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Network Topologies for Scalable Multi-User Virtual Environments

Network Topologies for Scalable Multi-User Virtual Environments. Lingrui Liang. Syllabus. Introduction Related work Network characteristics Network topologies Experimental result Conclusion. Introduction.

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Network Topologies for Scalable Multi-User Virtual Environments

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  1. Network Topologies for Scalable Multi-User Virtual Environments Lingrui Liang

  2. Syllabus • Introduction • Related work • Network characteristics • Network topologies • Experimental result • Conclusion

  3. Introduction • Network bandwidth and graphics performance are increased, distributed visual simulation systems are allowed multiple users to interact in a shared 3D virtual environment(VE) • Workstations run 3D graphics interface program to simulate the virtual environment, each user can be a role to see other roles via wide-area network

  4. Introduction • Avatars controlled by users and kept the newest information in the workstation through messages • Support: visual interactions bewteen multiple users in a shared 3D VE

  5. Applications Distributed training simulations Collaborative design Virtual meetings Multiplayer games

  6. Challenge • Keep consistent state among a larger number of workstations • E.g. One entity moves or modifies the shared environment, an update must be applied on each workstation • N entities move, M times per second. Updates should be M*N per second to a shared database

  7. Goal and Aim • Goal: trade-offs of different network topologies and messaging protocols for multi-user virtual environments • Aim: represent the design of system that can support very large numbers of users at the same time

  8. Related Work • A virtual environment is represented by these systems as a set of independent entities. Each entity has a geometric description and a behaviour • Types of entity: • Static entity • Dynamic entity

  9. Related Work • Conditions for activating distributed simulation with multiple entities interact in a shared VE: • Sending message to one another to update the geomotry or behaviour of entities • Modifications to the shared environment • Impact on other entities

  10. Related Work – Entity Management • Every entity is managed by one of the workstation in the distributed system • Workstation may map user input to control of entities and may include viewing capabilities • To manage its own entities (local entities), each workstation maintains surrogate for some entities managed by other workstation (remote entities)

  11. Related Work – Surrogate • It contatins representations for the geometry and behaviour of entity • If a workstation receives an update message from a remote entity, it will update the geometric and behavioural models for the entity’s local surrogate • Surrogate behaviour is simulated by each workstation in the processing of update

  12. Communication Mode for Network Nodes Four routing schemes: • Unicast • Multicast • Broadcast • Anycast

  13. Unicast • Unicast transmission is the sending of information packets to a single destination • E.g. Reality Bulit for Two, VEOS and MR Toolkit are based on unicast peer-to-peer

  14. Multicast • Using multicast to send update message to a subset of participating workstation. The general idea is to map entity properties into multicast groups, and send update message only to relevant groups • E.g. NPSNET and DIVE are multicast peer-to-peer systems

  15. Broadcast • Broadcast refers to transmitting a packet that will be received by every device on the network • E.g. VERN and SIMNET are broadcast peer-to-peer systems

  16. Anycast • Anycast is a network addressing and routing scheme whereby data is routed to the "nearest" or "best" destination as viewed by the routing topology • E.g. DNS and IPv6 are based on the anycast systems

  17. Client-Server System • Communication between client workstation is managed by message server with intelligent server message processing • Key feature of client-server design: servers can process messages before propagating them to other cilents, selecting, augmenting, or modifying messages

  18. Example for Client-Server Design • A server may determine to send a particular update message only to a relevant small subset of clients and then broadcast the message only to those clients and their servers • It can be applied to many users at the same time

  19. Client-Server Design • Motivations: • To support modem connections to clients • To simplify implementation • Assumption: a client can send a message to any one or set of clients and/or servers at any time • Result: with better processing and messaging properties, a variety of alternate system topologies are possible

  20. Network Characteristics • Communication between workstations participating can be implemented by a various possible network with different features • Logical networks: • Transport is orientedconnection or connectionless • Message delivery is unicast or multicast • Message latency • Data bandwidth

  21. Wide-Area Network - Connections • Connections: • data exchange between two workstations • two-way, orientedconnection, unicast transport • low latency and low bandwidth(14.4Kb/s or 28.8Kb/s) • e.g. A network is a modem using a standard telephone cable

