SIGNAL field L-SIG

One OFDM symbol, always sent at 6 Mb/s with BPSK and rate-1/2 coding so that any receiver can read it. Tells the receiver the rate and length of what follows.

Reading a capture

This field is why a station that cannot decode a transmission can still defer for the right amount of time — RATE and LENGTH together give the duration. It is also a single point of failure: corrupt the SIGNAL field and the whole PPDU is lost even if the DATA field was received cleanly.

Subfields

• RATE — Selects the modulation and coding rate used for the DATA field.
• LENGTH — The number of octets in the PSDU, from 1 to 4095.

Where it sits

non-HT PPDU > SIGNAL field

• Open in the explorer — Ack
• Open in the explorer — TCP over IPv4, in a protected QoS Data frame, aggregated
• Open in the explorer — Association Request
• Open in the explorer — Association Response
• Open in the explorer — Beacon
• Open in the explorer — Compressed Block Ack
• Open in the explorer — CTS
• Open in the explorer — Four-way handshake message 1
• Open in the explorer — Four-way handshake message 2
• Open in the explorer — Four-way handshake message 3
• Open in the explorer — Four-way handshake message 4
• Open in the explorer — Probe Request
• Open in the explorer — Probe Response
• Open in the explorer — ARP request in a QoS Data frame
• Open in the explorer — ICMP echo over IPv4, in a QoS Data frame
• Open in the explorer — UDP over IPv6, in a QoS Data frame
• Open in the explorer — TCP over IPv4, in a protected QoS Data frame
• Open in the explorer — TCP over IPv4, in an open QoS Data frame
• Open in the explorer — UDP over IPv4, in a QoS Data frame
• Open in the explorer — RTS
• Open in the explorer — Trigger frame

Accuracy

Clause

802.11-2024 §17.3.4

Verified

Not verified against the standard. Treat this as a claim, not a fact.