Each client maintains a host cache with the IP address and port numbers of reachable supernodes. The network contains three types of entities: supernodes, ordinary nodes, and the login server. Skype was the first peer-to-peer IP telephony network. The deprecation became effective in the second week of August 2014. The new Skype protocol- Microsoft Notification Protocol 24-promised better offline messaging and better messages synchronization across Skype devices. No announcement has been made on whether SmartTV and hardware phones with built-in Skype functionality will continue to work without interruptions.
Within several months from this date, in order to continue using Skype services, Skype users had to update to Skype applications released in 2014, and users were not able to log in to older Skype versions (clients). On June 20, 2014, Microsoft announced the deprecation of the old Skype protocol.
Numerous attempts to study or reverse-engineer the protocol have been undertaken to reveal the protocol, investigate security or allow unofficial clients. The Skype network is not interoperable with most other Voice over IP (VoIP) networks without proper licensing from Skype. The protocol's specifications have not been made publicly available by Skype and official applications using the protocol are closed-source. The Skype protocol is a proprietary Internet telephony network used by Skype.
