-1- Peer-to-Peer (P2P) Computing Tutorial April 29, 2003 한재선 ([email protected]) SSL...

-1-

Peer-to-Peer (P2P) Computing

Tutorial

April 29, 2003

한재선 ([email protected])

SSL (System Software Lab), EECS, KAIST

-2-

Roadmap

▣ The Past of P2P Computing◈ P2P File Sharing System◈ P2P Distributed Computing◈ P2P Collaboration

▣ The Present of P2P Computing

▣ The Future of P2P Computing

-3-

P2P Fils Sharing : Napster

▣ Centralized lookup◈ Centralized directory service◈ Single point of failure

CentralizedDirectoryServer

(napster.com)

N1

N2N3

N4

N5

… …a.mp3 N5

… …

file node

Search(a.mp3)

N5 IP addr.

Request(a.mp3)

File(a.mp3)

-4-

P2P Fils Sharing : Gnutella

▣ Flooding-based lookup◈ Completely decentralized lookup◈ High network overhead

N1

N2

N3

N5

N4

N7

N6N8

N9

Search(a.mp3)

Search Result N3, N5, N8Selected Node N5

-5-

P2P Fils Sharing : Freenet

Node N120

130 N128142 N140149 N145

key node

Lookup Key = 325

Routing table

Node N145

Node N200

Node N315

164 N160185 N182204 N200

key node

240 N228288 N280321 N315

key node

340 N338378 N372399 N387

key node

Value(325)

▣ Key-based lookup◈ Key components : key, nodeId, routting table◈ File is not stored in the node of creator◈ Cannot guarantee the lookup hop count

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P2P Distributed Computing

CentralizedServer

N1

N2N3

N4

N5

code + parameters

results

◈ Sharing computing resources (CPU time) Cycle-stealing◈ @home projects (SETI@home, folding@home, genome@home etc), distributed.net

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P2P Collaboration

N1

N2N3

N4

N5

N6

CollaborativeDesign

Instant Messaging

◈ Instant messaging, P2P Groupware (e.g., Groove) etc

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Discussion on the past of P2P

▣ Summary◈ P2P File Sharing System sharing files◈ P2P Distributed Computing sharing CPU time◈ P2P Collaboration

▣ Questions◈ What are the common features among three types of P2P

applications?

◈ When comparing to traditional client/server computing, which advantages and disadvantages does P2P computing

involve?

◈ Which challenges or issues must P2P computing address?

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Roadmap


▣ The Present of P2P Computing◈ The characteristics of P2P computing◈ The issues of P2P computing - P2P algorithms - P2P applications - P2P platforms


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What is P2P Computing?

▣ What is P2P computing?◈ New computing paradigm◈ Every node is both client and server◈ Sharing computing resources(e.g., storage, CPU power etc)

among peer nodes

CentralizedServer

Client

ClientClient

Client

Peer node

Client/Server Computing Peer-to-Peer Computing

N1

N2

N3

N4

N5

N6

Search(a.mp3)

Search(b.mp3)

a.mp3b.mp3

-11-Characteristics of P2P Computing▣ Resource sharing : Storage, Processing, Networking, Information etc▣ Fully decentralized : no distinction between client and server▣ Node characteristics : heterogeneous, unreliable, insecure

▣ Scalability ◈ vs. determinism and performance guarantee◈ C/S Napster & SETI@home Gnutella&Freenet DHT

▣ Fault Resilience◈ No single point of failure, but disconnections/unreachability, partitions, nod

e failures, and non-availability of resources▣ Self-organization

◈ Needed for scalability, fault resilience, ad hoc resources, cost of ownership▣ Ad-Hoc connectivity

◈ How can guarantee quality of service? e.g., redundancy▣ Anonymity

◈ Author, Publisher, Reader, Server, Document, Query etc◈ Freenet (Identity spoofing), Free Heaven&Publius (Covert path)

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Issues of P2P Computing▣ Issues on P2P Algorithm

◈ Lookup mechanism : structured & unstructured◈ Locality-aware or topology-aware routing◈ Load balancing & Replication & Caching◈ Security◈ Search◈ Incentive & reputation◈ Measurement & Theoretic analysis

▣ Issues on P2P applications◈ Wide-area file system : CFS, PAST, Ivy, OceanStore, Farsite etc◈ Overlay Multicast : Scribe, CAN multicast, Bayeux etc◈ Web applications : Squirrel, Backslash etc◈ Many other applications : Naming System(P2P DNS, INS), Comm. (I3) etc

▣ Issues on P2P platform◈ JXTA

-13-Structured Lookup : DHT-based(1)▣ Distributed Hash Table (DHT)-based lookup

◈ Lookup Key hashing the file name◈ NodeId hashing the node’ IP address◈ Each node stores a certain range of keys according to nodeId◈ lookup(key) returns the value or the IP address of the node stori

ng the object with that key▣ Examples of DHT-based lookup

◈ Chord (MIT), CAN (UCB), Pastry (Rice&MS), Tapestry (UCB), etc

Distributed hash tables

Distributed applications

Lookup (key) data

node node node….

