UMTS FP: Improved MAC multiplexing detection

Previous detection was based on DCH ID 31 or 24 and specific TB Size.
New method checks if the 'Transport Format' looks like the commonly used format for DCCH over DCH or DCH ID 24 and specific TB size (To not break that special case which I'm not familiar with personally)

Change-Id: I59fe7772ec05f7cc15351ef78276085e25570461
Reviewed-on: https://code.wireshark.org/review/21304
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>

1 files changed, 74 insertions, 99 deletions

diff --git a/epan/dissectors/packet-umts_fp.c b/epan/dissectors/packet-umts_fp.c
index 4c1d3d71aa..5a1faa175d 100644
--- a/epan/dissectors/packet-umts_fp.c
+++ b/epan/dissectors/packet-umts_fp.c
@@ -4834,6 +4834,7 @@ fp_set_per_packet_inf_from_conv(conversation_t *p_conv,
     guint8    tfi, c_t;
     int       offset = 0, i=0, j=0, num_tbs, chan, tb_size, tb_bit_off;
     gboolean  is_control_frame;
+    gboolean  is_known_dcch_tf,is_special_case_dch_24;
     umts_mac_info *macinf;
     rlc_info *rlcinf;
     guint8 fake_lchid=0;
@@ -4983,113 +4984,87 @@ fp_set_per_packet_inf_from_conv(conversation_t *p_conv,
 
