LINKTYPE_DECT_NR_TAP

DECT‑2020 NR frames with custom metadata TAP header

LINKTYPE_DECT_NR_TAP (with DLT_DECT_NR_TAP = 304) is a link‑layer header type for DECT‑2020 New Radio (NR) frames that are captured with a custom TAP‑style metadata header prepended. The payload after the metadata header is a standard DLT_DECT_NR MAC‑layer frame, so dissection can be done using the same parsers as for raw DLT_DECT_NR.

Overall frame layout

Each captured packet has this structure:

• 8‑byte custom header
• N 8‑byte metadata entries
• Raw DLT_DECT_NR modem‑layer data (PCC bytes followed by PDC bytes)

All multi‑byte integer fields are little‑endian unless noted otherwise.

The header layout

1. Custom header (8 bytes)

All fields are little‑endian.

Offset	Field	Size, bytes	Value / Notes
0	Version	1	1
1	Reserved1	1	0
2–3	Metadata entry count	2	Number of following fixed metadata entries (each entry is exactly 8 bytes)
4–5	Modem length	2	Length in bytes of the modem data (PCC + PDC)
6–7	Reserved2	2	0

2. Metadata entry format

Each metadata entry is a fixed 8‑byte structure. All fields are little‑endian.

Field	Size, bytes	Notes
Type	2	Identifies entry semantics
Reserved	2	0 (for future use)
Value	4	Padded; if actual payload is < 4 bytes, trailing bytes are 0

Known metadata entry Types

Type	Metadata name	Value size, bytes	Meaning
1	Data Type entry	2	Indicates the length of PCC bytes and presence of PDC data: 1 - PCC length is 40 bits; 2 - PCC length is 80 bits; 3 - PCC length is 40 bits, PDC bytes is absent due to PDC CRC error; 4 - PCC length is 80 bits, PDC bytes is absent due to PDC CRC error; 5 - PCC CRC error, neither PCC nor PDC bytes are included;
2	Header status entry	2	Indicates PCC status retrieved from modem: 0 - PHY header is valid; PDC can be received. 1 - PHY header is invalid; PDC can't be received. 2 - PHY header is valid, but RX operation ends before PDC reception;
3	PCC RSSI2 entry	2 signed	PCC RSSI (Received Signal Strength Indicator). Values are in dBm with 0.5 dBm resolution (Q14.1). For example, -87 is -43.5 dbm, -84 is -42,0 dbm.
4	PCC SNR entry	2 signed	PCC Signal‑to‑Noise Ratio. Values are dB values with 0.25 dB resolution (Q13.2)
5	PDC RSSI2 entry	2 signed	PDC RSSI (Received Signal Strength Indicator). Values are in dBm with 0.5 dBm resolution (Q14.1). For example, -87 is -43.5 dbm, -84 is -42,0 dbm.
6	PDC SNR entry	2 signed	PDC Signal‑to‑Noise Ratio. Values are dB values with 0.25 dB resolution (Q13.2)
7	Transaction ID entry	2	Session / transaction ID. Used to map PCC data with corresponding PDC data.
8	Channel entry	2	Radio channel ID
9	Trace log entry number	4	Nearest trace log entry string index

3. After the Metadata

After the metadata entries the actual DLT_DECT_NR MAC‑layer data (PCC bytes followed by PDC bytes) is present.

Usage notes

• This link‑type is intended for DECT‑2020 NR captures where the RF‑layer or tester adds a per‑packet metadata header with signal‑quality and channel information.
• Dissectors should skip the 8‑byte header and metadata entries, then pass the remaining bytes to a standard DLT_DECT_NR dissector for interpretation.

For details on the DECT‑2020 NR base protocol, see ETSI TS 103‑636‑4 (MAC‑layer) and ETSI TS 103‑636‑5 (DLC and convergence layers).