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!