Universal Plug and Play (UPnP)

Project/DLNA 2013. 10. 28. 22:31


PnP (Plug-and-Play) ; 플러그 앤 플레이

PnP[플러그앤 플레이 또는 피앤피]는 새로운 장치를 컴퓨터에 집어 넣었을 때, 컴퓨터가 그 장치를 자동으로 인식할 수 있는 능력을 주는 표준이다. 사용자는 컴퓨터에게 새로운 주변장치가 추가되었음을 알려줄 필요가 없다. 이러한 새로운 능력이 있기 전에는, 전통적으로 운영체계는 추가 장치의 부착내역을 포함하여 사용자에 의해 정의된 기계장치 구성 내역을 가지고 있어야 했다. 마이크로소프트가 플러그-앤-플레이를 윈도우95 운영체계를 판매하기 위한 홍보전략으로 삼았다. (이와 비슷한 능력이 매킨토시컴퓨터에는 이미 오래 전에 있었다).


UPnP (universal plug and play) ; 범용 플러그 앤 플레이

UPnP는 PC, 주변장치, 지능형 가전제품, 무선 장비 등과 같은 장치들을 네트웍에 접속시켰을 때, 인터넷과 웹 프로토콜을 사용하여 서로를 자동으로 인식할 수 있도록 해주는 표준이다. UPnP를 이용하면, 사용자가 어떤 장치를 네트웍에 추가하면 그 장치는 스스로 구성을 완료하며, TCP/IP 주소를 받고, 다른 장치들에게 자신의 존재를 알리기 위해 인터넷 HTTP에 기반을 둔 발견 프로토콜을 사용하게 된다. 예를 들어, 현재 네트웍에 접속되어 있는 카메라와 프린터가 있고 그 프린터를 통해 사진을 출력하려고 할 때, 카메라의 단추를 누르면 카메라가 "발견 요청" 신호를 네트웍에 보냄으로써 이용 가능한 프린터가 네트웍 상에 있는지 찾도록 할 수 있다. 그러면 그 신호를 받은 프린터는 자신의 위치를 URL의 형태로 카메라에게 응답하게 된다.

카메라와 프린터는 공용의 언어로 XML을 사용하거나, 또는 프로토콜 협상을 통해 어떤 방식으로 의사소통을 할 것인지를 정할 수 있게 된다. 의사소통을 위한 공용언어가 결정되면, 카메라는 프린터를 제어하고 선택된 사진을 출력할 수 있게 된다. 마이크로소프트와 그밖에 UPnP를 후원하는 28개 회사들은 UPnP가 소켓에 전구를 꼽는 것만큼이나 쉽게 어떤 장치나 가전제품들을 가정이나 회사의 데이터 네트웍에 쉽게 추가할 수 있게 되기를 희망하고 있다.


출처 - http://www.terms.co.kr/





Universal Plug and Play (UPnP) is a set of networking protocols that permits networked devices, such as personal computers, printers, Internet gateways, Wi-Fi access points and mobile devices to seamlessly discover each other's presence on the network and establish functional network services for data sharing, communications, and entertainment. UPnP is intended primarily for residential networks without enterprise-class devices.

The UPnP technology is promoted by the UPnP Forum. The UPnP Forum is a computer industry initiative to enable simple and robust connectivity to stand-alone devices and personal computers from many different vendors. The Forum consists of over eight hundred vendors involved in everything from consumer electronics to network computing.

The concept of UPnP is an extension of plug-and-play, a technology for dynamically attaching devices directly to a computer, although UPnP is not directly related to the earlier plug-and-play technology. UPnP devices are "plug-and-play" in that when connected to a network they automatically establish working configurations with other devices.

Overview[edit]

The UPnP architecture allows device-to-device networking of personal computers, networked home appliances, consumer electronics devices and wireless devices. It is a distributed, open architecture protocol based on established standards such as the Internet Protocol Suite (TCP/IP), HTTP, XML, and SOAP. UPnP control points are devices which use UPnP protocols to control UPnP devices.[1]

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. Dynamic Host Configuration Protocol (DHCP) and Domain Name System (DNS) servers are optional and are only used if they are available on the network. Devices can disconnect from the network automatically without leaving state information.

