1.5b - cliff white
TRANSCRIPT
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Challenges for SatelliteCommunications in the Tactical
Environment
Session 1.5b
10 November 2009
Major Clifford White
Directorate of Network Enabled Warfare (DNEW-A)[email protected]
Ph: +61 2 62667039
mailto:[email protected]:[email protected] -
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THIS PRESENTATION IS
UNCLASSIFIED!! Disclaimer !!
The information content covered in this presentation doesnot reflect Army requirements in any way.
The information is a tutorial only providing a theoreticaloverview and the issues Army are likely to face in adopting
these technologies.
The information presented in this brief is available in thePublic Domain
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Tutorial Aim
Wideband SATCOM on the Move (SOTM) in the LandDomain
Fundamental design considerations for SOTM systems Basic theory of operation, constraints, system design
considerations in the Land tactical environment.
SOTM Terminals and how they differ from fixed terminals
SOTM frequency selection
SOTM architectures
Modems / Waveforms
Baseband Network Architecture and issue
IP Over Satellite Communications
Cover Issues that the Military face using IPv4 over tactical satellitecommunication systems
Basic overview of IPv4 and the protocol limitations over satellite.
Real Life Design examples of Military SOTM System
Assumption is that Audience has a fundamentalunderstanding of SATCOM and IP principles.
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Wideband SATCOM on the Move
Design Processand Engineering
Considerations
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SATCOM Fundamentals
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Common SATCOM Terminology
Bandwidth (MHz) vs Information Rate (Mbps)
Symbol Rate (sps)
Forward Error Correction (FEC) coding
Direct Sequence Spread Spectrum (DSSS)
Rolloff Factor ()
FDMA / TDMA
Eb/No and Es/No G/T
Bit Error Rate (BER)
Antenna Aperture
Block Up Converter (BUC)
High Power Amplifier (HPA) Solid State Power Amp (SSPA)
Low Noise Block (LNB)
Look Angle
Effective Isotropic Radiated Power (EIRP)
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Satellite Engineering
'the game of Tradeoffs' For a 1.5Mbps (T1) link, what is the satellite bandwidth I require if I
use a QPSK modulation, a 7/8 FEC and my modem tx/rx has a
cosine filter of 1.2. QPSK has 2 bits per symbol
My overhead from FEC is 1 bit in 8 (8/7 = 1.14)
Symbol Rate = data rate * overhead / modulation = 0.857 Msps
Bandwidth = symbol rate * = 1 MHz
To transmit with the same information rate with a FEC wouldrequire 1.3MHz.
Requires less power but more bandwidth Increasing to a high order modulation such as 8 PSK (3 bits per
symbol) with 7/8 FEC would require 0.57MHz. Less bandwidth but requires more power
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Review of Basic SATCOM Terminal
Components / Terminology
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SOTM Design Process
1. User Requirement Analysis
2. Frequency Band Selection3. Antenna Selection
4. Satellite NetworkArchitecture Design
Modem / Waveform Selection
5. Baseband NetworkArchitecture Design
6. Implementation
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Stage One : User Requirement Analysis
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Information Exchange
Requirements What is the Concept of Employment?
What are the applications and services that will drive the bandwidthrequirements?
VoIP : How many concurrent calls? CODEC?
Video : frame rate vs image quality?
Data : E-Mail, Web, SA Tools, collaboration tools? Management / Network traffic?
Security overhead for IP Encryption?
What Quality of Service (QoS) do these applications require?
Will the SOTM be used as a reach back or network extension capability?
Gateway for other systems?
Final result should be a table listing the information rates for all IERS
Half-duplex / Full-duplex information rates !!
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Environmental Considerations
Possible Deployment locations
Weather wet, dry, average rainfall Link to possible freq band selection
Urban vs open area Linked to the ability of the system to
reacquire after possible blockages
Desert, light or heavy foliage
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Platform Requirements
What variants of the Platformwill the system go into?
Real estate to mount antennaand system components?
HMI impact of using SOTM.
How does one operate a PC/VoIP phone while on the move?
Available on board power? Room for cabling?
Camouflage?
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Training
System cannot introduce an increased
training overhead? Where possible use existing trades to
maintain the system? Must be very easy to use and seamless to
the User?
