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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)clifford.white@defence.gov.au

Ph: +61 2 62667039

mailto:clifford.white@defence.gov.aumailto:clifford.white@defence.gov.au

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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

http://popimage%28%27img_78%27%2C%27http/images.books24x7.com/bookimages/id_3517/fig135_02_0.jpg','687','1000')

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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

http://www.raysat.com/?CategoryID=197

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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

http://www.raysat.com/?CategoryID=211

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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