Alice                         Bob
[new msg]  ----------------->
          <----------------- [ack]
[ack]      ----------------->

##</code><code>##

[new msg]  ----------------->
...
[new msg]  ----------------->
...
[new msg]  ----------------->
          <----------------- [ack]
[ack]      ----------------->

##</code><code>##

[new msg]  ----------------->
          <----------------- [ack]
          ............
          <----------------- [ack]
          ............
          <----------------- [ack]
[ack]      ----------------->

##</code><code>##

[new msg]  ----------------->
          <----------------- [ack]
          ............
          <----------------- [ack]
          ............
          <----------------- [ack]
          ............
[new msg]  ----------------->
          <----------------- [ack]
[ack]      ----------------->