What is Internet Service Provider (ISP)?

An internet service provider (ISP) is a commercial entity that provides internet services to the end-users. There are three tiers of ISP services that depend on the physical resources available to them to be utilized for free as peering/transit value differential (PVD).

The internet essentially functions as a global network that consists of smaller, interconnected networks. Each smaller network is known as an autonomous system (AS) and has its own full routing policy. Autonomous systems consist of thousands of nodes and devices that are interconnected.

The networks of devices may play several roles in maintaining an autonomous system. Some act as routing and switch devices that enable easier communication within the AS. End nodes are responsible for data transmission. Each network device comes with an IP address that helps track the transmissions of data packets.

IPs can be either public or private. Private IPs are used by companies to manage the internal LAN services. The devices interact with each other via the routing protocols in place.

Autonomous systems use routing protocols known as interior gateway protocols (IGPs) for internal communications. All outbound communications exiting the AS use the exterior gateway protocols (EGPs). While ISPs used to be able to own a single autonomous system, they now must maintain a network of AS in several locations for efficiency.

Tier 1 ISPs are usually not required to pay for the internet traffic given their position at the top of the hierarchy. Tier 2 ISPs are required to pay the settlement and often have transit agreements with tier 1 carriers.

Tier 3 ISPs have transit agreements with tier 2 and are considered to be the last-mile providers. They do not invest in the infrastructure and provide their services for commercial and home consumers’ use.

ISPs have been an intrinsic part of commercial internet history. They act as access, hosting, and information services providers. Some ISPs may offer limited services, while others may provide all three, depending on the requirements of the entity. Some of the most frequent uses enabled by ISPs are:

• Web browsing for professional purposes
• Private mail servers for client communication
• Email encryption software
• Data storage on Cloud Services

ISP users that wish to access any website must first enter the URL in the browser. The input request is transferred from their devices to the local network routers which are typically installed via tier 3 ISPs. The routers contain the source IPs and route tables. They read the destination IPs and route the URL request to the server hosting the website.

If the router does not contain the routing table of stored IPs, they are forwarded to DNS servers maintained by the ISPs to locate the stored website cache and transfer it back along with the website IP address.

Some of the roles of ISPs are traffic shaping and route optimization. Such responsibilities come with certain rules that must be followed when the services are being provided. They include restricting websites containing unlawful content. ISPs perform deep packet inspections to reinforce these policies. Every website visit is compared against governmental databases.