No matter how we position the window, it's never at risk of receiving a packet with a old sequence number.īy the time the window wraps around, we are positive that we've received the previous ones in order. Efficiency Sender Window Size in Protocol / (1 + 2a) In selective repeat protocol, if sender window size N, then. Look what happens when we increase the sequence number space to, say 6. Efficiency of any flow control protocol is given by. Therefore, to ensure that the window is never expecting sequence numbers that could possibly be used by potential outstanding packets (either coming from a normal transmission or re-transmission of a missing ack) we have to either decrease the window size or increase sequence numbers. It uses the concept of sliding window, and so is also called sliding window protocol. It will then send bit by bit to the receiver which will then send the acknowledgement back to the sender. It will convert the inputted message in the sender into binary and then ask for the window size. But the receiver is looking at 1! So is this the new one as it expects (nope), or the old one? The Sliding Window ARQ (Automatic Repeat reQuest) protocols are of two categories Go Back N ARQ Go Back N ARQ provides for sending multiple frames before receiving the acknowledgment for the first frame. The two codes Sender and Receiver are the implementation of Go Back N ARQ protocol of networking. Now, the receiver receives ALL the acks but ONE correctly. But are 0,1 OLD or NEW? The receiver can't tell. Receiver window after properly receiving packets 0,1,2.īut what if the ACKs sent are lost? Well, the sender will resend 0,1,2. Why? Because there's always the possibility that the receiver is looking at a sequence number that MAY be contained in a packet coming from the sender that is NEW or OLD. Now, this problem will occur insofar as the window size is greater than half of the sequence number space. Is it the first packet or the fourth? No clue. This means that the window has two occurrences of 0.Ġ,1,2,0 <- modulo wrap. Lets say we have sequence numbers 0, 1, 2. The window size is greater than the sequence number space. The receiver identifies packets based on sequence numbers, and there is a finite number of unique numbers for each connection. Alternatively, download a zip archive with all the images or a printable PDF of the notes.Because the receiver will fail to distinguish between an old packet or a new packet. When an error is de- tected, only the frame in question is retransmitted. Hover over the image to see a description right-click and view the image to zoom in. Selective-reject ARQ: Based on sliding-window flow control. Notes from last year as a printable PDF.Last year: Need for Flow and Error Control, Stop-and-wait Flow Control, Stop-and-wait Performance Example, Sliding Window Flow Control, Sliding Window Efficiency, Error Control.Flow Control Examples - example questions (with answers) on flow control efficiency. missing packets or packets with errors are called ARQ systems.Sliding Window Flow Control - two examples of sliding window flow control with different maximum window sizes, W: View.Stop and Wait Flow Control calculator - set parameter values for links, devices and traffic, and automatically calculate the throughput and efficiency of stop-and-wait flow control.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |