Emerging Paradigms · Study deck

DSR Worked Examples

Picture a rescue tracker discovering a route, using it twice, then losing a relay as the team moves.

Blueprint Bina is your guide for this deck.

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After studying this chapter

Learning objectives

You will be able to:

Explain: If a packet carries an 8-hop route and each compact node ID takes 2 bytes, the route list alone is 16 bytes.
Explain: This proves one worked lifecycle, not every mobility pattern; the deeper examples compare good reuse with stale knowledge and repair costs.
Explain: That lifecycle lets you trace why DSR can be efficient for sparse traffic and why it can stumble in mobile networks.
Explain: A worked trace should separate the first route that reaches the destination from the total work done by the network.

Major section

Start Simple

A protocol means the agreed rules and message order devices use to exchange routing information.

This proves one worked lifecycle, not every mobility pattern; the deeper examples compare good reuse with stale knowledge and repair costs.
Each packet carries part of that story.
The example matters because it shows when cached knowledge saves airtime and when that same knowledge becomes a liability.

Major section

Overview: Read DSR as a Route Lifecycle

Dynamic Source Routing examples are useful only when they show the whole route lifecycle.

A worked trace should separate the first route that reaches the destination from the total work done by the network.
That lifecycle lets you trace why DSR can be efficient for sparse traffic and why it can stumble in mobile networks.

A DSR Route Request spreads outward and accumulates a path record. Duplicate filtering keeps each relay from forwarding the same source and request ID repeatedly.

Major section

Tune Cache Age to Mobility

DSR cache settings should be chosen from deployment behavior, not from a generic default.

A cached route is valuable when traffic reuses it before the topology changes.
If movement changes useful paths about every 90 seconds, a 300-second cache timeout is too long.

The practical DSR decision is a balance among route discovery cost, cache freshness, traffic interval, and the route-error behavior expected after movement.

Major section

DSR Header, State, and Repair

The mechanics behind DSR examples are small enough to audit, but each one has a scaling consequence.

A stale cached route fails only after a relay tries to use it and cannot reach the next hop.
If a packet carries an 8-hop route and each compact node ID takes 2 bytes, the route list alone is 16 bytes.

DSR packets carry the ordered route, which removes per-hop route-table lookup but adds header bytes to every packet on that path.

Major section

DSR Caching and Route Maintenance

A DSR cache is helpful until it becomes stale.

Dynamic Source Routing can reuse paths it has discovered or overheard.
Maintenance is the discipline of detecting broken links, removing bad assumptions, and deciding when discovery must run again.

A DSR node can learn route information by overhearing packets that carry a source route, then reuse that route when it is still valid.

Deck summary

Key takeaways

A protocol means the agreed rules and message order devices use to exchange routing information.

Dynamic Source Routing examples are useful only when they show the whole route lifecycle.
DSR cache settings should be chosen from deployment behavior, not from a generic default.
The mechanics behind DSR examples are small enough to audit, but each one has a scaling consequence.
A DSR cache is helpful until it becomes stale.

Retrieval practice

Recall check 1 of 6

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

Q1A DSR Route Request reaches a destination over a 3-hop path in both a 50-node network and a 1000-node network. Which statement best describes the discovery timing?

AThe 1000-node network must take 20 times longer because it has 20 times more nodes.

BThe first-route latency is mainly the RREQ path out plus the RREP path back.

CDSR discovery is independent of hop count because every node broadcasts at the same time.

DThe destination can reply before receiving a Route Request if it has a cached route to the source.

Show answer

Answer: B DSR examples separate first-route latency from network-wide flood cost.

Retrieval practice

Recall check 2 of 6

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

Q2A DSR deployment has assets that change useful neighbor relationships about every 90 seconds. The current 300-second cache timeout causes many route errors. Which adjustment is the best first change?

AIncrease the timeout to 900 seconds so the source performs fewer discoveries.

BSet the timeout around 45 to 90 seconds and monitor whether route errors fall without excessive discoveries.

CDisable duplicate RREQ filtering so the destination receives more candidate routes from each discovery flood.

DKeep the timeout unchanged and rely on the application to retry failed packets.

Show answer

Answer: B DSR cache timeouts are deployment parameters.

Retrieval practice

Recall check 3 of 6

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

Q3A DSR source gets a route error after a relay link breaks. What should its recovery trace keep?

AThe failed link, cache age, error time, repair choice, and time until a usable route returns.

BOnly the route that worked before the fault.

COnly the first packet received after repair.

DOnly the number of cached routes.

Show answer

Answer: A This trace ties the error and rediscovery to delay and cost.

Retrieval practice

Recall check 4 of 6

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

Q4Which statement best describes the main tradeoff in DSR route caching?

ACaching can avoid repeated discovery, but cached source routes must expire or be invalidated when links change.

BCaching removes the need for Route Error handling because all future packets already know the path.

CCaching is always harmful because every route should be rediscovered for every packet.

DCaching turns DSR into a proactive table-driven protocol with periodic updates for every destination.

Show answer

Answer: A DSR caching trades discovery savings against stale-route risk.

Retrieval practice

Recall check 5 of 6

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

Q5Why is targeted invalidation safer than clearing the whole DSR route cache after one Route Error?

AIt removes paths that use the failed hop while preserving unrelated cached routes that may still be valid.

BIt guarantees that a valid alternate is always available, so no future route discovery flood will ever be needed.

CIt converts DSR from source routing to hop-by-hop forwarding, so packets no longer depend on cached route lists.

DIt keeps the failed route cached in a suspect state so that later retries can test whether the broken hop has recovered.

Show answer

Answer: A DSR maintenance should match the scope of the fault.

Retrieval practice

Recall check 6 of 6

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

Q6Which measurement best tests DSR route-error recovery for urgent traffic?

AThe number of cached routes before any link fails.

BThe time from a failed link to resumed delivery on a valid path.

CThe advertised radio range of the source.

DThe age of the newest route entry alone.

Show answer

Answer: B Measure elapsed time from failure to valid delivery; include error handling and any rediscovery.

Print reference

Answers

Answer key.

B · DSR examples separate first-route latency from network-wide flood cost.
B · DSR cache timeouts are deployment parameters.
A · This trace ties the error and rediscovery to delay and cost.
A · DSR caching trades discovery savings against stale-route risk.
A · DSR maintenance should match the scope of the fault.
B · Measure elapsed time from failure to valid delivery; include error handling and any rediscovery.