UPnP was published as a 73-part international standard, ISO/IEC 29341, in December, 2008.[2][3][4]

Other UPnP features include:

Media and device independence
UPnP technology can run on many media that support IP including Ethernet, FireWire, IR (IrDA), home wiring (G.hn) and RF (Bluetooth, Wi-Fi). No special device driver support is necessary; common network protocols are used instead.
User interface (UI) Control
UPnP architecture enables devices to present a user interface through a web browser (see Presentation below).
Operating system and programming language independence
Any operating system and any programming language can be used to build UPnP products. UPnP does not specify or constrain the design of an API for applications running on control points; OS vendors may create APIs that suit their customer's needs.[clarification needed]
Programmatic control
UPnP architecture also enables conventional application programmatic control.[clarification needed]
Extensibility
Each UPnP product can have device-specific services layered on top of the basic architecture. In addition to combining services defined by UPnP Forum in various ways, vendors can define their own device and service types, and can extend standard devices and services with vendor-defined actions, state variables, data structure elements, and variable values.

Protocol[edit]

UPnP uses HTTP over UDP (known as HTTPU and HTTPMU for unicast and multicast). UPnP uses UDP due to its lower overhead in not requiring confirmation of received data and retransmission of corrupt packets. As streaming media is time sensitive this has proven a good compromise, even though HTTPU and HTTPMU are specified only in an Internet-Draft that expired in 2001.[5]

UPnP uses UDP port 1900 and TCP port 2869.[6]

Addressing[edit]

The foundation for UPnP networking is IP addressing. Each device must implement a DHCP client and search for a DHCP server when the device is first connected to the network. If no DHCP server is available, the device must assign itself an address. The process by which a UPnP device assigns itself an address is known within the UPnP Device Architecture as AutoIP. In UPnP Device Architecture Version 1.0,[7] AutoIP is defined within the specification itself; in UPnP Device Architecture Version 1.1,[8] AutoIP references IETF RFC 3927.[9] 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.

Discovery[edit]

Once a device has established an IP address, the next step in UPnP networking is discovery. The UPnP discovery protocol is known as the Simple Service Discovery Protocol (SSDP). When a device is added to the network, SSDP allows that device to advertise its services to control points on the network. Similarly, when a control point is added to the network, SSDP 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.

Description[edit]

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.

Control[edit]

Having 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). Much like function calls, the service returns any action-specific values in response to the control message. The effects of the action, if any, are modeled by changes in the variables that describe the run-time state of the service.

Event notification[edit]

An additional capability of UPnP networking is event notification, or eventing. The event notification protocol defined in the UPnP Device Architecture is known as General Event Notification Architecture (GENA). 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. 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).

Presentation[edit]

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 standards[edit]

UPnP AV is an audio and video extension of UPnP. On 12 July 2006 the UPnP Forum announced the release of version 2 of the UPnP Audio and Video specifications,[10] with new MediaServer version 2.0 and MediaRenderer version 2.0 classes. These enhancements are created by adding capabilities to the 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.

The UPnP AV standards have been referenced in specifications published by other organizations including Digital Living Network Alliance Networked Device Interoperability Guidelines,[11] International Electrotechnical Commission IEC 62481-1,[12] and Cable Television Laboratories OpenCable Home Networking Protocol.[13]

UPnP AV components[edit]

Media server[edit]

A UPnP AV media server is the UPnP-server ("master" device) that provides media library information and streams media-data (like audio/video/picture/files) to UPnP clients on the network. It is a computer system or a similar digital appliance that stores digital media, such as photographs, movies, or music and shares these with other devices.

UPnP AV media servers provide a service to UPnP AV client devices, so called control points, for browsing the media content of the server and request the media server to deliver a file to the control point for playback.

UPnP media servers are available for most operating systems and many hardware platforms. UPnP AV media servers can either be categorized as software-based or hardware-based. Software-based UPnP AV media servers can be run on a PC. Hardware-based UPnP AV media servers may run on any NAS devices or any specific hardware for delivering media, such as a DVR. As of May 2008, there were more software-based UPnP AV media servers than there were hardware-based servers.