Insert(key, data)

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Structured Lookup : Chord (1)

▣ Key and Node are uniformly distributed and exist in the same ID space▣ Each node is responsible to keys between predecessor node and itself▣ Simple Lookup algorithm - Naïve version

◈ Lookup request is forwarded to the successor until (node ID < key < successor)

◈ In worst case, the number of nodes that must be contacted : O(N)

N32

N10N5

N20

N110

N99

N80N60

Lookup(K19)

K19

Lookup using successor

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N32

N10N5

N20

N110

N99

N80N60

Lookup(K19)

K19

▣ Finger table : m entries (2m ID space), Allows logN-time lookup▣ Lookup using finger table

◈ O(N) O(logN)

Lookup using finger table

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Node Join Node Leave

▣ Consistency problem : finger table must be updated consistently

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Structured Lookup : CAN

▣ Virtual d-dimensional Cartesian coordinate space▣ hold information about a small number of “adjacent”

zones : 2d▣ Average routing path length : (d/4)(N 1/d)▣ Node join, departure soft-state style updates and refreshes

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Structured Lookup : Pastry

▣ Lookup cost : log2bN

▣ Leaf set : Numerically closest nodeIds▣ Neighborhood set : Node set that are closest to local node

Lookup from node 65a1fc with key d46a1c

-19-Structured Lookup : DHT-based(2)▣ Advantages

◈ Highly scalable : small routing table, small pathlength (O(logN))◈ Guarantee lookup performance (?)◈ Good Interface easy to support a wide-range of applications - minimal interface : insert(key, data), lookup(key) - Keys have no semantic meaning◈ Robust in the face of failures and attacks◈ Self-organizing across administrative domains

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Unstructured Lookup : SuperNode

▣ Relieve flooding overhead▣ Small-world network vs. Scale-free network▣ Supernode election

◈ Not firewalled, Sufficient CPU, Sufficient BW, Sufficient uptime etc▣ Gnutella’s Ultrapeer, FastTrack’s SuperNode, JXTA’s Rendezvous Peer

N11

N13

N14

N12

N21 N22

N23N42

N43

N41

N31

N32

…

…

…

a.mp3

Lookup(a.mp3)

Supernode

-21-Discussion : Structured vs. Unstructured▣ What are the strong and weak points of each approach?

◈ Performance considering determinism vs. Overhead◈ Scalability◈ Fault Resilience◈ Security – easily attacked?◈ Easiness to use and deploy◈ …

▣ What type of application each approach is suitable for?

◈ File sharing system◈ Distributed computing◈ Collaboration◈ Another new type of applications

▣ What is the intermediate approach between structured and unstructured?

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Locality-aware routing

▣ Nodes close on ring, but far away in Internet Implicit problem of overlay network▣ Goal

◈ put nodes in routing table that result in few hops and low latency

▣ Landmark scheme (CAN), Client clustering scheme etc

CA-T1CCIArosUtah

CMU

To vu.nlLulea.se

MITMA-CableCisco

Cornell

NYU

OR-DSLN20

N40N80N41

L2

L1

L3

49

105

87

“L1L2L3

”

Landmarks

“L3L2L1

”

“L3L2L1

”

A

B

Landmark schemeInefficient routing

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Security

▣ What’s new in P2P for security?◈ Fully Decentralized

– No Authorization and authentication◈ Nodes are much more powerful

– Assign nodeID themselves– Act as a router (routing table, forwarding messages)

◈ Malicious node may mis-route, corrupt, or drop messages and routing information

▣ Attacks and Solution◈ Secure nodeID assignment – certified nodeIds◈ Secure routing table maintenance – constrained routing table◈ Secure message forwarding – failure test, redundant routing

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Incentive for sharing

▣ The problem of free-riding◈ Users that only download files for themselves without providing files for dow

nload by others, or provide files that are of low quality ◈ 70% Gnutella users shared no files, nearly 50% of all responses were retur

ned by the top 1% of sharing hosts. [August, 2000]◈ 25% Gnutella users shared no files, 75% 100 files or less, just 7% more th

an 1000 files. [May, 2001]▣ Solutions

◈ Micro-Payment charge download & reward upload◈ Point System rewards for sharing - accounting component - award component : level of service - enrollment and aggregation agent - e.g., KaZaa : Participation Level = (upload / download) * 100 (0 ~ 1000) the higher participation level, the higher priority of downloading

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Wide-area file system

▣ Wide-area file system◈ CFS(Chord), Ivy(Chord), PAST(Pastry), OceanStore(Tapestry) etc

▣ CFS

995:key=901key=732Signature

File System key=995

……

“a.txt” ID=144

key=431key=795

…

…

(root block)(directory blocks)

(i-node block)

(data)

