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Operating Systems > Mobile Devices > Flashcards

Mobile Devices Flashcards

1
Q

How has the use of computers in networks changed over time?

A

In the past;computers in networks were mostly stationary;but now there is an increasing number of mobile computers in use.

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2
Q

What role do radio networks play in mobile computing?

A

Radio networks are crucial for mobility;as they provide connectivity almost everywhere through modern mobile networks and Wi-Fi standards.

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3
Q

What is mobile computing?

A

Mobile computing refers to the integration of mobile devices with the internet;enabling users to access and exchange data while on the move.

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4
Q

What challenges does mobile computing face compared to stationary computing?

A

Mobile computing faces challenges such as error-prone connections in radio networks and the heterogeneity between different networks;requiring frequent changes between networks and address ranges.

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5
Q

Why do mobile devices require more frequent network configurations than stationary computers?

A

Mobile devices need frequent network configurations because they switch between different networks and internet addresses;unlike stationary computers that typically require only a one-time setup.

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6
Q

Why is the user context important in mobile applications?

A

The user context;such as the user’s location;is important for tailoring mobile applications to meet the specific needs and conditions of the user.

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7
Q

How do mobile networks differ from traditional internet connections in terms of configuration?

A

Mobile networks require ongoing configuration due to the need for devices to frequently switch networks and addresses

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8
Q

How has the access method for mobile devices to the internet changed compared to stationary computers?

A

Mobile devices access the internet via wireless networks which have different requirements and characteristics compared to wired connections used by stationary computers.

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9
Q

What are some challenges associated with mobile computing?

A

Challenges include mobility leading to varying environments, communication delays, fluctuating data rates, increased proneness to errors, and issues with maintaining uninterrupted connections as devices move between different radio network cells.

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10
Q

What is a planned disconnection in the context of mobile computing

A

A planned disconnection is a user-initiated suspension of a connection, typically to save energy or costs, or due to approaching the boundary of a radio network.

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11
Q

How do transport protocols like TCP help maintain communication in mobile computing?

A

TCP ensures reliable data transmission and can maintain transparency during short interruptions, allowing communication to continue as long as there is no timeout from missing packets.

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12
Q

What is the role of a proxy in mobile computing?

A

A proxy acts as an intermediate computer that decouples communication between the mobile device and the server helping to provide connectivity transparency during disconnections by continuing to manage data transfer.

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13
Q

Where can a proxy be placed in the communication path?

A

A proxy can be placed close to the base station to manage interruptions or directly on the mobile device to emulate a connection to the server ensuring data is cached and transferred once connectivity is restored.

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14
Q

How does combining two proxies benefit mobile communication?

A

Using one proxy on the client side and another on the base station side allows for seamless operation maintaining connections and managing data transfers in a way that is undetectable to both the client and server.

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15
Q

How does contextual information enhance mobile applications?

A

Contextual information, such as the device’s location, can be used to tailor applications to provide relevant information, like local weather forecasts or recommendations for nearby places.

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16
Q

What methods can determine the location of a mobile device?

A

Location can be determined explicitly using positioning systems like GPS or implicitly through Wi-Fi positioning services that use the MAC address of transmitters and routers.

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17
Q

What types of contextual information can be utilized by context-aware mobile applications?

A

Context-aware applications can use environmental parameters (e.g., brightness, temperature, noise level) and technical parameters (e.g., battery level, usage frequency) to adapt their presentation and behavior.

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18
Q

Why is maintaining connection during movement between radio network cells a challenge?

A

The uninterrupted transfer of responsibility between different base stations can lead to disconnections or interruptions in service as the mobile device moves.

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19
Q

What can happen when a mobile device experiences a connection interruption during data transmission?

A

If a connection is interrupted, protocols like TCP can help resume the data transmission without starting over, provided the interruption is brief. Longer interruptions may require special services or protocols to maintain transparency.

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20
Q

What are the crucial components in mobile computing that allow for flexibility and mobility?

A

The crucial components are radio networks;which enable mobile devices to move freely through various sub-networks of the internet.

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21
Q

Which types of radio networks are
particularly suitable for mobile devices?

A

Digital cellular networks (originally intended for telephony) and local wireless computer networks (set up according to the Wi-Fi standard) are particularly suitable.

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22
Q

What is the role of modulation in radio communications?

A

Modulation involves changing electromagnetic waves to transmit digital data;utilizing methods such as frequency shift keying;amplitude shift keying;and phase shift keying.

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23
Q

How does Frequency Shift Keying (FSK) work?

A

FSK modulates data by using different frequencies; for example, a higher frequency represents a “1” and a lower frequency represents a “0.”

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24
Q

What is Amplitude Shift Keying (ASK)?

