Scalability of network environments

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. Approaches MASSIVE & RING The overall problem Discussion

3. The overall problem Approaches Introduction Discussion 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. Review Introduction Goals of CVE Scaling Where we are

4. The overall problem Approaches Goals of CVE Discussion 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) Review Introduction Goals of CVE Scaling Where we are

5. The overall problem Approaches Scaling Discussion 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. Review Introduction Goals of CVE Scaling Where we are

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

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

8. Scalability 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) The overall problem Approaches Definition of Scalability Discussion Review 。。。 。。。 。。。 Space structuring Topologic Scalability Definition … … Where we are

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

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

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

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

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

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

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

16. implicitlythrough 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 Explicitlyby 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 nimbus The overall problem Approaches Spatial model of interaction - Three manipulation ways Discussion MASSIVE Spatial model … … Where we are

17. MASSIVE 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: Scale - supporting as many simultaneous users as possible It uses a spatial model of interaction The overall problem Approaches MASSIVE functionality - Introduction Discussion MASSIVE … Functionality … Where we are

18. User-level features 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. Text users may interact with graphical users and vice-versa. All media are controlled by aura, focus and nimbus. It includes adaptor objects (e.g. conference table, podium). There may be any number of worlds with portals to move between worlds. Each process obtains and uses only (spatially) local information. New media can be added without affecting the core system. The overall problem Approaches MASSIVE functionality - key feature for scalability(1) Discussion MASSIVE … Functionality … Where we are

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

20. MASSIVE functionality - A example of virtual conference Graphics user’s interface Text 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 connections The overall problem Approaches MASSIVE Architecture - Introduction Discussion MASSIVE … … Architecture Where we are

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

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

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

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

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

27. The overall problem Approaches RING Mechanism Discussion MASSIVE … • Message 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(N2)  O(NP) • Network topology: IP-Multicast +Message Filtering … … RING Architecture Character … Where we are

28. Partition Regions(1)

29. Partition Regions(2)

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

31. Regions

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

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

34. Table: Average message processing rates (messages per second)

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

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

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

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

39. Discussion Approaches MASSIVE & RING The overall problem Discussion

40. The overall problem Approaches Discussion Discussion 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 • Multiplayer computer games

41. The overall problem Approaches Discussion Discussion • Will cyberspace as described by William Gibson or Neal Stephenson ever be built