1. Comparison between Skype and SIP- based Peer-to-Peer Voice-Over-IP Overlay Network Johnson Lee EECE 565 Data Communications

2. 2 Outline P2P versus Client-Server P2P-SIP design goal Overlay Network of Skype and P2P-SIP Login Sequences Advance Service Comparison Security Performance

3. 3 Peer-to-Peer / Client-Servier Client-Server vs P2P –Scalability –Infrastructure cost Structured vs Unstructured –Search time –Data distribution

4. 4 P2P-SIP Design Goals

5. 5 Skype Overlay Network Unstructured KaZaA predecssor based –Super node –Ordinary node –Login server STUN and TURN protocols for firewall and NAT traversal –Simple Traversal of UDP over NAT –Traversal Using Relay NAT

6. 6 P2P-SIP Overlay Network Based on Chord Distributed Hash Table (DHT) Structured O(log N) lookup time Finger table STUN and TURN firewall and NAT traversal as well

7. 7 Login Sequence 1 - Skype Start Send UDP packet(s) to HC IP address and port Response within 5 s TCP connection attempt with HC IP address and port Connected TCP connection attempt with HC IP address and port 80 (HTTP port) Connected TCP connection attempt with HC IP address and port 443 (HTTPS port) Connected Connection Attempt == 5 Failure Wait for 6 seconds Success Yes No Yes No Yes No Yes No

8. 8 Login Sequence 2 – P2P-SIP Multicast TTL = 1 Service Location Protocol (SLP) [LAN peers] Bootstrap Cached

9. 9 Advanced Services Comparison Offline Messaging Issue – Where to store? –Skype stores at it message originator –P2P-SIP proposes storing it at DHT Replication strategy for reliability Call transfer and call forwarding are SIP features that would be available in non-P2P SIP. –Super node instead of centralized database –Required feature for SIP (not as crucial for Skype)

10. 10 Security P2P-SIP –Malicious Node Hop-by-hop TLS (Tunneling) –Freeriding Incentives –Problem: No centralized login server to certify. Trust via reputation? Skype –Encryption AES 256bits –Key Exchange RSA 2048 –Public Key Certified by Login Server

11. 11 Performance P2P-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 delay –Skype Average 3-8 second for user location based on a 2004 study = C = 10, c = 1/60, and r = 1/60 =

12. 12 References 1.Skype Networks. http://www.skype.com 2.KaZaA. http://www.kazaa.com 3.K. 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. 4.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 2002 5.P2P-SIP. http://www.p2psip.org/ 6.Singh, 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= http://doi.acm.org/10.1145/1065983.1065999

13. Questions/Comments? Thank You For Listening

14. 14 Login Sequence - Incoming

15. 15 Service Location Protocol RFC 2608 Allows computers and other devices to find services in a local area network without prior configuration.local area network “service:printer:lpr://myprinter/myqueue”

16. 16 Advanced Encryption Standard Aka Rijndael Block Cipher Replaces DES (and the modified 3DES) 128, 192, 256 bits keys 1.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. key schedule 2.SubBytes — a non-linear substitution step where each byte is replaced with another according to a lookup table.lookup table 3.ShiftRows — a transposition step where each row of the state is shifted cyclically a certain number of steps. 4.MixColumns — a mixing operation which operates on the columns of the state, combining the four bytes in each column using a linear transformation.