Networks Flashcards
What is a network
I
A group of 2 or more devices that can communicate
Connected by physical or wireless connections
If cable breaks then only one device is affected
What is a LAN
A network that connects devices that are within a small geographical area
E.g. an office, school etc.
What is a WAN
A network that connects geographically remote devices and LANs
E.g. Internet
What are the benefits of networking
Sharing devices e.g. printers and scanners
Accessing Internet
Accessing shared data and software (from a server)
What is a server
A server is similar to a pc but is usually left on at all times
What is a disadvantage of devices on networks
Without good security they could be vulnerable to unauthorised access (hacking), viruses etc.
What are topologies
Arrangements of devices for a network
Each device that is connected is called a node
All different topologies have their advantages and disadvantages
What would larger networks contain
Many servers carrying out different roles including file and software sharing.
They also authenticate users who wish to login and dealing with access rights (files that the user is allowed to access)
What would smaller peer-to-peer (e.g. home) networks contain
May not have a server
Will instead have a PC on the network that may have files that other devices access
Describe a STAR network
Each device has its own cable linking to a device called a switch or router
Creates a star shape
Advantages of a STAR network
Faster speeds are possible
No collision of data packets (wire is only used by 2 devices using full-duplex)
If cable breaks then only one device is affected
Easier to extend/add new stations
Disadvantages of STAR network
More cabling required so more expensive
Describe a BUS network
each device shares a cable
Therefore the more devices added the greater the liklihood of collision, therefore slower
Disadvantages of a BUS network
The more devices added, the greater the liklihood of collision, therefore slower
If the cable breaks then all devices lose connection
All data is broadcast so security can be compromised
Advantages of a BUS network
Less cabling required so cheaper to install
Describe a RING network
Packet of data is sent from device to device in one direction
Circular shaped
What are the advantages of a RING network
No collisions
What are the disadvantages of a RING network
If cable breaks then network fails
Difficult to extend / add new stations
What is a packet
Data to be transmitted across a modern network is separated into blocks of data called packets
What are the contents of the packet
The data to be sent (payload)
Specifying the type of packet (e.g. whether using TCP/IP or UDP protocol)
Source address (IP address of where being sent from)
Destination address (IP address of computer data being sent to)
Packet sequence number (if data is split into a number of packets, first packet would have sequence number 1, then 2 etc.
A checksum
What is a checksum
A calculation/formula that is applied to data in a packet
The computer receiving the data can apply the same formula and if result differs from the checksum then the data has been corrupted/damaged
What does a network consist of
It consists of links between nodes (network routers or switches)
What does a packet switched network do
Data to be sent is split into packets and passed from node to node until it reaches the destination
Multiple routes can be used (if one route is busy a packet can be sent a different way)
At the destination the packet sequence number is used to put the data packets back in order
Advantages of packet switched networks
Less likely to be affected by network failure: if one line fails there are usually other routes
Better security: data is less likely to be intercepted because packets are sent down multiple routes and are likely to be interleaved with other packets
What is handshaking
The exchange of signals between devices to establish their readiness to communicate
I.e.
One device says: “are you ready to receive data?”
Other device when ready says: “yes I am”
And then communication can begin
If the connection has not been established, the operating system must time out the transfer and display an error message
What is the hardware required for a wireless network connection
A wireless router
Wireless network card (or wireless adapter) for each device
Although infraseingly wireless chips and antenna are built into devices
What are protocols
Standards or rules
Data formats specified to allow communication
Networking software and equipment need to follow protocols in order to be able to communicate
What is the TCP/IP protocol
Transmission control protocol/Internet protocol
The protocol used for transferring information across the internet and around most modern local and wide area networks.
What is the UDP protocol
User Datagram Protocol
An alternative to TCP/IP
much less sophisticated
Used to broadcast data across a network without error correction or handshaking. Used for very simple data transfer.
