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
[email protected] =>128.59.19.194
INVITE [email protected]
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:[email protected]
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 14
8+2 = 10
14
8+4 = 12
14
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/RTCP
Codecs
Audio devicesDHT (Chord)
On startup
Discover
User location
Multicast REGISTERPeer found/Detect NAT
REGISTER
REGISTER, INVITE,MESSAGE
Signup,Find buddies
JoinFind
Leave
On resetSignout,transfer
IM,call
SIP-over-P2P
P2P-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([email protected])
REGISTER
DB
sipd
Detect peers
columbia.edu
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32
5812
42
REGISTER 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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42
REGISTER
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Dialing Out (message Dialing Out (message routing)routing)
Call, instant message, etc.INVITE sip:[email protected] sip:[email protected]
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 (?)
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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:[email protected] Unknown node: sip:[email protected] User: sip:[email protected]
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 11REGISTER
To: <sip:[email protected]>
From: <sip:[email protected]>
SIP/2.0 200 OK
To: <sip:[email protected]>
Contact: <sip:[email protected]>; predecessor=sip:[email protected]
Update my neighbor about meREGISTER
To: <sip:[email protected]>
Contact: <sip:[email protected]>; predecessor=sip:[email protected]
1
10
15
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Find(11) gives 15
7
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SIP messagesSIP messages
User registrationREGISTER
To: sip:[email protected]
Contact: sip:[email protected]:8094
Call setup and instant messagingINVITE sip:[email protected]
To: sip:[email protected]
From: sip:[email protected]
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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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8
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32
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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 14
8+2 = 10
14
8+4 = 12
14
8+8 = 16
21
8+16=24
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8+32=40
42
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ComparisonComparison
Property/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
P
P
PP
PP
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:[email protected]:[email protected]
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 (?)
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42 14
32
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56
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REGISTER 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