What is RTT in CDN context?

RTT (Round-Trip Time) is the time it takes to send a request to a CDN server and receive a response. It is measured in milliseconds and indicates the network's response speed.

What is the difference between TTFB and RTT?

TTFB (Time To First Byte) measures the time from sending an HTTP request until receiving the first byte of the response. RTT measures the complete data exchange cycle at the network level. TTFB is usually greater than RTT because it includes the server's request processing time.

What Availability metric is considered good for CDN?

For professional CDN providers, an Availability (uptime) rate of 99.9% or higher is considered standard. Market leaders achieve 99.99% or even 99.999% availability.

Comparison of CDN Provider Availability

How many nines does each CDN have according to independent monitoring?

Comparison CDNvideo EdgeCenter Curator Megafon MWS CDN

RTT TTFB Throughput Availability cached

not cached Conduct a test

Dynamics of availability

Availability
for period

What is Availability and why measure it?

Availability — the percentage of time the CDN correctly serves user requests. This is the fundamental reliability metric of a provider.
The practical difference between availability levels:

Availability	Downtime per year
99,0%	87 hours
99,9%	8,7 hours
99,99%	52 minutes

Even brief outages directly impact revenue, reputation, and search rankings — Google takes site availability into account when ranking pages.

What do the availability charts show?

Availability trend chart (HTTP/HTTPS) — reveals brief outages that do not always appear in providers' official reports. A divergence between HTTP and HTTPS lines may indicate SSL termination issues on specific nodes.
Cities with low availability — locations with unstable CDN node operation. An incident in a specific city may be invisible in aggregate statistics, but can be critical for the local audience.
Providers with low availability — a comparative reliability ranking. Shows how closely the declared SLA matches real-world independent monitoring data.