What RTU Is Best For A Small Outside-plant (OSP) Site With T1 Only?

The data transport you have available will often determine the difficulty of your RTU search. If LAN is available, you can choose from alarm remotes offered by a wide range of manufacturers.

Your job gets a lot more difficult when you have special transport requirements. Consider the example of a site that doesn't have LAN but does (or very inexpensively could) have T1. An outside-plant (OSP) site like that requires a much more accommodating RTU manufacturer who can offer native T1 support.

Let's walk through an example scenario. First, we'll address the topic at hand: getting an RTU that can support T1, regardless of its other capacities and functions. Second, we'll walk through the same analysis you'd need to complete for any RTU at any site: how many inputs and outputs does it need, and what special requirements must it meet?

Finding and choosing an RTU with native T1 support
Any RTU you're going to deploy at a site that doesn't have LAN must have an alternative. In this current scenario, you need to find one that specifically does support T1.

Pinout of RTU T1 WAN port
A T1 WAN port, like the one shown in this pinout diagram, allows an RTU to utilize T1 transport that can often be inexpensive at a site that doesn't have the IP transport needed by typical LAN devices.

So, what manufacturers offer native T1 support? Look for one with small-business agility, because high-mix, low-volume companies will have a much broader selection than those who sell massive quantities of just a few.

There are also a few design considerations you must make. What protocol will your T1 use? Two of the most common are FrameRelay and PPP. Whatever it will be in your case, make sure your RTU is compatible.

Next, don't overlook you chance to supply LAN to other LAN-only devices at a remote site. Yes, you're deploying an RTU. Its primary job is always going to be remote monitoring and control. Some, however, also have an ethernet switch on the back panel. Combine that will native T1 and a bit of engineering magic, and your RTU can "break out" LAN for several external devices. This goes way beyond a typical alarm remote, performing the function of a dedicated transport card that would otherwise be an expensive additional purchase.

T1 WAN port with a 7-port LAN switch from the back panel of an RTU
A T1 RTU that also has a LAN switch, as shown in this back-panel photo from an NG216T, means that your RTU can "break out" LAN for external devices at the site.

Finally, don't fumble your future by purchasing an RTU that only supports T1. Someday, you may very well get LAN rolled out to this location. Do you really want to have yet another purchasing and install headache? Don't go down that road. Deploy a remote that supports both T1 and LAN. When you get LAN out to the site, unplug the T1 WAN port and plug LAN into the LAN port. Your transition will be complete within minutes.

Monitoring the revenue-generating equipment you have at this site
Now that we have data transport sorted, let's not forget that this is still an RTU. It has to monitor and control various other equipment and environmentals.

Take stock of your revenue-generating equipment (we call it "revenue-generating" because it's the gear that directly provides service to your customers). It's difficult to offer specific guidance here, because there's a lot of variance by industry. If you're a phone company, you'll be monitoring phone switches and other gear that enables calls for your customers. If you're a power company, you'll be monitoring substation IT gear. Public safety agencies will have network equipment and radio systems.

Fortunately, the process of calculating capacity requirements does not vary much among these diverse industries. Here's the process you must follow:

  1. Collect manufacturer specs for all your revenue-generating equipment (or look at the I/O panels if the manufacturer specs cannot be found).
  2. Count the total discrete contact-closure outputs for all devices.
  3. Count the total discrete inputs for all devices.
  4. Count opportunities to use analog inputs effectively (temperature monitoring next to important equipment, for example).
  5. Subtotal all counts and move on to the next steps below.

Manufacturer specs will tell you what kind of outputs a device has. A phone switch, for example, might have 4 discrete outputs that report card failures, transport failures, high traffic. If you don't have access to manufacturer documentation (ex. they're out of business), just look at the equipment itself. Most output ports are labeled somewhat intuitively, although you may need to decipher a few port-label abbreviations. A quick web search can be surprisingly helpful, even for obscure equipment. You're probably not the first person to encounter this problem!


Revenue-generating equipment monitored and controlled by an RTU
Developing an RTU spec doesn't have to be difficult. Draw out a simple diagram and count up the discretes, analogs, and control relays you'll need.

So discretes, then, are fairly simple. Analogs, however, require a more complex analysis. Most equipment won't have any ports labeled "Analog Output 0-5v". With analog inputs, you're more commonly measuring power voltages or taking in data from environmentals. You need to ask yourself what you want to protect using monitoring.

Temperature sensors are the most common analog sensor to tie into an RTU. For the ultimate monitoring granularity, put temperature sensors near individual pieces of revenue-generating equipment. In most cases, a single sensor is adequate to cover a large area. Air disperses heat enough that any isolated heat spike will be detected within a reasonable time.

You should also monitor humidity. Not only does monitor for high humidity that could lead to liquid condensation, but rising humidity can be a sign of a water leak (although a discrete floor water sensor is a better tool for detecting such a leak).

Finally, you can decide to monitor input voltages to various equipment, but we'll pick up most of that later when we review our rectifier, generator, and battery plant in the next section.

What about controls? Just like discretes, these are fairly simple. You just need to look at your remote-site equipment (or documentation) and find any control input points. Do you have any ports labeled "on/off" or "5V trigger"? That's a clear sign that equipment will accept commands from an RTU's control relay output.

This is a small site, so let's say we want one analog temperature sensor, one analog humidity sensor, and a single control relay to reboot our switch.

