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Questions and Answers
The IP address of the primary address must be specified for DNS over HTTPS.
The IP address of the primary address must be specified for DNS over HTTPS.
False
DNS over HTTPS requires the specification of a secondary IP address for proper functioning.
DNS over HTTPS requires the specification of a secondary IP address for proper functioning.
True
Only one IP address is needed for DNS over HTTPS to work effectively.
Only one IP address is needed for DNS over HTTPS to work effectively.
False
The configuration for DNS over HTTPS includes specifying both the primary and secondary addresses.
The configuration for DNS over HTTPS includes specifying both the primary and secondary addresses.
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Specifying the secondary IP address is optional for DNS over HTTPS.
Specifying the secondary IP address is optional for DNS over HTTPS.
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Contact information available on the network is accessible while the device is disconnected from the network.
Contact information available on the network is accessible while the device is disconnected from the network.
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A device must be connected to the network to access contact information that exists only on that network.
A device must be connected to the network to access contact information that exists only on that network.
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Contact information stored locally can be accessed without a network connection.
Contact information stored locally can be accessed without a network connection.
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When disconnected from the network, a device can still view all types of contact information.
When disconnected from the network, a device can still view all types of contact information.
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Disconnection from the network prevents access to network-specific contact information.
Disconnection from the network prevents access to network-specific contact information.
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The Wi-Fi standard released in 1997 has not been succeeded by any new versions.
The Wi-Fi standard released in 1997 has not been succeeded by any new versions.
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802.11ac is also known as Wi-Fi 5.
802.11ac is also known as Wi-Fi 5.
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Wi-Fi 6 is identified by the designation 802.11ax.
Wi-Fi 6 is identified by the designation 802.11ax.
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The original Wi-Fi standard is still seen as the most advanced version available.
The original Wi-Fi standard is still seen as the most advanced version available.
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802.11n is a newer version than 802.11ac.
802.11n is a newer version than 802.11ac.
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Data can be transferred between different geographical locations.
Data can be transferred between different geographical locations.
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Communication cannot occur between different networks.
Communication cannot occur between different networks.
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It is possible to send information between different communication devices.
It is possible to send information between different communication devices.
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Data exchange is limited to different applications on the same device only.
Data exchange is limited to different applications on the same device only.
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There are several methods for sharing data between different applications.
There are several methods for sharing data between different applications.
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Packets in a router buffer are dropped if there are no free buffers available.
Packets in a router buffer are dropped if there are no free buffers available.
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The transmission delay is the time taken for a bit to travel from one end of the link to the other.
The transmission delay is the time taken for a bit to travel from one end of the link to the other.
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Nodal processing typically takes longer than queueing delay in routers.
Nodal processing typically takes longer than queueing delay in routers.
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Queueing delay is influenced by the congestion level of the router.
Queueing delay is influenced by the congestion level of the router.
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The total packet delay consists of propagation, transmission, processing, and queueing delays.
The total packet delay consists of propagation, transmission, processing, and queueing delays.
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Selendroid is a tool that allows you to create functional tests for iOS using knowledge from Selenium.
Selendroid is a tool that allows you to create functional tests for iOS using knowledge from Selenium.
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If you have experience with Selenium, you will find Selendroid easy to use.
If you have experience with Selenium, you will find Selendroid easy to use.
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Selendroid can be used for both functional and performance testing on Android applications.
Selendroid can be used for both functional and performance testing on Android applications.
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Selenium knowledge is completely irrelevant when working with Selendroid.
Selenium knowledge is completely irrelevant when working with Selendroid.
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Selendroid is a tool that is used only for automated testing on Windows platforms.
Selendroid is a tool that is used only for automated testing on Windows platforms.
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Study Notes
Wireless Networks and the Internet
- WSN Technologies AG is focused on wireless network technologies, particularly sensor applications.
- The company aims to "Sense, Transmit, Manage" data using wireless networks.
Introduction
- The overview/roadmap covers fundamental internet concepts like protocols, the network edge (hosts, access points, physical media), network core, performance metrics (loss, delay, throughput), protocol layers, and service models.
The Internet: a "nuts and bolts" view
- Internet is a network of networks comprising interconnected ISPs.
- Protocols like HTTP (Web), streaming video, Skype, TCP, IP, WiFi, and Ethernet are ubiquitous in controlling the transmission of messages.
- Internet standards are documented using Request for Comments (RFCs) produced by the Internet Engineering Task Force (IETF).
Internet protocol
- An Internet Protocol translates device addresses to locate them on the network.
- IP version 4 (IPv4) uses 32-bit addresses, represented in a dotted-decimal format.
- Internet Protocol Version 4 (IPv4) is a protocol for sending data across a network and includes addressing information to ensure data reaches the correct destination.
