>"I've rented some of these lines as part of a financial trading infrastructure."
Unless you were lighting that fiber yourself you were renting wavelengths and not the physical fiber.
>"What's immediately obvious is the line is much faster than going over the public internet, and there's no jitter: every time you ping it comes back in the same amount of time, whereas the internet pings will vary by several ms"
Jitter is caused by congestion which happens at router interfaces. The absence of jitter is not due to the use of dedicated submarine fiber spans per se as the speed of light in fiber is a constant. What you are likely seeing is the result of a network operator who has optimized for low and consistent latency by having fewer hops in their network before and after the cable landing stations.
Unless you were lighting that fiber yourself you were renting wavelengths and not the physical fiber.
>"What's immediately obvious is the line is much faster than going over the public internet, and there's no jitter: every time you ping it comes back in the same amount of time, whereas the internet pings will vary by several ms"
Jitter is caused by congestion which happens at router interfaces. The absence of jitter is not due to the use of dedicated submarine fiber spans per se as the speed of light in fiber is a constant. What you are likely seeing is the result of a network operator who has optimized for low and consistent latency by having fewer hops in their network before and after the cable landing stations.