C# WCF works inside corporate firewall but not outside

I am running into an “interesting” error with my WCF JSONP web service. It is the only one I have and it only exposes one method. If I hit my service via web browser internally it pops up with a message that, effectively, MEX is not enabled (true). If I hit it from outside our network (like you would unless you were on a machine in my company) it just sits and finally times out. The URL is: http://demo.rivworks.com/services/Negotiate.svc. Any ideas as to what might be causing this behavior?

Here is the web.config:

  <!-- WCF configuration -->
  <system.serviceModel>
    <behaviors>
      <endpointBehaviors>
        <behavior name="JsonpServiceBehavior">
          <webHttp />
        </behavior>
      </endpointBehaviors>
    </behaviors>

    <services>
      <service name="RivWorks.Web.Service.NegotiateService">
        <endpoint address=""
                binding="customBinding"
                bindingConfiguration="jsonpBinding"
                behaviorConfiguration="JsonpServiceBehavior"
                contract="RivWorks.Web.Service.INegotiateService" />
      </service>
    </services>

    <extensions>
      <bindingElementExtensions>
        <add name="jsonpMessageEncoding" type="RivWorks.Web.Service.JSONPBindingExtension, RivWorks.Web.Service, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
      </bindingElementExtensions>
    </extensions>

    <bindings>
      <customBinding>
        <binding name="jsonpBinding" >
          <jsonpMessageEncoding />
          <httpTransport manualAddressing="true"/>
        </binding>
      </customBinding>
    </bindings>    
  </system.serviceModel>
</configuration>

Here is the code:

namespace RivWorks.Web.Service
{
    //----------------------------------------------------------------------------------------------------------//
    // Data class                                                                                               //
    //----------------------------------------------------------------------------------------------------------//
    [DataContract(Name = "NegotiateSetup", Namespace = "http://rivworks.com/DataContracts/2009/01/15")]
    public cl开发者_如何学Goass NegotiateSetup : INegotiationInitialize
    {
        #region Declarations
        ...
        #endregion


        #region INegotiationInitialize Members
        ...
        #endregion
    }

    //----------------------------------------------------------------------------------------------------------//
    // Service Implementation                                                                                   //
    //----------------------------------------------------------------------------------------------------------//
    [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
    public class NegotiateService : INegotiateService
    {
        public NegotiateService() { }

        public INegotiationInitialize GetSetup(string method, string jsonInput)
        {
            ...
            return resultSet;
        }
    }
}

I am after a couple of things here:

1. Why can I NOT hit it from outside my local network?
2. How can I get MEX working properly

Note: I am using the JSONP classes found here: http://msdn.microsoft.com/en-us/library/cc716898.aspx

To enable your MEX, add this inside your service tag:

<endpoint address="mex"
          binding="mexHttpBinding"
          contract="IMetadataExchange" />

Inside your behaviors tag, add:

  <serviceBehaviors>
    <behavior name="JsonpServiceBehavior">
      <serviceMetadata httpGetEnabled="true"/>
    </behavior>
  </serviceBehaviors>

About why that service isn't accessible from outside, can this be a firewall issue?