内容英特介绍

1、1Automotive EthernetTransport LayerUDP / TCP1234567Network LayerIP Addressing, RoutingPhysical LayerBit stream, Physical MediumSession LayerInterhost communication, HTTP, FTP,.Presentation LayerApplication LayerData Link LayerThe ETHERNET Frame, MAC AddressUDP (User Datagram Protocol) and TCP (Trans

2、mission Control Protocol)Intrepid Automotive Ethernet TrainingWhat role?What role do higher level protocols have in an automotive setting?Theoretically, regular CAN messaging and raw Ethernet frames are functionally interchangeable (save network switching)Layer 2 and Layer 3 protocols cause us to th

3、ink about automotive messaging in a different waySignal based messagingModern automotive communications use “implicit availability” CAN frames are always periodically transmitted with latest valuesWorks well for simpler systems to just get signal values from point A to point BWhat happens if two nod

4、es need to negotiate some parameters?CAN not very well suited for this taskSignal based messaging, 2This is because CAN was always meant to be a sensor networkModern automotive applications require much more than passive sensor dataStateful connections between many functional units are a reality tod

5、ay (think of the communication between a hands free phone and the head unit)Signal based messaging, 3Automotive Ethernet bridges this gap provides many protocols that give different level of control and reliabilityMultiple protocols can coexist on the same networkSome protocols, such as AVB, give ex

6、treme latency guarantees on data for applications such as audio/video streamingProcess-Level Addressing: PortsIP address identifies a device (ECU)Port identifies a software process (function or virtual ECU within the module)TCP and UDP messages include 16-bit source and destination port addresses (0

7、 to 65,535)Well-known ports solve the problem of how to know where to send particular types of requests on a device (e.g., 80 for Web servers)IP address + port = socket; source and destination sockets uniquely identify an Internet connectionUser Datagram Protocol (UDP)TCPs simpler little brotherPlay

8、s same role, but provides fewer servicesLike a “stripped down” race carUsed where timely delivery is more important than service guaranteesSimilar to CAN frame without acknowledgementTransmission Control Protocol (TCP)If UDP is a race car, TCP is a chauffer-driven limousine: features, convenience an

9、d ease, but at the cost of overhead, complexity, reduced speedConnection-based protocolMultiple connections with endpoint identificationBidirectionalStream-oriented (bytes, not whole messages)Reliable (which doesnt mean guaranteed)Acknowledgments and flow controlKey to operation: sliding window mech

10、anismTCP “Three-Way Handshake”TCP Segment FormatTCP Sliding Window SystemUsed to keep track of bytes sent and receivedSpecial pointer maintained for each connectionISO 15765-2 has a sliding window, but it only acknowledges one group of frames at a timeUDP - HeaderSource Port (whats a port)Destinatio

11、n Port (whats a port)Optional checksum, 0 = no checksum,All 1s = 0 checksumWhat is an IP address doing in a UDP header!?!Length of UDP up to 64K Bytes13User datagram protocolUnreliableDoes not guarantee delivery and packet orderWhy would anyone use UDP?14User datagram protocolUnreliableDoes not guar

12、antee delivery and packet orderWhy would anyone use UDP?15Transmission control protocol INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) TCP is the Cadillac (no offense intended!) of IP protocolsTCP turns Ethernet into

13、a reliable, connection orientated streamAs mentioned previously, the closest CAN analogue is ISO 15765-216Transmission control protocol, 2 INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) Unlike other protocol, TCP has

14、the native concept of a connectionFor two nodes to talk, one must initiate a connection to another, and it must be acceptedCreates an implicit client/server modelOur web browsers talk to websites over TCP17Transmission control protocol, 3 INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madis

15、on Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) TCP guarantees that all packets willArrive to the clientArrive in the same order they were sentThe second point is one often overlooked by other protocolsSince Ethernet is switched, each packet could take different paths and arrive

16、 out-of-orderNot as big of a concern on smaller networks18Transmission control protocol, 4 INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) How does TCP guarantee delivery?By explicitly acknowledging each packet receive

17、dThis essentially doubles the latencyFor a packet to be successfully read by an application, it must be received, then acknowledged back to the senderIf no acknowledgment, the packet is retransmitted19Transmission control protocol, 5 INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison He

18、ights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) TCP is also stream-orientedApplication layer does not see individual packets, just a seamless stream of bytesTCP is well suited for data that must arrive exactly as it was sent, exactly in the order it was sentTCP also has flow control

19、to deal with asynchronous receive/transmit speeds20Transmission control protocol, 6 INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) Send Packet 1Start TimerRetransmit Packet1Start TimerPacket should arrive ACK should b

20、e sentACK would normallyArrive at this timeReceive Packet 1Send AXK 1Time ExpiresReceive ACK 1Cancel TimerPacket LostTimerTimer21Transmission control protocol, 7 INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) TCP has

21、IP protocol number 0 x06Source port same use as UDPDestination port same as UDP22Transmission control protocol, 8 INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) TCP has IP protocol number 0 x06Sequence number, used to

22、 guaranteein-order deliveryThe next sequence number the sendercan receive; all previous sequencenumbers are acknowledged as received23Transmission control protocol, 9 INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) TCP

23、 has IP protocol number 0 x06Size of the TCP header in 32-bytewordsThese flags indicate the current stateof the connection24Transmission control protocol, 10 INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) TCP has IP p

24、rotocol number 0 x06Checksum of header and dataThe maximum number of bytes thesender is able to receive implementsflow control25A full TCP/IP packet INTREPID CONTROL SYSTEMS, INC. 31601 Research Park Dr., Madison Heights, MI 48071 USA 1- Presented by: Dave Robins, President ( ) 26A full TCP/IP packet (Ethernet) INTREPID CONTROL SYSTEMS, INC. 31601 Research Park