# Presentation: 354163

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

**Will Ivancic**
**wivancic@grc.nasa.gov**
**216-433-3494**
**roland.grc.nasa.gov/~ivancic**

## Presentation Outline

- 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

## Space Communication ArchitectureSupporting 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

## Projected Growth in DSN Downlink Requirements

## Evolving the Lunar Architecture(One of many early concepts)

- 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 satellites******One inclined elliptical orbit******Advantage: long dwell times over the South Pole ***

**The 2 relays are moved to a circular orbit to support **_**South and North Pole**_** missions*****1 relay satellite is added to the constellation ************ 3 total******One circular polar orbit******Advantage: 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 coverage**_***3 relay satellites are added ************ 6 total******Two polar circular orbits******Advantage: increased coverage at the poles, global coverage achieved ***

**The orbital planes are inclined to support **_**global, far-side, and equatorial missions**_**Final Configuration:*****6 relay satellites******Two inclined circular orbits******Advantage: global coverage, coverage is distributed more evenly than for polar orbits ************ better support to exploration at lower latitudes ***

## Example Service and Data Rate Scenario for Lunar Communication (Work in progress)

|  | User | Channel Content | Latency | # of Channels | Channel Rate | Total Rate |
| --- | --- | --- | --- | --- | --- | --- |
| Operational | Base | Speech | NRT | 2 | 10 kbps | 20 kbps |
|  |  | Engineering | NRT | 1 | 100 kbps | 100 kbps |
|  | Astronauts | Speech | NRT | 4 | 10 kbps | 40 kbps |
|  |  | Helmet camera | NRT | 4 | 100 kbps | 400 kbps |
|  |  | Engineering | NRT | 4 | 20 kbps | 80 kbps |
|  | Human Transports | Video | NRT | 2 | 1.5 Mbps | 3 Mbps |
|  |  | Engineering | NRT | 2 | 20 kbps | 40 kbps |
|  | Robotic Rovers | Video | NRT | 8 | 1.5 Mbps | 12 Mbps |
|  |  | Engineering | NRT | 8 | 20 kbps | 160 kbps |
|  | Science Orbiters | Quick Look | NRT | 4 | 1 Mbps | 4 Mbps |
|  |  | Engineering | NRT | 4 | 20 kbps | 80 kbps |
| High Rate | 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 |
|  | Robotic Rovers | Surface Radar | 1 day | 1 | 100 Mbps | 100 Mbps |
|  |  | Hyperspectral Imaging | 1 day | 1 | 150 Mbps | 150 Mbps |
|  | Science Orbiters | Orbiting Radar | 1 day | 2 | 100 Mbps | 200 Mbps |
|  |  | Hyperspectral Imaging | 1 day | 2 | 150 Mbps | 300 Mbps |
|  | Total |  |  |  |  | 980 Mbps |

## 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.

## Why so Much Misinformation?

**The Preverbial Rice Bowl**

- $$$

- POLITCS

- Much of this has been perpetuated by political turf battles and funding battles to the detriment of sound technical analysis

## 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

## An Example of TCP Steady State Performance

**Chart is from “Why not use the Standard Internet Suite for the Interplanetary Internet?” **
- By Robert C. Durst, Patrick D. Feighery, Keith L. Scott

- Does this infer that all Internet Protocols are not suitable for Interplanetary operations?

## Theoretical Steady State Throughput

- Increasing Delay

- Delay Tolerant

- 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.

**Don’t Use TCP for long delays.**
**However, one can still use IP**
**and a rate-base protocol.**

## 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

## Technology Evolution

- Multiplexer

- Modulator

- Yesterday

## Technology Evolution

- Today

## Ubiquitous Network Society

**Next Generation**
**Core Network**

** ****Digital Information**
** ****Appliances**

- 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

**RFID Tag**

- Sensor Network

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

- Space Communications technology

- Quantum Communications technology

- Robot

- Seamless Network
- Authentication

- Ad-hoc Network

- This document is based on the material of MIC

- Source: IPv6 Promotion Council of Japan

- Security

- Home Networks

- Tomorrow

## 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.)

## COTS, CCSDS and the Internet

## COTS Satellite Modem Operation

- COTS
- Router

- Commercial Satellite Modem

- Baseband
- Framing

- RF Framing
- (Media Access)

- UP/Down Converter

- RF

- IF

**Radio**

## Common CCSDS Operation

- Front
- End
- Processor

- Modem

- Baseband

- UP/Down Converter

- RF

- IF

- Bit Synchronizer

**Radio**

## CCSDS relationship with the OSI Layers

## Slide 21

## CCSDS and HDLC Ground Support Comparison

**Downconvert**

**Receiver**

**Demod**

**Bit sync**

**Derandomize**

**Conv. Decode**

**Upconvert**

**Transmitter**

**Modulator**

**Randomize**

**Conv. Encode**

**CCSDS**

**Downconvert**

**Receiver**

**Demod**

**Bit sync**

**Derandomize**

**Conv. Decode**

**FEC Decode**

**Upconvert**

**Transmitter**

**Modulator**

**Randomize**

**Conv. Encode**

**FEC Encode**

**Antenna**

**HDLC Framing**

**HDLC Framing**

**IP**

**IP**

**101010**
**(bits)**

**Frame**

**Net PDU**

**Commercial Router/**
**Frame Relay Switch**

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

- Using standard internet protocols and applications in space - Hogie

## 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

## Gateway or Encapsulation

- NIC

- Space

- Ground

- COTS
- Interface

## Performances Enhancing Proxies

**Control Loop 1**

**Control Loop 3**

**Control Loop 2**

**End-to-End Control Loop**

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

## 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 won’t know where to find these.

## Operational Environments

- 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

## Top Level Solar SystemSpace Communication Architecture

**~6.5 - 40 Minutes**

**Hours**

**~4 Minutes**

## Spiral 2 – Lunar Surface Exploration Network

**Lander**

**Surface **
**Terminal**

**Human **
**on EVA**

**Autonomous**
**Robot**

**Lunar**
**SBN Relay**

**Earth**

**Repeater**

**Teleoperated**
**Robot**

**(4-6)**

**(1)**

- 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

**Legend**

## Interplanetary Communications

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

## 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.

## 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.

## Conclusion

- Protocols are tools for communication

- One size does not fit all.