U4 Flashcards
(349 cards)
1
Q
The core idea behind IoT technology is to ?
A
connect physical devices to the Internet and enable communication between users and their devices.
2
Q
By connecting a huge number of devices to the Internet, one often has to deal with?
A
so-called constrained devices which have physical limitations in the allocated energy, size, and memory footprint.
3
Q
To provide these constrained devices with connectivity, IoT developers have to ?
A
implement a communication protocol stack.
4
Q
The figure below demonstrates the widely adopted networking protocols within IoT and where they fit within the TCP/IP layers.
A
5
Q
Many emerging networking technologies, offered by different vendors, are being adopted within the ———————–. These competing technologies mostly provide alternative implementations of the same————————.
A
IoT space
standard protocols
6
Q
For example,
A
IEEE 802.15.4 describes the operation of low-rate wireless personal area networks (LR-WPANs) and is implemented by several competing technologies including ZigBee, Z-Wave, SNAP, and 6LoWPAN.
7
Q
It is worth mentioning that some Internet protocols, e.g., Ethernet and Wi-Fi, can be?
A
applied in the IoT framework.
8
Q
Nevertheless, new technologies are being developed specifically to?
A
meet the IoT challenges.
9
Q
Nevertheless, new technologies are being developed specifically to?
A
meet the IoT challenges.
9
Q
Nevertheless, new technologies are being developed specifically to?
A
meet the IoT challenges.
9
Q
Nevertheless, new technologies are being developed specifically to?
A
meet the IoT challenges.
9
Q
Nevertheless, new technologies are being developed specifically to?
A
meet the IoT challenges.
9
Q
Nevertheless, new technologies are being developed specifically to?
A
meet the IoT challenges.
10
Q
The structure of a network is known as ?
A
its topology.
11
Q
The most common network topologies that are adopted within IoT are?
A
star and mesh topologies.
12
Q
In mesh topologies, IoT devices connect to ?
A
other devices within range.
13
Q
The nodes within a network can act as ?
A
simple sensor nodes which route traffic.
14
Q
Mesh networks are more complex than networks with star topologies but?
A
have the advantage of being more resilient to failure because they do not depend on a single central gateway.
15
Q
Now, we discuss two communication patterns that are commonly used in the IoT applications.
A
Publish/Subscribe Pattern
Representational State Transfer Pattern
16
Q
The publish/subscribe pattern concentrates on ?
A
the non-direct exchange of messages between a sender and a receiver.
As delineated below, the sender, referred to as the publisher, sends the message not directly to the receiver, but publishes it to a message-oriented middleware.
17
Q
This middleware is called ?
A
a broker and manages the distribution of messages.
18
Q
A sender publishes?
A
a message to the broker.
19
Q
A receiver, referred to as?
A
the subscriber, can subscribe to the content/topics of interest and then will receive all messages that are relevant.
20
Q
The broker must handle all incoming messages and distribute them correctly to?
A
all subscribed receivers.
21
Using this pattern enables ?
a loose coupling between senders and receivers.
22
In this context, loose coupling means that?
they do not depend on each other regarding time, space, and synchronization.
23
Senders and receivers do not need to?
know where the other end-device is located (e.g., IP address).
24
They also do not need to run at the same time to receive/send------------------------. For synchronization, they do not need to --------------------local operations to send or receive messages.
a message
interrupt
25
Publish/subscribe provides three different types of message filtering:
.
The first filter approach is a “subject-based filtering” performed with topics hosted on the broker.
Each message published to the broker has a specific topic and each subscription of a client is related to a specific topic.
The broker distributes messages tagged with different topics. The topics are in general string with a hierarchical structure which enables limited filtering
26
In general, a huge benefit of the publish/subscribe pattern is:
the fact that it is loosely coupled, and thus is extremely scalable and flexible.
27
The only task done by the IoT devices is ?
generating the content—every other step is done through a separated message broker.
28
the content can easily be scaled and modulated to the architecture and design of the solution.
The only task done by the IoT devices is generating the content—every other step is done through a separated message broker.
29
Furthermore, the publish/subscribe pattern lends itself very well to?
testing.
30
A subscriber is?
narrowly limited to a set of events that they have requested under a certain topic.
31
If a failure occurs, this natural segmentation informs the provider as ?
to where the fault is, and which class of users is experiencing the fault.
32
Unfortunately, decoupling is seen as a ?
huge disadvantage for this pattern.
33
Brokers in the publish/subscribe pattern cannot effectively notify the publishers that?
a certain message has been sent.
34
The subscribers are entirely separated from the event and thus?
may not know if a message was not erroneously sent.
35
While the system is extensible and flexible, network instability may occur with ?
an increase in traffic load.
36
Such a high load will lead to ? its own difficulties when these relationships need to be modulated.
the aforementioned instability together with increased complexity.
37
Although the relationship between the publisher and subscriber in this model may be beneficial, it also comes with?
37
Although the relationship between the publisher and subscriber in this model may be beneficial, it also comes with?
its own difficulties when these relationships need to be modulated.
38
The Representational State Transfer (REST) pattern enables IoT applications to?
represent objects as resources with universal resource identifier (URI).
39
REST is based on the client/server architecture which relies on?
the HTTP protocol.
40
In this context, a resource is ?
a source of specific information, i.e., sensor readings, identified with an URI identifier.
41
Such resources can be?
readily manipulated by using the HTTPmethods, i.e., GET, PUT, POST, and DELETE.
42
Using the REST architectural style allows?
an independent implementation of clients and servers.
43
Such an independency leads to a stateless system, where neither the server nor the client needs to?
know anything about the current state of the other end-device.
