965  6LoWPAN Overview: IPv6 for Constrained Networks

965.1 Learning Objectives

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

  • Explain 6LoWPAN’s Purpose: Describe how 6LoWPAN enables IPv6 over IEEE 802.15.4 networks
  • Identify the Core Challenge: Understand the size mismatch between IPv6 packets and 802.15.4 frames
  • Describe Key Solutions: Explain header compression and fragmentation at a high level
  • Recognize Use Cases: Identify scenarios where 6LoWPAN is the right protocol choice
ImportantThe Challenge: IPv6 Headers Don’t Fit in 802.15.4 Frames

The Problem: There’s a fundamental mismatch between Internet and IoT radio standards:

  • IPv6 header: 40 bytes minimum (fixed by standard)
  • UDP header: 8 bytes
  • 802.15.4 frame: 127 bytes maximum (only ~102 bytes after MAC headers)
  • Available for payload: 102 - 40 - 8 = 54 bytes (barely enough for sensor data!)

Why This Is Hard:

  • Can’t change IPv6—it’s a global Internet standard
  • Can’t change 802.15.4—it’s a hardware limitation
  • Fragmentation wastes bandwidth and drains batteries
  • Need end-to-end IP addressing for seamless IoT integration

The Solution: 6LoWPAN provides an adaptation layer with intelligent header compression (IPHC) that reduces 40-byte IPv6 headers to just 2-7 bytes, plus fragmentation support for larger payloads.

965.2 Prerequisites

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

965.3 Getting Started: For Beginners

TipNew to 6LoWPAN? Start Here!

The name “6LoWPAN” might seem intimidating, but the concept is straightforward once you understand the problem it solves.

Simple Analogy: 6LoWPAN is like a translator that fits full IPv6 internet messages into tiny wireless packets.

Think of it this way: You want to send a detailed letter (IPv6 packet) through a very small mail slot (802.15.4 radio). 6LoWPAN is the smart postal service that:

  • Removes unnecessary words from your letter (header compression: 40 bytes to 2-6 bytes)
  • Splits long letters into smaller envelopes if needed (fragmentation)
  • Reassembles everything perfectly at the destination
  • Makes it possible to connect billions of sensors directly to the internet!

Why this matters: Without 6LoWPAN, your tiny sensor couldn’t speak internet language. With it, every sensor gets its own IPv6 address and can talk directly to cloud servers anywhere in the world.

Key Terms You’ll Learn:

  • IPHC Compression: Intelligent compression that reduces 40-byte IPv6 headers to 2-6 bytes (85-95% reduction)
  • Fragmentation: Splitting large IPv6 packets (up to 1280 bytes) into tiny 102-byte radio frames
  • Mesh Addressing: How sensors find routes through multi-hop networks
  • Border Router: The gateway that connects your sensor network to the internet

965.3.1 Breaking Down the Name

6LoWPAN = IPv6 over Low-Power Wireless Personal Area Networks

Let’s decode each part:

Part Meaning Why It Matters
IPv6 Internet Protocol version 6 The language of the internet
Low-Power Battery-operated devices Sensors, wearables, monitors
Wireless No cables Radio communication
PAN Personal Area Network Short-range network (~10-100m)

In simple terms: 6LoWPAN lets tiny, battery-powered sensors speak the same language as the internet.

965.4 What is 6LoWPAN?

TipDefinition

6LoWPAN (IPv6 over Low-Power Wireless Personal Area Networks) is an adaptation layer that enables IPv6 packets to be carried over IEEE 802.15.4 networks. It provides header compression, fragmentation, and forwarding to make the full internet protocol stack work on constrained devices with limited memory, processing power, and battery life.

Key Characteristics:

  • Standard: RFC 6282, RFC 4944, RFC 6775
  • Physical Layer: IEEE 802.15.4 (Zigbee, Thread use this too)
  • IP Support: Full IPv6 (not IPv4)
  • Header Compression: Up to 95% reduction in overhead
  • MTU: 1280 bytes (IPv6 minimum) over 127-byte 802.15.4 frames
  • Addressing: Global IPv6 addresses for every sensor
Table 965.1: 6LoWPAN technology characteristics and capabilities {#tbl-6lowpan-summary}

965.5 6LoWPAN Technology Summary

Property Details
Name 6LoWPAN
Standard protocol is based on IEEE802.15.4
Designed for Extends the use of Internet Protocol for low power devices with limited processing capabilities in a Personal Area Network (PAN)
Connection range 10s (tens) of metres
Data rate Maximum data rate of 250kbps
Example Smart meters in a small network

965.6 The Problem 6LoWPAN Solves

6LoWPAN protocol architecture showing the adaptation layer that bridges IPv6 networking with IEEE 802.15.4 low-power wireless networks, enabling header compression and fragmentation for constrained IoT devices.

6LoWPAN Protocol Overview
Figure 965.1: Source: CP IoT System Design Guide, Chapter 4 - Networking Protocols

Without 6LoWPAN:

  • IPv6 header: 40 bytes
  • UDP header: 8 bytes
  • Total overhead: 48 bytes
  • 802.15.4 payload: ~102 bytes
  • Usable data: Only 54 bytes! (53% overhead!)

