COMPARATIVE SIMULATIVE ANALYSIS OF WDM LANS FOR AVIONICS PLATFORMS

1
COMPARATIVE SIMULATIVE ANALYSIS OF WDM LANS FOR
AVIONICS PLATFORMS

• Casey B. Reardon, John D. Profumo,
• and Alan D. George
• HCS Research Laboratory
• University of Florida

2
Outline

• Introduction
• Modeling Overview
• Proposed Network Architectures
• Ring-Ring
• Optical Trees
• Switched Hybrid
• Optically Switched Clos
• Experimental Setups
• Platform Configurations
• Simulation Parameters
• Results
• Latency Statistics
• Analysis of Results
• Conclusions

3
Introduction

• Optical network technology for avionics is
  rapidly maturing
• Increased reliability, performance,
  cost-effectiveness of optical components
• Emergence of optical switch technology offers
  further augments to performance, flexibility and
  scalability to WDM networks
• Desire for unified backbone local-area network
  (LAN) on avionics platforms
• Provide universal network for all avionics
  devices to simplify design, wiring, and increase
  scalability
• Introduces a challenge to provide packet-switched
  LAN performance using connection-based components
• WDM an attractive option for next-generation
  avionics network
• Huge bandwidth capacities, better weight
  characteristics, protocol transparency, etc.
• First phase of on-going research project to
  design and evaluate WDM avionics architecture
  designs via virtual prototyping

4
Modeling Overview

• MLDesigner selected as simulation modeling tool
• Discrete-event simulation environment, developed
  by MLDesign Technologies Inc.
• Advantages offered by MLD
• Models are fully extendible and user-definable
• Inherent hierarchical design facilitates modeling
  at multiple levels
• LION Library for Integrated Optical Networking
  1
• Bridge gap between optic-centric and
  network-centric modeling and simulation analysis
  tools

• LION currently contains 39 optical component
  modules
• Components include couplers, splitters, lasers,
  receivers, etc.
• Parameters model key timing and physical
  component effects
• Low-level components used to realize any number
  of higher-level modules

Example Optical Receiver Model in LION
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Proposed Architectures and Requirements

• Requirements of the WDM avionics LAN
• Support up to 256 nodes
• High-speed, deterministic communication between
  any two nodes
• Easy implementation on contemporary platforms
  with fewer nodes
• Detection and recovery from one or two faults,
  graceful degradation after three faults
• To design and identify an ideal WDM avionics LAN
  architecture to meet above requirements, numerous
  disparate approaches need to be evaluated
• Candidate designs represent examples of optical
  network architectures developed for alternate
  networking applications
• Six candidate architectures proposed, modeled,
  and evaluated in this study
• Ring-ring
• Optical tree
• Both with TDMA and RSVP control protocols
• OSMOSIS-based Optical Clos
• Matisse-based Hybrid

6
Ring-Ring Architecture

• Based off proposed ROBUS architecture design 2
• Nodes connected among several local rings
• Up to 16 nodes per ring
• Local rings connected by a central master ring
• Dual-fiber rings allow operation in presence of
  fiber cut(s)
• Ring-leader node provides inter-face between
  local master ring
• Two control protocols used with this topology
• Each destination on local rings assigned one
  wavelength for both protocols
• Wavelengths re-used among rings
• TDMA protocol, static timeslots assigned to each
  transmitter
• RSVP protocol, control wavelength used to
  schedule transmissions, ring-leader grants
  requests
• Inter-ring traffic buffered at ring-leader of
  destination for both protocols

Ring-Ring Architecture Diagram
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Optical Tree Network

• Nodes connected to one of several local trees 3
• Up to 16 nodes per tree
• Local trees connected by a central coupler
• Dual-fiber rings allow operation in presence of
  fiber cuts
• Tree-leader node provides interface between local
  trees
• Two control protocols used with this topology
• Each destination on local trees assigned one
  wavelength
• Wavelengths re-used among trees
• TDMA protocol, static timeslots assigned to each
  transmitter
• RSVP protocol, control wavelength used to
  schedule transmissions, tree-leader grants
  requests
• Inter-tree traffic buffered at tree-leader of
  destination for both protocols

Optical Tree Architecture Diagram
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Optic-Electro Switched Hybrid

• Example of a optical-electrical hybrid network
• Network consists of COTS Ethernet switches,
  inter-connected with a WDM ring
• 32-port Ethernet switches, all w/ electronic GigE
  links
• Optical receiver arrays allow for a dedicated
  wavelength between each pair of switches
• Central memory switching models, w/ QoS disabled
• Nodes interface with avionicsEthernet NICs
• Use of Ethernet componentsmakes network
  cost-efficient
• Network design based largelyoff commercial
  solutions, e.g. Matisse Networks 5

Hybrid Architecture Diagram
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OSMOSIS Clos Network

• Optical-switch Clos network using OSMOSIS-based
  modules 4
• Each connection includes both an optical and
  electronic link
• Optical path used for data transmission
• Electronic path used to request and reserve
  optical paths
• Transmission requests are made to the switch
  arbiter, which services requests in round-robin
  format
• Data transmissions broken up into timeslots
• Senders are granted a number of timeslots for
  data transmission by the arbiter
• Broadcast-and-select optical switching, allows
  each output to select any input optical signal
• 100 ns of each timeslot reserved to perform
  optical switching w/ SOAs
• Network connected in Clos topology 7
• Nodes connected to one of eight 32-node
  perimeter switches
• Each perimeter switch connected to three
  backbone switches
• Inter-switch traffic buffered at intermediate
  switches

Optical Clos Architecture Diagram
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Experimental Configurations

• Federated Commercial Platform
• Based off avionics network traffic data provided
  by Rockwell Collins Inc.
• Processing and communication distributed among
  subsystems
• Commercial Platform Layout
• 86 Nodes, in 8 subsystems
• 300 Mbps baseline traffic

Commercial Configuration Diagram

• Centralized Military Platform
• Based off of the F-22 Raptor platform 6
• Most processing, inter-system traffic flows
  through Core Processing (CP)
• Military Platform Layout
• 97 Nodes, in 7 subsystems
• 200 Mbps baseline traffic

Military Configuration Diagram
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Simulation Parameters

• Four simulative experiments run for each system
• Commercial and military configurations
• Baseline and 10x traffic rates
• Global simulation constants
• All optical transmitters and receivers operate at
  2.5 Gbps, per wavelength
• Results accumulated for 1 second of network
  traffic
• 1 µs tuning delay in tunable lasers and receivers
• Message sizes uniformly distributed between 100
  and 2,500 bytes
• Architecture-specific simulation parameters
• 1 Gbps electronic link speed used with Clos and
  Hybrid architectures
• 500 ns OSMOSIS switch timeslot used in the Clos
  architecture
• Timeslot periods in both TDMA architectures were
  500 µs for local traffic and 600 µs for traffic
  between rings or trees
• Reported Results
• Average packet latency for entire system
• Average worst-case packet latency the average of
  the 10 highest packet latencies in the system

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Results - Summaries
Table 1 Summary of Overall Packet Latency (us)
Table 2 Average Worst-case Packet Latency (us)
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Analysis of Results

• Clos network exhibits the highest performance in
  all four experiments
• Average latency twice as fast as the next best
  network, due to high bandwidth in switches and
  fast parallel scheduling techniques
• Average latencies constant in the 20-25 us range
  in all cases, showing excellent scalability
  capabilities
• Easy to support additional nodes by adding
  switches to perimeter

• High-performance of Clos network comes at a price
• Clos networks are highly connected, leading to
  complex wiring demands
• Optical switch components are unproven for use in
  avionics
• Fault-tolerance requires redundant switches at
  each perimeter location

Average Latency (Baseline Military)
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Analysis of Results

• Hybrid network exhibited second-best performance
  throughout experiments
• Latencies twice as slow as Clos, but orders of
  magnitude faster than ring and tree networks
• Electronic switching does not waste bandwidth,
  and allows flexibility for network to handle
  traffic bursts
• Low-cost of deployment another key advantage for
  architecture

• Performance dropped as traffic scaled, especially
  on military platform
• Limited switch bandwidth compared to optical
  switches
• High contention levels created on core
  processings switch
• Use of smaller switch modules and AFDX techniques
  could relieve strain on individual switches, add
  deterministic behavior

Average Latency (Baseline Commercial)
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Analysis of Results

