Send message between two blockchain nodes

Question

How can I send messages from user A to user B on the blockchain network? A diagram has been mentioned below:

If I have a blockchain network with 5 nodes. Each node represents one "Organisation". How can User A in Organisation 1 send a message to exact User B in organisation B? Can send messages between two blockchain nodes, for example node 1 and node 3 or other node in the blockchain network. But, at User A, how can he determine "where is User B" ? 

Answer 1

The answer is Blockchain as at the end, a Blockchain network provides you the validated and verified information that is registered in the network and is sent to all the participants of the network. In the case of Hyperledger-Fabric, you would have to generate a channel for organisations 1 and 3 of your illustration. In this way, only those two organisations will see the data registered by User A.