Vehicle Networks. Multimedia Protocols. Univ.-Prof. Dr. Thomas Strang, Dipl.-Inform. Matthias Röckl

Transcription

1 Vehicle Networks Multimedia Protocols Univ.-Prof. Dr. Thomas Strang, Dipl.-Inform. Matthias Röckl

2 Outline Introduction to media-oriented networking: Media Oriented Systems Transport (MOST) Physical Layer Application Framework Higher Layer Protocols

3 Introduction to media-oriented networking

4 Introduction Automotive media-oriented networking Automobiles have evolved from having a simple radio with perhaps a cassette or CD player to having a variety of sophisticated entertainment and information systems that need to communicate and interact with each other and with a human user [Most Cooperation] Why do these devices need networking? Muting of the radio when a phone call is received Shared displays for radio, navigation, rear-view camera, etc. Traffic information transmitted to the radio (RDS/TMC) can be used for efficient navigation Why do media-oriented devices need a new networking protocol? Safety-critical applications require reliable, real-time networking Information/Entertainment (=Infotainment) applications require fast, short-delay networking with continuous bandwidth availability

5 Introduction Bandwidth requirements High data rate required, e.g. audio signal: khz * 16 bit quantization (CD quality) * 2 channels (stereo) required data rate = 1.4 MBit/s (cannot be achieved by CAN) Streaming data (audio, video) as well as packet-based data (e.g. map data for navigation) need large amount of bandwidth with short delay Based on: Audi: Neute Datenbussysteme

6 RECAP Introduction Sampling

7 Introduction Sampling The analog to digital conversion obtained through a sampling process with fixed frequency f s, with a uniform quantization over N levels is named Pulse Code Modulation (PCM) Voice telephony (ISDN): 8 khz * 8 bit quantization CD: khz * 16 bit quantization Nyquist-Shannon Theorem f S 2B f S = Sampling rate B = Bandwidth of the signal RECAP

8 Media-Oriented Systems Transport (MOST)

9 Overview Media Oriented Systems Transport (MOST) MOST cooperation (BMW, Daimler, Audi, Harman-Becker, Oasis) founded in 1998 Used by 16 car makers and more than 70 suppliers Application in BMW series 7, Audi A6/A8/Q7 Transmission of streaming data (e.g. entertainment system) and packetbased data (internet information) Based on D2B (developed by Daimler) Standardization of all 7 ISO/OSI protocol layers

10 MOST in ISO-OSI reference model No. of layer ISO/OSI ref model 7 Application 6 Presentation 5 Session 4 Transport 3 Network Function Block MOST protocol specification Function Block Function blocks Network Service Layer 2 (Application Socket) Network Service Layer 1 (Basic Level) Function Block 2 Data Link Low-level System Services 1 Physical Physical Layer Stream Service

11 Source: MOST Cooperation

12 Types MOST25 3 channels: asynchronous, synchronous and control information Max. data rate: 25 MBit/s@48kHz Optical transmission over Plastic Optical Fiber (POF) MOST50 More flexibility in channel assignment Max. data rate: 50 MBit/s@48kHz Electrical transmission over Unshielded Twisted Pair (UTP) MOST150 October 2007 Isochronous transmission on synchronous channel for HDTV Max. data rate: 150 MBit/s@48kHz Enhancement for 100Base-T Ethernet

13 Topology Logical ring with n nodes Physically there are (n-1) Point-to-Point connections with signal regeneration in every node Logical ring can be implemented on a physical ring or star network Inactive nodes bypass the data (bypass mode) Active nodes receive the data stream, add data and transmit the resulting data stream to their successor

14 Physical Layer Outer cladding Inner cladding Line Coding: Differential Manchester Plastic Optical Fiber (POF): Resistance against Electro-Magnetic Interference (EMI) High data rates Little weight Little heat emission Cheaper than glass fiber Based on: Audi: Neute Datenbussysteme Fluorinated Polymers Core (polycarbonate) Signal reflection

15 Functioning at a glance Time master periodically generates frames One after the other slave on the logical ring 1. receives the signal, 2. synchronizes itself with the preamble 3. parses the frame 4. processes the desired information (control or data) 5. adds information to the free slots in the frame 6. transmits the frame to its successor When the frame eventually returns to the time master it synchronizes itself and subsequently generates the next frame in accordance to the frame rate Source: Grzemba 2008: MOST

16 Synchronization Time master sends MOST frames to its successor in the logical ring with a network-wide consistent frame rate Periodicity: up to 48 khz (DVD) typical khz (CD) If a time slave works with a different sampling rate (e.g. DVD player), the slave has to convert the data according to the system s frame rate Every slave synchronizes with the frame preamble by a Phase-Locked Loop (PLL) Time master often integrated in the HMI of the infotainment system Source: Grzemba 2008: MOST

17 Application Framework Application e.g. audio player Uses a function of a Slave or HMI Data sources Application e.g. route guidance Controller Slave Provides functions to the Controller Human-Machine Interfaces

18 Function blocks Functions are grouped in standardized interfaces (= function blocks) Interoperability and interchangeability: e.g. device that provides a GUI interface can be used by every device that requires a GUI Similar to Profiles of Bluetooth and CANopen Function blocks provide functions, i.e. Properties: specification of a specific device characteristic (e.g. current frequency of the radio tuner) Methods: trigger an action (e.g. radio station scan) Controller application reads and modifies properties of the slaves registers for particular events (property changes) of the slaves calls messages of the slaves

