PTP 450i: How to reduce jitter?


I have a PTP 450i link with very good conditions.

It's short (1km) and in a clean spectrum environment, set to 2.5ms frame size.

This is what I can see in Alignment Tool:

Path V:QPSK:32% 16-QAM:30% 64-QAM:19% 256-QAM:19% 
Path H:QPSK:28% 16-QAM:27% 64-QAM:23% 256-QAM:22%

This is the actual ping from the router at remote end to the router at the local end:

round-trip min/avg/max/stddev = 1.338/2.754/7.688/0.966 ms

64 bytes from icmp_seq=238 ttl=63 time=1.650 ms
64 bytes from icmp_seq=239 ttl=63 time=2.130 ms
64 bytes from icmp_seq=240 ttl=63 time=3.212 ms
64 bytes from icmp_seq=241 ttl=63 time=1.498 ms
64 bytes from icmp_seq=242 ttl=63 time=2.277 ms
64 bytes from icmp_seq=243 ttl=63 time=1.769 ms
64 bytes from icmp_seq=244 ttl=63 time=1.667 ms
64 bytes from icmp_seq=245 ttl=63 time=2.890 ms
64 bytes from icmp_seq=246 ttl=63 time=2.195 ms
64 bytes from icmp_seq=247 ttl=63 time=2.872 ms
64 bytes from icmp_seq=248 ttl=63 time=5.995 ms
64 bytes from icmp_seq=249 ttl=63 time=3.423 ms
64 bytes from icmp_seq=250 ttl=63 time=3.000 ms
64 bytes from icmp_seq=251 ttl=63 time=1.396 ms

As you can see there is a little jitter.

I think that's normal on a TDD system, but I would like to ask if it's possible to have a ping always rock stable to a value, like it was a cabled link.

Is it possible on PTP 450i?

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That amount of jitter is perfectly fine for every type of service that a residential connection, and most commercial apps would need. I think you're still running into a tiny bit of interference, as if it was a perfect link, with no noise, each modulation would be at 25%. When you do a link eval, is the link efficiency 100% on both the downlink and uplink?

I think the only way to get less jitter would be to go with a licensed link, like the PTP820.

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Sure, the jitter is perfectly fine and it works great.

I wanted to know if it's possible to achieve this result :-)

Here's link eval result.

SNR is different between upload and download because transmit power is different, but the link is very good.

At this time I can see:

Path V:QPSK:28% 16-QAM:28% 64-QAM:22% 256-QAM:22% 
Path H:QPSK:26% 16-QAM:25% 64-QAM:24% 256-QAM:24%

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Giuseppe - This is about as good a link as I have ever seen... and about as good as it's going to get using the PTP 450i equipment. 209 Mbps throughput (in a 30 MHz channel, I  assume).

The only application that I can think of that would require less or more stable latency would be something like HFT (High Frequency Trading).  I would not recommend our equipment for use with that application.  Those guys spend big bucks to imitate "wired" connections.

All in all, a great little link you have there!

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Thank you Matt :-)

That's a link in a very rural area and works great. 

I'm waiting for 40MHz channel support to test it and have more bandwidth to support bandwidth demand increase. Will PTP 450i support split channels (for example 20+20) in the future? It's very useful in crowded environments.

I asked about jitter only to do a "technical experiment" and to know how stable can a PTP 450i be on latency times.

The PTP 650 is stabler than PTP 450i.

I can also achieve super stable ping times on AirFiber24, but it's on FDD not TDD.


I repeat, that's only a technical experiment, and the latency I can achieve is very very good for a 5GHz link.