Delay-Tolerant Networks (DTNs) A tutorial ipnsig/reports/DTN_Tutorial11.pdf

1. Delay-Tolerant Networks (DTNs)A tutorialhttp://www.ipnsig.org/reports/DTN_Tutorial11.pdf Eun Kyoung Kim

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

3. Evolving Wireless Networks Outside the Internet • Independent networks, each supporting specialized communication requirements and adapted to a particular homogeneous communication region • Support long and variable delays, arbitrarily long periods of link disconnection, high error rates, and large bidirectional data-rate asymmetries

4. Evolving Wireless Networks Outside the Internet • 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 • Require the intervention of an agent that can translate between incompatible networks characteristics and act as a buffer for mismatched network delays

5. The Concept of a Delay-Tolerant Networks (DTN) • A network of regional networks supporting interoperability among them • An overlay on top of regional networks, including the Internet • accommodate long delays between and within regional networks, and translate between regional network communication characteristics

6. Why a Delay-Tolerant Network (DTN)? • 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!

7. Store-And-Forward Message Switching • The problems 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

8. Intermittent Connectivity • Assume communicating devices (nodes) in motion and/or operation with limited power • When nodes must conserve power or preserve secrecy, links are shut down -> intermittent connectivity, network partition • On the Internet, intermittent connectivity causes loss of data, while DTNs isolate delay with a store-and-forward technique

9. Opportunistic Contacts • Network nodes may need to communicate during opportunistic contacts, in which a sender and receiver make contact at an unscheduled time

10. Scheduled Contacts • If potentially communicating nodes move along predictable paths, they can predict or receive time schedules of their future positions and thereby arrange their future communication sessions • Require time-synchronization

11. The Bundle Layer • A new protocol layer overlaid on top of heterogeneous region-specific lower layers, with which application programs can communicate across multiple regions

12. Bundles and Bundle Encapsulation • Bundles (messages) consist of • A source-application’s user data • Control information, provided by the source application for the destination application • A bundle header, inserted by the bundle layer

13. A Non-Conversational Protocol • DTN bundle layers communicate between themselves using simple sessions with minimal or no round-trips • Any acknowledgement from the receiving node is optional, depending on the class of service selected

14. DTN Nodes • An entity with a bundle layer • Host – sends and/or receives bundles, but does not forward them. Optionally supports custody transfers. • Router – forwards bundles within a single DTN region. Optionally supports custody transfers. • Gateway – forwards bundles between tow or more DTN regions. Must support custody transfers.

15. Delay Isolation via Transport-Layer Termination • DTN routers and gateways terminate transport protocols at the bundle layer

16. Custody Transfers • The bundle layer supports node-to-node retransmission by means of custody transfers • If no ACK is returned before the sender’s time-to-ACK expires, the sender retransmits the bundle • A bundle custodian must store a bundle until • Another node accepts custody, or • Expiration of the bundle’s time-to-live • Do not guarantee end-to-end reliability

17. Moving Points of Retransmission Forward • The bundle layer uses reliable transport-layer protocols together with custody transfers to move points of retransmission progressively forward toward the destination

18. Internet vs. DTN Routing • The protocol stacks of all nodes include both bundle and transport layers • DTN gateways can run different lower-layer protocols (below the bundle layer) on each side of their double stack, which allows gateways to span two regions that use different lower-layer protocols

19. Classes of Bundle Services • Custody Transfer • Return Receipt • Custody-Transfer Notification • Bundle-Forwarding Notification • Priority of Delivery • Authentication

20. DTN Regions • A region composing a DTN, in which communication characteristics are homogeneous • Has a unique region ID

21. Names and Addresses • Each DTN node has a two-part name, consisting of a region ID and an entity ID

22. Security • Forwarding nodes are authenticated as well as user identities and the integrity of messages • Sender information is authenticated by forwarding nodes

23. Security • Both users and forwarding nodes have private and public key-pairs and certificates • Senders can sign their bundles with their private key, producing a bundle-specific digital signature • Receivers can confirm the authenticity of the sender, the integrity of message, and the sender’s CoS rights using the signature and the sender’s public key