UNIT-3 COMMUNICATION NETWORKING

IoT Access Technologies: Physical and MAC layers, topology and Security of
IEEE 802.15.4, 802.15.4g, 802.15.4e, 1901.2a, 802.11ah and LoRaWAN –
Network Layer: IP versions, Constrained Nodes and Constrained Networks –
Optimizing IP for IoT: From 6LoWPAN to 6Lo, Routing over Low Power and
Lossy Networks – Application Transport Methods: Supervisory Control and Data
Acquisition -Application Layer Protocols: CoAP and MQTT- Data aggregation &
dissemination.
What is communication networking?
The IoT processes data from the devices and communicates the information via
wired and wireless networks, including Ethernet, Wi-Fi, Bluetooth, 5G and LTE
cellular, radio frequency identification (RFID), and near
field communication (NFC). Typically, IoT devices connect to IoT gateways or
edge devices that collect data.
Communication and networking in IoT involves the following key points:
1. Data processing and communication: IoT devices process data and
communicate information via wired and wireless networks, including
Ethernet, Wi-Fi, Bluetooth, 5G, and cellular networks1.
2. IoT Network Protocols: Different protocols govern data exchange between
IoT devices2.
3. IoT network infrastructure: It enables devices to connect, communicate,
and exchange data securely3.
4. Unique identifiers (UIDs): These establish the context of a device within
the larger network, enabling communication
IoT access technologies:
IoT access technologies serve as the foundation for connecting devices to the
internet. These technologies enable seamless communication between IoT devices
and the cloud, facilitating data transfer and control.
They can be categorized into
 wired and
 wireless access technologies.
(i)Wired Access Technologies: Wired access technologies offer reliable and secure
connectivity for IoT devices. Ethernet, for instance, has been a longstanding wired
technology used in both industrial and residential settings. Power over Ethernet
(PoE) further enhances the capabilities of Ethernet by providing power alongside
data transmission. This section will explore the advantages and considerations of
wired access technologies.
(ii)Wireless Access Technologies: Wireless access technologies have gained
immense popularity due to their flexibility and scalability. Wi-Fi, Bluetooth, and
Zigbee are among the most widely used wireless technologies in the IoT
landscape. Each technology has its own strengths and limitations, making them
suitable for different IoT use cases. This section will discuss the key features and
applications of these wireless access technologies.
PHY Vs MAC in IoT networking
In the context of IoT (Internet of Things) networking, the PHY (Physical) layer
and MAC (Media Access Control) layer are two fundamental layers of the OSI
(Open Systems Interconnection) model that play crucial roles in enabling
communication between devices. They represent different layers of the
networking stack and serve distinct functions.
The PHY layer occupies the lowest layer-1 of OSI stack and handles the physical
aspects of communication. The MAC layer occupies the lowest layer-2 and
manages access to the communication medium and ensures efficient and secure
data transmission in IoT networks. Let us understand functions of phy and mac
layer before we explore difference between physical and mac layer.
What is PHY Layer
PHY is the short form of Physical Layer. It is the layer-1 in OSI stack. It
interfaces physical medium with MAC and upper layers. Physical medium can be
copper wire, fiber optic cable, twisted pair or even wireless channel.
Function : The PHY layer is the lowest layer in the OSI model and is responsible
for the physical transmission of raw bits over the communication medium.

Following are the key responsibilities of PHY layer :

➨It converts MAC layer format suitable to be transported over the medium.
➨Defines the characteristics of the physical medium, such as cables, wireless
channels, or optical fibers.
➨Converts digital data into analog signals for transmission and vice versa.
➨Incorporates modulation and demodulation functionalities which transforms bits
into symbols and vice versa.
➨Specifies the data transfer rate and the encoding scheme used for transmitting
data over the physical medium.
➨Provides error correction capability by using convolutional encoder or turbo
encoder at transmit end and suitable decoder at the receive end.
➨Describes the physical connectors, pinouts, and electrical properties required for
data transmission.
 There are different physical layers as per different wireless and wired
standards. The variation in physical layer depends on medium requirement and
system performance requirement (i.e. BER, SNR, spectral efficiency or
Bandwidth efficiency, power efficiency). Different PHY layers will have different
FEC configurations and modulation formats.
What is MAC Layer?
MAC is the short form of Medium Access Control Layer. It is the layer-2 in OSI
stack. It interfaces PHY layer and Upper layers (i.e. network and above).
Function: The MAC layer operates at a higher level than the PHY layer and is
responsible for managing access to the shared communication medium.

