The document discusses 6LoWPAN (IPv6 over Low-Power Wireless Personal Area Networks), which allows IP networking for small, low-power devices. It describes how 6LoWPAN compresses IPv6 headers to reduce overhead and fragments packets to meet small MTU sizes. 6LoWPAN networks use an edge router to connect to the wider IP network and support two routing modes: route-over and mesh-under. The document also discusses related topics like CoAP, MQTT, and publish/subscribe messaging.

1. 6LowPAN etc

2. Non-IP Based WPAN
 WPAN Networks have adopted protocols that
are typically not TCP/IP.
 Non-IP communication systems are optimal as
for cost and energy
 IEEE 802.15: Wireless personal area network
definitions
 IEEE 802.15.1: Original foundation of the
Bluetooth PAN

3. Other Standards
 IEEE 802.15.2: Coexistence specifications for WPAN and WLAN
for Bluetooth
 IEEE 802.15.3: High data rate (55 Mbps+) on WPAN for
multimedia
 IEEE 802.15.3c: High-Speed (>1 GBps) using mm-wave
(millimeter wave) technology
 IEEE 802.15.4: Low data rate, simple, simple design, multi-year
battery life specifications (Zigbee)
 IEEE 802.15.5: Mesh networking
 IEEE 802.15.6: Body area networking for medical and
entertainment

4. IP-based WPAN
 The protocol stacks for Bluetooth, Zigbee, and
Z-Wave have similarities to a true TCP/IP
protocol but don't inherently communicate over
TCP/IP.
 There are adaptions of IP on Zigbee (using
Zigbee-IP) and IP over Bluetooth (using
Internet Protocol Support Profile (IPSP) to
support 6LoWPAN) that do exist.

5. IPv6 Header Format
• Version field for version number 0110
• Traffic class to support differentiated services
• Flow: sequence of packets from particular source to particular
destination for which source requires special handling
Version Traffic Class Flow Label
Payload Length Next Header Hop Limit
Source Address
Destination Address
0 4 12 16 24 31

6. IPv6 Header Format
• Payload length: length of data excluding header, up to 65535 B
• Next header: type of extension header that follows basic header
• Hop limit: # hops packet can travel before being dropped by a router
Version Traffic Class Flow Label
Payload Length Next Header Hop Limit
Source Address
Destination Address
0 4 12 16 24 31

7. IPv6 Datagram

8. IPv6 Address Generation Through
DHCPv6 or SAA
 Stateless Address Autoconfiguration (SAA) is a
distributed mechanism that allows devices to obtain a
unique unicast IPv6 address that serves for proper
routing of datagrams.
 A device relying on SSA dynamically generates its
IPv6 address by combining its 64-bit Interface
Identifier (IID) with the router supplied prefix.
 The IID is derived from the device link layer address
and depends, therefore, on the link layer technology in
use.

9. 6LoWPAN
 Purpose to allow IP networking over low-power
RF devices that are power and space
constrained and do not need high bandwidth
services.
 Protocol can be used with other WPAN
communications such as IEEE 802.15.4 as well
as Bluetooth, sub-1GHz RF protocols, and
power line controller (PLC).

10. IPv6 over Low power Wireless Personal
Area Networks (6LoWPAN )
 IPv6 header field and the protocol itself is unsuitable for IoT
applications
 All devices in a WPAN have IPv6 addresses that share the
same prefix.
 The prefix and an IID that are derived via SAA from link layer
addresses and edge router parameters received in 6LoWPAN
Neighbor Discovery (ND) RA messages.
 6LoWPAN ND messages are ICMPv6 ND messages that are
exchanged in the context of 6LoWPAN and have been
optimized to work in WPANs as per IETF RFC 6775.

11. WPAN Types
 There are three types of WPANs;
1) Simple WPANs that have connectivity to the IP
core by means of edge routers,
2) Ad hoc WPANs that locally connect devices and
have no access to the IP core, and
3) Extended WPANs that have connectivity to the IP
code by means of several edge routers along a
backbone link.

