@falccros if the 2.4 Ghz network disappears and reappears, it sounds like the wifi transmitter in the modem is failing. For the wifi speed issue, have a look at the following settings and change your wifi settings as required to match:
UPNP: If you're not a gamer or don't require UPNP for VOIP phone purposes, disable it. If you are a gamer, you can manually set the ports required for port forwarding. This is found in BASIC .... GATEWAY FUNCTION ..... UPNP .... Disabled.
2.4 Ghz wifi parameters:
Wireless Mode: 802.11 n Channel Bandwidth: 20/40 Mhz. In a crowded wifi environment, I would set this for 20 Mhz. It will default to 20 Mhz in a crowded environment. Wireless channel: Channel 1, 6, or 11. I'd set this to the channel that offers the least interference from neighbouring routers and modems as seen with inSSider. WPS Enabled: OFF (WPS is not secure and hasn't been since it was first released) Security Mode: WPA-Personal Auth Mode: WPA2-PSK Encrypt Mode: AES only (Do not use any form or TKIP/AES combo as TKIP is no longer secure)
Check/set the following 5 Ghz wifi parameters:
Wireless Mode: 802.11 a/n/ac mixed Channel Bandwidth: 80 Mhz Wireless channel: 149 to 165 Use this higher channel range as it runs higher transmit power levels. WPS Enabled: OFF Security Mode: WPA-Personal Auth Mode: WPA2-PSK Encrypt Mode: AES only
If you had to change any parameters, reboot your router after the changes have been saved.
Do you happen to have ethernet devices that are gigabit capable that you can use to confirm the modem's data rate capability. This should always be tested with a gigabit ethernet device.
In terms of wifi performance of any device, there are two main components to consider, the number of antenna on the device, and, the design and construction of the device beyond the wifi adapter, which in the end will determine the end data rate capability of the device.
That chart shows the raw data rates that you can expect between a wifi transmitter and receiver. The actual data rate can be calculated as indicated below. The orange component is the original 802.11n design, the blue is the 802.11ac component added years later. There is a newer edition with the 802.11ax capability, but, we'll keep this simple for now. On that chart the spatial streams basically equate to the number of antenna on a given device. Typically a run of the mill laptop these days will have one, probably two antenna on it. Same for a cell phone. Mac Pro's have three from what I understand, and there is one, maybe two gaming laptops on the market with four antenna. So, if you look at that chart and follow it down, you can see the max data rates offered at the bottom line for each section, 1, 2, 3, 4 spatial streams. Going right, you can see columns marked with 800 nano-seconds and 400 nano-seconds, which is the guard interval (no transmit period) between successive wifi broadcasts. When you're attempting to evaluate any wifi performance of a device, you need to keep in mind, how many antenna does it have, does it support 800 and 400 ns intervals and does it support 802.11n, or 802.11ac?
The range of speeds available in each spatial stream section, 1, 2, 3, streams etc is dynamic in practice and also depends on the construction of the wifi adapter itself. As you move around the home with a mobile device, the received signal level and signal to noise ratio changes at both ends of the transmit/receive path, and as a result the data encoding that is used varies, literally moving up and down that range that is seen in each stream section. If you have a windows laptop, right click on the wifi icon in the taskbar on the right and select "Open Network and Internet Settings". Then scroll down the popup page and select "View your network properties". On that page is a Link speed. On a fixed ethernet device that should indicate 1000/1000 Mp/s for a gigabit adapter. On a wifi device that link speed will show the raw data rate, as indicated in the MCS chart. As you move around the home, that link speed will change and is dependent on the received signal level, signal to noise ratio and limitations built into the wifi adapters hardware and firmware. The actual max data rate can be calculated by taking that raw data rate shown in the MCS table and Wifi Link speed and multiplying it by the Modulation and Coding rate in the chart. For example, index line 15. Take 130 Mb/s or any number to the right and multiply that number by 5/6, as in 5 of 6 bits are actual data bits, with one bit used for error correction. So, as the received signal level and signal to noise ratio changes, the number of data bits and error bits changes dynamically, moving up and down the chart. Normally, you can take the number that you see in the Link speed and match that up with a raw data rate indicated in the chart. From there you can determine what the guard interval is, and what the current split happens to be between data bits and error bits. The additional wild card in all of this is the presence of other networks on your channel which include those that are recognized as active networks, which cause channel sharing, and those that that are recognized as noise as their far enough away not be recognized as an active network, but, their transmissions end up being received as background noise. The end result is a reduced data rate either due to channel sharing or background noise.
One problem in all of this theory is that the wifi adapter and device manufactures typically don't release the performance data for the wifi adapters. They will show a maximum data rate but won't list whether or not the adapter can use both short (400 ns) and long (800ns) guard intervals, and, they won't specify if the adapter has one or two or more antenna connected and if the adapter can make use of the full range of transmit speeds listed in each section of 1, 2, 3, etc, spatial streams. Very rarely will a manufacturer show that data in some location that is easy to find. End result, you don't know what you're getting until you actually have the device at home and your experiments result in either a pleasant or unpleasant surprise. Anyone looking to maximize the wifi data rates on their home network has to do a considerable amount of homework to find out how many antenna are on a device and what data rates the adapter will actually support. One point to note, an adapter with multiple antenna has better performance than an adapter with a single antenna. Essentially that's due to the math behind reception of the same signal by multiple receivers. For that reason, the modem, with three 2.4 Ghz antenna and four 5 Ghz antenna is pretty sensitive compared to a normal laptop, so, it might be detecting an already occupied channel while your laptop shows nothing. An occupied channel will cause the modem to wait until its clear to transmit, slowing your data rate. Also note, the adapters don't necessarily support the full range of speeds listed in the chart. Some have cut off points at some point down the chart, which is not specified anywhere by the adapter or device manufacturer.
Ok, so, thats a little background info on wifi data rates. Unfortunately its not cut and dried as they say. Its a mix of adapter hardware and firmware limitations and dynamic inputs in the form of signal level and signal to noise ratios. Given the devices that anyone has, the best that one can do is optimize the modem/router wifi settings and use the best channel available. For a 2.4 Ghz network, thats usually pretty tough and there's usually no good choice. For a 5 Ghz network, use a channel in the 149 to 161 range with an 80 Mhz wide channel. Unfortunately the modem doesn't offer good control of the base channel when you set an 80 Mhz wide channel. So all you can select is the 149-153-157-161 selection. If you knew what any other network in that region was using as a base channel, you should be able to select a different base channel in order to maximize the performance of your network. With a router you can do that.
Last but not least, there is the modem performance. That will depend on the cable signal levels. If your interested and have time, log into the modem and navigate to the STATUS .... DOCSIS WAN tab. Select of highlight the signal table, from the Downstream Overview line, all the way to the bottom right hand corner of the OFDM/OFDMA section. Select that entire area, right click .... Copy. Then start a new post and paste that into a post, right click .... Paste. That should paste in the entire table and it should look like the table in the modem's user interface. Its worth having a look at this just to see if there are any cable issues that might cause slow data rates.