Reliable Multicast in the STOW RTI Prototype 97S-SIW-119 Harry - - PowerPoint PPT Presentation

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Reliable Multicast in the STOW RTI Prototype 97S-SIW-119 Harry - - PowerPoint PPT Presentation

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Reliable Multicast in the STOW RTI Prototype 97S-SIW-119 Harry Wolfson <HarryWolfson@LL.MIT.EDU> Steve Boswell <Boswell@LL.MIT.EDU> Daniel J. Van Hook <dvanhook@LL.MIT.EDU> Steve McGarry <smcgarry@LL.MIT.EDU> MIT Lincoln

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Wolfson 1 97S-SIW-119

Reliable Multicast in the STOW RTI Prototype

97S-SIW-119

Harry Wolfson <HarryWolfson@LL.MIT.EDU> Steve Boswell <Boswell@LL.MIT.EDU> Daniel J. Van Hook <dvanhook@LL.MIT.EDU> Steve McGarry <smcgarry@LL.MIT.EDU> MIT Lincoln Laboratory March 6, 1997

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Wolfson 2 97S-SIW-119

Outline

  • Introduction
  • Message Transport Services
  • Reliable Multicast
  • Discovery Service
  • Emulation of Reliable Multicast in RTI-s
  • Performance Measurements
  • Summary
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Wolfson 3 97S-SIW-119

Federation using the HLA / RTI

Fe de ra te RTI C o mm Fe d e ra te RTI Co mm Fe de ra te RTI Co m m Fe de ra te RTI C o mm Fe d e ra te RTI Co mm Fe de ra te RTI C o mm

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Wolfson 4 97S-SIW-119

RTI-s Sponsors

  • Defense Modeling and Simulation Office (DMSO)

– Part of larger DoD 1.0 RTI 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

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Wolfson 5 97S-SIW-119

RTI-s Development

  • STOW Requirements (RTI perspective)

– ~ 25 Federate classes on 350-450 host computers – 10 – 20 sites (LANs connected via a WAN) – 10,000 objects (scaleable to 100,000)

  • MIT Lincoln Laboratory is developing the

prototype RTI-s for use by STOW

– Full RTI functionality except for Time and Ownership Management – Focus on real-time performance and very large exercise scalability » Low latency, High throughput, Low bandwidth

  • verhead

– Early availability of RTI (15 Oct 96)

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Wolfson 6 97S-SIW-119

RTI-s Block Diagram

Distribution Databas e Be st Effort Minimum Ra te S tate Consistent Reliable Consistency Mana ger Consistency P rotocol Discovery P rotocol create delete update Stream Manager Transport Ma nager Update Attr, S end Interaction Refle ct Attr, Re c Interaction {

  • id, attribute_values
  • r, class , param_values }

Subs cription P rincipa l Local S ubscription Agent S ubscribe, P ublish, Assoc Regions Remove Obj, P rovide Attr Remove Obj, Provide Attr Control Updates S ubscriptions , Publications , Resources Res ource s Reques t Streams

  • f Interest

RTI Ambassador Object Ma nager { stream, data, count} UDP TCP Rel Distrib Fe d Create, Join, etc. Create, Delete Obj RTI Initializa tion Data (FED + RID) Set Trans p Mode S trea m Mappings Communication Managers {

  • id, attribute_value s
  • r, class , param_values }

Federa tion Manager Buffe r Manager

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Wolfson 7 97S-SIW-119

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

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Wolfson 8 97S-SIW-119

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 RTI-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)

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Wolfson 9 97S-SIW-119

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

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Wolfson 10 97S-SIW-119

advert ms gs Fe d e rat e DS M RTI

Se rvice s

Fe d e rat e Advert Dis cov er Monitor Reques tor

  • C A

RD S erv ices

  • RTI

DS M

Periodic Timer s end lis ten and callb ack adv ert ms gs advert ms gs advert ms gs Fe d e rat e DS M RTI

Se rvice s

advert ms gs Fe d e rat e DS M RTI

S e rvice s

Discovery Service Manager (DSM)

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Wolfson 11 97S-SIW-119

Implementation of Reliable Multicast in RTI-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

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Wolfson 12 97S-SIW-119

Sample Network Topology for Reliable Servers / Clients

  • STOW is using fully connected mesh

– Could configure Server connections as a-cyclic tree

Fe de ra te RTI RD tcp Fe de ra te RTI tcp Fe de ra te RTI tcp LAN # 2 Fe de ra te RTI tcp RD Fe de ra te RTI tcp LAN # 1 Fe de ra te RTI RD tcp Fe d e ra te RTI tcp Fe de ra te RTI tc p LAN # 3

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Wolfson 13 97S-SIW-119

Features of RTI-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

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Wolfson 14 97S-SIW-119

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

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Wolfson 15 97S-SIW-119

Latency Performance

Reliable Transport Service in RTI-s

  • Dominated by Ethernet bit rate

5 0 1 0 0 1 5 0 2 0 0 1 0

1

10

2

1 0

3

1 0

4

1 0

5

3 hop la te ncy (mS e c) 2 hop la te ncy (mS e c) Latency (mSec) Me s s a g e s iz e (b yte s )

Snd Rcv RD RD

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

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Wolfson 16 97S-SIW-119

1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 10

1

10

2

1 0

3

1 0

4

1 0

5

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 Latency (mSec) Me s s a g e s iz e ( b yte s )

Latency Performance

with Receiver “Fan Out”

Reliable Transport Service in RTI-s

Predicted Latency for N th Receiver: L R N = L R 1 / 2 + ( N * L R 1 / 2 )

Snd RcvN RD Rcv2 Rcv1

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Wolfson 17 97S-SIW-119

Throughput Performance

Reliable Transport Service in RTI-s

1000 2000 3000 4000 1 10 100 1000 10000 10 5

messages per second m e s s a g e s iz e (byte s )

Snd Rcv RD

Ethernet-limited

  • perating region

3 Sun Ultra 1/140’s, using 10Mbps Ethernet Snd updates, Rcv reflects Rates are sustained, with no packet loss

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Wolfson 18 97S-SIW-119

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 RTI 1.0 to create RTI 1.1
  • Re-visit evaluation of available reliable

multicast protocols

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Wolfson 19 97S-SIW-119

Summary

  • Reliable Message Transport Service in

RTI-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