Charlie Boisseau (@charlieboisseau), Commsworld / Fluency (ISP in the UK).

What makes a company an ISP is their presence on the Internet.

**The telephone exchange **

The Glasgow central telephone exchange

Many UK exchanges are in old buildings due to origins as providing telephone services.

Edinburgh exchange

All the way to “shed” exchanges, which may have a radio based link to the network.

Telehouse exchange in London, where many ISPs connect to the wider Internet.

A typical ISP network, a combination of owned & leased network links, with transit connections to other networks, including to global scale tier network providers (e.g. Level3, NTT).

LINX in London is one of the main providers in the UK that interconnects networks, reducing the physical complexity and cost of connecting (peering) with other networks. An ISP would just need to have a connection to that exchange to allow it to peer with other networks.

Manchester is the second most important as it also has a physical fibre connection across the Atlantic.

Scotland has one in Edinburgh (IX Scotland). What can make interconnect exchanges successful is media providers deciding to use the exchange to store a copy of their content (e.g Netflix). Storing locally / caching reduces bandwidth usage across the Internet, and also adds resiliency in the event of network failures.

Juniper Networks is a popular provider of hardware to provide carrier network connections.

How do networks connect to each other?

Each ISP is allocated a unique numerical reference, and a system called BGP is used to allow physical devices (routers) to share route information by announcing what IP addresses it is responsible for. Examples of how this works: is a site that lets you see the peering that is occurring in near real time.