The Internet is, as its name suggests, a complex “network of networks”. And sending an email or accessing a webpage requires data to travel through multiple networks, owned and operated by different Internet Service Providers (ISPs). Decision makers striving to improve the availability and affordability of high-speed, or broadband, Internet services must understand how data travels through the millions of miles of pipes, cables, wires, and other equipment belonging to various ISPs between users across the country and around the world.
Three main components of broadband networks connect to each other to carry data from one point to another on the Internet:
- The spine consists of large fiber optic pipes, often buried deep underground, which are the main data routes on the Internet and the main path for Internet traffic between countries.
- The average mile is the part of a network that connects the backbone to the last mile and is also called “backhaul”. These are usually fiber optic lines, but can be wireless, and in some cases can provide Internet service directly to large customers, such as schools or health care centers. health.
- The last mile is the segment that connects a local ISP to a customer, for example via a cable line to the home. The type of technology used to provide last mile service is the primary determinant of the speed and quality of service delivered to consumers.
ISPs, which can be municipal utilities, electric and telephone cooperatives, or private companies such as cable or telephone companies, fall into three tiers based on how they transport and exchange data between networks . These classifications are defined by the provider’s geographic reach and whether it pays for “transit” on other providers’ networks.
- Tier 1: Large providers who own, operate and maintain the infrastructure, including the Internet backbone. These ISPs, including AT&T, Deutsche Telekom, Lumen (CenturyLink), Verizon, and Zayo, have global reach. Since they all carry roughly the same amount of data over their networks, the costs they each incur (and any fees they might charge each other) for exchanging data over the networks are in fact the same. As a result, they exchange traffic at no cost under mutually beneficial arrangements.
- Tier 2: Providers, typically large cable companies and multi-state telecommunications companies such as Comcast, Cox, Frontier, and TDS, who exchange data for free with other providers in parts of their network but purchase transit services, which allows them to move user data. over another provider’s network to reach other parts of the Internet.
- Tier 3: Typically last mile service providers or those that only offer direct connections to customers who need to purchase wider Internet access, either through direct contracts with Tier 1 providers or by purchasing services from a Tier 2 provider that include connections to Tier 1 networks.
Contracts, known as interconnection or peering agreements, govern the exchange of data between the networks of different ISPs, allowing data to travel freely around the world. Exchanges occur at Internet Exchange Points (IXPs), which are usually large buildings where multiple carriers house equipment to link their networks and transfer data. Network switches within IXPs operate much like railroad switches, directing data from one ISP to another to ensure it travels along the most direct route and to the correct destination.
Much of the online content we access on our computers and phones is generated by “edge providers”, usually large retail, social media, technology or video streaming companies, but also sometimes individuals who offer content such as websites, web applications or web hosting. services.
The transmission of this data is facilitated by Content Delivery Networks (CDNs), server systems around the world that are typically owned by large technology companies such as Amazon CloudFront and Akamai and improve the efficiency of transmission of data on the Internet. CDNs work like data warehouses, storing copies of web content in various places to shorten the time between when a user clicks on a link and when a web page loads. CDNs connect to networks operated by ISPs and speed up data transmission by “shipping” content from a nearby facility, rather than requiring it to travel from the peripheral provider’s headquarters, to the end user .
Internet speeds enjoyed by customers are determined by the slowest link in that system (usually the last mile) and depend on two related network metrics:
- Bandwidth is the amount of data a network can transmit, measured in megabits per second (Mbps). More bandwidth allows for a faster connection.
- Throughput is the amount of data that can pass through a communication system.
The relationship between them is like a road. Bandwidth is the number of lanes and throughput is the amount of traffic. The wider the road, the more traffic it can carry at full speed before becoming congested and slowing down. The backbone is most like an interstate highway, providing high bandwidth, while the middle mile could be a major urban artery and the last mile would be more like a residential street.
However, congestion can occur at any part of the network. For example, a last mile provider may have sufficient bandwidth to serve local customers, but traffic may be slowed by congestion at the point of connection to the middle mile portion of the network.