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Web Services on Devices (WSD) expand the existing Web services architecture to resource-constrained devices, examples like consumer electronics, PDAs, computer peripherals and computing appliances. Web Services on Devices is one of four technologies that consist of the Network Connected Device (NCD). The four technologies are PnP-x, Function Discovery, WSD and Publication Services.
These NCD technologies enable virtually-connected devices (those connected to a computer over a network) to appear and act as if they were physically connected. Such devices are loosely connected to one or more computers and use the network as a communication bus.
Web Service on Devices API (WSDAPI) is an implementation of the Devices Profile for Web Services (DPWS). WSDAPI is implements for Windows Vista and Windows Server 2008. The DPWS force Web Services specifications so clients can easily discover devices. Once a device is discovered, a client can retrieve a description of services hosted on that device and use those services.
Devices are components, usually means hardware, which are attached to the network. Eg. printers, Web cameras, and video systems.
Devices may consist of zero or more services. For eg, a video device may include services that support power on and off, media ejection, play control and video streaming. Play control may support actions such as play, pause, rewind, and fast forward.
Discussion: Discovering And Manipulating Web Services On Devices
WSDAPI expands the local Plug and Play model by providing a client to discover and access a remote device. The devices associated services across a network. The services support discovery, one-way and two-way control messaging, and eventing.
The following figure shown WSDAPI is connecting the client and device together using WSDAPI. WSDAPI is a bridge between client and devices.
DPWS devices declare their occurrence and discover services (if any) using a unique address and a standardized set of XML messages. DPWS clients can use the discovery process as below:
find the device,
enumerate its services, and
connect to those services to perform specific actions.
A WSDAPI client first inquiry the device for complete descriptions of its services, including the service types. The service types such as a scanner service type or a printer service type. The client then controls the device by calling commands defined by a service type. For example like by calling CreatePrintJob on a device with a printer service type. In others, the client also can monitor each state changes in each service by subscribing to events that occur during command execution.
The above figure shown the device is joins to the client 1, client 2 and client 3 network. Client 3 cans discovery and manipulating the device as following steps:
client discovery the devices
device respond the description to the client
client can control the device after receive the description
device will send the event to client from time to time
What is Web Services for Devices?
A web service for devices is a collective term that is used for a number of products and services and enhanced the use of Internet technology. Basically, many products that we used in past are built on a foundation of technologies other than the World Wide Web are now enhanced by the presence of Internet connections.
Examples of Common Web Services For Devices
The first web services for devices developed were use Internet to allow remote printing. Formerly, printers need a direct wire connection to a network hub in order to function. Now, a person who travels out can send documents for printing directly to a printer at the home office, and the document print out in few minutes. In a same theory, we possible to use the Internet to send a document to a fax machine for printing as well.
PDA and the Internet phone are also examples of web services for devices. Wireless technology has made the devices to connect with an Internet service provider, browse the web, telephone calls, faxes documents, and send email, all from a handheld device.
Voice over Internet Protocol is also considered part of the basic web services for devices enhancements as well. It is now possible to use traditional land lines as part of the equipment that is used to make local, national, and international phone calls using audio streaming across the Internet. Essentially, the signal is converted from a standard phone signal to a data stream, and makes its way across the Internet to the point of termination. The point of termination may be a land line using traditional fiber optic technology, a cell phone, or a computer connected to the Internet and set up with software for making and receiving phone calls. The use of the latest versions of JAVA and XMTL make this process appear seamless to users, and help to maintain the integrity of the connections.
Web services for devices also make use of home security and control as well. Persons who are traveling may use the Internet to manage activities at home, such as turning lights off and on, adjusting the heating thermostat, of even viewing images that are captured by security cameras on the premises. The ability to manage home controls while away is one of the more current developments in web services for devices, and will no doubt become increasing popular over the next few years.
Web services for devices are generally developed with an eye toward taking something that persons already use, and making that use even better by means of a connection to the Internet. As time goes on, there will no doubt be additional devices that will become part of the family of web services that we all reply upon.