Scalable group communications and systematic group modeling
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Scalable Group Communications and Systematic Group Modeling. Jun-Hong Cui University of Connecticut [email protected] http://www.cse.uconn.edu/~jcui. Cool Application 1 : Teleconferencing. Cool Application 2 : Telemedicine. Cool Application 3 : Net Gaming. Multicast: What and How?.

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Scalable Group Communications and Systematic Group Modeling

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Scalable Group Communications and Systematic Group Modeling

Jun-Hong Cui

University of Connecticut

[email protected]

http://www.cse.uconn.edu/~jcui


Cool Application 1 : Teleconferencing


Cool Application 2 : Telemedicine


Cool Application 3 : Net Gaming


Multicast: What and How?

  • Multicast:

    • One to many or many to many communications (group communications)

  • To achieve multicast:

    • Multiple unicast (one to one)

    • Network multicast---IP multicast

    • Overlay multicast (using proxies)

    • Application layer multicast (end host)


Outline of this talk

  • Scalable Group Communications

    --- Aggregated Multicast

  • Systematic Group Modeling

    --- GEM Model

  • Research Directions


group

NHop

g1

Ab, A3

Domain B

A2

B1

Domain A

Ab

Aa

A3

A1

Domain C

X1

Y1

C1

Domain X

Domain Y

D1

Customer Networks, Domain D

IP Multicast

  • Group: IP D class address

  • Use Tree delivery structure

  • Routers: keep forwarding entries per-group/source (multicast state)

  • IP multicast

    • Resource efficient

    • Scalable to group size


group

NHop

Domain B

g1

Ab, A3

A2

B1

g2

Domain A

Ab, A3

Ab

Aa

A3

A1

X1

Domain C

Y1

C1

Domain X

Domain Y

D1

Customer Networks, Domain D

The Problem: Not Scalable to the Number of Groups

  • More groups  more trees

    • More forwarding entries

    • More tree maintenance overhead

  • IP multicast NOT scalable to the number of groups

    • State Scalability problem

    • Serious in transit domains

  • Our solution

    • Aggregated multicast to improve state scalability


group

NHop

Domain B

g1

Ab, A3

A2

B1

g2

Domain A

Ab, A3

Ab

Aa

A3

A1

X1

Domain C

Y1

C1

Domain X

Domain Y

D1

Customer Networks, Domain D

Key Insight

  • There are many overlaps among multicast trees in transit domains


Tree

NHop

Domain B

T1

Ab, A3

A2

B1

Domain A

Ab

Aa

A3

A1

X1

Domain C

Y1

C1

Domain X

Domain Y

D1

Customer Networks, Domain D

Aggregated Multicast

  • Key idea:

    • Force multiple groups share a single delivery tree (aggregated tree)

  • Benefits:

    • Reduce state at core routers

    • Reduce tree maintenance overhead

    • Push complexity to edge

  • Target:

    • Multicast provisioning in transit domains


Tree

NHop

Domain B

T1

Ab, A3

A2

B1

Domain A

De-aggregation

Ab

Aa

A3

De-aggregation

Aggregation

A1

X1

Domain C

Y1

C1

Domain X

Domain Y

D1

Customer Networks, Domain D

Aggregated Multicast (cont.)

  • Core routers:

    • Keep state per-tree

  • Edge routers:

    • Keep group state

  • Groups:

    • Aggregate at incoming edge router

    • De-aggregate at outgoing edge routers


Tree

NHop

Domain B

T1

Ab, A3

A2

B1

Domain A

Ab

DiscardPackets

Aa

A3

A1

X1

Domain C

Y1

C1

Domain X

Domain Y

D1

Customer Networks, Domain D

Perfect Match vs. Leaky Match

  • Group-Tree match

    • Perfect match

    • Leaky match

  • Bandwidth waste in leaky match

    • Data delivery to non-member nodes


Aggregation Control

  • Leaky match

    • Good for tree aggregation

    • But waste bandwidth

  • There is a trade-off

  • Static group-tree matching: NP hard

  • A dynamic group-tree matching algorithm to control the trade-off

    • Under a given bandwidth waste threshold


Group-Tree Matching

Domain B

Domain E

E1

A2

B1

Domain A

A4

Ab

Aa

A3

A1

X1

Domain C

Y1

C1

Domain X

Domain Y

D1

Customer Networks, Domain D


Domain B

Domain E

E1

A2

B1

Domain A

A4

Ab

Aa

A3

A1

X1

Domain C

Y1

C1

Domain X

Domain Y

D1

Customer Networks, Domain D

Group-Tree Matching


Implementation Issues

  • Multiplex multiple groups over a shared tree

    • IP encapsulation

    • MPLS (Multi-Protocol Label Switching)