Following are the key responsibilities of MAC layer :

➨Addressing: Assigns unique MAC addresses to devices on the network for
identification. MAC Header is added at the beginning of IP packet for this
purpose.
➨Channel access: Controls how devices on the network gain access to the
communication channel, especially in shared or wireless environments.
CSMA/CD and CSMA/CA are examples of media access control protocols used
in Ethernet networks.
➨Frame formatting: Divides data into frames, adds addressing information,
control bits, and error-checking, creating a structured format for transmission.
CRC is added at the end of frame for error detection and retransmission (using
ARQ protocol).
➨Flow control: Manages the flow of data to ensure efficient communication
between devices. This is achieved by segmentation (at transmit end) and re-
assembly (at receive end).
Difference between PHY and MAC layer
Following table mentions difference between PHY and MAC layer.

Parameters PHY Layer MAC Layer

Layer position in
OSI stack Lowest layer (i.e. Layer-1) Higher layer (i.e. Layer-2)

Managing access to the

Major function Physical transmission of raw bits communication medium

"Frames" are constructed

for transmission including
Data format Deals with "bits" addressing information.

It interfaces with medium It interfaces with PHY

wired/wireless (RF) through layer at one end and
ADC/DAC at one end and MAC network layer at the other
Layer interaction layer at the other end. end.

Assigns unique MAC

Does not involve device addresses for device
Addressing addressing identification

PHY code which requires low

Implementation latency and high complexity runs MAC code runs on
perspective on FPGA processor

