CODEWITHSUNDEEP
can-busj1939
user3380188
user3380188

Reputation: 1

what will happen if two nodes with same name claiming same address in j1939?

If two nodes with same name claiming same address in j1939 what will happen in this situation? will any one of node will claim address or error will occour ?

Upvotes: 0

Views: 1359

Answers (3)

SamL
SamL

Reputation: 37

J1939-81 says

"Repeated Collisions Occur, devices go BUS OFF CAs should retry using a Pseudo-random delay before attempting to reclaim and then revert to Figures 2 and 3."

Upvotes: 0

Christian Herrera
Christian Herrera

Reputation: 81

From the network standpoint, there is no way to distinguish that the nodes are different since they are identifying themselves as the same entity. What would happen is that the first requests will be addressed, and the second request will be ignored. In other words, this is race condition because only one message is processed at a time in the datalink. By the time the second node tries to claim the same address, the address table is already occupied and the late request node won't be able to get the notification that the address was assigned to it. Remember that each node has its own internal states/configuration.

Upvotes: 0

RufusVS
RufusVS

Reputation: 4127

My copy of the specification is dated, but I'm sure this rule hasn't changed since 2003 (SAE J1939-81):

"Manufacturers of ECUs and integrators of networks must assure that the NAMEs of all CAs intended to transmit on a particular network are unique."

Of course, that being said, it is of course possible to put devices with the same NAME on the same set of wires, either through ignorance or malicious intent.

I personally haven't played with it, but in theory, if your device has the exact same NAME as another, your address claim will exactly overlap the other, neither would be aware of the other's presence, the message would go through successfully, and each device will assume it is the one that sent it.

I may be wrong, but I think the only thing odd an CA might see is message coming in from an address it thought it had claimed, a problem which it may not even be checking for.

Upvotes: 0

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