Other components[edit]

  • UPnP MediaServer ControlPoint - which is the UPnP-client (a 'slave' device) that can auto-detect UPnP-servers on the network to browse and stream media/data-files from them.
  • UPnP MediaRenderer DCP - which is a 'slave' device that can render (play) content.
  • UPnP RenderingControl DCP - control MediaRenderer settings; volume, brightness, RGB, sharpness, and more.
  • UPnP Remote User Interface (RUI) client/server - which sends/receives control-commands between the UPnP-client and UPnP-server over network, (like record, schedule, play, pause, stop, etc.).
  • QoS (Quality of Service) - is an important (but not mandatory) service function for use with UPnP AV (Audio and Video). QoS (Quality of Service) refers to control mechanisms that can provide different priority to different users or data flows, or guarantee a certain level of performance to a data flow in accordance with requests from the application program. Since UPnP AV is mostly to deliver streaming media that is often near real-time or real-time audio/video data which it is critical to be delivered within a specific time or the stream is interrupted. QoS (Quality of Service) guarantees are especially important if the network capacity is limited, for example public networks, like the internet.
    • QoS (Quality of Service) for UPnP consist of Sink Device (client-side/front-end) and Source Device (server-side/back-end) service functions. With classes such as; Traffic Class that indicates the kind of traffic in the traffic stream, (for example, audio or video). Traffic Identifier (TID) which identifies data packets as belonging to a unique traffic stream. Traffic Specification (TSPEC) which contains a set of parameters that define the characteristics of the traffic stream, (for example operating requirement and scheduling). Traffic Stream (TS) which is a unidirectional flow of data that originates at a source device and terminates at one or more sink device(s).
  • Remote Access - defines methods for connecting UPnP device sets that are not in the same multicast domain.

NAT traversal[edit]

One solution for NAT traversal, called the Internet Gateway Device Protocol (IGD Protocol), is implemented via UPnP. Many routers and firewalls expose themselves as Internet Gateway Devices, allowing any local UPnP control point to perform a variety of actions, including retrieving the external IP address of the device, enumerate existing port mappings, and add or remove 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.

Problems with UPnP[edit]

Lack of authentication[edit]

The UPnP protocol, as default, does not implement any authentication, so UPnP device implementations must implement their own authentication mechanisms, or implement the Device Security Service.[15] There also exists a non-standard solution called UPnP-UP (Universal Plug and Play - User Profile)[16][17] which proposes an extension to allow user authentication and authorization mechanisms for UPnP devices and applications. Unfortunately, many UPnP device implementations lack authentication mechanisms, and by default assume local systems and their users are completely trustworthy.[18][19]

Due to the lack of authentication mechanisms, routers and firewalls running the UPnP IGD protocol are vulnerable to attack. For example, Adobe Flash programs are capable of generating a specific type of HTTPrequest which 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.[20] 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. 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.[21] As a result, some UPnP devices ship with UPnP turned off by default as a security measure.

Access from the Internet[edit]

In 2011, researcher Daniel Garcia developed a tool designed to exploit a flaw in some UPnP IGD device stacks that allow UPnP requests from the Internet.[22][23] The tool was made public at DEFCON 19 and allows portmapping requests to external IP addresses from the device and internal IP addresses behind the NAT. The problem is widely propagated around the world, with scans showing millions of vulnerable devices at a time.[24]

In January 2013 the security company Rapid7 in Boston reported[25] on a six-month research programme. A team scanned for signals from UPnP-enabled devices announcing their availability for internet connection. Some 6900 network-aware products from 1500 companies at 81 million IP-addresses responded to their requests. 80% of the devices are home routers, others include printers, webcams and surveillance cameras. Using the UPnP-protocol, many of those devices can be accessed and/or manipulated.

Future developments[edit]

UPnP continues to be actively developed. In the fall of 2008, the UPnP Forum ratified the successor to UPnP 1.0, UPnP 1.1.[26] See [27] for documents describing the published standard.

The DPWS standard was a candidate successor to UPnP, but UPnP 1.1 was selected by the Forum.

The UPnP Internet Gateway Device (IGD)[28] standard has a WANIPConnection service that contains a competing solution known as NAT-PMP, which is an IETF draft introduced by Apple Inc. in 2005. However, NAT-PMP is focused only on NAT traversal. Version 2 of IGD is currently under development.[29]

See also[edit]



출처 - http://en.wikipedia.org/wiki/Universal_Plug_and_Play#UPnP_AV_standards



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