Delay Tolerant Networks (DTN)

1. Delay Tolerant Networks (DTN) Anitha Vijayakumar Chun-Ching Tsan (James) For EE206a Spring 2004

2. Agenda • Problems with internet • Insight into DTN Architecture • Examples of DTN Networks – • Interplanetary networks • DTNLite – DTN in sensor networks

3. Implicit Internet Assumptions • End-to-end path exists for communication • Small Rtt and end-to-end packet loss • All nodes support TCP/IP • End point security sufficient • Application need not worry about physical layer performance • Symmetric data rates

4. Characteristics of Challenged Networks • Path and Link Characteristics • High latency and low data rates • Mobile routers with disconnection (Zebranet) • Periodic mobility (satellites) • Intermittent connectivity • Network Architecture • Interoperability Considerations • End-to-end security not desirable • End system characteristics • Limited Longevity • Low duty cycle operation • Limited resources

5. Achieving Interoperability • “Fool” the Internet , do something so that end-points do not detect that there is no link. • Attach the challenged network to the “edge” of the Internet.

6. What do we need • Interwork with heterogeneous networks • Give good performance in high delay and high error environments • API providing non-interactive messaging • Routing – delay-tolerant and disconnection tolerant

7. Delay Tolerant Networks (DTN) • What is needed is a system that uses routing as in present day peer-to-peer systems with delay tolerancy and disconnection properties (like e-mail) This is the DTN

8. DTN – Design Principles • Provide a class-of-service and delivery options based on non-real-time services • Use network storage to provide end-to-end reliable delivery • Security mechanism in the infrastructure • Store and forward message switching

9. DTN Architecture - Bundles

10. DTN – Regions & Elements • Regions : DTN is a network of networks. Each network is a region • Elements • Hosts • Routers • Gateway

11. DTN Gateway

12. DTN Naming Names and addresses Bundles:// < region ID> : <entity ID> Example: bundles://earth.internet.tcp://www.ee.ucla.edu:5000 • Region ID • Globally unique • Variable length sub-string • Entity ID • Late binding • Variable length sub-string

13. DTN - Routing • Types of routes • Persistent Contacts ( DSL subscriber ) • On Demand contacts ( Dial up user) • Intermittent opportunistic contacts • Intermittent predictable contacts • Intermittent scheduled contacts (Satellites)

14. Time Synchronization • Needed for routing with scheduled and predicted contacts • Implemented by having a source and expiration timestamp in bundle header • Used for purging – Non strict time sync requirements

15. Bundles – Custody Transfer • Custody Transfer : A bundle is stored at a node until the next node accepts custody or till the ttl of the bundle expires

16. Bundles – Custody Transfer • Advantages • End-to-end reliability with return receipt • Resource recoverability

17. Congestion and Flow Control • Discussion not complete • Congestion might never occur • Local decisions on flow and congestion control • Region specific flow control

18. Class of Bundle Services • DTN has 6 class of service • Custody Transfer • Return receipt notification • Custody transfer notification • Bundle forwarding notification • Priority • Bulk – best effort • Normal • Expedited – highest priority • Authentication

19. DTN - Security • Forwarding nodes are authenticated • Drop traffic as early as possible • Asymmetric key cryptography • Sender signs a bundle with private key • Forwarding node verifies using stored user certificates • Forwarding node replaces signature with its own signature and forwards bundle • Next node verifies the previous node using stored router certificates • Next node replaces with its own signature and forwards bundle

20. DTN - Security • Advantages • Denial of Service attacks are harder • Drop traffic at the earliest • No persistent storage for dropped traffic • Disadvantages • Computation cost ( >>low-delay environment ) • Key distribution might not be resource efficient

21. Bundle Header

22. Is this just e-mail ? • Primary difference is in routing • Cannot move messages closer to destination • E-mail security authenticates only user-to-user • SMTP not delay tolerant or efficient for long RTTs

23. Summary and Status • Summary • Addresses many problems of non-continuous end-to-end connectivity • Based on asynchronous store-and-forward messaging like USPS • Accommodates different forms of connectivity • Implements infrastructure enabled security • Status • IRTF working group • Source code available

24. Examples: • Examples of DTN Networks – • Interplanetary networks • DTNLite – DTN in sensor networks

25. Interplanetary networks

26. Overview of CFDP • A hypothetical protocol • Operate in either ACK (reliable) or unACK mode • No connection protocol: the time required to establish a connection might exceed the duration for a communication opportunity • Never wait for ACK due to long round-trip latency, so need attach a common transfer identifier to messages for a given file transfer • Use nonvolatile storage for retransmission buffer

27. Maximum Latency transmit from earch

28. Why not TCP/IP in interplanetary networks • Sender and receiver negotiate for a connection • Delivers received data to the application only in transmission order • Throughput diminishes with increasing round-trip latency

29. Bundling-Based Interplanetary Internet

30. Interplanetary Internet based on Tunneling and RLI

31. DTNLite – DTN in sensor networks

32. Reliable delivery in sensor networks • Achieve Reliable delivery • Acknowledgement • Retransmission • Retransmission and storage

33. Challenges in Sensor networks • High round trip delay • Disconnections • Unreliable nodes • Large messages • High Mobility

34. Reliability Mechanisms

35. DTNLite Design issues • Custody transfer with reliability • Persistent storage management • Duplicate management • Application awareness @Design env: use nesC progrmming in TinyOS plateform

36. DTNLite architecture

37. Important Components in the Architecture • Bundle storage manager • Use Matchbos file system • Bundle agent • An interface for sending and receiving bundles. • Custody transfer handshake • Allocation of memory for bundles • Convergence layer • LRX • Reliable muti-hop transfer of a budle from one custody hop to anther • MultiHop • Sending and receiving lustody querries and ACKs.

38. Some issues of Custody Transfer • Dealing with Duplicates • Explicit duplicate elimination initiated at destination and brocasting deletion packets • Congestion and custody transfer • Messages can not be discarded safely • Transfer to another hop • Drop if expiration deadline expired • Keeping additional information with every message for judgement • Choosing the next custody hop • Routing metrics

39. Routing strategy for global optimization • Minimizing the overall energy consumption in the network • Obtaining a uniform distribution of the energy levels of nodes • Minimizing the delay in message delivery and the number of undelivered messages

40. Metrics for routing decision making Choose the node with • Highest energy level remaining • Least average delivery time • Minimum average consumption for message delivery

41. Querrying mechanisms • Unicast • Flood limited to a given number of hops • Full flood

42. Custody Transfer

43. Simulation setup

44. Results (I) AVG_DELAY Decreasing NEAREST FARTHEST

45. Results (II) NEAREST FARTHEST FARTHEST FARTHEST

46. References • http://www.dtnrg.org/ • http://www.dtnrg.org/tutorials/warthman-1.1.pdf • ftp://ftp.rfc-editor.org/in-notes/internet-drafts/draft-irtf-dtnrg-arch-01.txt • ftp://ftp.rfc-editor.org/in-notes/internet-drafts/draft-irtf-dtnrg-bundle-spec-01.txt • http://www.cs.berkeley.edu/~rkpatra/cs294_deep/deep_proj/deep_rabin_sergiu/dtnlite_rabin_sergiu.pdf • http://www.cs.berkeley.edu/~kfall/dtn-luby-class.pdf • http://www.dtnrg.org/papers/ieee-comsoc-article.pdf • http://today.cs.berkeley.edu/retreat-1-04/slides/Sergiu_Nedevschi_DTNLite_paper.pdf