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Wireless and mobile networks > Nätverksarkitektur > Flashcards

Nätverksarkitektur Flashcards

1
Q

What is Internet of Everything, IoE? Describe each of the terms.

A

IoE is an intelligent system that unites people, data, processes and things (IoT). It is a network of connections.

People: connecting people in more valuable ways.

Data: converting data into intelligence to make better decisions.

Process: delivering the right information to the right person or machine at the right time.

Things: IoT. Physical devices connected to the Internet.

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2
Q

What is Internet of Things, IoT?

What is the purpose of IoT?

A

IoT describes the network of physical objects (things), that are embedded with software, sensors and other technologies.

The purpose is to connect and exchange data with other devices over the Internet.

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3
Q

What is a backhaul topology and when is it used?

A

A backhaul topology transports traffic between a remote site and the Internet via a centralized backbone, such as the headquarters of an organization.

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4
Q

What is delat tolerant networking, DTN?

A

DTN is an approach to computer network that wants to address technical issues in heterogenous networks that may lack continuous network connectivity.

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5
Q

What is Quality of Experience, QoE?

Which parameters are measured?

A

A measure of the overall level of customer satisfaction.

Some of the parameters that are measured are availability and access.

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6
Q

What is Quality of Service, QoS?

Which parameters are measured?

A

QoS measures software and hardware.

Some of the parameters that are measured are latency, availability, delay and reliability.

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7
Q

How is data sent?

A

Data is sent in packets.

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8
Q

What does a packet contain?

Which kind of information does the header contain?

A

Header, data and sometimes a trailer.

The header contains protocol information, for example the destination.

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9
Q

What is best-effort delivery?

A

It is a network service in which the network does not provide any guarantee that data is delivered or that delivery meets any quality of service.

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10
Q

What is ARPAnet?

A

The first wide-area packet switched network, a predecessor to today’s internet. Developed in 1969.

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11
Q

What is routing?

A

Rules for how data packets are transmitted between networks. It is a process of selecting a path for traffic in a network or between networks.

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12
Q

What is internetworking?

A

The protocols and functions needed to send data over several networks.

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13
Q

What is the OSI model and how many layers does it have? Name the layers.

A

The OSI model consists of seven layers. The purpose of the model is to find technical problems related to data communication.

  1. Application
  2. Presentation
  3. Session
  4. Transport
  5. Network
  6. Data link
  7. Physical
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14
Q

What is peer-to-peer, P2P?

A

P2P is a network architecture that consists of a decentralized network or peer nodes that act as both clients and servers. P2P does not have a base station that controls the network.

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15
Q

What is the TCP/IP model?

A

It is like a counterpart to the OSI model. It consists of four layers:

  1. Application
  2. Transport
  3. Network
  4. Network interface

Layers 2-4 are what makes the Internet.

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16
Q

What is the network layer responsible for?

A

Sending packets between a source and a host, they can belong to different networks.

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17
Q

What is the internet protocol and what does it do?

A

The internet protocol (IP) is the only protocol allowed on the internet.

  • It consists of two versions, IPv4 and IPv6.
  • IP is a connectionless transmission.
  • IP is a best effort protocol, no error control.
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18
Q

How many bits does an IPv4 protocol have?

Which two parts does it consist of?

A

32 bits, 4 bytes.

192.168.xx.xxx. The address is written in dotted-decimal format.

The two parts are net id (prefix) and host id (suffix).

Net id identifies the network that the terminal is connected to.

Host id identifies the terminal itself on this network.

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19
Q

What is the transport layer responsible for?

A

This layer is responsible for sending data (messages) between two application processes.

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20
Q

What is encapsulation?

A

Encapsulation adds information to the packet as it travels to the destination.

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21
Q

What is decapsulation?

A

Decapsulation reverses the process by removing the information, so the destination device can read the original data.

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22
Q

What are the two main transport layer protocols?

A

TCP: transmission control protocol. TCP provides a connection-oriented reliable data transmission. Uses go-back-n ARQ for error and flow control.

UDP: user datagram protocol. UDP provides a connectionless best-effort data transmission without error control or flow control.

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23
Q

What is the application layer responsible for?

A

This layer is responsible for providing application to users.

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24
Q

Which are the two main user models for internet applications?

A

Client-server model. For example www, social media and online games.

P2P. For example bit torrent and ace stream.

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25
Q

What is the data link layer responsible for?

A

This layer is responsible for sending frames between two nodes that are connected via a physical link.

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26
Q

How does CSMA/CA work?

A

Carrier-sensing multiple access/collision avoidance. The goal is to avoid collisions from occurring, not detecting them.

Nodes attempt to avoid collisions by starting transmission after the channel is sensed to be idle. Important for wireless networks.

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27
Q

What is TDMA?