12. Adopting IPv6 into IoT Systems
 Adopting IPv6 in constrained environments
through 6LoWPAN introduces:
 packet fragmentation (into small link-layer
frames) and compression at the transmitter;
 fragment reassembly (from small link-layer
frames) and decompression at the receiver.

13. Effect of Small Size Packets
 In 6LoWPANs, fragmentation can increase the probability of
packet delivery failure.
 Given the small packet size of LoWPANs, applications must send
small amounts of data:
 Less data ⇒ fewer fragments to be sent ⇒ lower energy
consumption (CPU/TX/RX);
 Less data ⇒ fewer fragments to be sent ⇒ lower packet loss
probability.
 Due to the limited capabilities of objects in the IoT, the distinction
among the different layers of the protocol stack is not as strong as
in the traditional Internet.

14. 6LoWPAN
 In an effort to bring IP addressability to the
smallest and most resource-constrained devices,
the concept of 6LoWPAN was formed in 2005.
 A working group formalized the design in the
IETF under the specification RFC 4944 and
later updated with RFC 6282 to address header
compression and RFC 6775 for neighbor
discovery.

15. 6LoWPAN
 6LoWPAN networks are mesh networks residing on the
periphery of larger networks.
 An Edge Router resides in between the access and core
networks and plays the role of a traditional IoT gateway
and relay device.
 Edge Router handles traffic in and out of the WPAN by
performing 6LoWPAN adaptation, ND for interaction
with devices on the same link and other types of
operations like IPv4-to-IPv6 translations for
communication with other entities in the IP core.

16. 6LoWPAN Architecture

17. Edge Router
 Performs compression of IPv6 headers by reducing a
40-byte IPv6 header and 8-byte UDP headers for
efficiency in a sensor network.
 A typical IPv6 header can compress to 2 to 20-bytes.
 Initiates the 6LoWPAN network and Exchanges data
between devices on the 6LoWPAN network.
 Form 6LoWPAN mesh networks on larger traditional
network perimeters.
 They can also broker exchanges between IPV6 and
IPV4 if necessary.

18. Node Characteristics in 6LoWPAN
 All nodes within a 6LoWPAN network share the same
IPv6 prefix that the edge router establishes.
 Nodes will register with the edge routers as part of
the ND phase.
 ND controls how hosts and routers in the local
6LoWPAN mesh will interact with each other.
 Multi-homing allows for multiple 6LoWPAN edge
routers to manage a network

19. Nodes in 6LoWPAN Mesh
 Nodes are free to move and reorganize/reassemble in a
mesh.
 A node can move and associate with a different edge
router in a multi-home scenario or even move between
different 6LoWPAN meshes.
 When such topology change occurs, the IPv6 address of
the associated nodes also change.
 In an ad hoc mesh without an edge router, a 6LoWPAN
router node could manage a 6LoWPAN mesh.

20. Other Nodes in 6LoWPAN
 Devices in a WPAN can behave like either hosts or
routers depending on source and destination
addresses of the datagrams.
 Router nodes: These nodes forward data from one
6LoWPAN mesh node to another.
 Routers can also communicate outward to the WAN
and internet.
 Host nodes: Hosts in the mesh network cannot route
data and are simply endpoints consuming or
producing data. Hosts sleep & occasionally wake to
produce data or receive data cached by their parent

21. 6LoWPAN Stack and Translation

22. An Example end-to-end IP network that combines a traditional IPv6
core with an 6LoWPAN access

23. Addresses
 Most link layer IoT technologies like IEEE 802.15.4
support 64-bit MAC addresses and configurable, 8-bit
or 16-bit short addresses typically assigned by the
PAN coordinator.
 In the context of 6LoWPAN either one of these types
of addresses can be used to form the 64-bit IIDs.
 Edge router exchanges 6LoWPAN ND messages that
not only support SAA but also enable it to keep track
of all devices in the link.
 End devices can behave like routers or hosts
depending on their location and their traffic

24. Addresses
 End devices do not have direct connectivity to the edge
router and rely on mesh routing to reach it.
 Bootstrapping phase starts when the edge router begins
to advertise the 2001:11::/64 prefix to the devices by
means of 6LoWPAN ND RA messages.
 Devices use this prefix and their own IID derived from
the 64-bit IEEE 802.15.4 MAC address to generate IPv6
addresses.
 Devices, also relying on 6LoWPAN ND, register with the
edge router and receive a 16-bit IID that is combined
with the prefix to generate a less complex IPv6 address.