With 6LoWPAN:

  • Compressed IPv6 header: 2-7 bytes (typical)
  • Compressed UDP header: 4 bytes
  • Total overhead: 6-11 bytes
  • Usable data: 91-96 bytes (94% efficient!)
NoteWhy IPv6, Not IPv4?

IPv6 is essential for IoT because:

  • Abundant addresses: 340 undecillion (enough for every sensor)
  • No NAT: Direct end-to-end connectivity
  • Auto-configuration: Stateless address autoconfiguration (SLAAC)
  • Built-in security: IPsec mandatory in IPv6
  • Future-proof: IPv4 exhausted, IPv6 is the future

6LoWPAN doesn’t support IPv4—it’s IPv6-only by design.

965.7 6LoWPAN Architecture Overview

965.7.1 Protocol Stack

6LoWPAN header formats showing dispatch byte patterns, mesh addressing header, fragmentation header, and IPHC compressed header structures

6LoWPAN header formats
Figure 965.2: 6LoWPAN encapsulation header formats for adaptation layer

6LoWPAN sits between IPv6 and IEEE 802.15.4:

  • Above: Standard IPv6 stack (applications don’t know about 6LoWPAN)
  • Below: IEEE 802.15.4 radio (PHY/MAC layers)
  • Transparent: Appears as regular IPv6 to upper layers

965.7.2 Network Topology

Device Roles:

  1. Border Router: Gateway between 6LoWPAN and regular IPv6 internet
  2. Router: Forwards packets, extends range (similar to Zigbee routers)
  3. Host: End device (sensor/actuator), may sleep to save power

965.7.3 Two Key Techniques

1. Header Compression (IPHC)

6LoWPAN uses IP Header Compression to reduce the 40-byte IPv6 header to as little as 2 bytes:

  • Version, Traffic Class, Flow Label: Often elided (always 6, usually 0)
  • Payload Length: Derived from 802.15.4 frame size
  • Hop Limit: Compressed to 2 bits for common values (1, 64, 255)
  • Addresses: Context-based compression using link-layer addresses

2. Fragmentation and Reassembly

When packets exceed 102 bytes:

  • Split into multiple 802.15.4 frames
  • Each fragment carries a tag for reassembly
  • Receiver buffers fragments until complete

Geometric diagram of 6LoWPAN fragmentation header structure showing dispatch type, datagram size, tag, and offset fields

6LoWPAN Fragment Header
Figure 965.3: 6LoWPAN fragmentation headers track datagram size, unique tag for reassembly, and offset for each fragment’s position in the original IPv6 packet.

965.8 Real-World Examples

Thread Smart Home Protocol uses 6LoWPAN:

The smart light has its own IPv6 address and can be controlled from anywhere in the world!

Industrial Sensors:

  • Factory sensors sending data to cloud
  • Each sensor directly addressable via IPv6
  • No proprietary gateways needed

965.9 Knowledge Check

Question: Why does 6LoWPAN support IPv6 exclusively rather than IPv4?

Explanation: 6LoWPAN chose IPv6 because: (1) Address space: IPv6’s 340 undecillion addresses mean every sensor can have a globally unique address—no NAT translation needed. (2) Auto-configuration: SLAAC allows sensors to self-configure addresses from router advertisements without DHCP. (3) Built-in security: IPsec is mandatory in IPv6. (4) Future-proof: IPv4 is exhausted.

The Problem (2005): The IEEE 802.15.4 standard provided an excellent low-power radio layer for wireless sensor networks, but there was a fundamental mismatch with Internet protocols. IPv6 headers are 40 bytes fixed, but 802.15.4 frames max out at 127 bytes. Running native IP over WSN radios seemed impossible.

The 6LoWPAN Solution (2007): RFC 4944 introduced the adaptation layer concept with three key innovations: (1) header compression, (2) fragmentation/reassembly, and (3) mesh addressing. RFC 6282 (2011) improved compression with IPHC, achieving 2-byte headers in the best case.

The Routing Layer (2012): RFC 6550 defined RPL (Routing Protocol for Low-Power and Lossy Networks), purpose-built for constrained devices.

Today’s Stack: 802.15.4 (physical/MAC) -> 6LoWPAN (adaptation) -> RPL (routing) -> UDP (transport) -> CoAP (application). Thread and Matter build on this foundation.

965.10 Summary

This chapter introduced 6LoWPAN (IPv6 over Low-Power Wireless Personal Area Networks):

  • 6LoWPAN bridges IPv6 and constrained networks by providing an adaptation layer over IEEE 802.15.4
  • The core challenge is the size mismatch: IPv6 requires 40-byte headers, but 802.15.4 frames only have ~102 bytes of usable payload
  • Header compression (IPHC) reduces IPv6 headers from 40 bytes to 2-7 bytes by eliding predictable fields
  • Fragmentation allows IPv6’s 1280-byte minimum MTU to work over tiny 802.15.4 frames
  • End-to-end IP connectivity means every sensor gets a globally routable IPv6 address

965.11 What’s Next

Now that you understand the 6LoWPAN overview, continue to: