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VoIP as in Skype

VoIP as in Skype. Presented by : Krishnan Ganesh Madras 04/24/2007. What is VoIP???. Voice over Internet Protocol (VoIP) is the family of technologies that allow IP networks to be used for voice applications, such as telephony, voice instant messaging, and teleconferencing.

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VoIP as in Skype

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  1. VoIP as in Skype Presented by : Krishnan Ganesh Madras 04/24/2007

  2. What is VoIP??? Voice over Internet Protocol (VoIP) is the family of technologies that allow IP networks to be used for voice applications, such as telephony, voice instant messaging, and teleconferencing.

  3. What is Skype??? Skype is a peer-to-peer VoIP client developed by KaZaa that allows its users to place voice calls and send text messages to other users of Skype clients. In essence, it is very similar to the MSN and Yahoo IM applications, as it has capabilities voice-calls, instant messaging, audio conferencing, and buddy lists. However, the underlying protocols and techniques it employs are quite different.

  4. Super node:-A super node is an ordinary host’s end-point on the Skype network. Ordinary node:- An ordinary host is a Skype application that can be used to place voice calls and send text messages. Skype login server:-Server used to check authenticity of user.

  5. Key Components of the Skype software • Ports • Host Cache • Codecs • Encryption • NAT and Firewall

  6. Skype Functions • Startup • Login • User search • Call establishment and tear down • Conferencing

  7. Login

  8. Login Server After a SC is connected to a SN, the SC must authenticate the user name and password with the Skype login server. The login server is the only central component in the Skype network. It stores Skype user names and passwords and ensures that Skype user names are unique across the Skype name space. SC must authenticate itself with login server for a successful login.

  9. Bootstrap Super Nodes • First-Time Login Process • Alternate Node Table • Subsequent Login Process • Login Process Time

  10. User Search Skype uses its Global Index (GI) technology to search for a user. Skype claims that search is distributed and is guaranteed to find a user if it exists and has logged in during the last 72 hours. Extensive testing suggests that Skype was always able to locate users who logged in using public or private IP address in the last 72 hours.

  11. Call Establishment and Teardown If both users were on public IP addresses, online and were in the buddy list of each other, then upon pressing the call button, the caller SC established a TCP connection with the callee SC. Signaling information was exchanged over TCP. In the second network setup, if the caller was behind port-restricted NAT and callee was on public IP address, signaling and media traffic does not flow directly between caller and callee. Instead, the caller sends signaling information over TCP to an online Skype node which forwards it to callee over TCP. This online node also routes voice packets from caller to callee over UDP and vice versa. For the third setup, if both users were behind port-restricted NAT and UDP-restricted firewall, both caller and callee SC exchange signaling information over TCP with another online Skype node. Caller SC sends media over TCP to an online node, which forwards it to callee SC over TCP and vice versa.

  12. Conferencing Conferencing is also a feature of Skype. This is similar to call between 2 Skype users. In this one of the Skype client acts as a mixer and send packets to others. Conclusion Skype is the first VoIP client based on peer-to-peer technology. There are three factors that are responsible for its increasing popularity. First, it provides better voice quality than MSN and Yahoo IM clients; second, it can work almost seamlessly behind NATs and firewalls; and third, it is extremely easy to install and use. Reference An analysis of the Skype Peer-to-Peer Internet Telephony Protocol. Salman A. Baset and Henning Schulzrinne

  13. Questions???

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