An overlay for latency gradated multicasting

Anwitaman DattaSCE, NTU Singapore

anwitaman@ntu.edu.sgIon Stoica, Mike Franklin

EECS, UC Berkeleyistoica@cs.berkeley.edu, franklin@cs.berkeley.edu

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?