A little sharing for my own record as well as others to read. Correct me if I made any mistakes in the explanation.
I will try to explain what is QOS and how it works. QOS is not a magic spell. There is a limit to what it can do. You may refer the longer explanation here
http://www.linksysinfo.org/index.php?threa...scussion.28349/Lets assume the following scenario.
- Multiple PC in your local network.
- Over at your ISP, they have the same as well. Instead of PC, it is servers.
Without long explanation, most QOS can only control upload and cannot control download. So forget about controlling this things :
- Download speed
- Fair share among multiple users
At its most basic, QOS only controls upload. It has two task :
1. Prioritize upload packet
2. Limit upload speed for that particular priority
Why you want to limit upload speed?If I sent 1 request for a website. That request will enter the upload queue. Let say that request is 5Kb. The server will return me the website(example: 100Kb worth of data). That is a ratio of 1:20. But this ratio may go up or down depending on what type of request it is. Assuming again in a 1:20 ratio, example if there is 1000 request in upload queue = 5000Kb, the return data is 100,000Kb. Upload speed determine how much request is allowed to go thru at once. If I say I limit my upload to only 100(500Kb) request, I will only get back 10,000Kb. So can you now see the relationship between upload n download. And how it influence the download speed. (* File upload works differently)
Why you need to prioritize packet?Without prioritizing packet, QOS assumes all data is the same type. There is no different between say a http request or an ftp request. So if someone is downloading a file from an ftp server, your website request will be have to wait in queue just like the ftp request. First in first out. From user perspective, he will notice a delay in loading the website. So what you want, is for your website request to jump the queue and go all the way to the front of the queue. So that your request will be process first. Sorting the correct packet priority is important and must be done with much trial and error. New router might have a preset that you can used for most commonly used ports to make configuration easier.
Why people say I need to set my upload speed limit to 85% of my actual upload speed?
Look the illustration above. Imagine the LAN upload queue like a deck of cards. The upload limit you set is how fast you remove the card from the top of the deck. New request is inserted at the bottom of the deck. If the deck did not clear fast enough from the top, your queue will be full and no more new card can be inserted from the bottom. New request will be thrown away. For example, if the queue is fully occupied by ftp request. And you try to open a http website. The http request tries to jump the queue to the front but there is no room in the queue any more because it is occupied by all the ftp requests. You have effectively killed the QOS function. So your goal is to NEVER let the queue become full.
So the max speed your internet can clear the deck, is your max internet upload speed. Due to the some other stuff, you might not always get the max speed all the time. So 85% is a pretty good value. This effectively tells the router, this is the max speed I can clear my queue. With this speed my queue will never be full. When you are greedy, and still insist to put the speed to max. Your router will try to sent the data towards your ISP at that speed, but your ISP says, nope. Your ISP then starts to throw away your request and you will have to re-transmit those packet again, thus making things worst.
When the upload to download ratio is very high, regardless of how low I set my upload speed, my internet is still slow.This will happen to things like torrent. Best to control on client side. Normal QOS can't really handle this very well. Advance routing command needed. For consumer router, only some with DDWRT or OPENWRT firmware only able to do this as far as I know.
Bandwidth sharing?For consumer router, only some with DDWRT or OPENWRT firmware only able to do this efficiently as I know. I currently use QOS HTB with DDWRT on my wireless AP. Generally of the shelf type of consumer router, from my test the bandwidth split is not stable and varies a lot on each repeated test.
This post has been edited by WhitE LighteR: Jul 30 2015, 04:48 PM 
Oct 30 2013, 08:20 AM
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