QoS and latency

RouterOS General
1

I’d like to know the behavior of a Qos system, consisting mangle+queue_tree, when the main queue of a router (example “download”) is not saturated.

Compared to a router with no QoS system, can it give advantages in terms of latency to services that have higher priority (voip, icmp)?

  1. Yes, it can.
  2. It doesn’t matter.
  3. No, and degrades latency’s performace for a little.
    Then, when we have availability of bandwidth, is it important build a QoS system?


    Thanks.
2

Its important if u have lot of clients who downloads large amount of data. Im running 18 mangle rules and queue tree for Qos and everything works nice. Users now can play online games with normal latency and enjoy online media (ect. youtube, soundcloud ..) without laags. But Anyway its not the same as Ubisoft Stream Engine.

3

In a general rule of thumb you need QoS to solve bottleneck problems..
If you think you don’t have any (even on client side), you don’t need it, since it doesn’t do any work..

4

As soon as you sell more bandwith then you buy you need Qos.

Example:
Your ISP delivers 1Mb.
You have two users and yourself.
Both users are allowed to download 512kb so they consume full download.
Now you want to do something on the internet…
Some packages get dropped now, so some might experiance some problems.

But if its only file download, probaly nobody will complain.
What if your internet use is VOIP? You need to prioritize this then over the download sessions of you other users. Now QoS comes in place.

Regarding the loss of latency in a router perfoming QoS:

  1. Speed of router is important. RB600 or better depending on your network.
  2. Amount of traffic running through router, and thus through filters. 1 or 2Mb of traffic can be handled even by a simple 411 router.
  3. Number and design of mangle filter rules. Try to avoid double marking.
  4. Other processes taking place in router (firewall filter, routing, authentication, client limiting etc.)

And off course each of these 4 have an influence on the total.
In my humble opinion it pays out to buy the best router you can to have all these task done for you.

My experiance.
I have 210 users with 3 to 6Mb download assigned that are limited and prioritised (business get higher then private, VOIP gets highest P). Then I have some routing policy depending on client subscription to split traffic over two Internet connections.
I have some basic firewall filters and srce nat is done for clients that go out to symmetric line with /24 network.

After this router there is another rb1000/rb600 (depending on the connection) that does do the traffic prioritizing and this 2nd rb1000 yet again splits traffic with PCC over three 10Mb adsl lines.

Before all my clients hit my rb1000 I have one rb439AH as concentrator for all my different fixed or wireless backhaul links. Here I do again mangle for Queuing towards my network since the backhauls are at times the bottlenecks compared to the overal traffic I can get from ISP’s (40Mb)

Still, I run several ping test towards the internet from my control PC that is on radio link and 4 routers away from my central location and all pings stay below 2-4ms when leaving my last routers onto the internet.

Delays I notice are in general on the first router of the ADSL lines providers, 30-50ms (symmetric only 0-10ms) and if the internet is busy I see further delays here. But that’s all beyond my reach…

Further do I get delays on my wireless links in times of saturations.

But the bottom line is, even under the busiest times for my network (20-25Mb of traffic over my main router) I hardly see my latency go up in my network.
Instead of 2-3ms I see 3-5ms for traffic to the first ISP’s routers.

Conclusion: If your router is powerfull enough and the rules are done with economity of use in the back of your head you should not worrie about the latency in your router.