What is the:
Structure of a data packet
no descriptions needed
- packet header
- Payload
- trailer
What is the:
Packet header
Contains the packet number, sender’s address (IP?) and destination IP address
What is the:
Payload
Actual data transmitted
What is the purpose of the:
Trailer
Marks the end of the packet
Process of:
Packet switching
- Data is broken down into packets
- Each packet is given a sequence number and is sent
- Each packet may take a different route depending on the quickest route at the time
- routers control the route that packets take
- Packets may arrive out of order, and once the last one has arrived they are put into order using the sequence number
What is:
Packet switching
not the steps
The process controlling the sending and receiving of packets across a network or the Internet
What are the:
Different ways of transmitting data
Serial/parallel
Simplex/half-duplex/duplex
What is:
Serial transmission
description, advantages and disadvantages
- Bits sent 1 at a time
- Very high data transmission speed
- lower transmission speeds than parallel however
- lower interference
- More reliable over longer distances
- Smaller, simpler and cheaper connection to produce
What is:
Parallel transmission
description, advantages, disadvantages
- several data bits are sent simultaneously
- faster than serial, but can only be used over short distances
- used with printer cables or internal device connections
- More interference issues between wires
- Data corruption over longer distances
- very fast data transfer
- Can send data in both directions at the same time
What is:
Half-duplex transmission
and the other 2
- Simplex - Data travels in one direction down a single cable
- Half-duplex - data travels in both directions but not at the same time
- Duplex transmission - Data can travel in both direction simultaneously using two communications channels
What is the:
Parity checks
- Computers use either odd or even parity
- if the sum of all the 0s and 1s do not form either the odd or even parity the data is resent as there is an error
- The first bit is a parity bit to make sure that the parity is correct before sent
What is:
Parity block check
- Multiple bytes in a transmission block
- Parity check on the bottom and right rows/columns
that way the incorrect bit can be indentified as it will render a row and column incorrect
What are:
Checksums
- an algorithm which sums all of the data which is sent in a transmission
- the transmission is sent with the total of the algorithm and if they do not match the data has to be resent
What is an:
Echo check
- When the computer recipient is asked to send back the data and if they match the data is deemed to arrive without error
What is:
ARQ
Automatic repeat request
Computers automatically send positive acknowledgement if data packet is correct
otherwise a timer is started and if an acknoweldgement is not received the data is resent
a negative acknowledgement is sent if the data is incorrect
What are:
Check digits
- Validates data entry rather than detection errors
- An algorithm is followed to calculate a check digit, and if it is the number at the end of the number they are deemed correct and in the right order
What are the:
2 types of encryption
- Symmetric encryption
- Assymetric encryption
How does:
Symmetric encryption work
- Private key to encrypt and de-crypt data
- This is pre-shared
How does:
Assymetric encryption work
- Two seperate but related keys
- A public key is shared with others and used by them to encrypt a message which can only be deciphered wiht the private key, which is never shared