  • Tree management and group-tree matching

    • Tree Manager (need to know group membership)

    • Distributed or centralized solutions

  • Have designed and implemented protocols:

    • ASSM for source specific multicast (SSM)

    • BEAM for shared tree multicast (ASM)

    • AQoSM for QoS multicast provisioning


Extend to Overlay and Adhoc Net

  • Overlay multicast

    • Implement multicast in overlay net

      • A collection of proxies (or gateways)

    • Processing power, memory & bandwidth more critical

    • Aggregated multicast reduces management overhead

  • Wireless multicast

    • Implement multicast in wireless adhoc net

      • No infrastructure, self-organized

    • Energy, memory, bandwidth, resilience very critical

    • Aggregated trees help to improve performance


Overlay Network


Adhoc Network


Outline of this talk

  • Scalable Group Communications

    --- Aggregated Multicast

  • Systematic Group Modeling

    --- GEM Model

  • Research Directions


The Problem: Group Modeling

  • The locations of the group members

    • Given a graph, where should we place them?

  • Current assumptions: uniform random model (unproven)

    • All members uniformly distributed

    • Not realistic for many applications


Group Modeling is Critical

  • Some studies have shown the locations of members have significant effects on

    • Scaling properties of multicast trees

    • Aggregatability of multicast state

    • Performance of state reduction schemes

  • Realistic group models

    • Improve effectiveness of simulation

    • Guide the design of protocols


Our Contributions

  • Measure real group membership properties

    • MBONE (IETF/NASA) and Netgames (Quake)

  • Design a model to generate realistic membership

    • GEneralized Membership Model (GEM)

    • Use Maximum Enthropy: a statistical method


Roadmap

  • Membership Characteristics

  • Measurement and Analysis Results

  • Model Design and Validation


Beyond Uniform Random Model

  • How close are the members in a group?

  • Are all the members same in group participation?

  • What are the correlations between members in group participation?


Member Router

Edge Router

An Illustration (Teleconference)

Seattle

0.7

Boston

0.5

Internet

1.0

Atlanta

0.4

Los Angeles

0.5


Membership Characteristics

  • Member clustering

    • Capture proximity of group members

    • Use network-aware clustering method

  • Group participation probability

    • Show difference among members/clusters

  • Pairwise correlation in group participation

    • Capture joint probability of two members/clusters

    • Use correlation coefficient (normalized covariance)


Measure Membership Properties

  • MBONE applications (from UCSB)

    • IETF-43 (Audio and Video, Dec. 1998)

    • NASA Shuttle Launch (Feb. 1999)

    • Cumulative data sets on MBONE (1997-1999)

  • Net Games (using QStat)

    • Quake I (query master server)

    • Choose 10 most popular servers (May. 2002)

  • Examine three membership properties


Member Clustering

MBONE cumulative data sets

(3, 0.64)

MBONE real data sets

Net game data sets

CDF of cluster size for MBONE and net games


Group Participation Probability

CDF of participation probability for Net Game data sets


Group Participation Probability

CDF of participation probability for MBONE applications


Pairwise Correlation in Group Participation

CDF of correlation coefficient for Net Game data sets


Pairwise Correlation in Group Participation

CDF of correlation coefficient for MBONE applications


Generalized Membership Model--- GEM (An Overview)

Network topology

Cluster method

Group behavior

Distr. of participation prob.

