UNIT 3

Syllabus: IoT Data Link Layer: PHY/MAC Layer (3GPP MTC, IEEE 802.11, IEEE
802.15), Wireless HART, ZWave, Bluetooth Low Energy, Zigbee Smart Energy,
DASH7

PHY/MAC Layer:

In IoT (Internet of Things) architecture, the PHY (Physical) and MAC (Media
Access Control) layers refer to the lower layers of the communication stack
responsible for establishing and managing the physical connectivity and data
transmission between IoT devices.

PHY Layer: The PHY layer is the lowest layer in the IoT communication stack
and deals with the physical transmission of data over the communication
medium. It defines the hardware and electrical specifications required for
transmitting and receiving signals. The PHY layer is responsible for aspects
such as modulation, coding, frequency bands, transmission power, and signal
propagation. It ensures reliable and efficient transmission of data between IoT
devices.

Depending on the specific IoT deployment, various wireless technologies can be

used at the PHY layer, including Wi-Fi, Bluetooth, Zigbee, Z-Wave, LoRa,
Sigfox, Cellular (2G/3G/4G/5G), and others. Each technology has its own PHY
layer specifications, such as frequency ranges, transmission power levels, and
modulation techniques.

MAC Layer: The MAC layer resides above the PHY layer and is responsible for
managing access to the shared communication medium and handling data
packet transmission between IoT devices. It defines protocols and rules for
devices to access the medium, avoiding collisions and ensuring fair and
efficient utilization of the available bandwidth.

The MAC layer controls the timing, synchronization, and channel access
methods for IoT devices. It can use various techniques such as contention-
based access (e.g., CSMA/CA - Carrier Sense Multiple Access with Collision
Avoidance), time-based access (e.g., TDMA - Time Division Multiple Access), or
scheduled access (e.g., FDMA - Frequency Division Multiple Access) depending
on the specific technology being used.
Additionally, the MAC layer may handle functions such as packet
fragmentation, error detection, acknowledgments, and retransmissions to
ensure reliable data transmission in the presence of interference or other
communication challenges.

Both the PHY and MAC layers play a crucial role in establishing robust and
efficient communication between IoT devices. They define the physical and
access control mechanisms necessary for transmitting data over various
wireless technologies, ensuring reliable and optimized connectivity in IoT
deployments.

3GPP MTC:

3GPP MTC (Machine Type Communication) in IoT (Internet of Things) refers to

the cellular communication technologies and standards developed by the 3rd
Generation Partnership Project (3GPP) specifically for IoT devices. It
encompasses the specifications and enhancements made to cellular networks
to support the unique requirements of IoT applications.

Here are some key aspects of 3GPP MTC in IoT:

Low-Power and Low-Complexity Devices: 3GPP MTC focuses on enabling

communication for low-power and low-complexity IoT devices. These devices
typically have limited processing capabilities, memory, and power supply,
requiring communication technologies that are optimized for efficiency and
resource conservation.

Coverage Enhancement: 3GPP MTC technologies, such as LTE-M (LTE for

MTC), eMTC (enhanced Machine Type Communication), and NB-IoT
(Narrowband IoT), offer coverage enhancements to ensure reliable connectivity
in challenging environments. These technologies provide extended coverage
range, improved signal penetration through buildings and underground areas,
and better performance in remote or rural areas.

Power Efficiency: Power consumption is a critical concern for IoT devices,

many of which operate on battery power. 3GPP MTC introduces power-saving
features such as extended discontinuous reception (eDRX) and power saving
mode (PSM) to minimize energy consumption. These mechanisms allow IoT
devices to enter sleep modes for extended periods while still maintaining
network connectivity.
Optimized Data Rates: 3GPP MTC technologies provide optimized data rates
suitable for IoT applications. While they may not offer the high data throughput
of traditional cellular networks, they provide sufficient bandwidth for
transmitting small amounts of data, periodic sensor readings, and control
messages required by IoT devices.

Quality of Service (QoS): 3GPP MTC supports differentiated QoS for different
types of IoT applications. It provides mechanisms to prioritize critical data
traffic and ensure reliable transmission for mission-critical applications. QoS
parameters can be adjusted to meet the specific requirements of diverse IoT
use cases.

Security and Authentication: 3GPP MTC includes robust security

mechanisms to protect IoT device communications. It utilizes encryption,
authentication, and access control measures to ensure the confidentiality and
integrity of data transmitted over the cellular network.

Integration with IoT Platforms: 3GPP MTC technologies are designed to

seamlessly integrate with IoT platforms and cloud services. They provide
standardized protocols and interfaces for data exchange, device management,
and integration with higher-level IoT systems.

By leveraging 3GPP MTC, IoT applications can benefit from the wide coverage,
reliable connectivity, power efficiency, and security features offered by cellular
networks. These technologies enable cellular communication for a wide range
of IoT devices and applications, facilitating the scalability and interoperability
of IoT deployments.

Machine-type communication (MTC) is a form of data communication which

involves one or more entities that do not necessarily need human interaction.

For MTC communication the following communication scenarios can be

identified:

1) Communication scenario with MTC devices communicating with MTC

server. MTC server is located in the operator domain
2) Communication scenario with MTC devices communicating with MTC
server. MTC server is located outside the operator domain:

The network operator provides network connectivity to MTC Server(s).

This applies to MTC Servers controlled by the network operator or to
MTC Servers not controlled by the network operator.

3) MTC devices communicating with each other:

The communication scenario where the MTC Devices communicate
directly without intermediate MTC Server
As technology evolves, there are important changes in capabilities and
costs. More computing power, memory and communication capabilities
make it possible for machines to take over tasks presently done by, but not
well suited to human beings. Lower costs make it practical for machines to
take over tasks not well suited to expensive human beings. Increasing
capabilities and lower costs together open new opportunities for revenue
generating services not previously economical to do.

The increasing capability of machines makes it possible to avoid dull and

repetitious work having to be done by people, freeing them to utilize their
capabilities and intelligence in better suited and much more fruitful
activities.

MTC Device: A MTC Device is a UE equipped for Machine Type

Communication, which communicates through a PLMN with MTC Server(s)
and/or other MTC Device(s).

MTC Feature: MTC Features are network functions to optimise the network
for use by M2M applications.

MTC Group: A MTC Group is a group of MTC Devices that share one or
more MTC Features and that belong to the same MTC Subscriber.