Complexity should be at theHub; dumb remote terminals.
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Stage Two: SOTM Frequency Band
Selection
SOTM antenna will be small aperture
Small aperture antennas have lower gainat lower the frequencies.
Low frequencies use larger waveguides. Higher frequencies have
high cable losses.
Low frequencies havelarger beam width.
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Mobile Satellite Frequency Bands of Interest
Frequency Band (GHz)Band
LetterUsage
1.5 1.6 L L Band Inmarsat (BGAN, etc..)
7.9 8.4 (uplink)
7.25 7.75 (downlink)X Military (Wideband Global Satellite)
13.75-14.5 (UL)
10.95 12.75 (DL*)Ku Commercial (Intelsat, etc..)
29.5 30.019.7 20.2 (uplink)
Ka Commercial Ka (eg Wildblue SatelliteInternet)
30.0 31.0 (uplink)
20.2 21.2 (Downlink)Ka Military Ka (Wideband Global Satellite)
* Region Dependant
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Rain Attenuation
More significant at Ka than Ku and X band
Extremely problematic at Ka band
Rain fade margins are a big considerationin link budgets
How do small aperture antennas and low powerBUCs perform in rain?
i i
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X KaKuL
Loss for
Heavy Rain
@ 3km high
L 0 dB
X 0.3 dB
Ku 3 dB
Ka 18 dB
Rain Attenuation
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Atmospheric Attenuation
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Look Angles
Low look angles have differing attenuation
More impact at Ka thanKu and X band
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Satellite Constellation Selection
Must try and choose a Satellite in an operating region with ahigh down link saturated EIRP (Hot Bird).
Figure relates to entire transponder saturated power and is
equally shared amongst all carriers that are using it. Lets choose Alaska with a +41dBW down link contour and see
the power equivalent bandwidth that a 4MHz carrier takes.
Ku Footprint map
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SOTM Power Equivalent Bandwidth
Assuming it is a multi-carrier transponder with a bandwidth of36MHz with a 9dB Input Back Off and a -4.0dB Output Back
Off.
The downlink operating EIRP will be +41-4 = +37dBW.
Therefore for a 4MHz signal the available EIRP is +37 10
Log10(36/4) = 27.5dBW.
4MHz signal uses approximately 10dBW. Critical in Link budgets and achieving desired information rates
You can request more power at the cost of available
bandwidth on the carrier. Very important to understand the power equivalent bandwidth
of SOTM systems !!!!
Not just their actual bandwidth usage. Some SOTM systems use high order spreading and low FECS which increases
BW requirement.
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Satellite Constellation Selection
SOTM has the advantage in using
satellites that have gone inclined. Cheaper access and better availability in
regions of high demand. More expensive hub as it requires a
tracking dish.
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Military V's Defence Satellites Are commercial satellites still an option for Defence?
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Adjacent Satellite Interference
This is the biggest impact on band selection.
Ku commercial satellites are spaced 2
o
apart inNorth America and 3o in Europe.
Currently there are very few Ka satelliteshowever as more Kasatellites come online,it may become a problem. Ka does have a smaller
beam width Aperture is a major factor
on ASI.
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Stage 3 : SOTM Antenna Selection
Platform real estate is the biggest factor inAntenna solution
No one antenna will suite allplatforms Mr Dale White FTGordon Battlelab
Band selection Large difference between uplink and downlink
frequencies in Ka band
Ku band seems to bemost popular
Ka is future
Some X band terminals areemerging on the market
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Phased Array Phased Array
Partial phased array seems most popular.
Phased elements create beam, electronically
steered. Flat Profile
Lower gains and can have poor look angles
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Parabolic Antennas
Parabolic
High Profile, sometime looks like a target.
Higher gain (better throughput) and better offaxis performance.
Better Look Angles.
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Unique SOTM Antennas
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Ground Station Receive Antenna
Small gains from small SOTM aperture antennas withlow power BUCs means receive signal strengths at
ground station (Hub) receive sites are very low.
Requires large apertureantenna.
Also, due to reciprocitylarge ground earthstation can tx more power,
therefore small SOTMantennas can receive higherinformation rates than theycan transmit.
