The functions provided by the data link layer are as follows: The main work of the data link layer is to convert the data into the form of frames (refer to the sub-section below for details about framing). If the two computer nodes are on the same networks then the data link layer provides a connection between the two nodes. The data link is the second layer of the OSI model which is used for the transmission of the error-free frames from one node to the other node. Now, let us discuss the data link layer briefly so that we can get a better understanding of the Selective Repeat ARQ protocol as it is one of the most widely used protocols of the data link layer to control errors. The data link layer is one of the seven layers of the OSI model. The OSI model is a 7-layered model so it is also known as a 7-layered architecture model. It is a conceptual reference model that describes the entire flow of information from one computer to the other computer. The OSI model stands for Open Systems Interconnection model. What is Sliding Window Protocol?īefore learning about the sliding window protocol, let us first learn about computer networks, the OSI model, and the data link layer (as the Sliding Window Protocol is related to the data link layer).Ī computer network is a set of devices (computers) connected to exchange information and resources such as files etc. There are two types of sliding window protocols namely - Go-Back-N ARQ, and Selective Repeat ARQ. The ACK lets the sender know that a particular frame is received by the receiver correctly. When the receiver receives the frame, it sends back an ACK (acknowledgment) to the sender. The sequence number also helps the receiver identify the loss of damaged packets. The sender associates a sequence number to the data frames so that the receiver can use this sequence number to arrange the frames in order if any frame was re-transmitted. The sliding window protocol uses a mechanism of sequence numbers. Using the sliding window protocol, the sender can send multiple frames at a time. T = Retrieve_Copy_Frame(s.The sliding window protocol is a data link layer protocol that is useful in the sequential and reliable delivery of the data frames. Resend all frames if acknowledgement havn’t been received If ( AckNo > SeqFirst & AckNo < SeqN ) then Wait_For_Event() //wait for availability of packet SeqN = 0 // Sequence number of Nth frame window SeqFirst = 0 // Sequence number of first frame in window S_window = power(2,m) – 1 //Assign maximum window size Sender Site Algorithm of Go-Back-N Protocol begin

The number of bits in the sequence number is 2 to generate the binary sequence 00, 01, 10, 11. For example, if the sending window size is 4, then the sequence numbers will be 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, and so on. The sequence numbers are numbered as modulo-n. Thus in order to accommodate a sending window size of 2 n−1, a n-bit sequence number is chosen. Consequently, the size of the sending window is 2 n−1. If the sequence number of the frames is an n-bit field, then the range of sequence numbers that can be assigned is 0 to 2 n−1. The size of the sending window determines the sequence number of the outbound frames. If the acknowledgment of a frame is not received within an agreed upon time period, all frames starting from that frame are retransmitted. The maximum number of frames that can be sent depends upon the size of the sending window. The frames are sequentially numbered and a finite number of frames. Go – Back – N ARQ provides for sending multiple frames before receiving the acknowledgment for the first frame. It is a case of sliding window protocol having to send window size of N and receiving window size of 1. Go-Back-N protocol, also called Go-Back-N Automatic Repeat reQuest, is a data link layer protocol that uses a sliding window method for reliable and sequential delivery of data frames.

Sliding window arq