* Check if new N(S) is equal to previous N(S) (to avoid adding retransmissions in reassembly table)
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As GUINT_TO_POINTER macro does not allow to differentiate NULL from 0, use 1-8 range instead of 0-7 */
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guint *p_last_n_s = (guint*)wmem_map_lookup(lapdm_last_n_s_map, GUINT_TO_POINTER(fragment_id));
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if (GPOINTER_TO_UINT(p_last_n_s) == (guint)(n_s+1)) {
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add_frag = FALSE;
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} else {
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add_frag = TRUE;
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wmem_map_insert(lapdm_last_n_s_map, GUINT_TO_POINTER(fragment_id), GUINT_TO_POINTER(n_s+1));
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}
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} else {
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add_frag = TRUE;
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}
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if (add_frag) {
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/* This doesn't seem the best way of doing it as doesn't
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take N(S) into account, but N(S) isn't always 0 for
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the first fragment!
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*/
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fd_m = fragment_add_seq_next (&lapdm_reassembly_table, payload, 0,
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pinfo,
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fragment_id, /* guint32 ID for fragments belonging together */
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NULL,
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/*n_s guint32 fragment sequence number */
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len, /* guint32 fragment length */
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m); /* More fragments? */
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reassembled = process_reassembled_data(payload, 0, pinfo,
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"Reassembled LAPDm", fd_m, &lapdm_frag_items,
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NULL, lapdm_tree);
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/* Reassembled into this packet
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*/
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if (fd_m && pinfo->num == fd_m->reassembled_in) {
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if (!dissector_try_uint(lapdm_sapi_dissector_table, sapi,
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reassembled, pinfo, tree))
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call_data_dissector(reassembled, pinfo, tree);
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if (!PINFO_FD_VISITED(pinfo)) {
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/* If reassembling is done, allow fragment_id reuse */
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wmem_map_remove(lapdm_last_n_s_map, GUINT_TO_POINTER(fragment_id));
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}
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}
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else {
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col_append_str(pinfo->cinfo, COL_INFO, " (Fragment)");
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proto_tree_add_item(lapdm_tree, hf_lapdm_fragment_data, payload, 0, -1, ENC_NA);
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}
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}
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/* Now reset fragmentation information in pinfo
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*/
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pinfo->fragmented = save_fragmented;
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}
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else if (hdr_type == LAPDM_HDR_FMT_B4)
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{
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/* B4 frames have no length octet at L2 level, but instead a L2 pseudo length octet
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* at L3. We must call the proper dissector for decoding them */
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call_dissector(b4_info_handle, payload, pinfo, tree);
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}
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else
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{
