1. Scalability of network environments Esau Libo and Damon Dept. of Computer Science University College London

2. Purpose of this seminar Describe the overall problem of scalability in virtual environment and two approaches (MASSIVE & RING) in some detail. Discuss some applications. Describe the overall problem of scalability in virtual environment and two approaches (MASSIVE & RING) in some detail. Discuss some applications. The overall problem Approaches MASSIVE & RING Discussion

3. Introduction Review Computers and networks strengthen an Collaborative Virtual Environment (CVE) Computer have limitations and differing capabilities Network technologies like Ethernet, ATM and wireless Each technology with bandwidth, delay characteristics and reliability. Where we are Approaches Discussion The overall problem Scaling Goals of CVE

4. Introduction Review Sharing the use of information is the primary goal. Design to run over a set of heterogeneous computers and networks. Maximise responsiveness and scalability while minimising latency (Roberts) Where we are Approaches Discussion The overall problem Scaling Goals of CVE

5. Scaling Scaling Introduction Review Scaling allows the amount of information in the environment with number of users, to increase, without reducing the fidelity of experience to any one user. Achieved by balancing each individuals need for information with what can be achieved. Where we are Approaches Discussion The overall problem Goals of CVE

6. Space structuring Approaches Discussion The overall problem 。。。 Review Space structuring Division of virtual space a) Separate Servers b) Uniform geometrical structure c) Free geometrical structure d) User-centered dynamic structure Where we are

7. Approaches Discussion The overall problem 。。。 Review Network Topologies Peer-to-peer Unicast Peer-to-peer Multicast Client/Server Multi-Server Topology Topologies Space structuring Where we are

8. Approaches Discussion The overall problem 。。。 Review Definition of Scalability Scalability Space structuring Topologic Definition … … ScalabilityScalability –How well a solution to some problem will work when the size of the problem increases. –For example… complexity of O(N), O(N^2) Where we are

9. Approaches Discussion The overall problem 。。。 Review Scalability Space structuring Topologic … … Factors Determining factors: graphical complexity behavioral complexity number of simultaneous participants Where we are

10. Approaches Discussion The overall problem 。。。 Review Scalability Space structuring Topologic … … Bottlenecks Bottlenecks: Network Server Dial-up Modems PCs of users Where we are

11. Approaches Discussion The overall problem 。。。 Review Scalability Space structuring Topologic … Solution: limited information exchange Example: audio: objects too far away to hear visual: objects behind the user … Solution Where we are

12. Two approaches (MASSIVE & RING) The overall problem Approaches MASSIVE & RING Discussion

13. facilitating scalabilityfacilitating scalability –it is based on the concept of aura. controlling spatial interactioncontrolling spatial interaction –it deals with the control of interaction or communication between two objects once they become aware of each other through aura collision. … Spatial model … MASSIVE Where we are Discussion The overall problemApproaches Spatial model of interaction -major components

14. Key concepts: medium : communication typemedium : communication type aura : subspace in which interaction can occuraura : subspace in which interaction can occur awareness: quantifies one object’s significance to another object (in a particular medium)awareness: quantifies one object’s significance to another object (in a particular medium) focus : represents an observing object’s interestfocus : represents an observing object’s interest nimbus : represents an observed object’s wish to be seennimbus : represents an observed object’s wish to be seen adapters : can modify an object’s auras, focus, and nimbusadapters : can modify an object’s auras, focus, and nimbus Awareness and the Spatial Model of Interaction (1) Where we are Discussion The overall problemApproaches … Spatial model … MASSIVE

15. Awareness and the Spatial Model of Interaction (2) Where we are Discussion The overall problemApproaches … Spatial model … MASSIVE A example about watching TV

16. implicitly through spatial actions such as moving and turning, e.g. when turning around my focus and nimbus follow me, resulting in an adjustment of my awareness of nearby objectsimplicitly through spatial actions such as moving and turning, e.g. when turning around my focus and nimbus follow me, resulting in an adjustment of my awareness of nearby objects Explicitly by choosing from among different shapes and sizes, e.g. switching between narrow or wide focusExplicitly by choosing from among different shapes and sizes, e.g. switching between narrow or wide focus via adapter objects which transform combinations of aura, focus and nimbusvia adapter objects which transform combinations of aura, focus and nimbus Where we are Discussion The overall problemApproaches … Spatial model … MASSIVE Spatial model of interaction Three manipulation ways - Three manipulation ways