44
Standard HTTP methods are used?
To get the content of some object or to modify it.
44
Standard HTTP methods are used?
To get the content of some object or to modify it.
44
Standard HTTP methods are used?
To get the content of some object or to modify it.
44
Standard HTTP methods are used?
To get the content of some object or to modify it.
44
Standard HTTP methods are used?
To get the content of some object or to modify it.
45
A request consists of ?
an HTTP method identifier,
a message header,
a path to a resource,
and an optional message body with data in case of a PUT or POST request.
46
In the request example above, a GET request is sent to a server with the specified path of the resource. In the header, the accepted content-type is defined as JSON. On the server side, a JSON file is located at the specified path. After the server gets the request, the response looks like the following:
Code
GET http://example.com/temperature/sensor1
Accept: application/json
47
The status codes are inherited from?
HTTP semantics.
48
The content behind the URI can be very different, e.g.,?
XML, JSON, images, or PDF files.
49
In general, REST is popular thanks to its simplicity where it builds upon existing systems and features of the Internet's HTTP to achieve?
its objectives, in lieu of creating new standards, frameworks, and technologies.
50
REST-based applications can be written using?
any language, e.g., Java, Kotlin,.
51
Another advantage of REST is being a?
language-agnostic architectural style.
52
NET, AngularJS, or JavaScript, as long as the programming language can make web-based requests using ?
HTTP
53
Accordingly, IoT developers have the freedom to select the?
technologies that are well suited for their situation.
54
We classify these technologies into :
IP-based protocols
and non-IP-based technologies.
55
The non-IP communication systems are?
optimized for cost and energy usage, whereas IP-based solutions usually have fewer constraints.
56
Furthermore, we divide the non-IP-based communication systems into?
short-range and long-range communication systems.
57
In general, IP represents the standard form of?
global communication for several reasons.
58
For instance,
IP stacks are provided by nearly every operating system and every medium. IP communication protocols can run on various WPAN systems, e.g., cellular, copper wire, fiber-optic, PCI Express, and satellite systems.
59
IP stacks are provided by ?
nearly every operating system and every medium.
60
IP communication protocols can run on various WPAN systems, e.g., ?
cellular, copper wire, fiber-optic, PCI Express, and satellite systems.
61
Furthermore, ---------------has withstood the test of time by users for ------ years. Longevity is paramount for many industrial and field --------------------------- that must support devices and systems for decades.
TCP
40
IoT solutions
62
Aside from longevity, TCP/IP is governed by?
the Internet Engineering Task Force (IETF) which IETF maintains a set of open standards focused on the Internet protocol.
63
System designers can trust IP for their application?
the Internet Engineering Task Force (IETF) which IETF maintains a set of open standards focused on the Internet protocol.
64
Additionally, IP-based networks have mostly demonstrated massive scaling to billions of users and many more devices To further enhance the scalability, IPv6 has been designed to provide?
a unique IP address to a virtually unlimited number of devices.
65
Finally, there exist various tools to manage IP networks and devices on an IP network:
Modeling tools,
network sniffers,
diagnostic tools,
and various appliances exist to assist in building,
scaling,
and maintaining networks.
66
IP addresses require a well-supported and robust transport layer, e.g., ?
TCP and user datagram protocol (UDP), for end-to-end communication.
67
TCP is used for connection-oriented transmissions, whereas UDP is used for?
connectionless transmissions.
68
UDP is naturally much simpler to implement than TCP, but ?
not as resilient.
69
Both services provide segment reordering as packets are?
not guaranteed to be delivered in order using an IP protocol.
70
TCP also provides the layer of reliability to an unreliable IP network layer using?
acknowledgment messages and retransmissions of lost messages.
71
Additionally, TCP provides flow control using ? a lightweight, high-speed facility for broadcasting data to various devices that may or may not be present.
sliding windows and congestion avoidance algorithms.
72
Alternatively, UDP provides?
a lightweight,
high-speed facility for broadcasting data to various devices that may or may not be present.
73
In fact, 6LoWPAN is the result of several efforts to bring IP addressability to?
the resource-constrained devices which do not need high bandwidth networking services.
74
6LoWPAN is an acronym that stands for ?
IPV6 over low-power WPANs.
75
The protocol can be used with?
other WPAN communications such as 802.15.4 as well as Bluetooth, and sub-1 GHz RF protocols.
76
The main advantage of 6LoWPAN is?
-the simplicity of implementing sensors which have IP addressability and act as a network citizen over 3G/4G/LTE/Wi-Fi/Ethernet routers.
- Moreover, IPV6 provides significant theoretical addressability of billions of unique addresses, thus more IoT devices can be easily connected.
77
6LoWPAN networks are typically?
mesh networks residing on the periphery of larger networks.
78
These topologies are naturally flexible, thus?
allowing for disjointed networks without any binding to the Internet or other systems.
79
Additionally, ad-hoc networks can form without ?
requiring an Internet connectivity of an edge router (Olsson, 2014).
80
The figure below depicts an example of an IPv6 network, including a 6LoWPAN mesh network.
81
The 6LoWPAN networks operates on the edge and is connected to the IPv6 network using?
an edge router.
82
As can be seen below, three different types of nodes exist within the 6LoWPAN mesh network:
router nodes,
host nodes
and edge routers.
83
The router nodes forward data from?
one 6LoWPAN mesh node to another.
84
The host nodes in the mesh network cannot?
-route data in the mesh
-and are simply endpoints consuming or producing data.
85
Hosts are allowed to be?
in sleep states, occasionally waking to produce data or receive data cached by their parent routers.
