8/28/2023 0 Comments Sliding window arq![]() ![]() ![]() Step 6 − If the sender doesn’t receive the ACK2 from the receiver within the time slot, it declares timeout for frame 2 and resends the frame 2 again, because it thought the frame2 may be lost or damaged. Step 5 − whenever the sender receives the ACK1 from the receiver, within the frame 1 timer then it is closed and sent to the next frame, frame 4. Step 4 − Whenever sender receives the ACK0 from receiver, within the frame 0 timer then it is closed and sent to the next frame, frame 3. Step 3 − In the same way frame2 is also sent to the receiver by setting the timer without waiting for previous acknowledgement. Step 2 − Without waiting for acknowledgement from the receiver another frame, Frame1 is sent by sender by setting the timer for it. ![]() Step 1 − Frame 0 sends from sender to receiver and set timer. Given below is an example of the Selective Repeat ARQ − The sender will send/retransmit a packet for which NACK is received. The receiver while keeping track of sequence numbers buffers the frames in memory and sends NACK for only frames which are missing or damaged. In Selective Repeat ARQ only the lost or error frames are retransmitted, whereas correct frames are received and buffered. Only erroneous or lost frames are retransmitted in this case, while good frames are received and buffered. In selective repeat protocol, the retransmitted frame is received out of sequence. Selective repeat protocol, also known as Selective Repeat Automatic Repeat Request (ARQ), is a data link layer protocol that uses the sliding window technique for reliable data frame delivery. In the selective repeat, the sender sends several frames specified by a window size even without the need to wait for individual acknowledgement from the receiver as in Go-Back-N ARQ. It is also known as Sliding Window Protocol and used for error detection and control in the data link layer. Let us see the working condition of Selective Repeat ARQ. If an ACK of data-frame previously transmitted does not arrive before the timeout, the sender retransmits the frame, thinking that the frame or it’s ACK is lost in transit Retransmission − The sender always maintains a clock and sets a timeout period. Negative ACK − Whenever the receiver receives a damaged frame or a duplicate frame, it sends a NACK back to the sender and sender must retransmit the correct frame. Positive ACK − Whenever a receiver receives a correct frame, it should acknowledge it. There are some requirements for error control mechanisms and they are as follows −Įrror detection − The sender and receiver, or any must ascertain that there is some error in the transit. Generally, there are three types of techniques which control the errors by Automatic Repeat Request (ARQ) they are − I'm currently doing this over an UDP socket in C, hence the C tag.Selective-repeat Automatic Repeat Request (ARQ) is one of the techniques where a data link layer may deploy to control errors. Should I send a CRC of the entire window? CRC is not perfect, so there may still be issues. The receiver think the packet is legit and stores it. The receiver gets the old frame 0 that was sent by the sender due to a timeout.It sends an ACK for having got them and open ups the buffer for: 15, 0, 1, 2, 3, 4, 5, 6. The receiver gets the following packets: 8, 9, 10, 11, 12, 13, 14.The sender gets ACK on all up to 7, so it sends the next frames: 8, 9, 10, 11, 12, 13, 14.The sender gets a timeout on frame 0, and re-sends it.The receiver gets the frames and sends an ACK back for having got all up to 7 (or for each one).The receiver got it so late it actually fills the next circle of the frame's buffer. My problem now is, let's say if a frame get lost on the way, but somehow make it back way too late. The window will slide by one when it got the oldest frame in the buffer filled. The receiver got a window that only allow 7 frames in any order to be accepted at any given time. Each frame has an id that fits in the 16 frames buffer (index in the array). In other words, each side has a buffer, an array, where they can store 16 frames. Let's say the sender and the receiver got a 16 size buffer with a 7 size window. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |