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The Skype protocol is a proprietary Internet telephony network based on peer-to-peer architecture, used by Skype. The protocol's specifications have not been made publicly available by Skype and official applications using the protocol are closed-source. The Skype network is not interoperable with most other Voice over IP (VoIP) networks without proper licensing from Skype. Numerous attempts to study and/or reverse engineer the protocol have been undertaken to reveal the protocol, investigate security or to allow unofficial clients. On June 20, 2014, Microsoft announced the deprecation of the old Skype protocol. 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).〔http://blogs.skype.com/2014/06/20/making-way-for-the-next-generation-of-skype-on-desktop/〕〔http://www.computerworld.com/s/article/9249275/Update_Skype_to_retire_recent_editions_for_Windows_Mac_upgrades_mandatory〕 There's no word on whether SmartTV and hardware phones with built-in Skype functionality will continue to work without interruptions. The new Skype protocol - Microsoft Notification Protocol 24 - promised better offline messaging and better messages synchronization across Skype devices. The deprecation became effective in the second week of August, 2014. ==Peer-to-peer architecture== Skype was the first peer-to-peer IP telephony network.〔Page 11 in 〕 The network contains three types of entities: ''supernodes'', ordinary nodes, and the login server. Each client maintains a ''host cache'' with the IP address and port numbers of reachable supernodes. The Skype user directory is decentralized and distributed among the supernodes in the network. Previously any client with good bandwidth, no restrictions due to firewall or NAT, and adequate processing power could become a supernode. This placed an extra burden on those who connected to the Internet without NAT, as Skype used their computers and Internet connections as third parties for UDP hole punching (to directly connect two clients both behind NAT) or to completely relay other users' calls. In 2012, Microsoft altered the design of the network, and brought all supernodes under their control as hosted servers in data centres. Microsoft at the time defended the move, saying they "believe this approach has immediate performance, scalability and availability benefits for the hundreds of millions of users that make up the Skype community." At the time there was some concern regarding the privacy implications of the change, which appear to have been proven true with the revelation of the PRISM surveillance program in June 2013. Skype does not support the use of the IPv6 protocol, which would greatly reduce the complexity associated with the aforementioned IPv4 communication structure. Supernodes relay communications on behalf of two other clients, both of which are behind firewalls or "one-to-many" Network address translation. Without relaying by the Supernodes, two clients with firewall or NAT difficulties would be unable to make or receive calls from one another. Skype tries to get the two ends to negotiate the connection details directly, but sometimes the sum of problems at both ends can prevent direct conversation being established. The problems with firewalls and NAT can be: * The external port numbers or IP address are not derivable, because NAT rewrites them, * The firewall and NAT in use prevents the session being received * UDP is not usable due to NAT issues, such as timeout * firewalls block many ports * TCP through many-to-one NAT is always "outward only" by default - Adding port-forwarding settings to the NAT router can allow reception of TCP sessions Supernodes are grouped into ''slots'' (9–10 supernodes), and slots are grouped into ''blocks'' (8 slots). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Skype protocol」の詳細全文を読む スポンサード リンク
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