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Internet Service Providers (ISPs)

Internet_Connectivity_Distribution_053020A
(Internet Connectivity Distribution - Wikipedia)
 

 
 
An Internet Service Provider (ISP) is a company such as AT&T, Verizon, Comcast, or BrightHouse that provides Internet access to companies, families, and even mobile users. ISPs use fiber-optics, satellite, copper wire, and other forms to provide Internet access to its customers. One ISP does not have access links to every Internet user in the world so there are thousands of ISPs: approximately 12,700 worldwide; 7,000 in the U.S. (about 100 or so larger-sized ones and lots of tiny regional ones). Most smaller ISPs that serve end users purchase Internet connectivity from other ISPs. 

ISPs provide the same service, except that they use different types of media to do so. ISPs bridge distant locations between cities, states, and countries. Because of these high speed backbone systems, we are able receive an email within seconds, stream our favorite movie without interruption, and play online games with no lag whatsoever.

ISPs connect to one another by forming backbones, which is another way of saying a main highway of communications. Backbones usually consist of satellite, copper wire, or even fiber-optic media. Media is a term that means cables or lines, and it's the physical means of connecting your home to the Internet.

ISP network are categorized by tiers. There isn’t a formal definition of what constitutes a tier but there are generally accepted conventions. 

 

- Tier 1 ISPs

At the very top of the hierarchy, Tier 1 ISPs own the infrastructure that forms the backbone of the Internet. Each Tier 1 ISP has a peering agreement with every other Tier 1 ISP. This means that they agree to forward and receive traffic from each other without charging the other ISP for it. Tier 1 ISPs have access to the Internet routing table, also known as the global routing table. What this means that they know the top-level ISP to which any IP address should be sent. They also know which of their lower-tier ISPs receive any given IP address. As such, there is no concept of a “default route” at this level. With lower-tier ISPs, a router can give up if it does not know where a certain packet should go and just send it to a higher-level ISP. Tier 1 ISPs do not pay for data transit. Examples of Tier 1 ISPs include AT&T, Verizon, CenturyLink, Level 3, Telefónica, and NTT.


- Tier 2 ISPs

Tier 2 ISPs purchase data transit from Tier 1 ISPs and other Tier 2 ISPs but may also peer with other networks for direct connectivity and cost saving. They may then resell Internet access. Examples of Tier 2 ISPs include Comcast, British Telecom, Vodafone, and Sprint Communications. 

 

- Tier 3 ISPs

Tier 3 ISPs occupy the lowest level and solely purchase Internet transit from one or more Tier 1 and Tier 2 IPSs. A Tier 3 ISP will typically provide coverage in a limited region of a country. Examples of these are Powernet Global, and Excel.Net. They concentrate on the retail and consumer markets. 

A packet will often pass through several networks en route to its destination, both within and between ISPs. Each link terminates at a router which makes a decision on where the packet should be delivered. Each transmission of a packet is called a hop. 

Within ISPs, edge routers are placed at the edge of an ISP’s network and communicate with other networks. For larger organizations, an edge router may sit at the edge of a customer’s network and connect to one or more ISPs. A core router is a router that connects routes on the Internet backbone. A core router may also be used in dispersed organizations to interconnect routers from multiple locations.

 

 

 

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