Data link layer or Medium

Other name Baseband or modem Access Control layer

Physical and mac layer implementation

The figure depicts hardware block diagram for PHY/MAC implementation for
wireless physical layer. In this example, PHY layer modules have been ported on
FPGA whereas MAC layer blocks have been ported on Intel Processor. PHY layer
interacts with wireless medium using radio frequency with the help of Maxim RF
board. Both PHY and RF are interfaced using DAC/ADC.
IEEE 802.15.4 Technology:
IEEE 802.15.4 is a low-cost, low-data-rate wireless access technology for devices
that are operated or work on batteries. This describes how low-rate wireless
personal area networks (LR-WPANs) function.
IEEE 802.15.4e:
802.15.4e for industrial applications and 802.15.4g for the smart utility networks
(SUN)
The 802.15.4e improves the old standard by introducing mechanisms such as
time slotted access, multichannel communication and channel hopping.
 IEEE 802.15.4e introduces the following general functional enhancements:
1. Low Energy (LE): This mechanism is intended for applications that can trade
latency for energy efficiency. It allows a node to operate with a very low duty
cycle.
2. Information Elements (IE) It is an extensible mechanism to exchange
information at the MAC sublayer.
3. Enhanced Beacons (EB): Enhanced Beacons are an extension of the 802.15.4
beacon frames and provide a greater flexibility. They allow to create application-
specific frames.
4. Multipurpose Frame: This mechanism provides a flexible frame format that can
address a number of MAC operations. It is based on IEs.
5. MAC Performance Metric: It is a mechanism to provide appropriate feedback
on the channel quality to the networking and upper layers, so that appropriate
decision can be taken.
6. Fast Association (FastA) The 802.15.4 association procedure introduces a
significant delay in order to save energy. For time-critical application latency has
priority over energy efficiency.
 IEEE 802.15.4e defines five new MAC behavior modes.
1. Time Slotted Channel Hopping (TSCH): It targets application domains such as
industrial automation and process control, providing support for multi-hop and
multichannel communications, through a TDMA approach.
2. Deterministic and Synchronous Multi-channel Extension (DSME): It is aimed
to support both industrial and commercial applications.
3. Low Latency Deterministic Network (LLDN): Designed for single-hop and
single channel networks
4. Radio Frequency Identification Blink (BLINK): It is intended for application
domains such as item/people identification, location and tracking.
 5. Asynchronous multi-channel adaptation (AMCA): It is targeted to application
domains where large deployments are required, such as smart utility networks,
infrastructure monitoring networks, and process control networks.
Properties:
1. Standardization and alliances: It specifies low-data-rate PHY and MAC layer
requirements for wireless personal area networks (WPAN).
IEEE 802.15. Protocol Stacks include:
 ZigBee: ZigBee is a Personal Area Network task group with a low rate task
group 4. It is a technology of home networking. ZigBee is a technological
standard created for controlling and sensing the network. As we know that
ZigBee is the Personal Area network of task group 4 so it is based on IEEE
802.15.4 and is created by Zigbee Alliance.
 6LoWPAN: The 6LoWPAN system is used for a variety of applications
including wireless sensor networks. This form of wireless sensor network
sends data as packets and uses IPv6 – providing the basis for the name –
IPv6 over Low power Wireless Personal Area Networks.
 ZigBee IP: Zigbee is a standards-based wireless technology that was
developed for low-cost and low-power wireless machine-to-machine
(M2M) and internet of things (IoT) networks.
 ISA100.11a: It is a mesh network that provides secure wireless
communication to process control.
 Wireless HART: It is also a wireless sensor network technology, that
makes use of time-synchronized and self-organizing architecture.
 Thread: Thread is an IPv6-based networking protocol for low-power
Internet of Things devices in IEEE 802.15. 4-2006 wireless mesh network.
Thread is independent.
2. Physical Layer: This standard enables a wide range of PHY options in ISM
bands, ranging from 2.4 GHz to sub-GHz frequencies. IEEE 802.15.4 enables
data transmission speeds of 20 kilobits per second, 40 kilobits per second, 100
kilobits per second, and 250 kilobits per second. The fundamental structure
assumes a 10-meter range and a data rate of 250 kilobits per second. To further
reduce power usage, even lower data rates are possible. IEEE 802.15.4 regulates
the RF transceiver and channel selection, and even some energy and signal
management features, at the physical layer. Based on the frequency range and data
performance needed, there are now six PHYs specified. Four of them employ
frequency hopping techniques known as Direct Sequence Spread Spectrum
(DSSS). Both PHY data service and management service share a single packet
structure so that they can maintain a common simple interface with MAC.
3. MAC layer: The MAC layer provides links to the PHY channel by determining
that devices in the same region will share the assigned frequencies. The
scheduling and routing of data packets are also managed at this layer. The
802.15.4 MAC layer is responsible for a number of functions like:
 Beaconing for devices that operate as controllers in a network.
 used to associate and dissociate PANs with the help of devices.
 The safety of the device.
 Consistent communication between two MAC devices that are in a peer-to-
peer relationship.
Several established frame types are used by the MAC layer to accomplish these
functions. In 802.15.4, there are four different types of MAC frames:
 frame of data
 Frame for a beacon
 Frame of acknowledgement
 Frame for MAC commands
4. Topology: Networks based on IEEE 802.15.4 can be developed in a star, peer-
to-peer, or mesh topology. Mesh networks connect a large number of nodes. This
enables nodes that would otherwise be out of range to interact with each other to
use intermediate nodes to relay data.
5. Security: For data security, the IEEE 802.15.4 standard employs the Advanced
Encryption Standard (AES) with a 128-bit key length as the basic encryption
technique. Activating such security measures for 802.15.4 significantly alters the
frame format and uses a few of the payloads. The very first phase in activating
AES encryption is to use the Security Enabled field in the Frame Control part of
the 802.15.4 header. For safety, this field is a single bit which is assigned to 1.
When this bit is set, by taking certain bytes from its Payload field, a field known
as the Auxiliary Security Header is formed following the Source Address field.
6. Competitive Technologies: The IEEE 802.15.4 PHY and MAC layers serve as
a basis for a variety of networking profiles that operate in different IoT access
scenarios. DASH7 is a competing radio technology with distinct PHY and MAC
layers.
The architecture of LR-WPAN Device:
IEEE 802.15.4
Advantages of IEEE 802.15.4:
IEEE 802.15.4 has the following advantages:
 cheap cost
 long battery life,
 Quick installation
 simple
 extensible protocol stack
Disadvantages of IEEE 802.15.4:
IEEE 802.15.4’s drawbacks include:
 IEEE 802.15.4 causes interference and multipath fading.
 doesn’t employ a frequency-hopping approach.
 unbounded latency
 interference susceptibility
Applications of IEEE 802.15.4:
IEEE 802.15.4 Applications:
 Wireless sensor networks in the industry
 Building and home automation
 Remote controllers and interacting toys
 Automotive networks.
1901.2a:
the majority of restricted network technologies are wireless, IEEE 1901.2a-2013
is a wired technology that updates the original IEEE 1901.2 standard. This is the
Narrow-band Power Line Communication standard (NB-PLC).
NB-PLC Scenarios :
NB-PLC is frequently used in the following scenarios as follows.
 Smart metering –
The NB-PLC can automate the reading of utility meters such as electric,
gas, and water meters.
 Distribution automation –
The NB-PLC may be used for distribution automation, which entails
monitoring and controlling all the power grid’s components.
 Public lighting –
It is a frequent application for NB-PLC, which includes lights seen in cities
and along roadways, highways, and public spaces like parks.
 Electric vehicle charging stations –
NB-PLC may be used to power charging stations for electric vehicles.
 Micro-grids –
NB-PLC may be used to create micro grids, which are small energy grids
that can run independently of the main grid.
 Renewable energy –
The NB-PLC may be utilized in solar, wind, hydropower, and geothermal
heat applications. There are several PLC standards, but the lack of a low-
frequency PLC solution prompted the creation of IEEE 1901.2a. Below 500
kHz.
Note :
Both continuous and direct current electric power lines are specified in IEEE
1901.2a. The data rate may be increased to 500 kbps. On terminals, the IEEE
1901.2a PHY and MAC layers can be blended with IEEE 802.15.4g/e, allowing
for a dual-PHY solution in some situations.
Features :
1. Standardization and Alliances –
Poor dependability, limited throughput, lack of management, and poor
compatibility affected the earliest generations of NB-PLC systems. As a
result, numerous organizations have developed their own generational
requirements. Orthogonal frequency-division multiplexing is used in the
current NB-PLC specifications (OFDM). Digital data is encoded using
OFDM on multiple carrier frequencies. IEEE 1901.2a was part of the Home
 Plug Netricity initiative, which was one of the key industry groups that
promoted the marketing and certification of PLC technology.

