Answers in Visual C#.NET

Print ECC200 in Visual C#.NET Answers

A. Correct: The address for the endpoint includes the net.pipe protocol, and the binding is appropriate (netNamedPipeBinding) for the endpoint. B. Incorrect: The wsHttpBinding binding cannot be used to communicate with an endpoint that is expected to be a named pipe transport type, and the address s protocol ( http ) is not appropriate for the endpoint. C. Incorrect: The protocol specified on the address is the incorrect type for the endpoint. D. Incorrect: The basicHttpBinding attribute is not appropriate for the endpoint s binding.

1. Correct Answer: D A. Incorrect: The standard HTTP binding does not support callback functionality. B. Incorrect: This binding is still an HTTP-based binding that does not support callbacks. It is basicHttpBinding with SOAP messages formatted to interact better with WCF services. C. Incorrect: This binding is still an HTTP-based binding, with cookie support added. D. Correct: Although this binding is still an HTTP-based binding, CompositeDuplexBindingElement has been added to support the client s listening for a request from the service. 2. Correct Answer: C A. Incorrect: The standard TCP bindings include support for the duplex functionality required to support callbacks. B. Incorrect: The underlying transport layer (named pipes) supports bidirectional communication. As such, any binding that uses named pipes as the transport layer supports callbacks. C. Correct: MSMQ does not provide support for callbacks. If you contemplate the mechanism used to transport the messages, you ll understand why this is the case. This is not to say that a custom binding providing such support isn t possible, only that the out-of-the-box implementation does not have any duplex channel functionality. D. Incorrect: Any binding that has TCP as the underlying transport layer is capable of supporting callbacks.

1. Yes, there are some protocols that cannot be supported. The limitation is not in WCF itself but in the transport mechanism used to send messages between the client and the service. For example, in an externally-facing WCF service, any protocol based on named pipes will not be possible. The reason for this is that the named pipes protocol can be used only when the client and service are on the same system. In addition, MSMQ-based bindings will probably not be appropriate. Using MSMQ-based bindings is more costly because it involves configuring certificates on both sides of the application and defining authorization based on these certificates. 2. The answer is no; it is not possible for the same service to support multiple protocols on the same endpoint, because, technically, an endpoint consists of an address, a binding, and a contract. Changing the address would mean there is a different endpoint. 3. Yes, a service can support multiple endpoints, as was demonstrated in one of the exercises in this chapter. 4. Yes, one service can expose multiple contracts on the same endpoint. However, there are a number of restrictions. First, the binding for each of the contracts must be the same. It is not possible to have the same URI support both basicHttpBinding and wsHttpBinding at the same time. Each contract would have to use the same binding type. 5. The second restriction arises from the mechanism that WCF uses to route the message to the appropriate operation. Two steps are involved: an address filter and a contract filter. The address filter examines the To attribute in the SOAP message to help determine the final destination. The contract filter uses the Action attribute in the SOAP message as the second part of the determination. The attribute values must be sufficient to identify the appropriate service object uniquely. If, for example, the Action attribute were the same for two different contracts, those contracts could not both be hosted within the same service host.