[c-nsp] effect of different packet size? and how to ensure video packet are not lost during other TCP communication

[Rodney Dunn]

On Sun, Dec 12, 2004 at 12:53:22PM +0000, Farhan Aleem wrote:
> I got two general conceptual question which are not specific to
> cisco.But i need to find out about these. Thanks in Advance. hope that
> it is not disliked to but general question
> 
> What will be the effect if the packet size is changed. like  using FTP
> and video confrencing which uses UDP. If packet size is varied then wt
> are the possible results as the link bandwidth is same transmissino
> rate is same.

I couldn't fully understand your question (the way you worded it).
But the general concept is this.

Aon a software forwarding platform features are applied (usually)
on a per packet basis.  So for the same link usage amount for
throughput you will see less packets/sec for larger packets.
The more packets/sec the more work the CPU has to do for each
packet so it's more CPU intensive.  Go with a hardware forwarding
device that can do all features faster than you can fill the
link up for small packets and it really doesn't matter.
It all depends on the setup you have.

> 
> 
> And how it can be  ensured that  video packet are not lost during
> other TCP communication like ftp on the link shared for ftp and video
> confrencing...?

That is what QOS is for.  You use MQC with CBWFQ/LLQ.  Put voice
in the priority class and assign a BW class to match your video
traffic.  A BW class basically says that during congestion you
guarantee X% of BW to that class at all times.

Search for MQC/CBWFQ/LLQ on CCO and there is a lot of information
out there about it.


Rodney

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