There are only 3 ways to avoid this bandwidth consumption without reducing the quality of the video from the cameras. Each IP cameras at the highest quality setting will require between 3-4 mbps of bandwidth. So 13 cameras will consume between 40-50 mbps of bandwidth. If you only have a standard network, then it will only support a maximum of 100 mbps and typically you should assume that you will only achieve 50% of the advertised bandwidth. Basically you are maxing out your bandwidth with the 13 cameras. When you are accessing the cameras remotely, either inside or outside the network you are using even more bandwidth. For 13 cameras, we recommend you set up a separate dedicated network for the cameras. If this is not something you want to do, then you need to convert your network to a gigabit network which will provide you with 10 times the available bandwidth. This is fairly simple to do. Just replace any switches and routers with Gigabit devices. The last option is to switch to an edge server configuration where you have cameras in close proximity connected through the network to nearby NVRs which will limit the bandwidth travel over your network to short distances. When you connect remotely, be sure to connect only to the substream to reduce the bandwidth consumption as well. Still, my recommendation is for you to have a dedicated network for your cameras.

If you mean that you are having problems with a slow network when you are outside the network (WAN) then there are only two ways to handle this. Either increase the "up" bandwidth from your ISP or make sure you are only accessing the substream of your system when outside the network and configure the substream to use only the available amount of bandwidth. 

If the problem is inside your network then you will want to create a subnet to isolate your security camera system from the rest of the network. This is normally done using a managed switch. I recommend you call us to help you with this configuration.