Chapters

15 Edge Cyber-Foraging: Placement and Caching Decisions

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15.1 Start With the Decision

This section: Start With the Decision — A phone should offload a task only when the nearby server can beat its deadline.

A phone should offload a task only when the nearby server can beat its deadline. Count radio energy and wait time first.

15.2 Route Overview

This section: Route Overview — This is part 1 of 2.

This is part 1 of 2. Continue with Edge Cyber-Foraging: Cost and Energy Calculations.

15.3 Part Objectives

This section: Part Objectives

  • Test cyber-foraging check with a concrete scenario and pass criteria.
  • Validate mobile figure summary: three-tier caching with a concrete scenario and pass criteria.

15.4 Chapter Roadmap

This section: Chapter Roadmap

  • Choose Where the Glasses Compute
  • Start With the Story
  • In 60 Seconds
  • Phoebe’s Field Notes: What the 249 mAh Actually Costs, and Why 5 GHz Was the Right Offload Radio
  • Cyber-Foraging Check
  • Key Concepts
  • Cyber-Foraging and Caching Basics
  • Prerequisites
  • Cyber-Foraging Overview
  • What is Cyber-Foraging?
  • Cyber-Foraging What Where When

15.5 Choose Where the Glasses Compute

This section: Choose Where the Glasses Compute — Imagine smart glasses need to map a room but their small battery cannot do all the work at once.

Imagine smart glasses need to map a room but their small battery cannot do all the work at once. The device must decide whether to work alone, use a nearby helper, or wait. Bandwidth means how much data a link can carry in a set time. Latency means the wait from a task’s start to its useful result.

For the glasses, offloading helps only when a nearby helper finishes the room-mapping task before the useful deadline and uses less battery than local work. Sending data, waiting for the helper, and receiving the answer all count; a cached room map needs an age check before use.

15.5.1 Check the Offload Handoff

  • How soon must the glasses show a useful room map?
  • How much work and energy would local processing use?
  • Can the nearby helper accept the data and return an answer over the current link?
  • What can the wearer do if the helper or link disappears?

Measure the complete local and offload paths, including transfer, helper load, and result age. Note the privacy boundary for the room data and keep a local or pause state for a failed handoff.

15.5.2 When Offloading Costs More

A nearby helper may compute quickly while the complete offload path still costs more than local processing. Sending task data, waiting for the helper and receiving the result contribute to elapsed time and battery use. Compare those measured costs with the local task before choosing where to run it.

For the room-mapping task, the returned map must meet the useful deadline, and offloading should use less battery than local work. Review battery charge, radio conditions and task measurements together: helper speed alone cannot establish that benefit. Include helper load in the timing comparison and retain the tested local or wait path if the transfer fails.

15.5.3 Before Using a Returned Map

Compare the measured result time with the mapping deadline before displaying it. If a saved map is older than the room state it describes, label it as old rather than treating it as a fresh view. A failed transfer should return the glasses to the tested local or wait path.

15.6 Start With the Story

This section: Start With the Story — Move work to a nearby cloudlet when discovery, transfer, and fallback meet the device timing need.

Move work to a nearby cloudlet when discovery, transfer, and fallback meet the device timing need.

In 60 Seconds

Cyber-foraging enables resource-constrained mobile devices to opportunistically discover and offload computation to nearby devices called surrogates. The What/Where/When framework guides offloading decisions: What task to offload (CPU-heavy, delay-tolerant tasks are best candidates), Where to offload (nearby devices with matching capabilities), and When to offload (based on battery state, network conditions, and urgency). Edge caching across three tiers (device, surrogate, cloud) further reduces latency and bandwidth.

The mathematical gist. At a stated 3.85 V, the chapter’s 249 mAh local run uses 0.959 Wh while the 18.7 mAh offload uses 0.072 Wh, saving 0.887 Wh or 92.5%. The same offload link at 5 GHz has a 6.00 cm wavelength and a 1.50 cm quarter-wave element; that compact, wide-channel radio trades range for the chapter’s 50 MB/s desk-to-laptop transfer.