IP v4
- A system of rules that allows two or more entities of a communication system to transmit information.
- The protocol may be implemented by hardware, software, or a combination of both.
- Internet Protocol defines the format, order, and actions taken on messages.
802.11
- 802.11 is a set of IEEE standards defining wireless networking communications, released in 1997.
- Subsequent versions like 802.11n, 802.11ac, and 802.11ax (Wi-Fi 4, 5, and 6) have improved the standard.
Wireless Computing
- Wireless Sensor Networks (WSNs) are networks of distributed sensors operating in ad-hoc mode.
- Devices in ad-hoc networks communicate directly with each other, without requiring a central access point.
- WSNs are designed to sense physical phenomena, process information, and generate relevant results.
- WSNs utilize self-organizing protocols and algorithms.
Wireless Computing Architecture
- WSNs consist of a large number of distributed sensor nodes.
- Sensor nodes in WSNs are often heterogeneous, with diverse capabilities and characteristics.
- Typical characteristics of sensor nodes include power, processing, storage, and radio capabilities.
Wireless Sensor Network
- Wireless sensor networks, or WSNs, monitor physical or environmental conditions such as temperature, sound, vibration, pressure, and motion at distributed locations.
- Sensor nodes collect sensing measurements and transmit them to a sink.
- Sinks (or base stations) act as transmission points that pass sensed data thorough internet networks to users.
Difference between Sensing and Sensors
- Sensing is the technique used to gather information about physical objects or areas.
- A sensor is an object that performs the task of sensing; converting one form of energy to another form of energy.
- Examples of biological sensors include eyes (optical information), ears (acoustic information), nose (olfactory information), and skin (tactile information).
Sensing (Data Acquisition)
- Sensors capture signals and phenomena from the physical world.
- Signal conditioning prepares captured signals for further use (e.g., amplification, attenuation, filtering).
- Analog-to-digital conversion (ADC) converts analog signals to digital signals.
- Digital signal processing follows to produce outputs often given (via converters) to an actuator (device able to control the physical world).
Sensor Node
- The architecture consists of five main hardware components: sensing device, processor, memory, power supply, and transceiver.
- Sensor nodes are easily deployable, as they do not require infrastructure support.
Main Components of Sensor Node
- Key components include a location finding system, mobilizer, memory, processing unit, sensors/ADC, and a power supply.
Wireless Network Architecture
- The architecture has cluster heads that manage multiple sensor nodes, along with a sink and internet-connected devices used for aggregation of sensor data.
Wireless Computing (Benefits)
- Sensor networks revolutionize sensing in a wide range of applications.
- They offer features including reliability, accuracy, flexibility, cost-effectiveness, and ease of deployment.
Wireless Computing (Defects)
- Each sensor node has wireless communication capability and sufficient intelligence for signal processing and disseminating data.
- Communication in sensor networks is not typically end-to-end.
- Energy in sensor networks is more limited because of difficulty in recharging.
- Bluetooth devices are not suitable for sensor applications due to energy and cost concerns.
- Dense networks can lead to congestion issues if improperly managed.
A hierarchical sensor network
- The architecture defines levels of commanders, generals, and soldiers.
- There are child nodes, cluster heads, and parent nodes.
- A hierarchical sensor network manages a large number of sensors, enabling efficient communication and processing.
Wireless Communication Platform
- The platform shows the flow of messages to and from sensor nodes to a base station(BS), which is then sent to a gateway to access the internet.
WSN Communication
- Typical WSN characteristics include low data rates, energy-constrained sensors, and use of IEEE 802.11 standards.
- 802.15.4 is often used for short-range communications and features specific designs for the properties of WSN environments.
Wireless Sensor Network (WSN)
- Multiple sensors (often hundreds or thousands) form a robust network to monitor environments.
- Data is wirelessly sent to a base station to enable processing, analysis, and storage.
Single-Hop versus Multi-Hop
- Star topologies have every sensor communicating directly with the base station. This can be inefficient for large geographic areas.
- Mesh topologies employ relays, to reduce transmit power and enhance the coverage area of sensor nodes.Multi-hop communication introduces the routing problem.
Sensor Classifications
- Sensor type is determined by the physical property to be monitored.
- Examples include temperature (thermistors, thermocouples), pressure (pressure gauges), optical (photodiodes, cameras), acoustic (microphones), mechanical (strain gauges), and more.
TinyOS
- TinyOS is a component-based operating system developed at UC Berkeley, specifically designed for WSNs.
- It's designed to effectively handle network protocols and sensor data, and it promotes interoperability.
- TinyOS provides an efficient scheduler and concurrency control.
Benefits of using TinyOS
- TinyOS separates concerns, focusing on networking, and handles complexity from the developer side regarding message transfer.
- Using TinyOS enables efficient concurrent control through an interrupt-driven execution model.
A closer look at Internet structure
- The network edge consists of hosts (clients and servers).
- Servers are often located in data centers.
- Access networks use wired and wireless links.
- Network core is a mesh of interconnected routers that transmit packets.
Wireless networks VS ad hoc networks
- Sensor networks possess several orders of magnitude more nodes than ad hoc networks, and their nodes are densely deployed and prone to failure.
- The topology often changes frequently in WSNs.
Access networks and physical media
- Access networks connect end systems to routers.
- They employ shared or dedicated access for users. Common technologies include residential, institutional, and mobile networks such as WiFi or 4G/5G.
WSN Management
- WSN deployment often happens without a predetermined design.
- Sensors may be dropped from planes or placed strategically based on need (patient tracking, emergency zones).
- Efficient deployment requires sensors with location-finding, neighbor identification, path configuration, and initialization capability.
WSN Management (continued)
- Sensor networks must be able to manage operations without human intervention.
- Adaptations are necessary to properly handle changes in topology, traffic, and failures.
- Sensor network management features include self-organization, optimization of limited resources, intrusion/attack detection, and self-repair/healing mechanisms.
WSN Distribution
- Centralized WSN management can be inefficient due to the large scale and limitations of the network and resources.
- Decentralized approaches improve by implementing algorithms that manage the routing function by relying on knowledge from local nodes, though this could lead to non-optimal solutions compared to centralized strategies.
Challenges in WSNs: Design Constraints
- Low processing speeds, storage capacity, and I/O components (e.g., GPS)
- Software features (such as multi-threading) are often absent in constrained environments
- Multi-hop communication introduces latency, failure, and problems with duty cycles.
Operational Challenges of Wireless Sensor Networks
- Energy efficiency is a major concern in WSN designs due to the limited battery life of sensor nodes.
- Storage and computation limits and high error rates in wireless communication must be addressed for effective solutions.
- Noisy measurements and node failures are common occurrences to be considered.
- Scalability and survivability in harsh environments are critical aspects of WSNs.
Example of WSN
- A diagram shows a WSN comprising outdoor and indoor deployed nodes.
- The system includes elements such as mobile gateways, and a service center.
- The nodes connect to a GSM, UMTS, or other network for communications.
Why use a WSN?
- Ease of deployment since wireless communication does not need infrastructure.
- Low cost since nodes use inexpensive off-the-shelf components.
- Fine-grained monitoring via dense deployment.
Applications of Wireless Sensor networks
- WSN applications are generally categorized into three key domains: monitoring objects, monitoring areas, or both.
Monitoring Area
- Categories include environmental monitoring, precision agriculture, indoor climate control, military surveillance, and intelligent alarms.
Example: Precision Agriculture
- Precision agriculture improves efficiency in farming by using sensors to optimize crop yields.
- The information gathered by sensors enables the optimal determination of parameters such as density, fertilizers, and other crop inputs.
Military applications
- Military applications monitor forces and other items (e.g., equipment, ammunition).
- They enable scouting, surveillance, damage assessments, and detection of attacks.
Health Applications
- Tele-monitoring is used in hospitals to track and monitor physiological data from patients and medical personnel.
- Some hospitals implement drug monitoring.
- Systems might monitor the activity level of residents of long-term care and elder care facilities.
Environmental applications
- WSNs are employed for many environmental sensing applications.
- Notable examples include forest fire detection, biocomplexity mapping, flood detection, and precision agriculture, to name a few.
- Data is collected from sensor nodes and sent to a central location via a satellite link (e.g., on Great Duck Island).
Detecting and monitoring car thefts
- GPS systems are used to monitor vehicles to prevent and deter vehicle theft.
Traffic Management & Monitoring
- Wireless sensors can be embedded in roads.
- They can monitor traffic flow and provide real-time route updates.
Smart Home/Smart Office
- Sensors control appliances, providing control of lighting and heating systems.
- The Pentagon has a known case study on a large WSN deployment for better management of office buildings.
Industrial & Commercial
- WSNs are used in various industrial and commercial applications, with considerable diversity.
- Key examples include monitoring of agricultural crops, tracking inventories, monitoring in-process parts, reporting automated problems, tracking theft and customers, and monitoring plant equipment.
Enabling Technologies
- Embedded systems utilize many distributed devices to interact with physical environments.
- These enable sensors and actuators to work together to perform tasks.
- Networked components will coordinate and perform higher-level processing tasks.
Wireless Mobile or Mobile Wireless?
- Mobile computing devices can exist independently of wireless networking technology.
