After sending four packets the sender waits for acknowledgement. So the sender sends four packets 0, 1, 2, and 3 without waiting for an acknowledgement. The window size in the example above is 4. let us understand the go-back-n protocol. The window size N determines the number of data packets that are not acknowledged yet. In go-back N protocol the sending host sends a series of the data packets which are sequentially numbered modulo to some maximum value. The go-back N protocol implements pipelining and is also based on sliding window protocol where the size of the window is N. The stop-and-wait protocol above does not implement pipelining as the sender waits for an acknowledgement before sending the next data packet. That is sending the next data packet before receiving the acknowledgement for the previously sent data packet. In general, pipelining specifies the beginning of the next task before the completion of the previous task. In this way, the protocol manages error control.īefore understanding the go-back N protocol let us understand pipelining in networking. If no acknowledgement is sent for a packet and the timer for that corresponding packet is expired, the packet is resent. If the checksum is found incorrect the packet is discarded and no acknowledgement is sent for that corrupted packet. The checksum is checked at the destination host. To manage error control, a checksum is added to each data packet. In this way, this protocol manages flow control. The source keeps the packet until it is acknowledged. If the acknowledge is not received before the timer expires the source host considers that either the packet is lost or is corrupted. If the acknowledgement is received before the timer expires the source host sends the next packet. The moment the source host sends the packet it starts a timer. As window size is 1 the source host sends only one packet at a time and waits for the acknowledgement. Stop-and wait protocol is a connection-oriented protocol that uses a sliding window protocol with window size 1. In simple protocol, it is assumed that the packets sent by the source host can be immediately handled by the receiver host so this protocol does not provide flow and error control. The simple protocol is a connectionless protocol. The transport layer protocol at the destination decapsulates the received packets and deliver them to the destination application layer. These packets are delivered to the transport layer of the destination host. The received message is divided into manageable segments and is encapsulated into packets. Simple protocol, as the name suggests is quite simple as the transport layer at the source host receives the message from its application layer. Though the TCP/IP transport layer protocols are either modifications of these general protocols or are the combination of some of these protocols. ![]() Here we are not discussing the TCP/IP transport layer protocols. In this section, we will only discuss the common transport layer protocols.
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