A process of elimination is the best approach to solving network issues.

When you get broadband, your internet service provider (ISP) normally supplies you with a broadband modem. This, plus your Mac, is the simplest network you can have, and for lots of people, it’s all the network they need. If you have DSL broadband -- the most common kind -- it’s delivered to your house through the phone line. At the phone socket, you plug in a filter that splits the frequency range so that the lower 4KHz is used by voice phone calls and the rest is sent to the modem.

All current iMacs come with built-in Wi-Fi capability as well as a wired Ethernet port.

The modem takes the analog electrical signal from the phone line and extracts the digital data stream encoded within it. This data takes the form of network “packets” that are wrapped up using an addressing protocol called TCP/IP. (This is a fairly meaningless acronym, so don’t bother trying to remember what it stands for.) Each TCP/IP packet contains a small piece of a website, or a graphic, or a downloaded file, or whatever is being sent from the internet. And every packet has a number, called an IP address, which identifies which computer or device it’s intended for.

Your broadband modem has an IP address assigned to it by your ISP and, if you have a modem that plugs into a USB port on your Mac, then this IP address is available exclusively for the use of that Mac. But if you want to connect more than one computer through the same broadband connection, you need a router -- if you’re not sure where yours is, that’s because many modern broadband modems have a router built in. If your modem has sockets for Ethernet cables, then it is actually a modem/router.

Router vs. Modem

The router is like a telephone exchange; it assigns separate IP addresses to all the computers connected to it and acts as a single point of contact for the wider network beyond it. When an incoming TCP/IP packet arrives from the internet, the router opens it and readdresses it using the local IP addresses of your home network. This process is called Network Address Translation, or NAT. As well as enabling your broadband connection to be shared among many computers, NAT provides a measure of security from hackers, as the IP address of your Mac is never exposed to the wider internet. Only the router uses the external IP address provided by your ISP.

It’s called a modem. But it’s actually a router, Wi-Fi access point, and firewall as well.

This anti-hacking function is called a firewall. By itself, NAT already does quite a good job, but almost all routers nowadays have much more sophisticated firewalls that actively block probing attacks and make it hard for a hacker to tell that you’re actually connected to the internet at all.

Going Wireless

A modem/router with a Mac connected via an Ethernet cable is the simplest configuration. But if your phone jack isn’t next to your Mac and you don’t want to start tacking Ethernet cable around the floor molding, the solution is wireless networking, also called Wi-Fi or AirPort. A Wi-Fi connection is provided using a wireless access point and, again, many broadband modems include this in the same device. Instead of converting the TCP/IP packet into an electrical signal to transmit it along an Ethernet cable, a wireless access point broadcasts it as a radio signal. This is received by the Wi-Fi antenna in your Mac.

There are several international standards for Wi-Fi devices. They are cryptically labelled as 802.11a, 802.11b, and so on, but they are usually just referred to by the last letter -- as “wireless n,” for example. The most widely used systems are b, g, and n. The later letters are faster, or more reliable, or both, but they are backward-compatible with earlier Wi-Fi standards. Generally, the slowest point in your network is your broadband connection, so unless you do a lot of transfers between devices on your network (to and from a networked disk, for example), it’s a nonissue.

If you want to print across your network, you can always connect the printer to one of your computers and share it from there (System Preferences > Sharing > Printer Sharing). But this only works when that computer is running. Some printers are network-aware and can be connected to your router directly. Otherwise, you can use a print server.

Your Printer is Served

This device connects to your router with a wired or wireless connection and lets you plug in one or more printers. It keeps its own queue of print jobs and makes sure they go to the right printer.

Apple’s own network devices are the AirPort Extreme Base Station, AirPort Express, and Time Capsule. An AirPort Extreme is a router with a wireless access point built in. This is the same as the Wi-Fi router/modem from your ISP, except that it doesn’t have the modem part. But you can still use an AirPort Extreme with a broadband modem -- the Extreme has a USB port that you can use to add an external hard disk or a printer (or both if you use a USB hub), which will then be accessible across the network.

More than just a wireless backup disk, Time Capsule is a Wi-Fi router and print server as well.

The AirPort Express is a cut-down version of the Extreme. It only supports 10 simultaneous wireless devices instead of 50, and only one wired connection instead of three. The USB port on the Express can only be used to network a printer, not a hard disk, but it does include a stereo speaker jack that you can use to connect speakers or an amplifier and stream your music wirelessly from your iTunes library on your Mac.

You can use an AirPort Express in “bridge mode” to extend the range of your Wi-Fi network to a distant part of the house or garden.

Time Capsule is an AirPort Extreme with a hard disk actually built in. You can use the disk for overflow storage or you can allocate it for use with Time Machine backups. You can also do this with a USB drive plugged into an AirPort Extreme, but it’s a setup that isn’t officially supported by Apple, and using Time Capsule is a little tidier.

Wireless Routers: Expand Your Network

LM009 Wireless 150Mbps 3G Pocket Router N
$96, lm-technologies.com
 
This router fits in the palm of your hand, which makes it ideal to take with you for creating impromptu networks in hotels. The USB port can be used to connect an external disk or a cellular broadband dongle, and there are also two wired Ethernet ports in case you need to connect non-Wi-Fi devices.

Belkin Share wireless router
$69.99, belkin.com

The dual-plane antennae in this router help to project the wireless signal through ceilings and floors, instead of just horizontally across a single floor. Self-healing technology continuously monitors your network and detects interference and other problems. These are either fixed automatically, or you’re notified via a message directly on your screen.

Linksys Ultra RangePlus WRT160N
$69.99 linksys.com

As well as a powerful antenna, this router uses Multiple In, Multiple Out (MIMO) technology to boost range. Normally, signal reflections from walls and metal surfaces reduce Wi-Fi range, but with MIMO, these reflections are carefully combined to actually boost the signal strength and reduce dead spots. The WRT160N also includes four wired Ethernet ports.

Wi-Fi Alternative: Powerline Networking

There are times when Wi-Fi networking isn’t a practical solution. Large, old houses often extend beyond the range of Wi-Fi networks; their thick walls are full of old cables and pipes, and the floorboards are studded with nails. All of this makes for very erratic Wi-Fi transmission. Unfortunately, this sort of building is also the kind most difficult to wire with ordinary Ethernet cable.

For small networks, where it’s just a question of getting a broadband connection to a single laptop, the simplest solution is often to use a 3G cellular modem in a USB dongle. You can plug this into the Mac directly, or you can plug it into the USB port on certain routers, such as the LM009 (lm-technologies.com).

But if you need more than that, powerline networking may be the answer. This uses the existing electrical wiring in your house to send a network signal that’s modulated on top of the main AC frequency. Powerline networking is much more robust than it used to be and offers speeds better than those of Wi-Fi networks. The disadvantage is that it is a little more expensive and it requires that all the devices on the network be on the same electrical supply phase. To get started, check out Netgear’s “Powerline in a Nutshell” video hosted at Newegg.com (bit.ly/i89ddX).