86
The edge router handles three actions:
(1) the data exchange between 6LoWPAN devices and the Internet;
(2) the local data exchange between devices inside the 6LoWPAN;
and (3) the generation and maintenance of the radio subnet (the 6LoWPAN network).
87
OSI model
This is a conceptual framework that describes functions of the networking and divides data communication into seven abstraction layers.
88
6LoWPAN significantly changes?
the IoT landscape.
89
Without 6LoWPAN, a complex application layer gateway is required to?
make devices such as ZigBee and Bluetooth connect to the Internet.
90
6LoWPAN solves this problem through introducing?
an adaptation layer between the IP stack’s link and network layers to enable transmission of IPv6 datagrams over IEEE 802.15.4 radio links.
91
As depicted in the following figure, the stack of 6LoWPAN comprises several layers, analog to the OSI model.
92
At the outset, the physical layer converts data bits into------------------------- and received over the air. Afterward, the data link layer provides a --------------------- between two directly connected ------------.
signals transmitted
reliable link
nodes
93
Such reliability is achieved by?
-detecting and correcting errors that may occur in the physical layer during transmission and receiving.
-Specifically, the data link layer includes the media access layer (MAC) which provides access to the media, using protocols such as the carrier sense multiple access–collision avoidance (CSMA-CA) where the radio listens that no other IoT device is transmitting before actually sending data over the network.
94
The data link layer also includes the 6LoWPAN adaptation layer which provide?
adaptation from IPv6 to IEEE 802.15.4.
95
The network layer addresses and routes data through?
the network over several hops.
96
The transport layer, e.g., TCP/IP, generates communication sessions among different applications running on?
end devices.
97
Additionally, it allows multiple applications, on each end device, to ?
have their own communications channel.
98
Bluetooth is ?
one of the most adopted wireless technologies that is designed for short-range communication.
Many of our everyday devices implement the Bluetooth feature such as mobile phones, smart watches, sensors, and more.
99
Furthermore, Bluetooth Low Energy (BLE), otherwise known as --------------------------------- is also a wireless communication technology that was first introduced as --------------------------------- in 2006. After that, the ------------------------------------ (SIG) adopted the technology and kept developing it as -------------- was introduced in the --------------------------------------------------------- version 4.0 in 2010.
Bluetooth Smart,
Wibree by Nokia
Bluetooth Special Interest Group
BLE
Bluetooth Core Specification
100
Although there are many wireless technologies that have been emerging in the market such as Zigbee and 6LoWPAN, BLE has?
drastically improved and grown exponentially more than those other technologies
due to its low power consumption
and also its prior support on many devices and smartphones.
101
BLE was first supported on the Android platform in?
API 18 (Android Jelly Bean version 4.3).
102
Android smartphones could interact with BLE devices which allowed them to ?
fetch services and even read or write data to these BLE smart devices. the expansion of BLE-integrated low-power devices such as heart rate monitors, proximity sensors, and fitness trackers.
103
This feature had a great influence on the Android community as it helped in ?
the expansion of BLE-integrated low-power devices such as heart rate monitors, proximity sensors, and fitness trackers.
104
Additionally, BLE has many great features as it is?
extremely power efficient and has an enhanced short communication range.
105
The ability of BLE devices to consume low energy and to operate on coin-cell batteries for months, or sometimes years, made it a very reliable technology to be used in many IoT applications.
106
Technically speaking, BLE has two implementation modes:
-single mode.
Devices that concentrate on low power consumption and low cost, such as smart watches and heart rate sensors.
-dual mode.
Devices that can operate on both Bluetooth Classic and BLE. For example, smartphones need Classic Bluetooth to connect to a Bluetooth headset. However, BLE is also required to connect to a smart fitness tracker.
107
The BLE Protocol Stack consists of two main parts:
the controller
and the host.
108
The controller part has two layers:
(1) the link layer which is responsible for providing medium access, error control, flow control, and connection establishment; and
(2) the physical layer which makes sure the transmission and reception of data bits are working properly.
109
Meanwhile, the host part has three main components:
-the control
and adaptation protocol (L2CAP),
Generic Attribute Profile (GATT), and Generic Access Profile (GAP).
-The Generic Access Profile (GAP) provides a framework which describes the procedures and modes for data broadcasting, device discovery, and establishing connections.
110
GAP specifies four possible roles for the BLE device to adopt:
Broadcaster,
Observer,
Central,
and Peripheral.
111
Each one of these roles will be?
further discussed in detail throughout this section.
112
Any IoT device with integrated BLE has the ability to use two communication mechanisms which are:
“connection” and “broadcast.”
113
First, the connection mechanism is ?
used for the establishment of a bi-directional communication to exchange data between two devices.
114
Two types of devices are present in this type of communication:
central device
and peripheral device.
115
Basically, the main role of the central device is to? sending advertisements and responding to connection requests, if received.
regularly scan for advertising packets that it can connect to,
and if found, it sends a connection request to the advertising devices to begin data transmission.
116
On the other hand, the peripheral device is responsible for ?
sending advertisements and responding to connection requests, if received.
117
The following figure illustrates the connection topology between the central and peripheral roles in BLE connection scenario.
118
the difference between central devices and peripheral devices?
Accordingly, the central devices have the privilege of connecting to more than one peripheral device at the same time, while the peripheral cannot connect to several central devices.
119
When the two devices establish a connection, the peripheral device stops?
advertising more packets and begins data exchange only between these two devices.
120
After establishing the connection, the central device deals with?
the timing intervals
and the exchange of data procedure.
120
After establishing the connection, the central device deals with?
the timing intervals
and the exchange of data procedure.
