Describe Go Back N and Selective Repeat protocol.

Sure, I can describe the Go Back N and Selective Repeat protocols step by step.

1. Go Back N Protocol:

   • In the Go Back N protocol, the sender can continuously send multiple packets without waiting for an acknowledgment from the receiver.
   • The sender maintains a window of sequence numbers for the packets it has sent but not yet received an acknowledgment for.
   • The receiver acknowledges the packets it receives by sending back an acknowledgment with the next expected sequence number.
   • If the sender receives an acknowledgment for a packet, it moves its window forward and sends the next packet.
   • If the sender does not receive an acknowledgment within a specified timeout period, it assumes that the packet or packets have been lost and retransmits all the packets in its window.
   • The receiver discards duplicate packets and delivers the packets to the upper layer in order.

2. Selective Repeat Protocol:

   • In the Selective Repeat protocol, the sender can send multiple packets without waiting for an acknowledgment, similar to Go Back N.
   • The sender maintains a window of sequence numbers for the packets it has sent but not yet received an acknowledgment for.
   • The receiver acknowledges the packets it receives by sending back an acknowledgment with the sequence number of the received packet.
   • If the sender receives an acknowledgment for a packet, it moves its window forward and sends the next packet.
   • If the sender does not receive an acknowledgment within a specified timeout period, it retransmits only the lost packet instead of retransmitting all the packets in its window.
   • The receiver buffers out-of-order packets and delivers them to the upper layer in order once the missing packets are received.

Both protocols are used in reliable data transfer over a network, but they differ in the way they handle retransmissions. Go Back N retransmits all the packets in the window, while Selective Repeat retransmits only the lost packets.