small lecturenumber - hepage : Peer-to-Peersmall lecturenumber - hepage : Examplessmall lecturenumber - hepage : Examplessmall lecturenumber - hepage : Historical examplessmall lecturenumber - hepage : Why did client/server become so popular?small lecturenumber - hepage : Potential advantages of peer-to-peersmall lecturenumber - hepage : Challenges of peer-to-peersmall lecturenumber - hepage : Challenges of Peer-to-Peersmall lecturenumber - hepage : Challenges of Peer-to-Peersmall lecturenumber - hepage : First-generation applicationssmall lecturenumber - hepage : Weaknesses of the first-generation modelsmall lecturenumber - hepage : Second-generation modelssmall lecturenumber - hepage : Example: Gnutellasmall lecturenumber - hepage : Example: Gnutellasmall lecturenumber - hepage : Example: Gnutellasmall lecturenumber - hepage : Example: Gnutellasmall lecturenumber - hepage : Hierarchical p2psmall lecturenumber - hepage : Hierarchical P2Psmall lecturenumber - hepage : Issues with file distributionsmall lecturenumber - hepage : Example: BitTorrentsmall lecturenumber - hepage : Example: BitTorrentsmall lecturenumber - hepage : Example: BitTorrentsmall lecturenumber - hepage : Current challenges in p2psmall lecturenumber - hepage : Coming AttractionsDistributed Software DevelopmentIntroduction to P2PChris BrooksDepartment of Computer ScienceUniversity of San FranciscoDepartment of Computer Science — University of San Francisco – p. 1/??14-2: Peer-to-Peer•Peer-to-peer is often touted as a hot new technology◦Really, it’s as old as the Internet (or earlier)•Fundamental idea: all nodes in a network should be capable ofthe same functionality.•Contrast this with client-server.•In practice, many systems are a hybrid of p2p and client-server.Department of Computer Science — University of San Francisco – p. 2/??14-3: Examples•What are some examples of p2p systems?Department of Computer Science — University of San Francisco14-4: Examples•File sharing apps (Morpheus, Kazaa, Limewire, etc)•IRC/ICQ•SETI@Home/distributed.net•Web caching•VoIP•SMTP•etcDepartment of Computer Science — University of San Francisco – p. 4/??14-5: Historical examples•USENET◦Peers within a domain would collect usenet posts andforward them via UUCP, then NNTP.◦No central server or repository.•DNS◦A hierarchical p2p systemDepartment of Computer Science — University of San Francisco – p. 5/??14-6: Why did client/server become so popular?•Asynchronous network structure•Ease of discovery•Centralized content development•Firewalls, NAT make it harder for users to host content.•Model changes: fewer developers, more browsers.Department of Computer Science — University of San Francisco14-7: Potential advantages of peer-to-peer•Reduce server bottlenecks•Move content closer to users•Allow users to publish as well as consume information◦Note that publishing and authoring can be different things.•Scalability•More able to deal with adaptive, dynamic networks.Department of Computer Science — University of San Francisco – p. 7/??14-8: Challenges of peer-to-peer•Finding peers (addressing)◦How does a peer join the network?◦How do peers identify each other?◦Is the network constructed statically, or dynamically?◦Does a peer always connect to the same set of peers?Department of Computer Science — University of San Francisco – p. 8/??14-9: Challenges of Peer-to-Peer•Searching for data◦Naming conventions◦How are queries distributed?◦Are all peers searched, or just a subset?◦Do peers keep track of the contents of other peers?Department of Computer Science — University of San Francisco14-10: Challenges of Peer-to-Peer•Other challenges:◦Interoperability and standards•Currently, every P2P network has its own protocol - youcan’t use a BitTorrent client to search on Gnutella.◦Dealing with dynamic networks◦Security•This includes the distribution of malicious files, protectionfrom snooping, and user authentication.Department of Computer Science — University of San Francisco – p. 10/??14-11: First-generation applications•So-called first-generation applications use a centralized nameserver.•All user addresses and file indexes are kept there.◦This can be used to build an application-leveladdress-resolution protocol.•Napster is the canonical example of this.•Most IM programs also work this way.•Central server is used to search.•Files are transferred between peers.Department of Computer Science — University of San Francisco – p. 11/??14-12: Weaknesses of the first-generation model•Central server provides a bottleneck.•Difficult to implement in a closed or dynamic environment.•Scalability can be a problem.•(also, legal issues in the case of Napster)Department of Computer Science — University of San Francisco14-13: Second-generation models•Second-generation models remove the central server.•All file information is distributed.•Advantage:◦Potentially more scalable◦Legal issues avoided.•Disadvantages:◦Search is more complex◦Discovery of peers more complicated.Department of Computer Science — University of San Francisco – p. 13/??14-14: Example: Gnutella•Gnutella is an example of an open P2P system.•Many clients use the same protocol◦LimeWire, BearShare, Gnucleus, etc•Gnutella uses no centralized server - all information is stored atthe peers.Department of Computer Science — University of San Francisco – p. 14/??14-15: Example: Gnutella•The Gnutella network is completely decentralized.•When a peer comes onto the network, it sends a ping to allknown peers.•Those peers respond with a pong, which identifies all theirknown peers.•Your peer can also remember previous connections.Department of Computer Science — University of San Francisco14-16: Example: Gnutella•When a peer wants to perform a search, it sends a query to allknown nodes.◦This request is then forwarded on to nodes one level away,who forard it to all nodes they know about, and so on.◦This is known as query flooding.◦If a hit is found, the node containing the file contacts thesearcher and download begins.Department of Computer Science — University of San Francisco – p. 16/??14-17: Example: Gnutella•Problems with Gnutella:◦Searching is unreliable - the network is often partitioned.◦Search based only on keywords - this produces namingissues.•If I want “Lost S1, Ep 3”, what do I search
View Full Document
Unlocking...