PDCP NR: rework UDP framing format

Change-Id: I6f4a17ed91d4cb6ea39b5938add6ee882b033687
Reviewed-on: https://code.wireshark.org/review/26893
Reviewed-by: Martin Mathieson <martin.r.mathieson@googlemail.com>
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>

2 files changed, 42 insertions, 40 deletions

diff --git a/epan/dissectors/packet-pdcp-nr.c b/epan/dissectors/packet-pdcp-nr.c
index b61d8dfcad..7ce9b132a1 100644
--- a/epan/dissectors/packet-pdcp-nr.c
+++ b/epan/dissectors/packet-pdcp-nr.c
@@ -784,9 +784,10 @@ static gboolean dissect_pdcp_nr_heur(tvbuff_t *tvb, packet_info *pinfo,
 
     /* Needs to be at least as long as:
        - the signature string
-       - mandatory fields
-       - at least the payload tag and a byte of data.
-       However, let attempted dissection show if there are any tags at all. */
+       - fixed header byte(s)
+       - tag for data
+       - at least one byte of PDCP PDU payload.
+      However, let attempted dissection show if there are any tags at all. */
     gint min_length = (gint)(strlen(PDCP_NR_START_STRING) + 3); /* signature */
 
     if (tvb_captured_length_remaining(tvb, offset) < min_length) {
@@ -811,15 +812,18 @@ static gboolean dissect_pdcp_nr_heur(tvbuff_t *tvb, packet_info *pinfo,
         infoAlreadySet = TRUE;
     }
 
+    /* Read fixed fields */
+    p_pdcp_nr_info->plane = (enum pdcp_nr_plane)tvb_get_guint8(tvb, offset++);
+    if (p_pdcp_nr_info->plane == NR_SIGNALING_PLANE) {
+        /* Signalling plane always has 12 SN bits */
+        p_pdcp_nr_info->seqnum_length = PDCP_NR_SN_LENGTH_12_BITS;
+    }
 
     /* Read tagged fields */
     while (tag != PDCP_NR_PAYLOAD_TAG) {
         /* Process next tag */
         tag = tvb_get_guint8(tvb, offset++);
         switch (tag) {
-            case PDCP_NR_PLANE_TAG:
-                p_pdcp_nr_info->plane = (enum pdcp_nr_plane)tvb_get_guint8(tvb, offset++);
-                break;
             case PDCP_NR_SEQNUM_LENGTH_TAG:
                 p_pdcp_nr_info->seqnum_length = tvb_get_guint8(tvb, offset);
                 offset++;
@@ -841,14 +845,12 @@ static gboolean dissect_pdcp_nr_heur(tvbuff_t *tvb, packet_info *pinfo,
                 p_pdcp_nr_info->ueid = tvb_get_ntohs(tvb, offset);
                 offset += 2;
                 break;
-
             case PDCP_NR_ROHC_COMPRESSION_TAG:
-                p_pdcp_nr_info->rohc.rohc_compression = tvb_get_guint8(tvb, offset);
-                offset += 2;
+                p_pdcp_nr_info->rohc.rohc_compression = TRUE;
                 break;
             case PDCP_NR_ROHC_IP_VERSION_TAG:
-                p_pdcp_nr_info->rohc.rohc_ip_version = tvb_get_ntohs(tvb, offset);
-                offset += 2;
+                p_pdcp_nr_info->rohc.rohc_ip_version = tvb_get_guint8(tvb, offset);
+                offset++;
                 break;
             case PDCP_NR_ROHC_CID_INC_INFO_TAG:
                 p_pdcp_nr_info->rohc.cid_inclusion_info = tvb_get_guint8(tvb, offset);
diff --git a/epan/dissectors/packet-pdcp-nr.h b/epan/dissectors/packet-pdcp-nr.h
index c4c3d7d869..e570f9a032 100644
--- a/epan/dissectors/packet-pdcp-nr.h
+++ b/epan/dissectors/packet-pdcp-nr.h
@@ -63,9 +63,7 @@ typedef struct pdcp_nr_info
 /* Several people have asked about dissecting PDCP by framing    */
 /* PDUs over IP.  A suggested format over UDP has been defined   */
 /* and implemented by this dissector, using the definitions      */
-/* below. A link to an example program showing you how to encode */
-/* these headers and send nr PDCP PDUs on a UDP socket is        */
-/* provided at https://wiki.wireshark.org/PDCP-nr                */
+/* below.                                                        */
 /*                                                               */
 /* A heuristic dissecter (enabled by a preference) will          */
 /* recognise a signature at the beginning of these frames.       */
@@ -79,55 +77,57 @@ typedef struct pdcp_nr_info
    terminating NULL */
 #define PDCP_NR_START_STRING "pdcp-nr"
 
