kivava chang's List: Research

• What is congestion?
• definitions of congestion focus on some aspect of network behavior under high load.
• the short term packet arrival rate at some switch exceeds its service rate.
• The additional delay can cause sources to time out and retransmit, increasing the load on the bottleneck
• packets are buffered, leading to delays
• retransmissions dominate the traffic, and effective throughput rapidly diminishes
• new packets may not be allowed to enter the switch
• packets might be delayed at a preceding switch as well
• three things happen simultaneously.  - First, the queueing delay of the data packets increases. - Second, there may be packet losses. - Finally, in the congested state, the traffic is dominated by retransmissions, so that the effective data rate decreases.
• The standard definitions of congestion are thus of the form: ‘‘A network is congested if, due to overload, condition X occurs’’, where X is excessive queueing delay, packet loss or decrease in effective throughput.
• First, delays and losses are indices of performance that are being improperly used as indices of congestion, since the change in the indices may be due to symptoms of phenomena other than congestion.
• Second, the definitions do not specify the exact point at which the network can be said  to be congested
• Third, a network that is congested from the perspective of one user is not necessarily cong- ested from the perspective of another.
• that network congestion depends on a user’s perspective
• The key point is the notion of the utility that a user gets from the network, and how this utility degrades with network loading.
• The concept of ‘utility’ used here is borrowed from economic theory. It is used to refer to a user’s preference for a resource, or a set of resources
• In classic microeconomic theory, utilities are represented by a function over the resources.
• the function can only be used to relatively rank two resource bundles from the point of view of a single user.
• In practice, a utility function may depend on a threshold.
• A network is said to be congested from the perspective of user i if the utility of i decreases due to an increase in network load.
• First, we make a clear distinction between a performance index and a congestion index.
• Second, the definition makes it clear that congestion occurs from the point of view of each individual user.
• Finally, the point of congestion is precisely the one where the user detects a loss of utility.

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