![]() These packets are sequentially numbered from 0 to 7, and the sequence is repeated again for the rest of the packets. Now consider that the sender has 12 packets to send. Note: We will go with the maximum size of the window 2 3 -1, i.e., 7 So, the packets will be numbered from 0 to 2 3 -1, i.e., from 0 to 7. Example of Go-Back N ARQ ProtocolĬonsider that the packet’s header allows 3 bits for the sequence number. Let’s understand with the help of an example. If any frame is not acknowledged within a particular time, all the frames starting from the unacknowledged one are retransmitted. The sender keeps a copy of the sent frames until their acknowledgement is received. Now, the packets are sequentially numbered, and only N number of frames are sent at once. This means the size of receiving window is one in Go-back N. However, the receiver can receive only one packet at a time. ![]() ![]() Here, N is the size of the sliding window. The packets are sequentially numbered, and at a time, only N number of packets are transmitted. In the Go-Back N Automatic Repeat Request protocol, the sender can transmit several packets before receiving the acknowledgements. The types of sliding window protocols differ in terms of efficiency, complexity and buffer requirement. However, some protocols have variable window sizes. The maximum size of the window can be 2 n – 1. How many frames can be sent without waiting for the acknowledgement depends on the size of the sliding window. Here, n is the number of bits that the packet’s header allows for the sequence number. The maximum number of the frame is 2 n – 1. We refer senders’ buffer as sending window and the receiver’s buffer as receiving window.įrames are assigned the sequence number from 0 to the maximum number. Working Principle of Sliding Window ProtocolĪs we know, both sender and receiver maintain a buffer window. Note: The acknowledgement is sent separately if there is no next outgoing packet. Thus, it applies the pipelining concept, where the transmission of the next frame starts even before the previous one is acknowledged. The sliding window protocol allows the sender to send multiple frames without waiting for an acknowledgement. ![]() Let’s learn more about this protocol in the section ahead. Sequencing helps the receiver identify whether all the packets have arrived successfully and helps to sort them in the proper order. However, the sliding window protocol offers error control by adding the sequence number to the transmitted frames. This is why we require a flow control mechanism that prevents the sender from overwhelming the receiver with the data. Now, if the sender sends the data faster than the receiver can receive, then within some time, the data buffer at the receiver’s end will fill up and overflow while the receiver is still processing the old data. However, the receiver maintains a data buffer as it has to process data before forwarding it to the upper layer. The rate at which the sender sends the data and at which the receiver receives the data may vary. ![]()
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