You can use Backbone to synchronize Jira Service Desk projects with other Jira Service Desk projects, Jira Software or Jira Core projects.

Backbone differentiates these Jira Service Desk use cases:

2nd Level Support (Jira Service Desk to Jira)
2nd Level Support (Jira Service Desk to Jira Service Desk)
Mirroring (same-level support)
Power Customer Support