Communication (Y12) Flashcards
(87 cards)
1
Q
What is communication?
A
The transfer or exchange of information between two parties via some medium.
2
Q
What is bit rate?
A
The number of bits transferred per second between two devices
3
Q
What is the baud rate?
A
A measure of how many symbol changes can take place within a second across a communication medium.
4
Q
What is bandwidth?
A
The frequency range available within a communication medium, measured in Hz. // The difference between the highest and lowest frequencies
5
Q
What is latency?
A
Time delay between the moment something is initiated and the moment its effect begins
6
Q
What is bit rate influenced by?
A
- Baud rate
- Bandwidth
- (Latency)
7
Q
When can the bit rate exceed the baud rate?
A
If each signal level represents more that on bit of data
8
Q
How do you calculate bit rate?
A
Bit rate = Baud rate x Bits per symbol
9
Q
What is serial data transmission?
A
The transmission of data through a single channel a single bit at a time
10
Q
What is parallel data transmission?
A
The transmission of data through multiple channels allowing for several bits to be transmitted simultaneously
11
Q
What are the disadvantages of parallel communication?
A
- Data Skew
- Crosstalk
- Communication requires more wires
12
Q
What is data skew?
A
The differences in time that each bit is received.
13
Q
What does data skew depend upon?
A
- Propagation delay between a single clock source and the transmission circuit for each bit
- Physical properties of the wiring used to transmit each bit
14
Q
What is crosstalk?
A
The interference that occurs between parallel wires resulting in the corruption of bits due to interactions in electric fields.
15
Q
What are the uses of parallel data transmission?
A
- Used in integrated circuits and between internal components (via busses)
- Short range connections
16
Q
What is a computer network?
A
Two or more computing devices connected together in order to exchange information and resources
17
Q
What’s is a LAN?
A
A network where computers are connected within a small geographic area and are owned and maintained by the organisation that uses them
18
Q
What is an example of a LAN?
A
- Home
- School
19
Q
What is a WAN?
A
A network where computers are connected over a large geographic area and are used by multinational organisations.
20
Q
What is an example of a WAN?
A
The internet
21
Q
What is baseband?
A
Communication between devices utilises the full capacity of the network
22
Q
What is broadband?
A
Multiple instances of communication can take place simultaneously
23
Q
What is a network topology?
A
The physical layout of the connection between the devices on a network
24
Q
Who owns a WAN?
A
The hardware infrastructure is owned by telecommunication companies and provide access to organisations for a fee
25
Compare LAN and WAN
Are baseband and so usually faster | Are broadband
Utilise cabled connections or radio | Utilise satellite communication and fibre optic cables
Lower latency |
26
What are the advantages of serial communication?
- More reliable over long distances
- Transfers at a higher bit rate per wire
- Less expensive as connectors are smaller and less complex
- Simpler form of communication
27
What are the two types of transmission?
- Synchronous
- Asynchronous
28
What is synchronous transmission?
Continuous transmission of data between devices whose time signals are synchronised via a common clock
29
How is synchronous transmission achieved?
Using a separate wire to transfer the clocks signal or using phase modulation to encode data over a clock signal
30
When is synchronous transmission used?
In computer systems where a clock coordinates components via the control bus
31
What is asynchronous transmission?
Transmission where the transmitter and receiver are not synchronised by an external common clock signal
32
What is a frame in asynchronous transmission?
A packet of data including a start,stop and parity bit and a byte of data
33
How does asynchronous transmission work?
- Communication line is kept idle and logically high (1)
- Start bit is low (0) so a change from idle state is detected
- Internal clock starts and one byte of data is captured
- Stop bit is opposite to start bit (1) and the line is held idle until the next frame
34
Describe the bus topology
Each node connects to a central backbone and when data is sent from one node it is broadcast to all other nodes
35
What are the advantages of the bus topology?
