Error detection and correction Flashcards
1
Q
Name all error detecting methods introduced in the lecture
A
- parity checking
- checksums
> Internet Checksum
> Cyclic redundancy check - error correction codes
> Hamming codes
> Reed Solomon Codes
2
Q
Name all error correcting methods introduced in the lecture
A
- ARQ >Stop and Wait ARQ >Go Back N ARQ >Selective Repeat ARQ - Forward Error Correction: >block codes >convolution codes
3
Q
Stop and Wait ARQ
A
Automatic Repeat Request implementation:
- Sender send frame
- Sender awaits ACK from receiver before next frame is sent
- if ACK not received before timeout time, resend
- frames, ACK’s are numbered
- efficiency: (time to send frame)/(total time between frame sent until next frame can be sent)
4
Q
Go back N ARQ
A
- send packets with sequence numbers
- allow for a number of sendable packets at any time (send window)
- await acknowledgment from receiver with seq number + 1
- send all packets up until seq number of window end
- if reached end of window, go back N
- for each seq number keep timeout clock
- if timeout expires, go back to last ack M packet and start sending again
- increment window end with each ack
5
Q
Selective ARQ
A
- similar to GBN ARQ
- for wrong received packet send NAK with SEQ nr of missing packet
- if NAK arrives resend last in window
- receiver buffers frames up until receiver-window sized buffer full
- receiver acks with the expected frame
- sender window slides forward
- if timeout expires send not acked frame
6
Q
Stop and Wait numbers
A
- efficiency: data bits / theoretically sendable bits
= effective data rate / raw bit rate= (1-P)(1-n,o/n,f) / (1+n,a/n,f+ 2(t,prop + t,prop)/n,f)
R,eff = ( n,frames - n,overhead ) / t,total
R,eff ~ 1/DBP
-Delay-bandwidth-product : capacity of link in bits
=> t,tot * R
7
Q
Go back N numbers
A
-efficiency:
U = (1- n,overhead / n,frame )* (1 - P,f) / (1 + (W,s - 1)* P,f )
8
Q
Selective Repeat ARQ numbers
A
-efficiency:
1-P,f)*(1- n,o/n,f