2. Physical Layer –
NB-PLC is defined for frequency bands from 3 to 500 kHz. IEEE 1901.2
working group has integrated support for all world regions in order to
develop a worldwide standard. IEEE 1901.2a supports the largest set of
coding and enables both robustness and throughput. Tone maps and
modulations for all bands, such as robust modulation (ROBO), differential
binary phase-shift keying (DBPSK), differential quadrature phase-shift
keying (DQPSK), differential 8-point phase shift keying (D8PSK), and
optionally 16 quadrature amplitude modulation (16QAM) for some bands,
are included in the standard.

3. MAC Layer –
The IEEE 1901.2a MAC frame format is related to the IEEE 802.15.4
MAC frame, however, it incorporates the most recent IEEE 802.15.4e-2012
amendment, allowing essential functionalities to be implemented.
Information elements are one of the important components that have been
moved over from IEEE 802.15.4e to IEEE 1901.2a. Additional features,
such as IE support, IEEE 802.15.9 Key Management Protocol, and SSID
are available. Segment Control is a field in IEEE 1901.2. This deals with
the segmentation or fragmentation of upper-layer packets that are bigger
than the MAC protocol data unit can carry (MPDU).

MAC Frame Format for IEEE 1901.2

Topology for IEEE 1901.2a :
IEEE 1901.2a scenarios and deployment topologies are based on physical power
lines. Signal transmission is limited by variables such as noise, interference,
distortion, and attenuation, just as it is with wireless technology. Because these
variables grow more prominent as distance increases, most NB-PLC
implementations have a mesh topology. Mesh networks provide the benefit of
allowing devices to relay traffic from other devices, allowing greater distances to
be separated. The IEEE 1901.2a standard allows any upper-layer protocol to be
used. As a result, IPv6 6LoWPAN and RPL IPv6 variants are supported. These
protocols allow mesh networks to be created over PLC using network layer
routing.
Security for IEEE 1901.2a :
IEEE 1901.2a security is identical to IEEE 802.15.4g security. AES is used for
encryption and authentication. Furthermore, IEEE 1901.2a is compatible with
IEEE 802.15.4g when it comes to supporting the IEEE 802.15.9 Key
Management Protocol. Among the distinctions are as follows.
 In all MAC frames carrying encrypted frame segments, the Security
Enabled A bit in the Frame Control field should be set.
 Data encryption should be performed before packet segmentation whether
it is necessary. The Segment Control field is not included in the input to the
encryption method during packet encryption.
 Data decryption occurs after packet reassembly on the recipient side.
 The ciphered payload plus the message integrity code (MIC) authentication
tag for non-segmented payloads make up the MAC payload when security
is enabled. The MIC only appears in the last packet (segment) if the
payload is segmented.
Competitive Technologies :
Two technologies compete against IEEE 1901.2a in the NB-PLC domain: G3-
PLC (formerly ITU G.9903) and PRIME (now ITU G.9904). Both of these
technologies were created with a single-use case in mind: smart metering
implementation across Europe using the CENELEC A band. IEEE 1901.2 is quite
close to G3-PLC. G3-PLC requires data link layer protocol choices for
bootstrapping and issuing device addresses, and it is incompatible with IEEE
802.15.4g/e and an end-to-end IPv6 paradigm, to name a few issues. PRIME is
more akin to an ATM system, with a Layer 7 protocol (DLMS/COSEM) running
directly on top of Layer 2. IP support necessitates the addition of Layer 3
protocols.
NETWORKLAYER

Constrained Nodes

In IoT solutions, different classes of devices coexist. Depending on

its functions in anetwork, “thing” architecture may or may not offer
similar characteristics compared to agenericPC orserver in an
ITenvironment.

Another limit is that this network protocol stack on an IoT node may
be required tocommunicate through an unreliable path. Even if a full IP
stack is available on the node, thiscauses problems such as limited or
unpredictable throughput and low convergence when
atopologychangeoccurs.

Finally, power consumption is a key characteristic of constrained

nodes. Many IoTdevices are battery powered, with lifetime battery
requirements varying from a few monthsto 10+ years. This drives the
selection of networking technologies since high- speed ones,such as
Ethernet, Wi-Fi, and cellular, are not (yet) capable of multi-year battery
life. Currentcapabilities practically allow less than a year for these
technologies on battery-powerednodes. Of course,power consumptionis
muchless of a concern on nodes that do notrequirebatteriesas anenergy
source.

