Chapter 2 Flashcards
(13 cards)
Detailed structure of a data packet:
Packet header: contains destination address, packet number and originators address
Payload: the actual data being sent
Trailer: marks the end of the packet, contains information about any error detection methods that may be used.
Packet switching:
A method of transmitting data packets across a network. A router examines a data packet to obtain its destination address then forwards the packet to this address.
Advantages of serial data transmission:
Less chance of data being skewed.
Less chance of interference.
Cheaper to manufacture and buy.
Disadvantages of serial data transmission:
Slower.
Additional data (start and stop bit) may need to be sent.
Advantages of parallel data transmission:
Faster.
No requirement to change it into serial later on.
Disadvantages of parallel data transmission:
More chance of data being skewed.
More chance of interference.
More expensive to manufacture and buy.
Advantages of USB:
Industry standard; most devices have a USB port.
Low chance of errors in connecting devices.
Doesn’t need a power source.
Data can be transferred relatively quickly.
Etc..
Disadvantages of USB:
Not as quick as Ethernet.
Length of USB cable can only reach around 5m.
State all error detection methods
Parity check, checksum, echo check, automatic repeat request, check digit
Define acknowledgment and timeout.
Acknowledgment: a message sent from one device to another to indicate whether data is received correctly. Timeout: a period of time set and used for an acknowledgment to be received.
Both used In ARQ.
Asymmetric encryption ≠ symmetric encryption, how?
Asymmetric encryption is more secure as it uses 2 keys, a public key to encrypt data and a private key to decrypt it. The same key is used to encrypt and decrypt data in symmetric encryption.
How does negative acknowledgment work?
Sending device transmits first data packet
Receiving device receives it and checks for errors
If no errors are detected, no further action is taken
If errors are detected, it will send negative acknowledgement to the sender
Sender received it, resends data packet
Timeout is set by sending device so it can be able to send data packets without receiving negative acknowledgment
How does positive acknowledgment work?
Sending device transmits first data packet
Receiving device receives it and checks for errors
After making sure there are no errors, it sends positive acknowledgement
When it is received, next packet is sent
If sender doesn’t receive positive acknowledgment within a set time period, timeout occurs
