Recommended Tests

 Sounds as if your savvy about networking so setting up your network as below should be no issue for you, then we'll get the QOS implemented.  Can you show me the exact layout of your network right now?

                 

 Did you set this up yourself?    I ask because I really would like not to have you dismantle this thing to re route , and then have you stuck w/ a pile of wires and no access to the net. Once you start  this , you have to be able to re connect things , and configure them properly. I will say this is what I would do, and if you chose to delve into it or not, I'll respect it.


 
                        QOS on max port 1              Line 1 & 2        Fax (Or where the numbers are on the ports) Make sure before removing
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  Modem>  Router (DHCP on) >>  port 1 >>>  Voip router >>>> Voip router
                      l                                                  l                         l
   Switch or other router w/ DHCP off                 DHCP Off             DHCP Off
                      l
                      l
                      l
    All other network connections


  Does this look possible?

QOS ~ quality of service.     So that that port, or that plug in the back of the router that the device is plugged into will be configured for priority bandwidth when open.

 DHCP ~Dynamic Host Configuration Protocol (protocol for automating the configuration of tcpip)  So that when the network card asks for an address, the server gives it an address in the form of numbers, or octets  (ie: 127.0.0.1 local host ) so the packets or data knows where to go, kinda like a street sign, or your house address , so the postman knows where to deliver mail.

 The router by default turns on the DHCP server, before we do this, we will walk through the router gui ( graphical user interface)   which on the linksys you have they shoud belocated at 192.168.15.1 or 192.168.1.1 so understanding what is going to happen, allows things to happen. All configuration will be done in this manner.

 The modem will be located at 192.168.100.1 There's not much you should do here, especially since you have DSL, there is sometimes many settings that can turn your connection into mush. But you could still reset them to the defaults.

 Before doing anything, take tape of some kind to write on, or if by any chance you have those little number stickies that are used to wrap around the wires to identify what they are connected to. Masking tape works well when nothing else is available. Note down everything , and the placement of everything. Making sure you know what goes where by numbers or by names , whatever works for you. Look into the router configuration, and make a few notes as to the settings, just be meticulous, and if all fails, you can just return things to where they were originally. If in doubt , don't change settings.

  Just take some time to "map out" the wires, get familiar w/ the router interfaces at the links below, and take notes on what you find, only when you feel  100% confident to get into this you should continue.

The port QOS is set in the router itself , so it really doesn't matter, personally, I put the highest needed device on port 1.

OK good for you for reading up, no really many people just want to jump in then get freaked out  lol.

 You should be able to log into the 1st router as you say is the wireless, and look under the client list to see the live IP addresses, I can't give you a screenshot, I am running dd wrt on my wireless. Just get a bit more familiar by looking a bit deeper into the setup , and you'll find the addressees.

OK it doesn't really work in a way that the numbers are given out in consecutive order. Lets say comp #1 -4 are on. You shut down, that ip goes back to the pool, you startt up the machine again, the IP wil be pulled from the pool within the parameters set within the router range, this also applies to any router  you may have .

 The reason you can't ping certain IP's may very well be that you have them stemming from a router that does not allow to be pinged, and or the machine specific firewall settings .

That must be the first one in the network right? the router you can access?    If you have the second router connected off the first one, and any devices off the second, it will be turned off, otherwise you would have no connection to the device connected to the second router due to a possible IP conflict.

 You can do that , if necessary, by connectiong  directly to the router you wish to turn DHCP off and typing 192.168.1.1 or 192.168.15.1or 192.168.0.1 or so on.