Download (Uas) SIP Proxy SIP Registar SIP Redirect Server

Introduction
 VoIP
 P2P Systems
 Skype
 SIP
 Skype - SIP Similarities and Differences
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Conclusion
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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.
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Normally there are three basic functions:
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› Resource location
› Session establishment and management
› Presence status
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P2P are dynamic, reliable and scalable networks.
Resources are shared between the peers (filesharing).
Resources can be accessed directly from other
peers.
There are different kinds of P2P networks:
› Structured
› Unstructured
 Centralized
 Pure
 Hybrid
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Pro’s
› No single point of failure
› Can provide anonymity
› Reduces the signaling load
without reducing the reliability
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Con’s
› Still signaling traffic
› Overlay topology not optimal
› Super nodes have to bear a
significantly higher load
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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.
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NAT TRANSVERSAL AND FIREWALL
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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.
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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.
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One of its applications is in VoIP (P2PSIP).
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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

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SIP authenticates by Digest Authentication.
Communication by extension (TLS).
Example:
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No differences in the main architecture.
› Hybrid P2P.
› Supernode in Skype, SIP Proxy and Redirect server in SIP.
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Login process is the same in SIP and Skype
› Register before direct transmission.
› Login Server in Skype and Registar Server in SIP.
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Similar NAT and firewall transversal protocol (STUN).
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SIP is open and Skype uses a proprietary protocol.
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Skype encrypts communications. SIP don’t (just by
extension).
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SIP just a little part of the whole protocol (more
flexible).
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SIP is a standard (compatibility and reuse). Skype
just an application.
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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!