Sliding window protocol is a flow control protocol. It allows the sender to send multiple frames before needing the acknowledgements. Sender slides its window on receiving the acknowledgements for the sent frames.

Sliding Window protocol efficiency is formulated as N/(1+2a) where N is no. of window frames and a is ratio of propagation delay vs transmission delay. Stop and Wait protocol is half duplex in nature. Sliding Window protocol is full duplex in nature.

To address this, sliding window protocols allow a selected number of packets, the window, to be sent without having to wait for an ACK. Each packet receives a sequence number, and the ACKs send back that number. The protocol keeps track of which packets have been ACKed, and when they are received, sends more packets.

In data link layer, flow control restricts the number of frames the sender can send before it waits for an acknowledgment from the receiver.

• Approaches of Flow Control. Flow control can be broadly classified into two categories −
• Flow Control Techniques in Data Link Layer.
• Stop and Wait.
• Sliding Window.

ARQ stands for Automatic Repeat Request also known as Automatic Repeat Query. ARQ is an error-control strategy used in a two-way communication system. It is a group of error-control protocols to achieve reliable data transmission over an unreliable source or service.

Go-Back-N: Go-Back-N(GBN) is a ‘Sliding Window Protocol’ that ensures pipelining. It first checks the window size of the sender and receiver, and then it sends multiple data frames at the same time. It will retransmit all the frames starting from that failed data frame.

In Go-Back-N ARQ, N is the sender window size, which we can see in the above example was 5. Now, here N should be greater than 1 in order to implement pipelining. If N=1, then our system reduces to Stop & Wait protocol. Now the efficiency of Go-Back-N ARQ = N/(1+2a), where a = tp/tt.

Conclusions- Go back N is more often used than other protocols. SR protocol is less used because of its complexity. Stop and Wait ARQ is less used because of its low efficiency.

You can configure error record handling at a stage level and at a pipeline level. That is, a pipeline might be configured to write error records to file, but if a stage is configured to discard error records those records are discarded. …

Some of the common techniques used in error control is acknowledgements, timeouts and negative acknowledgements. In a network, two types of errors occur: single-bit errors and burst errors. Forward error control and feedback error control are the two types of error-control mechanisms used in communications.

Basic approach used for error detection is the use of redundancy bits, where additional bits are added to facilitate detection of errors. Blocks of data from the source are subjected to a check bit or parity bit generator form, where a parity of : 1 is added to the block if it contains odd number of 1’s, and.

In networking, error detection refers to the techniques used to detect noise or other impairments introduced into data while it is transmitted from source to destination. Error detection minimizes the probability of passing incorrect frames to the destination, known as undetected error probability.

NAK is used in systems where message loss is infrequent, so NAKs would only rarely have to be used to retransmit lost messages. When communication links are noisy and loss rate high, ACK schemes are preferred: a sender has to receive an acknowledgment from each receiver of a message.

Effective Bandwidth(EB) or Throughput – Number of bits sent per second. Capacity of link – If a channel is Full Duplex, then bits can be transferred in both the directions and without any collisions. Number of bits a channel/Link can hold at maximum is its capacity.

Sliding Window Characteristics

• Opens and closes horizontally with a sliding motion.
• Width is greater than height.
• Large glass area.
• Two to three panels.

Sliding Window Algorithm – Practice Problems

1. Find the longest substring of a string containing k distinct characters.
2. Find all substrings of a string that are a permutation of another string.
3. Find the longest substring of a string containing distinct characters.

It is a special case of the general sliding window protocol with the transmit window size of N and receive window size of 1. It can transmit N frames to the peer before requiring an ACK. The receiver process keeps track of the sequence number of the next frame it expects to receive.

TCP is similar to selective repeat because, when packets are lost due to congestion, the protocols do not require the sender to retransmit EVERY unACK’d packet sent by the sender.

Which protocol – Go-Back-N or Selective-Repeat – makes more efficient use of network bandwidth? Why? Answer: Selective repeat makes more efficient use of network bandwidth since it only retransmits those messages lost at the receiver (or prematurely timed out).

The main difference between flow control and congestion control is that the flow control is a mechanism that controls the traffic between sender and receiver. On the other hand, the congestion control mechanism controls the traffic that is placed by the transport layer into the network.