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Author Topic: QOS how it really works  (Read 50746 times)

PCTechie

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QOS how it really works
« on: January 11, 2009, 05:45:57 PM »

Link>QoS
Let me start of by saying no matter what type of VOIP phone system you have, if your network is not good, then the phone system will be no good.

I see a lot of postings here and other places regarding QOS (or COS as some vendors refer to it as).  QOS is becoming more known now that VOIP is taking over.  Many people misunderstand how and what QOS really is and does.

My background is I am a Network/Systems Administrator.  I have been doing this for 11 years.  I am Cisco and Microsoft Certified.  

QOS stands for Quality Of Service.  Quality being the key word.  A person can setup a switch or router to handle QOS marked traffic so that priority traffic is handled first.  Without QOS, traffic is First in First Out.  What people do now is have their voice traffic marked with a higher priority than the rest of the data traffic, so that it gets the priority when needed.  Basically makes sure voice is ahead of the data.

Now the big misunderstanding with QOS.  ANY QOS policy only kicks in when the switch or router is fully saturated.  You read that right.  Just because you have a QOS policy in place, does not mean it is active.  Most of the time it is not.  The QOS policy only activates when you have such high traffic that the router or switch deems it saturated.  If your network is saturated so much that you have QOS issues, then you should really look at your network.

Most small offices on a 100 MB switch should not have much saturation.  Unless you are moving gigs of data from you to the server or vice versa, then it is doubtful that you will saturate a 100MB network.  Even less likely if you are Gigabit to the desktops.  Even larger networks, setup properly, should not have much saturation.

I still recommend using a higher end switch (not a WalMart special) that gives you the ability to have a QOS policy, and also look at your data utilization.  You still want the safety net of QOS to prevent Bob from accounting to taking down the phone system because he wanted to copy 15 movies and 1000 songs to the server.  

I have been using the Cisco Express series, but other brands work well too.  The Express has some limitations, but the price is much more attractive to my small office customers.  I know this is a DLink site, but I have little experience with their switches.  I do see they make a higher end one, but I do not know much about it.

Anyone running VOIP on a HUB?  I hope not.  Hubs are pretty much gone, but I run across some every now and then.  Anyone with a hub should replace them immediately with a switch.  A hub is a D-U-M-B device.  A switch has some logic ability behind it.  The only good place for a HUB is the trashcan.  Look at your network devices and make sure they say SWITCH, not HUB.

Remember, QOS is good, but rarely comes into play in the quality of your VOIP calls.  It only works when the network is saturated.

One other misnomer is using QOS over a VPN or the internet.  QOS does not, and will not work over any internet connection.  You can mark your packets for QOS all you want, but once they hit the internet the markings are ignored and handled first come first serve.  The internet could care less what traffic you are sending.  There are thousands of internet users, and you are no more special than your neighbor, sorry.  If QOS did work on the internet, then I would mark my traffic all HIGH priority so that I could be first!!!  The only connection types that overcome this is MPLS, or private point to point T1's or other private connections.

Enough from me.  I just wanted to clarify some misunderstandings about QOS.

Good luck to all.

PCTechie
« Last Edit: December 11, 2013, 06:54:15 AM by FurryNutz »
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funchords

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Re: QOS how it really works
« Reply #1 on: January 11, 2009, 09:38:22 PM »

Really good stuff!

One other misnomer is using QOS over a VPN or the internet.  QOS does not, and will not work over any internet connection.  You can mark your packets for QOS all you want, but once they hit the internet the markings are ignored and handled first come first serve.  The internet could care less what traffic you are sending.  There are thousands of internet users, and you are no more special than your neighbor, sorry.  If QOS did work on the internet, then I would mark my traffic all HIGH priority so that I could be first!!!  The only connection types that overcome this is MPLS, or private point to point T1's or other private connections.

From the perspective of a home user, their home gateway's QOS policies do bias the outbound queuing of packets when their uplink is congested.  After they're admitted to the ISP's network, you're 100% right -- the user's QoS settings have no further influence. 

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Layer2

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Re: QOS how it really works
« Reply #2 on: December 11, 2013, 05:25:38 AM »

I wish I had read your post earlier.
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