Transcript Taking the Politics out of Satellite and Space- Based Communications Protocols

Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
Taking the Politics out of Satellite and SpaceBased Communications Protocols
Will Ivancic
[email protected]
216-433-3494
roland.grc.nasa.gov/~ivancic
IEEE Globecom, September 2005
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Presentation Outline
Glenn Research Center
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Communications Technology Division
Space Exploration Program
I’m so special! …….. Really?
Why so much misinformation?
Vocabulary
Technology Evolution
COTS, CCSDS and the Internet
Gateways and Proxies
Operational Environments
Summary
IEEE Globecom, September 2005
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Satellite Networks & Architectures Branch
Space Communication Architecture
Supporting Exploration and Science
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
• Components
–
–
–
–
Earth
Moon
Mars
Deep Space
Communication protocols must
match the needs of the emerging
Exploration Program as it matures
• Key Technologies
– Interplanetary laser communications
– New standard protocols
– Advanced low-power avionics
IEEE Globecom, September 2005
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Projected Growth in DSN Downlink Requirements
Glenn Research Center
IEEE Globecom, September 2005
Communications Technology Division
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Satellite Networks & Architectures Branch
Evolving the Lunar Architecture
(One of many early concepts)
Glenn Research Center
Communications Technology Division
An initial architecture recommendation is
made based on an assumed human base
at the South Pole
The
2 relays
are moved to a circular orbit
2 relay
satellites
to
support
South
and North
One
inclined
elliptical
orbit Pole missions
1
satellite
added
to
Advantage:
longis
dwell
times
over the
A relay
second
plane
of
relays
is the
added
to
constellation

3
total
South
Pole
increase coverage at the South and North
One
circular
polar orbit
Poles,
and provide
global coverage
Advantage:
equalare
coverage
of 6both
poles,
3 relay
satellites
added

total
The
orbital
planes
are
inclined
to
support
simpleminimized
number of relays
Two polar
circular
orbits
global,
far-side,
and
equatorial missions
Advantage:
increased coverage at the
Final
Configuration:
poles,
coverage achieved
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relayglobal
satellites
Two inclined circular orbits
Advantage: global coverage, coverage is
distributed more evenly than for polar
orbits  better support to exploration at
lower latitudes
IEEE Globecom, September 2005
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Satellite Networks & Architectures Branch
Example Service and Data Rate Scenario for
Lunar Communication (Work in progress)
Communications Technology Division
Glenn Research Center
User
Satellite Networks & Architectures Branch
Channel Content
Latency
# of Channels
Channel Rate
Total Rate
Speech
NRT
2
10 kbps
20 kbps
Engineering
NRT
1
100 kbps
100 kbps
Speech
NRT
4
10 kbps
40 kbps
Helmet camera
NRT
4
100 kbps
400 kbps
Engineering
NRT
4
20 kbps
80 kbps
Video
NRT
2
1.5 Mbps
3 Mbps
Engineering
NRT
2
20 kbps
40 kbps
Video
NRT
8
1.5 Mbps
12 Mbps
Engineering
NRT
8
20 kbps
160 kbps
Quick Look
NRT
4
1 Mbps
4 Mbps
Engineering
NRT
4
20 kbps
80 kbps
Base
HDTV
1 day
1
20 Mbps
20 Mbps
Human
Transports
HDTV (PIO)
NRT
2
20 Mbps
40 Mbps
Hyperspectral Imaging
1 day
1
150 Mbps
150 Mbps
Surface Radar
1 day
1
100 Mbps
100 Mbps
Hyperspectral Imaging
1 day
1
150 Mbps
150 Mbps
Orbiting Radar
1 day
2
100 Mbps
200 Mbps
Hyperspectral Imaging
1 day
2
150 Mbps
300 Mbps
Base
Astronauts
Operational
Human
Transports
Robotic Rovers
Science Orbiters
High Rate
Robotic Rovers
Science Orbiters
Total
IEEE Globecom, September 2005
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980 Mbps
My situation is unique! ….. Really?
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Volume, mass and power are at a premium in space
– mobile and ad-hoc communication
• Intermittent connectivity is a common for planetary
relays
– Common for many military operations.
• Delay and latency have to be considered for spacebased protocols
– Low-bandwidth, highly-processed, links may be in the order of seconds
– Email and text messaging and are not terribly concerned about the
delay so long as the message gets through eventually.
• Reliability and redundancy are of major concern
– Aeronautical, military and commercial networks
• Space hardware must withstand radiation effects
– Present in military and high-altitude applications.
IEEE Globecom, September 2005
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Why so Much Misinformation?