120
After establishing the connection, the central device deals with?
the timing intervals
and the exchange of data procedure.
120
After establishing the connection, the central device deals with?
the timing intervals
and the exchange of data procedure.
121
The other communication mechanism is ------------------------. Broadcasting is a simple way to establish -----------------------connection for the --------------devices to send data to central devices, if they are within the ---------------------.
broadcast
one-way
peripheral
range
122
In addition, this mechanism has two discrete roles:
(1) broadcaster and
(2) observer.
The broadcaster role is to send advertising packets periodically to nearby listening devices while the observer can receive and collect these advertising packets sent by the broadcaster.
123
Moreover, an advertising packet is mainly composed of?
a 31-byte payload.
124
An advertising packet is mainly composed of a 31-byte payload. These bytes include:
device descriptive data
and other information that can be transmitted to an observer during the connection period.
125
Additionally, this payload can be extended with an optional second packet of 31 bytes which means that ?
the advertising packet’s size can be up to 62 bytes.
126
The figure below demonstrates the advertising process between a broadcaster (i.e., peripheral device) and an observer (i.e., central device).
127
A peripheral specifies a certain ------------interval. As each interval passes, it ------------------its advertising ----------. Setting long intervals reduces the energy consumption but a device only advertising itself once every --------------------- is considered less responsive compared to when advertising itself every------------------------.
advertising
re-transmits
packet
circa 2 seconds
20 milliseconds
128
Additionally, if the observer wants the scan response payload which is available on the peripheral device, it can?
request this scan payload and the broadcasting peripheral responds with the additional data.
129
The two communication mechanisms have their advantages and disadvantages. Specifically, the connection mechanism has the advantage of ?
better privacy and security, as the data packets are received and read by only the two connected devices which is different from broadcasting, as it enables any device in the listening range to scan its data.
129
The two communication mechanisms have their advantages and disadvantages. Specifically, the connection mechanism has the advantage of ?
better privacy and security, as the data packets are received and read by only the two connected devices which is different from broadcasting, as it enables any device in the listening range to scan its data.
130
Therefore, the use of the broadcast mechanism in some applications that include the transmission of sensitive information is?
not preferable.
131
Nonetheless, broadcasting is suitable for applications that require?
sending small amounts of data or sending it to multiple devices.
132
Nonetheless, broadcasting is suitable for applications that require?
sending small amounts of data or sending it to multiple devices.
133
In addition, the connection mechanism conceivably has less?
power consumption, as the devices connected to peripherals can increase the delay between connection intervals as well as limiting the transmission of data to just when the data is updated or changed.
134
On the other hand, broadcasting devices only?
advertise their data continuously whether there is an observer listening.
135
The Generic Attribute Profile (GATT) defines?
the procedure of transferring data back and forth between two BLE devices.
136
Specifically, GATT defines?
the way of how central and peripheral devices can exchange data based on services and characteristics.
137
Furthermore, it sets the rules and guidelines that BLE devices have to follow in order to?
be able to discover, read, and write data of the respected connected devices.
138
The Attribute Protocol (ATT) is the basis of?
GATT data exchange procedure where it stores services and characteristics in a look-up table.
139
Furthermore, GATT deals with:
the peripheral device
as a server,
while the IoT device that act as a central device
is referred to as a client.
140
The server holds the ATT look-up table containing ?
both service and characteristic definitions, and the GATT client sends requests to this server.
141
When establishing a connection between central and peripheral devices, the transaction starts?
from the central device. Afterward, the central device waits for the peripheral’s response.
142
The peripheral device suggests a “--------------------------” to the central device, and the central device tries to -----------------every connection interval to check if any new data is --------------------.
connection interval
reconnect
available
142
The peripheral device suggests a “--------------------------” to the central device, and the central device tries to -----------------every connection interval to check if any new data is --------------------.
connection interval
reconnect
available
143
The first level of the GATT Data hierarchy is?
the profile which is composed of services created by Bluetooth SIG or peripheral designers to identify the application present in the server.
144
For instance,
-a heart rate profile contains heart rate and device information services.
-Each service may contain several characteristics, e.g., a heart rate monitor service could include a heart rate measurement characteristic.
- Additionally, each characteristic consists of a piece of user data called the characteristic value which contains the actual application data,
-as well as metadata that describe the characteristic value.
-The last component is the characteristic properties which decide what operation can be executed on the associated characteristic value.
145
In what follows, we provide a brief explanation of each property:
-read.
This property is used when a GATT client asks for a specific characteristic to be obtained from the GATT server. Therefore, the GATT server sends the desired data to the GATT client.
-write.
This property is used when the GATT client assigns a new value to a specific characteristic stored in the GATT server.
-notify/indicate.
If the GATT server needs to send data to the GATT client, the GATT server must notify the client and wait for a response from the client. The GATT client cannot directly obtain data from a server. Instead, the server must subscribe to the client’s characteristic data and the GATT client may write back the needed data to the GATT server.
146
In wireless communication, mobile cellular network technologies, such as ?
4G networks,
cover great areas
and are used ubiquitously,
being developed to serve users with high data rates.
147
However, a primary disadvantage of these cellular networks when?
being used in IoT applications is the high energy consumption that is needed to achieve these high data rates over a greater range.
148
Wi-Fi was also developed to achieve high data rates, but only ?
covering small areas of up to a few tens of meters.
149
To assure the high data rates, Wi-Fi also needs ?
a high energy consumption to operate.
150
A much lower energy consumption is addressed by?
technologies such as BLE or ZigBee.
In contrast, these technologies are based mostly on top of mesh networks
and therefore need network routing.
