[DoCAN] Vehicle Diagnostic Communication Part 5 [ISO-TP 1]

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Introduction.
ISO-TP
Network layer of DoCAN
Parameters used in addressing formats
Conclusion.

Introduction.

The network layer of vehicle diagnostic communication will be explained from this time on.

ISO-TP

Since we have finished discussing the data link layer (i.e., CAN) in the previous issue, I will now start explaining the network layer.
The network layer and the transport layer in DoCAN are described in ISO 15765-2, and these two layers together are sometimes abbreviated as ISO-TP.
It is good to recognize that they are the network layer and the transport layer in conformance with ISO.

Network layer of DoCAN

In Ethnernet, the network layer would be IP address related content.
Is there an IP address equivalent in DoCAN?

The answer is yes.
It is called a physical address or a functional address.
However, the concept is closer to a MAC address than to an IP address.

By the way
Physical address transmission is equivalent to unicast (one-to-one communication).
Functional address transmission is equivalent to broadcast or multicast (one-to-many communication).

This address conforms to the following four addressing formats.

Normal Addressing
Normal fixed addressing
Extended addressing
Mixed addressing

These four types differ in the volume of information they contain.
Some have simple specifications, while others are more complex.
The bottom line is that the appropriate one is supposed to be chosen based on the complexity of the network.

Unlike PC networks, in-vehicle networks are likely to have a mixture of nodes with low processing power for reasons of cost, size, and power conservation.
In order to balance these factors, the communication specifications also need to have a certain range of specifications so that a balance can be achieved.

So far, we have discussed physical addresses, functional addresses, and addressing formats.
Which should you examine first?
The answer is to examine them all at the same time.
The reason is that physical addresses and functional addresses are determined in addressing formats, so it is not possible to discuss them in isolation.

Parameters used in addressing formats

Before going into the description of addressing formats, there are some parameters that must be understood.
They are listed in the table below.

Name	Description
N_AI	network address information
N_TAtype	network target address type
N_TA	network target address
N_SA	network source address
N_AE	network address extension

N_TA and N_SA are the destination and the source, so you can kind of understand.
Other than that, you don’t know what you are describing, do you?
Furthermore, they may or may not be used, depending on the addressing format.
As for N_AI and N_AE, there is no particular way to use them.

There is a learning method to delve into this part, but since they are components built into addressing formats, it is better to learn them together when learning specific addressing formats.

I will explain about addressing formats in the next and subsequent articles.

Conclusion.

There are physical addresses for one-to-one communication and functional addresses for one-to-many communication.
Physical and functional addresses are composed of four different addressing formats
The addressing formats consist of N_AI, N_TAtype, N_TA, N_SA, and N_AE.
- However, they may or may not be used depending on the addressing format.

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