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Membership (2). CS 525, Spring 2008, UIUC Presented by Zixia Huang and Yuhao Zheng. What Is Membership. “Who knows whom” relation A knows C, C knows F But D does not know C, J does not know B . Background Information. P2P Overlay network

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membership 2

Membership (2)

CS 525, Spring 2008, UIUC

Presented by Zixia Huang and Yuhao Zheng

what is membership
What Is Membership
  • “Who knows whom” relation
    • A knows C, C knows F
    • But D does not know C, J does not know B

CS525 SP08, UIUC

background information
Background Information
  • P2P Overlay network
    • A computer network which is built on top of another network
    • Nodes in the overlay: connected by logical links
    • Designed to handle a much higher rate concerning joining and leaving nodes
  • Application
    • Multimedia streaming with high QoS
    • Reliable and efficient content delivery

CS525 SP08, UIUC

background information4
Background Information
  • Membership Management of P2P Overlay
    • Be resilient to massive node failures
    • Be able to deal with a high node churn (high frequency membership changes)
  • Application
    • Build on-demand overlay
    • Facilitate semantic-based content searching
    • Self-monitor large clusters of nodes to avoid centralized or hierarchical architectures
    • Good for multicast and broadcast

CS525 SP08, UIUC

background information5
Background Information
  • Traditional gossip-based protocols
    • Called full membership protocol
    • Require each node should know every other node
    • Rely on gossip targets being chosen uniformly at random from among all known members
    • Impose high requirements on memory and synchronization, and affect their scalability

CS525 SP08, UIUC

papers to be presented today
Papers to be Presented Today
  • Peer-to-peer membership management for gossip-based protocols
    • A.J. Ganesh et al
    • IEEE TOC, Feb 2003
  • CYCLON: Inexpensive Membership Management for Unstructured P2P Overlays
    • S. Voulgaris et al
    • Journal Network Systems and Management, June 2005
  • T-Man: Fast Gossip-based Construction of Large-Scale Overlay Topologies
    • M. Jelasity et al
    • U. Bologna Tech Report

CS525 SP08, UIUC

cyclon inexpensive membership management for unstructured p2p overlays

CYCLON: Inexpensive Membership Management for Unstructured P2P Overlays

Spyros Voulgaris,

Daniela Gavidia,

Marrten van Steen

outline
Outline
  • Motivations of CYCLON
  • Protocols
  • Basic properties
  • Adding and removing nodes
  • Self-healing behavior
  • Discussions

CS525 SP08, UIUC

cyclon inexpensive membership management
CYCLON: Inexpensive Membership Management
  • Only maintains a partial view of node membership
  • Enhanced version of shuffling: better node degree distributions
  • Better management of node additions and removals (in terms of efficiency and quality) which does not disrupt the randomness

CS525 SP08, UIUC

protocol basic shuffling
Protocol: Basic Shuffling
  • Randomly choose a neighbor to shuffle

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protocol cyclon s enhanced shuffling
Protocol: Cyclon’s Enhanced Shuffling
  • Select the neighbor whose information is the earliest one to shuffle
    • Result in a more up-to-date overlay
    • Impose a predictable lifetime on each pointer so that pointers can be distributed in an even way across all nodes

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basic properties i
Basic Properties (I)
  • Connectivity
    • Given a fail-free environment, connectivity of the overlay is guaranteed.
    • No nodes becomes disconnected as the result of a shuffling operation

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basic properties ii
Basic Properties (II)

C: Cache Size

  • Convergence
    • Average Path Length: average shortest path lengths between any two nodes

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basic properties ii14
Basic Properties (II)
  • Convergence
    • Clustering Coefficient (of a node): the ratio of existing links among the node’s neighbors over the total number of possible links among them
    • Show what percentage the neighbors of a node are also neighbors among themselves

