Choosing between LES and LIS diagram

Hi all,

I would like to create a sequence diagram to represent the exchange of messages between different components. However, I am unsure whether LES or LIS would be better for my case. I have already defined the exchange items and the interfaces to which my exchange items are allocated on a CDB diagram. If I work on a LES, I would allocate my exchange items to different messages that are exchanged between components. Alternatively, if I work on a LIS, my messages would automatically become exchange items.

Is there someone who can clarify this for me ?