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if (!PINFO_FD_VISITED(pinfo) && ((control & XDLC_S_U_MASK) == XDLC_U) && ((control & XDLC_U_MODIFIER_MASK) == XDLC_SABM)) {
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/* SABM frame; reset the last N(S) to an invalid value */
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guint32 fragment_id = (conversation_get_id_from_elements(pinfo, CONVERSATION_GSMTAP, USE_LAST_ENDPOINT) << 4) | (sapi << 1) | pinfo->p2p_dir;
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wmem_map_insert(lapdm_last_n_s_map, GUINT_TO_POINTER(fragment_id), GUINT_TO_POINTER(0));
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}
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/* Whole packet
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If we have some data, try and dissect it (only happens for UI, SABM, UA or I frames)
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*/
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if (!dissector_try_uint(lapdm_sapi_dissector_table, sapi,
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payload, pinfo, tree))
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call_data_dissector(payload, pinfo, tree);
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}
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return tvb_captured_length(tvb);
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}
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void
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proto_register_lapdm(void)
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{
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static hf_register_info hf[] = {
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{ &hf_lapdm_address,
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{ "Address Field", "lapdm.address_field", FT_UINT8, BASE_HEX, NULL, 0x0,
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"Address", HFILL }},
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{ &hf_lapdm_ea,
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{ "EA", "lapdm.ea", FT_UINT8, BASE_DEC, VALS(lapdm_ea_vals), LAPDM_EA,
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"Address field extension bit", HFILL }},
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{ &hf_lapdm_cr,
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{ "C/R", "lapdm.cr", FT_UINT8, BASE_DEC, NULL, LAPDM_CR,
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"Command/response field bit", HFILL }},
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{ &hf_lapdm_lpd,
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{ "LPD", "lapdm.lpd", FT_UINT8, BASE_DEC, VALS(lapdm_lpd_vals), LAPDM_LPD,
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"Link Protocol Discriminator", HFILL }},
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{ &hf_lapdm_sapi,
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{ "SAPI", "lapdm.sapi", FT_UINT8, BASE_DEC, VALS(lapdm_sapi_vals), LAPDM_SAPI,
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"Service access point identifier", HFILL }},
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{ &hf_lapdm_control,
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{ "Control Field", "lapdm.control_field", FT_UINT8, BASE_HEX, NULL, 0x0,
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NULL, HFILL }},
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{ &hf_lapdm_n_r,
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{ "N(R)", "lapdm.control.n_r", FT_UINT8, BASE_DEC,
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NULL, XDLC_N_R_MASK, NULL, HFILL }},
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{ &hf_lapdm_n_s,
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{ "N(S)", "lapdm.control.n_s", FT_UINT8, BASE_DEC,
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NULL, XDLC_N_S_MASK, NULL, HFILL }},
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{ &hf_lapdm_p,
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{ "Poll", "lapdm.control.p", FT_BOOLEAN, 8,
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TFS(&tfs_true_false), XDLC_P_F, NULL, HFILL }},
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{ &hf_lapdm_f,
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{ "Final", "lapdm.control.f", FT_BOOLEAN, 8,
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TFS(&tfs_true_false), XDLC_P_F, NULL, HFILL }},
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{ &hf_lapdm_s_ftype,
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{ "Supervisory frame type", "lapdm.control.s_ftype", FT_UINT8, BASE_HEX,
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|
VALS(stype_vals), XDLC_S_FTYPE_MASK, NULL, HFILL }},
|
|
|
|
{ &hf_lapdm_u_modifier_cmd,
|
|
{ "Command", "lapdm.control.u_modifier_cmd", FT_UINT8, BASE_HEX,
|
|
VALS(modifier_vals_cmd), XDLC_U_MODIFIER_MASK, NULL, HFILL }},