MTC Server: A MTC Server is a server, which communicates to the PLMN

itself, and to MTC Devices through the PLMN. The MTC Server can also have
an interface which can be accessed by the MTC User. The MTC Server can:
Provides services for other servers (e.g. The MTC Server is a Services
Capability Server for an Application Server), and/or

Provides services for applications and can host the application (e.g. The
MTC Server is an Application Server).

MTC User: A MTC User uses the service provided by the MTC Server.

MTC Subscriber: A MTC Subscriber is a legal entity having a contractual

relationship with the network operator to provide service to one or more
MTC Devices.

IEEE 802.11 STANDARDS:

IEEE 802.11 standard, popularly known as WiFi, lays down the architecture
and specifications of wireless LANs (WLANs). WiFi or WLAN uses high
frequency radio waves for connecting the nodes.

There are several standards of IEEE 802.11 WLANs. The prominent among
them are 802.11, 802.11a, 802.11b, 802.11g, 802.11n and 802.11p. All the
standards use carrier-sense multiple access with collision avoidance
(CSMA/CA). Also, they have support for both centralized base station based
as well as ad hoc networks.
IEEE 802.11

IEEE 802.11 was the original version released in 1997. It provided 1 Mbps
or 2 Mbps data rate in the 2.4 GHz band and used either frequency-hopping
spread spectrum (FHSS) or direct-sequence spread spectrum (DSSS). It is
obsolete now.

IEEE 802.11a

802.11a was published in 1999 as a modification to 802.11, with orthogonal

frequency division multiplexing (OFDM) based air interface in physical layer
instead of FHSS or DSSS of 802.11. It provides a maximum data rate of 54
Mbps operating in the 5 GHz band. Besides it provides error correcting code.
As 2.4 GHz band is crowded, relatively sparsely used 5 GHz imparts
additional advantage to 802.11a.

Further amendments to 802.11a are 802.11ac, 802.11ad, 802.11af,

802.11ah, 802.11ai, 802.11aj etc.

IEEE 802.11b

802.11b is a direct extension of the original 802.11 standard that appeared

in early 2000. It uses the same modulation technique as 802.11, i.e. DSSS
and operates in the 2.4 GHz band. It has a higher data rate of 11 Mbps as
compared to 2 Mbps of 802.11, due to which it was rapidly adopted in
wireless LANs. However, since 2.4 GHz band is pretty crowded, 802.11b
devices faces interference from other devices.

Further amendments to 802.11b are 802.11ba, 802.11bb, 802.11bc,

802.11bd and 802.11be.

IEEE 802.11g

802.11g was indorsed in 2003. It operates in the 2.4 GHz band (as in
802.11b) and provides a average throughput of 22 Mbps. It uses OFDM
technique (as in 802.11a). It is fully backward compatible with 802.11b.
802.11g devices also faces interference from other devices operating in 2.4
GHz band.

IEEE 802.11n

802.11n was approved and published in 2009 that operates on both the 2.4
GHz and the 5 GHz bands. It has variable data rate ranging from 54 Mbps
to 600 Mbps. It provides a marked improvement over previous standards
802.11 by incorporating multiple-input multiple-output antennas (MIMO
antennas).

IEEE 802.11p

802.11 is an amendment for including wireless access in vehicular

environments (WAVE) to support Intelligent Transportation Systems (ITS).
They include network communications between vehicles moving at high
speed and the environment. They have a data rate of 27 Mbps and operate
in 5.9 GHz band.

IEEE 802.11 protocol architecture:

Wireless LANs are those Local Area Networks that use high frequency radio
waves instead of cables for connecting the devices in LAN. Users connected
by WLANs can move around within the area of network coverage. Most
WLANs are based upon the standard IEEE 802.11 or WiFi.

The components of IEEE 802.11 architecture are as follows

1) Stations (STA) − Stations comprise all devices and equipments that are
connected to the wireless LAN. A station can be of two types:

Wireless Access Pointz (WAP) − WAPs or simply access points (AP) are
generally wireless routers that form the base stations or access.

Client. − Clients are workstations, computers, laptops, printers, smart

phones, etc. Each station has a wireless network interface controller.

2) Basic Service Set (BSS) −A basic service set is a group of stations

communicating at physical layer level. BSS can be of two categories
depending upon mode of operation:

Infrastructure BSS − Here, the devices communicate with other devices

through access points.

Independent BSS − Here, the devices communicate in peer-to-peer basis in

an ad hoc manner.

3) Extended Service Set (ESS) − It is a set of all connected BSS.

4) Distribution System (DS) − It connects access points in ESS.

An ESS can also provide gateway access for wireless users into a wired
network. Each end station associates itself with one access point. Above Figure
shows three BSSs interconnected through three APs to a distribution system. If
station A associated with AP-1 wants to send a frame to another station
associated with AP- 2, the first sends a frame to its access point (AP-1), which
forwards the frame across the distribution system to the access point AP-2. AP-
2 finally delivers it to the destination station.
The technique used for this purpose is known as scanning, which involves the
following steps:

• A station sends a probe frame.

• All APs within reach reply with a probe response frame.

• The station selects one of the access points, and sends the AP an
Association Request frame.

• The AP replies with an Association Response frame.

Medium Access Control:

Most wired LANs products use Carrier Sense Multiple Access with Collision
Detection (CSMA/CD) as the MAC protocol. Carrier Sense means that the
station will listen before it transmits. If there is already someone transmitting,
then the station waits and tries again later. If no one is transmitting then the
station goes ahead and sends what it has. But when more than one station
tries to transmit, the transmissions will collide and the information will be lost.
This is where Collision Detection comes into play. The station will listen to
ensure that its transmission made it to the destination without collisions. If a
collision occurred then the stations wait and try again later. The time the
station waits is determined by the back off algorithm. This technique works
great for wired LANs but wireless topologies can create a problem for
CSMA/CD. However, the wireless medium presents some unique challenges
not present in wired LANs that must be dealt with by the MAC used for IEEE
802.11. Some of the challenges are:

• The wireless LAN is prone to more interference and is less reliable.

• The wireless LAN is susceptible to unwanted interception leading to

security problems.

• There are so called hidden station and exposed station problems.

In the discussion of both the problem, we shall assume that all radio
transmitters have fixed range. When the receiver is in the range of two active
transmitters then the signal will be garbled. It is important to note that not all
stations are in range of two transmitters.

