P2P-SIPP2P-SIPPeer to peer Internet telephony using Peer to peer Internet telephony using SIPSIP

Kundan Singh and Henning Schulzrinne Columbia University, New York

Dec 15, 2005http://www.cs.columbia.edu/IRT/p2p-sip

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AgendaAgenda Introduction

What is P2P? and SIP? Why P2P-SIP? Architecture

Design choices: SIP using P2P vs P2P over SIP; Components that can be P2P

Implementation Choice of P2P (DHT); Naming; adaptor;

SIP message Conclusions

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What is P2P?What is P2P? Share the resources of

individual peers CPU, disk, bandwidth,

information, …

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Computer systems

Centralized Distributed

Client-server Peer-to-peer

Flat Hierarchical Pure Hybrid

mainframesworkstations

DNSmount

RPCHTTP

GnutellaChord

NapsterGroove

Kazaa

File sharing

Communication and collaboration

Distributed computing

SETI@Homefolding@Home

NapsterGnutellaKazaaFreenetOvernet

MagiGrooveSkype

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What is SIP? Why P2P-SIP?What is SIP? Why P2P-SIP?

Bob’s hostAlice’s host128.59.19.194

(1) REGISTER alice@columbia.edu =>128.59.19.194

(2) INVITE alice@columbia.edu

(3) Contact: 128.59.19.194

columbia.edu

Client-server=> maintenance, configuration, controlled infrastructure

P2P overlay

Alice128.59.19.194

(1) REGISTER(2) INVITE alice

(3) 128.59.19.194

No central server, search latency

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How to combine SIP + How to combine SIP + P2P?P2P?

SIP-using-P2P Replace SIP

location service by a P2P protocol

P2P-over-SIP Additionally,

implement P2P using SIP messaging

P2P network

Alice128.59.19.194

INSERT

INVITE sip:alice@128.59.19.194

P2P-SIPoverlay Alice

128.59.19.194

REGISTERINVITE aliceFIND

SIP-using-P2P P2P SIP proxies

P2P-over-SIP

Maintenance P2P P2P SIPLookup P2P SIP SIP

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Deployment scenarios?Deployment scenarios?

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P2P proxies

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P2P database

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P2P clients

Plug and play; May use adaptors;Untrusted peers

Zero-conf server farm; Trusted servers and user identities

Global OpenDHT; Clients or proxies can use;Trusted peers (?)

Interoperate among these!

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What else can be P2P?What else can be P2P? Rendezvous/signaling (SIP) Configuration storage Media storage (e.g., voice mail) Identity assertion (?) PSTN gateway (?) NAT/media relay (find best one)

Trust models are different for different components!

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What is our P2P-SIP?What is our P2P-SIP? Unlike server-based SIP architecture Unlike proprietary Skype architecture

Robust and efficient lookup using DHT Interoperability

DHT algorithm uses SIP communication Hybrid architecture

Lookup in SIP+P2P Unlike file-sharing applications

Data storage, caching, delay, reliability Disadvantages

Lookup delay and security

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Background: DHT (Chord)Background: DHT (Chord) Identifier circle Keys assigned to

successor Evenly distributed

keys and nodes Finger table: logN

ith finger points to first node that succeeds n by at least 2i-1

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Key node

8+1 = 9 148+2 = 10

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8+4 = 12

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8+8 = 16

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8+16=24

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8+32=40

42Find

Map key to nodeJoin, Leave, or Failure

Update the immediate neighborsSuccessor and predecessor

Stabilize: eventually propagate the info

ReliabilityLog(N) successors; data replication

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Design AlternativesDesign Alternatives

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Use DHT in server farm

Use DHT for all clients; But some are resource limited

Use DHT among super-nodes

1. Hierarchy2. Dynamically adapt

servers

clients

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ArchitectureArchitecture

User interface (buddy list, etc.)

SIPICE RTP/RTCPCodecs

Audio devicesDHT (Chord)

On startup

Discover

User location

Multicast REGISTERPeer found/Detect NAT

REGISTERREGISTER, INVITE,MESSAGE

Signup,Find buddies

JoinFind

Leave

On resetSignout,transfer

IM,call

SIP-over-P2P

P2P-using-SIP

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Naming and Naming and authenticationauthentication SIP URI as node and user identifiers

Known node: sip:15@192.2.1.3 Unknown node: sip:17@example.com User: sip:alice@columbia.edu

User name is chosen randomly by the system, by the user, or as user’s email

Email the randomly generated password TTL, security

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SIP messagesSIP messages DHT (Chord) maintenance

Query the node at distance 2k with node id 11REGISTERTo: <sip:11@example.invalid>From: <sip:7@128.59.15.56>

SIP/2.0 200 OKTo: <sip:11@example.invalid>Contact: <sip:15@128.59.15.48>; predecessor=sip:10@128.59.15.55

