09 Communication And Networking Flashcards
What is serial data transmission?
One cable is used and the bits are sent one after the other along it
Two lines are required for two way transmission
What is parallel data transmission?
Parallel cables are a ribbon of several smaller cables
Several bits are sent at once along different channels however it has to wait until one set of data has been sent in order to send the next set
What are the advantages of serial data transmission?
Only one line is required
They are reliable over very long distances at very high frequencies
Serial connectors are cheaper and smaller
What are two problems with parallel data transmission?
Skew - As each wire has different properties, bits may travel slightly faster in one wire compared to another which causes skew
Crosstalk - It is the electromagnetic interference between two adjacent channels or parallel wires and gets more pronounced as frequency (speed of transmission) increases
What are the advantages and disadvantages of parallel data transmission?
It is fast over a short distance such as inside computers
It can only be used in short distances of up to 2m
Liable to crosstalk and skew
Uses much more lines/cables
Give an example of a serial and parallel connector
Serial - USB
Parallel - VGA
What is synchronous data transmission?
All data transfers coincide with an internal clock pulse
Data is sent as one long stream or block of data with no gaps
Receiver counts the bits and reconstructs it
What is asynchronous data transmission?
Each byte is sent separately the moment it is available
Each byte starts with a start bit and ends with a stop bit.
How is a parity bit used in asynchronous data transmission?
It is added as the 8th bit and is used for error detection
What are the advantages and disadvantages of asynchronous transmission?
It is relatively slow due to the increased number of bits being sent
It is a cheap and effective form of serial transmission well suited to low speed connections such as a mouse and keyboard
What is latency?
The time delay between the moment the first byte starts and when it is received at its destination
What is a protocol?
The set of rules relating to communication between devices
Two devices can be linked if they have the same protocol
What does a protocol need to define?
Standards for physical connections and cabling Rate of transmission (bit or baud rate) Data format Asynchronous or synchronous Error checking procedures
What is bit rate?
The number of bits transmitted in one second over a wired or wireless data link
Higher signal change means higher bit rate
What is baud rate?
How many times a signal changes per second
Measured in megabits per second (Mbit/s
What is baseband?
It carries one signal at a time. A bit is represent by high or low voltage
In baseband, bit rate is the same as baud rate and at each signal change one symbol is transmitted
What is broadband?
It carries multiple signals on a fixed carrier wave and bits are sent as variations on the wave
What is the relationship between bit and baud rate?
Bit rate = baud rate x number of bits per signal
What is bandwidth?
The maximum capacity of a communications channel
Data transfer rate
What is a local area network (LAN)?
Two or more computers connected together within a small geographical area (building)
What is a network topology?
The arrangement of the devices which make up a computer network
What is bus topology?
All nodes are connected to a single backbone cable
Each end has a terminator which stops signals bouncing back
Each node is passive
Data is sent in one direction at a time
Only one computer can transmit successfully at one time
What are the advantages of a bus network?
Cheap to set up
Easy to add more devices
Good for small networks
What are the disadvantages of a bus network?
If the main cable fails, everything fails
Limited cable length
Poor security
Low performance under heavy use due to data collisions
What is Carrier sense multiple access with collision detection (CSMA/CD)?
It detects two nodes attempting to transmit at the same time
Both nodes stop and wait a random amount of time before transmitting again
Used in wired networks
CSMA/CA (Collision Avoidance) is used in wireless networks
What is star topology?
Computers are connected to a central node which is either a hub or a switch
What is a switch and what is a hub?
A switch sends each communication to the specific computer it is intended for. It uses MAC addressing
A hub broadcasts the message to every computer on the LAN
What are the advantages of a star network?
Easy to isolate problems
Good performance
More secure if a switch is used as data is only sent to the recipient
What are the disadvantages of a star networks?
Can be expensive to set up because of the length of cable required
If the central device fails everything else fails
What is physical and logical topology?
Physical - How the devices are physically connected
Logical - How the devices communicate across the physical topologies
What is a client-server network?
Server provides services or resources required by clients
Client requests services or resources
Suitable for small and big organisations but requires an IT specialist
What does the server do in a client server network?
Manage security
Hold some files
Some processing tasks
What is peer to peer networking?
No central server
All computer can see each other’s files and communicate with each other
If a computer is switched off data cannot be retrieved
What are the advantages of cloud computing?
Some software does not have to be downloaded
Accessible from anywhere with anything
Automatic backup and doesn’t take any storage on the device
What is the purpose of Wi-Fi and what is needed for it?
Wireless network which devices can connect to through the WAP (wireless access point)
Need an ISP, modem and wireless router, device with an NIC
How does Wi-Fi work?
A station consists of a computer and a network interface card
Stations share a radio frequency channel
WAP requires a connection to a router and router requires a connection to the modem
What is SSID?
Service set identifier
Identifies each network by a unique name
How can u secure Wi-Fi connections?
WPA
WPA2
MAC address whitelist
How does CSMA/CA work?
Assemble a frame
Is channel idle?
If no wait a random amount of time
If yes transmit data
What is the hidden node problem?
Nodes A and B are hidden from each other but the WAP can hear them both
What is CSMA/CA using RTS/CTS?
Assemble a frame Is channel idle If no wait a random amount of time If yes transmit RTS Is CTS received? If no wait a random amount of time and go back to is channel idle? If yes transmit data
