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Tuesday, August 27, 2013

What are general principles of congestion control?

- Problems such as the loss of data packets occur if the buffer of the routers overflows.
- This overflow is caused by the problem of the congestive collapse which is a consequence of the network congestion. 
- If the packets have to be re-transmitted more than once, it is an indication that the network is facing the problem of congestion. 
- Re-transmission of the packets is the treatment of only this indication but not for problem of the network congestion. 
- In the problem of congestive collapse, there are a number of sources that make attempts for sending data and that too at a quite high rate. 
- For preventing this problem of the network congestion, it requires mechanisms that are capable of throttling the sending node if in case the problem of network congestion occurs. 
- Network congestion is a real bad thing as it manifests in the network’s performance that the upper layer applications receive. 
- There are various approaches available for preventing and avoiding the problem of network congestion and thus implementing proper congestion control. 
- When the capacity of the network is exceeded by the demands for the resources and too much queuing occurs in the network causing loss of packets, congestion of packets is said to occur. 
- During this problem of network congestion, the throughput of the network might drop down to zero and there might be a high rise in the path delay. 
Network can recover from the state of congestive collapse using a congestion control scheme. 
- A network can operate in a region where there is high throughput but low delay with the help of the congestion avoidance scheme.
- These schemes keep the network away from falling in to a state of congestive collapse. 
- There is a big confusion over congestion control and congestion avoidance. Most of us think it is the same thing but it is not. 
- Congestion control provides a recovery mechanism whereas the congestion avoidance provides a prevention mechanism. 
- Today’s technological advances in the field of networking have led to a rise in the network links’ bandwidth. 
- In the year of 1970, ARPAnet came in to existence and built using the leased telephone lines that had a 50 kbits/second bandwidth. 
- LAN (local area network) was first developed in the year of 1980 using token rings and Ethernet and offered a bandwidth of 10 mbits/ second. 
- During the same time many efforts were made for standardizing the LAN using the optical fibers providing a 100 mbits/seconds and higher bandwidth. 
- Attention to the congestion control has been increased because of the increase in the mismatching that occurs between the various links composing the network. 
- Routers, IMPs, gateways, intermediate nodes links etc. are the hot-spots for the congestion problems. 
- It is at these spots that the bandwidth of the receiver falls short for accommodating all the incoming traffic. 
- In the networks using the connection-less protocols, it is even more difficult to cope with the problems of network congestion. 
- It is comparatively easy in the networks using the connection-oriented protocols.
- This happens so because in such networks, the network resources are kept under advance reserve during setting up the connection.
- One way for controlling congestion problems is preventing the setting up of new connections if congestion is detected anywhere in the network but it will also prevent the usage of the reserved resources which is a disadvantage. 

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