Technology principle of mobile phone projection screen

Basic Concept DLNA

The full name of DLNA is digital LIVING network ALLIANCE, which aims to enjoy your music, photos and videos, anywhere anytime, DLNA Living network Alliance) has been launched by Sony, Intel, Microsoft and so on to solve the personal pc, consumer appliances, mobile devices, including wireless networks and wired network interconnection, making digital media and content services unrestricted sharing and growth is possible, At present, the member companies have reached more than 280.

The DLNA standard includes a number of protocols and standards, the most important of which is UPnP. For our current requirements, UPnP will meet all the requirements.

UPnP

Universal Plug and Play (English: Universal Plug and play, referred to as UPnP) is a "Universal Plug and Play Forum" (UPnP? Forum) to promote a set of network protocols. The goal of this Protocol is to enable seamless connectivity between home networks (data sharing, communication and entertainment) and various devices in the corporate network, and to simplify the implementation of the associated networks. UPnP achieves this by defining and publishing UPnP device control protocols based on open, Internet Communication protocol standards.

The concept of UPnP is derived from Plug and Play (Plug-and-play), and Plug and Play is a hot-plug technology.

Protocol stack

The UPnP device architecture includes communication between devices, control points, devices, and control points. The complete UPnP consists of device addressing, device discovery, device description, device control, event notification, and HTML-based description interface components.

1. UPnP is a framework system composed of multilayer protocols, each of which is based on adjacent lower layers and is the basis of adjacent upper layers. Until the application layer is reached. The bottom of the graph is IP and TCP, a total of two layers, which is responsible for the IP address of the device.
2. Layer three is HTTP, HTTPU, HTTPMU, which belongs to the Transfer Protocol layer. The delivery is that the content is "encapsulated" and stored in a specific XML file. The corresponding SSDP, GENA, and soap refer to the data format that is stored in the XML file. To this layer, the IP address of the UPnP device and the problem of transmitting information have been resolved.
3. The fourth layer is the UPnP device architecture definition, which is simply an abstract, common device model. This layer must be used by any UPnP device.
4. The fifth layer is the equipment definition layer of the various professional committees of the UPnP Forum, in which different electrical equipment is defined by different professional committees, for example: the Television committee is responsible for defining the network TV equipment section only, and the air Conditioner Committee is only responsible for defining the parts of the HVAC equipment, and so on. All of the different types of devices are defined as a dedicated architecture or template for use when setting up a device. It can be inferred that the device has been assigned a definite purpose for entering this layer. Of course, these must conform to standardized norms. From now on, UPnP has been able to support most of the devices: from computers, computer peripherals, mobile devices and household consumer electronics, and so on, with the popularity of this system, there will likely be more manufacturers to recognize this standard, ultimately, may evolve into recognized industry standards.
5. The top layer, the application layer, is defined by the UPnP device manufacturer. This layer of information is by the equipment manufacturers to "fill", which is generally provided by the device manufacturer, the device control and operation of the underlying code, and then, is the name of the serial number Ah, the manufacturer of information and other things.

Equipment

A device is a network entity that provides services and is a logical concept in which a house device can contain one or more logical devices. For example, a PC can have two logical devices ——— a video player and a picture browser.

Service

The service is the smallest controllable unit in UPnP, and it includes a series of controllable actions and a set of states that record the current situation of the service. Services are dependent on the presence of the device.

Points

A network terminal that controls the functioning of a UPnP device, which includes a list of device descriptions and related services, a description of the service that is of interest, a control message to control device actions, and a subscription message to the service of interest so that when the service status changes, the time notification is automatically obtained.

Some terms

• Uuid

The UUID meaning is a universal unique identifier (universally unique Identifier), which is designed to allow all elements in a distributed system to have unique identification information, without the need to specify the identification information through the central control terminal. The format is xxxxxxxx-xxxx-xxxx-xxxxxxxxxxxxxxxx (8-4-4-16), respectively, the current date and time, the clock sequence, the globally unique IEEE machine identification number, if there is a network card, from the network card MAC address obtained, no network card is obtained in other ways.

• UDN

A single device name, which is based on a UUID, that represents a device. This value should be unique for the same device at different times.

• Uri

Each resource available on the Web-HTML documents, images, video clips, programs, and so on-is positioned by a common resource identifier (Universal Resource Identifier, referred to as "URI"). URIs generally consist of three parts: a naming mechanism for accessing resources, a host name for a resource, and a name for the resource itself, represented by a path. Consider the following URI, which represents the current HTML 4.0 specification: http://www.webmonkey.com.cn/html/html40/It represents a resource that can be accessed through the HTTP protocol. Located on the host www.webmonkey.com.cn, accessed through the path/HTML/HTML40.

• Url

A URL is a subset of the URI naming mechanism, and the URL is the abbreviation for Uniform Resource location, translated as "Uniform Resource Locator." In layman's words, URLs are strings used on the Internet to describe information resources, mainly used in various WWW client programs and server programs. URLs can be used in a unified format to describe various information resources, including files, server addresses and directories.

• Urn

An updated form of Urn:url, the Uniform Resource name (urn,uniform Resource name). Uniquely identifies an identifier for an entity, but cannot give the location of the entity. Identify persistent Internet resources. Urns can provide a mechanism for locating and retrieving schema files that define a particular namespace. Although normal URLs can provide similar functionality, in this regard, urns are more powerful and easier to manage because urns can reference multiple URLs.

Implementing the work mechanism

The discovery and control of UPnP devices is divided into 6 steps: Addressing, Discovery, description, control, events, and presentation.

These three points are described in the following three articles, respectively.

Overall process

The overall workflow is as follows:

Technology principle of mobile phone projection screen