Home networking for Dummies

I have a BT phone line. Into this is plugged a microfilter, allowing me to have both a telephone line and a broadband connection. The phone line plugs into a cordless phone base station. The broadband (DSL) line plugs into a router. The router transmits wirelessly so that our smart phones and laptops can connect. So far, so good.

Sadly, someone else has been connecting to the wireless, having broken the key used to secure it and is costing me money in excess bandwidth every month. So I have a new (to me, it's actually secondhand from a trusted source) router, which has several snazzier security features which should stop the bandwidth thief. It should be simple to swap them over: 1) note down the username and password for the broadband connection; 2) unplug the old router; 3) plug the new one in; 4) connect it by ethernet cable to my laptop; 5) type in the username and password; 6) tell my laptop and phone about the new wireless network and password; and 7) off we go.

Oh, no. Oh, no we don't, not by a long shot.

Steps 1 through 4 worked fine. Step 5, however, failed miserably. I tried three different approaches to the router configuration settings, and it resolutely denied there was an internet connection to configure. Huh? So I tried to ring my internet provider to ask what was going on. I dialled the number, the DTMF (tone dialling) played a merry tune and I waited. And waited. Rang off, tried again. Nothing apart from a gentle hiss. Ring the number from my mobile, connected straight away. By this time, however, I've realised it's not my broadband provider that's the problem - or at least, not the first problem I need to fix - it's the phone line. Or lack of one.

There's a model of networking which goes something like this - it's a while since I've had to use it in anger. I've been stepping through it layer by layer trying to identify the problem(s) I have:
Physical layer (cables, sockets)
Data Layer (zeros and ones transmitted over physical layer)
Network layer (slightly higher level addressing, eg MAC addresses?)
Transport layer (TCP/IP - the mechanisms of getting the bits to your computer in the right sequence)
Session layer (linking the bits together properly)
Presentation layer (layout and making things look nice)
Application layer (doing stuff - the layer the user actually interacts with most of the time).

(You can remember it with the mnemonic Please Do Not Throw Sausage Pizza Away.)

Each layer relies on the one before to work. I can't influence the S, P and A layers, and they rely on the T and N layers, which are the ones you usually worry about when setting up a network connection. These, in turn, rely on the D and P layers. It seems that it's my Physical layer that's the problem. All the components are plugged in, and the router will talk to my laptop all the way up to the Application layer. However, it won't talk to the microfilter, and somehow breaks the phone line's Physical connection too. If you think of the router as a barrier, all communications are fine INSIDE the barrier. The internet continues to work OUTSIDE the barrier, but messages aren't getting through the barrier like they should. To confirm this is the problem, I did the following:

Unplug router from microfilter. Pick up phone, get dial tone. So far, so good. Replace phone. Plug old router in to microfilter. Pick up phone, get dial tone. Okkayyy... Replace phone. Plug in new router to microfilter. Pick up phone. Get no dial tone.

Interesting. In the sense of the Chinese curse "May you live in interesting times."

Pull the sofa away from the wall. Remove the faceplate. Ooooh, that doesn't look like it should:



On the back of the faceplate, not connected to anything, is this:



I've put that lot back together, and asked around on Facebook for advice as well as briefly googled the router model. It's probably that my BT line has a rubbish signal-to-noise ratio and the router can't handle that. I'm going to try to get the router plugged into a friend's network at the weekend to confirm that the router is A-OK, then assuming it is, call BT and ask them what they can do to clean up my phone line.

And this, ladies and gentlemen, is why I hate doing anything with technology. It's not quite black magic, in as much as I understand the principles of how it should work. It is, however, not simple. And I like things to be simple, especially when they're built on logic, and should thus work as predicted.