+/* Fixed fields:
+   - plane (1 byte) */
 
-/* The format for fields is to have the tag, followed by the value
-  (there is no length field, it's implicit from the tag).
-  The allowed values for each field should be taken from pdcp_nr_info above. */
+/* Conditional field. This field is mandatory in case of User Plane PDCP PDU.
+   The format is to have the tag, followed by the value (there is no length field,
+   it's implicit from the tag). The allowed values are defined above. */
 
-#define PDCP_NR_PLANE_TAG                  0x02
-/* 1 byte, mandatory */
-
-#define PDCP_NR_SEQNUM_LENGTH_TAG          0x03
-/* 1 byte, mandatory */
+#define PDCP_NR_SEQNUM_LENGTH_TAG          0x02
+/* 1 byte */
 
-#define PDCP_NR_DIRECTION_TAG              0x04
-/* 1 byte, mandatory */
+/* Optional fields. Attaching this info should be added if available.
+   The format is to have the tag, followed by the value (there is no length field,
+   it's implicit from the tag) */
 
-#define PDCP_NR_BEARER_TYPE_TAG            0x05
-/* 1 byte, mandatory */
+#define PDCP_NR_DIRECTION_TAG              0x03
+/* 1 byte */
 
-#define PDCP_NR_BEARER_ID_TAG              0x06
-/* 1 byte, mandatory depending upon bearer type */
+#define PDCP_NR_BEARER_TYPE_TAG            0x04
+/* 1 byte */
 
-#define PDCP_NR_UEID_TAG                   0x07
-/* 2 bytes, network order.  Optional, but needed if > 1 UE logged. */
+#define PDCP_NR_BEARER_ID_TAG              0x05
+/* 1 byte */
 
+#define PDCP_NR_UEID_TAG                   0x06
+/* 2 bytes, network order */
 
-#define PDCP_NR_ROHC_COMPRESSION_TAG       0x08
-/* 1 byte, network order (mandatory for user-plane) */
+#define PDCP_NR_ROHC_COMPRESSION_TAG       0x07
+/* 0 byte */
 
 /* N.B. The following ROHC values only have significance if rohc_compression
    is in use for the current channel */
 
-#define PDCP_NR_ROHC_IP_VERSION_TAG        0x09
-/* 2 bytes, network order */
+#define PDCP_NR_ROHC_IP_VERSION_TAG        0x08
+/* 1 byte */
 
-#define PDCP_NR_ROHC_CID_INC_INFO_TAG      0x0A
+#define PDCP_NR_ROHC_CID_INC_INFO_TAG      0x09
 /* 1 byte */
 
-#define PDCP_NR_ROHC_LARGE_CID_PRES_TAG    0x0B
+#define PDCP_NR_ROHC_LARGE_CID_PRES_TAG    0x0A
 /* 1 byte */
 
-#define PDCP_NR_ROHC_MODE_TAG              0x0C
+#define PDCP_NR_ROHC_MODE_TAG              0x0B
 /* 1 byte */
 
-#define PDCP_NR_ROHC_RND_TAG               0x0D
+#define PDCP_NR_ROHC_RND_TAG               0x0C
 /* 1 byte */
 
-#define PDCP_NR_ROHC_UDP_CHECKSUM_PRES_TAG 0x0E
+#define PDCP_NR_ROHC_UDP_CHECKSUM_PRES_TAG 0x0D
 /* 1 byte */
 
-#define PDCP_NR_ROHC_PROFILE_TAG           0x0F
+#define PDCP_NR_ROHC_PROFILE_TAG           0x0E
 /* 2 bytes, network order */