1. peer-to-peer and agent-based computing Case Study: Skype

2. peer-to-peer and agent-based computing 2 Free software to make phone calls over the Internet –Free calls to other Skype users –Low-cost calls to mobile phones and landlines –Videoconferencing –1-to-many, many-to-many calls Created by Niklas Zennström and Janus Friis (2003) –Team of software developers based in Tallinn, Estonia –Uses proprietary VoIP network –Protocol not public – apps proprietary & closed-source Bought by eBay in Sep 2005 for US$ 2.6 billion Web site http://www.skype.com Skype

3. peer-to-peer and agent-based computing 3 How Skype Works

4. peer-to-peer and agent-based computing 4 Overlay peer-to-peer network – all peers are nodes –Ordinary hosts: Skype app used to send/receive calls –Super nodes (SNs): ordinary hosts end-point When we use Skype as ordinary hosts –We register with Skype login server Login server not a peer/node! Usernames, passwords, credit information User authentication is done at the login server –We connect to a super node No central Skype servers (just the login server) –On-line and off-line user information stored and propagated in a decentralised fashion –Queries also decentralised How Skype Works (2)

5. peer-to-peer and agent-based computing 5 How Skype Works (3) Message exchange with login server during login Skype login server Ordinary host Super node Neighbour relationship

6. peer-to-peer and agent-based computing 6 Phone/text non-Skype users –Users buy credits (EUR10, 15, etc.) and use them to phone non-skype users (landlines and mobile phones) –Cheaper calls than conventional phone operators –International calls are dirty cheap SkypeIn –User subscribe to a local Skype number (pays a fee) –Allows users to receive phone calls from non-Skype users Special-purpose Hardware: –Phones connected to PC –WiFi Phones (no computer reqd) –Skype WiFi Phone –PocketSkype (WiFi-enabled PDAs) Skype as a Busine$$

7. peer-to-peer and agent-based computing 7 Security: –256-bit encryption (safe) US wanted to wiretap calls through Skype –Skype says NO –(but, how can we know this it true?) Poor customer support Delays in Unix version Skype cooperates with Internet censorship Issues

8. peer-to-peer and agent-based computing 8 Skype on WikiPedia http://en.wikipedia.org/wiki/Skype An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol, S. A. Baset & H. Schulzrinne http://www1.cs.columbia.edu/~library/TR- repository/reports/reports-2004/cucs-039- 04.pdf Further Reading