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
Much of this has been perpetuated by
political turf battles and funding
battles to the detriment of sound
technical analysis
IEEE Globecom, September 2005
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TCP over Noisy Links with Long Delays
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• TCP slow start takes a long time to reach equilibrium
– log2 (bandwidth × delay) round-trip times (RTTs)
• poor performance over long fat networks
• particularly for short flows
– on retransmission timeout, TCP enters slow start again
• poor performance over lossy high capacity links
• TCP infers congestion on all packet drops
– even if the loss is due to packet corruption due to noise TCP
congestion avoidance throttles source unnecessarily
• TCP sends a burst of packets when window opens
– this can cause congestion drops in intermediate routers
IEEE Globecom, September 2005
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An Example of TCP Steady State Performance
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
Does this infer that all
Internet Protocols are
not suitable for
Interplanetary
operations?
Chart is from “Why not use the Standard Internet Suite for the Interplanetary Internet?”
By Robert C. Durst, Patrick D. Feighery, Keith L. Scott
IEEE Globecom, September 2005
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Theoretical Steady State Throughput
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
TCP Performance equitation is from Mathis, M. et al, "The Macroscopic Behavior of the Congestion Avoidance
Algorithm",Computer Communications Review, volume 27, number 3, July 1997.
Delay Tolerant
Increasing Delay
IEEE Globecom, September 2005
Don’t Use TCP for long delays.
However, one can still use IP
and a rate-base protocol.
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Vocabulary
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
Circuit
The complete path between two terminals over which oneway or two-way communications may be provided.
Channel
A single path provided by a transmission medium via
either (a) physical separation, such as by multipair cable or
(b) electrical separation, such as by frequency- or timedivision multiplexing..
Link
A conceptual circuit, i.e., logical circuit, between two users
of a network that enables the users to communicate, even
when different physical paths are used.
At any level you are circuit-switched, you can always subvert
that by being packetized at the next level up. Thus, you have
virtual circuits running across packets running over circuits
IEEE Globecom, September 2005
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Technology Evolution
Glenn Research Center
Communications Technology Division
Multiplexer
IEEE Globecom, September 2005
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Satellite Networks & Architectures Branch
Modulator
Technology Evolution
Glenn Research Center
IEEE Globecom, September 2005
Communications Technology Division
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Satellite Networks & Architectures Branch
Ubiquitous Network Society
Source: IPv6 Promotion Council of Japan
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
– The society to be realized in 2010
• Anybody can / anytime / anywhere
• without being aware of the network
• benefits from the use of the terminals and networks
RFID
Space Communications
technology
Seamless Network
Authentication
RFID Tag
Mobile Network
• 4G Systems
• High-speed WLAN
Robot
Digital Information
Appliances
Home Networks
Sensor Network
IEEE Globecom, September 2005
Next Generation
Core Network
Security
Quantum Communications technology
Ad-hoc Network
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This document is based on the material of MIC
Lunar Access Surface Module
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Initial operating capability 2015, but no later than 2020
• Technology freeze 6 years before first use for subsystems,
9 years before first use for systems of systems technologies
• Communications Requirements
– Provide the crew interface to monitor & command onboard
systems and trajectory for TBD nominal and contingency
operations.
– Provide voice, video and data communications with Earth
(Daily ops and planning, science, PMC, PFC, PAO events, vehicle
systems status and navigational state telemetry, etc.)
IEEE Globecom, September 2005
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Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
COTS, CCSDS and the Internet
IEEE Globecom, September 2005
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COTS Satellite Modem Operation
Communications Technology Division
Glenn Research Center
COTS
Router
Satellite Networks & Architectures Branch
Radio
Commercial
Satellite
Modem
IF
Baseband
Framing
IEEE Globecom, September 2005
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UP/Down
Converter
RF
Common CCSDS Operation
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
Radio
Bit
Synchronizer
Front
End
Processor
IEEE Globecom, September 2005
Modem
IF
Baseband
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UP/Down
Converter
RF
CCSDS relationship with the OSI Layers
Glenn Research Center
IEEE Globecom, September 2005
Communications Technology Division
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Satellite Networks & Architectures Branch
IP 4/6
NIC
NIC
Modem
CCSDS and HDLC Ground Support Comparison
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
Very similar except the HDLC commercial world separates FEC and framing at a
bitstream level interface
Commercial Router/
Frame Relay Switch
CCSDS
NP or IP
NP or IP
Packet Insert
VCDU Framing
FEC Encode
Packet Extract
VCDU Framing
FEC Decode
Randomize
Derandomize
Conv. Encode
Conv. Decode
Net PDU
IP
IP
Frame
HDLC Framing
HDLC Framing
FEC Encode
FEC Decode
Randomize
Derandomize
Conv. Encode
Conv. Decode
101010
(bits)
Bit sync
Bit sync
Modulator
Demod
Modulator
Demod
Transmitter
Receiver
Transmitter
Receiver
Upconvert
Downconvert
Upconvert
Downconvert
Antenna
Using standard internet protocols and applications in space - Hogie
IEEE Globecom, September 2005
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Gateways
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Provide a translation interface between two different protocols
at the same layer of the protocol stack.
• Require maintenance when protocols change – and they do
change!
• Unintentionally break some protocols as you move data between
one protocol with one set of assumptions and semantics and
another, different, protocol with different assumptions and
semantics.