19 Function blocks Every MOST node has to implement at least one function block, the NetBlock Examples of function blocks: NetBlock: Management of all function blocks on the device Management of all addresses of the device (physical address, logical address, group address) Power Master: startup and shutdown of the network Network Master: Startup of the system Monitoring of the network status Administration of the Central Registry (list of all function blocks within the network) Connection Master: setup and disconnection of the synchronous channel Application-specific function blocks: Application-specific functions (start playing, mute, etc.) Proprietary device functions of the manufacturer (e.g. software update)

20 Addressing Addressing scheme: [DeviceID.]FBlockID.InstID.FktID.OptType.Length(Data) Element Bit Size Description DeviceID FBlockID InstID FktID OptType Length Data 16 bits Identifiers the device (optional) 8 bits Identifies the Function block 8 bits Identifies the instance of the function block 12 bits Identifies the function to use (number of property or method) 4 bits Identifies the type of operation (set, get, start, stop, etc) 16 bits Indicates the length of the data bits Data area for the parameters of the function Address scheme allows addressing of function blocks (FBlockID + InstID) independent of the device that implements the function block Address types: Functional addressing: Every node has a unique address according to its position in the logical ring Logical addressing: Arbitrary addressing of nodes independent of underlying topology (address assignment controlled by master) Broadcast address: Addressing of all nodes in the logical ring Group address: Addressing of logical groups (e.g. all diagnostic FBlocks)

21 Message sequence Get-Operation: Notification-Function: Source: Grzemba 2008: MOST

22 MOST25 Frame (values between ) Based on: Grzemba 2008: MOST

23 Control channel Transportation of commands, status and diagnostic information Control channel is used to set up what streaming data channels the sender and receiver are to use Once the connection is established, data can flow continuously and no further addressing or processing of packet label information is required Features: Low data rate (768 kbit/s) and short packets for low control overhead Error detection by CRC and positive/negative acknowledgements (ACK/NAK) by overwriting acknowledgement field Automatic retry after error (low level retries) In order to prevent high control overhead in frames, control information (2 bytes in every MOST25 frame) is distributed over 16 frames (=1 block) Prioritization by arbitration

24 Synchronous channel Transportation of streaming data (audio, video) Continuous high data rate Multiple static connections, e.g.: up to 15 stereo connections with 16 bit quantization (CD quality) or up to 60 mono connections with 8 bit quantization (telephony) No addressing, channel source and sink defined during channel setup No error detection Point-to-Multipoint (connection between one streaming source and one or several streaming sinks) Setup and shutdown of connections is done on control channel Streaming data rate (MOST25): Net data rate = (BoundaryDescriptor * 4) * 8bit * SamplingRate Net data rate example (sampling rate = khz) Minimum data rate: MBit/s (BoundaryDescriptor=6) Maximum data rate: MBit/s (BoundaryDescriptor=15)

25 Asynchronous channel Transportation of spontaneous packet-based data (e.g. map updates, internet) Temporary high data rate (e.g. graphics, picture formats, and navigation maps) transmitted in bursts Error detection by CRC and positive and negative acknowledgements (ACK/NAK) Max. 58 byte (1024 for fast transceivers) Prioritization by arbitration

26 Arbitration Node A Prioritization based on backoff mechanisms (similar to CSMA/CA with IEEE e priority classes) Idea: Prioritization in time Transmission delay depends on the packet priority (packets with lower priority have to wait longer until getting access to the network) Lower priority packets do not access the next received frame but skip the next n frames and thus leave n frames for packets with higher priority Synchronous Asynchronous Control Synchronous Asynchronous Control Synchronous Asynchronous Control Frame n-1 Frame n Frame n+1 Node B Low priority Control Packet High Priority Control Packet

27 Transmission characteristics of streaming data High Quality of Service (QoS) requirements Short delays (in particular for voice streams) Continuous guaranteed transmission rate Thus network congestion, interruptions, collisions or bandwidth bottlenecks have to be avoided MOST guarantees that the bandwidth of the streaming data channels is always available and reserved for the dedicated stream so there are no interruptions, collisions or slow-downs in the transport of the data stream

28 Transmission characteristics of packet-based data Reliability managed by MOST High Protocol (MHP) Connection-oriented transport layer protocol for asynchronous channel and control channel Connection setup Connection shutdown Flow control by granting transmission window to the sender Error detection by CRC, parity and acknowledgements Automatic retransmission after error

29 MOST Asynchronous Medium Access Control (MAMAC) Adaptation layer for the transmission of TCP/IP (including IPX, NetBEUI, ARP) data through the asynchronous channel Can be used in combination with MOST High Protocol Automatically set by MOST node

30 Digital Transmission Content Protection (DTCP) Authentication + Encryption Developed by the 5C Group (Intel, Matsushita, Toshiba, Sony, Hitachi) DTCP was originally designed for the safe transmission of signals from a settop-box to the DVD video recorder Used for instance by Sony and Warner for digital exchange of films Fully integrated in MOST Support for HD-DVD and Blue-ray Phases: Authentication: 320 bit public device key Key Exchange: Diffie Hellmann based on Elliptic Curve Cryptography En-/decryption: M6-56bit, AES-128bit

31 MOST implementation by AUDI Audi A8, A6, Q7 Source: Grzemba 2008: MOST

32 Questions Why is CAN not suitable to transport multimedia data? What are the individual channels of MOST and what kind of information is transported therein? What medium access schemes are used in the individual channels? Are packet collisions possible in MOST? Why is there no addressing in the synchronous channel? Describe how synchronization works in MOST? How is application layer interoperability solved in MOST? What is DTCP and how does it work?

33 Literature