The Hidden Station Problem

Consider a situation when A is transmitting to B, as depicted in the Fig. If C

senses the media, it will not hear anything because it is out of range, and thus
will falsely conclude that no transmission is going on and will start transmit to
B. the transmission will interfere at B, wiping out the frame from A.

The problem of a station not been able to detect a potential competitor for the
medium because the competitor is too far away is referred as Hidden Station
Problem. As in the described scenario C act as a hidden station to A, this is
also competing for the medium.

Fig: Hidden Station Problems

Exposed Station problem

Now consider a different situation where B is transmitting to A, and C sense

the medium and detects the ongoing transmission between B and A. C falsely
conclude that it cannot transmit to D, when the fact is that such transmission
would cause on problem. A transmission could cause a problem only when the
destination is in zone between B and C. This problem is referred as Exposed
station Problem. In this scenario as B is exposed to C, that’s why C assumes it
cannot transmit to D. So this problem is known as Exposed station problem
(i.e. problem caused due to exposing of a station). The problem here is that
before transmission, a station really wants to know that whether or not there is
any activity around the receiver. CSMA merely tells whether or not there is any
activity around the station sensing the carrier. Security

Wireless LANs are subjected to possible breaches from unwanted monitoring.

To overcome this problem, IEEE 802.11 specifies an optional MAC layer
security system known as Wired Equivalent Privacy (WEP). The objective is to
provide a level of privacy to the wireless LAN similar to that enjoyed by wired
Ethernets. It is achieved with the help of a 40-bit shared key authentication
service. By default each BSS supports up to four 40-bit keys that are shared by
all the clients in the BSS. Keys unique to a pair of communicating clients and
direction of transmission may also be used. Advanced Encryption Standard
(AES) (802.11i) for authentication and encryption is recommended as a long-
term solution.

Frame Format of IEEE 802.11

The main fields of a frame of wireless LANs as laid down by IEEE 802.11 are −

Frame Control − It is a 2 bytes starting field composed of 11 subfields. It

contains control information of the frame.

Duration − It is a 2-byte field that specifies the time period for which the frame
and its acknowledgment occupy the channel.

Address fields − There are three 6-byte address fields containing addresses of
source, immediate destination, and final endpoint respectively.

Sequence − It a 2 bytes field that stores the frame numbers.

Data − This is a variable-sized field that carries the data from the upper layers.
The maximum size of the data field is 2312 bytes.
Check Sequence − It is a 4-byte field containing error detection information.

Frame Control(FC) –
It is 2 bytes long field which defines type of frame and some control
information. Various fields presentin FC are:
1. Version:
It is a 2 bit long field which indicates the current protocol version which is fixed to
be 0 for now.
2. Type:
It is a 2 bit long field which determines the function of frame i.e
management (00), control (01) ordata (10). The value 11 is reserved.
3. Subtype:
It is a 4 bit long field which indicates sub-type of the frame like 0000 for
association request, 1000 forbeacon.
4. To DS:
It is a 1 bit long field which when set indicates that destination frame is for
DS(distribution system).
5. From DS:
It is a 1 bit long field which when set indicates frame coming from DS.
6. More frag (More fragments):
It is 1 bit long field which when set to 1 means frame is followed by other fragments.
7. Retry:
It is 1-bit long field, if the current frame is a retransmission of an earlier frame, this
bit is set to 1.
8. Power Mgmt (Power management):
It is 1-bit long field that indicates the mode of a station after successful
transmission of a frame. Set to 1 the field indicates that the station goes into
power-save mode. If the field is set to 0, the station stays active.
9. More data:
It is 1-bit long field that is used to indicate receiver that a sender has more data
 to send than the current frame. This can be used by an access point to indicate
to a station in power-save mode that more packets are buffered or it can be used
by a station to indicate to an access point after being polled that more polling is
necessary as the station has more data ready to transmit.
10. WEP:
It is 1 bit long field which indicates that the standard security mechanism of 802.11 is
applied.
11. Order:
It is 1 bit long field, if this bit is set to 1 the received frames must be processed in
strict order.

IEEE 802.5 Standards:

IEEE 802.15 is a standard for wireless personal area networks (WPANs)

developed by the Institute of Electrical and Electronics Engineers (IEEE). It
defines the physical layer (PHY) and medium access control (MAC) layer
specifications for short-range wireless communication.

The IEEE 802.15 architecture consists of multiple task groups, each focusing
on specific applications and requirements. Here are some key task groups
within the IEEE 802.15 standard:

IEEE 802.15.1 (Bluetooth): This task group defines the specifications for
Bluetooth wireless technology, which enables short-range communication
between devices such as mobile phones, laptops, and peripherals.

IEEE 802.15.4: This task group specifies the PHY and MAC layers for low-rate
wireless personal area networks (LR-WPANs). It is commonly used in
applications like home automation, industrial control, and wireless sensor
networks. The most well-known standard built on IEEE 802.15.4 is Zigbee.

IEEE 802.15.3: This task group focuses on high-rate wireless personal area
networks (HR-WPANs). It defines the PHY and MAC layers for applications that
require higher data rates, such as streaming multimedia.

IEEE 802.15.6: This task group concentrates on wireless body area networks
(WBANs). It addresses the specific requirements of medical, healthcare, and
fitness applications by defining the PHY and MAC layers suitable for wearable
and implantable devices.

IEEE 802.15.7: This task group defines the PHY and MAC layers for visible
light communication (VLC). It enables communication using light-emitting
diodes (LEDs) and is often used for indoor positioning, smart lighting, and
other applications.

IEEE 802.15.4

IEEE 802.15.4 is a subgroup of features that refers to physical and medium

access control layers that can support ZigBee and 6LoWPAN upper. IEEE
802.15.4 focuses on physical and data link layer specifications while ZigBee
Alliance aims to provide the upper characteristics [33]. It is a standard that
defines PHY and MAC layers for personal area networks that demand low rate
and low cost applications. This also called a LR-WPAN protocol and has some
advantages. Among them are a simple and flexible protocol stack, low cost, low
energy consumption, short-range operation, reliable data transfer, and ease of
operation [34]. These features are more important when operating in the
Personal Operating Space (POS) also defined as Personal Area Network (PAN)
that involves the human body.

Physical Layer

The 802.15.4 standard supports an extensive number of PHY options that

range from

2.4 GHz to sub-GHz frequencies in ISM bands. (ISM bands are discussed
earlier in this chapter.) The original IEEE 802.15.4-2003 standard specified
only three PHY options based on direct sequence spread spectrum (DSSS)
modulation. DSSS is a modulation technique in which a signal is intentionally
spread in the frequency domain, resulting in greater bandwidth. The original
physical layer transmission options were as follows:

■ 2.4 GHz, 16 channels, with a data rate of 250 kbps

■ 915 MHz, 10 channels, with a data rate of 40 kbps

■ 868 MHz, 1 channel, with a data rate of 20 kbps

You should note that only the 2.4 GHz band operates worldwide. The 915 MHz
band operates mainly in North and South America, and the 868 MHz
frequencies are used in Europe, the Middle East, and Africa. IEEE 802.15.4-
2006, 802.15.4-2011, and

IEEE 802.15.4-2015 introduced additional PHY communication options,

including the following:
■ OQPSK PHY: This is DSSS PHY, employing offset quadrature phase-shift
keying (OQPSK) modulation. OQPSK is a modulation technique that uses four
unique bit values that are signaled by phase changes. An offset function that is
present during phase shifts allows data to be transmitted more reliably.

■ BPSK PHY: This is DSSS PHY, employing binary phase-shift keying

(BPSK) modulation. BPSK specifies two unique phase shifts as its data
encoding scheme.

■ ASK PHY: This is parallel sequence spread spectrum (PSSS) PHY,

employing amplitude shift keying (ASK) and BPSK modulation. PSSS is an
advanced encoding scheme that offers increased range, throughput, data rates,
and signal integrity compared to DSSS. ASK uses amplitude shifts instead of
phase shifts to signal different bit values.

These improvements increase the maximum data rate for both 868 MHz and
915 MHz to 100 kbps and 250 kbps, respectively. The 868 MHz support was
enhanced to 3 channels, while other IEEE 802.15.4 study groups produced
addendums for new frequency bands. For example, the IEEE 802.15.4c study
group created the bands 314–316 MHz, 430–434 MHz, and 779–787 MHz for
use in China.

Figure shows the frame for the 802.15.4 physical layer. The synchronization
header for this frame is composed of the Preamble and the Start of Frame
Delimiter fields. The Preamble field is a 32-bit 4-byte (for parallel construction)
pattern that identifies the start of the frame and is used to synchronize the
data transmission. The Start of Frame Delimiter field informs the receiver that
frame contents start immediately after this byte.

Fig: PHY header

The PHY Header portion of the PHY frame shown in Figure 4-5 is simply a
frame length value. It lets the receiver know how much total data to expect in
the PHY service data unit (PSDU) portion of the 802.4.15 PHY. The PSDU is the
data field or payload.

MAC Layer

The IEEE 802.15.4 MAC layer manages access to the PHY channel by defining
how devices in the same area will share the frequencies allocated. At this layer,
the scheduling and routing of data frames are also coordinated. The 802.15.4
MAC layer performs the following tasks:

■ Network beaconing for devices acting as coordinators (New devices use

beacons to join an 802.15.4 network)

■ PAN association and disassociation by a device

■ Device security

■ Reliable link communications between two peer MAC entities

The MAC layer achieves these tasks by using various predefined frame types.
In fact, four types of MAC frames are specified in 802.15.4:

■ Data frame: Handles all transfers of data

■ Beacon frame: Used in the transmission of beacons from a PAN

coordinator

■ Acknowledgement frame: Confirms the successful reception of a frame

■ flAC command frame: Responsible for control communication between

devices

Each of these four 802.15.4 MAC frame types follows the frame format shown
in Figure . In Figure, notice that the MAC frame is carried as the PHY payload.
The 802.15.4 MAC frame can be broken down into the MAC Header, MAC
Payload, and MAC Footer fields.

The MAC Header field is composed of the Frame Control, Sequence Number
and the Addressing fields. The Frame Control field defines attributes such as
frame type, address- ing modes, and other control flags. The Sequence Number
field indicates the sequence identifier for the frame. The Addressing field
specifies the Source and Destination PAN Identifier fields as well as the Source
and Destination Address fields.
The MAC Payload field varies by individual frame type. For example, beacon
frames have specific fields and payloads related to beacons, while MAC
command frames have different fields present. The MAC Footer field is nothing
more than a frame check sequence (FCS). An FCS is a calculation based on the
data in the frame that is used by the receiving side to confirm the integrity of
the data in the frame. IEEE 802.15.4 requires all devices to support a unique
64-bit extended MAC address, based on EUI-64. However, because the
maximum payload is 127 bytes, 802.15.4 also defines how a 16-bit “short
address” is assigned to devices. This short address is local to the PAN and
substantially reduces the frame overhead compared to a 64-bit extended MAC
address. However, you should be aware that the use of this short address
might be limited to specific upper-layer protocol stacks.

Fig: IEEE 802.15.4 MAC Format

The IEEE 802.15.4 BE and NBE operational modes have being strongly
investigated over recent years. Thus, some limitations have been addressed
and the most important ones are the unbounded delay, low communication
efficiency, low interference robustness, and/or fading and main powered relay
nodes Figure compares IEEE 802.15.4 stack with the OSI reference model.
 Fig: IEEE 802.15.4 compared with OSI reference model.

Advantages of IEEE 802.15.4:

IEEE 802.15.4 has the following advantages:

-cheap cost

-long battery life,

-Quick and simple installation

-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
Wireless HART:

Wireless HART is a datalink protocol that operates on the top of IEEE 802.15.4
PHY and adopts Time Division Multiple Access (TDMA) in its MAC. It is a
secure and reliable MAC protocol that uses advanced encryption to encrypt the
messages and calculate the integrity in order to offer reliability. The
architecture, as shown in fig consists of a network manager, a security
manager, a gateway to connect the wireless network to the wired networks,
wireless devices as field devices, access points, routers and adapters. The
standard offers end-to-end, per-hop or peer-to- peer security mechanisms. End
to end security mechanisms enforce security from sources to destinations while
per-hop mechanisms secure it to next hop only.

Wireless HART is a wireless communication standard specifically designed for

industrial process automation. It is based on the Highway Addressable Remote
Transducer (HART) protocol, which is widely used in industrial control
systems.

Fig: Wireless HART architecture

Wireless-HART (Highway Addressable Remote Transducer Protocol) is a

variation of IEEE 802.15.4 design to work essentially as a centralized wireless
network. IEEE 802.15.4 is designed to meet the requirements of industrial
wireless applications with hard timing parameter restrictions, critically security
issues, and severity on obstacle interferences. The Wireless-HART protocol has
the same specifications as IEEE 802.15.4 PHY, but develops its own MAC layer
based on the TDMA technique. Using Bluetooth, there is no guarantee to delay
values on an end-to-end wireless communication.
The absence of a hopping channel technique and a quasi-static star Bluetooth
topology works against its scalability. These characteristics make them
inappropriate to be used in industrial scenarios. Wireless HART comes as a
solution for process control applications through the effort of some industrial
organizations such as International Society of Automation 100 (ISA 100),
HART, Wireless Industrial Networking Alliance (WINA) and ZigBee Alliance to
attend their specific requirements ratified by the HART Communication
Foundation in 2007.

Using the IEEE 802.15.4 PHY layer, Wireless-HART operates in the license-free
ISM of 2.4–2.4835 GHz with 2 MHz bandwidth of each one of the 16 channels.
The channels are numbered from 11 to 26 with a gap of 5 MHz between IEEE
802.11b/g adjacent channels, delivering up to 250 Kbps. Wireless-HART uses
its own Time Division Multiple Access (TDMA) on the MAC layer including the
10 ms synchronized time slot features. These characteristics allow the
messages routing through a network topology obstacle and interference. This is
possible due to the use of self-organizing and self-healing mesh networking
techniques supported by the network layer. Even being essentially a centralized
wireless network, Wireless-HART uses a network manager in its stack in order
to provide routing and communication schedules. This can guarantee network
performance and satisfy the wireless industrial applications. The focus of
Wireless-HART is communication on a one-hop level and the network layer has
its responsibility to the network devices vicinity allocation.

Differing from IEEE 802.15.4, Wireless-HART uses time-synchronized the

TDMA technique combined with frequency hopping on its MAC layer, thus
allowing multiple devices to transmit data at the same time along different
channels. During the joining process of the devices onto networks, the network
manager distributes the communication links and the channel hop patterns
to the devices. It also manages the enabling or disabling of the use of channels
that are frequently affected by considerable interference levels, calling this
feature channels blacklist,wHart-n-802-15- 4e,petersen2011wirelesshart. The
eight types of devices defined on Wireless-HART are: routers, gateways,
adapters, network managers, network security devices, access points and field
devices on a mesh topology. All of them support the implementation of features
to attend network creation, maintenance issues, data and signaling routing
capability, and a minimum of reliability. A comparison between the OSI
reference model and Wireless-HART protocol layers and its main features is
shown in Figure
 Fig: Wireless HART Protocol Stack.

Another addressable characteristic of Wireless-HART is the information blocks

that each network device maintains on its memory. The information of
neighbor nodes and the next reachable device is called a neighbor information
block. The connection with the network layer is made through the block
information, adding data to the network layer routing table. Working with
TDMA as a medium access technique, the network devices have very stringent
timing requirements to accomplish network synchronization premises. This
happens because synchronization occurs both in the joining process and in
normal operations.

Wireless HART technology allows users to access the vast amount of unused
information stranded in these installed HART smart devices—85% of the
installed HART devices. It also provides a simple, reliable and secure way to
deploy new points of measurement and control without the wiring costs.

1. Simple:

Wireless HART is a robust technology that is simple to implement. It enables

users to quickly and easily gain the benefits of wireless technology while
maintaining compatibility with existing HART devices, tools and systems.

• Easy Installation and Commissioning:-

-Familiar tools, work flow and procedures

-Multiple power options

-Reduced installation and wiring costs

-Coexistence with other wireless networks

-Supports both star and mesh topologies

-Add devices one at a time

• Automatic Network Features:-

-Self-organizing and self-healing

-Always-on security

-Adjusts as new instruments are added

-Adjusts to changes in plant infrastructure

2. Reliable:

Industrial facilities with dense infrastructures, frequent movement of large

equipment, changing conditions, or numerous sources of radio-frequency and
electromagnetic interference may have communication challenges. Wireless
HART includes several features to provide built-in 99.9% end-to-end reliability
in all industrial environments.

• Standard Radio with Channel Hopping

-Radios comply with IEEE 802.15.4-2006

-2.4GHz license free frequency band

-“Hops” across channels to avoid interference

-Delivers high reliability in challenging radio environments

• Coexistence with Other Wireless Networks

-Clear Channel Assessments tests for available channels

-Blacklisting avoids frequently used channels

-Optimizes bandwidth and radio time

-Time synchronization for on-time messaging

• Self-Healing Network

-Adjusts communication paths for optimal performance

-Monitors paths for degradation and repairs itself

-Finds alternate paths around obstructions

-Mesh network and multiple access points

3. Secure: Wireless HART employs robust security measures to protect the

network and secure the data at all times. These measures include the latest
security techniques to provide the highest levels of protection available.

• Protects Valuable Information

-Robust, multi-tiered, always-on security

-Industry standard 128-bit AES encryption

-Unique encryption key for each message

-Data integrity and device authentication

-Rotate encryption keys used to join the network

• Protects Wireless Network

-Channel hopping

-Adjustable transmit power levels

-Multiple levels of security keys for access

-Indication of failed access attempts

-Reports message integrity failures

-Reports authentication failures

-Safe from Wi-Fi type Internet attacks

Z-Wave:
Z-Wave is a low-power MAC protocol designed for home automation and has
been used for IoT communication, especially for smart home and small
commercial domains. It covers about 30-meter point- to-point communication
and is suitable for small messages in IoT applications, like light control, energy
control, wearable healthcare control and others. It uses CSMA/CA for collision
detection and ACK messages for reliable transmission. It follows a master/slave
architecture in which the master control the slaves, send them commands, and
handling scheduling of the whole network. Z-Wave was developed and is
overseen by the company Zensys to provide wireless communication between
devices with a focus on residential automation. Monitoring and controlling of
lighting, ambient temperature and security through sensors and actuators by
tablets, smartphones or computers are some applications in its portfolio. Z-
Wave devices are arranged in mesh networktopology. They can send and
receive messages from any device that is connected to the network.

The protocol is a proprietary standard based on the ITU G.9959 specification

that operates in the Industrial, Scientific, and Medical (ISM) radio frequency
band. Z-Wave transmits on 868.42 MHz (Europe) and 908.42 MHz (United
States) frequencies working with FSK and Gaussian Fase Shift Keying (GFSK)
modulations. With low transmission rates of 9.6 Kbps, 40 Kbps and 100 Kbps,
it employs symmetric AES-128 encryption. The MAC layer uses the CSMA-CA
technique for a medium access control technique and, based on ITU G.9959,
has the following characteristics: a capacity of 232 unique network identifiers
that allows the same quantity of nodes joining the network; collision avoidance
mechanism; back-off time when collision occurs; reliability guaranteed by
receiving acknowledgments; frame validation and retransmission mechanisms.
A power saving mechanism is achieved due to a sleep mode with a dedicated
wake-up pattern Figure depicts the Z-Wave protocol stack.

The Z-Wave basic device classes are the following: Portable Controller, Static
Controller, Slave, and Slave with Routing Capabilities. Different classes provide
the device with a certain role in the Z- Wave network. Inside a Basic Class,
Generic and Specific device classes are used to achieve the wanted
functionality in the control network. In the Z-Wave protocol, the unique
identification of the devices is used through a 32-bit ID. This ID value cannot
be changed as it is written in the device chipset by the device manufacturer. A
Z-Wave network has only one primary controller device at a time.

Each of the 232 nodes of this network can also be a repeater for forwarding
data to its neighbors, mediating a connection. Battery-powered nodes do not
enjoy this facility. In an environment with a certain level of device drift or even
when a device is removed from the network for some reason, the network
topology may change. Changing network topology can lead to problems in
packet forwarding and packet routing in the network. To minimize this effect,
routing tables should be kept up-to-date, optimized and any new topology
detected; Z-Wave supports the discovery and suitability of the new network
topology.
 Fig: Z-Wave protocol stack.

This is possible by keeping the routing table up-to-date on each device and
showing all neighboring devices. When a node changes its position or is
removed from the network, a topology failure can start an automatic topology
and healing procedure to detect the new topology and define the best routes to
update the routing tables. This mechanism is subjected to unauthorized
modification of routing table attacks by rouge nodes.

The transfer (or transport) layer management functions are: communication

between two neighbor nodes, packet acknowledgment, low power network
nodes awake (Beaming), and packet origin authentication. This layer controls
the Beam frames used to wake-up battery powered Z-Wave devices, as each
primary controller device of a cluster can handle up to 232 nodes. All nodes
can act as a packet repeater, except those devices that are batteries powered.
This is Z-Wave mesh topology formed. Z-Wave data security is based on AES
and on the cipher block chaining message authentication code (CBC-MAC).
However, standards and rules for command classes, device types and timers
are missing. These characteristics are only acquired in the new advanced
security framework (S2) determined by the Z-Wave Alliance and developed in
conjunction with the cyber security community. For the certification of new
products as of 2017, Z-Wave brings devices a higher level of security. The
structure of S2 is based on the protection of the devices that is already
associated with the network, so they are not hacked while still connected to the
network. Once the device has already been associated to the network through
its pin-code or QR (Quick Response) code, there is an exchange of security keys
through the Elliptic Curve Diffie- Hellman (ECDH) algorithm.
DASH7:

DASH7 is a wireless communication protocol for active RFID that operates in

globally available Industrial Scientific Medical (ISM) band and is suitable for
IoT requirements. It is mainly designed for scalable, long range outdoor
coverage with higher data rate compared to traditional ZigBee. It is a low-cost
solution that supports encryption and IPv6 addressing. It supports
master/slave architecture and is designed for burst, lightweight, asynchronous
and transitive traffic. Its MAC layer features can be summarized as follows

Filtering: Incoming frames are filtered using three processes; cyclic

redundancy check (CRC) validation, a 4-bit subnet mask, and link quality
assessment. Only the frames that pass all three checks are processed further.

Addressing: DASH7 uses two types of addresses: the unique identifier which is
the EUI-64 ID and dynamic network identifier which is 16-bit address specified
by the network administrator.

Frame format: The MAC frame has a variable length of maximum 255 bytes
including addressing, subnets, estimated power of the transmission and some
other optional fields.

The RFID technologies such as NFC and Dash7 are widely used in WSN
(wireless sensor networking). Most of the Smartphone will have these
technologies integrated to provide many facilities to the users. These include
building access, mobile payments, advanced location services, home
automation, ticketing and more. This means that Dash7 will be part of
IoT(Internet of Things) which acquires sensors data and use that to manage
social network applications.
There are four different device classes defined in D7A (Dash7 Alliance Protocol).

Blinker: It only transmits and does not use a receiver.

Endpoint: It can transmit and receive the data. It also supports wake-up
events.

Sub controller: It is full featured device. It is not always active. It uses wake on
scan cycles similar to end points.

Gateway: It connects D7A network with the other network. It will always be
online. It always listens unless it is transmitting.

D7A describes full functional RFID tag. All the devices in Dash7 network
support one or more of the above-mentioned device classes.

DASH7 supports two communication models: pull and push.

The dialogs between tags and interrogators are query response based (referred
as pull model). This request response mechanism is described by the D7A
Query Protocol Data transfer initiated from the tags to the gateway on the other
hand is based on the push model. Both of these models are depicted in the
figure. This approach for instance is implemented as an automated message or
beacon which is sent on specific time intervals. This system is called Beacon
Transmit Series.

DASH7 defines two types of frames viz. a foreground frame and a background
frame. The foreground frames are regular messages which contain data or data
requests. Background frames on the other hand are very short broadcast
messages. Background frames are used by the D7A Advertising Protocol for
rapid ad-hoc group synchronization.

Background frame = { subnet(1 byte), payload(3 bytes), CRC16(2 byte) }

Foreground frame = {length(1 byte), headers(3-38 bytes), payload(0 to 249
bytes), Footer(0 to 20 bytes), CRC16( 2 bytes) }

DASH7 (Data and Sensing Hierarchy 7) is an open standard and wireless

communication protocol designed for low-power, long-range, and low-data-rate
applications in the Internet of Things (IoT) domain. It focuses on providing
reliable communication with extended range and efficient power consumption
for battery-operated devices.
Zigbee Smart Energy:

ZigBee Smart Energy (SE) is a standard for interconnecting and interoperating

devices, via radio frequency, directed towards monitoring, managing and
automating energy, gas and water usage. It seeks to be a useful tool for
creating “Green Homes”, and is aimed at coordinating energy usage, optimizing
its generation and consumption.