Relatively inexpensive to implement as a single backbone is required and short connections to each node
36
What are the disadvantages of the bus topology?
- Backbone is a single point of failure
- Performance degrades when under high load/traffic due to increase in collisions
- Less secure as data can be accessed by all nodes
- Collisions are a common problem
37
How can collisions be handled in a bus topology?
Utilising a “back-off” algorithm that increases delays between attempts to retransmit data once a collisions has been detected.
38
What protocol is used to deal with collisions in Ethernet?
With Carrier Sense Multiple Access / Collision Detection (CSMA/CD)
39
What is the star topology?
- Devices are individually connected to a central hub or switch
- The switch makes temporary connections between communicating devices
40
What are the advantages of the star topology?
- Rest of the network is unaffected if the connection for a particular node fails
- Relatively easy to isolate faults
- Switch enables packets to be broadcast without colliding
- Switch can screen packets and remove corrupted packets
- Switch ensures data is sent only to the intended device
41
What are the disadvantages of the star topology?
- Whole network fails if the central switch fails
- Expensive to lay cable from switch to each node
42
What is a physical topology?
Describes the physical layout of connections between the devices on a network
43
What is a logical topology?
Describes the flow of data (packets) across a network as controlled by protocols and network hardware
44
What is a logical bus topology?
Only one device can communicate at a time and data is broadcast to all hosts, with only the intended recipient accepting and processing the data.
45
Explain how Ethernet works
-Data packaged into an Ethernet frame that includes a destination MAC address along with original data
- Frame is broadcast to the network, having checked the carrier is free using CSMA/CD
- Switch identifies the destination and forwards the frame to appropriate host’s port
46
What is an overhead?
The number of additional bits that are transmitted within a frame beyond the data itself
47
What is a protocol?
An agreed set of rules that facilitate interaction or exchange of information between communicating parties
48
What is a disadvantage of synchronous transmission?
Requires extra wiring
49
What is a disadvantage of asynchronous transmission?
Overhead is required which decreases the rate of transfer of useful data
50
Why does asynchronous data transmission require stop and start bits?
- Start bit synchronises receiver clock to transmitter’s clock/ starts the clock
- Stop bit allows next start bit to be recognised
51
What are the types of networks between hosts?
- Client - Server
- Peer-to-peer
52
Describe the client-server relationship?
- Consists of a central server and one or more clients
- Sever provides resources and services to clients
- Clients send requests and resources to the server which it processes and returns a response
53
What are the advantages of client-server networking?
- User’s files can be stored centrally and can be accessed from any connected client computer
- Backups can be made centrally ensuring all files will be included
- Provides centralised security
- Team members can work on the same version of the file
54
What are the disadvantages of client-server networking?
- If server becomes unavailable users cannot access their files
- Server hardware is typically more expensive than ordinary computers
- Cyberattacks need only to focus on the server
55
Describe the peer-to-peer relationship.
- Each computer has equal status and resources are stored on each individual peer
- Peers communicated directly and any peers can access any resource from any other peer
56
What are the advantages of peer-to-peer networking?
- Decentralised with no dependence upon a central server
- Easy to set up
- No expensive or dedicated hardware
- More robust as no single point of failure
57
What are the disadvantages of peer-to-peer networking?
- Software and security of peers may need to be updated individually
- No centralised back-up
- Files are duplicated when transferred leading to multiple versions
- Peers may go offline whilst being accessed
58
What are some uses of peer-to-peer networking?
- Distributed cryptocurrencies
- Decentralised, distributed file sharing
59
What are some examples of server-client networking?
- Mail Servers
- Web Servers
60
What is the purpose of WiFi?
Provide a wireless local area network based on international standards that enables devices to connect to a network wirelessly.
61
What is a Wireless Access Point?
Item of network hardware that connects to a network switch and allows wireless devices to connect to a LAN.
62
What is an SSID?
A locally unique Service Set Identifier
63
What is a Wireless Network Adapter?
