Ethernet Links

[FMROB]

Hello all,

Happy Thanksgiving. I have a situation where I need to do a microwave hop for a remote site. All the equipment is running on Ethernet backbone, so at the remote site will be a JPS NXU, TB9100 (IP backbone) and a switch. At the dispatch office is the other end of the NXU connected to the console and the rest of the TB9100 network. The remote site is about .3 miles away, but I just cant get a completely clear shot with micro, as we are just in the tree tops and the two sites have a sharp drop off for being very close due to terrain. The area has no fiber, and the Telco circuits are from the year of the flood and failing (the reason of the micro upgrade), so I really have no other options to get up to the site.

Is there anything that anyone could suggest that may work in a quazi NLOS fashion that will give a Ethernet connection. Keep in mind the data rate requirement is low, probably less than 20 kbs at full operation, however latency could be an issue with the linking medium.

I was looking at those RF neulink NL900s ISM 900 MHz data radios that have native IP links built in, but they worry me. I would assume if I use two large high gain yagi style antennas I should be able to get a clean signal between the two sites. Some years back I remember a few people trying out some similar 900 links, but they just spewed nasty noisy RF at the site up into the UHF band (where our equipment will be) and they had some atmospheric issues with I guess ducting during certain times of the day/year. No, their hop was about 5 miles, and this was about 6 years ago, so maybe this stuff got better. There has to be some reliable way to accomplish NLOS data hops?

Thanks all, any help would be appreciated.


Link to radio http://www.raveon.com/rfneulink/NL900s.htm
Rob

[Bill_G]

Any budget for 50-75ft guyed towers to get you above the canopy to establish LOS? Are there existing tall structures that you can build a long-way-round multi-hop solution?

Canopy (now Cambium), Redline, and several others make OFDM product that can deal with SOME NLOS issues. The closer the two endpoints are, the better. But, they aren't magic. A few tree branches they can handle, but a forest? No. Hills and buildings definitely not. However, they can moon bounce off a glass building front to get around corners, and actually be reliable. 900M stuff is a coin toss. Depends on how much other 900M activity is in the area.

[FMROB]

Bill,

Remote site is on top of a 96' water tank and at HQ there is 50 of Rohn 25 on the 30' high roof of the building. However the tank is on top of a large hill and the HQ is in the valley below about .3 miles away. The issue is I cant get high enough to overcome the drop off and tops of trees.

Have you used any of the 900 stuff? I think anything micro is going to be a no go, unfortunately.

Rob

[Bill_G]

Shoot me the lat/long so I can look at the path.

[Bill_G]

Shoot me the lat/long so I can look at the path.

[wavetar]

Most vendors will run path loss calculations for you to determine feasibility. Radwin, Cambium, Exalt, 4RF (Aprisa) are a few that come to mind. You'll have to give them average tree height if they don't have 'clutter' data for your particular area.

I've seen the Cambium PTP500 stuff do some pretty difficult near and non line of sight links...sure you might only get a stable 5MB/s link out of a possible 105...but as you say you won't even need 100KB/s. Their Link Planner software is very cool & will give you specs on reliability at whatever threshold you define...by default it looks for 99.999% at 1MB/s.

[Bill_G]

Most vendors will run path loss calculations for you to determine feasibility. Radwin, Cambium, Exalt, 4RF (Aprisa) are a few that come to mind. You'll have to give them average tree height if they don't have 'clutter' data for your particular area.

I've seen the Cambium PTP500 stuff do some pretty difficult near and non line of sight links...sure you might only get a stable 5MB/s link out of a possible 105...but as you say you won't even need 100KB/s. Their Link Planner software is very cool & will give you specs on reliability at whatever threshold you define...by default it looks for 99.999% at 1MB/s.

In my experience, the BER is the final determinate in link quality. If it falls below 1e6, T1's and voip blow up. I've watched Canopy PTP links shift gears, successfully auto-rate down, and still maintain the radio traffic until the BER hits 1e5. Then, it all goes bye-bye. If it's carrying voip, you can't understand a word. Bubble wobble garble. If it's carrying T1, that bounces, all DS0's chatter, voters go clickety clack, and repeaters are kerchunking like frogs in Sprng. Good times.

