Why are the sliding window protocols required What is the fundamental difference

Question

Why are the sliding window protocols required What is the fundamental difference between the GO Back to N and Selective Repeat protocols? In an example TCP communication, 10 packets (numbered 0 through 9) are to be scot to a pew TCP layer. Assuming a window size of 5, illustrate with two separate message flow diagrams between the sender-tide and receiver-side TCP layers how the GO Rack to N and Selective Repeat implementations handle the scenario in which packet# 3 is lost Stark any changes in the sliding windows upon receipt of messages/ACKs at either end For your convenience, a typical message flow diagram for the Selective Repeat method (and. of course, for a different scenario) it given in Fig. I. In a "Selective Repeal" implementation two bits are allocated for the sequence number to that the packets can be numbered 0 through 3. Explain by means of a diagram, if necessary, any problem that could arise if a sliding window sire of J is chosen in the implementation.

Explanation / Answer

1. Sliding window protocol is a protocol which has a feature of packet-based data transmissionprotocols. Sliding window protocols are protocols which are used where reliable in-order delivery of packets is required, such as in the Data Link Layer (OSI model) as well as in the Transmission Control Protocol (TCP).

2. Conceptually, each portion of the transmission (packets in most data link layers, but bytes in TCP) is assigned a unique consecutive sequence number, and the receiver uses the numbers to place received packets in the correct order, discarding duplicate packets and identifying missing ones.

3. The problem with this is that there is no limit on the size of the sequence number that can be required.

4. By placing limits on the number of packets that can be transmitted or received at any given time, a sliding window protocol allows an unlimited number of packets to be communicated using fixed-size sequence numbers.

5. The term "window" on the transmitter side represents the logical boundary of the total number of packets yet to be acknowledged by the receiver. The receiver informs the transmitter in each acknowledgment packet the current maximum receiver buffer size (window boundary).

6. The TCP header uses a 16 bit field to report the receive window size to the sender. Therefore, the largest window that can be used is 216 = 64 kilobytes.

7. Go Back N ARQ is inefficient for noisy link and Selective repeat ARQ is efficient for noisy links.

8. Go Back N ARQ is less complicated than Selective repeat ARQ and

Selective Repeat ARQ is complicated.

9. Go Back N weakness is the fact that when the window size is too large, the number of packets in the pipeline grows and one packet error causes the retransmition of many packets unnecessarily.

10. Selective Repeat solves this by acknowleding just the suspicious packets, which sightly makes performance better, but if a wrong window size is chosen, then the reciever doesn't know if a packet is being retransmitted or another packet is being sent by first time.

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