 Introduction  VoIP  P2P Systems  Skype  SIP  Skype - SIP Similarities and Differences  Conclusion

 Voice over Internet Protocol.  Two or more people can speak with each other over internet using their computers.  Skype is the first peer-to-peer based IP telephony.  Normally there are three basic functions: › Resource location › Session establishment and management › Presence status

 P2P are dynamic, reliable and scalable networks.  Resources are shared between the peers (file- sharing).  Resources can be accessed directly from other peers.  There are different kinds of P2P networks: › Structured › Unstructured  Centralized  Pure  Hybrid

 Pro’s › No single point of failure › Can provide anonymity › Reduces the signaling load without reducing the reliability  Con’s › Still signaling traffic › Overlay topology not optimal › Super nodes have to bear a significantly higher load

 Most VoIP system used.  Privative.  Architecture: › Host nodes › Super nodes › Login node  Skype uses a central authentication server to authenticate users.

LOGIN  A skype client authenticates its username and password with login server.  Advertises its presence to other peers and buddies.  Determines the type of NAT and firewall it is behind. NAT TRANSVERSAL AND FIREWALL  A variation of the STUN and TURN protocols to determine the type of NAT and firewall it is behind.

SECURITY  Username and password for authentication.  Uses the Advanced Encryption Standard (AES) for the calls.

 The Session Initiation Protocol is a signaling protocol, used for setting up and tearing down multimedia communication sessions.  One of its applications is in VoIP (P2PSIP).  SIP entities › User Agents (Uas) › SIP Proxy › SIP Registar › SIP Redirect Server

LOGGING IN  By registration Server. The SIP registration server also stores the IP address and port used to connect to each SIP client. NAT TRANSVERSAL AND FIREWALL  Uses STUN to translate Information inside IP packets for NAT and firewall traversal

SECURITY  SIP authenticates by Digest Authentication.  Communication by extension (TLS). Example:

 No differences in the main architecture. › Hybrid P2P. › Supernode in Skype, SIP Proxy and Redirect server in SIP.  Login process is the same in SIP and Skype › Register before direct transmission. › Login Server in Skype and Registar Server in SIP.  Similar NAT and firewall transversal protocol (STUN).

 SIP is open and Skype uses a proprietary protocol.  Skype encrypts communications. SIP don’t (just by extension).  SIP just a little part of the whole protocol (more flexible).  SIP is a standard (compatibility and reuse). Skype just an application.

 SIP and Skype are two different approaches to VoIP communication.  SIP has the strength of flexibility, Skype is easy to install, use and has transparent network access; both offer excellent sound quality.  Nobody knows, whether Skype is a backdoor and really secure.  Skype uses the own “clients” –supernodes- of servers. Less cost more escalability.  SIP-P2P has still work to do for VoIP communications (security, performance…).

Thank you!