17. MASSIVE is the “Model, Architecture and System for Spatial Interaction in Virtual Environments”, an experimental distributed virtual reality system intended to support collaborative activityMASSIVE is the “Model, Architecture and System for Spatial Interaction in Virtual Environments”, an experimental distributed virtual reality system intended to support collaborative activity It has been driven by key requirement:It has been driven by key requirement: Scale - supporting as many simultaneous users as possible Scale - supporting as many simultaneous users as possible It uses a spatial model of interactionIt uses a spatial model of interaction Where we are Discussion The overall problemApproaches … MASSIVE Functionality … MASSIVE functionality Introduction - Introduction

18. User-level features It is a multi-user distributed V.R. system.It is a multi-user distributed V.R. system. There are textual, graphical and audio client programs (usable in any combination) allowing users to communicate by graphical gestures, typed messages or real-time packetised audio.There are textual, graphical and audio client programs (usable in any combination) allowing users to communicate by graphical gestures, typed messages or real-time packetised audio. Text users may interact with graphical users and vice-versa.Text users may interact with graphical users and vice-versa. All media are controlled by aura, focus and nimbus.All media are controlled by aura, focus and nimbus. It includes adaptor objects (e.g. conference table, podium).It includes adaptor objects (e.g. conference table, podium). There may be any number of worlds with portals to move between worlds.There may be any number of worlds with portals to move between worlds. Each process obtains and uses only (spatially) local information.Each process obtains and uses only (spatially) local information. New media can be added without affecting the core system.New media can be added without affecting the core system. Where we are Discussion The overall problemApproaches … MASSIVE Functionality … MASSIVE functionality key feature for scalability(1) - key feature for scalability (1)

19. Lower-level features keyword-based interface trading for coordinating client programs for different media.keyword-based interface trading for coordinating client programs for different media. spatial interface trading based on aura collisions.spatial interface trading based on aura collisions. medium-independent peer connections implementing focus, nimbus and awareness.medium-independent peer connections implementing focus, nimbus and awareness. integrated support for focus, nimbus and aura adaptors.integrated support for focus, nimbus and aura adaptors. MASSIVE functionality key feature for scalability(2) - key feature for scalability (2) Where we are Discussion The overall problemApproaches … MASSIVE Functionality …

20. MASSIVE functionality A example of virtual conference - A example of virtual conference Graphics user’s interfaceText user’s interface

21. The interactions in MASSIVE are a mixture of client-server (between objects and the trader or aura manager) and peer-to-peer (between objects in the world). Most of the interactions are bidirectional, being symmetrical in the case of peer connections and involving asynchronous notifications in the case of client server notifications in the case of client serverconnections Where we are Discussion The overall problemApproaches MASSIVE … MASSIVE Architecture Introduction - Introduction Architecture …

22. two conditions of interaction between objects in the virtual world two conditions of interaction between objects in the virtual world –compatible interfaces –objects must become sufficiently proximate as determined by their auras Where we are Discussion The overall problemApproaches MASSIVE Architecture - Aura and spatial trading MASSIVE … Architecture …

23. Where we are MASSIVE Architecture - how spatial trading operates Discussion The overall problemApproaches MASSIVE … Architecture …

24. RING Architecture(1) RING represents a virtual environment as a set of independent entities each of which has a geometric description and a behavior.RING represents a virtual environment as a set of independent entities each of which has a geometric description and a behavior. Where we are Discussion The overall problemApproaches MASSIVE Architecture … RING … … … …

25. Entity:Entity: Multi-user interaction is supported by matching user actions to entity updates Multi-user interaction is supported by matching user actions to entity updates Client-Server designClient-Server design Reliability, Redundancy, Load- Balacing Reliability, Redundancy, Load- Balacing Where we are Discussion The overall problemApproaches MASSIVE … … … RING Architecture(2) Architecture … RING …

26. Entity, Client, RINGEntity, Client, RING Every RING entity is managed by exactly one client workstationEvery RING entity is managed by exactly one client workstation Communication between clients is managed by serversCommunication between clients is managed by servers Where we are Discussion The overall problemApproaches MASSIVE RING … … … RING Architecture(3) Architecture … …