The power consumption requirements on battery-powered

nodes impact communicationintervals. To help extend battery life,
one could enable a “low-power” mode
instead of
onethatis“alwayson.”Anotheroptionis“alwaysoff,”whichmeanscommunicati
onsareena bledonly whenneededtosenddata.

While it has been largely demonstrated that production IP stacks

perform well inconstrainednodes.IoTconstrainednodes canbeclassifiedas
follows:

 Devices that are very constrained in resources, may communicate

infrequently totransmit a few bytes, and may have limited security and
management
capabilities:ThisdrivestheneedfortheIPadaptationmodel,wherenodescommun
icatethroughgateways andproxies.
 Devices with enough power and capacities to implement a stripped-
down IP stackor non- IP stack: In this case, you may implement either an
optimized IP stack anddirectly communicate with application servers (adoption
model) or go for an IP ornon-IPstackandcommunicatethroughgatewaysandproxies
(adaptationmodel).
 Devices that are similar to generic PCs in terms of computing and power
resourcesbuthaveconstrainednetworkingcapacities,suchasbandwidth:T
hesenodesusuallyimplementafullIPstack(adoptionmodel),butnetworkdesignan
dapplication behaviorsmustcopewiththebandwidthconstraints.

The definition of constrained nodes is evolving. The costs of computing

power,
memory,storageresources,andpowerconsumptionaregenerallydecreasing.
Atthesame time,
networking technologies continue to improve and offer more bandwidth
and reliability. Inthefuture,the
pushtooptimizeIPforconstrainednodeswilllessenastechnologyimprovements
andcostd ecreasesaddressmanyofthesechallenges.

Constrained Networks

In the early years of the Internet, network bandwidth capacity was

restrained due totechnical limitations. Connections often depended on
low-speed modems for transferringdata. However, these low-speed
connections demonstrated that IP could runover low-bandwidth networks.
Buttoday,theevolution of networking has seen the emergence of high- speed
infrastructures. However, high-speed connections are not usable by some IoT
devices in thelast mile. The reasons include the implementation of
technologies with low bandwidth, limited distance and bandwidth due to
regulated transmit power, and lack of or limitednetworkservices.
When link layer characteristics that we take for granted are not
present, the networkis constrained. A constrained network can have high
latency and a high potential for packetloss. Constrained networks have
unique characteristics and requirements. In contrast withtypical IP
networks, where highly stable and fast links are available,
constrained networksarelimitedbylow-
power,lowbandwidthlinks(wirelessandwired).Theyoperatebetweena few
kbps and a few hundred kbps and may utilize a star, mesh, or combined
networktopologies,ensuring properoperations.

With a constrained network, in addition to limited bandwidth, it is

not unusual forthe packet deliveryrate (PDR) to oscillate between low and
high percentages. Large burstsof unpredictable errors and even loss of
connectivity at times may occur. These behaviourscan be observed on
both wireless and narrowband power-line communication links,
wherepacketdeliveryvariationmay fluctuategreatly
duringthecourseofaday.

Unstable link layer environments create other challenges in terms of

latency andcontrol plane reactivity. One of the golden rules in a
constrained network is to “underreactto failure.” Due to the low
bandwidth, a constrained network that overreacts can lead to
anetworkcollapse—whichmakes theexisting problemworse.

Control plane traffic must also be kept at a minimum; otherwise, it

consumes
thebandwidththatisneededbythedatatraffic.Finally,onehastoconsiderthepo
werconsum ption in battery-powered nodes.Any failure or verbose control
plane protocol mayreducethelifetimeofthebatteries.
 Tosummarize,constrainednodesandnetworksposemajorchallengesfor
IoTconn ectivity in the last mile. This in turn has led various standards
organizations to work onoptimizingprotocols forIoT.

IPVersions

For 20+years,
theIETFhasbeenworkingontransitioningtheInternetfromIPversion 4 to IP
version 6. The main driving force has been the lack of address space in
IPv4 asthe Internet has grown. IPv6 has a much larger range of addresses
that should not beexhausted for the foreseeable future. Today, both
versions of IP run over the Internet, butmosttrafficis still IPv4based.

While it may seem natural to base all IoT deployments on IPv6, you
must take intoaccount current infrastructures and their associated
lifecycle of solutions, protocols,
andproducts.IPv4isentrenchedinthesecurrentinfrastructures,andsosupportfo
ritisrequir ed in most cases. Therefore, the Internet of Things has to
follow a similar path as
theInternetitselfandsupportbothIPv4andIPv6versions concurrently.

