Sliding window protocol
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This document describes the sliding window protocol. It discusses key concepts like both the sender and receiver maintaining buffers to hold packets, acknowledgements being sent for every received packet, and the sender being able to send a window of packets before receiving an acknowledgement. It then explains the sender side process of numbering packets and maintaining a sending window. The receiver side maintains a window size of 1 and acknowledges by sending the next expected sequence number. A one bit sliding window protocol acts like stop and wait. Merits include multiple packets being sent without waiting for acknowledgements while demerits include potential bandwidth waste in some situations.
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Sliding window protocol
- 1. SlidingSliding WindoWWindoW ProtocolProtocol (1 bit protocol)(1 bit protocol) By : W.M.L.S.Abeythunga A.A.D.S Nirmani 2010/ICT/12 2010/ICT/23
- 2. Content âą âą Communication âą âą Sliding Window Protocol âą âą Key concepts âą âą Piggybacking âą âą Sender Side âą âą Receiver Side âą âą One bit Sliding Window âą âą Merits & demerits
- 4. Sliding Window Protocol âą Sliding window algorithms are a method of flow control for network data transfers. âą Data Link Layer uses a sliding window algorithm, which allows a sender to have more than one unacknowledged packet "in flight" at a time, which improves network throughput.
- 5. Key concepts of the Sliding Window âą Both the sender and receiver maintain a finite size buffer to hold outgoing and incoming packets from the other side. âą Every packet sent by the sender, must be acknowledged by the receiver. The sender maintains a timer for every packet sent, and any packet unacknowledged in a certain time, is resent. âą The sender may send a whole window of packets before receiving an acknowledgement for the first packet in the window. This results in higher transfer rates, as the sender may send multiple packets without waiting for each packet's acknowledgement. âą The Receiver advertises a window size that tells the sender how much data it can receive, in order for the sender not to fill up the receivers buffers. âą Efficiency can also be improved by making use of the full-duplex line A B
- 7. Piggybacking âą when a data frame arrives, instead of immediately sending a separate control frame, the receiver restrains itself and waits until the network layer passes it to the next packet. âą The acknowledgement is attached to the outgoing data frame (using the ack field in the frame header). âą The acknowledgement gets a free ride on the next outgoing data frame. âą The technique of temporarily delaying outgoing acknowledgements so they can be hooked onto the next out going data frame is piggybacking
- 8. Sender Side âą To keep track of the frames, sender station sends sequentially numbered frames. âą Since the sequence number to be used occupies a field in the frame, it should be limited size. âą If the header of the frame allows k bits, the sequence numbers range from 0 to 2k â 1. âą Sender maintains a list of sequence numbers that it is allowed to send(sender window). âą The size of the senders window is at most 2k â 1. â Eg:- if frame allows 3 bits, then the size of the window is 23 -1=7 âą The sender is provided with a buffer equal to the window size. 0 1 2 3 4 5 6
- 9. Receiver Side âą Receiver always maintains window size as 1. âą The receiver acknowledges a frame by sending an ACK frame that includes the sequence number of the next frame expected. âą This also explicitly announces that it is prepared to receive the next N frames, beginning with the number specified. âą This scheme can be used to acknowledge multiple frames. âą It could receive frames 2,3,4 but withhold ACK until frame 4 has arrived. By returning an ACK with sequence number 5, it acknowledges frames 2, 3, 4 at one time. âą The receiver needs a buffer of size 1.
- 10. One bit Sliding Window âą Here K=1 at the senders side. âą Then the size of the senders window is, 2k â 1 K=1 21 -1=2-1=1 âą This is same as the stop and wait protocol.
- 11. -A sliding window of size 1, with a 3-bit sequence number- (a) Initially. (b) After the first frame has been sent. (c) After the first frame has been received. (d) After the first acknowledgement has been received.
- 12. One bit Sliding Window protocol âą The notation is (seq, ack, packet number). Part (a): If B waits for Aâs first frame before sending one of its own. Each frame arrival brings a new packet for the network layer; there are no duplicates. Part (b): If A and B simultaneously initiate communication, their first frames cross, and the data link layers gets into a situation. Half of the frames contain duplicates, even though there are no transmission errors
- 13. Merits âą Multiple packets can be transmit without waiting for acknowledgements.(not like stop & wait) âą Piggibacking (using full-duplex lines) Demerits âą No limit of the size or sequence numbers that can be required in this protocol. âą The bandwidth may be wasted in some special situations.
- 14. Reference âą Sliding window animation reference: www.youtube.com/watch?v=zY3Sxvj8kZA