151
To fill the gap of these communication technologies, LPWANs have been adopted in?
many modern IoT applications.
152
Together with similar approaches like Sigfox and Ingenu RPMA, LoRa was developed to achieve?
low-power consumption over large ranges.
153
The main goal of LoRa is to build ?
IoT applications on top of long-ranging devices that have a low power consumption and can therefore last up to 10 or 20 years.
154
In contrast to wireless technologies like BLE and Zigbee, the topology of LoRa/LoRaWAN is?
shaped as a star-of-stars instead of a mesh.
155
LoRa devices communicate directly to one (or more) gateway(s) and not routed over other LoRa devices?
in contrast to wireless technologies like BLE and Zigbee, the topology of LoRa/LoRaWAN is shaped as a star-of-stars instead of a mesh.
156
The great advantage of this topology is that there is?
no need for costly forwarding messages over nodes to the gateways.
157
Through a backbone network, such as Ethernet, the gateways are connected to a central network server?
The great advantage of this topology is that there is no need for costly forwarding messages over nodes to the gateways.
158
Such topology highly improves the energy efficiency since?
there is no forwarding mechanism needed on the LoRa nodes themselves.
159
Below, the protocol stack of LoRaWAN is depicted, including :
the various layers.
160
LoRa PHY is?
the physical layer of the LoRa network. LoRa operates in sub-gigahertz unlicensed bands at 868 MHz in Europe, 915 Mhz in the United States, and at 433 Mhz in Asia and it can be used in both acknowledged and unacknowledged modes.
161
It uses chirp spread spectrum (CSS) as its?
modulation technique.
162
CSS differentiates between ?
upchirps and downchirps corresponding to 1 and 0.
163
The transmission frequency is increased inside a predefined bandwidth for ?
an upchirp, and decreased accordingly for a downchirp.
164
The time interval of each chirp can be configured by using?
different spreading factors (SFs).
165
The SFs are integer values between ?
7 and 12, and they manipulate the chirp duration.
166
The data frames sent over the wireless connection start with ?
a preamble and a start of frame delimiter (SFD) which are used to synchronize a sender and receiver.
167
The preamble is, for example, ?
built up with eight following upchirps.
168
The following part of the frame is?
the PHY Header which probably contains information about the payload length.
169
After the PHY Header, the frame contains a cyclic redundancy check (CRC)?
which checks for possible errors in the payload data, followed by the payload data.
170
Aside from the physical layer, LoRaWAN medium-access control (MAC) protocol runs on?
the network server and is based on the ALOHA protocol.
171
It can be further configured to allow listening before talking?
Because Aside from the physical layer, LoRaWAN medium-access control (MAC) protocol runs on the network server and is based on the ALOHA protocol.
172
The payload of a data frame in a LoRa PHY message includes:
-the MAC header of length one byte,
the MAC payload
and a 4-byte long code to ensure message integrity.
173
The MAC payload is then further partitioned into ?
device address,
a few control features and the payload which can vary between 227–242 bytes for a low spreading factor 7 and for a high spreading factor of 8 between 36 and 51 bytes.
174
In terms of activation and security, the data link layer (and also the layers above) of LoRa is called ?
LoRaWAN.
175
Packets that are sent via PHY are forwarded from?
the gateway to a network server.
176
Since the network is a star topology, routing is?
not
required on the network.
177
The backhaul connection between the gateway and the network server is?
an IP-based connection, e.g., 3G and Ethernet.
178
The network server is used to ?
authenticate the LoRa nodes and builds a connection when a newly arrived nodes which enters the range of the gateway.
179
The network server additionally forwards the payload to?
one or more application server.
180
Both connections from LoRa end-device to network server and from the network server to the application server are?
end-to-end secured by session keys.
181
There are two techniques provided for a LoRa node to join a network:
Over-the-Air Activation (OTAA)
and Activation by Personalization (ABP).
182
OTAA uses an Application ID together with an Application Key and the Device ID to?
authenticate the LoRa device.
183
LoRaWAN has three device classes to address the trade-off between?
the battery lifetime and the downlink network communication latency.
184
LoRaWAN has three device classes:
Class A devices
Class B devices
Class C devices
185
Class A devices
=Class A devices schedule their up- and downlink transmissions depending on the need for transmission by the LoRa device.
=For every uplink transmission, two windows of short downlink transmissions are opened.
=The time in which a transmission can be sent is called the “duty-cycle” and is given in percentage of time.
=Class A devices are the most power saving option of the three device classes, as it is mostly not possible to send downlink messages from the network server to the end-node.
186
Class B devices
Class B devices additionally serve with another receive window that is opened corresponding to the synchronized time of the gateway.
187
Finally, Class C devices
are always listening except during data transmission.
188
Besides LoRa, Sigfox is currently accepted as?
an efficient LPWAN technology.
189
Furthermore, Ingenu RPMA claims that it has gained?
momentum in recent years.
190
Sigfox is another long-range wireless technology that has?
already been developed earlier than LoRa/LoRaWAN in 2009.
191
In general, Sigfox has similar characteristics as LoRa but ?
differs especially in technological details.
192
For the physical transmission, each message is:
100 Hz wide and transferred at 100
or 600 bits per second data rate, depending on the region.
193
Sigfox covers higher ranges then?
Battery lifetime strongly depends on?
LoRa, namely 10 km in urban areas and up to 50 km in rural regions.
the frequency of sending messages.
194
For example,
using a 3.6 V lithium AA-cell battery, the lifetime can vary from six years while sending ten times a day to more than ten years while transmitting once a day.