27. RING Mechanism Message FilteringMessage Filtering  Area of Interest (exploit communication locality)  Regular subdivision (NPSNET), proximity (DIVE)  Pre-determined inter-cell occlusion (SPLINE)  Visibility culling (RING)  Explicitly registering interest( NPSNET)  Dead Reckoning (NPSNET, PARADISE) messages: O(N 2 )  O(NP) messages: O(N 2 )  O(NP) Network topology: IP-Multicast +Message FilteringNetwork topology: IP-Multicast +Message Filtering Where we are Discussion The overall problemApproaches MASSIVE RING … … … Architecture Character …

28. Partition Regions(1)

29. Partition Regions(2)

30. RING Algorithm Changing "periodic" update messages when entities cross cell boundaries.Changing "periodic" update messages when entities cross cell boundaries. Using cell visibility "look-ups“Using cell visibility "look-ups“  Each cell  a multicast group  Sends messages to its “cell”  Receive messages from its interest zone (including neighbouring cells) (including neighbouring cells) Where we are Discussion The overall problemApproaches MASSIVE RING … … … Architecture Character …

31. Regions

32. Visibility Culling Occlusion: indoor (rooms,buildings), outdoor(‘fog of war’)Occlusion: indoor (rooms,buildings), outdoor(‘fog of war’) Visibility culling carried out with:Visibility culling carried out with: –‘Potentially visible sets’ of cells (pre-computed) –Temporal Bounding Volumes, Update Free Regions

33. Different RING systems 1. Peer to Peer1. Peer to Peer O(NP), scale finitely O(NP), scale finitely 2. Client-Server ( single server, static)2. Client-Server ( single server, static) scale finitely scale finitely 3. Client-Server ( any server, regional)3. Client-Server ( any server, regional) scale infinitely  region finite scale infinitely  region finite 4. Other systems4. Other systems Where we are Discussion The overall problemApproaches MASSIVE … … … … RING … Compare

34. SystemDesign Number of Services ClientServer InputOutputInputOutput From Server To Server From Client From Server Total To Client To Server Total Static(A)24.250.5046.844.090.8290.544.0334.5 45.090.4624.164.488.5148.664.7213.3 83.290.4512.070.482.371.371.5142.8 164.160.376.174.780.837.275.8113.0 Regional(B)24.670.4248.21.950.2270.72.0272.7 43.890.5324.24.328.5153.04.3157.3 84.150.4612.33.615.883.53.687.1 164.410.435.93.49.337.53.541.0 Table: Average message processing rates (messages per second)

35. Experimental results Static system design: total number of server-server messages increases, sub-linearStatic system design: total number of server-server messages increases, sub-linear Regional system design: inter-visibility decrease  server- server messaging reduceRegional system design: inter-visibility decrease  server- server messaging reduce Where we are Discussion The overall problemApproaches MASSIVE … … … … RING … Compare

36. Experimental Conclusion Different network characteristics and different system designs can significantly affect the message processing rates requiredDifferent network characteristics and different system designs can significantly affect the message processing rates required Hierarchical system (regional) scales better than hierarchical system (static)Hierarchical system (regional) scales better than hierarchical system (static) Where we are Discussion The overall problemApproaches MASSIVE … … … … RING … Compare

37. RING system advantage 1. Less storage, processing, and network  bandwidth requirements;  very dynamic and complex message processing may be performed by servers 2. High-level management Where we are Discussion The overall problemApproaches MASSIVE … … … … RING … Compare

38. RING system disadvantage 1. Extra latency 2. Currently support only visual interactions Discussion The overall problemApproaches MASSIVE … … … … RING … Compare Where we are

39. Discussion The overall problem Approaches MASSIVE & RING Discussion

40. Multiplayer computer gamesMultiplayer computer games Discussion The overall problemApproaches Quake includes a multi-player mode to play over LAN or the Internet with or against other humans. The network play uses a client/server model, where the actual game runs on the server only and all players "log in" there to participate. Depending on the client's specific route to the server, different clients will get different ping times. The lower your latency (ping time), the smoother your in-game motions, and the easier it is to accurately aim and score. Someone playing on the server PC gets a substantial advantage due to essentially zero lag LANInternetclient/serverpingPClag

41. Discussion Will cyberspace as described by William Gibson or Neal Stephenson ever be builtWill cyberspace as described by William Gibson or Neal Stephenson ever be built Discussion The overall problemApproaches