A

TDMA: time-division multiple access. It is a channel access for method for shared-medium networks.

TDMA allows several users to share the same frequency channel by dividing the channel into different time slots.

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28
Q

Where is CSMA/CA used?

A

In a contention-based MAC protocol.

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29
Q

Where is TDMA used?

A

In a contention-free MAC protocol.

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30
Q

What is the physical address also called?

How many bytes?

A

MAC address.

It consists of 6 bytes, 48 bits, 12 hex digits.

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31
Q

What is the physical layer responsible for?

A

This layer is responsible for sending bits between two nodes connected through a physical link.

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32
Q

What is digital transmission?

A

The bits are represented by a digital signaler (different voltage levels).

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33
Q

What is analog transmission?

A

The bits are represented by analog signals (modulated signal).

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34
Q

What are three basic methods for error detection?

A

Simple parity-check code.

Cyclic redundancy check (CRC).

Checksum.

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35
Q

How does simple parity-check code work?

A

An extra bit is added to the sequence. A k-bit data word is changed to an n-bit code where n = k + 1.

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36
Q

How does cyclic redundancy check work?

A

Used in digital networks to detect changes of digital data.

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37
Q

How does checksum work?

A

Checksum is a small-sized block of data derived from another block of digital data with the purpose of detecting errors.

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38
Q

What is forward error correction (FEC)?

A

Data is coded in such a way that errors can be detected.

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39
Q

Which are the three basic types of automatic repeat request, ARQ?

A

Go-back-n ARQ.

Stop-and-wait ARQ.

Selective repeat ARQ.

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40
Q

What is a gateway?

A

A gateway is connected to the internet and acts as a router. A gateway allows data to flow from one network to another.

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41
Q

How does a centralized network work?

Give some examples.

A

A base station/AP controls the data transmission. The base station/AP is connected to a gateway through a backhaul link.

Examples: cellular network, WLAN, satellite networks.

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42
Q

How does a decentralized network work?

Give some examples.

A

It is a self-organized network where each host can also act as a router. Sinks connect to the gateway that connects to the internet.

Examples: mobile ad-hoc networks, mesh networks, sensor networks.

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43
Q

Which are the three basic types of wireless communication?

A

RF communication (radio). Works on earth, underwater and in outer space.

Optical communication (light). Works on earth and underwater.

Acoustic communication (sound). Works underwater.

44
Q

How does RF communication work?

A

The frequency ranges from 3 Hz to 300 GHz. Mainly used for voice transfer applications and home applications. It consists of different radio bands such as UHF, SHF and HF.

45
Q

How does optical communication work?

A

Infrared (IR) or ultraviolet (UV) light is used to carry a signal. It has five ranges of communication, from ultra-short range to ultra-long range. It usually requires line-of-sight (LoS) between transmitter and receiver.

46
Q

How does acoustic communication work?

A

Acoustic is the dominant wireless communication underwater. Whales can communicate with each other by making low-frequency sounds.

47
Q

What is signal propagation?

A

It is the movement of radio waves from the transmitter to the receiver. When the waves travel, they can be affected by light reflection or absorption.

48
Q

What is a licensed frequency band?

A

A licensed band is owned by a specifik operator. In Sweden there are two operators thath control the radio spectrum, Svenska Posten and Post - och Telestyrelsen (PTS).

Advantage: no disturbance from other services.

Disadvantage: only open for specific operators and with a fee.

49
Q

What is a unlicensed frequency band?

A

The ISM band is unlicensed. It is open for everyone to operate on.

Advantage: free of use.

Disadvantage: disturbance from other services.

50
Q

What is a point-to-point link?

Give some examples.

A

A channel that is shared between two devices, one sender and one receiver.

Examples: space links, cellular networks, backhaul links.

51
Q

What is a point-to-multipoint link?

A

The channel is shared between several devices, one sender and multiple receivers.

Examples: WiFi and cellular networks.

52
Q

What is an organizationally unique identifiers, OUI?

A

OUI is a 24 bit number that uniquely identifies a vendor, manufacturer or organization.

53
Q

On which layer is a physical address used?

A

Used on the link layer, used within a network.

54
Q

On which layer is an IP address used?

A

Used on the network layer, used between networks.

55
Q

What three tasks are the MAC protocol responsible for?

A
  1. Decide when a node can access the shared medium.
  2. Resolve conflicts between nodes.
  3. Perform activities such as flow control, framing and addressing.
56
Q

What is ALOHA?

A

It is the simplest contention-based protocol for wireless networks. Works both in centralized and decentralized networks.

57
Q

Which are the three data transmission modes?

A
  1. Simplex.
  2. Half-duplex.
  3. Full-duplex.
58
Q

How does a simplex data transmission mode work?

A

Only one of the two devices on a link can transmit, the other one can only receive. The channel is open to send data in one direction.

