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Skype VoIP service- architecture and comparison

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Call Establishment and Teardown, Media Transfer and Codecs, Security. VoIP Network ... Codecs. VoIP. Various standards. Compress the data stream. Silence ... – PowerPoint PPT presentation

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Title: Skype VoIP service- architecture and comparison


1
Skype VoIP service- architecture and comparison
Hao Wang
INFOTECH Seminar June 30, 2005
2
Agenda
  • 1. Background knowledge of VoIP
    Architecture and components
  • 2. Skype A P2P VoIP Service
  • What is peer-to-peer ?
  • Skype Introduction and Overview
  • 3. Comparison of different scenarios between
    Skype and VoIP
  • Login, NAT and Firewall Traversal, User
    Search,
  • Call Establishment and Teardown, Media
    Transfer and Codecs, Security

3
VoIP Network
Signaling protocols H.323, SIP
Data transfer Real-time Transport Protocol.
4
VoIP Transmission
  • Step 1 The callers voice is digitized.
  • Step 2 Digital voice is compressed and then
    separated into packets the packets are
    addressed and sent across the network.
  • Step3 Error detection and correction systems are
    used to create sound to fill in the gaps.
  • Step4 Restore the data to an approximation of
    the original form.

5
Skype Peer-to-peer internet telephony (VoIP)
network
A pure peer-to-peer network only have equal peer
nodes that simultaneously function as both
"clients" and "servers" to the other nodes on
the network.
6
Main Difference
  • The main difference between Skype and other VoIP
    clients is that it operates on a peer-to-peer
    model rather than the more traditional
    server-client model.

7
Login Process
  • VoIP A client may only have to authenticate its
    user name and password with login server.
  • Skype
  • Connects to a Super Node
  • Determines the type of NAT and firewall
  • Discovers online Skype nodes with public IP
    addresses (Alternate Node Table)

8
NAT and Firewall
  • VoIP
  • NAT port forwarding manual configuration or via
    UPnP (Universal Plug and Play)
  • STUN protocol (Simple Traversal of User Datagram
    Protocol)
  • ALG (Application Layer Gateway)

9
NAT and Firewall
  • Skype
  • Variation of typical schemes such as STUN
  • Natural and elegant, involving little management
    structure and overhead.

10
User Search
  • SIP caller will search the users by asking the
    SIP server
  • Skype
  • Perhaps use Chord like hash-based methods,
  • combined with traditional blind searching
    techniques.
  • SN acts like a search proxy for SC and caches
    searched results.

11
Call Establishment and Teardown
  • Process in SIP
  • The SIP proxy uses
  • DNS to find the SIP
  • registrar of Bob .

12
Call Establishment and Teardown
  • Process in Skype
  • Call signaling is always carried over TCP.
  • Call placement is equal to user search plus call
    signaling.
  • If users are behind port restricted NAT and
    UDP-restricted firewall, both caller and callee
    SC exchange signaling information over TCP with
    another online Skype node.

13
Media Transfer
  • VoIP
  • H.323 and SIP are only the signaling protocols.
    Audio data is carried using RTP (Real-time
    Transport Protocol).
  • Skype
  • The Skype protocol seems to prefer the use of UDP
    for voice transmission as much as possible. If
    not possible , it will make use of TCP .

14
Codecs
  • VoIP
  • Various standards
  • Compress the data stream
  • Silence suppression
  • Skype
  • Global IP Sound multiple description coding,
  • variable bit-rate
  • No silence suppression

15
Security in VoIP
  • IP security
  • IPsec is a suite of protocols to provide
    security services on the network layer in IP
    based networks.
  • Often in combination with VPN (Virtual Private
    Network )
  • Firewall
  • Located at border to public Internet
  • Control incoming and outgoing traffic

16
Security in Skype
  • Skype is encrypted end-to-end
  • Skype uses AES (Advanced Encryption Standard) to
    protect sensitive information.
  • Skype uses 1024 bit RSA to negotiate symmetric
    AES keys.
  • User public keys are certified by the Skype
    server at login.

17
Conclusions
  • Skype is a successful combination of several
    technologies basic on p2p overlay networks
  • Much better voice quality, ability to traverse
    the NAT and firewalls, encrypted media channel
  • Ability to scale up to handle large-scale
    connection-oriented real-time services
  • Heavy software based DSP operations at Skype
    clients

18
d
  • Q A Session

19
D
  • Thank you for your attention!
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