Introduction to MTP (Media Transfer Protocol) and PTP (Picture Transfer Protocol)

1. MTP & PTP
William.L
wiliwe@gmail.com
2011-10-13

2. Outline
Overview
Protocol Intro
MTP & DRM
MTP & UMS
MTP/PTP in Android

3. Overview

4. PTP / MTP (1/2)
Picture Transfer Protocol
Define a common protocol of controlling and transferring
files (photographs) for digital still image devices (ex:
cameras)
PIMA / ISO 15740
Commonly implemented over the USB and FireWire
Media Transfer Protocol
An extension of PTP
USB-IF MTP 1.0
Target primarily at
Digital Still Cameras
Portable Media Players
Cellular phones
Support DRM

5. PTP / MTP (2/2)
PTP and MTP are application layer protocols
The term ”media” in MTP
Used to identify any binary data
Not restricted to audio/video formats
Non-audio/video objects include contacts, schedules
and text files

6. PTP/MTP Supported by OS (1/2)
Microsoft Windows
WIA (Windows Image Acquisition/Architecture)
A driver model and API for Windows Me and later Windows
operating systems
Enables software to communicate with imaging device such as
scanners, digital cameras and digital video equipments
Still Image Connectivity for Windows
http://msdn.microsoft.com/en-us/windows/hardware/gg463507.aspx
MTP is part of the "Windows Media" framework and thus
closely related to Windows Media Player
Built-in support : Windows Visa and Win7
WinXP with Windows-Media-Player 10 or higher
PlayForSure certification for devices

7. PTP/MTP Supported by OS (2/2)
Linux
mtpfs
libptp2
libgphoto2
libmtps
Tools : gMTP(GUI), mtptools(CLI), etc

8. MTP v.s PTP
MTP permits transfer of large(>4GByte) items
MTP allows the data to be broken into different
USB packets
This allows USB chips to process the packets more
efficiently

9. MTP Enhanced
From Microsoft
Based on MTP 1.0
Contains additional operations, events and responses
to enable more advanced functionality specific to
particular device classes, media types and application
scenarios
Devices designed for Windows should implement MTP
Enhanced
Specification
http://www.microsoft.com/download/en/details.aspx?id=196
78

10. Protocol Intro

11. Layered Protocol
Physical layer : USB protocol
Transport layer is taken directly from PTP (USB Still
Image Class, class ID is 6)
Command layer
PTP/MTP treat most things on devices as Objects
Most of PTP/MTP commands deal with Objects,
ex:GetObjectInfo, GetNumObjects

12. Device Roles in Protocol
Initiator - Responder
Initiator
Send operations/requests
Responder
Responds for requests
Fires events
Connect, identifies as using MTPConnect, identifies as using MTP
Device capabilityDevice capability
Request device informationRequest device information
Request list of contentsRequest list of contents
Request metadata describing contentRequest metadata describing content
Array of handles to contentArray of handles to content
Send metadataSend metadata
Object exchangeObject exchange
Responder Initiator

13. Other Transport Media (1/2)
Transport-Independent
MTP/PTP were originally implemented for use
across USB but extended for use across TCP/IP
and Bluetooth
Over TCP/IP
PTP-IP, "Picture Transfer Protocol" over TCP/IP networks
CIPA DC-005-2005 standard
Windows 7 and Windows Vista support
Ideal for devices with WiFi that can be connected and
synchronized anywhere in the home

14. Other Transport Media (2/2)
Over Bluetooth
Over the L2CAP (Logical Link Control and
Adaptation Protocol)
The specification is available in the Windows Portable
Device Enabling Kit
Windows 7 and Windows Vista (with the Platform
Update) support
Requires Bluetooth 1.2 or higher with the Microsoft
Bluetooth stack installed
Great for low power, low speed scenarios like
synchronizing PIM data or a quick file transfer

15. MTP & DRM

16. DRM
Digital Rights Management
The protection of licensed or purchased audio or
video content, is extemely important in the
handheld consumer market
DRM prevents a copyrighted file from being
played in another player than the one it was
originally downloaded to
But, if one place where has DRM-Unlock tools, it can
play file normally
With uncontrolled ability to transport digital
content, content provider will remain reluctant to
release digital material such as movies

17. DRM Support In MTP
MTP provide DRM specific properties
DRM status
Determine if an object has DRM protection
To expose whether an object will be playable after being
transferred to a different device
URL
To allow DRM to ask for money when the license rights
expire (link to the payment site)
Use count
The number of times of an object has been played or
viewed

18. MTP & UMS

19. USB Mass Storage (1/2)
USB Mass Storage
Also called USB MSC(Mass Storage Class)
An USB device that can store data
Most portable media players and still image
devices have adopted for their internal memory
where users save their media files
Lack DRM support

20. USB Mass Storage (2/2)
Can not be accessed by the PC and device
itself at the same time
Device Storage
USB/ATAPI Bridge
Driver Framework
USBStor
Device
Player CPU
Automatic
Switch
MSC
PCPC
DeviceDevice
With MSC,
content
Storage is
managed
by the PC
“switch” means “mount/unmount”.
When the device storage is used by
the PC, the storage will be
unmounted from the device.
Otherwise, it is mounted to the device.

21. MTP v.s UMS
YESNONeed specific driver to access device’s
storage on Microsoft Windows
7/Vista/XP
YESNOCan do common disk recovery
MoreLessAmount of Devices Ready to Support
YES
MTP
NODRM Support
UMS

22. MTP/PTP in Android

23. Support MTP/PTP file transfer since Android
3.0(Honeycomb)
MTP programming APIs are provided from
Android 3.1
MtpObjectInfo::getProtectionStatus()
To retrieve the DRM protection status