CS525 SP08, UIUC

basic properties iii
Basic Properties (III)
  • Degree distribution
    • Degree (of a node): the number of links it has to other nodes (in a undirected connection graph)
      • Related to the robustness of the overlay in the presence of failures
      • Indication of the way epidemics are spread
      • Indication of how fairly links are distributed among nodes (also an indication of resource usage including bandwidth, processing, etc)
    • Directed version of graph
      • Out-degree: # edges leaving from a node, fixed = cache size
      • In-degree: # edges ending at the node

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basic properties iii16
Basic Properties (III)
  • Degree distribution

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cyclon adding nodes
CYCLON: Adding Nodes
  • A new node P needs to know any single node that is already part of the overlay (called its introducer)
  • P’s introducer initiates c (cache size) random walks, setting their TTL to a small value close to the expected average path length. The random walk ends at Q.
  • Q replaces one of its cache’s entries with a new entry of age 0 and the address of P, and forward the replaced entry to P.
  • P’s entry is filled up with c randomly chosen neighbors

CS525 SP08, UIUC

cyclon removing nodes
CYCLON: Removing Nodes
  • When a node initiates a shuffle with a neighbor and gets no reply within a predefined timeout, it simply assumes the neighbor to be disconnected and removes entry.
  • Timeout >= twice typical latency
  • Enhanced shuffling: an older node is less likely to be alive

CS525 SP08, UIUC

cyclon self healing behavior
CYCLON: Self-healing Behavior
  • By using CYCLONE, most nodes are more likely to be connected in a single large cluster at the presence of node failure.

CS525 SP08, UIUC

cyclon bandwidth consideration
CYCLON: Bandwidth Consideration
  • Per-node network load depends on
    • Amount of data transferred per cycle: two on average
    • Cycle duration: depends on the underlying network bandwidth availability
  • Set cache entry size to be 8 and each entry 10 bytes long and cycle duration 10 sec, the result of each node is 32 bytes/s  very low BW

CS525 SP08, UIUC

discussions
Discussions
  • Assumption: older nodes are less likely to be alive. Is it really true?
  • Remove nodes if time out: if jitter happens over the internet  Node failure?
  • In P2P overlay, is the cycle duration 10 sec too large?
  • How many nodes will use CYCLON? And what is the effect of CYCLON if # nodes is small?
  • If # nodes is high, will accumulating traffic be very high? Even though traffic for each node is low.

CS525 SP08, UIUC

peer to peer membership management for gossip based protocols

Peer-to-Peer Membership Management for Gossip-Based Protocols

Ayalvadi J. Ganesh,

Anne-Marie Kermarrec,

Laurent Massoulie

outline23
Outline
  • Motivations
  • Basic protocol
  • Refinements
  • Experimental results
  • Conclusions
  • Discussions

CS525 SP08, UIUC

motivations
Motivations
  • Aiming at the weakness of traditional full membership protocols, this paper proposes a protocol that
    • Each node maintains a partial view of the group membership
    • Is simple, fully decentralized, and self-configuring
    • Is as resilient to failures as full membership protocols

CS525 SP08, UIUC

basic protocol
Basic Protocol
  • Basic Protocol Concerns
    • Node joins: subscription
    • Node leaves: unsubscription
    • Recovery from Isolation
      • Simply solved by using heartbeating and resubscribing
      • Will not be discussed in this presentation

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basic protocol subscription
Basic Protocol - Subscription
  • Subscription (new node join)
    • Contact: New nodes join the group by sending a subscription request to an arbitrary member.

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basic protocol subscription27
Basic Protocol - Subscription
  • Subscription (new node join)
    • New subscription: When a node receives a new subscription request, it forwards the new node-id to all members of its own local view. It also creates c additional copies (to be discussed later).