25. 6LoWPAN Adaptation Layer
 6LoWPAN standard provides header compression to
reduce the transmission overhead, fragmentation to
meet the IPv6 MTU requirement, and forwarding to
link-layer to support multi-hop delivery.
 Constrained device characteristics necessitate an
adaptation layer in 6LoWPAN protocol stack that fits
IPv6 packets to the IEEE 802.15.4 specifications.

26. 6LoWPAN Adaptation Layer
 6LoWPAN provides an adaptation layer within layer
three (network layer) and on top of layer two (data
link layer).
 This adaptation layer is defined by the IETF.
 6LoWPAN adaptation layer provides reliability by
means of error detection and correction.
 The adaptation layer must also support security
through encryption and authentication.

27. IPv6 Encapsulation/Routing

28. Route-over Network
 In a route-over topology, networks will incur the
charge of forwarding packets up to layer three
(network layer) of the stack.
 Route-over schemes manage routes at an IP level.
 Each hop represents one IP router.
 A route-over network implies that every router node
is equally capable and can perform the larger set of
functions as a normal IP router, such as duplicate
address detection.

29. Route-over Network...
 When 6LoWPAN is in place, communication between
devices is by means of capillary networking where
devices acting as routers have only one interface.
 Datagrams enter the router and leave the router on
the same interface.
 Not all devices on a single link can talk to each due to
the power limitations that prevent long distance radio
transmissions.
 6LoWPAN layer should decompress IPv6 addresses
that are used for routing.

30. Route-over Network
 RFC 6550 formally defines the route-over protocol
RPL (ripple).
 RPL provides multipoint-to-point communication (where
traffic from devices in a mesh communicate to a central
server on the internet) and point-to-multipoint
communication (central service to the devices in the
mesh).
 Storing vs Non-storing network

31. 6LoWPAN route-over

32. IPv6 Routing

33. Mesh Forwarding to the 6LoWPAN
Adaptation Layer (Mesh Under)
 The alternative to route-over routing is to rely on the link layer to
perform multihop frame mesh forwarding and enable local link
connectivity.
 The link layer keeps track of source and destination MAC
addresses for immediate hop communication but also original
source and destination MAC addresses for end-to-end support.
 In the context of IEEE 802.15.4, mesh forwarding is introduced
as part of IEEE 802.15.5.
 Link layer mesh forwarding is invisible to both 6LoWPAN and
IPv6.

34. Mesh-under Network
 In a mesh-under topology, routing is transparent and
assumes a single IP subnet representing the entirety
of the mesh.
 A message is broadcast in a single domain and is sent
to all devices in the mesh.
 This generates considerable traffic.
 Mesh-under routing will move from hop to hop in the
mesh but only forward packets up to layer two (data
link layer) of the stack.
 IEEE 802.15.4 handles all the routing for each hop in
layer two.

35. Link layer mesh forwarding

36. Mesh-under Network
 Here, 6LoWPAN keeps track of original source
and destination MAC addresses since the link
layer keeps tracks of source and destination
MAC addresses for immediate hop
communication.

37. Mesh-under Network
 Essentially at every single hop source and destination
MAC addresses are overwritten at the link layer by
means of the original source and destination
addresses carried in the 6LoWPAN mesh header.
 Knowing source, destination, original, andfinal MAC
addresses is not only needed for mesh forwarding but
also for other services provided by 6LoWPAN like
fragmentation and reassembly

38. 6LoWPAN Mesh Forwarding example

39. Mesh Header
 The header defines two 1-bit fields, O and F that,
respectively, indicate whether the original and final
MAC address is 16-bit PAN coordinator assigned or 64-
bit based.
 Since the mesh header carries all information needed
for forwarding, it is the very first header included in a
6LoWPAN datagram.

