Flow Control Flashcards
what is the function of the link layer in the OSI stack
to move frames from one node to another
why does the link layer expect a header in front of the data
to interpret what it is receiving
what does flow control do
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
if there is a fast sender and a slow receiver does this cause problems
yes
if there is a slow sender and a fast receiver does this cause problems
no
what are the protocol(s) for a noiseless channel
stop and wait
what are the protocols for a noisy channel
Stop and Wait ARQ
Go Back N ARQ
Selective Repeat ARQ
what does ARQ stand for
automatic repeat request
what is a timeout
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
what does ack stand for
acknowledgement
what does NACK stand for
negative acknowlegement
what does TCP stand for
transmission control protocol
how many frames can the stop and wait arq protocol send at one time
1
when does the sender in the stop and wait arq protocol send another frame
after ack received
or after timeout
what does unidirectional mean in relation to stop and wait arq protocol
a frame is either being sent or received at any one time
only ever one frame in transmit
how does stop and wait work without timeout
same but no solution for lost data -> receiver or sender will wait an infinite amount of time
how does stop and wait arq differ from stop and wait in a noiseless channel
it has timeouts
what is the window size in go back N ARQ
N
What does the window size mean in go back ARQ
N frames can be sent before the sender expects an ack back from the receiver
what concept does go back n ARQ use
pipelining
what concept does go back n ARQ use
pipelining
if a frame is not received in the current window, which frames are sent back (Go back N)
all the frames in the current window
why is go back n more efficient than stop and wait
no waiting time
what is selective repeat ARQ
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