901= SHA-1 144 = SHA-1431=SHA-1

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Overlay Multicast

▣ Overlay Multicast◈ Scribe (Pastry), CAN Multicast, Bayeux (Tapestry) etc

▣ Scribe

1100

1111

1101

1001

0111

0100

root

Joining member

Joining member

gID1

gID2

…

GroupList chID1

chID2…

chID4chID7chID1

…

ChildrenTable

Forwarder Node

gID:1100Ch :0100 0111

gID:1100Ch :1001

gID:1100Ch :1101

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Web Applications (1)

▣ Web Applications◈ Squirrel (client-side web caching), Backslash (Backup CDN)

▣ Squirrel

server

client

otherother

req

home

req

req

a : object or notmod from home

b : object or notmod from origin3

1

b2

(WAN)(LAN)

origin

b : req

Home-Store Protocol

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Web Applications (2)

dir

server

servere : cGET req

origin

origin

otherother

req

home

req

client

req

2

b : not-modified

3

e3

21c ,e : req

c ,e : object1

4a , d

2a , d : req 1a : no dir, go to origin. Also d2

3

1

not-modifiedobject or

dele-gate

Directory Protocol

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P2P Platform▣ Project JXTA

◈ Key concepts: peer, peer group, advertisement, service, module◈ Key protocols: Peer Discovery Protocol, Peer Resolver Protocol,

Pipe Binding Protocol, Endpoint Routing Protocol, Peer Membership Protocol, Peer Information Protocol

•Interoperability•Platform Independence•Ubiquity

JXTA Objectives

-30-Discussion on The Present of P2P▣ Another P2P algorithm issues ?

▣ Another P2P applications ?

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Rodemap


▣ The Present of P2P Computing◈ The characteristics of P2P computing◈ The issues of P2P computing - P2P algorithms - P2P applications - P2P platforms


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AP2PC 2003▣ Second International Workshop on

Agents and Peer-to-Peer Computing

◈ Intelligent agent techniques for P2P computing ◈ P2P computing techniques for multi-agent systems ◈ The Semantic Web, Semantic Coordination Mechanisms and P2P systems ◈ Scalability, coordination, robustness and adaptability in P2P systems ◈ Self-organization and emergent behavior in P2P networks ◈ E-commerce and P2P computing ◈ Participation and Contract Incentive Mechanisms in P2P Systems ◈ Computational Models of Trust and Reputation ◈ Community of interest building and regulation, and behavioral norms ◈ Intellectual property rights in P2P systems ◈ P2P architectures ◈ Scalable Data Structures for P2P systems ◈ Services in P2P systems (service definition languages, service discovery, filtering and compo

sition etc.) ◈ Knowledge Discovery and P2P Data Mining Agents ◈ P2P oriented information systems ◈ Information ecosystems and P2P systems ◈ Security issues in P2P networks ◈ ad-hoc networks and pervasive computing based on P2P architectures and wireless commun

ication devices

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GP2P 2003▣ Third International Workshop on Grid and Peer-to-Peer Computing

◈ * Global Computing and Peer-to-Peer computing platforms * P2P Merging / Interoperability with Grid systems (OGSA/I) * Software technologies evaluation: Web Services, Grid services * Middleware, programming models, environments and toolkits * Protocols for resource management/discovery/reservation/scheduling

* Economic considerations of resource usage (protocols, accounting) * Storage in Global Computing Infrastructures (strategies, protocols) * Performance monitoring, benchmarking, evaluation and modeling of Global Computing and Peer-to-Peer systems and/or components thereof * Security, management and monitoring of resources * Result certification (detection/tolerance of corrupted results) * Parallel computing on large scale distributed systems * Compute & I/O driven applications (scientific, engineering, business) * Global and P2P computing applications (programmed from scratch, ported from sequential, or parallel version, adaptations to fit a global computing environment)

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DBISP2P 2003

▣ International Workshop On Databases, Information Systems and Peer-to-Peer Computing

◈ Data models and query languages for P2P systems ◈ Data placement and query answering in P2P systems ◈ Indexing, caching and replication techniques for P2P systems ◈ Transaction management for P2P Systems ◈ Metadata management in P2P systems ◈ Dynamic schema integration ◈ P2P systems and the Semantic Web ◈ Self-organisation and emergent behaviour in information systems and d

atabases ◈ Complex Adaptive Information Systems ◈ Resource allocation in P2P systems

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What’s next?

▣ P2P is New Type of ??

◈ New type of algorithm (X)◈ New type of protocol (X)

◈ New type of application (X) ◈ New type of network (X)

P2P is New Computing Paradigm !!!

▣ See broader Merge with other emerging technologies

◈ Mobile computing : mobile P2P, mobile infrastructure using P2P◈ Ubiquitous computing : ubiquitous P2P, ubiquitous infrastructure

using P2P◈ Grid computing : desktop grid, global computing system◈ Internet Distributed Computing (Intel) : P2P + Grid + Web Service

-1- Peer-to-Peer (P2P) Computing Tutorial April 29, 2003 한재선 ([email protected]) SSL...

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Transcript of -1- Peer-to-Peer (P2P) Computing Tutorial April 29, 2003 한재선 ([email protected]) SSL...