Flow Control

Question 1

what is the function of the link layer in the OSI stack

Answer 1

to move frames from one node to another

Question 2

why does the link layer expect a header in front of the data

Answer 2

to interpret what it is receiving

Question 3

what does flow control do

Answer 3

speed matching mechanism

co ordinates the amount that can be sent before receiving an acknowledgement

flow control ensures the sender is not overwhelming the receiver

Question 4

if there is a fast sender and a slow receiver does this cause problems

Answer 4

yes

Question 5

if there is a slow sender and a fast receiver does this cause problems

Answer 5

no

Question 6

what are the protocol(s) for a noiseless channel

Answer 6

stop and wait

Question 7

what are the protocols for a noisy channel

Answer 7

Stop and Wait ARQ
Go Back N ARQ
Selective Repeat ARQ

Question 8

what does ARQ stand for

Answer 8

automatic repeat request

Question 9

what is a timeout

Answer 9

a specific period within which the acknowledgement has to be sent by the receiver to the sender

if not sent within the period, it is assumed that the frame has been corrupt or lost during transmission

Question 10

what does ack stand for

Answer 10

acknowledgement

Question 11

what does NACK stand for

Answer 11

negative acknowlegement

Question 12

what does TCP stand for

Answer 12

transmission control protocol

Question 13

how many frames can the stop and wait arq protocol send at one time

Answer 13

1

Question 14

when does the sender in the stop and wait arq protocol send another frame

Answer 14

after ack received
or after timeout

Question 15

what does unidirectional mean in relation to stop and wait arq protocol

Answer 15

a frame is either being sent or received at any one time

only ever one frame in transmit

Question 16

how does stop and wait work without timeout

Answer 16

same but no solution for lost data -> receiver or sender will wait an infinite amount of time

Question 17

how does stop and wait arq differ from stop and wait in a noiseless channel

Answer 17

it has timeouts

Question 18

what is the window size in go back N ARQ

Answer 18

N

Question 19

What does the window size mean in go back ARQ

Answer 19

N frames can be sent before the sender expects an ack back from the receiver

Question 20

what concept does go back n ARQ use

Answer 20

pipelining

Question 21

what concept does go back n ARQ use

Answer 21

pipelining

Question 22

if a frame is not received in the current window, which frames are sent back (Go back N)

Answer 22

all the frames in the current window

Question 23

why is go back n more efficient than stop and wait

Answer 23

no waiting time

Question 24

what is selective repeat ARQ

Answer 24

both the sender and receiver have a window

if an error occurs, it is corrected and then the sender and receiver go back to where the process left off

Question 25

when does the sender progress the window in go back ARQ

Answer 25

when an ack is received

Question 26

can receiver side take in frames that are not in its window in selective repeat ARQ

Answer 26

no

Question 27

how can you use binary to tell when different frames end and begin

Answer 27

flag bytes

Question 28

what is piggybacking

Answer 28

when data and acknowledgements are sent out together