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N-SAW N Stop And Wait

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The N-Stop-and-Wait (N-SAW) protocol is a simple and widely used flow control protocol in computer networks. It is a variation of the Stop-and-Wait (SAW) protocol, which is used to ensure reliable data transfer between two nodes in a communication network. The N-SAW protocol is a sliding window protocol that allows multiple packets to be sent in one go before waiting for an acknowledgment, unlike SAW, which sends a single packet at a time.

In this protocol, the sender sends a packet to the receiver, waits for an acknowledgment from the receiver, and then sends the next packet. The receiver, after receiving a packet, sends an acknowledgment to the sender, indicating that the packet has been received successfully. If the sender does not receive an acknowledgment within a certain amount of time, it retransmits the packet.

The N-SAW protocol is mainly used in scenarios where the communication channel is prone to errors and packet loss, such as in wireless communication and satellite communication. In such scenarios, the N-SAW protocol ensures reliable and efficient data transfer between the sender and the receiver.

Working of N-SAW Protocol:

The working of the N-SAW protocol can be explained using the following steps:

  1. Sender sends the packet: The sender sends a packet to the receiver. The packet contains the data to be transmitted along with a sequence number, which is used to identify the packet.
  2. Receiver receives the packet: The receiver receives the packet and checks its sequence number. If the sequence number is expected, the receiver sends an acknowledgment (ACK) to the sender. The ACK indicates that the packet has been received successfully.
  3. Sender receives the ACK: The sender waits for an ACK from the receiver. If it receives an ACK, it sends the next packet. If it does not receive an ACK within a certain amount of time, it retransmits the packet.
  4. Receiver receives the retransmitted packet: If the receiver receives a retransmitted packet, it discards the packet if it has already received it. If it has not received the packet before, it sends an ACK to the sender.
  5. Sender receives duplicate ACK: It has already sent, it assumes that the previous ACK was lost and retransmits the packet.
  6. Sender receives out-of-order ACK: If the sender receives an ACK for a packet that it has not sent yet, it assumes that the previous ACK was lost and retransmits the packet.
  7. Sender and receiver maintain a window: The sender and receiver maintain a window of packets that can be sent and received. The size of the window determines the number of packets that can be sent and received at any given time.

Advantages of N-SAW Protocol:

The N-SAW protocol has the following advantages:

  1. Efficient use of bandwidth: The N-SAW protocol allows multiple packets to be sent in one go before waiting for an acknowledgment. This makes efficient use of the available bandwidth and reduces the overhead of the protocol.
  2. Reliable data transfer: The N-SAW protocol ensures reliable data transfer between the sender and the receiver by retransmitting the packets that are lost or corrupted during transmission.
  3. Simple implementation: The N-SAW protocol is a simple protocol that is easy to implement. It does not require any complex algorithms or hardware.
  4. Automatic flow control: The N-SAW protocol provides automatic flow control, which ensures that the sender does not overwhelm the receiver with too much data.

Disadvantages of N-SAW Protocol:

The N-SAW protocol has the following disadvantages:

  1. Inefficient for high-bandwidth networks: The N-SAW protocol is not suitable for high-bandwidth networks as it allows only a limited number of packets to be sent and received at any given time. This can lead to a significant delay in the data transfer, which can be unacceptable in high-performance networks.
  2. Increased latency: The N-SAW protocol introduces additional latency into the data transfer process as the sender has to wait for an ACK from the receiver before sending the next packet. This can be a significant drawback in real-time applications where low latency is critical.
  3. Limited scalability: The N-SAW protocol is not scalable to a large number of nodes as it requires each node to maintain a window of packets that can be sent and received. As the number of nodes increases, the overhead of maintaining these windows also increases, which can lead to a significant performance degradation.
  4. Limited error detection: The N-SAW protocol relies on the receiver to detect and report errors in the received packets. If the receiver fails to detect an error, the sender assumes that the packet was received successfully, which can lead to data corruption and loss.

Conclusion:

In summary, the N-Stop-and-Wait (N-SAW) protocol is a simple and widely used flow control protocol in computer networks. It provides efficient and reliable data transfer between the sender and the receiver by allowing multiple packets to be sent in one go before waiting for an acknowledgment. However, it has some drawbacks, such as increased latency, limited scalability, and limited error detection, which make it unsuitable for high-performance networks. Overall, the N-SAW protocol is an effective protocol for low-bandwidth and error-prone networks, where reliability and simplicity are critical.