Internet Service Provider (ISP)

November 21, 2023 - Around 3 mins mins to read

What Is an Internet Service Provider (ISP)?

An Internet Service Provider (ISP) is a commercial entity that offers internet access to end-users. ISPs can be classified as tier 1, 2, or 3 depending on the availability of physical resources that can be utilized without any cost, which is known as peering/transit value differential (PVD).

Tier one ISPs have abundant resources and typically do not have to pay for internet traffic as they are at the top of the hierarchy. Conversely, tier 2 ISPs must make settlements, usually through transit agreements with tier 1 carriers. Tier 3 ISPs act as last-mile providers, delivering internet services to commercial and home consumers without investing in infrastructure. They have transit agreements with tier 2 ISPs.

ISPs have been an integral part of the internet since its inception. They provide access, hosting, and information services. Some ISPs may specialize in one type of service, while others offer a combination of access, hosting, and information services based on the specific needs of individuals or businesses. These services include browsing the web, remote emailing using encryption software, and storing data files like images on websites.

What Is the Internal Hierarchy of ISPs

The internet is a vast network composed of multiple interconnected smaller networks. Each small network, known as an autonomous system (AS), operates as a standalone unit with its own routing policy. Autonomous systems consist of numerous interconnected devices and nodes, including routing and switching devices for internal communication and end nodes for data transmission. Each device is assigned an IP address to track the movement of data packets. Due to the large number of devices, IP addresses are divided into public and private IPs. Organizations can use private IPs to manage their internal LAN. Communication within an AS relies on interior gateway protocols (IGPs), while exterior gateway protocols (EGPs) are used for outbound communications that exit the autonomous system.

Initially, ISPs owned a single autonomous system. However, they now maintain multiple autonomous systems efficiently by establishing points of presence at various locations.

How Sending Data Through ISPs Work

To comprehend how ISPs facilitate end-users’ internet access, let’s consider an example. When users want to access CoinMarketCap, they enter the URL in their browser or use the app. The request travels from their devices to the local network routers, typically installed by a tier 3 ISP, which assigns source IPs. The routers have route tables and, based on destination IPs, either directly route the request to the server hosting CoinMarketCap or send the packet to DNS servers maintained by the ISP. The DNS servers retrieve the stored cache and return the IP address at which CoinMarketCap’s servers are hosted.

ISPs as Rule Enforcing Agents

ISPs are responsible for traffic shaping, route optimization, and other related tasks. They have a set of rules that must be followed when providing services to customers, including restrictions on accessing certain websites with unlawful content. ISPs enforce these policies through deep packet inspection, scanning every website visit against government databases. They play a crucial role in ensuring a secure internet.

Glossary

Internet Service Provider (ISP)

What Is an Internet Service Provider (ISP)?

What Is the Internal Hierarchy of ISPs

Initially, ISPs owned a single autonomous system. However, they now maintain multiple autonomous systems efficiently by establishing points of presence at various locations.