A

ASK uses the amplitude (height) of the wave’s crests and troughs for modulation; a higher crest might correspond to a “1

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25
Q

Explain Phase Shift Keying (PSK) and how it works.

A

PSK uses the phase (angle) shift of the transmitted wave relative to a fundamental wave for modulation; a positive phase shift could represent a “1

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26
Q

How can modulation methods be combined in radio communications?

A

Modulation methods can be combined to achieve higher data rates than those possible using a single method.

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27
Q

What is Frequency Division Multiple Access (FDMA)?

A

FDMA is a method where different transmitters operate on different frequencies;allowing them to transmit data simultaneously without interference.

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28
Q

Describe Space-Division Multiple Access (SDMA).

A

SDMA divides the coverage area into cells

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29
Q

What is Time Division Multiple Access (TDMA)?

A

TDMA assigns specific time slots to devices within a cell to communicate with the base station on the same frequency;ensuring that devices share the channel without interference.

30
Q

How do local wireless computer networks and cellular networks utilize multiplexing methods?

A

Both types of networks can employ frequency division;space division;and time division multiplexing to provide internet access to mobile devices.

31
Q

What is the typical communication volume pattern in mobile computing?

A

The communication volume is typically much greater in the downstream direction (from base to end device) than in the upstream direction.

32
Q

What advancements have been made in modern mobile networks compared to previous generations?

A

Modern networks like LTE+ (4G) provide universal;packet-oriented data services with high-speed internet connectivity;while previous networks were primarily designed for voice transmission at lower data rates.

33
Q

What protocol is used for traditional voice communication in modern mobile networks?

A

Voice-over-LTE (VoLTE) is used for traditional voice communication in modern mobile networks.

34
Q

What are the benefits of high-speed internet connectivity in mobile multimedia applications?

A

High-speed connectivity allows for downstream data transfer rates of several hundred megabits per second;enhancing mobile multimedia applications and user experiences.

35
Q

What are the primary protocols used on the mobile internet?

A

The primary protocols used are those from the TCP/IP protocol family similar to those used across the rest of the internet.

36
Q

Why is the Dynamic Host Configuration Protocol (DHCP) important for mobile computing?

A

DHCP dynamically assigns IP addresses from a local address range when new clients enter a subnet making it particularly useful for mobile computing in local wireless networks.

37
Q

What does the DHCP dynamic allocation mode do for mobile devices?

A

It assigns IP addresses to new computers for a limited time (lease period). Once the lease expires the IP address is freed and can be reassigned to other devices.

38
Q

What are the implications of mobile devices changing IP addresses when accessing different networks?,

A

Changing IP addresses allows mobile devices to log onto different networks flexibly, but it prevents them from acting as globally accessible servers, limiting direct communication from other computers on the internet.

39
Q

How does the Mobile IP protocol address the challenges of mobile computing?

A

Mobile IP allows a mobile client to maintain a permanent IP address from its home network while also receiving a temporary IP address from a foreign network enabling continued communication without losing connection due to changing IPs.

40
Q

What is the role of the home agent in the Mobile IP protocol?

A

The home agent keeps track of the mobile client’s location in the foreign network and facilitates communication by forwarding packets to the mobile client’s temporary IP address.

41
Q

What process occurs when a third-party computer wants to contact a Mobile IP client?

A

The third-party computer contacts the client’s home network using its permanent address. The home agent accepts the request and encapsulates the IP packet in a message sent to the foreign agent which then delivers it to the client.

42
Q

How does the Transmission Control Protocol (TCP) ensure reliable data transmission?

A

TCP guarantees reliable delivery by retransmitting lost packets through confirmation messages and using a Go-Back-N automatic repeat request (ARQ) mechanism.

43
Q

What challenge does TCP face in wireless networks, particularly concerning multimedia applications?

A

In wireless networks with high error rates, TCP can lead to frequent resets of the data stream when packets are lost, significantly reducing effective data throughput, which can disrupt multimedia applications.

44
Q

What is the Selective Acknowledgment (SACK) feature in TCP?

A

SACK is an ARQ variant that allows only the retransmission of truly lost packets improving efficiency compared to the Go-Back-N method.

45
Q

When might the User Datagram Protocol (UDP) be preferable over TCP for multimedia applications?

A

UDP may be preferable because it accepts packet loss without halting the data stream, making it suitable for applications where occasional quality loss is acceptable, such as video streaming.

46
Q

What is the Real-Time Streaming Protocol (RTSP) used for?

A

RTSP controls multimedia streams, supports both UDP and TCP and provides functionalities like pausing and rewinding during playback.

47
Q

What is the function of the Real-Time Control Protocol (RTCP) in multimedia applications?

