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Monday, August 26, 2013

What is the difference between congestion control and flow control?

Flow control and congestion control are similar sounding concepts and often confuse us sometimes. In this article we shall discuss about the differences between these two. 

- Computer networks use the flow control mechanism for keeping control over the data flow between two nodes in such a way that the receiver if it is slower when compared to the sender is not outrun by it. 
- The mechanism of flow control also provides ways to the receiver to maintain control over the speed with which it transmits the information.
- On the other side, the congestion control provides mechanism for the controlling the data flow under the condition of actual congestive collapse. 
- The mechanism keeps a control over the entry of data in to the network so that this traffic can be handled by the network effectively.  
- The mechanism of flow control does not let the receiving node get overwhelmed by the traffic that is being sent by another node. 

There are several reasons why this flow of data gets out of control and affects the network negatively. 
- First reason being that the receiving node might not be capable of processing the incoming data as fast as it is being sent by the sender node. 
Based on these reasons there are various types of flow control mechanisms available. 
- However, the most common categorization is based on the fact whether the feedback is being sent to the sender or not. 
- There is another flow control mechanism called the open loop flow control mechanism. 
- In this mechanism no feedback is sent to the sender by the receiver and this perhaps the most widely used flow control mechanism. 
- Opposite of open loop flow control mechanism is the closed loop flow control. 
- In this mechanism, the receiver sends back congestion information to the sender. 
- Other commonly used flow control mechanisms are:
Ø  Network congestion
Ø  Windowing flow control
Ø  Data buffer etc.

- Congestion control offers such methods that can be used for regulating the incoming traffic in the network to such an extent where the network itself can manage all that.
- In congestion control, the network is prevented from falling in to a state of congestive collapse. 
- In such a state either little or no communication happens.
- This little communication is of no help. 
- Switching networks usually require congestion control measures than any other type of networks. 
- The congestion control is driven by the goal of keeping the number of data packets at such a level that the performance of the network would be reduced dramatically.
- Congestion control mechanism can be seen even in protocols such as UDP (user datagram protocol), TCP (transport control protocol) and other transport layer protocols. 
- TCP makes use of the exponential back off and slow start algorithms. 
- We classify the congestion control algorithms based up on the feedback that is given by the network, the performance aspect that has to be improved, and modifications that have to be made for the present network, fairness criterion that is being used and so on. 

- Congestion and flow control are two very important mechanisms used for keeping the traffic flow in order. 
- Flow control is a mechanism that stretches from one end to another i.e., between the sender and the receiver where the speed of sender is much higher than that of the receiving node. 
- Congestion control is implemented for preventing packet loss as well as delay that is caused as a side effect of the network congestion. 
- Congestion is meant for controlling the traffic of the entire whereas flow control is limited to transmission between two nodes.

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