|
|
|
|
{ &hf_lapdm_u_modifier_resp,
|
|
{ "Response", "lapdm.control.u_modifier_resp", FT_UINT8, BASE_HEX,
|
|
VALS(modifier_vals_resp), XDLC_U_MODIFIER_MASK, NULL, HFILL }},
|
|
|
|
{ &hf_lapdm_ftype_i,
|
|
{ "Frame type", "lapdm.control.ftype", FT_UINT8, BASE_HEX,
|
|
VALS(ftype_vals), XDLC_I_MASK, NULL, HFILL }},
|
|
|
|
{ &hf_lapdm_ftype_s_u,
|
|
{ "Frame type", "lapdm.control.ftype", FT_UINT8, BASE_HEX,
|
|
VALS(ftype_vals), XDLC_S_U_MASK, NULL, HFILL }},
|
|
|
|
{ &hf_lapdm_length,
|
|
{ "Length Field", "lapdm.length_field", FT_UINT8, BASE_HEX,
|
|
NULL, 0x0, NULL, HFILL }},
|
|
|
|
{ &hf_lapdm_el,
|
|
{ "EL", "lapdm.el", FT_UINT8, BASE_DEC,
|
|
VALS(lapdm_el_vals), LAPDM_EL, "Length indicator field extension bit", HFILL }},
|
|
|
|
{ &hf_lapdm_m,
|
|
{ "M", "lapdm.m", FT_UINT8, BASE_DEC,
|
|
VALS(lapdm_m_vals), LAPDM_M, "More data bit", HFILL }},
|
|
|
|
{ &hf_lapdm_len,
|
|
{ "Length", "lapdm.length", FT_UINT8, BASE_DEC,
|
|
NULL, LAPDM_LEN, "Length indicator", HFILL }},
|
|
|
|
/* Fragment reassembly
|
|
*/
|
|
{ &hf_lapdm_fragment_data,
|
|
{ "Fragment Data", "lapdm.fragment_data", FT_NONE, BASE_NONE,
|
|
NULL, 0x00, NULL, HFILL }},
|
|
|
|
{ &hf_lapdm_fragments,
|
|
{ "Message fragments", "lapdm.fragments", FT_NONE, BASE_NONE,
|
|
NULL, 0x00, "LAPDm Message fragments", HFILL }},
|
|
|
|
{ &hf_lapdm_fragment,
|
|
{ "Message fragment", "lapdm.fragment", FT_FRAMENUM, BASE_NONE,
|
|
NULL, 0x00, "LAPDm Message fragment", HFILL }},
|
|
|
|
{ &hf_lapdm_fragment_overlap,
|
|
{ "Message fragment overlap", "lapdm.fragment.overlap", FT_BOOLEAN, BASE_NONE,
|
|
NULL, 0x0, "LAPDm Message fragment overlaps with other fragment(s)", HFILL }},
|
|
|
|
{ &hf_lapdm_fragment_overlap_conflicts,
|
|
{ "Message fragment overlapping with conflicting data", "lapdm.fragment.overlap.conflicts", FT_BOOLEAN, BASE_NONE,
|
|
NULL, 0x0, "LAPDm Message fragment overlaps with conflicting data", HFILL }},
|
|
|
|
{ &hf_lapdm_fragment_multiple_tails,
|
|
{ "Message has multiple tail fragments", "lapdm.fragment.multiple_tails", FT_BOOLEAN, BASE_NONE,
|
|
NULL, 0x0, "LAPDm Message fragment has multiple tail fragments", HFILL }},
|
|
|
|
{ &hf_lapdm_fragment_too_long_fragment,
|
|
{ "Message fragment too long", "lapdm.fragment.too_long_fragment", FT_BOOLEAN, BASE_NONE,
|
|
NULL, 0x0, "LAPDm Message fragment data goes beyond the packet end", HFILL }},
|
|
|
|
{ &hf_lapdm_fragment_error,
|
|
{ "Message defragmentation error", "lapdm.fragment.error", FT_FRAMENUM, BASE_NONE,
|
|
NULL, 0x00, "LAPDm Message defragmentation error due to illegal fragments", HFILL }},
|
|
|
|
{ &hf_lapdm_fragment_count,
|
|
{ "Message fragment count", "lapdm.fragment.count", FT_UINT32, BASE_DEC,
|
|
NULL, 0x00, NULL, HFILL }},
|
|
|
|
{ &hf_lapdm_reassembled_in,
|
|
{ "Reassembled in", "lapdm.reassembled.in", FT_FRAMENUM, BASE_NONE,
|
|
NULL, 0x00, "LAPDm Message has been reassembled in this packet.", HFILL }},
|
|
|
|
{ &hf_lapdm_reassembled_length,
|
|
{ "Reassembled LAPDm length", "lapdm.reassembled.length", FT_UINT32, BASE_DEC,
|
|
NULL, 0x00, "The total length of the reassembled payload", HFILL }}
|
|
|
|
};
|
|
static gint *ett[] = {
|
|
&ett_lapdm,
|
|
&ett_lapdm_address,
|
|
&ett_lapdm_control,
|
|
&ett_lapdm_length,
|
|
&ett_lapdm_fragment,
|
|
&ett_lapdm_fragments
|
|
};
|
|
|
|
module_t *lapdm_module;
|
|
|
|
proto_lapdm = proto_register_protocol("Link Access Procedure, Channel Dm (LAPDm)", "LAPDm", "lapdm");
|
|
proto_register_field_array (proto_lapdm, hf, array_length(hf));
|
|
proto_register_subtree_array(ett, array_length(ett));
|
|
|
|
register_dissector("lapdm", dissect_lapdm, proto_lapdm);
|
|
|
|
lapdm_sapi_dissector_table = register_dissector_table("lapdm.sapi", "LAPDm SAPI", proto_lapdm, FT_UINT8, BASE_DEC);
|
|
|
|
lapdm_module = prefs_register_protocol(proto_lapdm, NULL);
|
|
prefs_register_bool_preference(lapdm_module, "reassemble",
|
|
"Reassemble fragmented LAPDm packets",
|
|
"Whether the dissector should defragment LAPDm messages spanning multiple packets.",
|
|
&reassemble_lapdm);
|
|
|
|
lapdm_last_n_s_map = wmem_map_new_autoreset(wmem_epan_scope(), wmem_file_scope(), g_direct_hash, g_direct_equal);
|
|
|
|
reassembly_table_register(&lapdm_reassembly_table,
|
|
&addresses_reassembly_table_functions);
|
|
|
|
/* B4 frames have no length octet at L2 level, but instead a L2 pseudo length octet
|
|
* at L3. We must call the proper dissector for decoding them, and gsm_a_ccch supports
|
|
* L2 pseudo length */
|
|
b4_info_handle = find_dissector_add_dependency("gsm_a_ccch", proto_lapdm);
|
|
}
|
|
|
|
/*
|
|
* Editor modelines - https://www.wireshark.org/tools/modelines.html
|
|
*
|
|
* Local variables:
|
|
* c-basic-offset: 4
|
|
* tab-width: 8
|
|
* indent-tabs-mode: nil
|
|
* End:
|
|
*
|
|
* vi: set shiftwidth=4 tabstop=8 expandtab:
|
|
* :indentSize=4:tabSize=8:noTabs=true:
|
|
*/
|