A

RTCP negotiates optimal transmission rates and corresponding quality for multimedia content.

48
Q

How does the Real-Time Transport Protocol (RTP) contribute to multimedia streaming?

A

RTP manages the actual transmission of data packets when using UDP ensuring a continuous media stream.

49
Q

What methods can be employed to adapt multimedia content quality to varying transmission rates?

A

Content can be pre-adapted by storing multiple quality levels on the server or dynamically adapted via source encoding to match the current data rate resulting in lossy multimedia data.

50
Q

Why is data protection particularly crucial for mobile devices?

A

Mobile devices are often used in unsecured environments and are at risk of physical theft, which increases the potential for unauthorized access, data theft, and data manipulation.

51
Q

What methods can be used to secure mobile devices against unauthorized access?

A

Secure encryption of data and strong access protection methods, such as full disk encryption (FDE), strong passwords, and biometric methods (e.g., fingerprint scanners), are recommended.

52
Q

What is full disk encryption (FDE) and how does it protect sensitive data?

A

FDE encrypts all data on the hard disk in an encrypted format making it transparent to the user and preventing unauthorized access if the device is stolen.

53
Q

How do mobile devices face risks when connected to insecure networks?

A

Insecure networks can allow unauthorized third parties to intercept Wi-Fi radio traffic and access exchanged data necessitating the use of encryption for secure communication.

54
Q

What encryption methods should be used to secure Wi-Fi connections?

A

Current encryption methods like Wi-Fi Protected Access 2 (WPA2) should be active to prevent unauthorized access to private wireless networks.

55
Q

How do applications ensure secure communication in public wireless networks?

A

Applications should use secure transport protocols such as Transport Layer Security (TLS), which are seen in HTTPS for web browsers and SMTPS, POP3S, or IMAPS for email clients.

56
Q

What is the purpose of a Virtual Private Network (VPN)?

A

A VPN provides a private network that enables secure, encrypted communication over the internet, protecting data from unauthorized access.

57
Q

What is meant by “tunneling” in the context of a VPN?

A

Tunneling refers to the practice of encrypting IP packets exchanged in the VPN and sending them as payloads within normal IP packets over the internet.

58
Q

What role does the VPN gateway play?

A

The VPN gateway acts as a router that manages entry into the virtual subnet of the VPN and facilitates secure communication between participants.

59
Q

Describe a site-to-site VPN.

A

A site-to-site VPN connects two or more physical networks over the internet through an encrypted tunnel allowing communication as if they were part of a local subnet.

60
Q

What is an end-to-end VPN?

A

An end-to-end VPN encrypts communication between client computers over the internet requiring a VPN gateway that serves as the entry point.

61
Q

Explain the end-to-site VPN configuration.

A

An end-to-site VPN allows authorized clients to access a physical subnet’s network services over the internet even when they are not physically on-site.

62
Q

What are mobile VPN solutions designed for?

A

Mobile VPN solutions are designed for mobile devices that may change IP addresses while the VPN connection is active ensuring persistent connections and secure communications.

63
Q

How does a communication server function in a mobile VPN?

A

The communication server transparently represents the mobile client in the wired network allowing the VPN connection to persist even if the wireless connection breaks and the IP address changes.

64
Q

How does a communication server manage the client’s IP address in a mobile VPN?

A

The server assigns a virtual address from its managed range to the mobile VPN client allowing the client to be identified by this address in the wired network.

65
Q

Why has mobile computing become increasingly important over the past decade?

A

Mobile computing has become more important due to the growing trend of clients becoming increasingly mobile and the shift of servers and services into the background;primarily through cloud computing.

66
Q

What is expected to happen to the trend of mobile computing in the coming years?

A

The trend of mobile computing is predicted to continue for years to come;with no end in sight.

67
Q

How are servers and services adapting to the rise of mobile computing?

A

Servers and services are transitioning to operate as abstract instances of cloud computing to support the mobile trend;often working in a transparent background.

68
Q

What must be ensured on the server side to accommodate mobile devices?

A

It must be ensured that protocols and services adapt to the special features and environments of mobile devices;either directly on the server side or through proxy approaches.

69
Q

What role does the proxy concept play in mobile computing?

A

The proxy concept helps to facilitate the adaptation of protocols and services to better support mobile devices and their specific needs.

70
Q

What are some adaptations made to the TCP/IP protocol stack for mobile computing?

A

Extensions to the TCP/IP protocol stack are made to support adapted data transmission;particularly for multimedia data and to enhance data security in distributed and mobile systems.

71
Q

How do adaptations in data transmission support mobile computing?

A

Adaptations in data transmission ensure that multimedia data can be effectively transmitted and that data security is maintained in mobile and distributed environments.

Operating Systems (6 decks)

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