Comparison between Skype and SIP-based Peer-to-Peer Voice-Over-IP Overlay Network

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Comparison between Skype and SIP-based Peer-to-Peer Voice-Over-IP Overlay Network. Johnson Lee. EECE 565 Data Communications. Outline. P2P versus Client-Server P2P-SIP design goal Overlay Network of Skype and P2P-SIP Login Sequences Advance Service Comparison Security Performance. - PowerPoint PPT Presentation

Text of Comparison between Skype and SIP-based Peer-to-Peer Voice-Over-IP Overlay Network

  • Comparison between Skype and SIP-based Peer-to-Peer Voice-Over-IP Overlay NetworkJohnson LeeEECE 565 Data Communications


    OutlineP2P versus Client-ServerP2P-SIP design goalOverlay Network of Skype and P2P-SIPLogin SequencesAdvance Service ComparisonSecurityPerformance


    Peer-to-Peer / Client-ServierClient-Server vs P2PScalabilityInfrastructure cost

    Structured vs UnstructuredSearch timeData distribution


    P2P-SIP Design Goals



    Zero Configuration

    The system should be able to automatically configure itself. (e.g. by detecting NAT and firewall settings, discovering neighbouring peers and performing initial registration.)

    Heterogeneous nodes

    It should be able to adapt to available resources and distinguish between peers with different capacity and availability constraints. This favors the distinction between nodes and super-nodes as in KaZaA.

    Efficient Lookup

    Blind search based on flooding is inefficient. The system should use an underlying DHT to optimize lookup.

    Advanced Services

    It should support advanced telephony services such as offline voice messaging, multi-party conferencing, call transfer and call forwarding as well as advanced Internet services such as presence and instant messaging.


    It should easily integrate with existing protocols and IP telephony infrastructure. We choose SIP as the signaling protocol for interoperability.


    Skype Overlay NetworkUnstructuredKaZaA predecssor basedSuper nodeOrdinary nodeLogin server

    STUN and TURN protocols for firewall and NAT traversalSimple Traversal of UDP over NATTraversal Using Relay NAT


    P2P-SIP Overlay NetworkBased on Chord Distributed Hash Table (DHT)StructuredO(log N) lookup timeFinger table

    STUN and TURN firewall and NAT traversal as well


    Login Sequence 1 - SkypeStartSend UDP packet(s) to HC IP address and portResponse within 5 sTCP connection attempt with HC IP address and portConnectedTCP connection attempt with HC IP address and port 80 (HTTP port)ConnectedTCP connection attempt with HC IP address and port 443 (HTTPS port)ConnectedConnection Attempt == 5FailureWait for 6 secondsSuccessYesYesNoNoYesNoYesNoYesNo


    Login Sequence 2 P2P-SIPMulticast TTL = 1Service Location Protocol (SLP) [LAN peers]BootstrapCached


    Advanced Services ComparisonOffline Messaging Issue Where to store?Skype stores at it message originatorP2P-SIP proposes storing it at DHTReplication strategy for reliabilityCall transfer and call forwarding are SIP features that would be available in non-P2P SIP.Super node instead of centralized databaseRequired feature for SIP (not as crucial for Skype)

    Offline Messaging

    Multi-Party Conference

    Call Transfer

    Call Forwarding


    Instant Messaging




    SecurityP2P-SIPMalicious Node Hop-by-hop TLS (Tunneling)Freeriding IncentivesProblem: No centralized login server to certify. Trust via reputation?SkypeEncryption AES 256bitsKey Exchange RSA 2048Public Key Certified by Login Server


    PerformanceP2P-SIP Scalable?Yes, suppose nodes support 10 request/sec, minimum refresh rate of one minute, call rate of one call per minute per node

    Latency?P2P-SIP: 10,000 node system avg 6 hopes, SIP call setup ~200ms; therefore, 1-2 s delaySkype Average 3-8 second for user location based on a 2004 study


    ReferencesSkype Networks. http://www.kazaa.comK. Singh and H. Schulzrinne. Peer-to-peer Internet telephony using SIP. Technical Report CUCS-044-04, Department of Computer Science, Columbia University, New York, NY, Oct. 2004.J. Rosenber, Henning Schulzrinne, G. Camarillo, A. R. Johnston, J. Peterson, R. Parks, M. Handley, and E. Schooler, "SIP: session initialiozation, protocol, RFC 3261, Internet Engineering Task Force, June 2002P2P-SIP., K. and Schulzrinne, H. 2005. Peer-to-peer internet telephony using SIP. In Proceedings of the international Workshop on Network and Operating Systems Support For Digital Audio and Video (Stevenson, Washington, USA, June 13 - 14, 2005). NOSSDAV '05. ACM Press, New York, NY, 63-68. DOI=

  • Questions/Comments?Thank You For Listening


    Login Sequence - Incoming


    Service Location ProtocolRFC 2608Allows computers and other devices to find services in a local area network without prior configuration.service:printer:lpr://myprinter/myqueue


    Advanced Encryption StandardAka RijndaelBlock CipherReplaces DES (and the modified 3DES)128, 192, 256 bits keys

    AddRoundKey each byte of the state is combined with the round key; each round key is derived from the cipher key using a key schedule. SubBytes a non-linear substitution step where each byte is replaced with another according to a lookup table. ShiftRows a transposition step where each row of the state is shifted cyclically a certain number of steps. MixColumns a mixing operation which operates on the columns of the state, combining the four bytes in each column using a linear transformation.