DTN Store-Carry-Forward Animation

Trace how delay-tolerant networks store a bundle, carry it through disconnection, and forward it during short contacts.

animation

dtn

wsn

architecture

routing

interactive

Interactive DTN store-carry-forward animation with moving bundles, contact windows, buffer pressure, forwarding strategy comparison, delivery estimates, and mobile-friendly learning support.

Delay-tolerant networking Store-carry-forward Intermediate

Store a bundle, carry it through disconnection, forward it when contact appears.

DTN does not assume a live end-to-end route. This animation shows how a bundle survives disconnected time by living in node buffers, moving with mobile carriers, and transferring only during short contact windows.

-- estimated delivery probability for this trace

-- expected delivery latency, not round-trip delay

-- active bundle copies carried in the network

-- copy overhead compared with one delivered bundle

Goal

See why DTN treats disconnection as normal operating state, not as a broken route.

Try

Switch strategies, then lower contact range or bandwidth to watch delivery become buffer-limited.

Watch

The bundle token should sit in storage, move with a carrier, and only cross links during contact windows.

Reflect

Pick the cheapest strategy that still meets the application delay and reliability requirement.

Bundle journey

A source stores a bundle while no path exists. Contacts appear as nodes move into radio range.

Store

Store at source The bundle waits in local storage because no simultaneous path to the destination exists.

1 copy

1 Store Bundle enters nonvolatile local storage.

2 Contact Nodes exchange summaries when radios overlap.

3 Carry Carrier moves while disconnected.

4 Forward Strategy decides whether a better carrier gets a copy.

5 Deliver Destination contact completes the payload transfer.

6 Retire TTL, status reports, or policy remove stale copies.

Readouts

-- payload size

-- one-contact capacity

-- buffer pressure

-- current forwarding decision

Strategy diagnosis

Spray-and-wait limits extra copies while still giving several mobile carriers a chance to meet the destination.

Controls

Select a deployment pattern.

Choose how a contact forwards the bundle.

Contact range 130 m

Contact bandwidth 80 KB/s

Bundle TTL 48 h

Buffer slots per node 4

Mobility predictability 60%

Learning support

DTN is not simply slow TCP/IP. Traditional routing expects a contemporaneous path. DTN accepts that the useful path may be spread over time.

Store: a bundle persists in a node buffer while disconnected.
Carry: mobility transports the bundle between disconnected regions.
Forward: a contact window lets nodes exchange summaries and transfer useful bundles.
Retire: delivery, TTL expiration, or policy removes stale copies.

Strategy quick reference

Strategy	Use when	Watch out
Direct	Source is likely to meet destination and energy is scarce.	Delivery may wait a long time or fail within TTL.
Epidemic	Message is critical and buffers, energy, and bandwidth are available.	Copies can overwhelm radios and storage.
Spray-and-wait	You need bounded overhead with better delivery odds than direct.	Too few tickets can strand the bundle.
PRoPHET-style	Mobility has history or regular patterns.	Bad history gives false confidence.

Technical checks

This demo uses teaching estimates, not a full simulator. The formulas connect the visible behavior to real design factors.

Contact capacity: bandwidth multiplied by contact duration. If it is smaller than the payload, a real system needs fragmentation or another contact.
Delivery probability: a rough trace estimate based on TTL, range, strategy, and predictability.
Bundle Protocol: BPv7 is RFC 9171. Reliability is not an end-to-end TCP session; it depends on bundle lifetime, status reports, convergence layers, and local policy.
Latency: DTN latency is often minutes, hours, or days. It is acceptable only when the application can tolerate delay.

TTL limits stale storage Buffers are finite Contacts are short Copies cost energy

Related resources

Use these after the animation to connect the trace to surrounding course material.