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Satellite Tracking
Servos must be quick to react to angularchanges.
Tracking rates up to 200O /s
Tracking Accelerations of 400O-600O /s2
Time to acquire satellite and maintainconnectively is a key design selection criteria fora tracking system.
Two basic type of Trackingsystems
Closed Loop
Open Loop
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Closed Loop Tracking Information on satellite location is fed back to the
antenna control unit.
Antenna control unit is the brain to track the satellite.
Usually tracks a reliable, known out of band signal onthe satellite of interest.
Uses information (e.g. Eb/No) from modem todetermine if locked onto the correct satellite.
RADAR problem - can be complex to design but can berelatively easy to implement.
Requires GPS and Flux Gate Compass to establish
position in space. If system loses track due to blockage or sharp turn,
must have unique algorithm to find satellite again. Takes time to require when satellite signal is lost due to
blockage.
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Open Loop Tracking
Antenna Control Unit has exact informationwhere it is in space.
Information is usually fed from an InertialNavigation Unit (INU) to Antenna Control Unit
Still requires GPS and Flux Gate Compass to
establish initial position in space. If system loses track due to blockage or sharp
turn, never loses location of antenna and
reacquires instantly. Can be very expensive due to cost of INU.
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Amplifier/Block Up Converters
Link budget will determine the BUC size you will need (e.g.Grid Amplifier)
BUC require high efficiency with low heat dissipation (mostSOTM antennas are sealed units).
Linear performance is very important.
How do you power it?
Reliability Vibration and harsh environments. Solid State Power Amps (SSPAs) provide better performance
and reliability than traditional Traveling Wave Tube Amplifiers
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Stage 4 : Satellite Network Architecture
A complete Defence Satellite network is likely tohave some the following attributes:
Large number of diverse satellite terminals all competing for the samebandwidth.
Differing Satellite apertures varying from large (up to 3.6m) to VSAT
terminals (down to .9m) No one dish has the same performance of another
Even those built to the same specification and from the same manufacture.
Communications is hierarchal (higher to lower) and vertical (across
equivalent Command Elements) Some terminals have a large pull requirement (receiving orders, video,
intelligence distribution) , while other terminals have a large pushrequirement (intelligence gathers, ISR)
Some terminals transmit in a bursty nature while others transmit with aconstant load.
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Satellite Architectures
Traditional Point to Point
Point to Multi Point : Hub Spoke Every terminal is one satellite hop
away from the center terminal and
two satellite hops away from eachother.
Fully Meshed
All terminals are one satellite hop away from each other.
Due to small apertures, unlikely to be achieved in a SOTM
architecture.
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Satellite Architectures (cont)
Partial Meshed
Larger aperture terminals are all one satellite hop awayfrom each other.
Small aperture (disadvantaged) terminals work in a hubspoke arrangement, nominate best terminal (most
advantageous) in network to transfer data to otherterminals (hub assist)
This is probably the most effective architecture to
supporting a SOTM network that has different aperturesatellite antennas
Whatever the choice, you must overlay it on-top of yourinformation exchange requirements.
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Satellite Waveforms
Frequency Division Multiplex Access (FDMA) Very spectrally efficient (bits/Hz)
Hogs bandwidth if not used for constant traffic Relatively easy to set up and manage
Separate channel required for receive and transmit channels
Not scalable
Good for large pipes from theater
back to Australia
Single Chanel Per Carrier
Carrier in Carrier modems uses the Same rx and tx freqs
Dynamic FDMA systems are aroundsuch as COMTECHs Vipersat
ELBIT have developedBurst Mode - FDMA
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S f
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Satellite Waveforms
Time Division Multiple Access (TDMA) Shares and divides bandwidth amongst terminal on an as needed
basis
Not very spectrally efficient (bits/Hz), however efficient inbandwidth sharing across a network.
