There are many types of ISP depending on the scale and scope some are small town operations others cover whole continents and partners with other giant to traverse the globe. However ISPs operate basically in the same manner regardless of the size in that they supply infrastructure for their customers to connect, supply an address pool, then deploy routers to collect and aggregate traffic before advertising those network addresses out to either another ISP, a transit ISP, or to an Internet Exchange.
The classes of ISP are:
- Access Provider – These ISPs supply local services to the community and will deal with domestic and small business customers. They will provide access equipment, perhaps DSL or Cable and provide IP addresses from their assigned IP block.
- Transit ISP – A transit ISP’s customers are typically large customers or more often smaller access ISPs. Transit ISPs aggregate and route traffic through diverse uplink channels to other transit ISPs via an Internet Exchange (IX) or sometimes even directly peering with larger ISPs. It is this meshing of peering relationships between ISPs over multiple levels that provides redundancy and high availability to the internet.
- Carrier (Tier-1) ISP – These are the largest global ISPs that own the global backbone links that traverse the globe. They will have direct connections to submarine and continental links. Tier-1 ISPs are responsible for delivering international trans-global traffic and high speed. Carrier charges across a tier-1 carrier network is very expensive, that is why most national ISPs will form an association to form an Internet Exchange.
- Internet Exchange – An Internet exchange is a non-profit exchange where members ISPs agree to fund the project in order to exchange their customer routes in order to avoid transit and tier-1 charges. An exchange is typically a site where each ISP places a BGP router that peers with other member routers. In this way, traffic flows from one ISP directly to the others, without traversing the Internets transit or tier-1 carriers.
- Of course, these are only the internet ISPs there are also local Wi-Fi service providers in every shopping mall and high footfall area that connect via backhaul to an access or transit ISP to provide internet access. Additionally, mobile operators now carry large amounts of mobile data, and they either off-load to local Wi-Fi service providers or run their own Wi-Fi networks in order to get the not very cheap data traffic off their very expensive bandwidth.