Techniques such as tunnelling and translation need to be employed

in IoT solutionsto ensure interoperability between IPv4 and IPv6. A variety
of factors dictate whether IPv4,IPv6, or both can be used in an IoT
solution. Most often these factors include a legacyprotocol or technology
that supports only IPv4. Newer technologies and protocols almostalways
support both IP versions. The following are some of the main factors
applicable toIPv4andIPv6supportinanIoTsolution:

 ApplicationProtocol:IoT devicesimplementingEthernetorWi-Fi
interfacescancommunicate over both IPv4 and IPv6, but the application protocol
may dictate thechoice of the IP version. For example, SCADA protocols such as
DNP3/IP (IEEE 1815),Modbus TCP, or the IEC 60870-5-104 standards are specified
only for IPv4. So, thereare no known production implementations by
vendors of these protocols over
IPv6today.ForIoTdeviceswithapplicationprotocolsdefinedbytheIETF,suchasHT
TP/HTTPS, CoAP, MQTT, and XMPP, both IP versions are supported. The
selectionoftheIPversionisonly dependentontheimplementation.
 Cellular Provider and Technology: IoT devices with cellular modems are
dependenton the generation of the cellular technology as well as the data services
offered bythe provider. For the first three generations of data services—GPRS, Edge,
and 3G—
IPv4isthebaseprotocolversion.Consequently,ifIPv6isusedwiththesegenerations
, it must be tunneled over IPv4. On 4G/LTE networks, data services
canuseIPv4orIPv6as abaseprotocol,depending ontheprovider.
  SerialCommunications:Manylegacydevicesincertainindustries,suchasmanuf
acturing and utilities, communicate through serial lines. Data is transferredusing
either proprietary or standards based protocols, such as DNP3, Modbus, or
IEC60870-5-101. In the past, communicating this serial data over any sort of
distancecould be handled by an analog modem connection. However, as service
providersupport for analog line services has declined, the solution for
communicating withthese legacy devices has been to use local connections. To make
this work, youconnect the serial port of the legacy device to a nearby serial port
on a piece ofcommunications equipment, typically a router. This local router then
forwards theserial trafficover IP tothe central serverforprocessing. Encapsulation of
serialprotocols over IP leverages mechanisms such as raw socket TCP or UDP.
While rawsocket sessions can run over both IPv4 and IPv6, current
implementations are mostlyavailableforIPv4only.
 IPv6 Adaptation Layer: IPv6-only adaptation layers for some physical and data
linklayers for recently standardized IoT protocols support only IPv6. While the
mostcommonphysicalanddatalinklayers(Ethernet,Wi-
Fi,andsoon)stipulateadaptationlayersforbothversions,newertechnologies,such
asIEEE802.15.4(Wireless Personal Area Network), IEEE 1901.2, and ITU G.9903
(Narrowband PowerLine Communications) only have an IPv6
adaptation layer specified. This means thatany device implementing a technology
that requires an IPv6 adaptation layer mustcommunicate over an IPv6-only sub
network. This is reinforced by the IETF routingprotocolforLLNs, RPL,which is
IPv6only.

6LoWPAN

While the Internet Protocol is key for a successful Internet of Things,

constrained nodes andconstrained networks mandate optimization at
various layers and on multiple protocols ofthe IP architecture. Some
optimizations are already available from the market or underdevelopment
by the IETF. Figure 2.12 highlights the TCP/IP layers where optimization
isapplied.
 Figure2.12:OptimizingIPforIoTUsinganAdaptatio
nLayer

In the IP architecture, the transport of IP packets over any given

Layer 1 (PHY) andLayer 2 (MAC) protocol must be defined and
documented. The model for packaging IP intolower-layerprotocols
isoftenreferredtoas an adaptationlayer.

Unless the technology is proprietary, IP adaptation layers are

typically defined by anIETF working group and released as a Request for
Comments (RFC). An RFC is

a
publicationfromtheIETFthatofficiallydocumentsInternetstandards,specificatio
ns,protoc
ols,procedures,andevents.Forexample,RFC864describeshowanIPv4packetg
etsenca psulated over an Ethernet frame, and RFC 2464 describes how
the same function isperformedforanIPv6packet.

IoT-
relatedprotocolsfollowasimilarprocess.Themaindifferenceisthatanadaptatio
n layer designed for IoT may include some optimizations to deal with
constrainednodes and networks.The main examples of adaptation layers
optimized for constrainednodes or “things” are the ones under the
6LoWPANworking group andits successor, the6Loworking group.

