Networks Flashcards
Define Serial data transmission
when bits are sent one after another along the same data line
Define Parallel data transmission
several bits are sent simultaneously along separate lines or channels
what is skew and how is it caused
it is when data arrives unsynchronised , as each individual wire has slightly different properties bits travel at slightly different speeds along each of the wires
what is crosstalk and its problems
it refers to electromagnetic interference between two adjacent channels or parallel wires. It gets more pronounced as the frequency increases.
What type of transmission is preferred for long distances
serial transmission is reliable over very long distances at very high data transfer rates (frequencies)
At what distance can parallel transmission be used up to?
around 2m due to crosstalk
what is an example of a serial connector and its benefit
USB connecters are much smaller and cheaper than parallel connectors
define synchronous data transmission
all data transfers are timed to coincide with an internal clock pulse.
How is Data sent using synchronous transmission
- The data is sent as one long stream with no gaps in transmission
- The receiver counts the bits and reconstructs bytes
Define asynchronous data transmission
each byte is sent seperately the moment it is available instead of waiting for a clock signal
How are bytes sent in asynchronous transmission
each byte is preceded by a start bit and ends with a stop bit or stop period - a short time gap between each set of bits
what is a parity bit
it is added as the 8th bit as a form of error detection, this bit is set to a 1 or 0 to make the total number of 1’s or 0’s in each byte odd or even depending on the machine
disadvantages and advantages to asynchronous transmission
- relatively slow owing to the increased number of bits sent
* it is a cheap and effective form of serial transmission suited to low speed connections like a KnM
Define Latency
It is the time delay between the moment the first byte or packet of a communication starts and when it is received at its destination
Define protocol
The set of rules relating to communication between devices, all communications between devices require the devices agree on a format of the data.
what things do the protocol need to define
- standards of physical connections
- rate of transmission
- data format
- type of transmission a/synchronous
- error checking procedures
Define bit rate
the number of bits transmitted in one second over a wired or wireless data link
Define Baud rate
the rate at which the signal in a communications channel changes state
What is a baseband, and how are bits sent along it.
it carries one signal at a time, a bit is represented by a high or low voltage in the cable
Define Broadband
it carries multiple signals on a fixed carrier wave. bits are sent as variations on the wave
what is the formula for bit rate
bit rate = baud rate x number of bits per signal
Define Bandwidth
it is a measure of the maximum capacity of a communications channel
Define Local Area Network
two or more computers connected together within a small geographical area
what is a network topology
it is the arrangement of the various computing devices which make up a computer network
what is a bus topology
an arrangement where nodes are connected in a daisy chain by a single central communications Channel
what is a star topology
an arrangement where a central node or hub provides a common connection point for all other nodes
how does a bus network operate
- All nodes are connected to a backbone cable
- Each end of the backbone is connected to a terminator which stops signals bouncing back
- Each node is passive
- Data is sent in one direction
- Only one computer can transmit at one time
what protocol is used to enable nodes to transmit on the same cable
carrier sense multiple access (CSMA/CD)
What are advantages to a Bus topology
- Cheap
- devices can easily be added
- Good for small networks
What are disadvantages to a Bus topology
- Main cable is a point of failure
- Limited cable length
- Performance degrades with heavy use due to data collisions
- Poor security
What does CSMA do
- It detects two nodes attempting to transmit simultaneously
- Both nodes cease transmission and wait a random time (backing off mechanism)
Difference between a hub and switch
a switch sends communications to the specific computer it is intended for and a hub broadcasts the message to every computer on the LAN
How does a switch identify and locate where to send data
it holds the MAC addresses for each device connected to it and uses these to direct packets of data to the correct device
What are advantages to a star network
- Easy to isolate problems
- Good performance
- More secure if a switch is used as data is sent only to recipient
what are disadvantages to a star network
- Can be expensive to set up because of the length of the cable
- Central device is point of failure
what is a physical topology of a network
it defines how the devices are physically connected to one another
what is a logical topology
it defines how the devices communicate across the physical topologies
what is a server
it is a powerful computer which provides services or resources required by any of the clients
what is a client
it is a computer which requests the services or resources provided by the server
what is the role of the client
- the client sends requests to the server
- waits for a reply
- receives the reply
what is the role of the server
- The server waits for requests from the clients
* it may need to pass the request to another server in which case It becomes the client
what are features of a client-server network
- central server is used to manage security
- some files are held on the central server
- some processing tasks are performed by the server
- can require specialist IT staff to administer the network
give examples of types of servers
- web server
- print server
- Mail server
- File server
- Database server
what is peer to peer networking?
when each node on a server is able to send requests and process them.
what are features of a peer to peer network?
- suitable for small companies
- cheaper as it doesnt require hardware
- all computers can easily share/see files on all other computers
- if a computer is switched off, data cannot be retrieved
what can peer to peer on a WAN be used for?
- the P2P configuration can be used for file sharing websites
- P2P networks are used for illegal distribution of material.
what is cloud computing?
internet computing using remote servers run by organisations
Advantages of cloud computing?
- some software doesnt have to be downloaded to the users computer.
- software and data is accessible from any computer anywhere in the world
- the data is automatically backed up so there is no danger losing it
define wi-fi
it is a wireless networking technology providing high-speed internet and network connections
How do devices connect to the internet
via a WAP
what is needed to connect to a wireless network
- ISP
- Modem and wireless router
- Device with NIC
what makes up wireless networking?
- wireless NIC
- station consists of a computer and a NIC
- stations share a radio frequency channel
- WAP requires a connection to a router, and the router requires a connection to a modem
What is an SSID
service set identifier ; identifies each network by a locally unique name
what are features of an SSID?
- can be set manually or automatically
- can be hidden to make it hard to detect
- must be used by all devices on that network
what are disadvantages to wireless networks
- wireless networks are less secure; prone to man in the middle attacks, packet interception, cookie stealing
- unauthorised users can be hard to spot
What are security measures used by wireless networks
- WPA
- WPA2
- MAC address whitelist
what is the CSMA (Carrier Sense Multiple Access) algorithm ?
what are the consequences of using CSMA
collisions are avoided by each station transmitting only when the channel is idle
what happens when you use CSMA/CA with RTS/CTS
