2 Flashcards
Structure of a packet
-Header
-Payload
-Trailer
State three components of the header
Destination address
Originator’s address
Packet number
payload
content to be sent
trailer
has data that indicates the end of the packet and error checking information
packet switching
1) Data is broken down into packets
2) As packets are sent through the network they could each take a different route
3) The router will control the route the packets go through
4) as packets arrive they may be out of order so it will need to be rearranged
serial transmission
one bit is sent at a time over a single wire
parallel transmission
many bits are send at a time over multiple wires
simplex
data can only travel in one direction
half-duplex
data travels in both directions but not at the same time (along only one cable)
full-duplex
data can move in both directions simultaneously using two cables
advantages and disadvantages of parallel
advantages:
- faster
- can send multiple bits at the same time
disadvantages:
- crosstalk (a signal in one line creates disturbance in another line)
- skew (as each wire has different properties, the data may arrive at different times, so you must wait until all the bits are sent until you can send the next set of bits. This slows down the data transfer - to solve this the transmission distance needs to be decreased)
advantages and disadvantages of serial transmission
advantages:
- no issue of crosstalk or skew
- cheaper as there is only one wire
- better for long transmission distances
disadvantages:
- slower fro short distances
A CPU communicates with RAM using parallel transmission.
Describe the reasons why parallel transmission is used over serial transmission
in this case.
- RAM and CPU are located very close together on a motherboard meaning they don’t really suffer from skewing.
- The lines on the CPU/RAM and motherboard are all hard wired with enough distance between them meaning they don’t suffer from crosstalk
- There are large amounts of data need to be transmitted between CPU and RAM so using
parallel transmission more data can be transmitted more quickly
USB
Universal serial bus (USB) is a serial cable that is commonly used to connect external devices to computers, laptops, tablets and smartphones
disadvantages and advantages of USB
BENEFITS
It cannot be inserted incorrectly
Supports different transmission speeds
High speed transmission
Automatically detected (not connected) // automatically downloads drivers
Powers the device (for data transfer)
Backward compatible
what is encryption
The purpose of encryption is to encode a file or data into something that cannot be read or understood
need for encryption
for privacy and personal information not to be stolen or seen by unwanted poeple
Symmetric encryption
- a key is shared between the sender and the receiver
-This key encrypts the data before it is transmitted
-The receiver uses the key to decrypt the data
Asymmetric encryption
In asymmetric encryption, two keys are created by the receiver. Private key and the public key.
This means that anyone can
encrypt the data with public key, but only the receiver can decrypt it with the private key.
Decrypt
decode encrypted data back into plaintext
Encrypt
encode data into an unreadable form
Plaintext
text that hasn’t been encrypted
Shared key
the secret key that is used to encrypt and decrypt the data
Public key
a key that anyone may see and use to
encrypt data before it is sent to someone
Private key
the key used to decrypt data
Error checking
Parity bits
Check digits
Check sums
Echo checks
Automatic Repeat reQuests (ARQ)
Parity bits
check hoe many ones a data has. If its supposed to be even then you should have an even number of ones.
If not change the last but to the correct number to make it even. Do the same if the number of ones is supposed to be odd
Check digits
A check digit is an additional digit at the end of a set of other numbers designed to check for mistakes in input or transmission
Checksums
The file is run through an algorithm that produces a checksum which it also sends
When the file arrives, the receiving computer generates the checksum and compares it with the checksum that was sent
If the checksums don’t match, the file may have been corrupted or altered in transmission
Echo check
The data is transmitted to the receiver
The same data is then echoed back to the transmitter
The transmitter compares the data with the original. If it isn’t the same, the data is transmitted again
Automatic Repeat reQuests
The sender first sends a block of data
The receiving computer then sends back an acknowledgement
When the sender receives the acknowledgement it sends the next block of data
If the acknowledgement is not received after a period of time, a timeout occurs and the data is resent
This process continues until the acknowledgement is received
