sequenceDiagram
  Alice->>Bob: Hello Bob
  Bob-->>Alice: Hi Alice
---
 +-------+       +-----+   
 | Alice |       | Bob |   
 +-------+       +-----+   
     |              |      
     |  Hello Bob   |      
     |-------------->      
     |              |      
     |  Hi Alice    |      
     <..............|      
     |              |      
 +-------+       +-----+   
 | Alice |       | Bob |   
 +-------+       +-----+