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QoS needed if there's no contention on a link?

Posted on 2016-09-07
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Last Modified: 2016-09-08
Supposed you had a 100Mbps link between switch 1 and switch 2. The latency between switch 1 and switch 2 at another site is 20ms consistently. The amount of bandwidth consumed on this link is never more than 10Mbps - 10% of the link except during backups when everyone's gone home. What is the chance that you'd run into an audio problem for a phone call over that link?
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Question by:amigan_99
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by:gheist
ID: 41789079
Is ist constant 20ms or there is sharp variation? In later case you need QoS, and even that may not help
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by:amigan_99
ID: 41789102
It's a constant 20ms throughout the day. Traffic is normal office type traffic - email, spreadsheets, CIFS, etc etc.
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Dr. Klahn earned 500 total points
ID: 41789163
What is the chance that you'd run into an audio problem for a phone call over that link?

The hardware and latencies described are adequate for uninterrupted voice-quality audio using

a:  one of the common VOIP codecs
b:  audio hardware in the PCs
c:  audio software in the PCs
d:  direct host-to-host communication.

However, if there's a third party involved such as Cisco VOIP or Google Voice, "adequate" goes out the door as the third party (codec, hardware, site, whatever) can cause significant delays.

QoS needed if there's no contention on a link?

If there's truly no contention, meaning no other traffic at all on the link ... then enabling QoS should have no effect as it can't make packets move faster in the absence of competing traffic.  If there's contention causing audio dropouts, then enabling QoS may have an effect.  And, imo, it will certainly demonstrate what a drag setting up QoS can be.
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by:amigan_99
ID: 41789577
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