In Windows 7, computers can interact with devices in the home network by using one of the following scenarios:
Scenario 1: The PC acts as the source of content for networked devices.
Scenario 2: The PC acts as the receiver of content from networked devices.
Scenario 3: The PC acts as a media manager and selects content from sources and sends content to receivers.
In Scenario 1, users keep a large collection of media in their PCs and make the content available to other devices that are connected to the home network by sharing their media libraries. The PC acts as a media server when it is connected to the network. Windows 7 improves the interoperability of this scenario by adding support for media players and media controllers that follow DLNA standards.
In Scenario 2, users store content in different storage devices such as NAS, DVR, and cameras, and use a PC to browse, search, and play the stored content. In this scenario, the receiving PC acts as a media player when it is connected to the network. Windows 7 improves the interoperability of this scenario by adding support for media servers that are based on DLNA standards, in addition to shared libraries from Windows PCs and Windows Home Server.
Figure 1 shows the three scenarios.
Figure 1. The three main scenarios for connecting devices with Windows 7 PCs
A second way exists to use a PC as a receiver. Some devices in the network include the ability to push content. In this case, the user browses content that is stored on the device itself by using the device user interface (UI), and then instructs a receiving PC to play the content. The PC acts as a media renderer when it is connected to the network.
In Scenario 3, a user discovers media servers and media renderers that are available in the network. The PC UI differentiates between content that exists in the local media library and content that exists in other media servers on the network. The user can search and browse the content and examine all the information that is available for each content item. The user can select content from any media server and push it to any media receiver. The PC acts as a media controller when the user selects content from a shared library on a media server; it acts as a push controller when the user selects content from the local media library.
Overview of Networked Media Device Roles for Windows 7
Windows 7 natively implements and interoperates with network media devices that perform the following roles:
Digital media server (DMS)
Digital media renderer (DMR)
Digital media player (DMP)
Digital media controller (DMC)
Digital Media Server
A user who opens Windows Media Player or Windows Media Center (from the PC or from an Extender for Windows Media Center) can browse, interact with, and play content from any device that implements the DMS role in the home network. A DMS is a DLNA-defined networked device role. A DMS exposes content to the network and, when content is requested, it transfers that content to the requesting device. Exposing and transferring content are the two fundamental functions that this device performs. A DMS exposes content to the network by using a UPnP service called a content directory service. The content directory service defines a protocol to query the DMS database and to describe the media in the database. A DMS transfers content to the network by using the HTTP protocol with extensions to support trick modes such as fast forward and fast rewind, transfer modes such as stream or download, and so on.
In Windows 7, discovery of media servers on the network is automatic and requires no configuration. In Windows Media Player, media servers are known as Other Libraries and are prominently displayed in the navigation pane. Figure 2 shows the automatic discovery of a digital media server named Karen (desktop) under Other Libraries in the navigation pane of Windows Media Player.
Figure 2. Windows 7 displaying shared libraries in Windows Media Player
In Windows Media Center, media servers can be browsed in the new shared pivot view of all libraries: music, pictures, videos, and recorded TV. The shared pivot is available from each music, pictures, video, and recorded TV media library. Figure 3 shows the discovery of media servers in the new shared pivot view of Windows Media Center.
Figure 3. Windows Media Center automatically discovering the shared music library
In addition to automatic DMS discovery in Windows Media Player and Windows Media Center, media servers are automatically discovered in Network Explorer. Network Explorer is available from the navigation pane of Windows Explorer. By selecting a media server in Network Explorer, Windows Media Player is started to interact with the shared media library. Figure 4 shows the discovery of media servers, media players, and media renderers in Network Explorer.
Figure 4. Network Explorer discovering available devices and services on the network
In addition to automatically discovering network media devices that implement the DMS role on the network, Windows 7 also performs the DMS role through the Windows Media Player NSS. Users can enable this functionality from the Advanced Sharing Settings in Control Panel or in Windows Media Player from the Share menu. Both methods open Share with Media Devices in Control Panel, which enables users to configure media sharing, including the ability to allow or block users and devices from accessing the shared media library. Figures 5 and 6 show the Share menu in Windows Media Player and the resultant Control Panel, which provides the option to enable sharing with media devices.
Figure 5. Windows Media Player displaying media-sharing features
Figure 6: The Share with Media Devices application in Control Panel displaying available media player and rendering devices
After they choose to share with media devices, other Windows PCs, media player devices, and media controllers (described in further detail later in this paper) can automatically discover the DMS and play content from the media library.
Figure 7 shows the protocol layers in a digital media server. DMS devices support Wi-Fi or Ethernet for connectivity. DMS devices implement Transmission Control Protocol/Internet Protocol (TCP/IP),User Datagram Protocol (UDP)/IP, and HTTP. DMS devices implement HTTP and extensions to transfer content to other devices in the network. Some DMS devices use RTP for transfer. DMS devices implement the UPnP MediaServer functionality that includes two services:
Content directory service (CDS)
Connection manager service (CMS)
Figure 7: Protocol stack for a digital media server
To expose media through the CDS from the Windows 7 NSS, the files must be added to the Windows Media Player library. Windows 7 and Windows Media Player provide a simple interface to identify which folders contain files to be shared as a library. Music, pictures, videos, and recorded TV that are added to the Windows 7 library are automatically added to the Windows Media Player library and shared, if media sharing is enabled. Only content that is supported for playback by Windows Media Player is shared. Figure 8 shows Windows 7 libraries. Media files or folders that are added to a library are added to Windows Media Player and can be shared by the NSS.
Figure 8. Windows 7 library view from Windows Explorer
The following sections describe the formats that are supported for each content type, including the associated file name extension and Multipurpose Internet Mail Extensions (MIME) type. The NSS does not expose content for which the MIME type cannot be determined. For a device to play a format that NSS supports, the device must also support the codec that is appropriate for the format. Note that various codecs can be used for some formats such as WAV, MPEG-4, and audio video interleave (AVI).
The Windows 7 Network Sharing Service supports audio formats shown in Table 1.
Format support in Windows Media Player is extensible. You can add media formats to Windows Media Player by installing the appropriate codec and creating the appropriate registry keys on the system that is running Windows Media Player. Formats that are supported in Windows Media Player are also supported by the Windows 7 NSS. For more information, see “Resources” at the end of this paper.