|
The Media Transfer Protocol (MTP) is an extension to the Picture Transfer Protocol (PTP) communications protocol that allows media files to be transferred atomically to and from portable devices.〔(Media Transfer Protocol Implementation Details ). MTP defined in slide 3〕 Whereas PTP was designed for downloading photographs from digital cameras, Media Transfer Protocol allows the transfer of music files on digital audio players and media files on portable media players, as well as personal information on personal digital assistants. MTP is a key part of WMDRM10-PD,〔 a digital rights management (DRM) service for the Windows Media platform. MTP is part of the "Windows Media" framework and thus closely related to Windows Media Player. Versions of the Microsoft Windows operating system from Windows XP SP2 support MTP. Windows XP requires Windows Media Player 10 or higher;〔(Final Availability of Windows Media Player 10 Brings More Music and More Choices to Music Fans )〕 later Windows versions have built-in support. Microsoft has also made available an MTP Porting Kit for older versions of Windows back to Windows 98. The USB Implementers Forum device working group standardised MTP as a full-fledged Universal Serial Bus (USB) device class in May 2008.〔(MTP, Portable Player Standard: Create Digital Music blog )〕 Since then MTP is an official extension to PTP and shares the same class code.〔(MTP Specification 1.1 on USB.org )〕 ==History== The main purpose of this protocol is to allow only the transfer of media files and associated metadata to and from portable devices, one transfer function, in or out, at a time. It does not support operations such as open, edit and modify. A workaround is to copy to the hosting system for these operations and then copy back. The protocol was originally implemented for use across USB but extended for use across TCP/IP and Bluetooth. Windows Vista supports MTP over TCP/IP. Windows 7 and Windows Vista with the Platform Update for Windows Vista also support MTP over Bluetooth.〔(MTP Over Various Transports )〕 The host connecting to an MTP device is called an ''MTP Initiator'' whereas the device itself is an ''MTP Responder''.〔(MTP Specification )〕 A main reason for using MTP rather than, for example, the USB mass-storage device class (MSC) is that the latter operates at the granularity of a mass storage device block (usually in practice, a FAT block), rather than at the logical file level. In other words, the USB mass storage class is designed to give a host computer undifferentiated access to bulk mass storage, such as compact flash, rather than to a file system, which might be safely shared with the target device (except for specific files which the host might be modifying/accessing). In practice, therefore, when a USB host computer has ''mounted'' an MSC partition, it assumes absolute control of the storage, which then may not be safely modified by the device without risk of data corruption until the host computer has severed the connection. Furthermore, because the host computer has full control over the connected storage device, there is a risk that the host computer may corrupt the file system, reformat it to a file system not supported by the USB device, or otherwise modify it in such a way that the USB device cannot completely understand it. MTP and PTP specifically overcome this issue by making the unit of managed storage a local file rather than an entire (possibly very large) unit of mass storage at the block level. In this way, MTP works like a transactional file system - either the entire file is written/read or nothing. The storage media is not affected by failed transfers. Where the device maintains a database/index of the content of the disk, MTP saves the cost of re-scanning the entire disk every time the content is modified. Additionally, the MTP allows ''MTP Initiators'' to identify the specific capabilities of device(s) with respect to file formats and functionality. In particular, MTP Initiators may have to provide passwords and other information to unlock files, or otherwise enable digital rights management. Nothing specific of this nature is in the core standard but the features are available via vendor extensions. MTPZ, the Zune Extension to MTP specifically denies access to files until authentication has been processed, which is only possible using Windows Media Player 10 or higher. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Media Transfer Protocol」の詳細全文を読む スポンサード リンク
|