An overlay for latency gradated multicasting Anwitaman Datta SCE, NTU Singapore Ion Stoica, Mike Franklin EECS, UC Berkeley ICDCS 2007 Presenter : Ankur Airan

Outline Introduction Problem Addressed and its Definition Previous Work Proposed Techniques Disadvantages and Future Works

Introduction Flooding based systems for P2P applications - Do not scale well due to bandwidth and processing requirements. - No guarantee of lookup times or content accessibility.

Introduction Overlay Networks can address issues of flooding systems - Network semantics layer above the basic transport protocol level - Define neighbor nodes by content stored - An overlay network operates like a distributed hash table by allowing key insertion, querying, and removal. - The structure is based on one or more mathematical functions that determine how the nodes are connected. - Overlays lookup data on the basis of identifiers derived from the content Advantages - Guaranteed data retrieval - Look-up time O(N) - Automatic Load balancing - Self-Organization

Problem Addressed Consumer- Source Communication Client(Consumer) – Server(Source) Communication -Advantage : Simple - Drawback : Not Scalable Time-constrain (Consumers) Limited Resources (Server) Privacy issue An alternative to Client/server is Peer-Peer communication

Problem Definition Distributing information from a resource-constrained source to the consumers with respect to the individual delay constraints of the consumers and restricted source bandwidth.

Previous Work Coral CDN, M.J Freedman - Advantage: Timely delivery of new updates in peer to peer manner -Disadvantage: Set of consumers is limited thus scalability is an issue Really Simple Syndication (RSS), D. Winer - Advantage: Timely delivery of new updates - Disadvantage: Bandwidth Overload problem

Problems of Existing schemes Bandwidth Overload problem Scalability RSS resource constrained server Infrastructure Cost ( more servers)

Proposed Techniques Latency Gradated Overlay - Consumers with strictest delay constraints are placed closer to the server. Periodically pull information from the server. - Nodes can take information from nodes upstream or nodes closer to the source can push the updates downstream. Thus no need to change RSS protocol for servers but only clients are needed to be changed so that clients self-organize into a Lagover to disseminate feeds in a P2P manner

Communication Primitive ( LagOver) In the system, Client nodes tell the maximum resource it can provide and number of nodes it can serve. Lagover should satisfy the delay constraints of individual nodes and the fan-out constraint of each node Heuristic Algorithm to construct dissemination tree overlay network which self-organize according to delay and bandwidth constraints. Evaluation based on simulations when consumers enter and leave the group Takes care of peer heterogeneity and individual consumers preferences. Assumption – Oracle model (partial knowledge of global information at the peers)

Basic Idea of the scheme A random oracle is a mathematical function mapping every possible query to a random response from its output domain. Random interaction among the nodes in order to decide which of the nodes should be closer to the source in comparison to other nodes. ( Assumption – Oracle). There may be several disjoint groups but they all combine to form a tree with source as the root node. The distance of each node from the source is according to their respective latency constraints and fan-out constraints. Greedy algorithm helps in converging of the isolated nodes to form a single source tree according to the delay constraints. Assumption - Node tries to contact the source periodically until it finds a suitable parent. If the node does not find a suitable parent it directly contacts the source.

Evolution of Lagover

Maintenance and Hybrid strategy Tree connections change over a period of time thus maintenance. Only the node in a chain which is the first one with its latency constraint violated needs need to leave the chain. Nodes downstream do not have to take any action. To combine both the latency constraints as well as to serve a large number of nodes downstream a hybrid strategy is needed. Higher fan-out ( Hybrid) given preference over latency constraint (Greedy).

Disadvantages and Future Works Disadvantages - The system assumes oracle random model but it has been proved it is little insecure - The creation of one dissemination tree might be not scalable if there are large number of nodes – maintenance operations might be difficult Future Works - Calculating Lagover for multiple sources who share common consumers - Building Lagover on the basis of locality contexts like ISP, or same domain forming overlay may improve resource usage and performance

THANK YOU QUESTIONS?