and video calls and chats over the Internet. Calls to other users within the Skype
service are free, while calls to both traditional landline telephones and mobile
phones can be made for a fee using a debit-based user account system. Skype has
also become popular for its additional features which include instant messaging,
file transfer, and video conferencing. Skype has 663 million registered users as of
2010. The network is operated by Skype Limited, which has its headquarters in
Luxembourg. Most of the development team and 44% of the overall employees of Skype
are situated in the offices of Tallinn and Tartu, Estonia.
Unlike other VoIP services, Skype is a peer-to-peer system rather than a client–
server system, and makes use of background processing on computers running Skype
software; the original name proposed – Sky peer-to-peer – reflects this.
Some network administrators have banned Skype on corporate, government, home, and
education networks, citing reasons such as inappropriate usage of resources,
excessive bandwidth usage, and security concerns.