As the title states!
- What is QoS
- When is it good to use it?
- When is it not good to use it?
As the title states!
QoS is Quality of Service. It's meant to flag traffic that should receive special attention. VOIP, for instance, should be low latency and put at the front of the queue. The problem with that is that anyone could mark their traffic just to be treated nicely, even if were a bulk download that had no special requirements. So across the internet almost nobody respects this flag and therefore it's irrelevant.
Within a network that you control you could implement this in your routers, and perhaps switches, to give priority to traffic that needs it.
QoS is quality of service. Think of it as an SLA between bandwidth and a certain application or port. For instance you have a VoIP phone on your desk that has a network jack built-in that you plug your computer into. Normally that data connection is just for that, data, but in this case your bandwidth is shared between data and voice data. Applying QoS on that port tells the port "OK, I will guarantee the voice data 40% of this bandwidth at all times no matter how much data is coming through". What does this mean for you? If you're downloading a 2 GB file and a call comes through the QoS guarantees that your call won't sound like its broken up and coming from a mysterious doctor in Myst. Yes, your download rates might take a hit for a bit but your voice data is what you're trying to preserve and make sure comes through. QoS is also usually applied to Video Conferencing lines so that the video doesn't stutter because its not getting the sufficient bandwidth needed to keep everything in sync.
In my home business network, I use my Linksys router to enable priority based QoS. This is protocol and port based rules. My configuration:
You can also define rate control based QoS. This is normally source or destination IP based rules. Sometimes you can also limit it to a particular protocol/port on that IP. This configuration is useful if you have a particular machine or service on a machine that should take priority over other machines or services in your network.
QoS is Quality of Service and is used to give priority to some packets over others. For example, if you use Voice over IP, you may want to configure your network to give priority to those packets to ensure they are routed with a higher priority than other traffic. You could also use it to de-prioritize file sharing traffic, assuming it isn't blocked entirely.