+------------------------------+
            |           client#1           |
            |              VDC             |
            |                              |
            |       +--------------+       |       +---------------------+                 +---------------------+
            |       |              +-------------->+                     +---------------->+                     |   ...
            |       |  replica-01  |       |       |  common-replica-01  |                 |  common-replica-02  |
            |       |              +<--------------+                     +<----------------+                     |
            |       +--------------+       |       +---------------------+                 +---------------------+
            |            |    ^            |                | ^                                      | ^
            |            v    |            |                | |                                      | |
            |       +--------------+       |                | |                                      | |
            |       |              |       |                | |                                      | |
            |       |  replica-02  |       |                | |                                      | |
            |       |              |       |                | |                                      | |
            |       +--------------+       |                | |                                      | |
            |                              |                | |                                      | |
            |                              |                v |                                      v |
            +------------------------------+       +---------------------+                 +---------------------+
                                                   |                     +---------------->+                     |
                                                   |  common-replica-03  |                 |  common-replica-04  |
                                                   |                     +<----------------+                     |
                                                   +---------------------+                 +---------------------+


                                                  ...                                                     ...