Reliable Multicast in the STOW RTI Prototype

Transcription

1 Reliable Multicast in the STOW Prototype Harry Wolfson Steve Boswell Daniel J. Van Hook Steve McGarry MIT Lincoln Laboratory March 6, 1997 Wolfson 1

2 Outline Introduction Message Transport Services Reliable Multicast Discovery Service Emulation of Reliable Multicast in -s Performance Measurements Summary Wolfson 2

3 Federation using the HLA / Fe de ra te F e de ra te Fe d e ra te F e de ra te Fe de ra te Fe d e ra te C o mm C o mm Co mm Co m m C o mm Co mm Wolfson 3

4 -s Sponsors Defense Modeling and Simulation Office (DMSO) Part of larger DoD 1.0 development effort Initial implementation of Data Distribution Management Services Support initial use of the HLA in a large scale, real-time system DARPA Synthetic Theater of War (STOW) program» STOW is an Advanced Concept Technology Demonstration (ACTD)» Customer is Atlantic Command (ACOM)» An HLA based simulation system Wolfson 4

5 -s Development STOW Requirements ( perspective) ~ 25 Federate classes on host computers sites (LANs connected via a WAN) 10,000 objects (scaleable to 100,000) MIT Lincoln Laboratory is developing the prototype -s for use by STOW Full functionality except for Time and Ownership Management Focus on real-time performance and very large exercise scalability» Low latency, High throughput, Low bandwidth overhead Early availability of (15 Oct 96) Wolfson 5

6 -s Block Diagram Amb assad or Remove Ob j, Provide Attr S ubscribe, P ublish, Asso c R egions Control Updates Create, Delete Obj Fe d Create, Join, etc. Update Attr, S end Interaction Refle ct Attr, Re c Interactio n R emo ve Obj, P rovide Attr Set Trans p Mo de {oid, attribute_valu es or, class, p aram_values } S trea m Mappings Subs cription P rincipa l Streams of Interest Con sistency Mana ger R eques t S ubscriptions, Pub lications, Reso urces Discovery P rotocol Local S ubscription Agent Res ource s Object Ma nager Federa tion Manag er create delete update C onsistency P rotocol Reliable Be st Effort Transpo rt Ma nager {oid, attribute_value s or, class, p aram_values } Minimum Ra te {stream, data, count} S tate Con sistent Bu ffe r Man ager Distribution Databas e Commu nicatio n Man agers Stream Manag er UDP TCP Rel Distrib R TI Initializa tion Data (FED + R ID) Wolfson 6

7 Message Transport Services Best Effort Based on UDP Multicast» Permits scaling to large exercises No mechanism for reliability or message ordering Minimum Rate Comparable to DIS Transport mechanism State Consistent Ensures delivery of the latest attribute value No guarantee of intermediate message delivery Reliable Guaranteed delivery of messages Messages delivered in order Wolfson 7

8 Reliable Multicast Reliable Multicast Protocols RAMP, RMP, SOM (MTP-2) Based on UDP to support multicast Some provide reliability based on NACKs May be optimized for single sender (one-to-many) Some are optimized for a fixed set of senders and receivers Emulation of Reliable Multicast in -s Dynamic message routing based on streams Reliability provided by use of TCP protocol Does not consume UDP multicast groups Multicast emulated via use of hierarchical topology of Reliable Distributors (exploders) Wolfson 8

9 Discovery Services General purpose mechanism to facilitate contact between distributed service providers and clients Predates similar capability in CORBA Supports multiple providers of same service type Provider advertises its service Service type Qualifier: discoverer can screen for desired value Invariant data: constant provider info (eg. socket addr) Variant data: time-varying provider status info Client discovers available providers Only receives advertisements from appropriate providers Initiates connection with provider based on information in advertisement (eg. Invariant data) Clients may monitor status of providers Fault detection Load balancing Wolfson 9

10 Discovery Service Manager (DSM) Fe d e rat e Fe d e rat e R TI S e rvice s D S M Fe d e rat e R TI S e rvice s D S M a dv e rt ms gs a dv e rt ms gs S e rv ice s C A RD DS M Adv e rt Dis cov e r Monitor Fe d e rat e R TI S e rvice s D S M R e que s tor s e nd lis te n a nd ca llb a ck Pe riodic Time r a dv e rt ms gs a dv e rt ms gs a dv e rt ms gs Wolfson 10

11 Implementation of Reliable Multicast in -s Based on TCP point-to-point connections Reliable Distributor services a number of clients that wish to send and / or receive reliable message traffic Clients connect to appropriate Reliable Distributor using information provided by the Discovery Service Wolfson 11

12 Sample Network Topology for Reliable Servers / Clients Fe de ra te LAN # 1 RD tcp Fe de ra te tcp Fe de ra te tcp RD Fe de ra te Fe d e ra te tcp LAN # 3 Fe de ra te tc p Fe de ra te tcp RD tcp Fe de ra te tcp LAN # 2 STOW is using fully connected mesh Could configure Server connections as a-cyclic tree Wolfson 12

13 Features of -s Reliable Multicast Robust Outgoing message queue (accommodates bursty traffic) Re-establishing connectivity (fault tolerance) Provides atomic message delivery within a stream based protocol (TCP) Framing of received messages Reassembly of fragmented messages Fragmentation of large outgoing messages Configurable Server hierarchy Auto-configuration for small Federation Execution, or in a small scale testing environment Configurable server / client topology for larger Federations that span LANs and WANs Stand-alone or integrated servers Wolfson 13

14 Performance Measurements Latency Limits the ultimate responsiveness of a system Defined as elapsed time between invocation of the updateattributevalues in one Federate, and the corresponding invocation of the reflectattributevalues method in the second Federate Throughput Defined as the number of transactions per second that can be processed by a system on a sustained basis Wolfson 14

15 Latency Performance Reliable Transport Service in -s RD RD Snd Rcv 3 Sun Ultra 1/140 s and 1 SGI Onyx, using 10Mbps Ethernet Time: Snd updates, Rcv reflects, Rcv updates, Snd reflects; divide result by 2 Latency (msec) hop la te ncy (ms e c) 2 hop la te ncy (ms e c) Me s s a g e s iz e (b yte s ) Dominated by Ethernet bit rate Wolfson 15

16 Latency Performance with Receiver Fan Out Reliable Transport Service in -s RD Rcv Snd Rcv 2 Rcv N Latency (msec) pre dicte d: 10 rcvr pre dicte d: 5 rcvr pre dicte d: 3 rcvr pre dicte d: 2 rcvr me a s ure d: 1 rcvr Predicted Latency for N th Receiver: L R N = L R 1 / 2 + ( N * L R 1 / 2 ) Me s s a g e s iz e ( b yte s ) Wolfson 16

17 Throughput Performance Reliable Transport Service in -s RD Snd Rcv 3 Sun Ultra 1/140 s, using 10Mbps Ethernet messages per second Ethernet-limited operating region Snd updates, Rcv reflects Rates are sustained, with no packet loss m e s s a g e s i z e ( b yte s ) Wolfson 17

18 Future Work Continue evaluation of Reliable multicast performance in the context of STOW Deliver rti-s/c to STOW, 24 March 97 Merge rti-s with 1.0 to create 1.1 Re-visit evaluation of available reliable multicast protocols Wolfson 18

19 Summary Reliable Message Transport Service in -s emulates reliable multicast protocol Based on TCP point-to-point connections Reliable Distributors service clients and interconnect with other RDs Provides adequate performance for STOW Discovery Service provides mechanism for Service providers to find each other, and for clients to find servers Provides connection information Allows monitoring of providers status Wolfson 19