① What Does "DoIP" Stand For?
DoIP stands for Diagnostics over Internet Protocol, meaning diagnostic communication over Internet Protocol.
Breaking down the name:
Diagnostics: This is the objective. DoIP enables service technicians to read diagnostic trouble codes, monitor real-time data, flash ECU firmware, and perform other tasks traditionally carried out through the OBD interface.
over: This refers to the communication carrier. Diagnostic data is no longer transmitted through the CAN bus, but through another communication channel.
Internet Protocol: This describes the communication method. DoIP uses the standard TCP/IP protocol stack to transmit diagnostic data - essentially the same underlying technology used when browsing websites or sending and receiving emails.
DoIP is defined by the ISO 13400 standard. It is not an entirely new diagnostic "language," but rather an extended transport protocol.
The core diagnostic content - Unified Diagnostic Services (UDS, ISO 14229) - remains unchanged. The diagnostic commands are the same; only the transport channel is different.
In other words:
What you "say" (UDS diagnostic services) has not changed, but how the information is delivered - from the CAN bus to an IP network - has fundamentally changed.
② Traditional Diagnostics Are Like "Sending Registered Mail," While DoIP Is Like "Instant Messaging"
To understand the fundamental difference between DoIP and traditional diagnostics, consider an everyday analogy that everyone is familiar with.
Traditional CAN diagnostics are like sending a traditional letter or registered mail.
You write a letter (send a diagnostic request), put a stamp on it, and drop it into a mailbox. The postal service sorts, transports, and delivers it to the recipient. After reading it, the recipient writes a reply and sends it back through the same process.
This process has several obvious characteristics:
Only one letter at a time: The design of the CAN bus means diagnostic requests are processed sequentially - you generally have to wait for the response to one request before proceeding with the next.
Limited envelope capacity: A standard CAN data frame can carry a maximum of 8 bytes (CAN-FD increases this to 64 bytes), much like using a standard-sized envelope. Large amounts of data must therefore be split into dozens or even hundreds of smaller messages.
One request and one response: A request corresponds to a response, making the overall process essentially half-duplex.
Slower transmission: Even with high-speed CAN-FD, which can reach up to 8 Mbps, transferring large files can still take considerable time.
DoIP diagnostics, by contrast, are like chatting through an instant messaging application such as WhatsApp, Telegram, or SMS.
You open your phone, type a message (send a diagnostic request), and tap Send. The recipient can receive it almost instantly and respond within seconds. The entire process is real-time, bidirectional, and continuous.
The characteristics of instant messaging include:
You don't have to wait for the previous reply before sending another message: You can communicate with multiple contacts simultaneously. Similarly, DoIP supports parallel access to multiple ECUs.
No comparable "message length" limitation: You can send text, images, videos, or even multi-gigabyte files. A single DoIP message can have a data length of up to 4 GB.
High speed: Once a message is sent, the recipient can receive it almost immediately.
This is the fundamental difference between CAN diagnostics and DoIP diagnostics.
Traditional mail is reliable and well-structured, but slow. Instant messaging is real-time and flexible, and much faster.
DoIP achieves this "instant messaging" experience because it moves automotive diagnostics onto an IP network.
Communication between the vehicle and diagnostic equipment is no longer simply a sequential "request-and-response" process. Instead, it is based on a continuous TCP/IP data stream.
The diagnostic tool first discovers the vehicle through UDP broadcast, then establishes a TCP connection. After that, the system enters a "chat mode" - requests can be sent and responses received continuously, with multiple requests able to be interleaved.
③ Transmission Speed Comparison: 100 Mbps vs. 500 kbps
How large is the speed difference? Let's look at the numbers.
Traditional high-speed CAN (ISO 11898):
Maximum speed of 1 Mbps. CAN-FD, as an upgraded version, can reach up to 8 Mbps. A single CAN frame can carry up to 8 bytes, while CAN-FD supports up to 64 bytes.
DoIP (Automotive Ethernet):
100BASE-T1 provides 100 Mbps, while 1000BASE-T1 provides 1 Gbps. Multi-gigabit variants at 2.5/5/10 Gbps have also entered mass production.
CAN tops out at 1 Mbps, while DoIP starts at 100 Mbps - a 100× difference right from the starting point.
However, these are only theoretical peak rates. In actual diagnostic scenarios, the difference can be even more significant:
Overall DoIP diagnostic speed is approximately 100–200× that of CAN, while network transmission speed can be 300–400× higher than CAN.
DoIP provides an overall data rate of 100 Mbps, while the typical effective CAN rate is approximately 500 kbps - a difference of 200×.
The overall speed difference can approach 50×.
At-a-Glance Data Comparison
| Comparison | CAN / CAN-FD | DoIP (Automotive Ethernet) |
|---|---|---|
| Typical Speed | 1–8 Mbps | 100 Mbps – 1 Gbps |
| Maximum Data per Frame / Message | 8–64 bytes | 4 GB per message |
| Overall Diagnostic Speed | Baseline (1×) | 100–200× |
| Network Transmission Speed | Baseline (1×) | 300–400× |
| 500 MB Firmware Flashing Time | Several hours | Several minutes |
| Communication Mode | Sequential, request-and-response | Parallel, continuous data stream |
From 500 kbps to 100 Mbps, from "sending letters" to "instant messaging" - this is the paradigm shift brought by DoIP.
DoIP Is the Future of Automotive Diagnostics
And this is only the beginning.
As the automotive Ethernet market continues to grow rapidly - with a global valuation of approximately USD 2.8 billion in 2024 and an expected value of nearly USD 10 billion by 2030 - DoIP is becoming an irreversible diagnostic standard for the era of software-defined vehicles.
In the future, remote diagnostics, cloud-based OTA updates, and AI-powered predictive fault detection will all be built on the IP communication foundation established by DoIP.
CAN diagnostics are the standard of "yesterday"; DoIP is the essential technology of "tomorrow."