195
If there are more messages sent a day, the battery lifetime can?
shrink to a few months.
196
A little later than LoRa and Sigfox, the company Ingenu published its LPWAN technology called?
“RPMA.”
197
Ingenu RPMA, in contrast to the other two LPWAN technologies, does not work on ?
sub-gigahertz frequency bands, but on 2.4 GHz.
198
,Accordingly, Ingenu RPMA has the advantage of being independent on the region, i.e.,?
the frequency does not change from Europe to the United States or Asia.
199
the frequency does not change from? to?
Europe to the United States or Asia.
200
Ingenu adopts the Code Division Multiple Access (CDMA) modulation technique which?
allows transmission of multiple senders within the same time slot.
201
The following table compares important measures of ?
LoRa/LoRaWAN, Sigfox, and Ingenu RPMA.
202
Sigfox comes out with a high range but ?
lacks in data transmission rate.
It also does not provide the highest maximum battery lifetime.
203
LoRa/LoRaWAN has slightly better values in all the metrics except?
the coverage range.
204
However, the long battery life depends on?
the device class used by the LoRa device.
205
In general, Ingenu RPMA outperforms in all of the listed categories where it provides?
-a relatively intermediate coverage range.
-Moreover, it provides the highest data rates and battery life.
-It also does not depend on regional differences in the frequency bands.
206
However, LoRa/LoRaWAN and Sigfox have already gained ?
a large group of companies and researchers working with their technologies.
207
Comparison of LPWAN Technologies
208
IoT technology is currently spreading in all domains. With an increasing number of IoT devices getting connected to the Internet, the requirements for ?
communication protocols also increase.
209
This section elaborates on some common communication protocols in the application layer, also referred to as?
messaging protocols,
in IoT architectures,
including message queuing telemetry transport (MQTT),
representational state transfer (RESTful), and constrained application protocol (CoAP).
210
These protocols must interoperate with many kinds of electronic devices with ?
different hardware specifications.
211
MQTT is a messaging protocol, built on?
top of the TCP protocol that aims at connecting embedded devices and networks with applications and middleware.
212
Using TCP requires to establish a connection before ?
exchanging information, the connection operation typically uses various routing mechanism, e.g., one-to-one, one-to-many, many-to-many.
213
In fact, MQTT is an optimal connection protocol for the IoT applications with?
resource-constrained devices that use unreliable or low bandwidth links.
214
MQTT utilizes the publish/subscribe pattern to provide?
transition flexibility and simplicity of implementation.
215
As introduced, using the publish/subscribe pattern the sender does not transmit the message directly to?
a receiver but via an MQTT message broker.
216
In this manner, the complexity of the MQTT protocol resides on?
the message broker which manages all subscriptions
and the publishing of new messages to the topics.
217
In general, the MQTT message format comprises a?
Similarly, the payload component contains the data being sent and it does not always present in an MQTT message, i.e., the connect message does not include a payload component. The minimum packet size is 2 bytes with a single byte control field and a single byte packet length field, i.e., the disconnect message is only 2 bytes. The size of the variable header can be up to 12 bytes.
2-byte fixed header, a variable header, and a payload.
218
The fixed header always presents in all MQTT messages while the variable header is?
not
always present in an MQTT message where its size depends on the message type and the QoS level.
219
It can contain additional information, including:
-QoS level,
-connect flags providing additional parameter such as a username or password for access to a broker,
-keep alive defines the maximum time between two control packets sent by the client; if the limit is reached, the broker closes the connection to this client,
-topic name describes the specific topic for subscribing or publishing, and
-packet identifier to explicit identify each packet.
220
MQTT messages may have some additional features, such as?
the “retained” message, the “Last WILL and Testament,” and the “persistent sessions.”
221
These features can be activated through?
flags in the variable header of the “connect” messages.
222
For storing the last published message of a topic at the server, the retained messages feature must be?
activated.
223
Accordingly, the broker always stores?
the newest message of a topic on the server so as to be able to retransmit the message if a client lost the connection.
224
If a client subscribes to a specific topic, this stored message is?
published to the client as the current value.
225
The "Last WILL and Testament" feature enables MQTT clients to store a so-called ?
WILL message at the broker.
226
The client can save this message for all topics it publishes. If the broker abnormally loses the connection to a publisher, then ?
the broker sends this WILL message to all subscribers of the concerning topics.
227
This message is useful in case of?
failure of a device to inform all others that depend on it about the failure.
228
Finally, the persistent sessions are ?
a broker-side feature.
229
If a client reconnects to a broker for a certain topic after a connection loss, it receives ?
all missed messages from this topic.
230
In addition, the client does not need to re-subscribe on topics because?
in the session on the broker all subscriptions are saved.
231
MQTT offers three QoS levels for?
the reliable delivery of messages.
232
The first level is referred to?
as QoS level 0 and it realizes an “at most once” delivery approach.
233
In the QoS level 0, the sender of a message does not wait for?
an acknowledgment of the receiver.
234
it does not perform message retransmission?
The sender does not know whether the message was delivered correctly.
235
Therefore, this QoS level is called ?
fire and forget and is the most lightweight QoS level within MQTT.
236
The second level, referred to as?
QoS level 1, enables an “at least once” delivery.
237
QoS level 1 guarantees that a message is ?
delivered at least one time to the receiver.
238
In this level, the MQTT messages get expanded by ?
a variable header in which an extra packet identifier is stored to identify every single message.
239
The QoS level 2 is the highest level of service in MQTT in which each message ?
is received only once by the intended receivers.
240
QoS 2 is considered the safest, but?
slowest, QoS level within MQTT.
