Communication Flashcards
1
Q
What is a symbol?
A
- A particular pattern of bits represented by a signal
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
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
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)
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
6
Q
What is a protocol?
A
- A set of rules relating to communication between devices
7
Q
What is serial transmission?
A
- Data is sent one bit at a time over one communication line
8
Q
What is parallel transmission?
A
- Numerous parallel communication lines send multiple bits between components simultaneously
9
Q
What is crosstalk?
A
- Signals from the tightly packed communication lines can “leak” into others
- Causes data corruption
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
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
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
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
14
Q
What is a physical network topology?
A
- Refers to the actual architecture of a network
- Two types:
- Star
- Bus
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
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
What is peer-to-peer networking?
- 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
Evaluate client-server vs peer-to-peer
- 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
What is wireless networking?
- 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
What is WiFi?
- 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
How does WPA/WPA2 secure a wireless network?
- Requires that new wireless clients enter a password in order to connect to the network
30
What is an SSID?
- Stands for Service Set Identifier
- A name that identifies a wireless network
31
How does disabling SSID broadcast secure a wireless network?
- 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
What is a MAC address?
- Stands for Media Access Control address
- Assigned to every wireless device
- Unique to their device
33
How does setting up a MAC address filer secure a wireless network?
- 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
What is CSMA/CA?
- 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
How does CSMA/CA work?
- 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
What is the issue with CSMA/CA?
- 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
What is RTS/CTS?
- 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
