State Transmission Mechanisms for a Collaborative Virtual Environment Middleware Platform João Orvalho, Pedro Ferreira and Fernando Boavida Communications and Telematics Group CISUC – Centre for Informatics and Systems of the University of Coimbra Polo II, 3030 COIMBRA – PORTUGAL {orvalho, pmferr,

Outline CVE’s Requirements ARMS STF State Definition and Categorization State Interaction Streams Reception lag and time warp Tests made to STF Further work

… maintenance of a consistent shared state … - dead reckoning Application Requirements Scalability, interaction and consistency QoS characteristics: Reliability, losses, delay and delay jitter Other factors: Data heterogeneity, frequency of events, synchronization delay, number of participants and playout time (display frequency) CVE’s Requirements

Data heterogeneity: real-time audio and video, scene description, 2D, control and state or update State synchronisation: essential or redundant … an issue for applications’ environment model Delay and jitter: 100/200 ms Reliability: different levels... Reliable transport protocol or network-aware applications... middleware Other requirements: Application Data Unit (ADU) CVE’s Requirements (Cont.)

ARMS – Augmented Reliable Multicast CORBA Event Service ARMS QoS API QoS features of the reliable multicast services offered STF(state transmission framework) API State transmission and reception, late join, virtual world partitioning and time synchronization on a distributed architecture ARMS architecture

What exactly is a state ? This is very application dependent However: A state always includes: Data ( the state itself ) Categorization information Representated by STFState interface. State messages are organized into streams of interaction Identified by a key : STFKey interface STF – Status Transmission Framework

State Categorization Redundancy: Redundant/Essential State Volatility: Volatile/Non-volatile State Late Join Protocol: Independent/Cumulative State Interaction Streams : STFStateMessage objects STF – Status Transmission Framework

Reception lag and time warp STF – Status Transmission Framework

Objective: measure the total message delay and throughput First set (A): increasing message transmission rate Second set (B): increasing message sizes Both sets: 3 different streams of states Stream 1: redundant, volatile and independent states; Stream 2: redundant, non-volatile and independent states; Stream 3: essential, non-volatile and independent states. with same priority = Highest (A) state size=22 bytes and key size=6 bytes => total 28 bytes Tests made to STF

CONCHA – CONference system based on java and corba event service CHAnnels The Test Application

Probing Points

Test’s Results (A) : Fixed size, increasing rate

Test’s Results (B): Fixed rate, increasing size

Test’s Results : Optimal use of ARMS layer capacity

Further Work Further testing STF/ARMS integration optimizations Scalability testing Reception lag testing Latejoin testing Proof-of-concept STF CVE Application development QoS capabilities: Multiple reliability levels STF evolution to an integrated platform for CVE application development Integration of more features ( support for video, audio, vrml streaming... )