241
To provide such a guarantee, at least two request/response flows (i.e., a four-part handshake) between?
a sender and a receiver are needed.
242
In this context, the sender and receiver use the packet identifier of the original PUBLISH message to coordinate?
a successful delivery of the MQTT message.
243
When a receiver, i.e., broker, gets a QoS 2 PUBLISH packet from a sender, i.e., publisher, it replies to?
the sender with a PUBREC packet that acknowledges the PUBLISH packet.
244
If the sender did not get a PUBREC packet from the receiver within a specific time, then?
it sends the PUBLISH packet again with a duplicate flag until it receives an acknowledgment.
245
Once the sender receives a PUBREC packet, then?
the sender stores it and responds with a message-release PUBREL packet which includes the data to be transmitted.
246
After the receiver gets the PUBREL packet, it can forward the message to?
any subscriber and responds to the sender with a publish-complete PUBCOMP packet.
247
The intuition behind this step is to?
avoid processing the message a second time.
248
If a packet gets lost, the sender is responsible to ?
retransmit the message within a reasonable amount of time.
249
Although MQTT enables :
lightweight communication
and an efficient distribution of messages, ?
it relies on the TCP/IP network stack.
250
WSNs are typically utilized in IoT applications such as :
industrial automation or transportation business.
251
To connect those sensor networks to existing MQTT based systems, MQTT-SN has been designed as?
an extension to the typical MQTT.
252
This protocol extension is optimized for?
low-cost and low-power devices and constrained networks, such as WSNs
253
Basically, MQTT-SN (MQTT for Sensor Networks) supports all features of MQTT, but MQTT-SN is aimed at?
embedded devices on non-TCP/IP networks, such as ZigBee.
254
This gateway is connected to the nodes in?
the WSN with MQTT-SN and to the main message broker with MQTT.
255
Such gateways translate between MQTT-SN and MQTT, and exchange messages between ?
a device and an MQTT broker.
256
Such gateways translate between MQTT-SN and MQTT, and exchange messages between ?
a device and an MQTT broker.
256
Such gateways translate between MQTT-SN and MQTT, and exchange messages between ?
a device and an MQTT broker.
257
To this end, a gateway discovery mechanism enables sensor nodes to?
automatically find gateways.
258
An MQTT-SN-supported WSN typically consists of two main components:
an MQTT-SN client and an MQTT-SN Gateway.
259
On the client side, MQTT-SN enables?
the sensor/actuator to publish data and connect to a gateway.
260
In this context, there are two different types of gateways. The first type is?
the transparent gateway which can serve only one MQTT-SN client and maintains a connection to the MQTT broker.
261
This approach can lead to ?
scalability problems where each client requires a dedicated gateway.
262
The second type is?
the aggregating gateway which holds many connections to different MQTT-SN clients.
263
It has only one connection to the MQTT broker and preprocesses the messages on the gateway to ?
reduce the message overhead.
264
Furthermore, a gateway can be directly integrated in?
a MQTT broker, or it can be a stand-alone.
265
Furthermore, MQTT-SN supports ?
point-to-point data transfer service and broadcast service.
266
The first service enables the transport of messages?
between two endpoints based on their network address as unicast services.
267
The second service ensures that a message sent by a WSN node can be received by?
all other nodes within its transmission range.
268
A network protocol which supports broadcast service is needed because?
clients need to discover reachable gateways.
269
MQTT-SN also supports multiple gateway connection for clients which means ?
devices have access to multiple gateways at the same time.
270
In case of a connection loss to one gateway, a client can then?
send its messages to the other gateways.
271
RESTful web services implement the REST architecture which is based on?
the request/response model.
272
RESTful relies basically on ?
the HTTP protocols for exchanging messages using the GET, PUT, POST, and DELETE methods.
273
A server implementing RESTful provides access to resources such as:
text files, images, or videos.
274
Each resource, e.g., certain sensors or phenomenon, has its ?
unique URI identifier which is exposed by the server.
274
Each resource, e.g., certain sensors or phenomenon, has its ?
unique URI identifier which is exposed by the server.
275
The basic protocol of RESTful Web services consists of three parts:
(1) the connection establishment,
(2) the request with a response,
and (3) the connection closing.
276
The connection establishment uses a three-way handshake which is?
a three-step method that requires both the client and server to exchange SYN (synchronize) and ACK (acknowledge) packets before actual data communication begins.
277
After the connection is established, a request is ?
sent to the server which responds with the requested data and a status code. To close the connection, the client initiates again a three-way handshake.
278
RESTful web services are commonly used in?
web applications.
279
However, when being used by resources-constrained networks, it offers?
some major disadvantages.
280
Generally, HTTP does not have a limit for?
the message size and the message header, knowing that each node must exchange three messages to set up a connection, according to the TCP transport protocol.
281
For a constrained node with a limited bitrate for sending and receiving messages, it is a big challenge to?
send real-time HTTP requests.
282
Furthermore, for each request all control information must be sent to?
the server because RESTful is stateless.
283
This overhead increases the size of ?
every message as well as the time for transmission.
284
In a larger network with many nodes, this overhead can impact the network ?
performance because of the number of messages.
284
In a larger network with many nodes, this overhead can impact the network ?
performance because of the number of messages.
284
In a larger network with many nodes, this overhead can impact the network ?
performance because of the number of messages.
285
As a result, a real-time exchange of information is no longer ?
sustainable.
286
Although TCP provides reliable delivery of??
large amounts of data which is an advantage in connections that do not have strict latency requirements, it creates challenges in resource-constrained environments.
287
For sporadically sending small amounts of data, we need to?
set up a TCP connection that takes a long time and produces unnecessary overhead.
