Using TTLB (throughput) to test performance

Which CDN is the fastest?

Many companies choose a CDN to boost their web performance. However, an underperforming CDN will still degrade your delivery. Latency is another factor to consider when choosing a CDN. Most latency-sensitive applications are adversely affected by more than 250 ms of latency.

Performance monitoring – what you need to know

Performance monitoring is about measuring and improving how long it takes for your site’s content to load. If you’re not monitoring, you can’t measure and improve. It’s important because consumers are getting more demanding. They want their content fast! Studies show that even one second of delay in page response can reduce conversions by 7%. To ensure that your site performs at its best, evaluate its current state with customer-facing measurements like SpeedIndex or Speed Scorecard tests.

CDN performance – what should I be looking for?

Your CDN should be able to serve content with an acceptable latency. Ideally, you want your CDN-hosted assets to have 10 ms or less round-trip time (RTT) when they are accessed from 50,000 miles away in California. Latency often increases with distance, so nearby users may also experience poor service. Here are some ways you can see how your CDN is performing.

Cedexis Radar and Real-User Monitoring (RUM)

-Many commercial services available: New Relic, Compuware Gomez, Dynatrace, Cedexis, SmartBear, Pingdom, Soasta, etc.
-Key Measurements: response time, throughput, error rate, page load time
-Generates actionable alerts

The Best Metrics to Measure CDN Performance

-Throughput a/k/a Time To Last Byte (TTLB)
-Availability

Why is it important to monitor my CDN performance?

A CDN is only as good as it can perform when delivering content. So even if you’re using one to boost your web performance, an underperforming CDN will still degrade your delivery. Why not monitor it?

TTLB, TTFB, throughput, latency and how they affect your website

Your site should load as fast as possible. Even if you’re using CDN, an underperforming CDN will still degrade your delivery. You can take your website’s speed for granted until you notice an unfortunate change in conversion rates. You could use some online tools like Pingdom Speed Test to see how long it takes for your site to load from different locations around the world and then compare it with other relevant websites in your industry and have similar traffic levels.

What’s the difference between TTFB and TTLB?
TTFB is the amount of time it takes to receive the first byte from the server. When a browser sends a request, it must then get to a server, calling another server or service, a database, or some other logic. When complete, the server starts sending back the response to the browser. So TTFB actually measures how long the browser request waited for the server to finish running its logic. In terms of end-user experience, this is essentially a useless metric. By now, it should be clear that even if the first byte is near-instant unless ALL the bytes are delivered, it’s not relevant from the end-user perspective. TTLB is when the last byte is received by the browser (or client). Only then does the computer assemble the data and make it into something digestible. Also, given that a web page has many components (CSS, Javascript, images, etc.), there will be a TTLB for each of them. Only after the last byte of every component is received by the browser/client–can the user actually enjoy the web page or app.

What causes a slow TTFB and TTLB?
-Overloaded origin server
-Geographic distance between request and content’s origin servers
-Connectivity issues

Some web performance experts argue that TTFB is more important for the user than TTLB since web browsers may start displaying files as soon as the first bytes are received—for FEO optimization.
The goal is to get the last byte to the user as quickly as possible. Everything else is noise.
How does your web performance stack up? Contact us to schedule an appointment with our CDN experts, who can evaluate your needs and determine a custom-fit solution for you.