Distr. of pairwise correlation

Distr. of member cluster size

Inputs

1. Create clusters in given topology

2. Select clusters as member clusters

According to input distributions

3. Choose nodes for each member clusters

GEM

Desired number of multicast groups

that follow the given distributions

Outputs


Member Distribution Generation

  • Definition:

    K clusters: C1 , C2 , … , Ci , … , CK

    Prob. pi for any i in [1, K]

    Joint prob. pi,jfor any i, j in [1, K]

    X=(X1 ,X2 , … , Xi , … , Xk): Xiis a binary indicator

    Xi = 1 if Ci is in the group

    Xi = 0 if Ci is not in the group

  • Objective:

    Generate vectors x=(x1 , x2 , … , xk) satisfying

    P(Xi = 1) = pi and P(Xi = 1 , Xj = 1) = pi,j


Maximum Entropy Method

  • To calculate the distribution of (X1,X2, …, Xk) requires O(2K) constraints

  • But we only know O(K+K2) constraints

  • We use Maximum Entropy Method

    • Entropy is a measure of randomness

    • We construct a maximum entropy distr. p*(x)

      • Satisfy constraints in specified dimensions

      • Keep as random as possible in unconstrained dimensions

      • i.e. maximize entropy while match given constraints


Three Cases

Considering P(Xi=1)= pi and P(Xi=1, Xj=1)=pi,j

  • Uniform distr. without correlation (easy)

    pi,j = pi * pj , and pi = pj

  • Non-uniform distr. without correlation (easy)

    pi,j = pi * pj , but pi = pj not necessary

  • Non-uniform distr. with pairwise correlation

    Neither pi,j = pi * pjnor pi = pj necessary

    Need to calculate the maximum entropy distr. p*(x)

    Entropy decreases from case 1 to case 3


Experimental Validation

  • Consider all membership properties

  • Consider three cases

  • Figures omitted …

  • Our experiments show

    • GEM can regenerate groups satisfying given distributions (from real measurement)


Summary

  • Uniform random model

    • Can capture net games approximately

    • But not realistic for MBONE applications

  • GEM: a generalized membership model

    • Three cases (case 1: uniform random model)

    • Realistic membership can be regenerated

  • Beyond multicast

    • Peer-to-peer network modeling

  • Beyond wired network

    • Wireless adhoc networks, sensor networks …


Outline of this talk

  • Scalable Group Communications

    --- Aggregated Multicast

  • Systematic Group Modeling

    --- GEM Model

  • Research Directions


Networking: Expanding Visions

(from Jim Kurose)


Peer-to-Peer Networking


Peer-to-Peer Networking

Focus at the application level


Applications & Challenges

  • Applications

    • P2P file sharing (Napster, Gnutella, Freenet, etc.)

    • Application-layer multicast

  • Characteristics

    • each node potentially same responsibility, functionality

    • logical connectivity rather than physical connectivity

  • Why P2P?

    • High resource utilization (bandwidth, memory, CPU)

  • Challenges

    • Self-organized and large scale (routing)

    • Reliability and security


Research Directions

  • Overlay multicast

    • Scalability, QoS, security, pricing, …

  • Multicast modeling

    • Systematic multicast evaluation

  • Peer-to-peer networks

    • measurement & modeling, complex queries

  • Wireless adhoc networks

    • Mobility modeling, scalable multicast

  • Sensor networks

    • Sensor deployment and security

    • Very large scale sensor network design


Questions?

[email protected]

http://www.cse.uconn.edu/~jcui


THANKS!!!


Network Characteristics

  • No fixed infrastructure, instantly deployable

  • Node portability, mobility

  • Error-prone channel

  • Limited resources

    • bandwidth, energy supply, memory and CPU.

  • Heterogeneous nodes

    • big/small; fast/slow etc

  • Heterogeneous traffic

    • voice, image, video, data

  • Wireless multihop connection

    • to save power, overcome obstacles, enhance spatial spectrum reuse, etc


The maximum entropy distr. p*(x) is the solution for:

Subject to

and

and

Calculate the Maximum Entropy Distribution

Use lagrange multipliers and numerical method to construct p*(x), Then Gibbs Sampler to sample it


Group Participation Probability

Participation probability distribution for IETF43-Video


Pairwise Correlation in Group Participation

Joint probability distribution for IETF43-Video


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