ZigBee SE is a world-leading standard widely used for smart metering

(electricity, gas and water) and home automation (wireless domotics). ZigBee is
a simple data transmission protocol designed to be used as a low rate wireless
personal area network (LR-WPAN). Based on the IEEE 802.15. ZigBee smart
energy is designed for a large range of IoT applications including smart homes,
remote controls and healthcare systems. It supports a wide range of network
topologies including star, peer-to-peer, or cluster-tree.

A coordinator controls the network and is the central node in a star topology,
the root in a tree or cluster topology and may be located anywhere in peer-to-
peer. ZigBee standard defines two stack profiles: ZigBee and ZigBee Pro. These
stack profiles support full mesh networking and work with different
applications allowing implementations with low memory and processing power.
ZigBee Pro offers more features including security using symmetric-key
exchange, scalability using stochastic address assignment, and better
performance using efficient many-to-one routing mechanisms.

Wireless protocol for device monitoring and control: Zigbee Smart Energy
(Zigbee SE) is a protocol designed for monitoring and actively managing energy
consumption at the end-user level. For both utilities and consumers, Zigbee SE
can help reduce waste, energy consumption and enables utilities to monitor
and manage customers’ energy use. Furthermore, the end-user can monitor
their energy consumption.

Affordable and easy to use

With Zigbee SE it easier to monitor energy consumption and lower the energy
costs – for both utilities and the end-user. Zigbee SE is easy to use because it
is interoperable with other Zigbee protocols and works across manufacturers.
The standardized protocol provides fast access to new markets for solution
providers, and it reduces research costs
Reducing energy consumption

Intelligent energy management with Zigbee SE also benefits the environment,

because it improves energy availability. With the access to monitor the energy
consumption, both utilities and end-users can regulate the use of energy, thus
saving money and reducing the impact on the environment. Increased energy
efficiency reduces the need for additional generation plants.

Zigbee Smart Energy features

The Zigbee SE offers real-time information, tracking of energy consumption,

multiple control methods e.g. emergency signals and duty cycling, and includes
the ability to randomize start and end times to avoid energy spikes. The
protocol naturally uses data encryption to safeguard data. The protocol fits
multiple commodities, e.g. electricity, gas, and water, and it has several
measurement types such as load profile, power factor, demand, and tiers.

ZigBee SE is a world-leading standard widely used for smart metering

(electricity, gas and water) and home automation (wireless domotics). ZigBee is
a simple data transmission protocol designed to be used as a low rate wireless
personal area network (LR-WPAN). Based on the IEEE 802.15.4 specification,
for a set of high-level communications protocols, it’s a low-powered, low-
bandwidth digital radio communication system. Among its most important
applications are automation in the home and smart metering. The protocol is
intended for devices requiring low-power, relatively low transmission speeds
and short distances between devices. In terms of transmission speeds, in the
best-case scenario and depending on the frequency used, it can reach 250
Kb/s. The maximum transmission distance can vary from 10 to 100 meters,
depending on the frequency, transmission power and environmental
conditions. Radio channel access is provided by CSMA/CA (Carrier Sense
Multiple Access with Collision Avoidance) – a low level network access control
protocol that permits multiple stations to use the same transmission medium.
ZigBee devices consume very small amounts of energy and are very low cost.
They use protocols from different layers (PHY, MAC, network, security, and
application). The network, security and application layers are defined by ZigBee
Alliance. The networks can work on different frequencies: 868 MHz, 915 MHz
and 2.4 GHz. ZigBee networks support around 65,000 devices.

ZigBee networks support star and mesh topologies. Three types of devices are
defined:
 1) Coordinator: this is the device that coordinates and forms the network,
which means that every network must always have one. Once this device
creates the network, other devices (Routers or End devices) can join. It is
responsible for selecting the frequency channels and assigning network
identifiers (PAN ID) to devices. The PAN ID is used to communicate
between network devices. The coordinator can help to route data over
mesh networks. It requires a permanent power supply, must always be
active and be able to support child devices.
2) Router: First, it must join the network, after which it can allow other
Routers and End devices to join. It requires a permanent power supply,
must always be active and be able to support child devices.
3) End Devices: These do not connect to other network devices. They are
usually battery-powered devices and can go into “sleep” mode to save
energy.

The following image is a graphical representation of a mesh network structure:

A number of standards use ZigBee as a base. The most common of these are:

ZigBee Home Automation (ZHA): This is a home automation-oriented global

standard for controlling applications like lighting, temperature control, energy
management, security and accident prevention. ZigBee Smart Energy (ZSE):
This is a global standard that allows service providers and Home Area Network
(HAN) electricity distribution companies to manage energy consumption. ZSE
also allows suppliers and customers to interact, so that both can
access smart communications. ZigBee Light Link (ZLL): This is a global
standard that permits consumer lighting elements and other elements to
interoperate with each other, giving consumers wireless access to these
elements. It allows consumers to control their home lighting, while managing
energy use and making their homes “greener”.

Reason for ZigBee Smart Energy

ZigBee SE provides service providers and power distributors with a simple

wireless access network within homes (Home Area Network, or HAN). Smart
Energy offers these groups and their customers the possibility of
communicating with each other directly in order to control smart applications
(e.g., thermostats and other devices used to control high energy use in the
home). Having access to customers’ instantaneous consumption enables power
distributors to more efficiently manage the electricity smart grid (generation
and distribution). Furthermore, customers can receive real-time information on
their energy use through devices installed inside the home, as well as by
accessing the HAN through the services provided by energy distributors and/or
service providers.

Bluetooth Low Energy:

Bluetooth low energy or Bluetooth smart is a short range communication
protocol with PHY and MAC layer widely used for in-vehicle networking. Its low
energy can reach ten times less than the classic Bluetooth while its latency can
reach 15 times. Its access control uses a contention-less MAC with low latency
and fast transmission. It follows master/slave architecture and offers two types
of frames: adverting and data frames. The Advertising frame is used for
discovery and is sent by slaves on one or more of dedicated advertisement
channels. Master nodes sense advertisement channels to find slaves and
connect them. After connection, the master tells the slave it’s waking cycle and
scheduling sequence. Nodes are usually awake only when they are
communicating and they go to sleep otherwise to save their power.

