Initiating Peer                    Responding Peer

@M [0] QUIC Packets

... Update to @N
@N [1] QUIC Packets
                      -------->
                                         Update to @N ...
                                      QUIC Packets [1] @N
                      <--------
                                      QUIC Packets [1] @N
                                    containing ACK
                      <--------
... Key Update Permitted

@N [1] QUIC Packets
         containing ACK for @N packets
                      -------->
                                 Key Update Permitted ...