What is the HTTP protocol
Hyper-text transfer protocol
Defines the standard for exchanging Web page information on the world-wide Web
What is the FTP protocol
File transfer protocol
Defines the standard for transferring files across the Internet
What is the SMTP protocol
Simple mail transfer protocol
Used for sending email, often in conjunction with POP (post office protocol)
What is the POP protocol
Downloads email from a mail server
What is the IMAP protocol
Internet message access protocol
A better alternative to POP
Allowed email to be accessed from a mail server but stays connected to a server over longer periods rather than downloading the email and disconnecting
What is the DHCP protocol
Dynamic Host Configuration Protocol
A computer or another device attached to a network can request an IP address from a DHCP server on a network
Helps to ensure the address used is unique and simplifies the job of the network manager so they don’t have to manually allocate IP addresses to network devices
What are the two types of data transmission
Serial transmission
Parallel transmission
What is serial transmission
When data bits are sent in a sequence one after the other over a single wire (one communication channel)
What is parallel transmission
Several bits are sent at the same time over their own dedicated wires (multiple communication channels)
What are the advantages of parallel transmission
More data can be sent at the same time
What are the disadvantages of parallel
Over longer distances the bits can get out of sequence
Parallel wiring is more expensive, therefore parallel transmission tends to only be used over short distances
What are the three different ways data can be transmitted
Simplex
Half duplex
Full duplex
What will simplex data transmission do
One way data transmission only
What will half-duplex data transmission do
2 way data transmission but not at the same time
What will full duplex data transmission do
Data transmission 2 ways at the same time
What type of data transmission does wireless networks use
Half duplex
What type of data transmission does most modern wired networks use
Full duplex
What is multiplexing
Allows several signals from different sources to be combined for transmission over a shared medium
The signals are combined at the multiplexor (mux) and split at receiver using a demultiplexor (de-mux)
What does switching do
Switching is required to ensure that lackers of data are only sent to the computers that require it
This saves on bandwidth
What do hubs do
Network devices and segments are connected to a hub
The hub broadcasts the information received from one of their connections to all those attached to ensure wherever the receiving device is, it got the data.
What is the difference between a router and a switch
They are very similar devices
But switches link devices connected on a LAN
And routers link different networks together
What is a collison
If two or more computers find the line is free and start to send packets at the same time the packets will be corrupted
What is collision detection
The computer sending the packets will detect a collision has taken place and stop sending
Each computer then waits a small random amount of time before checking the line is free again and attempting to send
Meaning that one of them gets to send the packet before the other, avoiding a collision
Why don’t modern wired networks require collision detection?
Lines only connect between 2 end points (e.g. network routers and computers) and full-duplex lines allow packets to be sent in both directions without collision
How does a router learn about the layout of the network?
Initially configured to only know networks attached to it directly
Routing protocol shares this information among neighbors, then throughout the network
This way, routers gain knowledge of the topology of the network
What does a router do to understand where it needs to send data?
It builds a routing map/graph in its memory so that it understands to which connected router it needs to send data
This allows a router to calculate the shortest path to a destination using the ‘hop count’
What does it mean by a data transfer rate?
The speed thst fats can be transmitted around a network
Usually measured using Bits per second (bit/s) or sometimes Bytes per second (B/sec)
How do you calculate data transfer rates
First make sure thst the rate is converted to ‘per second’
So divide 3 GB by 2 * 60 (120 seconds) = 0.025 GB per second (0 025 GB/s)
Then to convert to bits per second multiply by 8
What speed does a typical wired Etherley network operate at
1Gbit/s
What is the internet
Global network of interconnected networks that communicate using a common standard of protocols
What data does Internet cabling carry
Streamed video and audio
Online games
What protocol is Web pages based on
They are based on the HTML protocol
Whar are the advantages of HTML
Entirely text based - meaning it can be loaded into just about any computer in the world.
Takes up very little space and is therefore quick to download
What is an error checking method when data is transmitted through a network
Checksum
What is a token ring network
Carry a single circulating token to which devices will attach a message for transmission
Only one message can be transmitted at a time, meaning no collisions
