Capgemini WCF Technical Interview Questions and Answers

If you are preparing for a Capgemini technical interview in .NET technologies, you will most likely face questions related to Windows Communication Foundation (WCF). WCF is a powerful Microsoft framework for building service-oriented applications that can communicate across different platforms and protocols.

I’ve compiled a set of commonly asked WCF interview questions with answers, ranging from basics to advanced, that will help you showcase your expertise confidently.

1. Basic WCF Questions

Q1. What is WCF?
WCF (Windows Communication Foundation) is a unified programming model by Microsoft used to build and deploy service-oriented applications (SOA). It allows applications to communicate via multiple protocols such as HTTP, TCP, MSMQ, and Named Pipes.

Q2. What are the key features of WCF?

• Interoperability across platforms

• Multiple message exchange patterns (Request-Reply, One-Way, Duplex)

• Security (Transport & Message-level)

• Reliability and Transactions

• Extensibility and Custom Behaviors

Q3. What are the major components of WCF?

• Service Class – Defines the business logic.

• Endpoint – Defines where, how, and what service is exposed.

• Binding – Defines how communication happens (protocols, transport, encoding).

• Contracts – Defines the service operations and data (Service Contract, Operation Contract, Data Contract).

Q4. What are the different types of contracts in WCF?

1. Service Contract – Defines operations available in the service.

2. Operation Contract – Defines the method that can be invoked.

3. Data Contract – Defines the data structure exchanged between client and service.

4. Message Contract – Allows full control over SOAP message structure.

5. Fault Contract – Defines the errors returned to the client.

Q5. What is an Endpoint in WCF?
Every WCF service exposes its functionality through endpoints, defined by the ABC rule:

• Address (Where the service is hosted)

• Binding (How communication happens)

• Contract (What service does)

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2. Intermediate WCF Questions

Q6. What are different types of WCF bindings?

• BasicHttpBinding – Interoperable with older ASMX services.

• WsHttpBinding – Secure and reliable, supports WS-* standards.

• NetTcpBinding – High performance, TCP protocol within intranet.

• NetNamedPipeBinding – Communication between processes on the same machine.

• NetMsmqBinding – Uses MSMQ for queued communication.

• WSDualHttpBinding – Supports duplex communication.

Q7. What are different message exchange patterns in WCF?

1. Request-Reply (default) – Client sends request, waits for response.

2. One-Way – Client sends message, no response expected.

3. Duplex (Callback) – Two-way communication, client and server both send messages independently.

Q8. What are Instancing Modes in WCF?

• Per-Call – New instance created per request.

• Per-Session – One instance per client session.

• Single – A single instance serves all clients.

Q9. What are Concurrency Modes in WCF?

• Single – Only one thread accesses service instance at a time.

• Multiple – Multiple threads can access simultaneously.

• Reentrant – Service can reenter when callback is called.

Q10. What is the difference between WCF and Web Services (ASMX)?

• WCF supports multiple protocols (HTTP, TCP, MSMQ), while ASMX supports only HTTP.

• WCF supports advanced features like transactions, reliability, and security.

• WCF is extensible, whereas ASMX has limited extensibility.

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3. Advanced WCF Questions

Q11. How is security implemented in WCF?

• Transport Security – Encrypts communication at the transport level (SSL, HTTPS, TCP).

• Message Security – Encrypts the message itself (WS-Security).

• Mixed Security – Combination of both.

• Authentication – Supports Windows, Username/Password, Certificate, and Custom authentication.

Q12. What are Fault Contracts in WCF?
Fault Contracts define strongly typed SOAP faults that can be returned to clients instead of generic exceptions, making error handling more structured.

Q13. How do you enable transactions in WCF?

• Use TransactionFlowAttribute on service operations.

• Configure WsHttpBinding or NetTcpBinding with transactions enabled.

• Use System.Transactions namespace to manage transaction scopes.

Q14. What is WCF Throttling?
WCF throttling helps in controlling resource usage by limiting:

• MaxConcurrentCalls – Maximum number of simultaneous calls.

• MaxConcurrentInstances – Maximum number of service instances.

• MaxConcurrentSessions – Maximum number of client sessions.

Q15. How do you improve WCF service performance?

• Use NetTcpBinding for intranet communication.

• Enable binary encoding instead of text encoding.

• Implement caching and throttling.

• Use asynchronous operations.

• Optimize instancing and concurrency modes.

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4. Real-Time Scenario-Based Questions

Q16. Your WCF service needs to be consumed by both .NET and Java clients. Which binding will you choose?

• BasicHttpBinding for SOAP 1.1 interoperability.

• WsHttpBinding if security and WS-* features are required.

Q17. How do you host a WCF service?

• IIS Hosting – Easiest, automatic activation.

• Windows Service Hosting – Runs continuously in background.

• Self-Hosting – Console or Windows application.

• WAS Hosting – For non-HTTP protocols.

Q18. How do you handle large data in WCF?

• Increase maxReceivedMessageSize in binding configuration.

• Use streaming mode instead of buffered.

• Optimize serialization (BinaryFormatter, DataContractSerializer).

Q19. If your WCF service is slow, what steps will you take to optimize it?

• Analyze service performance with WCF tracing & diagnostics.

• Switch from text encoding to binary encoding.

• Enable compression for large messages.

• Optimize queries in the backend database.

Q20. What is the difference between REST and WCF services?

• WCF can be configured to expose REST endpoints but primarily supports SOAP.

• REST uses HTTP verbs (GET, POST, PUT, DELETE).

• REST is lightweight and stateless, while WCF is feature-rich but heavier.

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Final Thoughts

At Capgemini, WCF interview questions often test your understanding of service contracts, bindings, hosting models, security, and real-world problem solving. A strong grasp of end-to-end service design and deployment will give you a big advantage.