# Presentation: 279783

## Transport Protocols and ApplicationsforInternet Use in Space

**Edward Criscuolo**
**Computer Sciences Corp**
**ed.criscuolo@gsfc.nasa.gov**
**November 14, 2000**

**Space Internet Workshop 2000**

## End-to-End IP Network Concept

**IP is the common thread**
**All upper layers sit on top of IP**

- Space Internet Workshop 2000

## Layered Model

**OSI 7 layer model**
_**IP is not TCP**_**!**
**Paper is on top two layers**

- Space Internet Workshop 2000

## Transport layer provides multiplexing

Three main transport layer protocols on the Internet
UDP - User Datagram Protocol (RFC-768)
Provides Multiplexing and error detection (checksum)
Atomic packet delivery
Delivery and delivery order not guaranteed

RTP - Real Time Protocol (RFC-1889)
Built “on top of” UDP
Adds sequence numbering, timestamping, and delivery monitoring

TCP - Transmission Control Protocol (RFC-793)
Provides multiplexing, flow control, sequencing, error detection, and automatic retransmission
Guaranteed in-order delivery
Provides a reliable “byte pipe” from sender to receiver.

**Three main transport layer protocols on the Internet**
- UDP - User Datagram Protocol (RFC-768)
- Provides Multiplexing and error detection (checksum)
- Atomic packet delivery
- Delivery and delivery order not guaranteed
- RTP - Real Time Protocol (RFC-1889)
- Built “on top of” UDP
- Adds sequence numbering, timestamping, and delivery monitoring
- TCP - Transmission Control Protocol (RFC-793)
- Provides multiplexing, flow control, sequencing, error detection, and automatic retransmission
- Guaranteed in-order delivery
- Provides a reliable “byte pipe” from sender to receiver.

**Transport layer**

- Space Internet Workshop 2000

## Application Layer

**UDP apps**
- Simple Data Delivery: Custom application
- Reliable File Transfer: PBP, MFTP, CFDP, NFS, TFTP
- Time Synchronization: NTP
**RTP apps**
- Audio and Video: QuickTime, RealVideo, I-Phone
**TCP Apps**
- Reliable Simple Data Delivery: Custom application
- Reliable File Transfer: FTP, HTTP
- Store and Forward (email): SMTP

**IP**
**Network**

- Space Internet Workshop 2000

## Space vs Terrestrial Issues

**Don’t Space Links Have Long Delay?**
- UDP is delay insensitive.  Will work to Pluto!
- LEO is close! 4 - 32 ms Round Trip Time.
- TCP has been used out to Geosync at over 400 Mbits/sec
**Aren’t Space Links too Noisy for IP?**
- Only _TCP_ throughput affected by noise.  IP & UDP are not.
- FEC used to improve space link BER.  10-5 is spec, 10-7 is typical.
- Uncorrected Telephone lines have a BER of 10-5!
- ECN, SACK, TCP/PEACH are coming

- Space Internet Workshop 2000

## More Space vs Terrestrial Issues

**Don’t Spacecraft Have Constrained ****Power, CPU, & Bandwidth?**
- Compare to an Internet-ready cell phone.
- New CPUs (StrongArm, PowerPC 750) are ready to fly.
**Isn’t Spacecraft Connectivity too Intermittent and too Variable for IP?**
- Just like laptop computers, cell phones, automobiles
- Mobile-IP, DHCP
**Spacecraft Have Huge Forward/Return Path Asymmetry**
- Driven by convention, not physics.
- STDN compatible receivers limited to 4 kbps uplink
- TDRSS can do 2 mbps symmetric

- Space Internet Workshop 2000

## IP Operations Scenarios

**Real time telemetry**
- Unidirectional - UDP
- Reliable - TCP
**Reliably Downlink Recorded Science & Engineering Data**
- Short Delay - FTP
- Long Delay - PBP / MFTP / CFDP
- Store & Forward - SMTP
**Onboard Clock Synchronization**
- Synchronization and drift mitigation - NTP
**Commanding**
- Store & Forward - SMTP
- Reliable Realtime - TCP
- Blind Realtime - UDP

- Space Internet Workshop 2000

## Results

- 4-Image Mosaic of Perth, Australia

- Error-Free Images Downlinked with FTP
- June 7, 2000

- Space Internet Workshop 2000

## Future

**Ground-based Flatsat Testbed**
- UDP-based reliable file transfer
- Mobile IP
- Mobile Router
- IPSEC, VPN
**Flight Validations**
- UDP-based reliable file transfer
- Blind Commanding
- HTTP-based reliable transfer
- Mobile IP
- Store & Forward

- http://ipinspace.gsfc.nasa.gov/

- Space Internet Workshop 2000