1. VOIP over Peer-to-Peer

2. Road Map Introduction Background VOIP with P2P architecture
SIP
Media routing
Interwork with PSTN
Problems
Summary

3. Introduction Advantages of P2P systems
High scalability
Robustness
Fault tolerance
Network self-organizes
Intelligence (cooperation)
How can VOIP be integrated within a P2P system?

4. Road Map Introduction Background VOIP on P2P architecture
SIP
Media routing
Interwork with PSTN
Problems
Summary

5. P2P Architecture Centralized Pure Hybrid (super-node)
Directory is stored in one server, but data is transferred between peers
Napster
Pure
Directory is stored in each peer, and lookup is by flooding query messages
Gnutella
Hybrid (super-node)
Directory is stored in each super node, and lookup is by requesting super-nodes
Kazza

6. P2P Architecture

7. Distributed Hash Table
Chord, Pastry, CAN, Tapestry, …
Lookup styles directly map to the redirect and proxy server
Chord

8. P2P Comparison Property/ scheme Un-structured CAN Chord Tapestry
Pastry
Viceroy
Routing
O(N) or no guarantee
d x N1/d
log(N)
logBN
State
Constant 2d
B.logBN
Join/leave
(logN)2
Reliability and fault resilience
Data at Multiple locations;
Retry on failure; finding popular content is efficient
Multiple peers for each data item; retry on failure; multiple paths to destination
Replicate data on consecutive peers; retry on failure
Replicate data on multiple peers; keep multiple paths to each peers
Routing load is evenly distributed among participant lookup servers

9. Server-based vs. Peer-to-Peer
Reliability, failover latency
DNS-based. Depends on client retry timeout, DB replication latency, registration refresh interval
DHT self organization and periodic registration refresh. Depends on client timeout, registration refresh interval.
Scalability, number of users
Depends on number of servers in the two stages.
Depends on refresh rate, join/leave rate, uptime
Call setup latency
One or two steps.
O(log(N)) steps.
Security
TLS, digest authentication, S/MIME
Additionally needs a reputation system, working around spy nodes
Maintenance, configuration
Administrator: DNS, database, middle-box
Automatic: one time bootstrap node addresses
PSTN interoperability
Gateways, TRIP, ENUM
Interact with server-based infrastructure or co-locate peer node with the gateway

10. Road Map Introduction Background VOIP on P2P architecture
SIP
Media routing
Interwork with PSTN
Problems
Summary

11. VOIP on P2P Architecture
Block diagram of a P2P-SIP node
SIP
Initialization
Registration and Peer discovery
Dialing out
Node shutdown
Media routing
Firewall and NAT traversal
Intelligent routing

12. Block diagram of a P2P-SIP node

13. Initialization

14. Initialization Calculate the key for DHT by IP7
Contact one of the node in DHT network
Request
REGISTER sip: SIP/2.0
To:
From:
Response
SIP/ OK
To:
Contact:

15. Initialization Insert self into correct position Build routing table
Between predecessor: 1 and successor: 10
Build routing table
10>= 7+2i-1, i = 1, 2
Send sip REGISTER from 11 (= )
REGISTER sip: SIP/2.0
To:
From:
Respond by 15
SIP/ OK
Contact: …

16. Initialization

17. Registration and Peer Discovery
columbia.edu DB
sipd
SIP
REGISTER with SIP registrar
DHT
Discover peers: bootstrap node
Join DHT using node-key =Hash(ip)
REGISTER with DHT using user-key
REGISTER
Detect peers
REGISTER alice=42 42 58 12 14
REGISTER bob=12 32

18. Dialing Out Call, instant message, etc.
INVITE
MESSAGE
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
INVITE key=42
302
INVITE
DHT 42

19. Node shutdown Graceful termination DHT system will re-organize
7 will send unregister message to its predecessor:1 and successor: 10
REGISTER SIP/2.0
To:
From:
Expires: 0
Contact: q=1.0;
Contact: q=.8 …
REGISTER SIP/2.0
DHT system will re-organize

20. Node shutdown Node failure
When nodes find a remote node failure, it removes it from its routing table
Resend the original query request to the new failover hop

21. Firewall & NAT Traversal
Signaling
SIP symmetric response routing
Connection reuse
Use existing connections to transmit signals
Media
ICE (interactive connectivity establishment) for media session
STUN and TURN