For voice traffic, the magic bit rate that seems to survive is above 2Mbps, and the target RSL threashold for most modern point-to-point equipment is (well) above -70bm.

[Jim202]

Sounds like a good candidate for some fast work with a chain saw. Have done this a few times over the years. just make sure you know who owns the land the tree is on.

Jim

[Bill_G]

Sounds like a good candidate for some fast work with a chain saw. Have done this a few times over the years. just make sure you know who owns the land the tree is on.

Jim

True dat. Sometimes it is as simple as cutting a hole in the forest. And sometimes not. Between path analysis software, Google Earth, and good old fashioned eyeballs, you can prove a link is viable pretty quickly, especially the short ones where line of sight literally means you can easily see both ends at elevation without a scope. OTOH, I've seen people put way too much trust in the N part of NLOS when what they really needed was T for telepathy, or M for magic.

Let me rephrase - I've seen some paths that prove that NLOS stands for No Link Out there Silly.

[FMROB]

Great stuff guys, thank you!!!

I want to take a moment to personally than Bill for his help and time (in more than one instance & project) on this little project. He is a gentlemen, plain and simple , who is a wealth of knowledge!

As this project moves closer I will take some pics and post a little synposis so the group can share. It is a nifty project with some intersting views.

Thanks, Rob

[Cam]

0.3 of a mile? Can you just run your own fiber?

[FMROB]

I guess we could, but that sounds very costly. I have no exceprience with running fiber on utlility poles?

Rob

[Bill_G]

You'd want to contract it out. It might be aerial cable, might be buried. Depends on the district, and who owns the utility right of ways. Around here, horizontal boring to install new fiber duct that you later pull your fiber through is around $30K/mile. If you haven't investigated it, you might want to find out from whomever controls the water tank what high speed service they have already, and whether it is intertied to your dispatch center network. You last option is the cable TV, FIOS/DSL internet, or business VOIP providers. They can maintain QOS if a site to site link stays on their side of the internet ensuring minimized latency.

[FMROB]

So the issue here is that the geographic area that the fire district is located has very, very, very old above ground copper. the Telco circuits are in bad shape. At this point, verizion has not pulled fiber in the area yet. Only choices are dsl or cable modem, none of which I would feel comfrotable running FD communications on.

Rob

[Cam]

I'm guessing this is a some what rural area based on the fact that you can't get good internet service. What does the path between your two points look like? If it could be open trenched it might be about to be done at a fairly reasonable cost. On the other hand if you have a bunch of road bores, lot of utility crossings that kind of thing the price goes up.

Also check with the power company that serves that area, lots of fiber out there setting unused. Even if if they don't have any in that area many will build a link like this for you and lease it to you.

[FMROB]

I will give them a shout and see what might be available, thanks.

[Cam]

Yeah that and like I said it's if it is a rural area it may make since to build your own fiber. I think people often think it cost much more then it really well.

[Bill_G]

It is rural-er than the surrounding metro area.

[groundrat99]

FWIW we have used PTP400 unlicensed (as a trial) through thick trees on a shot about 5 miles. Both 2 ft panels were shooting directly through pine and oak trees on both ends. We had a -60 ish RSL and about 5-10 Mbps throughput. The only time we had a fade was during a couple extremely heavy rain storms. Contact Cambium, they may be willing to send you a trial set to see if the link will work.

Bill

[Bill_G]

FWIW we have used PTP400 unlicensed (as a trial) through thick trees on a shot about 5 miles. Both 2 ft panels were shooting directly through pine and oak trees on both ends. We had a -60 ish RSL and about 5-10 Mbps throughput. The only time we had a fade was during a couple extremely heavy rain storms. Contact Cambium, they may be willing to send you a trial set to see if the link will work.

Bill

Was it 5 miles of coniferous forest, or a copse of trees at each end with several miles of clearance between?

I've shot Canopy through trees too, but it was a few trees about halfway with clear LOS before and after. I've never been able to shoot through a fully obscured path.