Making PeertoPeer Work for SIP

1
Making Peer-to-Peer Work for SIP

• Henning Schulzrinne
• with Salman Baset, Jae Woo Lee
• Dept. of Computer Science, Columbia University,
  New York
• hgs_at_cs.columbia.edu
• SIP 2008 (upperside.fr)
• Paris, France
• January/February 2008

2
Outline

• Why peer-to-peer?
• Three types of peer-to-peer systems
• Protocol architecture
• A prototype for a P2P SIP system
• Issues and challenges

3
Peer-to-peer systems
Service discovery
High
NAT
Data size
Data size
Replication
NAT
Performance impact / requirement
Medium
Replication
Replication
Data size
Low
NAT
File sharing
VoIP
Streaming
4
Three kinds of P2P systems
structured P2P system (DHT)
unstructured P2P system
mDNS
network size
Fortune 500
SME
ad-hoc 802.11 network
dentist office
5
DNS-SD/mDNS overview

• DNS-Based Service Discovery (DNS-SD) adds a level
  of indirection to SRV using PTR
• _daap._tcp.local. PTR Toms Music._daap._tcp.loc
  al.
• _daap._tcp.local. PTR Joes Music._daap._tcp.loc
  al.
• Toms Music._daap._tcp.local. SRV
• 0 0 3689
  Toms-machine.local.
• Toms Music._daap._tcp.local. TXT
• "Version196613" "iTSh Version196608"
  
• "Machine ID6070CABB0585"
  "Passwordtrue
• Toms-machine.local. A 160.39.225.12
• Multicast DNS (mDNS)
• Run by every host in a local link
• Queries answers are sent via multicast
• All record names end in .local.

1n mapping
6
SIP URI Advertisement Format

• Service instance name Instance.Service.Domain
• Instance ( SIP-URI / SIPS-URI ) SP
  description
• Service _sipuri._udp / _sipuri._tcp /
  _sipuri._sctp
• E.g. sipbob_at_example.com - PDA._sipuri._udp.local
  .
• Contact TXT record attribute
• Similar to Contact SIP header except
• It contains only a single URI
• Non-SIP URIs are not allowed
• UA capabilities advertised via field parameters
  (RFC3840)

7
z2z Zeroconf-to-Zeroconf interconnection
rendezvous point - OpenDHT
Import/export services
Import/export services


z2z
z2z
Zeroconf subnet A
Zeroconf subnet B
8
Structured P2P networks (overlays)
idx
Neighbor table(successor)
Routing table

• Maps key to data object
• Can start search at any node
• Finds in O(log N) steps
• Examples Chord, Kademlia, CAN
• Distance metric differs

9
Unstructured P2P network

• full or partial mesh
• nodes keep search index of neighbors
• forward queries (e.g., random walk)
• allow search expressions
• resilient against churn
• examples Gnutella, Gnutella2

10
P2PSIP architecture
Bootstrap / authentication server
alice_at_example.com
Overlay2
Peer
SIP
NAT
Overlay1
STUN TURN
P2P
NAT
SIP
bob_at_example.com
Client
P2P
11
Protocol stack
SIP
H(URL) ? data (Contact URL, proxy)
OR
peer-to-peer lookup
DNS
TLS
DTLS
UDP?
SCTP
TCP
HIP
IPv4
IPv6
12
IETF efforts

• mDNS work in SIP WG
• done waiting for mDNS publication
• P2PSIP working group
• generic lookup mechanism
• DHT-agnostic (CAN, Kademlia, Chord, ...)
• many protocols ASP, RELOAD, P2PP, P2NS, XPP,
  SEP, ...
• HIP proposals HIPHOP, draft-hautakorpi-p2psip-wit
  h-hip
• Open issues
• how general?
• role of HIP?
• service discovery
• NAT traversal in HIP? specialized ICE?

13
P2PP implementation

• Chord, Kademlia, Bamboo (in-progress)
• SHA1, SHA256, MD5, MD4
• Runs on Windows Linux
• Integrated with OpenWengo (VoIP phone)
• Available for download (Linux Windows)
• http//www1.cs.columbia.edu/salman/p2pp/setupp2p
  p.html

14
Screen snapshot

• Alice and Bob are part of Kademlia network
• Alice calls Bob
• The lookup is performed using P2PP
• Call is established using SIP

15
P2PP Planet Lab

• 500 node network, 160 machines
• OpenDHT 150-200 nodes/machines
• Integrated with Nokia Symbian OS

geographical view
routing table
16
P2PP Planet Lab
DHT view
17
P2P issues performance

• Look-up performance for N peers is O(log N)
• affects call setup delay
• e.g., Skype delay much higher than client-server
  calls
• ? use combination of peers and clients
• only small fraction of participants should be
  clients
• media generally not routed through overlay
• spare capacity ? more resilient to overload
• harder to compensate for resolution hot spots

18
P2P issues economics

• Operator saves on
• bandwidth
• minimal for SIP signaling
• interesting for media (TURN NAT traversal, media
  relay, mixing, transcoding)
• servers
• single SIP server can handle gt 100,000 users gt
  0.10/month
• except for NAT traversal (heartbeat)
• except for media processing and storage

19
P2P issues reliability

• CW P2P systems are more reliable
• Catastrophic failure vs. partial failure
• single data item vs. whole system
• Node reliability
• correlated failures of servers (power, access,
  DOS)
• lots of very unreliable servers (95?)
• Natural vs. induced replication of data items

20
Security privacy

• Security much harder
• user authentication and credentialing
• usually now centralized (enrollment server)
• sybil attacks
• byzantine failures
• Privacy
• storing user data on somebody elses machine
• Distributed nature doesnt help much
• one attack likely to work everywhere
• CALEA?

21
OAM

• Hard to see whats going on
• No real peer-to-peer management systems
• system loading (CPU, bandwidth)
• automatic splitting of hot spots
• user experience (signaling delay, data path)
• call failures
• IETF effort design for manageability and
  debugging
• P2PP adds mechanism to query nodes for
  characteristics
• Who gathers and evaluates the overall system
  health?

22
P2P issues locality

• Most P2P systems location-agnostic
• each hop half-way across the globe
• Locality matters
• media servers, STUN servers, relays, ...
• Working on location-aware systems
• keep successors in close proximity
• AS-local STUN servers

23
P2P issues mobility

• Mobile nodes are poor peer candidates
• power consumption
• unreliable links
• asymmetric links
• But no problem if clients
• Useful for moving networks (train, plane)

24
Conclusion

• P2P for SIP can provide
• easier configuration
• operation in challenged environments
• lower infrastructure costs
• But at a cost
• greater system complexity
• possibly longer call set-up delays
• new security threats
• IETF designing common protocol for identifier
  lookups
• likely to be useable for other purposes