From: gladston@br.ibm.com
Date: Fri Aug 20 2004 - 09:53:04 GMT-3
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quoted
1. Can some explain what are the options we have for the VoIP BW (with priority for voice quality)?
2. Also how do we select one against the other?
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The main goal is to avoid Delay. As you know, if voice packet are delayed, when it is converted back to analogic signal it will sound bad.
You can control how layer 3 packet are serviced when they are wainting on the layer 3 queue.
When a packet from the layer 3 queue is select to be transmitted it is sent to the interface where there is a layer 2 queue; you can not control how packet are serviced in this FIFO queue. With some technologies like ATM you can control the size of this queue to minimize delay.
Back to layer 3 queue, there are many Cisco feature that allow you dealing with how packets are serviced. If it give us flexibility, on the other hand it confuses us.
But lets not lost the focus: we want voice packets to be serviced first; more than that, we do not want packets too big cause serialization delay on voice packets. This calls for fragmentation.
So, to priorize voice we can use PQ, IP RTP Priority, LLQ.
Besides this, we need Fragmentation.
PQ should be avoid, because there are improvements on LLQ that avoid starving other type of traffic.
LLQ gives us more flexibility than IP RTP Priority.
Also, we must remember that besides RSVP, the other features just guarantee delay on the local router.
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