Originally, when Skype was launched, it was a proprietary VoIP system. However, Microsoft has made quite enhancements in its back-end infrastructure and it has now completely moved to a cloud-based service powered by Azure. However, Skype for Business can essentially be used and connected with a SIP Trunk to carry outcalls.
Originally, Skype came from a more distributed system. Every device that needed to communicate over Skype had to install a client application due to which it became a node in a network of nodes. The communication was carried out via the Peer-to-Peer network and used the Skype Protocol. Presently, Skype for Business has emerged as a centralized Cloud-based infrastructure in which call management is more controlled and streamlined. Today, Skype can be integrated well into the Business Phone system which includes SIP Phones or VoIP Phones.
Get in touch with a MachCloud Expert for more details on Skype for Business Server and Migration to Microsoft Teams.