- Wireless communication systems themselves are a particular type of communication system.
- Four key elements include the user, device, application, and network.
Characteristics of mobile computing environment
- User mobility: accessing services while moving.
- Network mobility: moving seamlessly between networks.
- Bearer mobility: using the same service while switching bearers.
- Device mobility: same service across different devices.
- Session mobility: moving a session from one environment to another.
- Host mobility: the ability to move while the host remains the same or changes to another host.
- Agent mobility: the ability to move while the agent remains the same or changes.
Dimensions of Mobile Computing
- Location awareness
- Network connectivity quality of service
- Limited device capabilities (e.g., limited power supplies)
- Support for wide variety of user interfaces (e.g., different devices)
- Platform proliferation (compatibility)
- Active transactions (processing demands)
Location
- A mobile device's location is constantly changing.
- Location-aware applications are designed to accommodate such dynamic changes.
- Location sensitivity in applications involves adjusting to changes in context.
- Localization technologies like triangulation, proximity, and scene analysis are employed.
Quality of Service (QoS)
- Mobility in wired or wireless networks introduces limitations to network connectivity reliability.
- Movement between physical locations creates a disconnect from the network.
- Mobile systems often must disconnect from wired ports for relocation, leading to disruptions.
- Wireless networks vary in stability depending on environmental factors like weather, solar flares, and other climate-related changes..
- QoS information in mobile applications allows the adaptability of system functions based on available bandwidth, resources, and other metrics.
Limited Device Storage and CPU
- Issues with limited resources in mobile applications are often due to storage space and compute speed limitations.
- Information may be stored on different devices in the network (e.g., cloud, PCs) or even accessed in real-time without being stored at the device.
- The availability of data must be considered for the design and implementation of mobile applications.
Limited Power Supply
- Size limitations cause devices to rely on batteries as their primary energy source.
- Mobile device users often operate in environments with limited access to AC power.
- The balancing between power, size, processing, and storage is a significant constraint to mobile device application development.
Architecture of Mobile Software Applications
- A critical step in mobile application development is creating a high-level plan of the architectural design.
- The plan defines the software components and their interactions.
- A bottom-up approach is used for flexibility based on design patterns.
Wireless Network Technology
- A wireless network technology infrastructure is shown.
- There are various components, including in-building, regional-area, remote clinics, emergency dispatch, hospital campus, hospital operating rooms, and emergency rooms.
Network Core
- The network core is a mesh of interconnected routers.
- Packet switching is essential to network communication.
- Packets are forwarded from one router to the next, traversing and transmitting across links.
- Link capacity is the maximum transmission rate.
Packet Switching: Store-and-Forward
- Transmission delay takes L/R seconds to transmit an L-bit packet at rate R (bits/sec).
- Packets must be completely stored at a router before transmission to the next node, to avoid data loss or corruption.
Examples
- Calculating end-to-end delay involves considering the transmission delay, propagation, queueing, and processing at each node over a path.
Packet switching: queueing delay, loss
- Queues in routers have finite capacity; if the arrival rate to the link exceeds the link capacity, packets can be dropped from the buffer (lost).
Two key network-core functions
- Forwarding is a local action where arriving packets are moved from input to output links in a router.
- Routing is a global process that determines the paths taken by packets between source and destination.
Alternative to packet switching: circuit switching
- In circuit switching, resources are reserved for a dedicated call between endpoints.
- Resources are allocated to the call and are no longer shared (unlike in packet switching).
- Circuit switching is used often in traditional telephone communications, but packet switching is more commonly used in data networks.
Circuit Switching: FDM and TDM
- Frequency-division multiplexing (FDM) divides the bandwidth of a channel into multiple separate channels.
- Time-division multiplexing (TDM) divides the use of a single communication channel into time slots.
Packet Switching versus Circuit Switching
- Packet switching allows for more users.
- Circuit switching requires reserving resources for a particular call.
Wireless Mobile or Mobile Wireless?
- Wireless communications and mobile computing often blend.
- Four key components encompass the mobile user, device, application, and network.
Characteristics of mobile computing environment
- User mobility, network mobility, bearer mobility, and device mobility are often considered separate, but overlapping.
- Mobility aspects are crucial in understanding design and implementation of mobile applications and services.
Mobile Computing - Major Advantages
- Location flexibility enables users to adapt to various locations and work anywhere there is a connection.
- Increased time efficiency for individuals, businesses, and companies since time spent traveling is minimized.
- Higher productivity levels and ease of research in mobile environments.
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Description
This quiz covers the essentials of DNS over HTTPS, including IP address specifications and network connectivity concerns. Participants will explore the importance of primary and secondary IP addresses, as well as access to contact information during network disconnection.