Being part of the Bluetooth v4.0 standard adopted in 2010-06-30, Bluetooth

Low Energy (BLE) is also known as Smart Bluetooth. BLE is an IEEE 802.15.1
variation with better and more suitable capacities for low power applications
than the classic Bluetooth Basic Rate. Devices that demand communication
with both standards of Bluetooth are required to implement and support both
protocol stacks due the incompatibilities among them. Star is the only topology
accepted by BLE due the standard definition that does not permit physical link
connections among slave devices. Any data exchanged between two slave
devices shall pass through the unique master and a slave device may not be
connected to two master units at the same time. These premises define the
formation of a BLE star pico-net.

Using a similar protocol stack as classic Bluetooth, the differences between

them starts above the L2CAP layer. Above the L2CAP layer, BLE is the
application layer that uses a set of functionalities, which are not present in the
classic Bluetooth specifications. These functionalities are the Attribute Protocol
(ATT), the Generic Attribute Profile (GATT), the Security Manager Protocol
(SMP) and the Generic Access Profile (GAP). Figure 7 depicts the BLE protocol
stack.

The two main roles of BLE are: controller and host. BLE differs from the
classical Bluetooth in the controller stack that defines the association methods
of the devices. A slave can belong to only one pico-net during an association
lifetime, and is synchronized with only one master element.

A Host Controller Interface (HCI) is a communication standard applied between

the slave and controller. In the Bluetooth Basic Rate, 79 channels are used
with a 1 MHz bandwidth to reduce interference with adjacent channels. In
Bluetooth Low Energy, the channels are defined in the 2.400– 2.4835 GHz
band with a 2 MHz guard band. To achieve scalability, the master device
controls the number of hosts associated with it by adjusting the value of the
connection interval (ConnInterval parameter) between hosts and controllers.

Link layer manages events generated by the hosts, at determined time

intervals, using the advertising channels. Bidirectional data flow is obtained
with a connection between elements, when slaves advertising packets are
received by master elements. The energy save handling done at MAC layer can
put the slaves in a sleeping mode by default and waking them periodically
through a Time Division Multiple Access (TDMA) scheme.

In the classic Bluetooth basic protocol, this layer a stop-and-wait flow control
mechanism is used to provide error recovery capabilities. At BLE, the L2CAP is
an adaption of the classic Bluetooth basic protocol stack but optimized and
simplified to receive the application layers designed for low energy platforms.
Data exchange between the application layer and link layer are also done by
L2CAP using no retransmission techniques or flow control mechanisms as
used on the classic Bluetooth. Not using retransmission or flow control
mechanisms (present in the classic Bluetooth) and segmentation and
reassembly capabilities, the Packet Data Units (PDU) (limited to 23 bytes in
BLE) received by the application layer is delivered ready to fit the maximum
size of the L2CAP payload.
 Fig: Bluetooth low energy protocol stack.

When two devices are connected under a server and client association
architecture, the server needs to maintain a set of attributes. The Attribute
Protocol (ATT) handles the attributes of this connection like the definition of
data structure used to store the information managed by the Generic Attribute
Profile (GATT) that works on top of the ATT. GATT defines the client or server
functionalities of a connection and this association is independent of the
master or slave roles. The attributes of the server need to be accessed by the
client through the requests sent, which trigger the response messages of the
server. It is also possible for a server to send to a client, unsolicited messages
like notifications that do not need any confirmation message to be sent by the
client. A server is also required to send indication messages, which need
confirmation messages to be sent by the client. The slave sends requests for
responses and indications prior to transactions confirmation following a stop-
and-waitscheme. Slaves can either write attributes values at the master.

A framework defined by GATT performs the role of discovery services using the
ATT attributes, and allows exchange of characteristics between devices
interconnected. An attribute carries a set of characteristics that includes a
value and properties of the parameter monitored by the device. For example, a
humidity sensor needs humidity characteristics and attributes to describe this
sensor, and to store its measurements. Thus, this sensor needs a further
attribute to specify the measurement units. Creating specific profiles with the
Low Energy Bluetooth standard takes place in the Generic Attribute

Profile (GATT). GATT uses the Attribute Protocol (ATT) protocol in addition to
the lower stack protocols, in order to introduce the subdivision of retained
server attributes into services and features. Services can contain a set of
features, which can include a single value (accessible from the client) and other
numerical data that describe such features. Among the assignments of GAP
profile specifications are: device role rights, discovery devices and services, as
well as establishing connections and security. A new profile based on the
existing profile requirements can be created following a profile hierarchy. The
interoperability of different devices can be handled through application
profiles.Bluetooth is designed to offer a low-cost alternative to Wi-Fi at the
expense of the transmission range. Its transmission range is considerably
shorter (up to 100 m LOS) and data rate does not exceed 721.2 Kbps in the
classic Bluetooth Basic Rate version and can reach 3 Mbps with the Enhanced
DataRate feature. BLE operates at 1Mbps rate on its physical layer, while its
application layer can handleonly 236.7 Kbps.

In Bluetooth Low Energy, there are no subdivisions in power classes but only
the maximum and minimum output power values of the transmitter are
provided. Only an approximate value of the maximum reachable distance can
be predicted. The low power required for transmission is the main feature of
the Bluetooth Low Energy standard and this result is due to enhancements
made on the classic version. These enhancements include reduced frequency
band and shorter PDU packets. An energy evaluation is offered at using
CC2640 radio chipset consumption reference measurements. The comparison
is made when operating on 0 dBm transmission power by gathering the main
characteristics of Bluetooth and BLE.
Bluetooth v5.0 has no functional block included in its first and second layers
when compared to versions v4.0, v4.1, and v4.2. A representation of the inter-
layer communication structure and the relationship with Bluetooth layers of
different Bluetooth versions can be seen in Figure 8. Device-to- device file
transfers, wireless speakers, wireless headsets, and Body Sensor Networks are
often enabled with Bluetooth versions.

Finally, some characteristics of the Bluetooth BR and BLE technologies are

summarized in Figure 9. This figure allows the comparison of their differences
according to the PHY and MAC layer characteristics.

Fig: Bluetooth power class classification.

Fig: Bluetooth basic rate versus Bluetooth low energy.