40. Mesh Header
 The header also includes a hops left field that indicates
how many times the packet can be forwarded before it
is dropped by the network.
 As the datagram traverses a network, and it is
forwarded by different devices acting as routers, this
counter is decremented.

41. 6LoWPAN on Other LL Technologies
 6LoWPAN requires that link layer protocols support
framing, unicast transmission and unique addresses that
can be used, in turn, to derive unique IPv6 addresses by
means of SAA.
 Because IPv6 fragments cannot be smaller than 1280
bytes, 6LoWPAN performs its own fragmentation to adapt
datagram transmission to link layer mechanisms with
small MTUs.
 It is therefore desirable for link layer frames to be as large
as possible with payloads of at least 60 bytes to minimize
the number of fragments that 6LoWPAN needs to track.

42. 6LoWPAN on Other LL Technologies
 For fixed network packet loss, it is always good to
minimize the number of fragments per datagram
since the more fragments the higher the probability
that a datagram will get dropped by the network.
 Also, 6LoWPAN compression can be used to
efficiently compress IPv6 and UDP headers in order
to maximize link layer payload size and therefore
minimize the number of fragments per datagram.

43. IETF CoRE (Constrained RESTful
Environments) Working Group (WG)
 Chartered to provide a framework for RESTful
applications in constrained IP networks.
 CoAP we know is used to let constrained devices
communicate with any node, either on the same
network or on the Internet, and provides a mapping
to HTTP REST APIs.
 CoAP also provides create-read-update-delete
(CRUD) primitives for resources of constrained
devices and pub/sub communication capabilities.

44. CoAP Observe Option - Recap
 CoAP Observe option is used in GET requests
in order to let the client register its interest in
the resource.
 The server then sends “unsolicited” responses
back to the client, echoing the token it specified
in the GET request
 Server also reports an Observe option with a
sequence number used for reordering purposes.

45. Message Queue Telemetry Transport
 MQTT is a lightweight broker-based
publish/subscribe application protocol that
provides session layer functionality.
 MQTT was developed and designed by IBM in
1999 for low transmission rate constrained
devices.
 It can be used in scenarios where two-way
communications between endpoints operating in
unreliable networks must occur.

46. Publish/subscribe
 Publish/subscribe, also known as pub/sub, is a
way to decouple a client transmitting a message
from another client receiving a message.
 Unlike a traditional client-server model, the
clients are not aware of any physical identifiers
such as the IP address or port.
 MQTT is a pub/sub architecture, but is not a
message queue

47. MQTT
 According to the pub/sub model, in MQTT,
messages are published to a shared topic space
inside the broker.
 Topics are used as filters on the message
stream from all publishers to the broker.
 MQTT supports hierarchical topics in the form
of a topic/sub-topic/sub-sub-topic path.

48. MQTT Broker
 A client transmitting a message is called a publisher;
a client receiving a message is called a subscriber.
 In the center is an MQTT broker who has the
responsibility of connecting clients and filtering data.
 In MQTT, the broker applies the subscription filters
to the message stream it receives in order to
efficiently determine to which clients a message
should be dispatched.

49. MQTT Broker

50. Matching the Condition Through Filter
 Messages are delivered to all clients that have
subscribed with a matching topic filter.
 This means that a single client can receive
messages coming from multiple publishers.
 The matching condition is applied to the topic’s
hierarchy, so it possible to subscribe to just a
portion of the topic.

51. Filters in Pub/Sub
 Subject filtering: By design, clients subscribe to topics and certain
topic branches and do not receive more data than they want.
 Each published message must contain a topic and the broker is
responsible for either re-broadcasting that message to subscribed
clients or ignoring it.
 Content filtering: Brokers have the ability to inspect and filter
published data. Thus, any data not encrypted can be managed by
the broker before being stored or published to other clients.
 Type filtering: A client listening to a subscribed data stream can
apply their own filters as well. Incoming data can be parsed and the
data stream either processed further or ignored.