reliablesession

Reliable session guarantees the ordered delivery of messages by default. Therefore in a request/reply exchange you cannot send the second request without receiving the reply for the first one (although you might think this is possible by calling the proxy method from a different thread).

But if you think ordered delivary is not required; try this.

<netTcpBinding>
  <binding name="NetTcpBinding">
    <reliableSession ordered="false" enabled="true" />
  </binding>
</netTcpBinding>