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basic protocol subscription28
Basic Protocol - Subscription
  • Subscription (new node join)
    • Forwarded subscription: When a node receives a forwarded subscription, it either accepts the subscriptionor forwards the subscription

CS525 SP08, UIUC

basic protocol subscription29
Basic Protocol - Subscription
  • Subscription (new node join)
    • Keeping a subscription: When a node decides to keep the subscription, it integrates the new subscriber in its PartialView, and informs the subscriber to update its InView

CS525 SP08, UIUC

basic protocol subscription30
Basic Protocol - Subscription

c is a

design parameter that determines the proportion of

failures tolerated

CS525 SP08, UIUC

properties of subscription
Properties of Subscription
  • All forwarded subscriptions are eventually kept by some node.
  • If the new node subscribes to a node with out-degree d, then d+c+1 arcs are added
  • Let E[Mn] denote the expected number of arcs when the number of nodes is n
    • E[Mn]≈(c+1)nlogn

CS525 SP08, UIUC

basic protocol unsubscription
Basic Protocol - Unsubscription
  • Unsubscription (node leaves)
    • PartialView: i(1)~i(L), InView: j(1)~j(L’)
    • Informs nodes j…(1)~j(L’-c-1) to replace its id with i(1)~i(L’-c-1) (mod L), respectively
    • Informs nodes j(L’-c)~j(L’) to remove it from their lists.

CS525 SP08, UIUC

properties of unsubscription
Properties of Unsubscription
  • If the leaving node has a in-degree d, the total number of arcs decreases by d+c+1
    • d-c-1 by replacing
    • (c+1)*2 by removing
  • E[Mn-1]≈(c+1)(n-1)log(n-1)
  • Unsubscriptions preserve the desired mean degree of arcs

CS525 SP08, UIUC

refinements indirection mechanisms
Refinements - Indirection mechanisms
  • Indirection mechanisms
    • How would a newly joint node select a node to contact? Choosing at random uniformly among existing members requires global information.
    • Solution: the initial contact forwards the newcomer’s subscription request to a node which is chosen approximately at random among all existing nodes.

CS525 SP08, UIUC

refinements lease mechanisms
Refinements - Lease mechanisms
  • Lease mechanisms
    • Each subscription has a finite lifetime
    • Each node needs to resubscribe at the time that its subscription expires
  • Advantages
    • Helps to rebalance the size of partial views across group members
    • Removes invalid information caused by leaving the group without unsubscribing

CS525 SP08, UIUC

experimental results
Experimental Results
  • Distribution of partial view size

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experimental results38
Experimental Results
  • Resilience to node failures

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experimental results39
Experimental Results
  • Impact of the lease mechanisms

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experimental results40
Experimental Results

?

  • Impact of indirection mechanisms

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conclusions
Conclusions
  • Pros
    • Fully decentralized protocol with O(logn) partial view size
    • With a very close performance to full membership protocol
  • Cons
    • The reason why indirection does not improve the performance is not solved completely

CS525 SP08, UIUC

discussions42
Discussions
  • How to set the system parameter c?
    • Self-adjusted by measuring percentage of node failures?
  • Without indirection, how to prevent a node from being contacted for too many time?
    • Allow a node to reject the contact when being contacted too frequently?
  • Why indirection does not improve the performance?

CS525 SP08, UIUC

motivations44
Motivations
  • For most applications, including gossip-based dissemination and routing
    • Geographically long range links be used less often than short range links
    • Meaning that topology also has to reflect physical proximity

CS525 SP08, UIUC

basic idea
Basic Idea
  • Each node
    • Periodically gossips with a randomly selected peer to exchange their partial views
    • Merges the received view with its local view
    • Selects the first c peers (based on a ranking function) of the merged view as its new view
      • The last two steps happen both actively and passively

CS525 SP08, UIUC

illustrative example
Illustrative Example

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conclusions47
Conclusions
  • Proposed protocol requires logarithmic convergence time independently of the target topology.
  • But the actual convergence time depends on the target topology itself.

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discussions48
Discussions
  • What is the advantages and disadvantages of using geographically short links more frequently?

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the end

The End

Thank you!