User talk:Djash
Sliding Window Protocols operated in Duplex mode, more than one frame sent in each direction. Piggybacking: ACK for the other station is piggybacked on the data frame being sent to it. Sender maintains a “sending window” and receiver maintains a “receiving window.” Sending window indicates frames sent but no ACK received yet. At the sender, whenever a new packet is received from the NW-layer, it is assigned a sequence number which is outside the sending window. The upper edge of the sending window is then shifted up to include it. Similarly, when an ACK is received for the frame at the lower end of the sending window, the lower end is moved up. Receiving window indicates frames that are permitted to be accepted at the receiver. A frame falling outside the window is discarded. When a frame whose seq# equal to the lower edge of the window is received, it is delivered to the network layer and the window is rotated up by one unit. To avoid having the sender and coder processes halt when more than one packet is to be sent over the link, a method of sending multiple packets before an acknowledgement is returned, could be used.
1-bit sliding window protocol, also called a stop-and-wait protocol, when sending packets to neighbour in the network. It takes some time until the message has been processed and acknowledged by the receiving neighbour at the other end of the link. Here, only 1-bit is used for the sequence number.
Go back n Protocol: Let us assume sender window size n > 1 and receiver window size = 1. While sender may send multiple frames before receiving an ACK, the receiver only receives the next expected one and send ACK for that one. So when a frame that is ahead of what is expected arrives, the receiver simply discards it. Similarly, when a sender timeout, it retransmits all unacknowledged frames (not just the one that timed out). It can waste a lot of bandwidth.
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