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QOS inside the same queue or class

hi,

I would like to know if cisco IOS is able to share equitably bandwith between two connection thats belong to the same class,

for example, if a create a class called FTP and I give 50 kbits/s (or 50% of my bandwith 100 kbits), if the first user start a ftp transfer at 40 Kbits, how much bandwith will get the second user ? the remaining bandwith 10 Kbits ? or will the IOS share the bandwith between the two connection : so 25 Kbits for first transfer and 25 Kbits for the second ?

thank you in advance for you reply

5 REPLIES

Re: QOS inside the same queue or class

Hi,

within one class all traffic shares the bandwidth. The only way of influencing this within a class is with WRED, which allows you to drop some traffic within a class earlier than other traffic within the same class.

Also be aware that in case there is no other traffic both FTP connections would roughly get 50kBit/s. Queueing starts when the interface is overloaded.

Hope this helps

Martin

Silver

Re: QOS inside the same queue or class

I think that will depend on the kind of queuing you are using. If you are using PQ, then new session will lead to a congestion (say the util of the link is 100) , then it will drop the new session(strict policing). If you use CBWFQ, then both will come in the same class and both sessions will have drops based on the WRED you have configured.

Re: QOS inside the same queue or class

Hi,

no the new session will not be dropped with PQ. DiffServ has no "session concept". All packets entering a class share the same fate - "priority" or "bandwidth" have nothing to do with it. This is why VoIP without call admission control will lead to problems.

Hope this helps

Martin

Silver

Re: QOS inside the same queue or class

No I didnt talk about a session. Iam talking purely about the traffic. PQ has a strict policer which would drop the packets if there is congestion in the link. This is something bandwidth(CBWFQ) wouldnt do as the bandwidth can still exceed the allocated rate.

Re: QOS inside the same queue or class

Hi,

yes exactly the policer will drop packets if the interface is congested and there is more traffic than the priority class should get. The point I wanted to make clear is that the packets are dropped across all voip calls. So if there is f.e. 60 kBps priority bandwidth and three voip calls with a total of 90 kBps traffic then EACH call will get statistically 30% drops.

It will NOT be two calls without drops and one call with 100% drops.

Sorry for not writing this clear enough.

Hope this helps

Martin

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