Relationship between endpoint and connection.

       transport_type                       transport_type::transport_con_type                    
       (                                    (                                 
        iostream::endpoint<>                 iostream::connection<>             
        asio::endpoint<>                     asio::connection<>                 
       )                                    )                                 
       +---------------------+              +---------------------+           
       |                     |              |                     |           
       |                     |              |                     |           
       +---------------------+              +---------------------+           
                  |                                    |                      
                  |                                    |                      
                  v                                    v                      
       endpoint                             connection                          
       +---------------------+              +---------------------+           
       |                     |              |                     |           
       |                     |    <====>    |                     |           
       |                     |              |                     |           
       +---------------------+              +---------------------+           
  
            /           \
          /               \
        /                   \
   client                  server
   +------------+          +------------+
   |            |          |            |
   +------------+          +------------+

The relationship between config.

       server config                       client config

       core                                core_client
       +-------------+                     +-------------+               
       |             |                     |             |               
       +-------------+                     +-------------+               
         /          \                        /          \                
        /            \                      /            \               
       /              \                    /              \              
   asio              asio_tls          asio_client       asio_tls_client        
   +---------+       +---------+       +---------+       +---------+     
   |         |       |         |       |         |       |         |     
   +---------+       +---------+       +---------+       +---------+