Component that provides the interface between a computer and a wireless network by establishing the connection with the Wireless Access Point.
64
What are the key components for wireless networking?
- Wireless network adapter
- Wireless access point
65
What does the WAP apart from allowing a computer to connect to it?
- Broadcast an SSID for the wireless network so that wireless clients know which to connect to
- Secure the wireless network by encrypting communications and implementing authentication methods
66
What relationship must a WNA and WAP have for a device to join a wireless network?
They must be compatible
67
Why does WiFi provide backward compatibility?
Older devices with different version of the standard can still join a network using a newer WAP.
68
What are the two frequencies used by Wifi?
- 2.4 GHz
- 5 GHz
69
Explain why Wifi is a broadband communication technology?
- Frequencies available for WiFi are split into smaller channels
- Each device connected to a WAP must be tuned to the same channel
- As channel is shared between devices, so is the bandwidth
- Therefore it is broadband
70
What is CSMA/CA?
Carrier Sense Multiple Access with Collision Avoidance is a protocol for avoiding collisions in wireless networks.
71
What is RTS/CTS
Request to Send / Clear to Send is a protocol used to further reduce the likelihood of collisions between wireless devices on the same network but out of range of each other.
72
What is the performance of a wireless network affected by?
- Number of connected clients
- Interference from other nearby access points
- Data collisions from within the network
73
Why is radio interference a common issue in wireless networks?
- The 2.4GHz and 5GHz frequencies are designated to be used by consumer electronics.
- Therefore there are lots of devices emitting radio signals which interfere with WiFi
74
What can interference cause and how is it measured?
- It can cause noise that competes with the desired signal.
- Measured as a signal-to-noise ratio (SNR) with unit dB
75
Describe the CSMA/CA (without RTS/CTS)
1. Sending device senses the local network to determine whether another device is transmitting
2. If no other device is transmitting then the sending device will send its message to the receiving device
3. If another device is transmitting then the sending device will wait a random time before sensing again
4. The sending device waits for and acknowledgment (ACK) from the recipient. If no ACK is received within an agreed timeframe the sending device assumes a collision has occurred and the packet is resent
76
Describe the RTS/CTS process
1. Sending device senses if the network is idle. If it is it sends a RTS to the receiving device. All other devices in range receive RTS and go silent
2. Receives RTS and sends CTS. Detected by all devices within range of the receiving device causing them to go silent
3. Once CTS is received, the sending device sends its data and waits for an ACK. This ACK is picked up by all other devices and communication resumes
77
What does the WiFi Protected Access (WPA) protocol achieve?
- Ensures only authorised people can join the network
- Encrypts communication between hosts on the network
78
How does WPA authenticate users?
Via the use of a pre-shared password
79
How does WPA encrypt data?
Encrypts each packet using AES encryption as it is sent from a host. A new encryption key is created for each new client session.
80
How does MAC address whitelisting work?
WAP only permits network interfaces with known MAC addresses to connect
81
How does disabling SSID broadcasting work?
Stops the wireless network appearing in lists of available networks for nearby clients. However clients can still join the network if they known its name.
82
What is an advantage of synchronous transmission?
Suitable for transmitting information in real-time systems
83
What is an advantage of asynchronous transmission?
Only need to synchronise their clocks for the duration of data transmission
84
Why is data skew a problem for parallel transmission?
- More chance of errors
- Limiting factor on transmission speeds
- Limiting factor on cable length
85
Why is crosstalk a problem for parallel transmission?
- More chance of errors
- Limiting factor on transmission speeds
86
Why is the requirement for more wires a problem for parallel transmission?
- Higher cost
- Difficult to manage when setting up the system
- More difficult to repeat/switch
87
What are the disadvantages of joining to public hotspot/network?
- Speeds could be limited for each device that is connected: throttling
- More clients connecting to access point
- Connection may have less bandwidth
- May be more collisions
