CAN Transfer Protocol

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Welcome to Internal Training Program

CAN Network Layer

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Agenda

What is Network Layer

Why Network Layer

Advantages of CAN

Road Vehicle Diagnostics on CAN

Network Layer Functions

Types of Frames in the Network Layer

Structure of Request and Response Messages

Network Layer Timing Parameters

Examples

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What is Network Layer

It Specifies protocol to meet the requirements of CAN-based vehiclenetwork systems on controller area networks . It has been defined in accordance with the diagnostic services established in ISO 14229-1 and ISO 15031-5

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Why Network Layer

The exchange of data between network nodes, e.g.from ECU to ECU, or between external test equipment and an ECU. If the data to be transferred do not fit intoa single CAN frame, a segmentation method is provided by Network Layer.

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Advantages of CAN

• Can is a multi-master Bus

• Prioritization of messages through “Identifiers”

•Theoriticaly No limitation on the number of nodes

• Multicast reception with the time synchronization

• System wide data consistency

• Error detection and error signaling

• automatic retransmission of corrupted messages as soon as the bus is idle again

• Distinction between temporary errors and permanent failures of nodes and autonomous switching off of defect nodes

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Application Layer

Tester ECURequest

Response

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Tester Application Layer

Physical Layer

ECU Application Layer

Physical Layer

Service Request

ServiceIndication

+ve or -veResponse

ServiceConformation

Application Layer talks about the Services available between the Tester Unit and the ECU (called Diagnostic Services)

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Structure of Request and Response Messages

SA- Source Address TA- Target AddressRA- Remote Address TA_type- Addressing type (Physical or Functional)SID- Service Identifier NR- Negative Response

Request Message

Positive Response

TA TA_typeSA RA(optional)

ResponseID

Result Bytes


NR SID


SIDParameter

Bytes

Negative ResponseReason for

NR

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Network Layer

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Network Layer Functions

Message Segmentation

Message Re-assembly

Flow-Control

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How the Network Layer fits in….

Appl Layer

Session LayerSession Layer

Appl Layer

Data link Layer Data link Layer

Physical LayerPhysical Layer

Network Layer Network Layer

Tester ECUServices

Maintain Diag Session

Flow Control

Segmentation

Re-Assembly

Segmentation

Re-Assembly

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Types of Frames in the Network Layer

Unsegmented Message Transmission:

Single Frame (SF): Used in short messages which can be transmitted in a Single CAN message.

Segmented Message Transmission:

First Frame (FF):First Frame to be transmitted as part of Segmented message transmission.

Consecutive Frame (CF):The Remainder of the message Frames that are sent by the Message transmitter following the First frame.

Flow-Control Frame (FC):Frame sent by the message- Receiver periodically to regulate the rate of arrival of the segmented messages.

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Unsegmented Message Segmented Message Transmission

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Transfer of Data between Network Layers of Two or more Nodes takes place through the Network-Protocol Data Units (N_PDU)

Address Information Protocol Control Info Data Field

N_AI N-PCI N_Data

N_PDU

N_AI parameters:Used to identify the Following:1. Source address, Target address of message senders and recipients2.Communication model for the message and 3.Optional Address extension

N_PCI Parameters:Used to identify the Type of N_PDU and other necessary Control Information

N_Data Parameters:Consists of the DataBytes to be Transmittedto the other Node.

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N_AI

N_SA(Source Address)

N_TA(Target Address)

N_TAtype

(Physical/Functional Address) N_AE

(Extended Address-Optional)

For Long messages that make use of Segmented MessageTransmission, the N_AI information has to be copied to every Frame Segment.

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N_PCI

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Single Frame N_PCI

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First Frame N_PCI

12 (4+8) bytes can be used to represent Data Length.

Max Data Length= 4095 bytes

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Consecutive Frame N_PCI

Sequence Number (SN):Used in the Consecutive Frame N_PDU to specify the order of the consecutive frames. Rules applying to the Sequence Number (SN):

1.Starts with zero (0) for all segmented messages.

2.For the First Frame, SN=0 by default.

3.SN is incremented by 1 for each Consecutive frame transmitted during a segmented message transmission.

4.When SN reaches 15 (Fh), it shall wraparound and be set to zero (0) for the Consecutive Frame (CF).

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Flow Control N_PCI

Flow Status

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Block Size (BS) : Byte 2 of the FC N_PCI

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Separation Time (Stmin): Byte 3 of FC N_PCI

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Network Layer Timing Parameters

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CAN message flow

User Interface for Reading Request / Response

Example 1 – Diagnostic message transmission on CAN

Unsegmented Message Transmission

s

Request

Response

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Request

Response

CAN message flow

Example 2 – Diagnostic message transmission on CAN

Segmented Message Transmission

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Documents for Reference

1.Documents on Road Vehicle Diagnostics on CAN - ISO 15765-1 : General Information ISO 15765-2 : Network Layer ISO 15765-3 : Application Layer

2. KWP Specifications - ISO 14230-1 to ISO14230-4

3. CAN Specification Documents Part A and Part B

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Questions??

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Thank you

CAN Transfer Protocol

Documents

Transcript of CAN Transfer Protocol