Is that site really down?

Can't get a website, then another one fails, bringing up a message that your browser can't find the server? Yes it happens, and mostly you'll just think Google, or wherever the link came from, is out of date and you move on. It recently happened to me but the site was mine, hosted on a server in Virginia and I had not received an SMS to tell me the server was down (which is a service I pay for). When I went to the site of the service which tells me whether my server is working, it was also unavailable, and that was the clue to what was happening. Most other sites I tried came up with no problems. So I phone one of the firms whose sites I host and all was OK for them, at that time, but some hours later when my sites are working I get a call from that firm to say their sites are down. But I'm getting them OK. It takes me a while but I track it to one of the dozen or so companies which provide the Internet backbone worldwide. One company's connections were on and off for periods of up to an hour. ISPs buy their Internet connections from more than one supplier (or at least all the good ones do) but many who have two suppliers would not buy enough from each to carry their whole load if the other goes down. Some requests will be met from the ISPs own cache so if a site is static you might not know that the connection is down. If anyone can be said to own the Internet it is the Tier 1 suppliers. They are the firms who get paid for the cable traffic they are providing to smaller providers, though they do swap their interconnected services among themselves, known as peering. The Tier 1 providers are AOL, AT&T, Global Crossing, Level 3, Verizon, NTT (formerly Verio), Qwest, Savvis (formerly C&W, Cable & Wireless) and Sprint. In the sense of their importance related to this part of the world, i.e. Australia, Telstra and SingTel (which owns Optus) are well down the tree and buy their connections for much of the world from the Tier 1 companies. Most Tier 1 suppliers are owned in the US but NTT is part owned by the Japanese Government and Global Crossing is based in Bermuda. Cogent, used by many Australian ISPs, and a contender for Tier 1 status, uses Verio for many of its worldwide connections. Problems with the Internet backbone are not common, but they do happen.