[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Multiple,
 InstanceContextMode = InstanceContextMode.PerSession,
 UseSynchronizationContext = false)]

<configuration>
  <system.net>
    <connectionManagement>
      <add address = "*" maxconnection = "2" />
    </connectionManagement>
  </system.net>
</configuration>