What is an ASN? Understanding the backbone of the Internet

Using the internet often feels effortless when clicking a link or joining a call, but behind that simplicity lies a highly structured system that ensures data moves efficiently across the globe. One of the key building blocks of this system is the Autonomous System Number (ASN).

What is an ASN?

An ASN is a unique identifier assigned to a network, or group of networks, that operate under a single routing policy. Think of it as a digital passport that allows networks to identify themselves and exchange routing information with others across the internet.

To put it simply: if an IP address is like a street address, an ASN is more like a postal code, it tells the broader internet where traffic should go at a higher level.

ASNs are essential for the functioning of the Border Gateway Protocol (BGP), the routing protocol that connects different networks together. Using ASNs, BGP determines the best path for data to travel from one network to another, ensuring efficient and reliable communication.

What is an ASN network?

To understand ASNs, you first need to understand Autonomous Systems (AS). The internet is often described as a “network of networks” and these individual networks are Autonomous Systems.

An Autonomous System is a collection of IP prefixes (ranges of IP addresses) that are managed by a single organisation such as an Internet Service Provider (ISP), university, government agency or large enterprise. Each AS follows a unified routing policy, meaning it controls how traffic flows within and outside its network.

Every device connected to the internet is, in some way, connected to one of these systems.

An ASN is what identifies that system globally. It is assigned by organisations like the Internet Assigned Numbers Authority (IANA), ensuring that every AS has a unique number.

What is an ASN made up of?

An ASN network is more than just a number, it represents a sophisticated infrastructure. Key components include:

• IP address ranges (prefixes): These define the addresses the network controls and advertises.

• Routing policies: Rules that determine how traffic enters, exits and moves within the network.

• BGP connectivity: The mechanism through which networks exchange routing information with others.

• Physical infrastructure: Data centres, fibre optic cables, routers and switches that carry data globally.

Some networks operate with a single ASN because they have a straightforward routing policy. Others, particularly large, global networks, may use multiple ASNs to manage complex routing strategies across regions or services.

Why ASNs matter

ASNs are fundamental to how the internet operates. Without them, networks wouldn’t be able to identify each other or exchange routing information effectively. They enable:

• Efficient routing: Data takes the best possible path across networks.

• Scalability: The internet can grow while maintaining structure.

• Policy control: Organisations can define how their traffic flows.

• Resilience: Traffic can be rerouted in case of outages or congestion.

In short, ASNs are what make global connectivity possible.

Why AS3491 matters

AS3491, operated by PCCW Global, is a Tier 1, transit-free IP network ranked among the top 10 globally, making it a critical part of the internet’s backbone. As a Tier 1 network, it can reach every other network worldwide without paying for transit. Instead, it uses settlement-free peering with other major providers which helps with cost efficiency, performance and control.

Built for scale and reliability, AS3491 carries vast volumes of data across continents, enabling fast, low-latency connectivity. Its strength include:

• Unmatched global reach: Spanning over 738,000 km of optical fibre across Asia, Europe, the Middle East, Africa and the Americas.

• Massive infrastructure: 140+ Points of Presence, 60+ subsea cables and multi-terabit global capacity.

• Private peering at scale: Over 30,000 Gbps of private peering for efficient, direct traffic exchange.

• Guaranteed throughput: No congestion or contention, eliminating bottlenecks and ensuring consistent performance.

• Reliable performance: 99.9% service availability for predictable, high-quality connectivity.

• Greater control: Advanced traffic management for precise routing, shaping and optimisation.

PCCW Global and what it provides

Through AS3491, PCCW Global delivers high-performance connectivity solutions to businesses worldwide. Its infrastructure supports everything from enterprise networking to cloud connectivity.

Importantly, AS3491 also powers the Console Connect platform, enabling on-demand, private connections between clouds, data centres and devices. This makes it a key enabler of modern digital infrastructure, where speed, security and flexibility are essential.

Additionally, it plays a key role in supporting cloud-based AI tools, where our high-performance backbone is essential to deliver the usability, speed and responsiveness users expect.

Ultimately, when it comes to global connectivity, networks like AS3491 play a pivotal role. As part of a top-tier, globally ranked infrastructure, it ensures that data moves quickly, reliably and efficiently. Get in touch to learn more.