Peer-to-peer approaches for SIP

1
Peer-to-peer approaches for SIP

• Henning Schulzrinne
• Dept. of Computer Science
• Columbia University

2
Applications

• Small stand-alone networks
• 2-50
• SOHO, events, emergency coordination
• may not have access to Internet infrastructure
• Corporate size networks
• 50-1000
• single administrator
• Global-scale networks
• 1000-100 million
• consumer applications
• serious trust issues

3
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

SIP-managed DHT
OpenDHT
4
P2P-SIP Implementation in SIPc

• OpenDHT
• Trusted nodes
• Robust
• Fast enough (lt1s)
• Identity protection
• Certificate-based
• SIP id email
• P2P for
• Calls, IM, presence, offline message, STUN
  server discovery and name search

5
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
• 200-300 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)

6
Hybrid architecture

• Cross register, or
• Locate during call setup
• DNS, or
• P2P-SIP hierarchy

7
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