             rlcinf = wmem_new0(wmem_file_scope(), rlc_info);
             macinf = wmem_new0(wmem_file_scope(), umts_mac_info);
-            offset = 2;    /*To correctly read the tfi*/
-            fakes  = 5; /* Reset fake counter. */
-            for (chan=0; chan < fpi->num_chans; chan++) {    /*Iterate over the what channels*/
-                    /*Iterate over the transport blocks*/
-                   /*tfi = tvb_get_guint8(tvb, offset);*/
-                   /*TFI is 5 bits according to 3GPP TS 25.321, paragraph 6.2.4.4*/
-                    tfi = tvb_get_bits8(tvb, 3+offset*8, 5);
-
-                   /*Figure out the number of tbs and size*/
-                   num_tbs = (fpi->is_uplink) ? p_conv_data->fp_dch_channel_info[chan].ul_chan_num_tbs[tfi] : p_conv_data->fp_dch_channel_info[chan].dl_chan_num_tbs[tfi];
-                   tb_size=  (fpi->is_uplink) ? p_conv_data->fp_dch_channel_info[i].ul_chan_tf_size[tfi] :    p_conv_data->fp_dch_channel_info[i].dl_chan_tf_size[tfi];
-
-                    /*TODO: This stuff has to be reworked!*/
-                    /*Generates a fake logical channel id for non multiplexed channel*/
-                    if ( p_conv_data->dchs_in_flow_list[chan] != 31 && (p_conv_data->dchs_in_flow_list[chan] == 24 &&
-                     tb_size != 340) ) {
-                        fake_lchid = make_fake_lchid(pinfo, p_conv_data->dchs_in_flow_list[chan]);
+            offset = 2; /* To correctly read the TFI */
+            fakes  = 5; /* Reset fake counter */
+            for (chan=0; chan < fpi->num_chans; chan++) { /* Iterate over the DCH channels in the flow (each given a TFI) */
+                /* Iterate over the transport blocks */
+                /* TFI is 5 bits according to 3GPP TS 25.427, paragraph 6.2.4.4 */
+                tfi = tvb_get_bits8(tvb, 3+offset*8, 5);
+
+                /* Figure out the number of tbs and size */
+                num_tbs = (fpi->is_uplink) ? p_conv_data->fp_dch_channel_info[chan].ul_chan_num_tbs[tfi] : p_conv_data->fp_dch_channel_info[chan].dl_chan_num_tbs[tfi];
+                tb_size =  (fpi->is_uplink) ? p_conv_data->fp_dch_channel_info[i].ul_chan_tf_size[tfi] :    p_conv_data->fp_dch_channel_info[i].dl_chan_tf_size[tfi];
+
+                tb_bit_off = (2+p_conv_data->num_dch_in_flow)*8; /*Point to the C/T of first TB*/
+                /*Set configuration for individual blocks*/
+                for (j=0; j < num_tbs && j+chan < MAX_MAC_FRAMES; j++) {
+                    /* Set transport channel id (useful for debugging) */
+                    macinf->trchid[j+chan] = p_conv_data->dchs_in_flow_list[chan];
+
+                    /* Checking for the common Transport Format of DCCH over DCH ( See ETSI TR 125.944 / 4.1.1.3.1.1 ) */
+                    is_known_dcch_tf = (tfi == 1 && num_tbs == 1 && tb_size == 148);
+                    /* Checking for DCH ID 24 and tb size of 340 bits */
+                    is_special_case_dch_24 = (p_conv_data->dchs_in_flow_list[chan] == 24 && tb_size == 340);
+
+                    /* In theses cases, the */
+                    if (is_known_dcch_tf || is_special_case_dch_24) {
+                        /* Channel is multiplexed (ie. C/T flag present) */
+                        macinf->ctmux[j+chan] = TRUE;
+
+                        /* Peek at C/T, different RLC params for different logical channels */
+                        /* C/T is 4 bits according to 3GPP TS 25.321, paragraph 9.2.1, from MAC header (not FP) */
+                        c_t = (tvb_get_bits8(tvb, tb_bit_off, 4) + 1) % 0xf;
+                        macinf->lchid[j+chan] = c_t;                     /* Logical Channel ID is the value in C/T */
+                        macinf->content[j+chan] = lchId_type_table[c_t]; /* Base MAC content on logical channel id (Table is in packet-nbap.h) */
+                        rlcinf->mode[j+chan] = lchId_rlc_map[c_t];       /* Base RLC mode on logical channel id */
                     }
-                    tb_bit_off = (2+p_conv_data->num_dch_in_flow)*8;    /*Point to the C/T of first TB*/
-                    /*Set configuration for individual blocks*/
-                    for (j=0; j < num_tbs && j+chan < MAX_MAC_FRAMES; j++) {
-                        /*Set transport channel id (useful for debugging)*/
-                        macinf->trchid[j+chan] = p_conv_data->dchs_in_flow_list[chan];
-
-                        /*Transport Channel m31 and 24 might be multiplexed!*/
-                        if ( p_conv_data->dchs_in_flow_list[chan] == 31 || p_conv_data->dchs_in_flow_list[chan] == 24) {
-
-                            /****** MUST FIGURE OUT IF THIS IS REALLY MULTIPLEXED OR NOT*******/
-                            /*If Trchid == 31 and only on TB, we have no multiplexing*/
-                            if (0/*p_conv_data->dchs_in_flow_list[chan] == 31 && num_tbs == 1*/) {
-                                macinf->ctmux[j+chan] = FALSE;/*Set TRUE if this channel is multiplexed (ie. C/T flag exists)*/
-
-                                macinf->lchid[j+chan] = 1;
-
-                                macinf->content[j+chan] = lchId_type_table[1];    /*Base MAC content on logical channel id (Table is in packet-nbap.h)*/
-                                rlcinf->mode[j+chan] = lchId_rlc_map[1];    /*Based RLC mode on logical channel id*/
-
-                            }
-                            /*Indicate we don't have multiplexing.*/
-                            else if (p_conv_data->dchs_in_flow_list[chan] == 24 && tb_size != 340) {
-                                macinf->ctmux[j+chan] = FALSE;/*Set TRUE if this channel is multiplexed (ie. C/T flag exists)*/
-
-                                /*g_warning("settin this for %d", pinfo->num);*/
-                                macinf->lchid[j+chan] = fake_lchid;
-                                macinf->fake_chid[j+chan] = TRUE;
-                                macinf->content[j+chan] = MAC_CONTENT_PS_DTCH; /*lchId_type_table[fake_lchid];*/    /*Base MAC content on logical channel id (Table is in packet-nbap.h)*/
-                                rlcinf->mode[j+chan] = RLC_AM;/*lchId_rlc_map[fake_lchid];*/    /*Based RLC mode on logical channel id*/
-                            }
-                            /*We have multiplexing*/
-                            else {
-                                macinf->ctmux[j+chan] = TRUE;/*Set TRUE if this channel is multiplexed (ie. C/T flag exists)*/
-
-                                /* Peek at C/T, different RLC params for different logical channels */
-                                /*C/T is 4 bits according to 3GPP TS 25.321, paragraph 9.2.1, from MAC header (not FP)*/
-                                c_t = (tvb_get_bits8(tvb, tb_bit_off/*(2+p_conv_data->num_dch_in_flow)*8*/, 4) + 1) % 0xf;    /* c_t = tvb_get_guint8(tvb, offset);*/
-                                macinf->lchid[j+chan] = c_t;
-
-                                macinf->content[j+chan] = lchId_type_table[c_t];    /*Base MAC content on logical channel id (Table is in packet-nbap.h)*/
-                                rlcinf->mode[j+chan] = lchId_rlc_map[c_t];    /*Based RLC mode on logical channel id*/
-                            }
-                        } else {
-                            fake_lchid = make_fake_lchid(pinfo, p_conv_data->dchs_in_flow_list[chan]);
-                            macinf->ctmux[j+chan] = FALSE;/*Set TRUE if this channel is multiplexed (ie. C/T flag exists)*/
-                            /*macinf->content[j+chan] = MAC_CONTENT_CS_DTCH;*/
-                            macinf->content[j+chan] = lchId_type_table[fake_lchid];
-
-
-                            rlcinf->mode[j+chan] = lchId_rlc_map[fake_lchid];
+                    else {
+                        /* Unfamiliar DCH format, faking LCHID */
+                        /* Asuming the channel isn't multiplexed (ie. C/T flag not present) */
+                        macinf->ctmux[j+chan] = FALSE;
 
