[UDS unified diagnostic service] i. overview of diagnosis (4) - basic concepts and terms

One 、 Diagnostic overview （4）— Basic concepts and terms

1. Client and server

client （Client)
The originator of the diagnostic request –Tester（ Diagnostic instrument 、 Upper computer ）, Send a diagnostic request
Server side (Server)
Provider of diagnostic response – Some ECU, Send diagnostic response
Remote client / The server （Remote Client /Server)
And Server (Client) Not in the same “ Network segment ”

2. Data transmission related

Protocol data unit (PDU)【Protocal Data Unit】
Protocol data unit is a set of information and data , It represents the information and data transmitted between the sender and the receiver peer entities .
The protocol data unit includes :

• Protocol control information （PCI)【Protocal Control Informaiton】
• data （Data)

Single frame transmission
Data length <6/7 Bytes
Message type ：

• A single frame （SF)【Single Frame】

Multi frame transmission
Data length >6/7 Bytes , Most allow 4095 Bytes
Message type ：

• First frame （FF)【First Frame】: Describe the beginning of the transmission
• Flow control frame (FC)【Flow Control】: During transmission , Message flow control port
• Consecutive frames （CF)【Consecutive Frame】: To transmit data

3. Communication related

Physical communication (1:1)
Scenario of physical addressing communication , And one-to-one diagnostic communication between client and server .
Functional communication (1:N)
The scenario of communication using functional addressing , And the communication mode in which the client sends diagnostic requests of the same function to multiple servers .
source address (SA)【SourceAddress】
Sending node address
Destination address (TA)【TargetAddress】
Receiving node address

4. Structure of automobile diagnosis system