  22. Wide-Area Network - Unicast • Unicast: • random number of workstations are connected to a network logically • the network supports connectionless and unicast messages • e.g. Internet

  23. Wide-Area Network - Multicast • Multicast: • random number of workstations communicate with each other with connectionless and multicast messages • e.g. Mbone(Multicaste Backbone)

  24. Network Characteristics • Different networks can be constructed using combinations of different types of networks • Each combination can affect the design of the multi-user virtual environments systems

  25. Basic Concept - Network Topology • Network topology is the study of the arrangement or mapping of the elements of a network, especially the physical (real) and logical (virtual) interconnections between nodes

  26. Peer-to-Peer Topologies • Arranged system with a set of workstations • Communication method: peer-to-peer (P2P) directly • Peers send a unicast message to other peers when an entity is updated (unicast message is available)

  27. Peer-to-Peer Topologies - Unicast

  28. Peer-to-Peer Topologies • Filters must be applied • What for? – Update messages are not sent to every peer for every update • Peers maintain lists of entities in each cell • Update messages are sent to all peers whenever an entity moves to a new cell, mapping must be changed among peers

  29. Peer-to-Peer Topologies • Peers can send a single multicast message to a subset of peers at one time (Multicast message is available) • A multicast group can be assigned to each cell • Peers do not maintain the lists of entities in each cell, but they join and leave multicast groups as their entities move between cells

  30. Peer-to-Peer Topologies - Multicast

  31. Hierarchical Topologies • Hierarchical Topologies = Tree Topologies • A hierarchical topology is created similar to an extended star topology. The primary difference is that it does not use a central node. Instead, it uses ad trunk node from which it branches to another nodes.

  32. Hierarchical Topologies • Multi-user VE can be designed by this topology • Each entity’s update, a client sends update message to server, the it propogates to other servers and clients • Types of network used for client-server and for server-server links

  33. Hierarchical Topologies

  34. Properties • Advantages: • Message distribution is shifted out of the client and into the server • Server: litter processing, storage or messaging to keep entities consistent in a large VE • Client: precessing, storage and network bandwidth requirements scale unlimited • Disadvantages • Extra latency may be introduced for each update message

  35. Communications – Client/Server • Oriented connection, unicast: each server manages message distribution for a subset of clients • Every entity’s update, client server, server other servers and client with entities, but maintaining mappings and periodic update are required • Not scale infinitely

  36. Communications – Client/Server • Connectionless, unicast: each server manages message distribution for separate regions of the VE • Advantage: fewer server-to-sercer messages are generated • Maintaining mappings and periodic update are also required • Scales infinitely and server are limited to finite subsets of the VE

  37. Communications – Server/Server • Multicast: similar to the P2P multicast system design • Region managed by each server is static, servers do not join and leave multicast group dynamically • No periodic update required • Scales infinitely

  38. VE conditions: 800 rooms connected by hallways consisting of 23,168 polygons and 2,219 cells Runs 256 computer-controlled entites at the same time With 2,4, 8 or 16 servers Experiment

  39. Experimental Scheme • Two schemes to demonstrate the eect of system design on the message processing requirements of workstations in a multiuser virtual environment: • A) clients made static connections to one server while servers passed messages to each other using a connectionless unicast network • B) clients and servers both passed messages on a connectionless unicast network, each server managed message distribution for a separate region of the virtual environment

  40. Experimental Results

  41. Experimental Analysis • A) the number of servers increased, the total number of server-server messages output by each server increased as separate unicast messages were sent to multiple servers. This is sublinear increase • B) the number of servers increased, and the intervisibility between server regions decreased, server-server messaging was reduced

  42. Experimental Result • Using B) system design, the message processing burden of each client and server can be quite small, and these systems can scale many users at the same time

  43. Conclusion • Characteristics of the networks can greatly impact the message distribution performance of a particular system design for multi-user VE • The results of experiments demonstrate that different network characteristics and different system designs can seriously affect the message processing rates required by workstations in a multi-user VE • Perhaps, by identifying network characteristics and system designs that improve the message distribution properites or decrease the cost of multi-user VE systems, we can help software and network architects in the design of future systems

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