-                            /*Generate virtual logical channel id*/
-                            /************************/
-                            /*TODO: Once proper lchid is always set, this has to be removed*/
-                            macinf->fake_chid[j+chan] = TRUE;
-                            macinf->lchid[j+chan] = fake_lchid;  /*make_fake_lchid(pinfo, p_conv_data->dchs_in_flow_list[chan]);*/
-                            /************************/
-                        }
+                        /* TODO: This stuff has to be reworked! */
+                        /* Generates a fake logical channel id for non multiplexed channel */
+                        fake_lchid = make_fake_lchid(pinfo, p_conv_data->dchs_in_flow_list[chan]);
+                        macinf->content[j+chan] = lchId_type_table[fake_lchid];
+                        rlcinf->mode[j+chan] = lchId_rlc_map[fake_lchid];
+
+                        /************************/
+                        /* TODO: Once proper lchid is always set, this has to be removed */
+                        macinf->fake_chid[j+chan] = TRUE;
+                        macinf->lchid[j+chan] = fake_lchid;
+                        /************************/
+                    }
 
-                        /*** Set rlc info ***/
-                        /* Trying to resolve the U-RNTI of the user to be used as RLC 'UE-ID' */
-                        /* Fallback - The RNC's 'Communication Context' for the user as seen in NBAP messages */
-                        user_identity = p_conv_data->com_context_id;
-                        if (p_conv_data->scrambling_code != 0) {
-                            guint32 * mapped_urnti = (guint32 *)g_tree_lookup(rrc_scrambling_code_urnti, GUINT_TO_POINTER(p_conv_data->scrambling_code));
-                            if (mapped_urnti != 0) {
-                                user_identity = GPOINTER_TO_UINT(mapped_urnti);
-                            }
+                    /*** Set rlc info ***/
+                    /* Trying to resolve the U-RNTI of the user to be used as RLC 'UE-ID' */
+                    /* Fallback - The RNC's 'Communication Context' for the user as seen in NBAP messages */
+                    user_identity = p_conv_data->com_context_id;
+                    if (p_conv_data->scrambling_code != 0) {
+                        guint32 * mapped_urnti = (guint32 *)g_tree_lookup(rrc_scrambling_code_urnti, GUINT_TO_POINTER(p_conv_data->scrambling_code));
+                        if (mapped_urnti != 0) {
+                            user_identity = GPOINTER_TO_UINT(mapped_urnti);
                         }
-                        rlcinf->urnti[j + chan] = user_identity;
-                        rlcinf->li_size[j+chan] = RLC_LI_7BITS;
+                    }
+                    rlcinf->urnti[j + chan] = user_identity;
+                    rlcinf->li_size[j+chan] = RLC_LI_7BITS;
 #if 0
-                        /*If this entry exists, SECRUITY_MODE is completed (signled by RRC)*/
-                        if ( rrc_ciph_inf && g_tree_lookup(rrc_ciph_inf, GINT_TO_POINTER((gint)p_conv_data->com_context_id)) != NULL ) {
-                            rlcinf->ciphered[j+chan] = TRUE;
-                        } else {
-                            rlcinf->ciphered[j+chan] = FALSE;
-                        }
-#endif
+                    /*If this entry exists, SECRUITY_MODE is completed (signled by RRC)*/
+                    if ( rrc_ciph_inf && g_tree_lookup(rrc_ciph_inf, GINT_TO_POINTER((gint)p_conv_data->com_context_id)) != NULL ) {
+                        rlcinf->ciphered[j+chan] = TRUE;
+                    } else {
                         rlcinf->ciphered[j+chan] = FALSE;
-                        rlcinf->deciphered[j+chan] = FALSE;
-                        rlcinf->rbid[j+chan] = macinf->lchid[j+chan];
-
-
-                        /*Step over this TB and it's C/T flag.*/
-                        tb_bit_off += tb_size+4;
                     }
+#endif
+                    rlcinf->ciphered[j+chan] = FALSE;
+                    rlcinf->deciphered[j+chan] = FALSE;
+                    rlcinf->rbid[j+chan] = macinf->lchid[j+chan];
 
-                    offset++;
+                    /*Step over this TB and it's C/T flag.*/
+                    tb_bit_off += tb_size+4;
+                }
+
+                offset++;
             }
             p_add_proto_data(wmem_file_scope(), pinfo, proto_umts_mac, 0, macinf);
             p_add_proto_data(wmem_file_scope(), pinfo, proto_rlc, 0, rlcinf);