Question Answers

Question Answers

3 (a, b)

Sliding window and Packet Lost Receive Management

The sliding window mechanism is directed to flow control of data between a transmitter and a receiver belonging to a computer network. The sliding window protocol is a protocol for transmission of data bidirectional the link level layer (OSI model). The sliding window is a device of type flow control software, that is, the flow control takes place through the exchange of specific character or control frames, with which the receiver indicates to the sender what state of availability to receive data.

This device is needed to avoid flooding the receiver with shipments of data frames. The receiver must receive data to processing it, if not performed at the same speed that the transmitter sends data will be saturated, and some of them may be lost. To avoid such a situation the sliding window controls this pace of shipments from sender to receiver. With this device, two major problems are solved: the data flow control and the efficiency in the transmission.

Operation of the transmission window

Figure 1 (a, b)

The protocol sliding window allows the sender to transmit multiple data segments before waiting for a receiver to confirm receipt of the segments; such confirmation is called validation, and involves sending messages called ACK from the receiver to the sender. The validation is performed from the receiver to the transmitter and containing the number of the next frame that the receiver expects to receive, or that of the last successfully received frame, ACK n (n being the number of the frame indicated). With this indication the issuer is able to distinguish the number of shipments successfully lost shipments and shipments expected to be received. Segments are denominated Unacknowledged if they are sent but have not been validated.

Technically the number of segments that can be Unacknowledged at a given time is limited by the size of the window, a small and fixed number is called the window width.

Figure 2

For example, in a sliding window of size 8, the sender may transmit up to 8 segments validation without receiving any of them (Figure 1a). Then wait for an acknowledgment from the receiver packet without sending any more. When the issuer receives a first packet validation sent pertaining to number 1 August sliding window, the window covering slide 8 position (the window width defined), but in this case from 2 to 9 and send frame number nine continuing pending more confirmations to continue slipping and sending the following frames (Figure 1b).

If you wait a validation protocol for each frame sent, not send more segments to receive the acknowledgment of the last packet sent. The sliding window concept means that there is continuous transmission of information, improving the network performance (Figure 2). The transmitter must be stored in a buffer all those packets sent and not validated (Unacknowledged packets), in case you need rebroadcast. You can only delete the buffer to receive validation from the receiver, and slide the window and one more unit. The smaller number of the sliding window corresponds to the first packet of the sequence that has not been validated. The buffer size should be equal to or greater than the ...