1. Peer to peer Internet telephony challenges, status and trend
Kundan Singh
Oct 2010
Peer-to-peer (P2P) systems inherently have high scalability, robustness and fault tolerance because there is no central point of failure and the network self-organizes itself. Skype is a popular and dominant example of P2P VoIP. The IETF P2P-SIP working group was formed to explore a P2P architecture for SIP-based telephony and beyond. Traversal through NATs and firewalls is a major challenge in getting end-to-end media in a distributed P2P network. Another major problem of P2P VoIP is security against malicious peers.
I will present an overview of P2P VoIP,  the challenges, status and current trend in practice. In particular you will learn the advantages and problems associated with P2P VoIP, comparison of various architectures, design decisions and implementations, and a summary of IETF effort.

2. What will you learn? What is P2P telephony? How is it implemented?
What are the benefits and limitations?
What is IETF doing about it?

3. Problem with servers Server-based Peer-to-peer
What is P2P telephony?
Problem with servers
Server-based
Operations cost: maintenance, configuration
Central points of catastrophic failures
Controlled infrastructure (e.g., DNS)
Peer-to-peer
Robust: no central dependency
Self organizing, no configuration
Inherently scalable C S P

4. Peer-to-peer ≠ cloud computing
What is P2P telephony?
Peer-to-peer ≠ cloud computing
Self management
Free resource sharing
No central co-ordination …
Self management
Utility computing
Central co-ordination …
managed

5. A brief history Napster initiated P2P file sharing
What is P2P telephony?
A brief history
1999
Napster initiated P2P file sharing
“for every one of you that falls, two shall arise.”
Distributed hash tables
Chord, CAN, Pastry, Tapestry, Kademlia, …
Skype (re-)invented P2P-VoIP
Now: 13% international calls, 54 billion minutes
Demonstrated P2P-SIP at Columbia University
IETF WG formed; several more implementations
Adobe added P2P to Flash Player
Proprietary, E2E but not quite P2P
2001
2003
2004
2008

6. PBX, H.320, H.324, RTMP, Asterix/IAX, B2BUA, SBC, …
What is P2P telephony?
signaling + media
PBX, H.320, H.324, RTMP, Asterix/IAX, B2BUA, SBC, …
signaling
media
SIP, H.323, XMPP/Jingle, Gtalk, RTSP, RTMFP, …
Skype, P2P-SIP, …

7. (mostly) unstructured Kazaa based  unstructured
What is P2P telephony?
File sharing
Skype
P2P-SIP
topology
(mostly) unstructured
Kazaa based 
unstructured
structured DHT  efficiency guarantee
inter-operability
implementation driven
proprietary/close needs gateway
open protocols + algorithms
efficiency
caching, delay storage, split-and-store
overloaded super-nodes
caching useless; bounded load
centralized
varies
login server
enrollment service
malicious nodes
incentive driven
proprietary software
open problem

8. What is a DHT? Chord consistent hashing data replication
What is P2P telephony?
What is a DHT?
Key
node
8+1 = 9 14
8+2 = 10
8+4 = 12
8+8 = 16 21
8+16=24 32
8+32=40 42 1 8 14 21 32 38 58 47 42 10 24 30 54 38
Chord
consistent hashing
data replication

9. How to combine SIP + P2P? SIP-using-P2P P2P-over-SIP
How is it implemented?
How to combine SIP + P2P?
SIP-using-P2P
SIP location service
P2P-over-SIP
+ implement P2P network using SIP
P2P network
SIP-using-P2P
P2P SIP proxies
P2P-over-SIP
Maintenance
P2P
SIP
Lookup
Alice
INSERT
INVITE
FIND
P2P network
Alice
REGISTER
INVITE alice
SIP overlay

10. What are super peers? Use DHT among super-peers How is it implemented?1 10 24 30 54 38
Use DHT among super-peers

11. Implementation examples
How is it implemented?
Implementation examples
SIPpeer
SIPc + OpenDHT
Sipeerior
SIPDHT
OpenVoIP
39 peers
SIP thor
P2P-over-SIP
SIP-using-P2P
Data model
Service model
Adaptor

12. What are the challenges?
What are the benefits and limitations?
What are the challenges?
Bootstrap a network
Security of stored data and keys
Data vs service model
NAT and firewall traversal
Working with free loaders
Getting around malicious peers

13. When to do P2P? if then most of the peers do not trust each other, AND
What are the benefits and limitations?
When to do P2P? if
most of the peers do not trust each other,
AND
There is no incentive to help peers
then
P2P does not evolve naturally to work
See

14. Unstructured P2P (blind-search) Structured P2P (Chord) Scaling
What are the benefits and limitations?
server-based
Unstructured P2P (blind-search)
Structured P2P (Chord)
Scaling
server count 
≈ {server-count}
user count 
K-degree no limit
≈ 2{node-capacity}*
uptime, churn, …
Efficiency
most efficient
#connections 
maintain = O((logN)2)
Call setup latency
one or two steps
lookup = O(logN)
Security
trust provider; boolean
connect to trusted nodes only
trust (most) super nodes; probabilistic
Availability
server redundancy
(1-(1-R)P);
catastrophic failure possible; bulk load
no guarantee
upper bound; catastrophic failure unlikely
* Node capacity of 10 register/s and refresh/call rates of 1/min 
more than 16 million peers (super-nodes) in the network

15. IETF P2P-SIP working group
What is IETF doing about it?
IETF P2P-SIP working group
Includes
peer protocol, client protocol, SIP usage, locating resources.
Excludes
modification to SIP, unique identities, “research”-type, search, multicast, dynamic DNS, …
Must
use existing tools from other WGs

16. Proposed architecture
What is IETF doing about it?
Proposed architecture
SIP usage
XMPP usage
MUST
Chord DHT
128-bit keys
DTLS and TLS
Message
transport
Storage
Topology
plugin
Forwarding and link
management
TLS
DTLS

17. REsource LOcation And Discovery
What is IETF doing about it?
REsource LOcation And Discovery
Creating pages of specifications
draft-ietf-p2psip-base-10 (154p), plus ICE+STUN +TURN+DTLS (260p), and: draft-ietf-p2psip-sip-05, -diagnostics-04, -self-tuning-02, service-discovery-01
Creating unnecessary complexity
No compliant implementation; discourages developers/start ups; real problems are out-of-scope
2010
2009

18. Summary What is P2P telephony? How is it implemented?
Versus client-server, end-to-end, and cloud
How is it implemented?
P2P-over-SIP, SIP-using-P2P, data vs service, adaptor & proxy,
What are the benefits and limitations?
Scalability, availability, maintenance, lookup
What is IETF doing about it?
RELOAD, SIP usage, …
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