In total so far, for our revenue-generating equipment alone, our RTU will need:

  • 4 discrete inputs.
  • 2 analogs.
  • 1 control relay.

Power supply: Your rectifier, battery plant, and generator
Your gear can't run without power. That's why your sites probably have primary power (commercial AC), short-term backup (battery plant), and long-term backup (diesel/propane generator). Let's start from best-case-scenario power and work our way down.

Your rectifier takes commercial AC power and outputs DC power (generally +24v or -48v in the United States) for your equipment. Monitoring DC output voltage from your rectifier using an RTU analog input is a great way to track the power flowing to just about all of your equipment. If voltage drops during brownout condition (or vanishes when the power goes out), you can react to prevent equipment damage and a site ultimately going dark. If, for some reason, you can't spare an analog input, you can at least use a discrete power-out-alert sensor that will tell you when commercial power fails.

When commercial power goes down, your battery plant (Uninterruptible Power Supply) kicks in. That represents a few more things you should be monitoring. Voltage output is certainly one. On a battery, this measurement does double duty. Yes, you're monitoring power quality, but declining voltage output is also how you estimate remaining battery life.

One analog input on your RTU measuring voltage can give you huge situational awareness about your batteries and when then may run out. At least one temperature sensor on the battery string itself can help you detect battery damage early - before expensive equipment damage occurs.

Backup diesel or propane generator for a remote hut
Your generator recharges your batteries when commercial power is down. You should really be monitoring the fuel tank (propane or diesel), tracking its run state, and remotely activating/deactivating with a good RTU.

Finally, dead commercial power and nearly dead batteries mean it's time for your generator to kick on and recharge your batteries. When that time comes, will you have enough fuel? Whether you use a propane (LPG) or diesel generator, a simple analog fuel tank sensor will give you tremendous confidence.

During an extended, widespread outage (ex. hurricane aftermath), your network of fuel sensors will help you prioritize your refueling truck dispatch to keep your sites running.

With a control relay, your RTU can directly control generator activation when it detects low battery-plant life.

Last, you want to know when your generator is actually running. This is important for a few reasons. First, it's great redundant visibility that you're having a power event. Second, you can verify regular generator maintenance "exercising" (ex. run 1 hour per month) that keeps the engine in good condition.


Rectifier, battery plant, and generator monitored and controlled by an alarm remote
Adding to our previous tally, we now have a count of all RTU I/O required for both revenue-generating equipment and power sources.

Should you not have enough analog capacity to actually monitor your fuel level, an RTU log of accumulated running time since the last fill up is a decent proxy.

Let's take a minute to recap our RTU I/O tally for this site's power supply:

  • Rectifier: 1 analog input for voltage.
  • Battery plant: 2 analog inputs for voltage and temperature.
  • Generator: 1 analog input for voltage, 1 control relay for remote activation, 1 discrete input for running state.

Adding this tally to our previous subtotal for revenue-generating equipment, we now have:

  • 5 discrete inputs
  • 6 analogs
  • 2 control relays
Other typical items to monitor

There's no way that any single article could cover every thing you could possibly monitor at your site. A complete site survey is up to you, but here are some common items to look for:

  • Tower lights (online/failure discrete sensor, if your site has a tower that falls under FCC/FAA lighting requirements).
  • Entry doors (open/close discrete sensor).
  • Motion sensors (discrete).
  • Floor water (to protect against leaks/flooding)
  • Visual status (add an IP camera to your monitoring system)

To help us choose an RTU in this example, let's add 5 more discrete inputs to our total. That brings us to a grand total specification of:

  • 10 discrete inputs.
  • 6 analogs.
  • 2 control relays.

Which RTU should I choose?
Good RTU manufactures make it easy to sort through your various options with a filterable "feature matrix". You just punch in your required specs (add a bit to cover growth) and see a list of options. Alternatively, you can call and talk to an expert directly, which you'll do anyway before making an investment decision. www.dpstele.com has a good example of a feature matrix for its NetGuardian line of RTUs. Using that feature matrix turns up two potential options:

  • The NetGuardian 216 G3 has 16 discretes (a bit more than we need, but discretes are inexpensive), up to 8 analog (we would want to order all 8), and 2 control relays (exactly to spec), but it doesn't have native T1 support. It only supports LAN/serial transport.
  • The NetGuardian 216T is similar to the 216 G3, but has native T1 WAN support in addition to LAN. There's also a "240T" variant of the 216T that has 40 discrete inputs, but that's overkill for us in this scenario.

Remember that there are lots of possibilities if you're working with a good manufacturer. Just look at this T1 solution that supports VLAN:

T1 RTUs with VLAN mux reporting to T/Mon master
Here, many native-T1 NetGuardian RTUs are reporting back to a T/Mon master station via a VLAN mux. We won't need to use this solution unless we have multiple T1 sites and need VLAN support, but it's a great example of what's possible when you work with an agile manufacturer who can address your special requests.

As you can see, finding the right RTU involves a few simple steps:

  1. Develop a spec for your site by surveying the equipment you have there and adding a bit for growth.
  2. Identify RTUs that match your required specs (or call and speak with a manufacturer who offers customization).
  3. Call the manufacturer(s) to make sure they're reliable. Ask for references from previous deployments.

If you need any assistance at any time with your remote monitoring project, call us at 1-800-693-0351. We're experts in this field, and we're happy to help you.

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