The Internet is a huge, global network of interconnected machines. Every Internet-enabled computer is somehow connected - your home laptop that you use to send emails and watch videos of cats on YouTube, is connected to someone at home in Australia - probably doing the exact same thing. Infact, you can instantly email your friend in Australia, with your favourite video of a cat on YouTube. But how? What makes up the Internet and how does information travel from A to B, all the way round the world?

First, before we get started, let’s quickly clarify the classification of network providers. There are three types:

• Tier 1 Network Providers: Do not buy transit / purchase Internet connectivity. Rather, they peer with other Tier 1 Network Providers and sell transit to lower level ISPs.
• Tier 2 Network Providers: Peer with other networks, but still purchase transit to reach parts of the Internet.

• Tier 3 Network Providers: Only purchase transit to reach the Internet, they do not peer with other networks.

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**The journey of your email:**

From one laptop to another, via everything in between

• On your laptop, you compose an email and press ‘Send’.

• This data is wirelessly transmitted from your laptop via radio signal to your home router, which decodes this signal. This is your home Local Area Network (LAN).

• The data packets i.e. your email, then leave your home and connect to the Internet via an ISP (Internet service provider), for example Virgin Media or BT. The ISP will either own a Tier 2 or Tier 3 network. Nowadays, the regional ISP's network will quite often consist of fibre-optic cables.

• The data then travels through the ISP's network to a core router in an Internet Exchange point (such as LINX’s London Telehouse East), where regional ISPs can peer i.e. interconnect and freely share, swap and exchange traffic. This is also the point where ISPs connect to an upstream provider’s network, after buying transit i.e. paying for Internet access, from an upstream provider. Internet Exchange Points (IXPs) are mostly carrier-neutral facilities, but can act as a Tier 1 provider’s PoP (Point of Presence).

• In this case, the ISP has bought transit from a Tier 1 network provider, such as NTT, and the data packets travel from the ISP’s network to the Tier 1 provider’s network. There are a small number of Tier 1 network providers, and their networks span globally, largely making up the backbone of the Internet. Tier 1 network providers often own or partly own international communication fiber-optic cables, but they do buy or rent capacity from global telecommunication companies, such as Apollo Submarine Cable System Ltd. This interactive map shows all submarine cables across the world, listing each cables owner(s) and landing points.

• The data packets - your email - will find the best possible, available path to Australia, passing through a number of intermediate nodes e.g. routers and switches. Path selection is determined by the Border Gateway Protocol - the principal routing protocol on the Internet. Your email may pass through nodes in New York City, Seattle, San Jose and Sydney, travelling under the Atlantic Ocean, across the US and under the Pacific during its journey.

• The data packets arrive at an Internet Exchange Point in Sydney, where a reverse process takes place: it passes from a Tier 1 network to an ISP’s (either Tier 2 or Tier 3) network to your Australian friend’s home router, to his laptop via radio signal.

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And there you have it; your Aussie friend opens the email and watches the YouTube video of the cat and laughs - or groans in despair - in a matter of seconds.

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