288
To summarize, HTTP and TCP as part of ?
a RESTful web service provide no ideal solution as a communication protocol for the constrained networks.
289
Instead, an alternative build-upon-REST protocol is ?
designed and presented in the next section.
290
The Constrained Application Protocol (CoAP) is a lightweight protocol designed for ?
the special requirements of constrained environments.
291
The headers, methods, and status codes are all binary encoded, thus?
reducing the protocol overhead in comparison with many protocols.
292
Moreover, CoAP runs over the less complex UDP transport protocol instead of?
TCP, thus reducing the overhead.
293
With UDP, messages can be exchanged without?
establishing a connection between the clients and the servers.
294
Such an overhead reduction comes at the expense of ?
degrading the reliability.
295
degrading the reliability.
295
degrading the reliability.
296
CoAP relies on a structure that is divided into two logically different layers?
, namely request/response
and message layer.
297
The former layer implements the RESTful paradigm and allows for?
CoAP clients to use the same methods as HTTP when sending requests.
298
In fact, CoAP provides the basic RESTful services to?
IoT devices and is generalized as a “compressed” HTTP.
299
CoAP realizes a subset of ?
the REST methods with HTTP.
300
CoAP realizes a subset of ?
the REST methods with HTTP.
301
CoAP realizes a subset of ?
the REST methods with HTTP.
302
This subset consists of?
the basic methods GET, PUT, POST, and DELETE.
303
It is fully interoperable with REST through?
proxies/gateways
and can support the request/response
as well as the publish/subscribe design pattern.
304
This means that CoAP requests can be converted to ?
HTTP requests, which are more conversant to the rest of the Web.
305
Messages in CoAP are exchanged using?
HTTP and URI relying on the UDP as the transport protocol.
306
HTTP and URI relying on the --------------as the transport protocol. These features of
---enable --------------------------message exchanges and a low header overhead because the sender of a message does not have to wait until a message is -----------------------------.
UDP
CoAP
asynchronous
acknowledged
307
A CoAP URI usually has the following format:
Code
coap://example.com:5683/sensors/temp.json
308
As a response to the GET request, the server sends?
replacing the prefix HTTP with the prefix CoAP.
a JSON file containing temperature values.
309
Obviously, the only CoAP query format differs from the HTTP requests in only
replacing the prefix HTTP with the prefix CoAP.
310
The second structural layer, referred to as?
the message layer, is mainly designed for retransmitting lost packets.
311
This layer defines four types of messages:
CON (confirmable),
NON (non-confirmable),
ACK (acknowledgable),
and RST (reset).
312
The CON messages are used for ensuring?
reliable communication,
and they demand an acknowledgement from the receiver side with an ACK message.
313
Such a feature is beneficial for marking ?
whether the messages need the acknowledgment.
314
On the other hand, NON messages are sent without being monitored whether they are received. Non-confirmable messages are used, for example, for periodic publishing of sensor data.
315
On the other hand, NON messages are sent without being ----------whether they are --------------------- Non-confirmable messages are used, for example, for periodic publishing of---------------------------.
monitored
received.
sensor data
316
CoAP has an additional feature that can be used to ---------------------the request/response model. Such a feature enables clients to continue receiving changes on a ------------------------------- from the server by adding an “---------------” option to a GET request. With this option, server adds the client to the list of observers for the specific resource, which will allow the client to receive the notifications when--------------------------------changes.
enhance
requested resource
observe
resource state
317
In lieu of relying on repetitive polling to check for changes in resource state, setting an observe flag in a CoAP client’s GET request allows?
an interaction much closer to publish-subscribe with server notifying a client when there are changes.
318
The core of IoT system architecture is ?
the possibility of data communication and exchange.
319
To connect heterogeneous devices the problems related to the physical limitations in terms of available energy, size and memory must be ?
dealt.
320
To provide connectivity, a communication protocol stack is?
to be adopted.
321
A widely adopted reference model is the --------------model, which introduces 4 layers: ----------------------------------------------------- responsible for the hardware addressing and the physical transmission of data; ---------------------------------- responsible for the logical transmission of data over the network; ----------------------------------------, responsible for the end-to-end communication and lossless, error-free delivery of data; -------------------------, responsible for the node-to-node communication and for the user-interface. Several protocols exist for each layer of the TCP/IP stack.
TCP/IP
the network access and physical layer,
the internet layer,
the transport layer
the application layer
322
The physical limitations of IoT devices ask for the development of new technologies and protocols which for instance?
enable the communication of devices with limited energy sources.
323
State-of-the-art IoT communication technologies can be classified in two categories:
IP-based (e.g., WLAN, 6LoWPAN)
and non IP-based (e.g., Bluetooth, ZigBee, LoRaWAN).
324
Several communication protocols are available at the application layer, like:
MQTT, RESTful and CoAP.
325
MQTT, RESTful and CoAP. Such protocols are able to interoperate with?
various devices based on different hardware platforms.
326
MQTT makes use of the publish/subscribe pattern and provides an?
optimal protocol for resource-constrained devices typical of IoT.
327
The RESTful architecture is based on?
a request/response pattern: a server provides the access to the resources, each having a unique identifier
328
Due to its stateless nature, the RESTful architecture is?
not optimized for resource-constrained devices and for real-time exchange of information.
329
The constrained application protocol (CoAP) is ?
a lightweight protocol designed for the specific requirements of constrained environments.
330
One of the main characteristics of CoAP ist that it runs over the UDP transport layer protocol, which is simpler than?
the TCP protocol. As a consequence, the reliability is worsened.
