3.5 PUBREC - release has been received (already received QoS 2 release, Part 1)
PUBREC PUBLISH packet is a response to packet data having a QoS 2. It is a protocol for exchanging a second QoS 2 data packets.
3.5.1 Fixed Header fixed title
FIG 3.14 - PUBREC fixed packet header
| Place |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
| Byte 1 |
MQTT control packet type (5) |
reserved |
||||||
|
|
0 |
1 |
0 |
1 |
0 |
0 |
0 |
0 |
| Byte 2 |
The remaining length (2) |
|||||||
|
|
0 |
0 |
0 |
0 |
0 |
0 |
1 |
0 |
The remaining length field
This is a variable length header. For PUBREC packet, a value of 2.
3.5.2 Variable Header variable head
Variable header contains a packet identifier being acknowledged PUBLISH package.
FIG 3.15 - PUBREC packet header variables
| Place |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
| Byte 1 |
MSB packet identifier |
|||||||
| Byte 2 |
LSB packet identifier |
|||||||
3.5.3 Payload Payload
PUBREC packet no load.
3.5.4 Actions Action
This is described in detail in Section 4.3.3.