Bandwidth for High Speed Networks

This yields c bnew bold 6 b f ti where tik tk tk1 and

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: fore the updating. We use b an analogous formula to update F . The updating rule for b depends on whether the link is congested or not. To lter out the estimation inaccuracies due to exponential smoothing we use a window of size Kc . b A link is assumed to be congested, if A  C at all times during an interval of length Kc. Conversely, a link is assumed b to be uncongested, if A  C at all times during an interval of length Kc . The value b is updated only at the end of an interval in which the link is either congested or uncongested according to these de nitions. If the link is congested then b is updated based on the equation F  b = C . We approximate F  by a linear function that intersects the origin and b has slope F= bold . This yields C bnew = bold 6 b F If the link is not congested, bnew is set to the largest rate of any active ow i.e., the largest label seen during the last Kc time units. The value of bnew is then used to compute dropping probabilities, according to Eq. 2. For completeness, we give the pseudocode of the CSFQ algorithm in Figure 2. We now describe two minor amendments to this algorithm related to how the bu ers are managed. The goal of estimating the fair share b is to match the accepted rate to the link bandwidth. Due to estimation inaccuracies, load uctuations between b's updates, and the probabilistic nature of our algorithm, the accepted rate may occasionally exceed the link capacity. While ideally the router's bu ers can accommodate the extra packets, occasionally the router may be forced to drop the incoming packet due to lack of bu er space. Since drop-tail behavior will defeat the purpose of our algorithm, and may exhibit undesirable properties in the case of adaptive ows such as TCP 9 , it is important to limit its e ect. To do so, we use a simple heuristic: every on receiving packet p if edge router i =classifyp; p:label = estimate rateri ; p; = use Eq. 3 = prob =max0; 1 , =p:label; if prob unif rand0, 1 =estimate p; 1; dropp; else =estimate p; 0; en...
View Full Document

This document was uploaded on 03/04/2014 for the course ENG 531 at Rice.

Ask a homework question - tutors are online