Drag

Sources of Drag

Drag is anything that prevents data from traveling at the clean speed of light througth fiber-in other words, anything other than prooagation delay. 

Serialization--Bandwidth drives serialization delay. A lack of bandwidth can add seconds to network latency. This is cheap and easy to solve. Telcos have done a good job of addressing serialization delay-cheap bandwidth is everywhere. But the drive for cheap bandwidth has introduced material drag from other sources.

How we address it: Owning a private network allows you to eliminate these sources of drag while continuing to enjoy almost unlimited bandwidth.


Queuing--Optical equipment can process 10 64-byte packets in the same time it takes to process one 640-byte packet. Routers and switches, however, need more time to process 10 64-byte packets than to process one 640-byte packet. This mismatch creates queuing. Queuing is the predominate source of jitter and is the most common bottleneck during traffic microbursts. Added latency from queuing is highly variable and difficult to predict. Telcos rely heavily on routers and switches to manage traffic flow, which results in queuing delays.

How we address it: Owning your own private network allows you to completely eliminate routers and switches and therefore queuing delay from your long-haul network.


Chromatic Dispersion--Any network running multiple channels over a single pair of fibers must compensate for chromatic dispersion. Chromatic dispersion occurs when multiple channels run together and become indistinguishable to the receiving optical hardware.

One approach implemented by telcos is to run an "all optical" network, which uses dispersion-compensating fiber to clean up the signal. The dispersion-compensating fiber is kept in a case located in the regenerator huts where the Optical-Electrical-Optical (OEO) regenerators used to be. The case contains anywhere from 7 to 17 miles of dispersion-compensating fiber for every 100 miles of single-mode fiber. If your regenerator hut is spaced every 60km, then the dispersion compensation module that replaced the old OEO regenerator will contain 4.2 to 10 km of fiber (coiled up in a box). Your data runs 60km, then runs for 10km around and around through this coil while the compensating fiber cleans up the signal. It then travels on to the next regenerator hut 60km away. A 1000 mile route would have an additional 70 to 170 miles of coiled-up compensating fiber, which adds about 1.1 to 2.6 milliseconds round trip over and above propagation delay.

 Drag Route 1