This is from the 'Qos' - 'Help' page on Smothwall....
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QoS
SmoothWall is able to decide if some of the network traffic is more urgent than others. Imagine your network connection is like a multilane freeway or motorway. The faster the connection, the more lanes. However, a motorway is not very fast if every lane is blocked by a large lorry!
Enabling QoS is like enforcing traffic regulations - such as Heavy Goods Vehicles(HGVs) are only permitted in the inside lanes. Smoothwall QoS defines four such 'lanes':
* slow - for traffic that you wish to force to go slow even if the motorway (Internet connection) is otherwise empty.
* low - for traffic that can use up to 40% of the available lanes but if there is other traffic on the road this is limited to 15%.
* normal - can use 90% of the capacity of the road if the road is otherwise empty and at least 40% in busier conditions.
* high - also can use 90% of an otherwise empty road and is guaranteed 20% if the road is busy, BUT has first call on any spare capacity, then normal then low.
You will notice that the promised bandwidth to each lane does not exceed 100% in total. If all classes of traffic want to use the network all the time they will each only get their allowed bandwidth. However, much traffic is 'bursty' such as loading web pages and sending emails so, in practice, there is often spare bandwidth to share about.
In order for QoS to work we need to know what actual bandwidth corresponds to the 100% we have to share out. This is done by choosing an appropriate speed for your connection. If you can, try to test what speed your connection actually is rather than believing promises of the ISP. Note that for ADSL connection speed can vary, so try to do speed tests at the busiest time of day, otherwise you may find that QoS will stop working if the line gets busier.
It is very important that the SmoothWall is the slowest part of the network (only by a few percent will do) - you may need to adjust the headroom parameter so that you have the minimum headroom where QoS is actually working. How to tell if it's working? Try doing a low priority task such as p2p file sharing at the same time as a normal or high priority task. The low priority task should not impact on your other task in the same way it does without QoS.
You can choose to assign different sorts of traffic to these different classes. The defaults are sensible, for example Peer to Peer traffic to the low class but ssh high so that accessing a remote system can be done with minimal echo delay.
The Voice over IP (VOIP) rule is special in that any traffic with the diffserv 'EF' option set will also be caught by this rule. If you assign high priority to VOIP - the default, be aware that you will only have 20% of the bandwidth guaranteed. If good VOIP performance is paramount to you then it is best to change it to use 'normal' but make everything else either 'low' or 'slow'.
If you do not want any of the rules to be active then simply change the class to 'none' for that rule. Such traffic will go into the class defined for 'Traffic that does not match below'.
QoS as a whole can be turned off with the 'Enable traffic shaping' checkbox. Traffic shaping will always cost a small amount of bandwidth so if you are only doing one thing with your connection, e.g. a large file transfer, then you can turn traffic shaping off to get maximum speed for the single task.
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