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A Level Computer Science > Communication > Flashcards

Communication Flashcards

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1
Q

What is a symbol?

A
  • A particular pattern of bits represented by a signal
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2
Q

What is the baud rate?

A
  • The number of signal changes in the medium per second
  • 1 Baud = 1 symbol change per second
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3
Q

What is the bit rate?

A
  • The number of bits that are transmitted over the medium per second
  • Measured in bits per second
  • = Baud rate x no of bits per signal
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4
Q

What is bandwidth?

A
  • The range of frequencies that a communication medium is capable of transmitting
  • Expressed in Hertz
  • Higher bandwidth results in a higher bit rate (direct relationship)
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5
Q

What is latency?

A
  • The difference in time between an action being initiated and its effect being noticed
  • Measured in milliseconds
  • Increases with distance
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6
Q

What is a protocol?

A
  • A set of rules relating to communication between devices
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7
Q

What is serial transmission?

A
  • Data is sent one bit at a time over one communication line
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8
Q

What is parallel transmission?

A
  • Numerous parallel communication lines send multiple bits between components simultaneously
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9
Q

What is crosstalk?

A
  • Signals from the tightly packed communication lines can “leak” into others
  • Causes data corruption
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10
Q

What is skew?

A
  • Each of the lines have slightly different properties
  • The time taken for one bit to be transferred differs slightly from line to line
  • Bits sent together may not be received together
  • Leads to bits from different pulses overlapping, causing a corruption of data
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11
Q

Evaluate serial vs parallel transmission

A
  • Serial doesn’t suffer from skew or crosstalk
  • Serial more reliable, especially over long distances
  • Serial uses only one line, making it cheaper to install
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12
Q

What is synchronous transmission?

A
  • A clock signal, shared by the sender and receiver, times when signals are sent
  • The signals, sent at regular intervals, will be received in the same order they were sent
  • Used within the busses of the processor in the fetch-execute cycle
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13
Q

What is asynchronous transmission?

A
  • Start and stop bits are used to indicate the duration of transmission
  • The start bit can be either a 1 or 0 and the stop bit is always the opposite
  • The sender and receiver must use the same baud rate
  • The sender and receiver must synchronise their clocks for the duration of transmission
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14
Q

What is a physical network topology?

A
  • Refers to the actual architecture of a network
  • Two types:
    • Star
    • Bus
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15
Q

What is a physical star network topology?

A
  • Each client has its own direct connection to a central hub
  • The hub receives packets for all clients and delivers them to the correct recipient
  • A server can be added to the network in the same way clients are connected to the hub
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16
Q

What are the advantages of a physical star network topology?

A
  • Packets are sent directly to the recipient, other clients cannot see packets that aren’t theirs
  • Easy to add and remove clients
  • Each cable has only one device, removing possibility of collision
  • Failure of one cable does not affect performance of the rest of the network
17
Q

What are the disadvantages of a physical star network topology?

A
  • Should the central hub fail, all communication is stopped
  • Expensive to install due to the amount of cable required
18
Q

What is a physical bus topology?

A
  • Connects clients to a single cable called a backbone
  • A device called a terminator is placed at either end of the backbone
  • There is no need for a central hub
  • Server can be connected to the backbone like a client
19
Q

What are the advantages of a physical bus topology?

A
  • No central hub, reducing chances of network failure, and reduces installation cost
  • Inexpensive to install, minimal length of cable required
20
Q

What are the disadvantages of a physical bus topology?

A
  • Packets are sent through the shared backbone, allowing every client on the network to see packets that aren’t intended for them
  • The backbone is used by multiple clients, risk of collision
  • Network is reliant on the backbone
21
Q

What is a logical network topology?

A
  • Refers to the flow of data packets within a network
22
Q

What is a host?

A
  • A device on a network that provides services
23
Q

What is client-server networking?

A
  • One or more central servers provide services to clients
  • Servers are connected to the network in the same way as clients, but servers are often more powerful machines than clients
  • Allows for central management of clients
  • Improves network security
  • Requires expertise to set up
24
Q

What are the services provided by servers in a client-server network?

A
  • File storage
  • Email management
  • User account management
  • Print queueing
25
Q

What is peer-to-peer networking?

A
  • Doesn’t use a shared server
  • Services are provided by the clients themselves
  • Every client has equal statues
  • All of the clients which provide services must be running in order for the network to be fully operational
26
Q

Evaluate client-server vs peer-to-peer

A
  • Peer-to-peer is more cost effective than client-server as there is no need for a powerful server to provide services
  • Peer-to-peer is easier to set up and maintain
27
Q

What is wireless networking?

A
  • Allows clients to communicate within a network without being physically connected
  • Requires a wireless access point (WAP), which connects to a wired network just like any other client would
  • Requires a wireless network adapter in the device that connects to the wireless network
28
Q

What is WiFi?

A
  • Refers to a wireless local area network that is based on international standards
  • Allows a device made in one part of the world to connect seamlessly to wireless networks around the world
29
Q

How does WPA/WPA2 secure a wireless network?

A
  • Requires that new wireless clients enter a password in order to connect to the network
30
Q

What is an SSID?

A
  • Stands for Service Set Identifier
  • A name that identifies a wireless network
31
Q

How does disabling SSID broadcast secure a wireless network?

A
  • Stops wireless devices within range of the network from displaying that the network is available
  • This allows only those who know the SSID to connect
32
Q

What is a MAC address?

A
  • Stands for Media Access Control address
  • Assigned to every wireless device
  • Unique to their device
33
Q

How does setting up a MAC address filer secure a wireless network?

A
  • MAC address whitelists can be created to allow only specific devices to connect to a network
  • MAC address blacklists can be created to block specific devices from connecting to a network
34
Q

What is CSMA/CA?

A
  • Stands for Carrier Sense Multiple Access with Collision Avoidance
  • A protocol used in wireless networks to avoid data collisions caused by multiple devices communicating simultaneously
35
Q

How does CSMA/CA work?

A
  • When a device is ready to transmit, it listens to its comms channel to check whether it is idle:
    • If so, then the data is transmitted
    • If the channel is busy, the device waits a random period of time before checking again
36
Q

What is the issue with CSMA/CA?

A
  • It cannot overcome hidden nodes
  • This is a problem when the device checking for an idle channel cannot “see” some parts of the network on which communication may be occuring
37
Q

What is RTS/CTS?

A
  • Gets around the problem of hidden nodes by adding an additional step to the CSMA process
  • Once the transmitting device has checked whether the channel is idle, it sends a RTS message to the server:
    • If the server is idle, it will respond with a CTS message at which the transmitting device can begin communication with the server
    • If no clear to send message is received, the server is busy communicating with a hidden node and the transmitting device must wait before starting the CSMA process again

A Level Computer Science (6 decks)

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