22. Intelligent Routing
In an overlay network, there are diverse paths through relay nodes
But how to select a good one? It needs extra measurements!
Criterions for selecting paths
Packet loss rate
End-to-end delay
Available bandwidth

23. Intelligent Routing
Most of those measurements require the cooperation of middle nodes
They are easier to be implemented in P2P architecture than others

24. Road Map Introduction Background VOIP on P2P architecture
SIP
Media routing
Interwork with PSTN
Problems
Summary

25. Interwork with PSTN (1/4)
How do they verify that the user owns the number if he registers his number?
Every gateway node can reach potentially every phone number in the world – at very different rates.
Registering a telephone prefix
Use tel URI (Not conformant with RFC 3966)
“tel:;phone-context=+1-212”

26. Interwork with PSTN (2/4)
Calling a telephone number
INVITE tel: SIP/2.0
To: <tel: >
From:
Request-Disposition: redirect
The basic key, K0, is “tel: ” derived from To header after removing any fillers.
Other keys, Kn−i, is computed as “tel:;phone-context=+first i digits prefix”, for i=1,2,..n-1, where n is total number of digits.

27. Interwork with PSTN (3/4)
Incoming INVITE handling
The canonical “tel” URI is formed to compute the DHT key by removing fillers and converting “sip” URI to “tel” URI.
For example, user=phone” is converted to “tel:;phone-context= ”.
This is used as the key to compute the next hop in routing.

28. Interwork with PSTN (4/4)
Response
SIP/ Moved temporarily
To: <tel:;phone-context= >
Contact: <sip:phone.cs.columbia.edu;lr> cost=0; q=1.0
To: <tel:;phone-context=+1212>
Contact: <sip:phone.cs.columbia.edu;lr> cost=USD.03/6s; q=1.0
Contact: <sip:manhattan.verizon.com;lr>; cost=USD.06/60s; q=.8
To: <tel:;phone-context=+1>
Contact: <sip:mci.com;lr> cost=USD.10/120s; q=1.0
Contact: <sip:att.com;lr>; cost=USD.09/60s; q=.8

29. Road Map Introduction Background VOIP on P2P architecture
SIP
Media routing
Interwork with PSTN
Problems
Summary

30. Problems Security issues in peer-to-peer system Malicious program
break-in, spying or spread virus, spy-wares or worms
Reducing risks by
Software developed by trusted entities or open source community
Running the application as a regular user instead of an administrator (on Windows) or super-user (on Unix)
Copyright violation
Easily extended to support file transfer
Reducing risk by
P2P-SIP does not have an efficient search method
Authenticate in Identifier protection

31. Problems Stolen identity Data Privacy
A malicious user may steal the identify of another user
Solved by doing Authentication
User identify must be a valid address
System generates a password for the user identify and sends it to the address
Using MD5 hash function
Data Privacy
Public/Private/Protected Data
Solved by using Public key mechanism

32. Problems
Trust
Misbehaving peers that route calls incorrectly or log information for misuse
Solved by
Hide the security algorithms

33. Summary P2P useful P2P/SIP Scalable, reliable No configuration
Not as fast as client/server
P2P/SIP
Basic operations easy
Some potential issues
Security
Performance
Quality (audio)

34. Reference
Kundan Singh and Henning Schulzrinne, "Peer-to-peer Internet Telephony using SIP", NOSSDAV. Skamania, Washington, June 2005.
Kundan Singh and Henning Schulzrinne, "Peer-to-peer Internet Telephony using SIP", New York Metro Area Networking Workshop, Sep 2004.
Kundan Singh and Henning Schulzrinne, "Peer-to-peer Internet Telephony using SIP", Columbia University Technical Report CUCS , Oct 2004.

35. Reference
An extension to the session initiation protocol (SIP) for symmetric response routing. RFC 3581, Internet Engineering Task Force, Aug. 2003
Connection reuse in the session initiation protocol (SIP). Internet Draft draft-ietf-sip-connect-reuse-00, Internet Engineering Task Force, Aug. 2003
Interactive connectivity establishment (ICE): a methodology for network address translator (NAT) traversal for the session initiation protocol (SIP). Internet Draft draft-ietf-mmusic-ice-00, Internet Engineering Task Force, Oct. 2003
Improving VoIP Quality Through Path Switching, in Proceedings of IEEE INFOCOM 2005, Miami, March, 2005
Exploring the Performance Benefits of End-to-End Path Switching. In Proceedings of ACM Sigmetrics/Performance (Extended Abstract), New York, June 2004