What is the formal technology of communication between head office and overseas office in business?

Nowadays, the communication between head and oversea offices or between oversea offices themselves mainly consist of traditional telephones, IP Phones or similar VoIP equipments, Emails, VPN Networks and softwares over Internet/VPN as well. And these softwares consists of virtual (video) meetings, request trackers, SOA-based softwares (HP Service Center, for example), Common view alignment software such as OpenView and their solid foundation: ERP systems.

And with the improvement of technology, IPv6 with its good capacity of single point data transmission over Internet, multi-point broadcast system, high security might be widely used through companies in the near future,and quantum internet would be a good choice in a long run.