1. Skype & its protocol Aaron Loar CPE 401

2. Introduction Skype’s Background Topology 3 Node Types Questions

3. Background Created in 2003 Same people as the makers of KaZaa Bought in 2005 by eBay Sold in 2009 Canada Pension Plan Investment Board Future uncertain

4. Overview Overlay network Peer-to-peer 3 types of nodes – Skype clients (SC) – Super nodes (SN) – Skype Login Server Able to operate over low bandwidth Offers IM chat, VoIP, Video chat, File sharing, …

6. Skype Clients Host Cache – Locally stored list of super nodes and ports – Locally stored Buddy List (Outdated) – Node cannot prevent Super Node promotion – Encrypted login Listens on particular ports Wideband CODECs

8. Super Nodes From P2P systems Help guide traffic between clients Global Indexing – Search for users Users have no control over promotion Store addresses and ports of clients Uses AES 256-bit encryption

9. Skype Login Servers Controlled by Skype Only communicate with clients for login No traffic passes through SLS Encrypted key generation

10. Placing A Call Real IPs = UDP Voice packets = 67 Bytes Use UDP as much as possible Silent Packages Little data about video protocols

11. Conclusion Skype’s History Overlay Peer-to-peer topology Skype Clients Super Nodes Skype Login Servers Questions

12. References http://ezinearticles.com/?How-Skype-Works&id=496462 http://www1.cs.columbia.edu/~library/TR- repository/reports/reports-2004/cucs-039-04.pdf http://www1.cs.columbia.edu/~library/TR- repository/reports/reports-2004/cucs-039-04.pdf http://www.recon.cx/en/f/vskype-part1.pdf http://www.recon.cx/en/f/vskype-part2.pdf http://en.wikipedia.org/wiki/Skype_protocol