8. Bindings

There are multiple aspects of communication with any given service, and there are many possible communication patterns: messages can be synchronous request/reply or asynchronous fire-and-forget; messages can be bidirectional; messages can be delivered immediately or queued; and the queues can be durable or volatile. There are many possible transport protocols for the messages, such as HTTP (or HTTPS), TCP, P2P (peer network), IPC (named pipes), or MSMQ. There are a few possible message encoding options: you can chose plain text to enable interoperability, binary encoding to optimize performance, or MTOM (Message Transport Optimization Mechanism) for large payloads. There are a few options for securing messages: you can choose not to secure them at all, to provide transport-level security only, to provide message-level privacy and security, and of course there are numerous ways for authenticating and authorizing the clients. Message delivery might be unreliable or reliable end-to-end across intermediaries and dropped connections, and the messages might be processed in the order they were sent or in the order they were received. Your service might need to interoperate with other services or clients that are only aware of the basic web service protocol, or they may be capable of using the score of WS-* modern protocols such as WS-Security and WS-Atomic Transactions. Your service may need to interoperate with legacy clients over raw MSMQ messages, or you may want to restrict your service to interoperate only with another WCF service or client.

To simplify these choices and make them more manageable, WCF groups together a set of such communication aspects in bindings. A binding is merely a consistent, canned set of choices regarding the transport protocol, message encoding, communication pattern, reliability, security, transaction propagation, and interoperability. Ideally, you would extract all these "plumbing" aspects out of your service code and allow the service to focus solely on the implementation of the business logic. Binding enables you to use the same service logic over drastically different plumbing.

The Standard Bindings

Basic binding	Offered by the BasicHttpBinding class
TCP binding	Offered by the NetTcpBinding class, this uses TCP for cross-machine communication on the intranet.
Peer network binding	Offered by the NetPeerTcpBinding class, this uses peer networking as a transport.
IPC binding	Offered by the NetNamedPipeBinding class, this uses named pipes as a transport for same-machine communication.
Web Service (WS) binding	Offered by the WSHttpBinding class, this uses HTTP or HTTPS for transport, and is designed to offer a variety of features such as reliability, transactions, and security over the Internet.
Federated WS binding	Offered by the WSFederationHttpBinding class, this is a specialization of the WS binding, offering support for federated security.
Duplex WS binding	Offered by the WSDualHttpBinding class, this is similar to the WS binding except it also supports bidirectional communication from the service to the client
MSMQ binding	Offered by the NetMsmqBinding class, this uses MSMQ for transport and is designed to offer support for disconnected queued calls.
MSMQ integration binding	Offered by the MsmqIntegrationBinding class, this converts WCF messages to and from MSMQ messages, and is designed to interoperate with legacy MSMQ clients.

Format and Encoding

Transport and encoding for standard bindings (default encoding is in bold)

Name	Transport	Encoding	Interoperable
BasicHttpBinding	HTTP/HTTPS	Text, MTOM	Yes
NetTcpBinding	TCP	Binary	No
NetPeerTcpBinding	P2P	Binary	No
NetNamedPipeBinding	IPC	Binary	No
WSHttpBinding	HTTP/HTTPS	Text, MTOM	Yes
WSFederationHttpBinding	HTTP/HTTPS	Text, MTOM	Yes
WSDualHttpBinding	HTTP	Text, MTOM	Yes
NetMsmqBinding	MSMQ	Binary	No
MsmqIntegrationBinding	MSMQ	Binary	Yes

Having a text-based encoding enables a WCF service (or client) to communicate over HTTP with any other service (or client) regardless of its technology. Binary encoding over TCP or IPC yields the best performance but at the expense of interoperability, by mandating WCF-to-WCF communication.

Choosing a Binding

Choosing a binding for your service should follow the decision-activity diagram shown below.

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