Universal Plug and Play (UPnP) is a set of computer network protocols promulgated by the UPnP Forum. The goals of UPnP are to allow devices to connect seamlessly and to simplify the implementation of networks in the home (data sharing, communications, and entertainment) and corporate environments. UPnP achieves this by defining and publishing UPnP device control protocols built upon open, Internet-based communication standards.
The term UPnP is derived from plug-and-play, a technology for dynamically attaching devices directly to a computer.
[hide]
The UPnP architecture allows peer-to-peer networking of PCs, networked appliances, and wireless devices. It is a distributed, open architecture based on established standards such as TCP/IP, UDP, HTTP and XML.
The UPnP architecture supports zero-configuration networking. A UPnP compatible device from any vendor can dynamically join a network, obtain an IP address, announce its name, convey its capabilities upon request, and learn about the presence and capabilities of other devices. DHCP and DNS servers are optional and are only used if they are available on the network. Devices can leave the network automatically without leaving any unwanted state information behind.
Other UPnP features include:
The foundation for UPnP networking is IP addressing. Each device must have a Dynamic Host Configuration Protocol (DHCP) client and search for a DHCP server when the device is first connected to the network. If no DHCP server is available, that is, the network is unmanaged, the device must assign itself an address. If during the DHCP transaction, the device obtains a domain name, for example, through a DNS server or via DNS forwarding, the device should use that name in subsequent network operations; otherwise, the device should use its IP address.
Given an IP address, the first step in UPnP networking is discovery. When a device is added to the network, the UPnP discovery protocol allows that device to advertise its services to control points on the network. Similarly, when a control point is added to the network, the UPnP discovery protocol allows that control point to search for devices of interest on the network. The fundamental exchange in both cases is a discovery message containing a few, essential specifics about the device or one of its services, for example, its type, identifier, and a pointer to more detailed information. The UPnP discovery protocol is based on the Simple Service Discovery Protocol (SSDP).
The next step in UPnP networking is description. After a control point has discovered a device, the control point still knows very little about the device. For the control point to learn more about the device and its capabilities, or to interact with the device, the control point must retrieve the device's description from the URL provided by the device in the discovery message. The UPnP description for a device is expressed in XML and includes vendor-specific, manufacturer information like the model name and number, serial number, manufacturer name, URLs to vendor-specific web sites, etc. The description also includes a list of any embedded devices or services, as well as URLs for control, eventing, and presentation. For each service, the description includes a list of the commands, or actions, to which the service responds, and parameters, or arguments, for each action; the description for a service also includes a list of variables; these variables model the state of the service at run time, and are described in terms of their data type, range, and event characteristics.
The next step in UPnP networking is control. After a control point has retrieved a description of the device, the control point can send actions to a device's service. To do this, a control point sends a suitable control message to the control URL for the service (provided in the device description). Control messages are also expressed in XML using the Simple Object Access Protocol (SOAP). Like function calls, in response to the control message, the service returns any action-specific values. The effects of the action, if any, are modeled by changes in the variables that describe the run-time state of the service.
The next step in UPnP networking is event notification, or "eventing". A UPnP description for a service includes a list of actions the service responds to and a list of variables that model the state of the service at run time. The service publishes updates when these variables change, and a control point may subscribe to receive this information. The service publishes updates by sending event messages. Event messages contain the names of one or more state variables and the current value of those variables. These messages are also expressed in XML and formatted using the General Event Notification Architecture (GENA). A special initial event message is sent when a control point first subscribes; this event message contains the names and values for all evented variables and allows the subscriber to initialize its model of the state of the service. To support scenarios with multiple control points, eventing is designed to keep all control points equally informed about the effects of any action. Therefore, all subscribers are sent all event messages, subscribers receive event messages for all "evented" variables that have changed, and event messages are sent no matter why the state variable changed (either in response to a requested action or because the state the service is modeling changed).
The final step in UPnP networking is presentation. If a device has a URL for presentation, then the control point can retrieve a page from this URL, load the page into a web browser, and depending on the capabilities of the page, allow a user to control the device and/or view device status. The degree to which each of these can be accomplished depends on the specific capabilities of the presentation page and device.
UPnP AV stands for UPnP Audio and Video, and is a grouping within the UPnP standards supervised by the DLNA (Digital Living Network Alliance), (formerly: Digital Home Working Group), which is a forum of vendors and manufacturers who work in the home entertainment industry, and offer a "DLNA CERTIFIED™" branding for those products which follow their Networked Device Interoperability Guidelines. The DLNA forum members "share a vision of a wired and wireless interoperable network of Personal Computers (PC), Consumer Electronics (CE) and mobile devices in the home enabling a seamless environment for sharing and growing new digital media and content services," and "DLNA is focused on delivering an interoperability framework of design guidelines based on open industry standards to complete the cross-industry digital convergence". On 12 July 2006 the UPnP Forum announced the release of 'Enhanced AV Specifications', this release was version 2 of the UPnP Audio and Video specifications (UPnP AV v2), with new MediaServer version 2.0 and MediaRenderer version 2.0 classes. These enhancements are created by adding capabilities to the UPnP AV MediaServer and MediaRenderer device classes that allow a higher level of interoperability between MediaServers and MediaRenderers from different manufacturers. Some of the early devices complying with these standards were marketed by Philips under the Streamium brand name. .
One solution for NAT (Network Address Translation) traversal, called the Internet Gateway Device (IGD) Protocol, is implemented via UPnP. Many routers and firewalls expose themselves as Internet Gateway Devices, allowing any local UPnP controller to perform a variety of actions, including retrieving the external IP address of the device, enumerate existing port mappings, and adding and removing port mappings. By adding a port mapping, a UPnP controller behind the IGD can enable traversal of the IGD from an external address to an internal client.
The UPnP protocol does not implement any authentication, so UPnP device implementations must implement their own authentication mechanisms, or implement the Device Security Service.[2] Unfortunately, many UPnP device implementations lack authentication mechanisms, and by default assume local systems and their users are completely trustworthy.[3][4] Most notably, Routers and firewalls running the UPnP IGD protocol are vulnerable to attack since the framers of the UPnP implementation omitted to add any standard authentication method.
For example, Adobe Flash programs are capable of generating HTTPU (HTTP over UDP) requests. This allows a router implementing the UPnP IGD protocol to be controlled by a malicious web site when someone with a UPnP-enabled router simply visits that web site.[5] The following changes can be made silently by code embedded in an Adobe Flash object hosted on a malicious website[6]:
This only applies to the "firewall-hole-punching"-feature of UPnP; it does not apply when the IGD does not support UPnP or UPnP has been disabled on the IGD.[citation needed] Also, not all routers can have such things as DNS server settings altered by UPnP because much of the specification (including LAN Host Configuration) is optional for UPnP enabled routers[7].
The standard DPWS is a candidate successor for UPnP. It solves many of the problems of UPnP. A DPWS client is included in Microsoft Windows Vista as part of the Windows Rally technologies.
Another alternative, NAT-PMP, is an IETF draft introduced by Apple Inc in 2005.
此内容由惯性聚合(RSS阅读器)自动聚合整理，仅供阅读参考。 原文来自 — 版权归原作者所有。