Peer-to-Peer Computing Mrs. Tugba Taskaya-Temizel 13/February/2006

Peer-to-Peer Networks Definition The sharing of computer resources and services by direct exchange between systems [ The Intel P2P working group ]. The sharing of computer resources and services by direct exchange between systems [ The Intel P2P working group ]. Peers depend on each other for getting information, computing resources, forwarding requests, etc. which are essential for the functioning of the system as a whole. Peers depend on each other for getting information, computing resources, forwarding requests, etc. which are essential for the functioning of the system as a whole.

Peer-to-Peer Networks Goals Cost sharing/reduction Cost sharing/reduction Resource aggregation and interoperability Resource aggregation and interoperability Improved scalability/reliability Improved scalability/reliability Increased autonomy Increased autonomy Anonymity/privacy Anonymity/privacy Dynamism Dynamism

Peer-to-Peer Networks Algorithms: Centralised directory model Central Directory Peers search download Peers publish information about the content they want to share to a central directory. A peer sends a request. The central directory will match the request with the best matching peer. The files are exchanged between the requester and the matching peer. Application: Napster Disadvantage: scalability

Peer-to-Peer Networks Algorithms: Flooded Requests Model search download A peer’s request is broadcasted to the directly connected peers, which themselves flood their peers until the request is answered or a maximum number of flooding steps (5 to 9) occur. Application: Gnutella Disadvantage: requires a lot of bandwidth, does not guarantee reachability.

Peer-to-Peer Networks Algorithms: Document Routing Model Each peer is assigned a random ID and each knows a certain number of its peers. An ID is generated based on the hash of the requested document content and name. Each peer sends the file to a peer that has a similar ID. It is repeated until the peer’s ID is identical to the document ID. The file is transferred between the peers. Application: FreeNet Disadvantage: Document IDs should be known, islanding problem. File id=0009File id=0030 File id=0010 File id=0005 Algorithms implemented: Chord, CAN, Tapestry, Pastry

Peer-to-Peer Networks Characteristics: Decentralisation User’s ownership and control of data and resources User’s ownership and control of data and resources Difficulty: finding the network, insertion of new nodes Difficulty: finding the network, insertion of new nodes

Peer-to-Peer Networks Characteristics: Scalability Limited by factors such as Limited by factors such as The amount of centralised operations The amount of centralised operations The amount of state that needs to be maintained The amount of state that needs to be maintained The inherent parallelism an application exhibits The inherent parallelism an application exhibits Programming model Programming model Scalability ~ Communication/Computation Scalability ~ Communication/Computation

Peer-to-Peer Networks Characteristics: Anonymity Goals: Goals: To allow people to use systems without concern for legal or other ramifications. To allow people to use systems without concern for legal or other ramifications. To guarantee that censorship of digital content is not possible. To guarantee that censorship of digital content is not possible. Types of anonymity: server, receiver, mutual Types of anonymity: server, receiver, mutual

Peer-to-Peer Networks Characteristics: Anonymity (Techniques) Multicasting : Multicasting : Broadcasting group Entity subscribes Entity document request sends request The identities of requester and sender are not known to the group.

Peer-to-Peer Networks Characteristics: Anonymity (Techniques) Spoofing the sender’s address: Spoofing the sender’s address: Message can be enforced by spoofing the sender’s IP address. Message can be enforced by spoofing the sender’s IP address. Problem: ISPs do not accept messages from invalid IP addresses. Problem: ISPs do not accept messages from invalid IP addresses. Identity Spoofing Identity Spoofing Cover paths: Two parties communicate through some middle nodes. Cover paths: Two parties communicate through some middle nodes.

Peer-to-Peer Networks Characteristics: Anonymity (Techniques) Intractable aliases: such as Lucent Personalised Web Assistant (LPWA) Intractable aliases: such as Lucent Personalised Web Assistant (LPWA) Send user name and secret Generate a set of consistent alias username, password, e- mail address in each time the user sends the same information Send the generated info

Peer-to-Peer Networks Characteristics: Anonymity (Techniques) Non-voluntary placement: A publisher forces a document onto a hosting node. Because the placement is non-voluntary, the host cannot be held accountable for owning the document. Non-voluntary placement: A publisher forces a document onto a hosting node. Because the placement is non-voluntary, the host cannot be held accountable for owning the document.

Peer-to-Peer Networks Characteristics: Self-Organisation P2P systems can scale unpredictably in terms of the number of systems, number of users, and the load. P2P systems can scale unpredictably in terms of the number of systems, number of users, and the load. Adaptation is required to handle the changes caused by peers connecting and disconnecting from the P2P systems. Adaptation is required to handle the changes caused by peers connecting and disconnecting from the P2P systems. For example in the FastTrack system, more powerful computers automatically become SuperNodes and act as search hubs. Any client can become a SuperNode if it meets processing and networking criteria (bandwidth and latency). For example in the FastTrack system, more powerful computers automatically become SuperNodes and act as search hubs. Any client can become a SuperNode if it meets processing and networking criteria (bandwidth and latency).

Peer-to-Peer Networks Characteristics: Cost of Ownership Shared ownership reduces the cost of maintaining the system and owning the systems. Shared ownership reduces the cost of maintaining the system and owning the systems. For example, in Napster, the users contributed to the pool of music files. is faster than the fastest computer in the world. For example, in Napster, the users contributed to the pool of music files. is faster than the fastest computer in the world.