59
Q

How does a half-duplex data transmission mode work?

A

Both devices can communicate with each other, but not simultaneously. The channel is open in one direction at a time.

60
Q

How does a full-duplex data transmission mode work?

A

Both devices can communicate with each other simultaneously. There are two communication channels between the sender and the receiver.

61
Q

Which are the three types of data dissemination (routing) schemes?

A
  1. Unicast.
  2. Multicast.
  3. Broadcast.
62
Q

How does unicast work?

A

Data transmission from one point to another, that is one sender and one receiver.

63
Q

How does multicast work?

A

Data transmission from one point to a group of destinations simultaneously.

64
Q

How does broadcast work?

A

Data transmission from one point to all destinations simultaneously.

65
Q

What is a single-hop network?

Give examples.

A

A host can reach the gateway in one hop.

Examples: WiFi, cellular networks, satellite networks.

66
Q

What is a multi-hop network?

Give examples.

A

To reach the gateway, a host can use other hosts as relays. All hosts are also routers.

Examples: sensor networks, satellite networks, mesh networks.

67
Q

What is energy harvesting?

A

The device derives energy from an external source (not the electricity grid), for example solar panels. Can be combined with another power supply, for example a battery.

68
Q

What defines a time-critical application?

Give examples.

Solution?

A

High bit rate and high power consumption.
Low latency and short radio range (high frequencies).

Examples: self-driving vehicles, industrial automation.

Solution: 4G/5G or IEEE 802.11 WLAN.

69
Q

What defines a non-critical application?

Give examples.

Solution?

A

Low bit rate and low energu consumption.
High latency and long radio range (low frequencies).

Examples: environmental monitoring, sensor applications.

Solution: low power WAN.

70
Q

Which three QoS requirements do “soft” real time systems have?

A
  1. Response time.
  2. Packet loss.
  3. Availability.
71
Q

What are the two types of arrival processes?

A

Deterministic process: the time between two arrivals is constant, always 1/M.

Poisson process: the time between two arrivals is exponentially distributed with mean 1/M seconds.

72
Q

What is throughput?

A

Throughput is defined as the average departure rate, that is the average rate of processed requests.

73
Q

What are two common distributed computing architectures?

A
  1. Fog computing for processing capacity.
  2. Content delivery networks (CDN) for storage capacity.
74
Q

What is fog computing?

A

Fog computing is the evolution of cloud computing. Data centers are distributed in the network and all the way down to base stations (also called edge clouds).

Advantage: can achieve both elasticity and low latency.

75
Q

What is a content delivery network (CDN)?

A

With a CDN, content can be distributed to cache servers (for example cloud data centers) placed in the internet.

76
Q

How is a cellular network built?

A

It is built in small cells, where each cell is controlled by a base station.

77
Q

What is beamforming?

A

Beamforming is sending a signal in a certain direction which results in a stronger signal.

78
Q

What is MIMO?

A

MIMO = multiple-input multiple-output. It is a method for multiplying the capacity of a radio link using transmission and receiving antennas to exploit multipath propagation.

79
Q

What is LTE?

A

LTE: long term evolution. It is the fastest standard for routers and smartphones for 4G today.

80
Q

What is enhanced mobile broadband, eMBB?

A

eMBB has low latency, extreme data rates and large data volumes. It is used in 5G. It is used for online games and broadcasting.

81
Q

What is a basic service set, BSS?

A

A BSS is a group of stations, with only one access point (AP). The AP is considered as the master that controls all wireless devices within the BSS. The devices share the same BSSID.

BSS is a small range network –> more secure.

82
Q

Which three strategies for collision avoidance does CSMA/CA have?

A
  1. Interframe space (IFS).
  2. Contention window.
  3. ACK.
83
Q

What is IFS and how does it work?

A

IFS = interframe spacing. IFS is a period of time where the medium is idle. IFS is the time from the end of one frame to the beginning of the next one.

IFS is part of a greater process which is used to avoid collisions with other frames.

84
Q

What is a contention window (CW)?

A

CW is also a time interval that comes after IFS. CW is divided into time slots. A terminal that is ready to transmit, waits a random number of time slots.

85
Q

What does RTS/CTS stand for and how does it work? Where is it used?

A

RTS = request to send. CTS = clear to send. RTS/CTS is used in DCF mode. A frame sends a RTS to see if the medium is idle, if it is then the frame is transmitted, CTS. If the medium is not idle, the medium waits for a random amount of time and then it sends a new RTS.

86
Q

What does DCF stand for and how does it work? At which layer is DCF used?

A

DCF = distribution coordination function.

DCF is the fundamental MAC technique of WLAN.