Allocate time slot for terminal totransmit on
Used for Full and Partial Meshednetworks
Very scalable, add numerous
terminals and more satellitebandwidth as required
Complex to Manage
Systems such as ViaSATs Linkway
DVB S d DVB S2
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DVB-S and DVB-S2
Digital Video Broadcast Satellite (DVB-S) FEC and modulation standard for video broadcast
MPEG-2
Useful for transmitting large amounts of data to multipleterminals
DVB-S2 next generation of DVB-S Adaptive Code and Modulation (ACM)
High order modulations up to 32 APSK
Low roll off factor down to 1.2
Very efficient FECs (1/4 to 9/10) using concatenation ofLow Density Parity Check (LDPC) and Bose and Ray-Chaudhurin codes within 0.7 of Shannon Limit
Use multiple video sources MPEG-2, MPEG-4 or H.264
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Spread Spectrum vs Low FEC
Due to ASI in some bands (Ku) and large beamwidths of small aperture antennas, SOTM
systems must transmit low power spectraldensities. (ITU states -18dB/4kHz)
One method to achieve this is to use spread
spectrum to reduce the energy density of thesignal. 2 times, 4 times, 8 times.
Another method is to use very low FECs 1/2 FEC is equivalent to 2 x spreading. 5/16 is
equivalent to 3 x spreading.
Achieve coding gain using low FECs, no gainachieved from spreading
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Illustration of Spread Spectrum
-18db/4kHz
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Coding Gain from Low Order FECs
3 timesspreading
2 timesspreading
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Link Budget
Once you have bandwidth requirements, chosena satellite, selected antennas for SOTM system
and ground station, a rough link budget can becompleted.
Link budget determine what BUC size you will
need.
Link budget will confirm selection of components
and determine if you are bandwidth limited orpower limited on the chosen satellite.
Link Budget will assist in Modem selection
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SOTM MODEM Requirements
Must reflect your overall satellite architecture.
Must account for frequency shift due to doppler effect.
Must understand your satellite architecture and adapt toyour environment.
Adaptive Code Modulation (ACM)
adaptive power control.
adaptive frequency and/or time burst allocation
Support multiple concurrent low/high order FECs
For example: In a TDMA system, every TDMA burst
parameter is set based on thereceive and transmit terminal.
Implemented by vendors such as HughesiDirect and ViaSAT's J oint IP Modem
MPM 100 N t k C t i W f
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MPM-100 Network Centric Waveform
Source: US Army Communicator Summer2008 Edition
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Packet Loss in IP Modems
Due to high processing requirements of some IP satellitemodems, can exhibit packet loss due to CPU overloading.
Generally happens when processing lots of small packetssuch as voice.
Reduce VoIP overhead by increasing voice sample size.
Becoming less of a problemas with high processingCPUs and using FPGAs.
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Stage 5: Network Architecture
Routing Protocols
How do you maintain network convergence with blockages and
the ad-hoc nature of SOTM terminals? Baseband network must conform to layer 3 network architecture.
May require an ad-hoc routing protocol such as:
Pro-active Reactive
Flow oriented
Situational aware routing Power Aware Routing
Multicast routing
N R l Ti A li ti
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Non Real-Time Applications
TCP over Satellite TCP was designed for reliable delivery of
packets. Assumes that links over the entire
network are reliable, with very low latency. Office type networks.
TCP was never initially designed to runover a satellite.
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TCP Services Effected by Satellite
TCP provides the following services at Layer 4 of
the OSI model:
Connection Establishment
Data Transfer in correct order sequence
Reliable Transmission
Error Detection
Flow Control
Congestion Control
Maximum Segment Size
Selective Acknowledgements
Window Scaling
TCP Flow Control and Sliding
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TCP Flow Control and Sliding
Window
TCP uses a scaling window for flowcontrol to avoid the sendertransmitting too much data too
quickly. To avoid congestion, TCP slowly
ramps up transmission speed untilpackets are lost. At this point TCPassumes that congestion isachieved.
Process is controlled by a slidingwindow algorithm.
Window Size tells sender how muchdata can be sent.
Maximum Data rate is a function ofthe round trip time (RTT) andwindow size. This is known as the
Bandwidth Delay Product.
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Bandwidth Delay Product Bandwidth Delay Product = TCP Window Size / RTT
For example a 600ms delay and a 64 byte window,
the max achievable TCP transmit rate is 64*8/.6 =853 kbps
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2
0
1000
2000
3000
4000
5000
6000
Throughput v's RTT
65.54
32.7716.38
Round Trip Time (s)
MaxTransmissionRate(kbps)
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Congestion Control
TCP uses lost packets as an indicator that
it has reached congestion over thenetwork.
