I want to know what cable I should be using to connect my demarc to my DSL modem. When I plug in my DSL modem in the utility room (which is about 20' of wire from the demarc) I get a pathetic 4Mbps download rate (I'm told the telco's hardware is very old in my neighbourhood). When I test the modem by plugging it directly into the demarc, it jumps to 6Mbps. I want to connect my modem closer to the demarc (but I can't plug it into the demarc, because it's outside) and maybe use a different cable, but what kind of cable should I use? I heard in one place that CAT-5 is better than phone cable, but I've also heard there wouldn't be an improvement.
Use a twisted pair wire instead of the parallel satin-coat wire normally used to connect telephones to wall-jacks. You may have to make your own - this is easy if you have the tools and connectors.
I purchase a lot of 3-pair telco cable - the wire guys often refer to it as "Cat-3" wire. This is 3 twisted pairs inside a pvc jacket. However, one pair of Cat-5 should work well as well.
The reason I would use Cat-3 cable over Cat-5 is that the number of twists per foot for Cat-3 is similar to the number of twists per foot of the cable between your premises and the telco central office. Cat-5 has many more twists per foot than Cat-3.
Regardless, this is quick and easy for you to test.