Comments on Tomek on Software: WCF net.tcp protocol in Silverlight 4

Tomasz, is there any reason an approach like this ...

2010-03-11T12:52:42.216-08:00

Tomasz, is there any reason an approach like this wouldn't work?

- On the server, expose your WCF service using both Net.TCP and PollingDuplexHttpBinding.
- On the client, try to open a connection to the web service using Net.TCP.
- If that succeeds, use Net.TCP.
- If that fails, fallback to the PollingDuplexHttpBinding.

That's the approach we're currently taking, and it seems to be working. Any reason why it wouldn't, or any reason why we shouldn't?

A cross-platform communications protocol that supp...

2010-02-10T20:15:23.546-08:00

A cross-platform communications protocol that supports real call-backs and that works across the Internet and firewalls is ICE (http://zeroc.com).

They have Silverlight 2/3 support as well.

Is it possible to have data validation attributes ...

2010-02-05T13:41:04.695-08:00

Is it possible to have data validation attributes in the classes on the server side and when adding a service reference to the server to have the classes generated with the data annotations on them?

Florin, you are right - polling duplex protocol is...

2010-02-02T10:16:04.106-08:00

Florin, you are right - polling duplex protocol is the way to go on the public internet.

So if I want to deploy a Silverlight 4 app which w...

2010-02-02T06:10:16.216-08:00

So if I want to deploy a Silverlight 4 app which wants to take advantage of a duplex wcf service over the web, I would need to expose the wcf service through a PollingDuplexHttpBinding endpoint? (because I cannot rely that everyone has the tcp outgoing port allowed - 4502-4534)

SCollard, a net.tcp WCF channel maps to a single u...

2010-01-14T13:32:09.386-08:00

SCollard, a net.tcp WCF channel maps to a single underlying TCP connection. This means that messages client sends over an instance of a net.tcp WCF channel will always reach the same instance of the backend service despite there being an NLB between them. If the net.tcp WCF channel instance is closed or faulted and subsequently recreated by the client, a different backend server may be used to serve the client in the absence of NLB affinity. So the key question is whether your application requires or relies on client affinity to any resources maintained by the server side with lifetime exceeding the lifetime of a net.tcp WCF channel. If you are building a pub\sub system, the question translates to whether your subscriptions are durable or not. If the answer is yes, you may have to look at mechanisms to share the durable state across backends, and Velocity is one technology that can speed it up.

Would the net.tcp duplex for Sl4 work in the follo...

2010-01-14T13:15:09.196-08:00

Would the net.tcp duplex for Sl4 work in the following scenario?

- Intranet with necessary ports opened
- WCF services layer on redundant servers behind NLB without a guarantee of backend affinity
- Subscriptions kept in Distributed Cache (Velocity)

When a server goes down what happens as the connection is made to another server through NLB?

Yes, net.tcp is subject to the same cross-domain s...

2010-01-06T14:54:18.626-08:00

Yes, net.tcp is subject to the same cross-domain security concerns as http, with the mitigation being the cross-domain policy file. Is there anthing specific you would want to do over port 808?

It is not as much a requirement as a restriction i...

2010-01-04T20:30:26.624-08:00

It is not as much a requirement as a restriction imposed by typical environments at the internet scale. If you deploy a service that accepts TCP connections in the specified port range, the firewall of your server and the network it is connected to (e.g. your company's network) must explicitly allow incoming connections on these ports. Next, client side environment must be configured to allow outgoing connections on this port, which in a general internet case is not a property that can be assumed as a default. If the default client configuration does not allow outgoing connections, client's must be aware of the limitation, knowledgeable and able to change it, and above all willing to do so, none of which can be safely assumed about an average user of the public internet. As such, the deployment of net.tcp based services is in practice limited to networks that are more tightly controlled.

I don't understand the intranet and firewall requi...

2010-01-02T18:01:04.750-08:00

I don't understand the intranet and firewall requirements.

If I build and deploy a WCF server that uses the required port range, and then deploy on a public web site a silverlight 4 app that talks to the WCF server, then are you saying that no one will be able to hit the service without messing with their firewall?

Is it their windows firewall on their own computer or is it their home routers or does it have something to do with NAT (Network Address Translation)? Why wouldn't the silverlight app be able to initiate a duplex tcp connection with the server like anything else?

Falguni, there are no plans to remove port restric...

2009-12-29T12:44:21.546-08:00

Falguni, there are no plans to remove port restrictions in the near future. The restrictions have been put in place for security reasons. Aaron Oneal has a great write-up about the rationale of the port restrictions at http://blogs.msdn.com/ncl/archive/2009/06/23/why-does-silverlight-have-a-restricted-port-range-for-sockets.aspx. What is your scenario that requires access to a port outside of this range?

Is there any plan to remove port restrictions in n...

2009-12-27T22:21:07.721-08:00

Is there any plan to remove port restrictions in near future??

Fantastic article Tomasz! I greatly appreciate th...

2009-12-11T19:42:30.658-08:00

Fantastic article Tomasz! I greatly appreciate the performance metrics. Instead of theorizing you actually quantify and compare performance. Thank-you. -Shaun

Anonymous, how is the net.tcp binding configured o...

2009-11-20T09:33:48.463-08:00

Anonymous, how is the net.tcp binding configured on the service? In particular, is security turned off? The binding should look similar to this:

<netTcpBinding>
<binding name="PubSub">
<security mode="None"/>
</binding>
</netTcpBinding>

Hi The Visual Studio 2010 integration is failing....

2009-11-20T04:56:16.282-08:00

Hi

The Visual Studio 2010 integration is failing. When I try to reference a tcp service in a SL 4.0 application, a message saying that there is no endpoints compatible with SL 3.

I uninstalled the SL 3 SDK before install 4.0, and the problem continues happening.

We realize lack of transport level security is a m...

2009-11-19T12:05:53.217-08:00

We realize lack of transport level security is a major drawback in the current implementation of net.tcp and we consider this an important feature to add going forward.

Silverlight does not currently support message protection (integrity and confidentiality) using WS-Security mechanisms. The only WS-Security feature supported by WCF in Silverlight is attaching basic username/password credentials to a message. However, such configuration requires transport level security. Given that net.tcp does not provide transport level security, basic credentials in WCF can only be added to messages sent over the HTTPS protocol.

There is no single "proper" duplex communication channel in Silverlight, the choice depends on the requirements. Net.tcp offers performance far superior to HTTP polling duplex; at the same time its practical use is restricted to intranets due to TCP port range limitation and lack of transport level security. Going forward we plan to invest in adding SSL security to net.tcp as well as improving HTTP polling duplex performance.

The System.ServiceModel.Extensions.dll and System.ServiceModel.NetTcp.dll are Silverlight extension assemblies and ship as part of Silverlight 4 SDK. They are typically located in "%Program Files%\Microsoft SDKs\Silverlight\v4.0\Libraries\Client" directory.

Where are these assemblies?

2009-11-19T05:33:26.572-08:00

Where are these assemblies?

So is this a "proper" duplex communication channel...

2009-11-19T03:51:39.005-08:00

So is this a "proper" duplex communication channel as opposed to polling duplex?

Is message-level security supported even though tr...

2009-11-18T18:16:35.384-08:00

Is message-level security supported even though transport-level isn't?

shame about the lack of security

2009-11-18T13:49:53.756-08:00

shame about the lack of security

Wow, interesting data. Do you have numbers for a O...

2009-11-18T12:34:14.138-08:00

Wow, interesting data. Do you have numbers for a OSX-based client?