Queues of PI 7.0

Hi All,

I am trying to get more knowledge on XI Queues in SAP PI 7.0.

As I understand, the incoming/outgoing messages are persisted in Adapter Engine and Integration Engine. In case of Adapter Engine, the persistence is twice and for Integration Engine, it is once.

What about the scenario when ccBPM is involved. The message is persisted again?

What types of queues does SAP PI have? It is definitely not JMS. They keep saying queues, but isn't it actually SAP tables that the messages are persisted?

Please let me more information on these.

Thanks,

Swapna