Sender becomes aware of packet loss thoughacks from receiver.
No acks for a specific time
Repeat acks Major issue with
high BER links.
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Packet Error Rate (PER) vs BER
Some vendors are
quoting systems bypacket error rate.
Very confusing asresults will vary basedon packet size,
modulation and FEC. Traditional BER vs
Eb/No should be applied
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What does PER it Mean?
Always ask for BER waterfalls from the MODEMVendor. Packet error rate presents a falsepicture.
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
0.0E+00
2.0E-03
4.0E-03
6.0E-03
8.0E-03
1.0E-02
1.2E-02
PER v's BER
1.0E-06
1.0E-07
1.0E-08
Packet Size (Bytes)
PER
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Application Layer Latency
Where applications, client server (Layers 4through 7) exhibit a send and wait protocol.
The most well know is Common Internet FileSystem (CIFS) or SMB (Server Message Block).
Predominant in MS Client and Server Applications(MOS, active directory) and Samba (Linux) for file andprint sharing.
CIFS has embedded security feature forauthentication, etc
Amplifies the Bandwidth Delay product if using
TCP for transport.
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Application Layer Latency
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Maintaining SOTM Services
Blockages are a sure thing in SOTM and
have the effect of inhibiting or stoppingnetwork services.
Applications using TCP sessions can breakdown due to timeouts.
VoIP call managers must be able to
maintain calls during blockages.
Must have SOPs in place to mitigate
blockages. There is software to maintain all services.
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WAN Optimisers
When selecting or testing a WAN Optimiser to improve TCP
performance over satellite it must do the following: Overcome Bandwidth Delay Product
Improve effects of Bit Error Rates on TCP congestion control
Overcome Application Layer Latency
Be Space Communication Protocol Standard Transport Protocol(CCSDS 714.0-B-1) compliant for interoperability.
Use bit level caching (nice to have)
Need ability to keep application sessions open
Needs to be on the red side of the IP encryptor. Information required by the WAN optimiser is lost after encryption
Options: CISCO WAAS, Riverbed, CITRIX WAN Scaler, Comtech
Turbo IP, Expand
Security Overheadson VoIP
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Security Overheads on VoIP
Standard G.729 Packet with 2 x 10 ms Samples
140 Bytes * 50 Packets Per Second = 56 Kbps
Modified G.729 Packet with 4 x 10 ms Samples
160 Bytes * 25 Packets Per Second = 32 Kbps
This is accomplished with approximately half the CPU utilization.
This allows for more CPU resources to be available for processing other traffic.
Call Manager allows up to 6 x 10 ms samples per packet.
S 6
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Stage 6: Implementation
Real world Examples
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Real world Examples
Source: Datapath Source: Datapath
Source: ADM/Elbit
SOTM Design Example : Remote
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g p
Combat Casualty Care on the Move
(RC3OTM)
Up to two VoIP calls
Integrated into existing US Army Medicalnetwork
Video feedback fromAmbulance to hospital
Reachback for SINCGARSnetwork using CNRoIP
Stage One: Information Exchange
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ApplicationBandwidth Requirements
(kbps)Quality of Service Needs Comments
Voice 112kbps real time highest priorityG.729 20ms sample sizewith up to 2 possible
concurrent calls
Video 328kbps
real time medium priority
for video, high priority
for voice channel
H323 x frame per second.
G.729 underlying voice
Blue Force
Tracking36 kbps non-real time, low priority
CNRoIP 56kbps real time highest priority connected to CNR withinthe cabin of the vehicle.
Thin Client 36 kbps
Total 558kbps
Stage One: Information Exchange
Requirements for RC3OTM
Network Diagram
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Network Diagram
Other Components
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Other Components
40W Wavestream BUC
Required a 200 amp alternator
Small aperture 2.4m flyaway dish Cisco WiFi phones
AES 256 encryption on all IP data
No WAN optimiser, no TCP applications FDMA modem with 5/16 FEC (Point to Point link)
Ku band operation
C4 CNRoIP
CISCO 2800 router with Call Manager Express
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Lets Look at the Result
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Lets Look at the Result