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Introducing Saratoga

Introducing Saratoga. Zequn Huang CISC856 11/20/2012 Thank Sophie Che for her slides. Sophie Che Dept. Computer and Information Science University of Delaware (some slides courtesy of Lloyd Wood). Outline. Introduction DTN background Saratoga Protocol Saratoga Transactions.

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Introducing Saratoga

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  1. Introducing Saratoga Zequn Huang CISC856 11/20/2012 Thank Sophie Che for her slides Sophie Che Dept. Computer and Information Science University of Delaware (some slides courtesy of Lloyd Wood)

  2. Outline • Introduction • DTN background • Saratoga Protocol • Saratoga Transactions

  3. What’s Saratoga? • Developed by Surrey Satellite Technology to transfer remote-sensing imagery from its IP- based satellites to ground. • Saratoga is a lightweight transport protocol that can also be Delay Tolerant Network (DTN) convergence layer.

  4. Original Use Case • Disaster Monitoring Constellation (DMC) • Used for rapid daily large-area imaging • Can observe effects of natural disasters fires in California, 28 October 2003 (UK-DMC)

  5. DMC in use: after Hurricane Katrina, 05 • In this image, dry land is red. Flooded and damaged land is shown as brown • DMC is working as part of the United Nations International Charter for Space and Major Disasters

  6. DTN Backgrounds

  7. Today’s Internet • Successful at interconnecting communication devices across the globe • Based on TCP/IP protocol suite • Connected in end-to-end, low-delay paths between sources and destinations • Low error rates and relatively symmetric bidirectional data rates

  8. Evolving Wireless Networks Outside the Internet • Support long and variable delays, arbitrarily long periods of link disconnection, high error rates, and large bidirectional data-rate asymmetries • Examples • Terrestrial civilian networks connecting mobile wireless devices • Wireless military battlefield networks connecting troops, aircraft, satellites, and sensors • Outer-space networks, such as the InterPlaNetary (IPN) Internet project

  9. Interplanetary Network Imagine If I say a “Hi” to you and you hear it after 9 Hours !!!!!

  10. Mars Mars Mars Interplanetary Network Earth

  11. WhyDelay-Tolerant Network ? • The Internet’s underlying assumptions • Continuous, bidirectional end-to-end path • Short round-trips • Symmetric data rates • Low error rates • The characteristics of evolving and potential networks • Intermittent connectivity • Long or variable delay • Asymmetric data rates • High error rates • New architectural concept is needed!

  12. Store-And-Forward Message Switching • Theproblems of DTNs can be overcome by store-and-forward massage switching • DTN routers need persistent storage for their queues because • A communication link may not be available for a long time • One node may send or receive data much faster or more reliably than the other node • A message, once transmitted, may need to be retransmitted for some reasons

  13. Layers in DTN DTN TCP/IP Protocol Suite

  14. Saratoga

  15. Where is Saratoga in DTN • An IP-based convergence layer • transport protocols that it uses to move data across different networks • Using UDP as a starting point Why not using TCP? • DTN has the features • No congestion • Long delay • Asymmetric data rate

  16. Basic Saratoga Design SNACK Flood data No congestion control Scalable on file size transferred Compatible on IPv4 and IPv6

  17. Basic Saratoga design • Flood data packets out as fast as possible • ACKs are Selective Negative ACK (SNACKs) indicating the gap to fill with resent data. • File sender can require ACK from file reciver

  18. TCP with SACK after timeout Timer TCP Sender TCP Receiver start 100-199 sender receiver 200-299 ACK 300 stop 300-399 start loss 400-499 300 399 ACK 300 SACK 400-500 500-599 ACK 300 SACK 400-600 timer expires timeout 300-599 resent ACK 600 stop

  19. File Offset Descriptor • Length is fixed within a transfer, but vary between different transfers • How to design a scalable file transfer protocol able to handle any size file? • Solved this problem with 16/32/64/128-bit pointers

  20. Sent periodically Advertise nodes’ presence, capabilities, and desires BEACON Ask for a download, upload, directory listing, or deletion operation _get_, _put_, _getdir_, _delete_ REQUEST Sent at start of transaction Description of the file Specify the max supported file size METADATA Saratoga Packets

  21. Actual file data being transferred Use chosen maximum file size MAY request an ack DATA Responds to REQUEST or DATA. Can signal list of unreceived data to sender during a transfer STATUS Saratoga Packets (cont’d)

  22. Data Packet Format

  23. Status Packet Format (HOLESTOFILL)

  24. An example

  25. Saratoga Transactions

  26. Saratoga Transactions

  27. GET without loss REQUEST METADATA DATA #1 Transfer accepted DATA #2 DATA #3 DATA #4 DATA #5 DATA #6 Request an ack completed HOLESTOFILL

  28. GET with loss REQUEST METADATA DATA #1 Transfer accepted DATA #2 X Request an ack DATA #3 Indicate a loss HOLESTOFILL for #2 Request an ack DATA #2 completed HOLESTOFILL

  29. GET with Inactivity Timer Start timer REQUEST METADATA Reset timer DATA #1 Reset timer HOLESTOFILL DATA #2 Reset timer No connection any longer Store the file for possible resuming later

  30. GET with Inactivity Timer(cont’d) REQUEST METADATA DATA #1 HOLESTOFILL DATA #2 Request an ack DATA #3 Start timer DATA #4 DATA #5 Cease to send DATA

  31. GET being Rejected • Transfer rejected • An error code is sent  The transaction is terminated REQUEST METADATA

  32. PUT METADATA Transfer accepted HOLESTOFILL DATA #1 DATA #2 DATA #3 DATA #4 DATA #5 DATA #6 Request an ack completed HOLESTOFILL

  33. DELETE • A REQUEST packet including the file path to be deleted • Trigger a HOLESTOFILL with a status code

  34. Reference • Saratoga: a Delay-Tolerant Networking convergence layer with efficient link utilization • Delay-Tolerant Networks(DTN) A Tutorial • TCP Selective Negative Acknowledgment over IEEE 802.11 Wireless Networks • Saratoga: A Scalable Data Transfer Protocol draft-wood-tsvwg-saratoga-12

  35. Video • http://www.youtube.com/watch?v=XTmYm3gMYOQ

  36. Thank You ! Questions? Ref: draft-wood-tsvwg-saratoga-02

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