Peer-to-peer approaches for SIP Henning Schulzrinne Dept. of Computer Science Columbia University

Applications Small stand-alone networks –2-50 –SOHO, events, emergency coordination –may not have access to Internet infrastructure Corporate size networks – –single administrator Global-scale networks – million –consumer applications –serious trust issues

SIP-managed DHT OpenDHT Three basic approaches Full distribution and search –similar to Bonjour –scales to small, local networks DHT built using SIP –see Kundan/Schulzrinne and Cao/Bryan/Lowekamp –dedicated to VoIP –Skype model Using an external DHT (Columbia) –using OpenDHT as generic service used by multiple applications –can provide mapping or pointer to mapping

P2P-SIP: Implementation in SIPc OpenDHT –Trusted nodes –Robust –Fast enough (<1s) Identity protection –Certificate-based –SIP id == P2P for Calls, IM, presence, offline message, STUN server discovery and name search

P2P-SIP: What is OpenDHT? Service model, unlike earlier library model of Chord or CAN –DHT accessed via SunRPC & XML-RPC –Easy deployment and maintenance Bamboo DHT nodes on PlanetLab –Public DHT service running since April 2004 –Many existing applications: i3, CFS, Ostream, HIP,… DHT API (server side on Bamboo nodes) –PUT(key,value,H(secret),ttl) where H() is SHA1 –GET(key)  (value,H(secret),remaining-ttl) –REMOVE(key,H(value),secret,ttl) ReDiR API (client side for lookup/join/leave) –Can build anycast, multicast, range search using this Fair resource (disk) allocation among clients (IP addr)

Hybrid architecture Cross register, or Locate during call setup –DNS, or –P2P-SIP hierarchy

Conclusion Lots of open issues… Motivation for P2P? –Low operational cost? –Ease of use? –Reliability? What to use p2p for? –identifier lookup (“location server)” –locating a NAT traversal server (STUN) –media file storage (voice mail) –presence –conferencing Some architectural open issues –trust (sybil, byzantine failures) “man-in-the-middle” –identifier ownership prevention? at least, detection –reliability