HOW YOUR NETWORK WORKS
Discover how your networked devices communicate with each other
How does data travel from one part of your network to another? The answer lies in the TCP/IP model. TCP (Transmission Control Protocol) is the method used by computers to connect over networks, while IP (Internet Protocol) is the way in which data is broken down into ‘packets’ of information and transferred. Each packet is labelled in such a way as to make it clear where it’s come from and what its destination is. When data is transferred, the TCP part of the process is responsible for ensuring that the data is checked for errors during transmission — if errors are found, the data is transferred again. This model can be broken down into four basic layers: Application, Transport, Internet and Link — see the explanation opposite for a basic breakdown of what happens on each of those layers. At the local network level, your devices are typically linked and managed through a single device — your router — in what’s termed a Local Area Network (LAN). Devices are uniquely identified on your network by their IP address, which consists of four separate digits, each of which can be a number from 0 to 255. The first two refer to the network address and are almost always 192.168. The last two refer to the host address. Of these, the first number (the subnet) is shared between all networked devices, while the final number (host) is what uniquely identifies that device on the network. For example, your Mac might be assigned 192.168.0.2 and your iPhone might be 192.168.0.3.
One IP address on your network — often 192.168.0.1 or 192.168.0.254 — is reserved for your router, and this address is known as the ‘gateway’, through which all other devices communicate. You’ll also see a reference to a subnet mask, which is usually 255.255.255.0, and can be safely ignored.
By default, IP addresses are handed out automatically by your router using a feature called DHCP (Dynamic Host Configuration Protocol), but you can set them manually for devices whose IP address needs to remain constant, though this is unusual in a home setting.
Data transferred over wires is generally considered secure, but data sent wirelessly can be intercepted, which is why wireless networks support various forms of encryption, the most secure of which, currently, is WPA-PSK2.
One way to secure your internet connection on an insecure wireless network is to use a Virtual Private Network (VPN), which effectively creates an encrypted ‘tunnel’ through which data is sent and received.
1. Application layer This layer is split into three main elements: at the top of this layer is the software you’re using to access the internet, such as a web browser. Next is the ‘presentation’ element, where data is translated into a format for sending — for example, if it’s to be encrypted or compressed. Finally, the ‘session’ element determines the type of connection made — HTTP or HTTPS for the web, and SMTP for email, say. 2. Transport layer (TCP) This manages how the data will be delivered by converting it into ‘packets’ for sending, then making sure they’re safely delivered and reassembled at the other end in the correct order. It also works in reverse for packets which have been received by your computer. 3. Internet (or Network) layer This is the layer that covers how the data will be addressed and then routed between devices. This means determining where the data is to be transmitted to on its route between your computer and its destination. It’s also where the actual delivery of data occurs, using IP packet switching, as described earlier. 4. Link layer The lowest layer, also known as the network access layer, is where error detection and correction take place as the data is packaged and transported. It’s also where you’ll find the physical hardware (typically Ethernet or Wi-Fi) that connects your device to your network and, ultimately, the internet.
Virtual Private Networks (VPNs) work by ‘tunnelling’ an encrypted connection through an unencrypted network, such as a public Wi-Fi spot.
If you want to apply a static IP address to your Mac, select your connection method in System Preferences > Network, click Advanced, choose ‘Using DHCP with manual address’ and assign one that isn’t already in use.