2. Data transmission Flashcards
how is data transmitted
it is broken down into packets to be transmitted
what is the structure of a pcket
- packet header
- payload
- trailer
what does the packet header include
- senders IP adress
- recievers IP adress
- Packet number
describe the process of packet switching
- Data is broken down into packets
- Each packet could take a different route
- A router controls the route a packet takes
- Packets may arrive out of order
- Once the last packet has arrived, packets are
reordered
what are the 2 methods of transmission
serial
parralel
what is serial transmission
serial transmission, a single wire is used to connect the sending device to the receiving device. Bits are transmitted one at a time.
it is reliable over long distance, less likely to get lost, wont arrive in wrong order, take long time
parralel transmission
multiple wires are used to connect the sneding device and recievig device. several bits aee sent simultaneously. each bit travels through a seperate wire. it is faster but bits may arrive rearanged and can be expensive
what are the 3 types of data transmission
simplex
half- duplex
full duplex
what is simplex
only 1 device can transmit data in 1 direction only eg:files sent to be printes
what is half duplex
data can be sent both directions but 1 at a time. eg: walkie talkies
what is duplex
data can be sent forward and backwards simultaneously eg: online video game
what is the universal serial bus
s a communication interface that has become a standard for connecting devices to their parent
does the usb use serial or parralel
serial transmission- only 1 direction
advantages of usb
- it is univeral
- can only be inserted a certain way
- compatible with many devices
- use other cables while using usb
what is parity check
involves a parity bit at the end or start of binary number and is sent along with the data. there is an even parity or add parity ( refering to th enumbers of 1s)
how to calculte checksum
if the sum of bytes is less than 255- that is the checksum
if not then
- divide the sum of bytes by 256
- round to nearest integer
multiply integer by 256
- origingal sum- product
what is echo check
- a method of error detection where the receiving computer sends back an exact copy of the data to the sending computer.
- The sending computer then compares the data it originally sent to the data it has received back.
- If there is a match between the two data sets, then the transmission took place without error. If there is an error, the sending computer resends the data, and the process starts all over again.
what is check digit
A check digit is an extra digit added to a number that is calculated from the existing digits in the number. It is used to check for errors during data entry.
eg: ISBN, barcodes
what is automatic repeat request
- controls errors
- when data is recieved computer sends the aknowladgement which indicates weather data was sent correctly. can be positive or negative
- if negative computer will re request the data
- this process is repeated until tmeout is passed
what is encryption
encryption scrambles data so it cant be understood without decoding it.
wat are the 2 types of tect
plaint text- regular
cipher text- encrypted
how does ceaser cypher work
shifts letter a number of positions to the right or to the left
what is symetric encryption
a single key is used for encrypting messege and decrypting it. messege and key are send to reciever in seperate texts
what is asymetric encryption
uses 2 keys, one private and one public- 1 for encryption and other is used for decryption.
advantages of asymetric encryption
much more reliable- a messege cant be decrypted withput both keys