Update my neighbor about meREGISTER To: <sip:1@128.59.15.60>Contact: <sip:7@128.59.15.56>; predecessor=sip:1@128.59.15.60

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Find(11) gives 15

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SIP messagesSIP messages User registration

REGISTERTo: sip:alice@columbia.eduContact: sip:alice@128.59.19.194:8094

Call setup and instant messagingINVITE sip:bob@example.comTo: sip:bob@example.comFrom: sip:alice@columbia.edu

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ImplementationImplementation sippeer: C++,

Unix (Linux), Chord Node join and

form the DHT Node failure is

detected and DHT updated

Registrations transferred on node shutdown

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Adaptor for existing Adaptor for existing phonesphones

Use P2P-SIP node as an outbound proxy

ICE for NAT/firewall traversal STUN/TURN

server in the node

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Hybrid architectureHybrid architecture Cross register,

or Locate during

call setup DNS, or P2P-SIP

hierarchy

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Advanced servicesAdvanced services Offline messages

INVITE or MESSAGE fails: responsible node stores voicemail, instant message.

Conferencing Three-party, full-mesh, multicast

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Performance predictionPerformance prediction Scalability

#messages = f(refresh-rate, call arrival, join/leave/failure rate)

M={rs+ rf(log(N))2} + c.log(N) + (k/t)log(N) + (log(N))2/N User availability

f(failure, refresh-rate, replication) Call setup latency

f(availability, retransmission timers) Known buddies; DHT optimizations

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More open issues (further More open issues (further study)study) Security

Anonymity, encryption, Attack/DOS-resistant, SPAM-resistant Malicious node Protecting voicemails from storage nodes

Optimization Locality, proximity, media routing

Deployment SIP-P2P vs P2P-SIP, Intra-net, ISP servers

Motivation Why should I run as super-node?

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P2P vs server-basedP2P vs server-basedserver-based P2P

scaling server count scales with user count, but limited by supernode count

efficiency most efficient DHT maintenance = O((log N)2), lookup = O(logN)

security trust server provider; binary

trust most supernodes; probabilistic

reliability server redundancy; catastrophic failure possible

unreliable supernodes; catastrophic failure unlikely

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ConclusionsConclusions P2P useful for VoIP

Scalable, reliable No configuration Not as fast as client/server

P2P-SIP Basic operations easy

Implementation (C++, Linux) Interoperates

Some potential issues Security Robustness Performance (?)

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http://www.cs.columbia.edu/IRT/p2p-sip

Backup slidesBackup slides

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Server-based vs peer-to-Server-based vs peer-to-peerpeer

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

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Related workRelated workP2PP2P P2P networks

Unstructured (Kazaa, Gnutella,…) Structured (DHT: Chord, CAN,…)

Skype and related systems Flooding based chat, groove, Magi

P2P-SIP telephony Proprietary: NimX, Peerio, File sharing: SIPShare

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Node StartupNode Startup SIP

REGISTER with SIP registrar DHT

Discover peers: multicast REGISTER

SLP, bootstrap, host cache Join DHT using node-

key=Hash(ip) Query its position in DHT Update its neighbors Stabilization: repeat periodically

User registers using user-key=Hash(alice@columbia.edu)

alice@columbia.edu

REGISTERDB

sipd

Detect peers

columbia.edu

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42REGISTER alice=42

REGISTER bob=12

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Node LeavesNode Leaves Chord reliability

Log(N) successors, replicate keys

Graceful leave Un-REGISTER Transfer registrations

Failure Attached nodes detect and

re-REGISTER New REGISTER goes to new

super-nodes Super-nodes adjust DHT

accordingly

DHT

REGISTER key=42

OPTIONS

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REGISTER

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Dialing Out (message Dialing Out (message routing)routing)

Call, instant message, etc.INVITE sip:hgs10@columbia.eduMESSAGE sip:alice@yahoo.com

If existing buddy, use cache first

If not found SIP-based lookup (DNS

NAPTR, SRV,…) P2P lookup

Use DHT to locate: proxy or redirect to next hop

DHT

Last seen

INVITE key=42

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INVITE

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Find(user)Find(user) Option-1: No REGISTER

Node computes key based on user ID

Nodes join the overlay based on ID

One node one user

Option-2: With REGISTER REGISTERs with nodes

responsible for its key Refreshes periodically Allows offline messages (?)

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42REGISTER alice=42

REGISTER bob=12

alice=42

sam=24

bob=12

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P2P-SIPP2P-SIPSecurity – open issues (threats, solutions, issues)Security – open issues (threats, solutions, issues) More threats than server-based

Privacy, confidentiality Malicious node

Don’t forward all calls, log call history (spy),… “free riding”, motivation to become super-node

Existing solutions Focus on file-sharing (non-real time) Centralized components (boot-strap, CA) Assume co-operating peers (

works for server farm in DHT Collusion Hide security algorithm (e.g., yahoo, skype)

Chord Recommendations, design principles, …