WCF (Windows Communication Foundation) Interview Preparation Guide
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Windows Communication Foundation (WCF) frequently Asked Questions in various WCF job Interviews by interviewer. Get preparation of Windows Communication Foundation (WCF) job interview

13 WCF (Windows Communication Foundation) Questions and Answers:

1 :: What is Fault Contract in WCF?

Suppose the service we consumed is not working in the client
application. we want to know the real cause of the problem.
How we can know the error? For this we are having Fault
Contract. Fault Contract provides documented view for error
occurred in the service to client. This helps us to easy
identity, what error has occurred.

2 :: We have already 2 hostings IIS and self hosting. There is another hosting ie WAS Hosting. What is the use of the WAS(Windows activation Service) compared to other hosting?

Windows Process Activation Server (WAS) supports the
communication protocols such as HTTP, TCP, Named Pipes and
MSMQ while IIS supports only HTTP. WAS is available with
Windows Server 2008 only. If the server is Server 2008 then
the better option to deploy WCF service is through WAS. If
the deployment server is Server 2003, the only possible way
to deploy the application with protocols other than HTTP is
using self hosting (using a Windows Application or a Windows
Service and if for a demo purpose can use Console
application also). So WAS is a gift with Vista and Server

3 :: What is the main advantage of WAS? (Windows activation service) When it is used?

Windows Process Activation Server (WAS) is a new server
available with Vista and Windows Server 2008. The new server
is capable of deploying WCF applications which is driven
through different communication protocols such as TCP, Named
Pipes, MSMQ etc together with HTTP. IIS can host WCF
services that communicates only using HTTP while WAS
supports all of the above given protocols. So for an
application that communicates internally using TCP can be
deployed in HTTP by adding a few changes in the
configuration. So the same applicaiton communicates with TCP
and HTTP under a host.

4 :: What is overloading in WCF? How to do authentication in WCF.?

Using the "Name" we can achieve operational overloading
interface IInterfaceName
[OperationContract (Name = "aliasName1")]
int MethodName (int param1, int param2);

[OperationContract (Name = "aliasName2")]
double MethodName (double param1, double param1);

For authentication:-
Say windows,

set the authentication mode as follows
<authentication mode="Windows" />

then in the end point set bind the configuration as below.

<endpoint address="basic" binding="basicHttpBinding"
bindingConfiguration="BND" />

<binding name="BND">
<security mode ="Transport">
<transport clientCredentialType ="Windows"/>

For to USE IIS,make sure that IIS Annonymous authentication

5 :: Explain Different ways to host WCF service?

there are 3 ways host wcf service
1) Self Hosting in managed applications
2) Windows Service
3) IIS
4) WIndows Process Actiation Service (WAS)

6 :: Explain What is DataContract and ServiceContract?

Service Contract:
Service contracts describe the operation that service can
provide. For Eg, a Service provide to know the temperature
of the city based on the zip code, this service is called as
Service contract. It will be created using Service and
Operational Contract attribute.

Data Contract:

Data contract describes the custom data type which is
exposed to the client. This defines the data types, that are
passed to and from service. Data types like int, string are
identified by the client because it is already mention in
XML schema definition language document, but custom created
class or data types cannot be identified by the client e.g.
Employee data type. By using DataContract we can make client
to be aware of Employee data type that are returning or
passing parameter to the method.

7 :: Could the IIS-hosted WCF service make use of HTTP transport security if the IIS virtual derectory that contains the service does not support it?

IIS-hosted WCF services can make use of HTTP transport
security (for example, HTTPS and HTTP authentication
schemes such as Basic, Digest, and Windows Integrated
Authentication) as long as the IIS virtual directory that
contains the service supports those settings. The HTTP
Transport Security settings on a hosted endpoint’s binding
must match the transport security settings on the IIS
virtual directory that contains it

8 :: Do we have to use the relative addresses when hosting in the IIS or the absolute addresses? Why?

IIS Addressing Considerations

When hosting in IIS, you don’t have to worry about creating
or managing the ServiceHost instance. IIS takes care of
this for you behind the scenes. You simply map a .svc
endpoint to your service class, configure the service
endpoints and behaviors in web.config, and let Windows
Communication Foundation manage the process of creating and
configuring the ServiceHost instance at runtime.

In this hosting scenario, the base HTTP address is
determined by the IIS virtual directory housing the service
along with the name of the .svc file. You, as the
developer, really have nothing to say about the base
address since it’s fully controlled by the IIS addressing

As a result, Windows Communication Foundation happily
ignores any base addresses you may specify in web.config in
this scenario. If you want to change the base address for
your endpoints, you’ll need to move the service to a
different IIS virtual directory.

Not only does IIS control the base address, it forces all
of your endpoints to actually use the same base address
(unlike self-hosting). This means that if you do specify an
absolute address for a particular endpoint, it must start
with the base address corresponding to the virtual
directory or you’ll get an exception. As a result, it
really only makes sense to use relative addresses when
hosting in IIS.

9 :: What hosting functionality is unique for the Vista OS?

Windows Activation service.(WAS) .WAS built in top of IIS
which comes from Windows Wista OS

10 :: Is the MsmqIntegrationBinding used the msmq.formatname scheme or the net.msmq scheme?

MSMQ uses paths and format names to identify a queue. Paths
specify a host name and a QueueName. Optionally, there can
be a Private$ between the host name and the QueueName to
indicate a private queue that is not published in the
Active Directory directory service.

Path names are mapped to “FormatNames” to determine
additional aspects of the address, including routing and
queue manager transfer protocol. The Queue Manager supports
two transfer protocols: native MSMQ protocol and SOAP
Reliable Messaging Protocol (SRMP).

The addressing of a queue in WCF is based on the following

net.msmq: // <host-name> / [private/] <queue-name>


•<host-name> is the name of the machine that hosts the
Target Queue.

•[private] is optional. It is used when addressing a Target
Queue that is a private queue.