Math Bridge · guided foundationsHow do 249 mAh and 5 GHz justify this offload?Let Data Dora turn charge into energy, then frequency into wavelength.

15.7 Learning Objectives

This section: Learning Objectives

By the end of this chapter, you will be able to:

  • Explain Cyber-Foraging Concepts: Describe how mobile devices opportunistically discover and leverage nearby computational resources
  • Apply the What/Where/When Framework: Evaluate offloading decisions based on task characteristics, surrogate capabilities, and timing constraints
  • Compare Virtualization vs Mobile Agents: Distinguish between cloudlet-based and agent-based approaches for different session durations and isolation requirements
  • Design Edge Caching Strategies: Implement multi-tier caching hierarchies for optimal latency and bandwidth
Cyber-Foraging Check

Key Concepts

This section: Key Concepts

  • Cyber-foraging: A mobile edge computing strategy where resource-constrained devices dynamically offload compute tasks to nearby, more powerful nodes (cloudlets, edge servers) discovered opportunistically on the local network.
  • Cloudlet: A trusted, resource-rich compute node located close to mobile or IoT devices, providing low-latency offloading without the round-trip delay of a public cloud data centre.
  • Task migration: The process of moving an in-progress computation from one node to another, requiring serialisation of the computation state and transfer of associated data.
  • Offload decision algorithm: The logic determining whether to execute a task locally or offload it to a nearby node, typically based on task size, local battery level, network round-trip time, and available remote resources.
  • Opportunistic networking: A communication paradigm where connections are established whenever nodes come within range of each other, without requiring persistent infrastructure, used to distribute processing in dense IoT environments.

Imagine your phone needs to do a really hard math problem but it is too slow. Instead of sending the problem all the way to a faraway server (the cloud), your phone looks around for a nearby laptop or tablet that can help. This “looking for nearby help” is called cyber-foraging. It is faster because the helper is close, and it saves your phone’s battery because it does not have to do all the hard work itself. Caching is like keeping a copy of answers you already got, so you do not have to ask again.

15.8 Prerequisites

This section: Prerequisites

Before diving into this chapter, you should be familiar with:

15.9 Cyber-Foraging Overview

This section: Cyber-Foraging Overview — Cyber-foraging extends edge computing concepts by enabling resource-constrained mobile devices to opportunistically discover and offload computation to nearby devices (surrogates).

Cyber-foraging extends edge computing concepts by enabling resource-constrained mobile devices to opportunistically discover and offload computation to nearby devices (surrogates).

15.10 What is Cyber-Foraging?

This section: What is Cyber-Foraging? — Definition: Cyber-foraging is the practice of augmenting the computing capabilities of wireless mobile computers by dynamically discovering and leveraging nearby computational resources.

Definition: Cyber-foraging is the practice of augmenting the computing capabilities of wireless mobile computers by dynamically discovering and leveraging nearby computational resources.

Core Concept: Instead of relying on fixed infrastructure (cloudlets, fog nodes), mobile devices scavenge for computational resources in their environment — nearby smartphones, laptops, vehicles, or IoT gateways.

Key Characteristics:

  • Opportunistic: Uses whatever resources are available nearby
  • Dynamic: Adapts to changing network topology and device availability
  • Heterogeneous: Works across diverse device types with varying capabilities
  • Autonomous: Devices make independent decisions about offloading

15.11 Cyber-Foraging What Where When

This section: Cyber-Foraging What Where When

Effective cyber-foraging requires answering three fundamental questions:

15.12 Continue to the Next Part

This section: Continue to the Next Part — Carry this evidence into Edge Cyber-Foraging: Cost and Energy Calculations, which begins with Putting Numbers to It.

Carry this evidence into Edge Cyber-Foraging: Cost and Energy Calculations, which begins with Putting Numbers to It.

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