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SixLoWPAN

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6LoWPAN

Overview

6LoWPAN (IPv6 over Low-Power Wireless Personal Area Networks) is an adaptation layer that enables IPv6 packets to be sent over IEEE 802.15.4 networks. It provides header compression, fragmentation, and mesh-under routing to bring native IP connectivity to constrained IoT devices.

1. Theory & Fundamentals

  • Adaptation layer between IPv6 and IEEE 802.15.4 MAC
  • Compresses 40-byte IPv6 header + 8-byte UDP header to 2–7 bytes (IPHC)
  • Fragments large IPv6 packets into 802.15.4 frames (127-byte MTU)
  • Enables standard IP protocols (UDP, TCP, CoAP, DNS) on constrained devices
  • Used by: Thread, Zigbee IP, Wi-SUN, and industrial mesh networks
  • RFC 4944 original; RFC 6282 IPHC compression; RFC 6775 ND optimization

2. Frame / Packet Structure

6LoWPAN Dispatch byte:
  00xxxxxx = Not 6LoWPAN
  01000001 = Uncompressed IPv6
  011xxxxx = LOWPAN_IPHC (compressed)
  1110xxxx = Mesh addressing
  11000xxx = FRAG1 (first fragment)
  11100xxx = FRAGN (subsequent fragment)

IPHC compression:
  Original IPv6 = 40 bytes → Compressed = 2–7 bytes
  Compress: Version, Traffic Class, Flow Label, Next Header, Hop Limit
  Source/Dest address: Inline, 64-bit, 16-bit, or elided (link-local)

Fragment header:
  Dispatch | Datagram Size(11b) | Datagram Tag(16b) | [Offset(8b)]

3. Protocol Mechanics

  • Mesh-under vs Route-over: Mesh-under handles routing at 802.15.4 level; Route-over uses IPv6
  • ND (Neighbor Discovery): RFC 6775 optimizes IPv6 ND for 6LoWPAN
  • Address registration: Devices register with Border Router
  • RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks (RFC 6550)
  • DODAG: RPL builds a destination-oriented directed acyclic graph

4. Hardware Implementation

  • OpenThread includes 6LoWPAN implementation
  • Contiki-NG: Full 6LoWPAN/RPL/CoAP stack for constrained devices
  • Zephyr RTOS: Built-in 6LoWPAN support
  • Border router: Linux + wpantund + 6LoWPAN driver for IEEE 802.15.4 interface
  • Hardware: Same as Zigbee (nRF52840, CC2652, EFR32)

5. Register-Level / Configuration

// Contiki-NG CoAP over 6LoWPAN
#include "net/app-layer/coap/coap.h"
COAP_RESOURCE(temp_resource, "title=\"Temperature\"",
    temperature_get, NULL, NULL, NULL);
// In temperature_get handler:
void temperature_get(coap_message_t *req, coap_message_t *res, ...) {
    char buf[16];
    int len = snprintf(buf, sizeof(buf), "%d.%02d", temp_int, temp_frac);
    coap_set_payload(res, (uint8_t*)buf, len);
}

6. Driver / Software Development

  • Initialize hardware peripheral or SoC block
  • Implement send/receive with interrupt or DMA
  • Handle errors: timeout, CRC, NAK, bus-off
  • Use circular buffers for RX data flow
  • Implement retry logic for reliability

7. Debugging & Testing

  • Wireshark with 802.15.4 capture + 6LoWPAN dissector
  • Contiki-NG cooja simulator: Run network in simulation
  • Common issues: IPv6 header not compressible (check IPHC settings); fragmentation reassembly timeout; RPL routing loops
  • 'ping6' from border router to verify connectivity

8. Real-World Applications

  1. Thread smart home devices
  2. Wi-SUN field area networks (smart grid)
  3. Industrial 802.15.4g mesh networks
  4. Building automation (KNX IPv6)
  5. Medical body area networks

9. Advanced Topics & Edge Cases

  • SCHC (Static Context Header Compression): Further compresses 6LoWPAN headers for LPWAN
  • Wi-SUN: Uses 6LoWPAN on sub-GHz 802.15.4g for grid infrastructure
  • RPL vs AODV: RPL is tree-based; AODV is on-demand; RPL preferred for 6LoWPAN
  • IPv6 multicast: Compressed in 6LoWPAN to save bandwidth

10. Standards & Variants

Aspect 6LoWPAN Native IPv6 ZigBee
Header 2–7B 40B Custom
IP Native Native No
MTU 127B 1280B 127B
Stack Adaptation Direct Custom

💡 Practical Examples

Ex 1: IPv6 ping over 6LoWPAN

Border router: ping6 fd00::1 where fd00::1 is node's IPv6 address.

Ex 2: CoAP GET resource

coap-client -m get coap://[fd00::1]/temperature  # Returns "23.50"

Ex 3: RPL routing

Nodes auto-form DODAG with border router as root; RPL DIO/DAO messages establish routes.

🧪 Practice Questions

Beginner

  1. What does 6LoWPAN stand for?
  2. Why is header compression necessary in 6LoWPAN?
  3. What is the MTU of IEEE 802.15.4?
  4. What routing protocol does 6LoWPAN commonly use?
  5. What is a Border Router in a 6LoWPAN network?

Intermediate

  1. Explain 6LoWPAN IPHC header compression.
  2. How does 6LoWPAN handle fragmentation of large IPv6 packets?
  3. Implement a CoAP sensor resource on Contiki-NG.
  4. What is RPL DODAG and how is it formed?
  5. How does 6LoWPAN handle IPv6 neighbor discovery?

Advanced

  1. Design a 100-node 6LoWPAN mesh using RPL.
  2. Implement SCHC compression on top of 6LoWPAN for LoRaWAN.
  3. Build a 6LoWPAN border router with Linux and OpenThread.
  4. Analyze RPL convergence time after node failure.
  5. Debug 6LoWPAN fragmentation reassembly timeout issues.

Projects

  1. 6LoWPAN Sensor Net: 5 nodes with Contiki-NG, CoAP, RPL to border router.
  2. Border Router: Raspberry Pi + USB 802.15.4 dongle, route IPv6 to mesh.
  3. CoAP Dashboard: Periodic CoAP GET to all nodes, display on web UI.

Checklist

  • [ ] Explain 6LoWPAN layer and its role
  • [ ] Understand IPHC header compression format
  • [ ] Set up Contiki-NG or Zephyr with 6LoWPAN
  • [ ] Implement CoAP server over 6LoWPAN
  • [ ] Configure RPL for mesh routing
  • [ ] Set up 6LoWPAN border router
  • [ ] Debug with Wireshark 6LoWPAN dissector
  • [ ] Use Cooja simulator for network testing
  • [ ] Handle fragmentation correctly
  • [ ] Integrate with cloud via CoAP-HTTP proxy
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