• Little variation observed between ring-ring and
  tree architectures
• Fault-tolerance of rings outweighs minimal
  performance gains of trees resulting from their
  fixed-length lightpaths
• Both RSVP architectures fared far better than
  TDMA architectures
• Observed average latencies of 140 and 230 µs in
  baseline experiments
• RSVP suffers in scenarios with several sources
  sending to one destination
• The slow method of optical arbitration causes
  significant delays when multiple bursts need to
  be sent to the same node
• A faster, parallel arbitration method would
  greatly increase the performance potential of the
  RSVP architectures
• Average and worst-case latencies saw large
  increases in 10x experiments
• Poor scalability of RSVP causes increases need
  for faster arbitration
• Available bandwidth for data transmission is not
  currently the major bottleneck
• Additional mechanisms necessary to increase
  determinism of RSVP protocol, as evidenced by
  observed worst-case latencies
• TDMA offered the slowest performance of all
  architectures
• Latency increased super-linearly as traffic rates
  scaled
• Worst-case latencies exceeded 1 second in 10x
  experiments
• TDMA not equipped to efficiently handle traffic
  bursts
• As the node count increases, the fraction of
  bandwidth available to each node decreases
• Alternate TDMA techniques likely would not
  improve performance by multiple orders of
  magnitude, thus pure TDMA does not appear to be a
  viable control protocol to serve an avionics LAN
  with a large number of nodes

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Conclusions

• Much insight gained from evaluation of several
  WDM architectures for avionics platforms
• Purely passive approaches do not offer optimal
  performance
• Dynamically establishing lightpaths on shared
  optical mediums with purely optical networks led
  to inefficient and disappointing performances
• Highly intelligent and efficient control
  protocols required for passive buses, rings or
  trees to serve a large number of nodes
  effectively
• Switched networks with buffering and fast
  scheduling capabilities exhibit superior
  performance
• Such networks have also proven effective for
  networks of varying scales
• Key tradeoffs between performance, reliability
  and ease of implementation need to be considered
• While optically switched networks may offer
  highest performance, reliability and wiring
  complexity need to be addressed
• Clos leads to complex wiring demands, and
  numerous redundant switches required to prevent
  single-point of failures
• Ring-based architectures provide inherent
  fault-tolerance
• An approach combining the benefits of electrical
  and optical technologies may lead to ideal
  avionics network solution
• Leverage the strengths of both optical and
  electronic technologies

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Future Work and Acknowledgements

• Future Work
• Study and evaluation of additional WDM
  architecture designs
• Consideration of alternate optical switching
  architectures, higher number of control protocol
  combinations
• Sensitivity analyses of variable parameters
  within each architecture
• e.g. timeslot periods, non-static timeslot
  allocations, varying switch port counts,
  available wavelengths, non-fixed wavelength
  allocations, etc.
• Investigate mechanisms for providing
  connection-oriented services
• e.g. pre-allocation of resources for periodic
  transmissions
• Consideration of multicast traffic in simulative
  experiments
• Incorporate legacy network protocols into
  experimental configurations
• e.g. MIL-STD-1553, AFDX, ARINC 429, etc.
• All investigated candidates and options to
  support SAEs avionics WDM LAN standard
  development
• Acknowledgement
• This work was made possible by Navy STTR WDM
  Fiber-Optic Network Architecture Analysis,
  Modeling, Optimization, and Demonstration for
  Aerospace Platforms (c/o NAVAIR)

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References

• 1 C. Reardon, I. Troxel and A. George, "Virtual
  Prototyping of WDM Avionics Networks," Proc. of
  Avionics Fiber-Optics and Photonics (AVFOP)
  Conference, MIT Lincoln Lab, Minneapolis, MN,
  Sep. 20-22, 2005.
• 2 Gardner, R., et al., High-Performance
  Photonic Avionics Networking Using WDM, MILCOM
  1999, Volume 2, 31 Oct.- 3 Nov. 1999, pp.
  958-962.
• 3 Gerla, M., Kova, M., and Bannister, J.,
  Optical Tree Topologies Access Control and
  Wavelength Assignment, Computer Networks and
  ISDN Systems Journal, Vol. 26, No. 6-8, pp.
  965-983, 1994.
• 4 Hemenway, R., and Grzybowski, R.,
  Optical-Packet-Switched Interconnect for
  Supercomputer Applications, Journal of Optical
  Networking, Vol. 3, No. 12, pp. 900, Dec. 2004.
• 5 Matisse Networks, www.matissenetworks.com.
• 6 Spitzer, Carl, The Avionics Handbook, CRC
  Press LLC, Boca Raton, Florida, 2001.
• 7 Clos, Charles, A Study of Non-Blocking
  Switching Networks, Bell System Technical
  Journal, March 1953, pp.406-424.