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.

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.
Explain: This assumption fails in many IoT scenarios.
Explain: Deliver: The final carrier reaches a base station, gateway, or destination node.

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

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

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 and multiple opportunistic contacts.
Some DTN architectures also use optional custody-transfer mechanisms; accepting custody is not final delivery.
Forward: When encountering new nodes, forward buffered packets.

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.
These six holders then wait for direct base-station contact.
Each 32-byte record waits locally until another collar or one of the three base stations creates a usable contact window.
In source spray-and-wait with L=6 total copies, the source keeps one copy and gives one copy to each of five distinct elephant contacts.

An African wild dog walks across rocky ground wearing a broad tracking collar, with another wild dog following behind. The photo shows the collar on the animal but does not reveal its antenna, battery, or electronics.

Major section

Putting Numbers to It

After all $L$ source-spray copies have been distributed, assume independent exponential base contacts at rate $\lambda_{eb}$ per holder.

$T_{wait} = \frac{1}{L \times \lambda_{eb}}$ .
where $\lambda_{eb}$ is the per-holder elephant-to-base contact rate ( $1/100.8$ hr $^{-1}$ here).

Major section

Why Internet Design Fails DTN

DTN violates fundamental Internet assumptions: end-to-end paths may not exist, ACKs may take hours, and connections close between packets.

TCP/IP protocols fail in DTN environments.
DTN requires designing around contact opportunities rather than continuous connectivity.

Major section

DTN vs Delay-Insensitive Apps

DTN is not a way to make any application work with delays.

Applications must be designed to function with minutes-to-hours of delivery delay.

Major section

DTN Buffer Management

Without systematic buffer management (priority queues, TTL enforcement, drop policies), storage fills and new important messages cannot be accepted.

Buffer management is a first-class design concern in DTN, not an optimization.

Major section

Custody Transfer Is Not Delivery

Custody transfer means the receiver takes responsibility for delivery -- but if all nodes holding custody of a message exhaust their buffers or fail before delivery, the message is lost.

DTN custody transfer improves reliability over hop-by-hop but does not provide absolute delivery guarantees.

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.
After all $L$ source-spray copies have been distributed, assume independent exponential base contacts at rate $\lambda_{eb}$ per holder.
DTN violates fundamental Internet assumptions: end-to-end paths may not exist, ACKs may take hours, and connections close between packets.

Retrieval practice

Recall check 1 of 4

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

Q1A wildlife researcher needs delayed GPS data from collared zebras in a savanna with no cellular coverage or fixed infrastructure, and no new infrastructure can be installed. The collars have 100 m radio range while zebras are usually 5–20 km apart. Which networking approach fits this constraint?

ATCP/IP with multi-hop routing through intermediate zebras

BDeploy Wi-Fi access points across the savanna for continuous coverage

CDTN store-carry-forward, exchanging data when zebras meet at watering holes

DUse reactive routing (DSR) to discover paths on demand

Show answer

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

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 a future DTN contact can carry locally buffered data when no path exists now.

BBecause storing readings increases the radio bit rate during the next bus contact.

CBecause TCP alone can hold undelivered readings until the twice-daily bus returns.

DBecause the bus accepts encrypted readings but cannot carry ordinary sensor data.

EBecause a known bus schedule creates a permanent forwarding path from the kiosk.

Show answer

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

Retrieval practice

Recall check 3 of 4

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

Q3What creates a DTN bundle even when no end-to-end route exists?

APersistent Buffer

BMobile Carrier

CBase Station Contact

DSource Node

Show answer

Answer: D The source node creates the bundle even when no end-to-end route exists.

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

ADTN assumes no end-to-end connected path exists at any single moment

BDTN assumes all nodes are stationary

CDTN assumes unlimited bandwidth is available

DDTN assumes faster hardware is available

Show answer

Answer: A Store-carry-forward lets data progress despite no simultaneous end-to-end route.

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?

AA mobile node physically transporting buffered data while moving

BForwarding packets through a series of routers

CCompressing data to reduce packet size

DEncrypting data for secure transmission

Show answer

Answer: A The sequence is store locally, carry the bundle as a person, animal or vehicle moves, then forward it when a suitable contact appears.

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

ANo continuous radio path exists between distant animals, so route discovery fails immediately

BThe protocols consume too much energy for animal collars

CThe protocols are too slow for animal movement speeds

DAnimals cannot carry routing hardware

Show answer

Answer: A DSDV, DSR and ZRP presume routes over current neighbours.

Print reference

Answers 1 of 2

Answer key.

C · DTN store-carry-forward is the only viable approach when no end-to-end path exists.
A · The core DTN assumption is that no current end-to-end path may exist.
D · The source node creates the bundle even when no end-to-end route exists.
A · Store-carry-forward lets data progress despite no simultaneous end-to-end route.
A · The sequence is store locally, carry the bundle as a person, animal or vehicle moves, then forward it when a suitable contact appears.

Print reference

Answers 2 of 2

Answer key.

A · DSDV, DSR and ZRP presume routes over current neighbours.