COMPUTER COMMUNICATION
NETWORKS - EXAM 1 QUESTIONS AND
ANSWERS
Error Control - Answer-Repairs frames that are received in error
- Requires errors to be detected at the receiver
- Typically retransmit the unacknowledged frames
- Timer protects against lost acknowledgements
Flow Control - Answer-Prevents a fast sender from out-pacing a slow receiver
- Receiver gives feedback on the data it can accept
- Rare in the link layer as NICs run at "Wire Speed"
Error Correction Codes - Answer-Hamming Codes
Binary Convolutional Codes
Reed-Solomon and Low-Density Parity Check codes
Hamming Code - Answer-Gives a simple way to add check bits and correct up to a
single bit error.
- Check bits are parity over subsets of the codeword.
- Recomputing the parity sums (syndrome) gives the positon of the error to flip, or 0 if
there is no error
Convolutional Codes - Answer-Operates on a stream of bits, keeping internal state
- Output stream is a function of all preceding input bits
- Bits are decoded with the Viterbi algorithm
CRCs - Answer-Adds bits so that transmitted frame viewed as a polynomial is evenly
divisible by a generator polynomial.
Ethernet 32-bit CRC:
x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + x^11 + x^10 + x^9 + x^7 + x^5 + x^4 + x^2
+ x^1 + 1
LAN - Answer-Local Area Network
A network serving a home, building, or campus
MAN - Answer-Metropolitan Area Network
WAN - Answer-Wide Area Network
LANs separated by geographic distance are connected by a network
Protocol Layers - Answer-The main structuring method used to divide up network
functionality.
Each layer adds its own header to the message to transmit and removes it on receive.
NETWORKS - EXAM 1 QUESTIONS AND
ANSWERS
Error Control - Answer-Repairs frames that are received in error
- Requires errors to be detected at the receiver
- Typically retransmit the unacknowledged frames
- Timer protects against lost acknowledgements
Flow Control - Answer-Prevents a fast sender from out-pacing a slow receiver
- Receiver gives feedback on the data it can accept
- Rare in the link layer as NICs run at "Wire Speed"
Error Correction Codes - Answer-Hamming Codes
Binary Convolutional Codes
Reed-Solomon and Low-Density Parity Check codes
Hamming Code - Answer-Gives a simple way to add check bits and correct up to a
single bit error.
- Check bits are parity over subsets of the codeword.
- Recomputing the parity sums (syndrome) gives the positon of the error to flip, or 0 if
there is no error
Convolutional Codes - Answer-Operates on a stream of bits, keeping internal state
- Output stream is a function of all preceding input bits
- Bits are decoded with the Viterbi algorithm
CRCs - Answer-Adds bits so that transmitted frame viewed as a polynomial is evenly
divisible by a generator polynomial.
Ethernet 32-bit CRC:
x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + x^11 + x^10 + x^9 + x^7 + x^5 + x^4 + x^2
+ x^1 + 1
LAN - Answer-Local Area Network
A network serving a home, building, or campus
MAN - Answer-Metropolitan Area Network
WAN - Answer-Wide Area Network
LANs separated by geographic distance are connected by a network
Protocol Layers - Answer-The main structuring method used to divide up network
functionality.
Each layer adds its own header to the message to transmit and removes it on receive.
