ABC of Windows Communication Foundation

Here I will explain about ABC of Windows Communication Foundation i.e WCF.


WCF is a collection of .NET distributed technologies that have existed for long time, but never got grouped under one roof.

It considered as collection of the following technologies.
 
  1. Web Services(ASMX)
  2. NET Enterprise Services
  3. MSMQ (Microsoft Messaging Queue)
  4. .NET Remoting

Code written in WCF can interact across components, applications and systems and is in accordance with SOA (Service Oriented Architecture).

Following Sections provide the details of these ABCs.

Addresses

In WCF, every service has a unique address. The address provides two important elements
  • Location of the service
  • Transport protocol or transport schema used to communicate with the service.

The location indicates the name of the target machine, site, or network; a communication port, pipe, or queue; and an optional specific path or URI.

WCF supports the following transport schemas:
  • HTTP
  • TCP
  • Peer network
  • IPC (Inter-Process Communication over named pipes)
  • MSMQ\

Addresses have the following format:

[base address]/[URI]
 
(Note: URI is optional and can be omitted, however when it is present it gets merged with the base address to provide the final address, where the service can be located).
 
base address format:
 
[transport]:// [machine or domain][:optional port]
 
Following section is meant only to make you familiar with the various formats that are used with specific type of transport protocol.
 
It can be skipped if desired.
 
Using different available address formats.

TCP Addresses

TCP addresses use net.tcp for the transport and generally uses a port:
 
net.tcp ://{ machine or domain}/ServiceName
 
e.g. Net.tcp//localhost/PService
 
(Note: If a port number is not specified, Port 808 is used as default)

HTTP Addresses

HTTP addresses use http for transport, and https can be used if secure transport is required.
 
e.g.http://localhost:8001
 
When the port number is not mentioned, it defaults to 80.

IPC Addresses

IPC addresses use net.pipe for transport.
 
Note: If a service uses this (i.e. named pipes, it can accept call only from the same machine).
 
e.g. net.pipe://localhost/PrPipe

MSMQ Addresses

MSMQ addresses use net.msmq for transport
 
When private queues are used, queue type needs to be mentioned and is  omitted for public queues:
 
net.msmq://localhost/private/PService (using private queue)
 
net.msmq://localhost/PService             (using Public Queue)

Peer Network Address

Peer network addresses use net.p2p for transport peer network name, path and port needs to be specified..
 
Bindings
 
There are  9 types of Standard Bindings are defined for WCF:

Basic Binding
 
BasicHttpBinding class provides this type of binding.

It  exposes a WCF service as a legacy ASMX web service

This binding is extremely useful when the intent is to design a WCF service that should provide backward compatibility with WebServices.
 
TCP binding
 
NetTcpBinding class provides this type of binding.

It uses TCP for cross-machine communication on the intranet.

It supports a variety of features, including reliability, transactions, and security, and is optimized for WCF-to-WCF communication.

Restriction: It requires both the client and the service to use WCF.

Peer network binding

NetPeerTcpBinding class provides this type of binding and  uses peer networking as a transport. The peer network-enabled client and services all subscribe to the same grid and broadcast messages to it.

IPC binding

NetNamedPipeBinding class provides this type of binding and uses named pipes as a transport for same-machine communication. It is the most secure binding as it cannot accept calls from outside the machine and it supports a number of features similar to the TCP binding.

Web Service (WS) binding

WSHttpBinding class provides this type of binding, and  uses HTTP or HTTPS for transport.

Federated WS binding

WSFederationHttpBinding class provides this type of binding, this is a specialization of the WS binding, offering support for federated security..

Duplex WS binding

WSDualHttpBinding class provides this type of binding .It is similar to the WS binding except it also supports bidirectional communication from the service to the client.

MSMQ binding

NetMsmqBinding class provides this type of binding and uses MSMQ for transport and is suitable for  disconnected queued calls.

MSMQ integration binding

MsmqIntegrationBinding class provides this type of binding and converts WCF messages to and from MSMQ messages.

This is most suitable for usage when Service legacy MSMQ clients interoperability is critical.

Message Transfer Patterns

WCF use the following three messaging patterns:

  1. Simplex,
  2. Duplex
  3. Request-Reply.

Simplex communication is commonly referred to as one-way communication. This approach is used when asynchronous write-only services are required. It simply means if only one directional (client to Service) communication is required, use this pattern.

Duplex communication provides true asynchronous two-way communications. (using callback  operations).

In simplex and duplex communication, the consumer is not locked into waiting for a reply.

Request-Reply: General enough not to provide any details

Defining Bindings is one the most critical stages in WCF Service development.

Correct type of binding can save a lot of time and effort need to build an effective service.

As an effort to make you comfortable in Service development below is the checklist that needs to be referred before finalizing bindings for your service.

Interoperability Level:

Make sure  if communication will only be in  a .NET to .NET scenario, or legacy ASMX service, or if it is to be used by a consumer that adheres to the WS* specifications.

Encoding:

Select correct type of encoding, from among Text Message Transmission Optimization Mechanism (MTOM) Binary.

Transport Protocols

Select from  transport options TCP, HTTP, Named Pipe, and MSMQ.

Messaging patterns : simplex, duplex, and request-reply.

Security Considerations: Windows security, WS-Security, Transport level security.

Transactions and reliable sessions

Contracts:

The contract is a platform-neutral and standard way of describing what the service does.

WCF defines 4 types of contracts.

  1. Service contracts

    Describe which operations the client can perform on the service.
     
  2. Data contracts

    Define which data types are passed to and from the service.
     
  3. Fault contracts

    Define which errors are raised by the service, and how the service handles and propagates errors to its clients.
     
  4. Message contracts

    Allow the service to interact directly with messages. Message contracts can be typed or untyped

Service Type Support

The following are the 3 types of services that can be written with WCF.

  1. Typed Services: These services use exact parameterization(passing the required parameters in the correct order, format and type) when calling a service method and respond with a well-defined type(as expected by the caller).
     
  2. Un-Typed Services: XML is the core of this type as it is used to transport the input parameters and the response output is also in XML. These services are the most flexible, but provide very little value back to the consumer.
     
  3. Typed Message Services: A custom type is defined that will contain the required input parameters and one more type that will wrap up the output parameters. 
             
    This approach is generally known as Request Object / Response Object, since these are the types of
    objects that are result of these types of services.