Emerging Paradigms · Study deck

Delay-Tolerant Networks: Disconnected Operations

This assumption fails in many IoT scenarios.

Blueprint Bina is your guide for this deck.

adhoc
Blueprint Bina, the module guide, in a scene from this chapter.
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After studying this chapter

Learning objectives

You will be able to:

  • Test disconnected ad hoc networks with a concrete scenario and pass criteria.
  • Validate custody transfer is not delivery with a concrete scenario and pass criteria.
  • test disconnected ad hoc networks with a concrete scenario and pass criteria
  • validate custody transfer is not delivery with a concrete scenario and pass criteria
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Major section

Disconnected Ad Hoc Networks

This assumption fails in many IoT scenarios.

  • DSR: Route discovery fails if no connected path.
  • The contact windows occur only at the first handoff and final delivery; between them, the carrier moves through a disconnected region while persistent storage protects the bundle.

Why it matters

Delay-Tolerant Networks enable communication across disconnected networks using store-carry-forward paradigm.

DTN store-carry-forward phases from source buffer to destination delivery
DTN store-carry-forward phases from source buffer to destination delivery
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Major section

Mobile Summary: Store-Carry-Forward

Deliver: The final carrier reaches a base station, gateway, or destination node.

  • The Bundle Protocol packages application data into self-contained bundles that can survive long storage periods, custody transfer decisions, and multiple opportunistic contacts.
  • Forward:: When encountering new nodes, forward buffered packets.
  • The source records data and stores it as a bundle.
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Major section

DTN Buffer Sizing for Tracking

Each collar collects GPS coordinates every 30 minutes and must deliver data to 3 base stations positioned at watering holes.

  • The collar photo grounds the sizing assumptions in a constrained field device: the antenna, electronics enclosure, and battery must carry both sensing and opportunistic relay work.
  • Each collar may carry copies for multiple other elephants.
A wild animal wearing a wide GPS tracking collar with a visible antenna and battery/electronics module
A wild animal wearing a wide GPS tracking collar with a visible antenna and battery/electronics module
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Major section

DTN Buffer Sizing for Tracking (continued)

Each 32-byte record waits locally until another collar or one of the three base stations creates a usable contact window.

  • Its buffer must survive the 4.2-day average base-station interval and the extra copies created by spray-and-wait, while its radio budget must cover brief exchanges without assuming a continuously reachable route.
  • Step 2 -- Buffer sizing for spray-and-wait (L=6):: Each collar carries its own data PLUS replicas received from other elephants.
  • With spray-and-wait, a source creates L=6 copies and distributes them to the first L/2 = 3 contacts.
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Major section

Putting Numbers to It

For spray-and-wait routing with $L$ copies among $N$ nodes and $M$ base stations, delivery probability follows an exponential contact process.

  • $$T_{wait} = \frac{1}{\frac{L}{2} \times \lambda_{eb}}$$.
  • where $\lambda_{eb}$ is the elephant-to-base contact rate ($1/100.8$ hr$^{-1}$ in our case).
  • With $L=6$ copies, this gives $T_{wait} = 33.6$ hours.
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Deck summary

Key takeaways

This assumption fails in many IoT scenarios.

  • Deliver: The final carrier reaches a base station, gateway, or destination node.
  • Each collar collects GPS coordinates every 30 minutes and must deliver data to 3 base stations positioned at watering holes.
  • Each 32-byte record waits locally until another collar or one of the three base stations creates a usable contact window.
  • For spray-and-wait routing with $L$ copies among $N$ nodes and $M$ base stations, delivery probability follows an exponential contact process.
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Retrieval practice

Recall check 1 of 4

Blueprint Bina says: answer from memory, then check your reasoning.

Q1A wildlife researcher wants to collect GPS data from collared zebras in a remote savanna with no cellular coverage. The collars have 100m radio range and zebras roam 5-20km apart. Which networking approach is appropriate?

ATCP/IP with multi-hop routing through intermediate zebras
BDTN store-carry-forward, exchanging data when zebras meet at watering holes
CDeploy Wi-Fi access points across the savanna for continuous coverage
DUse reactive routing (DSR) to discover paths on demand
Show answer

Answer: B DTN store-carry-forward is the only viable approach when no end-to-end path exists.

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Retrieval practice

Recall check 2 of 4

Blueprint Bina says: answer from memory, then check your reasoning.

Q2A rural sensor kiosk only meets a data-collection bus twice per day. Why should it buffer readings locally instead of dropping them when the internet is unreachable?

ABecause DTN assumes a future contact may deliver data even when no current path exists
BBecause buffering makes the radio transmit at a higher data rate
CBecause TCP retransmission can preserve pending readings until the data-collection bus restores the missing link
DBecause the bus can only carry encrypted data, not normal sensor readings
EBecause a contact schedule gives the kiosk a persistent forwarding route to the bus
Show answer

Answer: A The core DTN assumption is that no current end-to-end path may exist.

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Retrieval practice

Recall check 3 of 4

Blueprint Bina says: answer from memory, then check your reasoning.

Q3Place each DTN role where it lives so you can follow a bundle through storage, movement without connectivity, and forwarding at contact.

ASource Node
BBase Station
CExpired Bundle
DContinuous Route
Show answer

Answer: A Follow store, carry, and forward so you can distinguish delay tolerance from conventional routing that assumes a continuous path.

Q4What is the fundamental assumption that distinguishes DTN from traditional TCP/IP networking?

ADTN assumes faster hardware is available
BDTN assumes no end-to-end connected path exists at any single moment
CDTN assumes all nodes are stationary
DDTN assumes unlimited bandwidth is available
ECompressing data to reduce packet size
FEncrypting data for secure transmission
Show answer

Answer: B

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Retrieval practice

Recall check 4 of 4

Blueprint Bina says: answer from memory, then check your reasoning.

Q5In the store-carry-forward paradigm, what does the "carry" phase involve?

ACompressing data to reduce packet size
BEncrypting data for secure transmission
CA mobile node physically transporting buffered data while moving
DForwarding packets through a series of routers
EThe protocols are too slow for animal movement speeds
FAnimals cannot carry routing hardware
Show answer

Answer: C

Q6Why would traditional routing protocols (DSDV, DSR, ZRP) fail in a wildlife tracking deployment where GPS-collared animals roam 5-20km apart?

AThe protocols are too slow for animal movement speeds
BAnimals cannot carry routing hardware
CNo continuous radio path exists between distant animals, so route discovery fails immediately
DThe protocols consume too much energy for animal collars
Show answer

Answer: C

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Print reference

Answers

Answer key.

  1. B · DTN store-carry-forward is the only viable approach when no end-to-end path exists.
  2. A · The core DTN assumption is that no current end-to-end path may exist.
  3. A · Follow store, carry, and forward so you can distinguish delay tolerance from conventional routing that assumes a continuous path.
  4. B
  5. C
  6. C
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