Dissect SL-SCH packets with MAC-LTE

Configuration

• Fixed fields
  • Set radioType to 1 (FDD)
  • Set direction to 0 (UL, dummy)
  • Set rntiType to 8 (SL-RNTI)
• Optional fields (given in hex format)
  • RNTI : 0065 (dummy value)
  • UE ID : 04D2 (dummy value)
  • SFN/SF : 0661 (dummy value)
• Data
  • Case 1: Padding subheader placed before MAC PDU Subheader
    • SL-SCH Subheader
      • byte 0: 0001 0 0 0 0 (V/R/R/R/R)
      • byte 1-3: 0000 0000 0000 0000 0000 0001 (24-bit ProSe UEID)
      • byte 4-5: 0000 0000 0010 0100 (16 bit Dest Layer-2 ID)
    • Padding Subheader --> indicates padding
      • byte 0: 0 0 1 11111 (R/R/E/LCID)
    • MAC PDU Subheader
      • byte 0: 0 0 0 01010 (R/R/E/LCID) --> no need to indicate length, take the remainder
    • MAC PDU Payload
      • Dummy 14 bytes: (in hex format) 55 aa 55 aa 55 aa 55 55 aa 55 aa 55 aa 55
  • Case 2: Padding subheader placed after MAC PDU Subheader
    • SL-SCH Subheader
      • byte 0: 0001 0 0 0 0 (V/R/R/R/R)
      • byte 1-3: 0000 0000 0000 0000 0000 0001 (24-bit ProSe UEID)
      • byte 4-5: 0000 0000 0010 0100 (16 bit Dest Layer-2 ID)
    • MAC PDU Subheader
      • byte 0: 0 0 1 01010 (R/R/E/LCID)
      • byte 1: 0 0000111 (F/L) --> indicates a 7 byte payload
    • Padding Subheader --> indicates padding
      • byte 0: 0 0 0 11111 (R/R/E/LCID)
    • MAC PDU Payload
      • Dummy 14 bytes: (in hex format) 55 aa 55 aa 55 aa 55 55 aa 55 aa 55 aa 55

Analysis by Wireshark

Reference: 36.321 6.1.6 (MAC PDU SL-SCH)

MAC-LTE SL-SCH: (SFN=102 , SF=1) UEId=1234 (Padding) (10:remainder)

Case 1: Successful Recovery

• MAC PDU Header (SL-SCH) (Padding) (10:remainder) [2 subheaders]
  • Sub-header (SL-SCH)
    • 0001 .... = Version: 1
    • .... 0000 = Reserved bits: 0x0
    • Source Layer-2 ID: 0x000001
    • Destination Layer-2 ID: 0x0024
  • Sub-header (lcid=Padding)
    • 00.. .... = Reserved bits: 0x0
    • ..1. .... = Extension: 0x1
    • ...1 1111 = LCID: Padding (0x1f)
  • Sub-header (lcid=10, length is remainder)
    • 00.. .... = Reserved bits: 0x0
    • ..0. .... = Extension: 0x0
    • ...0 1010 = LCID: 10 (0x0a)
  • SDU (10, length=14 bytes): 55aa55aa55aa5555aa55aa55aa55

Case 2: Failed Recovery

• MAC PDU Header (SL-SCH)
  • Sub-header (SL-SCH)
    • 0001 .... = Version: 1
    • .... 0000 = Reserved bits: 0x0
    • Source Layer-2 ID: 0x000001
    • Destination Layer-2 ID: 0x0024
  • Sub-header (lcid=10, length is remainder)
    • 00.. .... = Reserved bits: 0x0
    • ..1. .... = Extension: 0x1
    • ...0 1010 = LCID: 10 (0x0a)
  • [Dissector bug, protocol MAC-LTE: field mac-lte.slsch.format is not of type FT_CHAR, FT_UINT8, FT_UINT16, FT_UINT24, or FT_UINT32]