What Is Network Latency?
Latency is the time it takes for a packet of data to travel from its source to its destination across a network. It's measured in milliseconds (ms), and even small amounts of it affect how snappy or sluggish a website feels.
Latency vs. bandwidth
Latency and bandwidth are often confused. Bandwidth is how much data can be transferred per second — think of it as the width of a pipe. Latency is the delay before any data starts flowing — the time it takes for the first drop of water to travel from one end of the pipe to the other.
You can have an extremely fast (high-bandwidth) connection and still experience sluggish websites if latency is high. This is especially noticeable on interactive applications — every click requires a round trip, and high latency makes each round trip feel slow.
What is round-trip time (RTT)?
RTT (Round-Trip Time) is the total time for a signal to travel from your device to a server and back. When you load a webpage, multiple round trips may happen: DNS lookup, TCP handshake, TLS negotiation, HTTP request, and response. Each round trip adds latency, which is why reducing RTT is one of the most impactful performance optimisations a website can make.
The ping command measures RTT to a given host. A ping of under 20ms is excellent; 50–100ms is normal for domestic connections; above 200ms starts to feel noticeably laggy for real-time applications.
Causes of high latency
Physical distance
Data travels at roughly the speed of light through fibre, but that still takes time. A request from London to a server in Sydney travels ~17,000 km — expect at least 250ms of latency just from the physical distance.
Network hops
Traffic doesn't travel in a straight line. It passes through many routers, switches, and internet exchange points. Each hop adds a small amount of latency, and poorly optimised routing adds more.
Congestion
When a network link or router is handling more traffic than its capacity, packets queue up and wait. This queuing delay increases latency, often dramatically during peak hours.
Server processing time
Latency isn't only about the network. If a server takes a long time to generate a response — due to slow database queries or heavy computation — that time is included in the total you experience.
Wireless networks
Wi-Fi and mobile networks introduce their own latency. Interference, signal strength, and protocol overhead all add delay before data even enters the wired internet.
How CDNs reduce latency
Content Delivery Networks (CDNs) tackle the physical distance problem by caching copies of a website's content on servers spread around the world. When you request a page, the CDN routes you to the nearest "edge node" — a server geographically close to you. Instead of your request travelling to a data centre on another continent, it only travels a short distance to a local edge server, dramatically cutting latency.
This is why a site served by Cloudflare, Akamai, or a major CDN almost always loads faster than a site hosted on a single server in one location — regardless of where you are in the world.
Latency and SiteAlive
SiteAlive measures the response latency of every site it checks. If a site responds in under 5 seconds, it's marked UP. If it responds but takes longer than 5 seconds, it's marked DEGRADED — indicating a performance problem even without a full outage. This distinction matters because a very slow site can be just as disruptive to users as a site that's completely down.