The London Internet eXchange (LINX), is the largest internet exchange in Europe. It carries about 90% of the UK's internet traffic. Almost any traceroute between UK ISPs, and many between the US and Europe, will show it passing through LINX.
It was set up in 1994 as a non-profit company, owned by its membership, which has since grown to over 120 ISPs and carriers. The organisation maintains facilities in several locations throughout London, expanding from its core sites at Telehouse and Telecity to include a number of expansion sites. All of these facilities are linked by a private fibre loop running gigabit ethernet. The LINX members are then connected to the switches in each facility. Virtually all UK ISPs use LINX to peer with each other, but it is also popular with US and continental European carriers. This is mainly due to the UK's position as the main gateway between the north America and Europe, with a large number of transatlantic cables dropping off the British coast. Other non-ISPs with high network usage requirements, such as the BBC and Microsoft, are also members of LINX, as is JANET, the Joint Academic NETwork.
Primary sites (all located in London's Docklands)
Most LINX members connect to the network with regular 100BaseTX ethernet, but some use gigabit ethernet. Total traffic between LINX and the wider internet is around 13.5 gigabits/second in each direction. The LINX traffics stats page (http://www.linx.net/tools/stats/) is an interesting place to follow the changes in internet traffic in near real time. If major events occur, you can see the spikes and troughs in the 12 hour graphs on that page. It's also a good place to check if a network problem is local or affecting the UK internet as a whole.
LINX is know for its early-adoption of new technologies that will help its network. It was trialling pre-standard gigabit ethernet long before it was commercially available, and has now installed pre-release hardware to enable 10 gigabit ethernet. It also supports IPv6 on its network.
The cost of membership is £10000 joining, plus £8500 per year. That gets you one 10/100 ethernet port. That is put into persective, however, when you learn that they have budgeted £2 million for hardware in 2002.