The MU-RTS frame is a Trigger Frame in 802.11ax which has a trigger sub-field type value of 3.

The MU-RTS frame purpose is to elicit a CTS response from atleast one of MU capable Stations addressed in the MU-RTS frame. The Trigger Frame format remains the same for MU-RTS. However,

1. Most of the common info –> Trigger dependent common info field and
2. Most of the elements in the user info –> Trigger dependent user info field are not required for an MU-RTS transmission.

The below diagram shows the parameters that are used and the parameters that are set as reserved in the MU-RTS frame for the above fields.

The fields that are used are marked “X” are reserved. The other elements are

1. Trigger Type – set to 3 for MU-RTS
2. More TF – set to 0 mostly. used for TWT or Power Save with UORA
3. CS Required – set to 1 if responding stations need to use ED values to sense and determine if medium is free before responding. Set to 0 otherwise
4. UL BW – For a MU-RTS frame, it determines the bandwidth of the frame carrying the MU-RTS

UL BW value	Description of value
0	20 MHz
1	40 MHz
2	80 MHz
3	80+80 or 160 MHz

The User info field for the MU-RTS variant also does not require many of the fields and is shown below

The fields that are used are marked “X” are reserved. The other elements are

1. AID12 – indicates the Station ID for each recipient
2. RU Allocation – for an MU-RTS, it determines on which primary channel the CTS frame should be sent by the non-AP station

Buffer Status Reports (BSR) – Unsolicited BSR