The initial focus of the 6LoWPAN working group was to optimize

the transmission
ofIPv6packetsoverconstrainednetworkssuchasIEEE802.15.4.Figure2.13show
sanexa mple of an IoT protocol stack using the 6LoWPAN adaptation layer
beside the well- knownIPprotocolstackforreference.
Figure2.13:ComparisonofanIoTProtocolStackUtilizing6LoWPANandanIPProt
ocolSta ck

The 6LoWPAN working group published several RFCs, but RFC 4994
is foundationalbecause it defines frame headers for the capabilities of
header compression, fragmentation,and mesh addressing. These headers
can be stacked in the adaptation layer to
keep
theseconceptsseparatewhileenforcingastructuredmethodforexpressingeac
hcapability
.Depending on the implementation, all, none, or any combination of these
capabilities andtheir corresponding headers can be enabled. Figure 2.14
shows some examples of typical6LoWPAN headerstacks.

Figure2.146LoWPANHeaderStack

HeaderCompression

IPv6headercompressionfor6LoWPANwasdefinedinitiallyinRFC4944and
subse quently updated by RFC 6282. This capability shrinks the size of
IPv6’s 40-byte headersand User Datagram Protocol’s (UDP’s) 8-byte
headers down as low as 6 bytes combined insome cases. Note that header
compression for 6LoWPAN is only defined for an IPv6 headerandnotIPv4.
 The 6LoWPAN protocol does not support IPv4, and, in fact, there is
no standardizedIPv4 adaptation layer for IEEE 802.15.4. 6LoWPAN header
compression is stateless, andconceptually it is not too complicated.
However, a number of factors affect the
amount
ofcompression,suchasimplementationofRFC4944versusRFC6922,whetherU
DPisincl uded,andvarious IPv6addressingscenarios.

At a high level, 6LoWPAN works by taking advantage of shared

information known by allnodes from their participation in the local
network. In addition, it omits some standardheader fields by assuming
commonly used values. Figure 2.15 highlights an example

thatshowstheamountof
reductionthatispossiblewith6LoWPANheadercompression.

Figure2.156LoWPANHeaderCompression

AtthetopofFigure2.15,youseea6LoWPANframewithoutanyheadercompr

ession
enabled: The full 40- byte IPv6 header and 8-byte UDP header are visible.
The6LoWPAN header is only a single byte in this case. Notice that
uncompressed IPv6 and UDPheaders leave only 53 bytes of data payload
out of the 127- byte maximum frame size in thecaseofIEEE802.15.4.

The bottom half of Figure 2.15 shows a frame where header

compression has beenenabledforabest-
casescenario.The6LoWPANheaderincreasesto2bytestoaccommodate

the compressed IPv6 header, and UDP has been reduced in half, to 4
bytesfrom 8. Most importantly, the header compression has allowed the
payload to more thandouble, from 53 bytes to 108 bytes, which is
obviously much more efficient. Note that the 2-
byteheadercompressionappliestointra-
cellcommunications,whilecommunicationsexternaltothecellmayrequiresom
efieldof theheaderto notbecompressed.

Fragmentation
The maximum transmission unit (MTU) for an IPv6 network must be at
least 1280 bytes. Theterm MTU defines the size of the largest protocol
data unit that can be passed. For IEEE802.15.4, 127 bytes is the MTU. This
is a problem because IPv6, with a much larger MTU, iscarried inside the
802.15.4 frame with a much smaller one. To remedy this
situation,
largeIPv6packetsmustbefragmentedacrossmultiple802.15.4framesatLayer
2.

The fragment header utilized by 6LoWPAN is composed of three primary

fields: DatagramSize, Datagram Tag, and Datagram Offset. The 1-byte
Datagram Size field specifies

the
totalsizeoftheunfragmentedpayload.DatagramTagidentifiesthesetoffragmen
tsforapayl oad. Finally, the Datagram Offset field delineates how far into
a payload a
particularfragmentoccurs.Figure2.16providesanoverviewofa6LoWPANfragm
entation header.

Figure2.166LoWPANFragmentationHeader

In Figure 2.16, the 6LoWPAN fragmentation header field itself uses a

unique bit valueto identify that the subsequent fields behind it are
fragment fields as opposed to anothercapability, such as header
compression. Also, in the first fragment, the Datagram Offset fieldis not
present because it would simply be set to 0. This results in the first
fragmentationheader for an IPv6 payload being only 4 bytes long. The
remainder of the fragments have
a5-
byteheaderfieldsothattheappropriateoffsetcanbespecified.

MeshAddressing

The purpose of the 6LoWPAN mesh addressing function is to forward

packets overmultiple hops. Three fields are defined for this header: Hop
Limit, Source Address, andDestination Address. Analogous to the IPv6 hop
limit field, the hop limit for mesh addressingalso provides an upper limit
on how many times the frame can be forwarded. Each hopdecrements this
value by 1 as it is forwarded. Once the value hits 0, it is dropped and
nolongerforwarded.
 TheSourceAddressandDestinationAddressfieldsformeshaddres
sing areIEEE
802.15.4addressesindicatingtheendpointsofanIPhop.Figure2.1
7detailsthe6LoWPANmeshaddressing headerfields.

