CRM 2016 integration.

Dear Experts,

                          We are running a separate organization in crm 2016 on premises for client, now client implemented there on crm 2016 on premises and they want to integrate their CRM with our crm specially for cases and contacts... So if we create a new contact or case it should show in client crm records and vice versa.

Can any one help me how we can integrate both crm.

Thanks in advance.