A station which only uses DCF might not gain access to the medium due to the fact that PFC > DCF. The solution to this is to use a repetition interval which covers both the contention free PCF and contention based DCF.

beacon frame - PCF - DCF
————-CFP————|CP

87
Q

What is the hidden terminal problem?

A

The hidden terminal means that there are stations hidden to one another. This means that the two stations can transmit a package at the same time to a third station in the middle, and collision will occur at the middle station since the outer two stations cannot sense each other and do therefore not know that the other one is already transmitting a package.

88
Q

What is the solution to the hidden terminal problem?

A

The solution is to use RTS/CTS, i.e., nodes send short packets to request permission of the AP to send longer data packets.

89
Q

What is vehicle-to-everything, V2X?

Advantages?

A

V2X is communication between a vehicle and any entity it may affect, or may be affected by the vehicle.

Advantages: mass surveillance, road safety.

90
Q

What is Starlink?

A

Starlink is a satellite Internet constellation operated by SpaceX, providing satellite internet access to over 45 countries.

With Starlink, high access speeds and low latencies can be achieved.

91
Q

Where are self-centralized networks used?

A

Personalized area network (Bluetooth) and VANETs.

92
Q

What are the two main approaches for routing in ad hoc networks?

A

Proactive: the collecting of route information happens in a scheduled manner.

Advantage: low latency.
Disadvantage: costly updates.

Reactive: path discovery mechanisms are only activated when necessary.

Advantage: no constant overhead.
Disadvantage: delay due to route discovery.

93
Q

Which five routing paths exist?

A
  1. Shortest path routing.
    Find the shortest path.
  2. Geographic routing.
    Forwarding based on nodes’ positions.
  3. Hierarchical routing.
    Some nodes act as cluster heads.
  4. Broadcast-based routing.
    Send to all nodes selected to some criteria.
  5. Gossip-based routing.
    Send data to one or more neighbours when there is connectivity.
94
Q

What is optimized link state routing protocol, OLSR?

A

It is a proactive protocol based on shortest path. OLSR uses hello and topology control (TC) messages to discover and then spread link state information throughout the ad hoc network.

95
Q

What is ad hoc on demand distance vector, AODV?

A

It is a reactive protocol based on shortest path. The AODV protocol builds routes between nodes only if they are requested by source nodes. Therefore, AODV is considered an on-demand algorithm, it does not create extra traffic for communication. It supports both unicast and multicast routing.

96
Q

Why is position-based routing used?

A
  1. Route discovery is costly in terms of time and energy.
  2. Routing tables quickly become out of date in mobile networks.
  3. Addressing a message to a position may be more useful than to a network address.

Must know the location of the nodes, can be done by using in-built location sensors such as GPS or we can localize relative to other nodes by measuring TDOA of beacons and then using trilateration.

97
Q

What is greedless perimeter stateless routing, GPSR?

A

GPSR is a protocol based on position-based protocol. A package is not sent to a certain receiver but to coordinates. The package should then be relayed to the node that is closest to the coordinates, this assumes that every node knows its position.

98
Q

What is cluster-based routing?

A

In cluster-based routing, a virtual network infrastructure must be created through the clustering of nodes in order to provide scalability.

Each cluster has a cluster head, responsible for intra and inter-cluster coordination.

Nodes inside a cluster communicate via direct links. Inter-cluster communication is performed via cluster heads.

99
Q

What are the two main approaches in routing in ad hoc networks?

A

Proactive: the collection of route information happens in a scheduled manner.

Advantage: low latency.
Disadvantage: costly updates.

Reactive: path discovery mechanisms are only activated when necessary.

Advantage: no constant overhead.
Disadvantage: delay due to route discovery.

100
Q

What is broadcast based routing?

A

Controlled flooding, where a node forwards data to its neighbours.

There can be rules for which data that can be forwarded and to which nodes the data should be forwarded.

101
Q

Which two routing types are there in geocasting?

A

Broadcast based routing and position-based.

102
Q

What is the objective of geocast routing?

A

The objective is to deliver the packet from a source node to all other nodes within ZOR.

103
Q

What is gossip-based routing and where is it used? (epidemic routing)

A

It can be used in ad hoc networks where the connectivity is sparse and dynamic, i.e., nodes that do not always have a neighbour to transfer data to.

Data can be forwarded to one or several neighbours.

104
Q

Which are the two basic types of ad hoc wireless multi-hop network?

A

MANET.
Each node participates in routing by forwarding data to other nodes.

WMN = wireless mesh network.
WMN is a local network topology in which the infrastructure nodes (switches, routers) connect directly, dynamically and non-hierarchically to as many other nodes as possible.

105
Q

What is a MANET?

A

Self-configuring networks in which nodes are free to move in any direction.

Each node also acts as a router since each node forwards traffic unrelated to its own use.

Gateway nodes are connected to the internet.

Wireless and mobile networks (2 decks)

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