P2P-SIPP2P-SIPPeer to peer Internet telephony using Peer to peer Internet telephony using SIP (Session Initiation Protocol)SIP (Session Initiation Protocol)

Kundan Singh and Henning Schulzrinne Columbia University, New York

June 2005http://www.cs.columbia.edu/IRT/p2p-sip

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AgendaAgenda Introduction

What is SIP? Why P2P-SIP? Architecture

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

Implementation Choice of P2P algorithm (DHT); Node join,

leave; message routing Conclusions and future work

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

Bob’s hostAlice’s host128.59.19.194

REGISTERalice@columbia.edu =>128.59.19.194

INVITE alice@columbia.edu

Contact: 128.59.19.194

columbia.edu

Client-server=> maintenance, configuration, controlled infrastructure

P2P overlay

Alice128.59.19.194

REGISTERINVITE alice

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

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P2P-over-SIPP2P-over-SIP P2P algorithm over SIP without

change in semantics No dependence on external P2P

network Reuse and interoperate with existing

components, e.g., voicemail Built-in NAT/media relays Message overhead

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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 (?) Gateway (?) NAT/media relay (find best one)

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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

14

8+4 = 12

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8+8 = 16

21

8+16=24

32

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-P2PP2P-using-SIP

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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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32

5812

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

42

42

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

302

42

INVITE

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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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ConclusionsConclusions P2P useful for VoIP

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

P2P-SIP Basic operations easy

Implementation sippeer: C++, Linux

Interoperates Some potential issues

Security Performance (?)

C

C

C

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SP

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P

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

Backup slidesBackup slides

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

individual peers CPU, disk, bandwidth,

information, …

C

C

C

C

C

SP

P

P

P

P

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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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

1

10

1522

Find(11) gives 15

7

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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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Distributed Hash TablesDistributed Hash Tables Types of search

Central index (Napster) Distributed index with flooding (Gnutella) Distributed index with hashing (Chord)

Basic operationsfind(key), insert(key, value), delete(key), no search(*)

Properties/types Every peer has complete table

Every peer has one key/value

Search time or messages

O(1) O(n)

Join/leave messages

O(n) O(1)

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ChordChord Identifier circle Keys assigned

to successor Evenly

distributed keys and nodes

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0 1 2 3 4 5 6 7 8

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ChordChord

Finger table: logN ith finger points to first node

that succeeds n by at least 2i-1

Stabilization after join/leave

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Key node

8+1 = 9 148+2 = 10

14

8+4 = 12

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8+8 = 16

21

8+16=24

32

8+32=40

42

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ComparisonComparisonProperty/scheme

Un-structured

CAN Chord Tapestry

Pastry Viceroy

Routing O(N) or no guarantee

d x N1/d log(N) logBN logBN log(N)

State Constant 2d log(N) logBN B.logBN log(N)Join/leave

Constant 2d (logN)2 logBN logBN log(N)

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

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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 work: Skype Related work: Skype From the KaZaA communityFrom the KaZaA community

Host cache of some super nodes Bootstrap IP addresses Auto-detect NAT/firewall settings

STUN and TURN Protocol among super nodes – ?? Allows searching a user (e.g., kun*) History of known buddies All communication is encrypted Promote to super node

Based on availability, capacity Conferencing

P

P

PP

PP

P P

P

P P P

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Reliability and scalabilityReliability and scalabilityTwo stage architecture for CINEMATwo stage architecture for CINEMA

Master

Slave

Master

Slave

sip:bob@example.comsip:bob@b.example.com

s1

s2

s3

a1

a2

b1

b2

a*@example.com

b*@example.com

example.com_sip._udp SRV 0 40 s1.example.com SRV 0 40 s2.example.com SRV 0 20 s3.example.com SRV 1 0 ex.backup.com

a.example.com_sip._udp SRV 0 0 a1.example.com SRV 1 0 a2.example.com

b.example.com_sip._udp SRV 0 0 b1.example.com SRV 1 0 b2.example.com

Request-rate = f(#stateless, #groups)

Bottleneck: CPU, memory, bandwidth?Failover latency: ?

ex

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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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Why we chose Chord?Why we chose Chord? Chord can be replaced by another

As long as it can map to SIP High node join/leave rates Provable probabilistic guarantees Easy to implement X proximity based routing X security, malicious nodes

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Related workRelated workJXTA vs Chord in P2P-SIPJXTA vs Chord in P2P-SIP JXTA

Protocol for communication (peers, groups, pipes, etc.)

Stems from unstructured P2P P2P-SIP

Instead of SIP, JXTA can also be used Separate search (JXTA) from signaling

(SIP)

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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 (?)

12

24

42 14

32

5812

24

56

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, …

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P2P so far…P2P so far…Applejuice network

Applejuice Client BitTorrent network

ABC Azureus BitAnarch BitComet BitSpirit BitTornado BitTorrent BitTorrent++ BitTorrent.Net G3 Torrent mlMac MLDonkey QTorrent SimpleBT Shareaza TomatoTorrent (Mac OS X)TorrentStorm

CAKE network BirthdayCAKE

Direct Connect network BCDC++ CZDC++ DC++ NeoModus Direct Connect JavaDC DCGUI-QT

Gnutella network Acquisitionx (Mac OS X) BearShare BetBug Cabos CocoGnut (RISC OS)Gnucleus Grokster iMesh Light gtk-gnutella (Unix) LimeWire (Java) MLDonkey mlMac Morpheus Phex Poisoned Swapper Shareaza XoloX

Gnutella2 network Adagio Caribou Gnucleus iMesh Light MLDonkey mlMac Morpheus Shareaza TrustyFiles

HyperCast Joltid PeerEnabler

Altnet Bullguard Joltid Kazaa, Kazaa Lite

eDonkey network aMule (Linux) eDonkey client (no longer

supported) eMule LMule MindGem MLDonkey mlMac Shareaza xMule iMesh Light

ed2k (eDonkey 2000 protocol) eDonkey eMule xMule aMule Shareaza

FastTrack protocol giFT Grokster iMesh, iMesh Light Kazaa , Kazaa Lite, K++, Diet

Kaza, CleanKazaa Mammoth MLDonkey mlMac Poisoned

Freenet network EntropyFreenet Frost

Kademlia protocol eMule MindGem MLDonkey

MANOLITO/MP2P network Blubster Piolet RockItNet

Napster network Napigator OpenNap WinMX

Peercasting type networks PeerCast IceShare Freecast 

WPNP network WinMX

other networks Akamai Alpine ANts P2P Ares Galaxy Audiogalaxy network Carracho Chord The Circle Coral[5] Dexter Diet-Agents EarthStation 5 network

Evernet FileTopia GNUnet Grapevine Groove Hotwire iFolder[6] konspire2b Madster/Aimster MUTE Napshare OpenFT Poisoned P-Grid[7]IRC @find XDCCJXTA Peersites [8]MojoNation Mnet Overnet network Scour Scribe Skype SolipsisSongSpy network Soulseek SPIN SpinXpress SquidCam [9]Swarmcast WASTE Warez P2P Winny