{plantuml}
Alice -> Bob: Authentication Request
alt successful case
    Bob -> Alice: Authentication Accepted
else some kind of failure
    Bob -> Alice: Authentication Failure
    group My own label
    	Alice -> Log : Log attack start
        loop 1000 times
            Alice -> Bob: DNS Attack
        end
    	Alice -> Log : Log attack end
    end
else Another type of failure
   Bob -> Alice: Please repeat
end
{plantuml}

{plantuml}
group TCP-Handshake
  Client  -> Server: <b>syn</b> seq=x
  Client <-- Server: <b>syn</b> ack=x+1 seq=y
  Client  -> Server: <b>ack</b>=y+1 seq=x+1
  Client  -> Server: [data]
end
...
group TCP-Teardown
  alt Client closes
    Client  -> Server: <b>fin</b> seq=x
    Client <-- Server: <b>ack</b>=x+1
    Client <-  Server: <b>fin</b> seq=y
    Client --> Server: <b>fin</b> seq=y+1
  else Server closes
    Client  <- Server: <b>fin</b> seq=x
    Client --> Server: <b>ack</b>=x+1
    Client ->  Server: <b>fin</b> seq=y
    Client <-- Server: <b>fin</b> seq=y+1
  end
end
{plantuml}