07-10-2010, 04:36 PM
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Introduction
The essential philosophy behind the Internet is expressed by the scalability argument: no protocol, algorithm or service should be introduced into the Internet if it does not scale well. A key corollary to the scalability argument is the end-to-end argument: to maintain scalability, algorithmic complexity should be pushed to the edges of the network whenever possible. Perhaps the best example of the Internet philosophy is TCP congestion control, which is achieved primarily through algorithms implemented at end systems. Unfortunately, TCP congestion control also illustrates some of the shortcomings of the end-to-end argument.
As a result of its strict adherence to end-to-end congestion control, the current Internet suffers from two maladies: congestion collapse from undelivered packets, and unfair allocations of bandwidth between competing traffic flows. The first malady--congestion collapse from undelivered packets--arises when bandwidth is continuously consumed by packets that are dropped before reaching their ultimate destinations . Unresponsive flows, which are becoming increasingly prevalent in the Internet as network applications using audio and video become more popular, are the primary cause of this type of congestion collapse, and the Internet currently has no way of effectively regulating them.
The second malady--unfair bandwidth allocation--arises in the Internet for a variety of reasons, one of which is the presence of unresponsive flows. Adaptive flows (e.g., TCP flows) that respond to congestion by rapidly reducing their transmission rates are likely to receive unfairly small bandwidth allocations when competing with unresponsive or malicious flows. The Internet protocols themselves also introduce unfairness. The TCP algorithm, for instance, inherently causes each TCP flow to receive a bandwidth that is inversely proportional to its round trip time . Hence, TCP connections with short round trip times may receive unfairly large allocations of network bandwidth when compared to connections with longer round trip times.
These maladies--congestion collapse from undelivered packets and unfair bandwidth allocations--have not gone unrecognized. Some have argued that they may be mitigated through the use of improved packet scheduling or queue management mechanisms in network routers. For instance, per-flow packet scheduling mechanisms like Weighted Fair Queueing (WFQ) attempt to offer fair allocations of bandwidth to flows contending for the same link. So does Core-Stateless Fair Queueing (CSFQ) , an approximation of WFQ that requires only edge routers to maintain per-flow state. Active queue management mechanisms like Fair Random Early Detection (FRED) achieve an effect similar to fair queueing by discarding packets from flows that are using more than their fair share of a link's bandwidth.
For more information about network border patrol,please follow the link:
http://studentbank.in/report-network-bor...s-in-the-i
http://studentbank.in/report-network-border-patrol
[i]NETWORK BORDER PATROL: PREVENTING CONGESTION COLLAPSE AND PROMOTING FAIRNESS IN THE INTERNET[/i]
Introduction
The essential philosophy behind the Internet is expressed by the scalability argument: no protocol, algorithm or service should be introduced into the Internet if it does not scale well. A key corollary to the scalability argument is the end-to-end argument: to maintain scalability, algorithmic complexity should be pushed to the edges of the network whenever possible. Perhaps the best example of the Internet philosophy is TCP congestion control, which is achieved primarily through algorithms implemented at end systems. Unfortunately, TCP congestion control also illustrates some of the shortcomings of the end-to-end argument.
As a result of its strict adherence to end-to-end congestion control, the current Internet suffers from two maladies: congestion collapse from undelivered packets, and unfair allocations of bandwidth between competing traffic flows. The first malady--congestion collapse from undelivered packets--arises when bandwidth is continuously consumed by packets that are dropped before reaching their ultimate destinations . Unresponsive flows, which are becoming increasingly prevalent in the Internet as network applications using audio and video become more popular, are the primary cause of this type of congestion collapse, and the Internet currently has no way of effectively regulating them.
The second malady--unfair bandwidth allocation--arises in the Internet for a variety of reasons, one of which is the presence of unresponsive flows. Adaptive flows (e.g., TCP flows) that respond to congestion by rapidly reducing their transmission rates are likely to receive unfairly small bandwidth allocations when competing with unresponsive or malicious flows. The Internet protocols themselves also introduce unfairness. The TCP algorithm, for instance, inherently causes each TCP flow to receive a bandwidth that is inversely proportional to its round trip time . Hence, TCP connections with short round trip times may receive unfairly large allocations of network bandwidth when compared to connections with longer round trip times.
These maladies--congestion collapse from undelivered packets and unfair bandwidth allocations--have not gone unrecognized. Some have argued that they may be mitigated through the use of improved packet scheduling or queue management mechanisms in network routers. For instance, per-flow packet scheduling mechanisms like Weighted Fair Queueing (WFQ) attempt to offer fair allocations of bandwidth to flows contending for the same link. So does Core-Stateless Fair Queueing (CSFQ) , an approximation of WFQ that requires only edge routers to maintain per-flow state. Active queue management mechanisms like Fair Random Early Detection (FRED) achieve an effect similar to fair queueing by discarding packets from flows that are using more than their fair share of a link's bandwidth.
For more information about network border patrol,please follow the link:
http://studentbank.in/report-network-bor...s-in-the-i
http://studentbank.in/report-network-border-patrol
