Virtual addresses and their use?

[SørenHN]

Bluetooth Mesh Glossary of Terms mentions 3 different kinds of addresses: Unicast Addresses, Group Addresses and Virtual Addresses.

I think I understand what a Unicast Addresses is. But just to be sure; it's the element number for which, whatever you are addressing is in, right?

Group Addresses, I also think I understand. It's an address, a group of model's can subscribe to and will listen after message from. It is an easy way of addressing many elements at the same time.

But I don't understand what Virtual Addresses are, and what they are used for. The Bluetooth Mesh Glossary has this to say about them:

A Virtual Address is an address which may be assigned to one or more Elements, spanning one or more Nodes.

This, to me, sounds very much like a group address. So what are they used for?

How do they differ from group addresses?

And why have both Group Addresses and Virtual Addresses?

[Eirik Midttun]

Good question; the confusion is understandable.

You are right about the Group Addresses. In addition to the 16k addresses that are classified as a group address there is an extension mechanism called Label UUID. A virtual address is a hash of the Label UUID. It means that a virtual address can correspond to many Label UUIDs, but in reality this is unlikely. And it greatly improves the address processing, dealing with 16 bits (mesh address) instead of 128 bits (Label UUID)

Source: www.bluetooth.com/.../mesh-faq

[SørenHN]

If I understand you correctly, Virtual Addresses are just another kind of Group Address but with many more address available?

What will happen if to UUID's will have the same hash? Will the network think the two nodes with the same address hashes is the same device or are there some built in process for handling this situation?

[Eirik Midttun]

The Label UUID is used as additional data for the MIC, so when a message sent to a virtual address (hash) is received it is checked against all registered Label UUIDs for authentication.