Seminar 3: Scalability

by

Zhexin Yang

Zhuomin Liu

Zhao Wang

Multi-User Virtual environments

– People interact in shared 3D VE• Interact with each other

– Co-located– geographically remote location

• Interact with information

– Simulate the experience of immersion in VE• Workstations connected by wide-area network• Run interactive 3D graphics interface program• Render images from user’s simulated viewport

Multi-User Visual Simulation

– 3D graphics scenes comprise the geometry and appearance of many objects

– Can be downloaded in advance– The scenegraph may be replicated at each

user’s computer– Incremental changes are sent across the

network

Challenges

– Maintaining consistent state among a large number of workstations distributed over a wide-area network.

– Network technologies have limitations and different characteristics

• Bandwidth, delay, reliability, etc.

– Balancing throughout limitations of computers and networks

– Systems designed to run over a set of heterogeneous computers and networks, each with very different dynamic, throughput and reliability

Goals of Collaborative Virtual Environments

– Sharing the use of the information is the primary goal

– Maximise responsiveness and scalability while minimising latency

– Maximise the fidelity of sharing where it is needed by reducing it where it is not

Scalability

– Our aim is to characterize the design of systems that can scale to very large numbers of simultaneous users

– The ability to expand a computing solution to support large numbers of users without impact performance

– For a given set of network characteristics, the design may have dramatic impact on the system’s scalability and message distribution performance

Scalability

– Scaling• Allows the amount of information in the environment,

including the number of users, to increase, without reducing the fidelity of experience to any one user

• Controlled in terms of extent, granularity and detail

– Network Topology• Peer-to-Peer Topologies• Hierarchical Topologies

Scaling

– Extent• Subdivide the environment and population according

to interest• Subdivision should be natural and appear

transparent• Balance resources usage across the areas of

interest• Different application genres are suited to distinct

definitions of interest and methods of subdivision

Scaling

– Approaches to subdivision• Multiple worlds• Static spatial subdivision• Locales

Scaling

– Approaches to subdivision• Dynamic space subdivision• Aura• Regions

Scaling

– Granularity• In the real world people are able to reason at

different levels of granularity• This approach of aggregation may be adopted in

CVEs to further increase the scalability• Aggregation reduces not only the rendering but also

the amount of information needed by some observing processes

Scaling

– Granularity• aggregation can increase the scalability of a

receiving process • Aggregation can decrease the scalability of the

sender and the use of the network when many receivers require distinct levels of aggregation for the same object

Scaling

– Detail• Scalability can be further increased by managing the

detail at which individual objects are replicated• Heuristic of interest such as distance or the

relationship between the role of the observer and the use of the observed may be applied

• Balancing the detail of communicated behaviour with the interest of remote users is important

• A hybrid approach might send the highest detail required by any to all and allow receivers to filter further

Spatial Interaction in Virtual Environments

MASSIVE

What is MASSIVE?

– Model, Architecture and System for Spatial Interaction in Virtual Environments

– a distributed virtual reality system

– bring together a number of users in a single virtual place

Definition of Spatial model of interaction

Two Major Components • facilitating scalability based on the concept of aura

• controlling spatial interaction the control of interaction or communication between two objects once they become aware of each other through aura collision

facilitating scalability

• Aura: the extent to which interaction with other objects is possible

- it is the subspace the interaction can occur

• Interaction between two objects becomes

enabled only when their auras together indicate

the possibility of interaction

So….

The use of aura facilitates scaling to many users by

limiting the number of object interactions that must

be handled.

controlling spatial interaction

• Awareness

object quantifies the subjective importance or relevance of the other object in a given medium

i.e. the volume of an audio channel between two users

• Combines

– observed object’s nimbus

– observer’s focus

One-way focus, nimbus and awarenessbetween two objects

Concepts:

-Focus: the observer’s

allocation of attention

-Nimbus: the observed

object’s manifestation or

observability

An example for spatial model of intereaction

So….

- under the spatial model, communication between objects is enabled when their auras collide

- communication is managed according to mutual levels of awareness

- there are three manipulated ways • Implicitly through spatial actions • Explicitly by choosing from among different

shapes and sizes• Via adapter objects

How Massive implement the spatial model of interaction?

The architecture of Massive• a communications architecture based on typed peer-peer connections• a spatial interface trading mechanism to dynamically broker interfaces following aura collisions• dynamic interaction between client programs supporting different media

Aura and Spatial Trading

• conditions of interaction between objects in the

virtual world

- compatible interfaces

- objects must become sufficiently proximate as

determined by their auras • spatial trading can satisfy both conditions

-trader

Spatial Trading

Spatial trading involving peer objects and an aura manager

Aura manger is the master trader

So

With this kind of architecture, MASSIVE can satisfy the following requirements:

- Scale supporting as many simultaneous users as possible - Heterogeneity supporting interaction between users whose equipment has different capabilities and who employ radically different styles of user interface

An example of MASSIVE

An virtual conference

Room

-Five users

-A conference table

as a adapter

Different kinds of interface

Graphic user’s interface

Different kinds of interface

Text user’s interface• display all currently known

objects along with mutual

awareness levels in the right

hand column

Summary

• a multi-user distributed V.R. system• a spatial model of interaction, spatial trading

based on aura collisions• medium-independent peer connections

implementing focus, nimbus and awareness• users can interact over combinations of graphics,

audio and text interfaces

RINGRING A client-Server System for Multi-User Virtual Environments

RING

Supports interaction between large numbers of users in virtual environments with dense occlusion

Takes advantage of the fact that state changes must be propagated only to hosts containing entities that can possibly perceive the change

Systems usingpoint-to-point connections

A

B C D

B

A C D

C

A B D

D

A B C

Systems using broadcast messages

Broadcast Network

A

B C D

B

A C D

C

A B D

D

A B C

Systems using broadcast messages

the key idea of RING

cell

Prior to simulation, the shared virtual environment is partitioned into a spatial subdivision of cells

The boundaries of cells are comprised of the static, axis-aligned polygons of the virtual environment

entity

RING represents a virtual environment as a set of independent entities.

Each entity has a geometric description and a behavior. Every entity is managed by exactly one client workstation.

static: buildings

autonomous: robots dynamic controlled: vehicles

Peer-to-Peer RING System

Peer-to-Peer RING System

hierarchical topology client

Execute the programs necessary to generate behavior for their entities

Maintain surrogates

for some entities

managed by

other clients

Manage communication between clients Process messages before propagating Send auxiliary messages Replace some set of messages

Shift burden away from the client workstations

and into servers

hierarchical topology server

System design

Staticconnection-oriented,

unicast network

scale finitelyscale finitely

Regionalconnectionless,

unicast network

scale infinitelyscale infinitely

Advantages of the RING

Requirements of the client workstations are not dependent on the number of entities in the entire distributed simulation.

High-level management of the virtual environment may be performed by servers without the involvement of every client.

Disadvantage of the RING

Extra latency is introduced when messages are routed through servers.

Multiplayer Computer Games

• Multiplayer networked games can be played over LAN or the Internet. These games use the client/sever topology. The game is run on the server and all the users need to log on to the server to play the game. Low latency is very important. Users with high speed networks will have advantages in playing the game.

Quake

Multiplayer Computer Games

• Virtual Casino– Online gambling room– Slow connection can

cause heavy losses

• Online Role-playing Games

Discussion

Will cyberspace as described by William Gibson or Neal Stephenson ever be built?