– An inconvenience on the ground compared with getting two different
systems to interoperate
– In space-based systems, gateway maintenance is much more difficult.
• Custom gateways are relatively expensive, as they must
completely implement and support more than one protocol at a
layer.
• Gateways are a tool that is best avoided if possible. However,
sometimes a gateway is a necessary evil.
– e.g. Interplanetary Internet
IEEE Globecom, September 2005
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Network
Cloud
COTS
Interface
NIC
Gateway or
Encapsulation
Space
Ground
Performances Enhancing Proxies
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
• Used to optimize for control loops
• Generally need to see into protocols
– Network layer encryption renders most gateways
useless
PEPs
Internet
Internet
Control Loop 1
Control Loop 2
End-to-End Control Loop
IEEE Globecom, September 2005
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Control Loop 3
Performances Enhancing Proxies
Glenn Research Center
•
•
•
•
•
•
•
Communications Technology Division
Satellite Networks & Architectures Branch
IETF RFC2488, "Enhancing TCP Over Satellite
Channels using Standard Mechanisms"
IETF RFC2760, "Ongoing TCP Research Related to
Satellites”
IETF RFC 3819, “Advice for Internet Subnetwork
Designers”
IETF RFC 3150, “End-to-end Performance Implications
of Slow Links”
IETF RFC 3155, “End-to-end Performance Implications
of Links with Errors”
IETF RFC 3366, “Advice to link designers on link
Automatic Repeat reQuest (ARQ)”
IETF RFC 3449, “TCP Performance Implications of
Network Path Asymmetry” – give URLs. Non-IETF
people won’t know where to find these.
IEEE Globecom, September 2005
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Operational Environments
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
– Surface
• Low Delay, Symmetric, 1/R2 where radius is small (power vs
bandwidth)
• Closely matches characteristics of today’s Internet
– Near Planetary
• Moderate Delay, Asymmetric, 1/R2 where radius is becoming a factor
(power vs bandwidth)
• Intermittent connectivity
– Interplanetary
• Extremely large delay, Highly asymmetric, 1/R2 where radius extremely
large (power vs bandwidth)
• Intermittent connectivity
• Feedback is an issue
• Ongoing research in IRTF Delay Tolerant Networks and previously in
IRTF Interplanetary Internet working groups
IEEE Globecom, September 2005
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Top Level Solar System
Space Communication Architecture
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
~6.5 - 40
Minutes
~4 Minutes
Hours
IEEE Globecom, September 2005
If the Moon is a test bed for Mars, should
we be developing and testing protocols for
the Moon or Mars?
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Spiral 2 – Lunar Surface Exploration Network
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
Lunar
SBN Relay
Earth
Rover
Human
on EVA
(1)
(4-6)
Surface
Terminal
Repeater
Lander
Teleoperated
Robot
Autonomous
Robot
Legend
(1)
Human
on EVA
Very high rate backbone network to Earth
(4-6)
High rate orbiter access network
Low power, medium rate surface-to-surface network
(Multiple)
Low rate, long range links
IEEE Globecom, September 2005
Science
Instrument
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Interplanetary Communications
Glenn Research Center
Communications Technology Division
Key Issues
• New Protocols
– Bundled/Messaging
Store and Forward
Protocols
• Interplanetary time
synchronization
• Scheduling Assets
– When to turn on and
off
IEEE Globecom, September 2005
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Satellite Networks & Architectures Branch
Summary
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Vocabulary is very important when speaking of networking. Be
precise.
• Packet-based switching is generally simpler to configure, more flexible
and often provides better bandwidth utilization than circuit-base
switching.
• The operating environment heavily dictates what protocols can be used
– particularly delay, bandwidth, and intermittent connectivity.
• Many protocols in the TCP/IP protocol suite operate well in space.
Others, such as TCP or routing protocols are applicable only to surface
and some near-planetary applications.
• CCSDS protocols have evolved over time as technology and
processing power has improved. Originally designed to optimize
power and processing on point-to-point links, CCSDS has begun
incorporating networking capabilities with the advent of SCPS.
• Neither IPv4 nor IPv6 interoperate with SCPS-NP. A gateway is
necessary.
IEEE Globecom, September 2005
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Summary
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Current CCSDS data-link protocols are incompatible with COTS datalink protocols, requiring a data-link gateway for interoperability.
• Many CCSDS protocols – particularly legacy systems – merge layers
and thus require application level gateways to operate with COTS
protocols such as general Internet protocols. Such merging of layers
results in one-off implementation and makes interoperation difficult.
• Great care should be taken when deploying PEPs. Understand their
limitations.
• Gateways, including PEPs, must be maintained as protocols change.
This can be an expensive proposition.
• Security is difficult anywhere. Sophisticated key management systems
are not practical for space-based networks. Thus space-based security
architectures should be as simple as policy will allow.
IEEE Globecom, September 2005
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Conclusion
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
Some should not be used.
Protocols are tools for
communication
Some work OK
Some are designed for
the job at hand
One size does not
fit all.
IEEE Globecom, September 2005
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