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Microwave Latency

Microwave Latency
Posted by Kimberli Itah

Microwave Latency

I don't think you'll notice any latency difference between a few meters or 20 miles. The signal travels at the speed of light, so provided it is a good link you will not notice the difference, because I would guess it would be much less than 1ms either way.

When talking satellite however, the distance is more like 23,000 miles or so up to the satellite, and same again on the way back to earth. This gives latency in the region of 800ms.

The problem is not going to be the latency of the 150 miles, but the latency introduced by all of the radios. Different equipment has different latencies, but you are going to have to determine how many hops there will be to arrive at any kind of reasonable answer. VSAT can be as low as 500ms from Router to Router.

As others have stated, the actual over air portion the link is going to have extremely low latency (less than 1 ms) what is really going to affect latency is how many hops you need to have and the type of equipment your using. For example I could do 150 miles on 5 hops of 2.4 using stock 802.11b gear. Most likely the total latency will be about 80ms. If I do the same number of hops with radios designed for making these links the latency will be about 10ms.

We have a trunking network that the distance from one pop to another is 110 miles. Latency is about 10ms or so. Going from one end of the network to the other is 150 miles and latency is about 20ms. If we were to swap out some of our radios for a better performing radio that would drop to about 10-15ms.

Redline operates at 5.8 GHz. NOT 28 GHz. The longest Redline/Link blaster shot right now is not over 100 Miles. ALCATEL MDR-8000 Boxes and they are using a licensed 6.5TX and 6.7RX band...

Each hop is going to cost you about 10 ms + the air latency, which is vanishingly small. Light travels at 186,000 miles per second. The actual travel time on a 150 mile straight shot is under 1 ms (about .0008 seconds).

Hops cost 10 ms each (for estimation purposes) because when a router receives a packet, it has to decide what to do with it. It has other processing it has to do, and there is no way to predict exactly where in the processing cycle it happens to be when the packet arrives. So lets suppose there are ten 15 mile hops. You're looking at 100+1 ms ONE WAY LATENCY. OTHO if there are 2 ,75 mile hops you're looking at 20+1 ms latency ONE WAY.

Unfortunately you also have to add in the hop from wire to air and from air to wire at each end SO... your mileage may vary about 20 ms from these. *GUESSES

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