Peer-to-Peer Networks Characteristics: Ad-hoc Connectivity Peers are not available at all times. Hence, P2P systems need to be aware of this ad- hoc nature. Peers are not available at all times. Hence, P2P systems need to be aware of this ad- hoc nature. P2P systems need to tolerate disconnection and ad-hoc additions to groups of peers. P2P systems need to tolerate disconnection and ad-hoc additions to groups of peers.

Peer-to-Peer Networks Characteristics: Performance P2P systems aim to improve performance by aggregating distributed storage capacity. P2P systems aim to improve performance by aggregating distributed storage capacity. Performance is influenced by: Performance is influenced by: Processing, storage and networking Processing, storage and networking Approaches to optimise performance: Approaches to optimise performance: Replication, caching, intelligent routing Replication, caching, intelligent routing

Peer-to-Peer Networks Characteristics: Security Multi-key encryption Multi-key encryption Sandboxing Sandboxing Digital rights management Digital rights management Reputation and accountability Reputation and accountability Firewalls Firewalls

Peer-to-Peer Networks Characteristics: Transparency and Usability End-to-end transparency: TCP/IP End-to-end transparency: TCP/IP Naming transparency Naming transparency Network and device transparency Network and device transparency Automatic and transparent authentication of users Automatic and transparent authentication of users

Peer-to-Peer Networks Characteristics: Fault Resilience P2P systems should deal with: P2P systems should deal with: Disconnections/unreachability Disconnections/unreachability Partitions Partitions Node failures Node failures Solutions: Solutions: Replication of crucial resources Replication of crucial resources Relays Relays Queuing messages Queuing messages

Peer-to-Peer Networks Characteristics: Interoperability Standards: IEEE standards for Ethernet, token ring and wireless Standards: IEEE standards for Ethernet, token ring and wireless Common specifications: Object Management Group Common specifications: Object Management Group Open source: Linux Open source: Linux De facto standards: Windows, Java De facto standards: Windows, Java P2P Working Group is an attempt to gather the community. P2P Working Group is an attempt to gather the community.

Peer-to-Peer Networks Comparison with Grid Computing Target communities and incentives Target communities and incentives Resources Resources Applications Applications Scale and failure Scale and failure Services and infrastructure Services and infrastructure

Peer-to-Peer Networks Comparison with Grid Computing Target communities and incentives: Target communities and incentives: Grids address the needs of scientific collaborations and commerce. Grids address the needs of scientific collaborations and commerce. P2P has been used mostly for file sharing and highly parallel computing applications. The communities comprise anonymous individuals. P2P has been used mostly for file sharing and highly parallel computing applications. The communities comprise anonymous individuals.

Peer-to-Peer Networks Comparison with Grid Computing Resources: Resources: Grid systems integrate resources that are more powerful, more diverse and better connected than P2P resource. Grid systems integrate resources that are more powerful, more diverse and better connected than P2P resource. The resources are aggregated within administrative domains via technologies such as Condor. The resources are aggregated within administrative domains via technologies such as Condor. Grid resources are more powerful than P2P resources. Grid resources are more powerful than P2P resources. P2P systems deal with intermittent participation and highly variable behaviour. P2P systems deal with intermittent participation and highly variable behaviour.

Peer-to-Peer Networks Comparison with Grid Computing Applications: Applications: Grid applications are dominantly scientific applications. Grid applications are dominantly scientific applications. P2P deal with specialised resource-sharing problems: current ones share either compute cycles or files. P2P deal with specialised resource-sharing problems: current ones share either compute cycles or files. Grid applications are far more data intensive. Grid applications are far more data intensive.

Peer-to-Peer Networks Comparison with Grid Computing Scale and failure: Scale and failure: Grid communities involve moderate number of participants, whereas P2P communities involve millions of users. However, the amount of activity in P2P is not larger than Grid communities. Grid communities involve moderate number of participants, whereas P2P communities involve millions of users. However, the amount of activity in P2P is not larger than Grid communities.

Peer-to-Peer Networks Comparison with Grid Computing Services and infrastructure: Services and infrastructure: There is an effort to standardise Grid technologies (OGSA). There is an effort to standardise Grid technologies (OGSA). P2P systems have tended to focus on the integration of simple resources via protocols designed to provide specific functionality. P2P systems have tended to focus on the integration of simple resources via protocols designed to provide specific functionality.

References Foster,I. and Iamnitchi,A. On Death, Taxes, and the Convergence of Peer-to-Peer and Grid Computing. Foster,I. and Iamnitchi,A. On Death, Taxes, and the Convergence of Peer-to-Peer and Grid Computing. Shirky,C. What is P2P… and What isn’t? hirky1-whatisp2p.html Shirky,C. What is P2P… and What isn’t? hirky1-whatisp2p.html hirky1-whatisp2p.html hirky1-whatisp2p.html Milojijic,D.S., Kalogeraki,V.,Lukose,R. Peer-to-Peer Computing, d05/papers/p2p-tutorial.pdf Milojijic,D.S., Kalogeraki,V.,Lukose,R. Peer-to-Peer Computing, d05/papers/p2p-tutorial.pdf