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An on-demand routing protocol establishes a route only when a device needs one. Also called reactive routing, this approach avoids maintaining routes for every possible destination in advance. It describes a way routing protocols operate, not one single protocol.
How on-demand routing works
When a node has data to send, it checks whether it has a suitable route to the destination. If not, it initiates route discovery. Once a route is found, the protocol can use it to forward data; what happens when that route fails depends on the protocol.
The IETF’s RFC 9854 defines on-demand routing as “Routing in which a route is established only when needed” and describes these protocols as reactive because their operations respond to a determination that a new route is needed.
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Dynamic Source Routing (DSR)
RFC 4728 specifies DSR for IPv4 mobile ad hoc networks. It divides the work into two functions:
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- Route Discovery: A node that has data for a destination but no known route searches for one using Route Request and Route Reply messages.
- Route Maintenance: While a sender is using a source route, the protocol responds to a link failure. The sender may use another route it already knows or discover a replacement.
DSR can retain multiple routes, leaving the sender able to select among routes it knows. These are DSR features, not requirements of every on-demand routing protocol.
AODV-RPL
RFC 9854 specifies AODV-RPL for low-power and lossy networks. Route discovery begins when a node has data to deliver and existing routes do not meet the application’s requirements. Where links are asymmetric, AODV-RPL permits separate routes in each direction; the return path therefore need not be the reverse of the forward path.
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Why use on-demand routing?
Its clearest potential benefit is less background routing activity. DSR does not require periodic routing advertisements, link-status sensing, or neighbor-detection packets. If the needed routes have already been discovered and nodes are approximately stationary relative to one another, DSR’s routing control overhead can fall to zero. That is a conditional behavior, not a guarantee: a new destination, a failed link, or changing communication needs can trigger control messages.
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“On-demand” tells you when routes are established, but it does not specify every other protocol behavior. For a practical comparison, check:
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- How the protocol represents and selects a route.
- What conditions trigger route discovery.
- How it detects a broken route and finds a replacement.
- Which network environment it targets.
- Whether it supports multiple routes or separate forward and return paths.
For example, DSR’s source-route maintenance and ability to retain multiple routes differ from AODV-RPL’s support for separate routes where link asymmetry calls for them. Those distinctions matter when choosing or evaluating a particular protocol; they should not be assumed from the on-demand label alone.
Quick Recap
Best Value
- Bright, high-resolution 5” glass capacitive touchscreen display lets you easily view your route
- Get more situational awareness with alerts for school zones, speed changes, sharp curves and more
- View food, fuel and rest areas along your active route, and see upcoming cities and milestones
- View Tripadvisor traveler ratings for top-rated restaurants, hotels and attractions to help you make the most of road trips
- Directory of U.S. national parks simplifies navigation to entrances, visitor centers and landmarks within the parks
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- 8” navigator with high-resolution, dual-orientation display and map updates of North America .Special Feature:Large Display; Voice Assist; Hands-Free Calling; Live Traffic and Weather; Traffic Cams and Parking; Smart Notifications,Driver Alerts; Tripadvisor; National Parks Directory; Find Places by Name; Garmin Real Directions Feature.
- Hands-free calling when paired with your compatible smartphone with BLUETOOTH technology and convenient Garmin voice assist lets you ask for directions to places you want to go
- Road trip–ready features include the HISTORY database of notable sites, a U.S. national parks directory, Tripadvisor traveler ratings and millions of Foursquare POIs
- Driver alerts for things such as school zones, sharp curves and speed changes help encourage safer driving and increase situational awareness
- Access live traffic, fuel prices, weather, parking and smart notifications when you pair this navigator with your compatible smartphone running the Garmin Drive app
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