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Friday, 13 July 2012

What is Data Flow Control?

 Flow control is the process of controlling the amount of data sent to a device so that it does not exceed the capabilities of the receiving system.
It enables a receiver to regulate the flow of data from sender so that the receivers’ buffers do not overflow. Flow control is technique of assuring that a transmitting entry does not over flow a receiving entity with data. The receiving entity typically all allocates a data buffer of some maximum length for a transfer. When data are received, the receiver must do a certain amount of processing before passing the data to the higher level software.
Describe Sliding Window Flow Control:
In communication system the transfer of data takes place in the form of frames when one frame reach their destination the next frame allowed to the transmitter to send, if we are using such a link which can support several frames in same times then transmitter will send a group of frames in same time and after reaching these frames to their destination the acknowledgement will come to send the next group of frames both source and destination maintain a lest of frame that has been send and received and also that frames which will be transmit and will be received and this type of flow control is called sliding window control.
Illustrate sliding window control:
The essence of the problem describe so for is that only one frame at a time can be in transit. In situations where the bit length of link I greater than the frame length (a>1) serious inefficiencies result. Efficiency can be greatly improved by allowing multiple frames to be in transit at the same time.
Let us examine how this might of work for two stations, A and B, connected via a full duplex link station B allocates buffer space for W frame. Thus, B can accept W frame and A is allowed to send W frame without waiting for any acknowledgement. To keep track of which frames have been acknowledged, each is labeled with a sequence number B acknowledges a frame by sending an acknowledgement that include the sequence number of the next frame excepted.


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