Taking the Politics out of Satellite and SpaceBased Communications Protocols

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

• Will Ivancic
• wivancic_at_grc.nasa.gov
• 216-433-3494
• roland.grc.nasa.gov/ivancic

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Presentation Outline

• Space Exploration Program
• Im so special! .. Really?
• Why so much misinformation?
• Vocabulary
• Technology Evolution
• COTS, CCSDS and the Internet
• Gateways and Proxies
• Operational Environments
• Summary

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Space Communication ArchitectureSupporting
Exploration and Science

• Components
• Earth
• Moon
• Mars
• Deep Space
• Key Technologies
• Interplanetary laser communications
• New standard protocols
• Advanced low-power avionics

Communication protocols must match the needs of
the emerging Exploration Program as it matures
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Projected Growth in DSN Downlink Requirements
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Evolving the Lunar Architecture(One of many
early concepts)
An initial architecture recommendation is made
based on an assumed human base at the South Pole
2 relay satellitesOne inclined elliptical
orbitAdvantage long dwell times over the South
Pole
The 2 relays are moved to a circular orbit to
support South and North Pole missions1 relay
satellite is added to the constellation ? 3
totalOne circular polar orbitAdvantage equal
coverage of both poles, simple- minimized number
of relays
A second plane of relays is added to increase
coverage at the South and North Poles, and
provide global coverage3 relay satellites are
added ? 6 totalTwo polar circular
orbitsAdvantage increased coverage at the
poles, global coverage achieved
The orbital planes are inclined to support
global, far-side, and equatorial missionsFinal
Configuration6 relay satellitesTwo inclined
circular orbitsAdvantage global coverage,
coverage is distributed more evenly than for
polar orbits ? better support to exploration at
lower latitudes
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Example Service and Data Rate Scenario for Lunar
Communication (Work in progress)
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My situation is unique! .. Really?

• 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
  space-based 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.

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Why so Much Misinformation?
Much of this has been perpetuated by political
turf battles and funding battles to the detriment
of sound technical analysis

POLITCS
The Preverbial Rice Bowl
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TCP over Noisy Links with Long Delays

• 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

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An Example of TCP Steady State Performance
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
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Theoretical Steady State Throughput
TCP Performance equitation is from Mathis, M. et
al, "The Macroscopic Behavior of the Congestion
AvoidanceAlgorithm",Computer Communications
Review, volume 27, number 3, July 1997.
Delay Tolerant
Increasing Delay
Dont Use TCP for long delays. However, one can
still use IP and a rate-base protocol.
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Vocabulary

• Circuit
• The complete path between two terminals over
  which one-way 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 time-division
  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
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Technology Evolution
Yesterday
Multiplexer
Modulator
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Technology Evolution
Today
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Ubiquitous Network Society
Source IPv6 Promotion Council of Japan

• 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

Tomorrow
RFID
Space Communications technology
Seamless Network Authentication
RFID Tag

• Mobile Network
• 4G Systems
• High-speed WLAN

Robot
Next Generation Core Network
Digital Information Appliances
Security
Quantum Communications technology
Home Networks
Sensor Network
Ad-hoc Network
This document is based on the material of MIC
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Lunar Access Surface Module

• 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.)

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COTS, CCSDS and the Internet
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COTS Satellite Modem Operation
RF Framing (Media Access)
COTS Router
Radio
Commercial Satellite Modem
UP/Down Converter
RF
IF
Baseband Framing
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Common CCSDS Operation
Radio
Bit Synchronizer
UP/Down Converter
Modem
RF
IF
Front End Processor
Baseband
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CCSDS relationship with the OSI Layers
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(No Transcript)
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CCSDS and HDLC Ground Support Comparison

• Very similar except the HDLC commercial world
  separates FEC and framing at a bitstream level
  interface

Commercial Router/ Frame Relay Switch
CCSDS
IP
IP
Net PDU
HDLC Framing
HDLC Framing
Frame
FEC Decode
FEC Encode
101010 (bits)
Derandomize
Randomize
Derandomize
Randomize
Conv. Decode
Conv. Encode
Conv. Decode
Conv. Encode
Bit sync
Bit sync
Demod
Modulator
Demod
Modulator
Receiver
Transmitter
Receiver
Transmitter
Downconvert
Upconvert
Downconvert
Upconvert
Antenna
Using standard internet protocols and
applications in space - Hogie
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Gateways

• 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

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COTS Interface
NIC
Gateway or Encapsulation
Space
Ground
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Performances Enhancing Proxies

• Used to optimize for control loops
• Generally need to see into protocols
• Network layer encryption renders most gateways
  useless

Control Loop 2
Control Loop 1
Control Loop 3
End-to-End Control Loop
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Performances Enhancing Proxies

• 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 wont know where to find these.

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Operational Environments

• Surface
• Low Delay, Symmetric, 1/R2 where radius is small
  (power vs bandwidth)
• Closely matches characteristics of todays
  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

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Top Level Solar SystemSpace Communication
Architecture
6.5 - 40 Minutes
4 Minutes
Hours
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Spiral 2 Lunar Surface Exploration Network
Lunar SBN Relay
Earth
Human on EVA
Surface Terminal
Repeater
(4-6)
Lander
Teleoperated Robot
(1)
Autonomous Robot
Legend
Very high rate backbone network to Earth High
rate orbiter access network Low power, medium
rate surface-to-surface network Low rate, long
range links
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Interplanetary Communications

• Key Issues
• New Protocols
• Bundled/Messaging Store and Forward Protocols
• Interplanetary time synchronization
• Scheduling Assets
• When to turn on and off

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Summary

• 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.

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Summary

• Current CCSDS data-link protocols are
  incompatible with COTS data-link 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.

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Conclusion
Protocols are tools for communication
One size does not fit all.