Actual data throughput and WiFi coverage will vary from network conditions and environmental factors, including the volume of network traffic, building material and construction, and network overhead, result in lower actual data throughput and wireless coverage. This item allows you to tweak the target SNR Margin. You could set to negative value to maximize the downstream performance. But please note that the lower the value, DSL modem router will be weaker to defend the line noise. Sync loss might occur. So please adjust with proper value. However, if your xDSL connection is unstable or not able to establish a connection, setting to a postive value. The Merlin build for the RT-AC88U might work but presumably you would lose the DSL functionality and so running it as a router only in which case you'll need a separate modem. Originally I was using a Fritzbox 7530 and was very happy with it but when I switched my line switched to g.fast it wouldn't work without an attached Huawei modem (MT992) which is where all the problems I'm having are. Or jump right in and shout if/ when you need to know a specific setting. The AC68U and AC88U firmwares are quite different but the settings to connect should be the same.