On Sun, Dec 23, 2007 at 10:59:10AM +0100, Federico Giannici wrote: >Tobias Wigand wrote: >>hi, >>> >>>Thank you for your suggestion. >>>Unfortunately I have found only generic sentences and not the answer >>>to my question: how exactly "priority" works? >>> >>>Or, from a practical point of view: a queue with an high "priority" >>>parameter gets ALL the bandwidth he wants from queues with lower >>>"priority" (except, maybe, for the "realtime" one)? >> >>well, if i get you right, your question is answered here: >>http://calomel.org/pf_hfsc.html >>quote: >>Cbq and HFSC queues with a higher priority are preferred in the case of >>overload. > >OK, but the word "preferred" is little generic for me, especially >because this sentences is used to differentiate from the behaviour of >the "Pri" queues: "Priq queues with a higher priority are always served >first". > >So, in HFSC queues with higher "priority" are not ALWAYS served before >queues with lower "priority"? > >Maybe the "realtime" bandwidth is alway served first and then the >"priority" parameters enters in action? > >Queues with higher "priority" gets ALL the bandwidth they need >regardless of the "linkshare" of queues of lower "priority"? > > >Bye. > >-- >___________________________________________________ > __ > |- [EMAIL PROTECTED] > |ederico Giannici http://www.neomedia.it >___________________________________________________
Federico, "priority" is not the amount of bandwidth a queue gets, but the order in which the packets are queued (buffered) when leaving the interface. Lets say we have three queue's (Qone, Qtwo, Qthree) where Qone has the highest priority and Qthree has the lowest. If the link is saturated then Qone will have its packets put at the front of the line in front of packets for Qtwo and Qthree which were already in line. When bandwidth is available the packets will be sent in the order of the line. HFSC allows us to make sure that an important queue always has the bandwidth it needs by using the "realtime" parameter. This guarantees bandwidth to the queue no matter what priority it is. If you use HFSC and the link is saturated then the highest priority queue with "realtime" bandwidth reserved will get sent out before the other saturated queues. If on the other hand the network link is saturated _AND_ all "realtime" reserved bandwidth is being used then the highest "priority" packets will be buffered first. I will take a look at the wording on the site and see if I can make it a little clearer. I hope this helps. Hierarchical Fair Service Curve (HFSC) of OpenBSD http://calomel.org/pf_hfsc.html -- Calomel @ http://calomel.org Open Source Research and Reference
