Title: COMPARATIVE SIMULATIVE ANALYSIS OF WDM LANS FOR AVIONICS PLATFORMS
1COMPARATIVE SIMULATIVE ANALYSIS OF WDM LANS FOR
AVIONICS PLATFORMS
- Casey B. Reardon, John D. Profumo,
- and Alan D. George
- HCS Research Laboratory
- University of Florida
2Outline
- 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
3Introduction
- 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
4Modeling 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
5Proposed 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
6Ring-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
7Optical 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
8Optic-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
9OSMOSIS 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
10Experimental 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
11Simulation 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
12Results - Summaries
Table 1 Summary of Overall Packet Latency (us)
Table 2 Average Worst-case Packet Latency (us)
13Analysis 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)
14Analysis 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)
15Analysis 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
16Conclusions
- 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
17Future 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)
18References
- 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.