Figure2.17:6LoWPANMeshAddressingHead
er

Note that the mesh addressing header is used in a

single IP subnet and is a Layer 2type of routing known as
mesh-under. RFC 4944 only provisions the function in
this case asthe definition of Layer 2 mesh routing
specifications was outside the scope of
the
6LoWPANworkinggroup,andtheIETFdoesn’tdefine“Layer2r
outin g.”Animplementationperforming Layer 3 IP routing
does not need to implement a mesh addressing header
unlessrequiredby agiventechnology profile.

RPL stands for Routing Protocol for Low Power and Lossy
Networks for heterogeneous traffic networks. It is a routing
protocol for Wireless Networks. This protocol is based on the
same standard as by Zigbee and 6 Lowpan is IEEE 802.15.4 It
holds both many-to-one and one-to-one communication.
It is a Distance Vector Routing Protocol that creates a tree-
like routing topology called the Destination Oriented Directed
Acyclic Graph (DODAG), rooted towards one or more nodes
called the root node or sink node.
The Directed Acyclic Graphs (DAGs) are created based on user-
specified specific Objective Function (OF). The OF defines the
method to find the best-optimized route among the number of
sensor devices.
Directed Acyclic Graph
The IETF chartered the ROLL (Routing Over Low power and
Lossy networks) working group to evaluate all three routing
protocols and determine the needs and requirements for
developing a routing solution for IP smart objects. After the
study of various use cases and a survey of existing protocols,
the consensus was that a new routing protocol should be
developed for IP smart objects, given the characteristics and
requirements of the constrained network. This new Distance
Vector Routing Protocol was named the IPv6 Routing Protocol
for Low power and Lossy networks(RPL). The RPL specification
was published as RFC 6550 by the ROLL working group.
In an RPL Network, each node acts as a router and becomes
part of a mesh network. Routing is performed at the IP Layer.
Each node examines every received IPv6 packet and
determines the next-hop destination based on the information
contained in the IPv6 header. No information from the MAC
layer header is needed to perform the next determination.
Modes of RPL:
This protocol defines two modes:
1. Storing mode
All modes contain the entire routing table of the RPL domain.
Every node knows how to reach every other node directly.
2. Non-Storing mode
Only the border router(s) of the RPL domain contain(s) the full
routing table. All other nodes in the domain maintain their list of
parents only and use this as a list of default routes towards the
border router. The abbreviated routing table saves memory
space and CPU. When communicating in non-storing mode, a
node always forwards its packet to the border router, which
knows how to ultimately reach the final destination.
RPL is based on the concept of a Directed Acyclic Graph (DAG).
A DAG is Directed Graph where no cycle exists. This means that
from any vertex or point in the graph, we cannot follow an edge
or a line back to this same point. All of the edges are arranged
in a path oriented toward and terminating at one or more root
nodes.
A basic RPL process involves building a Destination Oriented
Directed Acyclic Graph (DODAG). A DODAG is a DAG rooted in
one destination. In RPL this destination occurs at a border router
known as the DODAG root. In a DODAG, three parents
maximum are maintained by each node that provides a path to
the root. Typically one of these parents is the preferred parent,
which means it is the preferred next hop for upward roots
towards the root. The routing graph created by the set of
DODAG parents across all nodes defines the full set of upwards
roots. RPL protocol information should ensure that routes are
loop-free by disallowing nodes from selected DODAG parents
positioned further away from a border router.
Implementation of RPL Protocol
The RPL protocol is implemented using the Contiki Operating
system. This Operating System majorly focuses on IoT devices,
more specifically Low Power Wireless IoT devices. It is an Open
source Model and was first bought into the picture by Adam
Dunkels.
The RPL protocol mostly occurs in wireless sensors and
networks. Other similar Operating Systems include T-Kernel,
EyeOS, LiteOS, etc.
Main Features and Advantages of RPL
The IPv6 Routing Protocol for RPL, is an efficient and effective
protocol for data routing in resource-constrained scenarios, such
Internet of Things devices as per requirement. Its many
essential features include the below points:
 Scalability: The protocol can accommodate such type of
big networks with low power and lossy connectivity, which
makes it appropriate for a range of Internet of Things
applications.
 Multipoint-to-point traffic generation: RPL offers a way to
send data to a single destination point from several
devices within the LLN as per requirement.
 Quality of Service (QoS) – The protocol guarantees QoS by
offering various types of methods for reliable packet
delivery system and congestion control systetm.
 Adaptive – RPL modifies the required routes in response to
link quality and energy availability changes in the network
environment or system.
 Security system: To guarantee various types of secure
communication within the LLN as per requirement, RPL
incorporates techniques for integrity protection,
authentication, confidentiality, and encryption for better
performance.