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Peer-to-Peer Internet Telephony using SIP

Peer-to-Peer Internet Telephony using SIP

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Peer-to-Peer Internet Telephony using SIP

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  1. Peer-to-Peer Internet Telephony using SIP Kundan Singh and Henning Schulzrinne Columbia University, New York Sep 10, 2004

  2. Introduction Client-server vs P2P for VoIP Related work: Skype P2P-SIP architecture Design alternatives DHT (Chord) and SIP Node startup, peer discovery, node failure Advanced services Offline messages Conferencing Conclusions and future work Agenda Total 18 slides

  3. JOIN FIND alice P2P overlay 128.59.19.194 Alice 128.59.19.194 No central server SIP: Session Initiation Protocol REGISTER alice@columbia.edu =>128.59.19.194 INVITE alice@columbia.edu Contact: 128.59.19.194 Alice’s host 128.59.19.194 Bob’s host columbia.edu Client-server=> maintenance, configuration, controlled infrastructure

  4. P2P Advantages • Resource aggregation - CPU, disk, … • Cost sharing/reduction • Improved scalability/reliability • Interoperability - heterogeneous peers • Increased autonomy at the network edge • Anonymity/privacy • Dynamic (join, leave), self organizing • Ad hoc communication and collaboration

  5. P P P P P P P P P P P P Related work: Skype From the KaZaA community • Host cache of some super nodes • Bootstrap IP addresses • Auto-detect NAT/firewall settings • STUN and TURN • Protocol among super nodes – ?? • Allows searching a user (e.g., kun*) • History of known buddies • All communication is encrypted • Promote to super node • Based on availability, capacity • Conferencing

  6. We propose: P2P-SIP • Unlike server-based SIP architecture • Unlike proprietary Skype architecture • Robust and efficient lookup using DHT • Interoperability • DHT algorithm uses SIP communication • Hybrid architecture • Lookup in SIP+P2P • Unlike file-sharing applications • Data storage, caching, delay, reliability • Disadvantages • Lookup delay and security

  7. Background: DHT (Chord) • Identifier circle • Keys assigned to successor • Evenly distributed keys and nodes • Finger table: logN • ith finger points to first node that succeeds n by at least 2i-1 • Stabilization for join/leave 1 54 8 58 10 14 47 21 42 38 32 38 24 30

  8. d471f1 1 d467c4 d46a1c 8 d462ba 58 54 d4213f 14 10 47 21 Route(d46a1c) d13da3 42 38 32 65a1fc 38 24 30 Design Alternatives servers 1 54 10 38 24 30 clients Use DHT in server farm Use DHT for all clients; But some are resource limited Use DHT among super-nodes Hierarchy Dynamically adapt

  9. Discover DHT (Chord) User location Audio devices User interface (buddy list, etc.) ICE RTP/RTCP Codecs SIP Architecture • DHT communication using SIP REGISTER • Known node: sip:15@192.2.1.3 • Unknown node: sip:17@sippeer.net • User: sip:alice@example.com Signup, Find buddies IM, call On reset Signout, transfer On startup Leave Find Join REG, INVITE, MESSAGE Peer found/ Detect NAT Multicast REG REG

  10. sipd DB Node Startup columbia.edu • SIP • REGISTER with SIP registrar • DHT • Discover peers: multicast REGISTER • Join DHT using node-key=Hash(ip) • REGISTER with DHT using user-key=Hash(alice@columbia.edu) REGISTER alice@columbia.edu Detect peers REGISTER alice=42 58 42 12 14 REGISTER bob=12 32

  11. Super-nodes • Initial bootstrap super-nodes • Never allow capacity to exceed • When to become super-node • Local decision; can be influenced by existing peer • If REGISTER received • Local key => store locally • Else, forward REGISTER to appropriate nodes • Super-node refreshes REGISTER on behalf • Should be in “public” address space (?) REGISTER key=42 REGISTER DHT 42

  12. Node Leaves • Graceful leave • Un-REGISTER • Transfer registrations • Failure • Attached nodes detect and re-REGISTER • New REGISTER goes to new super-nodes • Super-nodes adjust DHT accordingly REGISTER key=42 REGISTER OPTIONS DHT 42 42

  13. Dialing Out • Call, instant message, etc. INVITE sip:hgs10@columbia.edu MESSAGE sip:alice@yahoo.com • If existing buddy, use cache first • If not found • SIP-based lookup (DNS NAPTR, SRV,…) • P2P lookup • Send to super-nodes: proxy • Use DHT to locate: proxy or redirect to next hop INVITE key=42 Last seen 302 INVITE DHT 42

  14. Offline messages • INVITE or MESSAGE fails • Responsible node stores voicemail, instant message. • Delivered using MWI or when online detected • Replicate the message at redundant nodes • Sequence number prevents duplicates • Security: How to avoid spies? • How to recover if all responsible nodes leave?

  15. Conferencing (further study) • One member becomes mixer • Centralized conferencing • What if mixer leaves? • Fully distributed • Many to many signaling and media • Application level multicast • Small number of senders

  16. Explosive growth (further study) • Cache replacement at super-nodes • Last seen many days ago • Cap on local disk usage (automatic) • Forcing a node to become super node • Graceful denial of service if overloaded • Switching between flooding, CAN, Chord, … • . . .

  17. More open issues (further study) • Security • Anonymity, encryption, • Attack/DOS-resistant, SPAM-resistant • Malicious node • Protecting voicemails from storage nodes • Optimization • Locality, proximity • Motivation • Why should I run as super-node?

  18. d471f1 d467c4 d46a1c d462ba d4213f 763 427 C C P P S 364 123 Route(d46a1c) d13da3 324 C C P P 365 135 564 65a1fc C P Conclusions • P2P useful for VoIP • Scalable, reliable • No configuration • Not as fast as client/server • P2P-SIP • Basic operations easy • Implementation • sippeer: C++, Linux • Interoperates • Some potential issues • Security • Performance