What Is an Internet Service Provider (ISP)?
An Internet Service Provider (ISP) is a commercial entity that offers end-users access to the Internet.
ISPs provide the necessary infrastructure, equipment, and services to enable individuals and organizations to connect to the internet and access online resources.
Categorizing ISPs Based on Network Infrastructure
ISPs can be classified into different tiers based on their network infrastructure and relationships with other ISPs.
The tier system helps categorize ISPs based on their position in the hierarchy of internet connectivity:
- Tier 1 ISPs: These top-level ISPs have extensive global networks and direct connectivity with other tier 1 ISPs. They do not have to pay for internet traffic because they operate at the highest level of the hierarchy.
- Tier 2 ISPs: These ISPs are connected to tier 1 ISPs and may pay for internet traffic through transit agreements. They provide connectivity to tier 3 ISPs and smaller networks.
- Tier 3 ISPs: These ISPs are often referred to as last-mile providers. They serve residential and commercial customers by connecting them to the internet through transit agreements with tier 2 ISPs. Tier 3 ISPs typically do not invest in extensive infrastructure and rely on larger ISPs for internet connectivity.
ISPs have played a fundamental role in the internet since its inception.
They offer services such as internet access, web hosting, and information services.
Some ISPs specialize in specific services, while others provide a range of services tailored to the needs of individual users or businesses.
These services may include web browsing, email hosting, data storage, and more.
What Is the Internal Hierarchy of ISPs?
The Internet is a vast network composed of numerous interconnected smaller networks.
Each small network operates as an autonomous system (AS) with its complete routing policy.
Autonomous systems consist of thousands of interconnected devices and nodes, including routing and switching devices for communication within the AS and end nodes that initiate data transmission.
Every device within an autonomous system is assigned an IP address, which allows for tracking and routing of data packets.
IP addresses are divided into public and private IPs to manage the sheer number of devices.
Organizations can use private IPs to manage their internal Local Area Networks (LANs).
Autonomous Systems
Devices within an AS communicate with each other using interior gateway protocols (IGPs) for internal communication, while exterior gateway protocols (EGPs) are used for outbound communication that exits the autonomous system.
Initially, each ISP owned a single autonomous system.
However, as the internet grew, ISPs maintained multiple autonomous systems to manage their network infrastructure efficiently.
This involved establishing points of presence (POPs) at various locations to enhance connectivity and redundancy.
ISPs as Rule-Enforcing Agents
ISPs play a role in enforcing specific rules and policies related to internet traffic.
They engage in activities such as traffic shaping and route optimization.
ISPs have policies in place to regulate customers’ use of their services, which can include restrictions on accessing certain websites with unlawful content.
ISPs enforce these policies through techniques like deep packet inspection (DPI), where they inspect the contents of network packets to determine if they comply with the defined rules.
This can involve scanning website visits against government databases or implementing other filtering mechanisms.
ISPs act as crucial intermediaries that help maintain a secure and reliable internet infrastructure.