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16 min read

SBA 280: BACnet IP vs MS/TP

By Phil Zito on Sep 20, 2021 6:00:00 AM

Topics: Podcasts

In this episode we take a slightly biased look at the pros and cons of IP enabled controllers versus MS/TP controllers. 

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Phil Zito 0:00
This is the smart buildings Academy podcast with Phil Zito Episode 280. Hey folks, Phil Zito here and welcome to Episode 280 of the smart buildings Academy podcast. And in this episode we are going to be discussing BACnet IP versus BACnet mstp. You know, I was in our big sales boot camp last week and one of the students asked about BACnet IP versus mstp. What are the pros and cons and I realize that we haven't really done a podcast episode about that. So that's what this episode is going to be about. If you're interested in getting a no BS, kind of assessment of why you would use BACnet IP or why you would use BACnet mstp, then stay tuned. And that's what we'll be discussing in this episode. As always, everything can be found at podcasts, smart buildings, academy.com, forward slash to Eddie. So as I started to dig into this topic, and I started to kind of just do the initial Google right, because that's what everyone's going to do. They're going to Google BACnet mstp vs. IP, I started to come across some like really goofy advice like reduced programming time BACnet mstp, or lawn, I don't even know why lawns in this conversation can take hours to communicate between controllers, whereas BACnet IP only takes minutes and like, know, what BACnet mstp can take seconds. And BACnet IP could take seconds. In some cases, it can take minutes, I've yet to run into a functioning at mstp network that takes hours. So there's this goofiest, Goofy, Goofy advice in here. Common scripting languages can be used, what does that even mean? Then you get into things like BACnet mstp, can be more difficult to troubleshoot? Yeah, I mean, maybe maybe not. I would argue back net IP can be very difficult to troubleshoot. If you don't know what you're doing. And you don't understand IP, and you'll get things like BACnet IP devices aren't susceptible to communication issues with only one device affecting multiple devices. Well, not really not if you are running a boss architecture, or potentially a ring architecture in both spanning tree ports goes down. So before we really dive into because because some of you are like whoa, what what, before we dive into any of that, let's do a quick primer on mstp and IP. And then let's talk through the benefits and the cons of both. And kind of what I would deploy If I were you sitting there figuring out what should I go and implement because at the end of the day, I'm not selling you controllers. I'm not selling you services for installations. So I have no dog in the fight, I have no need to convince you either way to go mstp or IP, I'm completely Well, no one's completely unbiased, but I'm pretty unbiased when it comes to this topic. So mstp right, our tried and true rs 45 wire standard, three to four wires, daisy chain mean hops from supervisory device to controller to controller to controller uses layer two communication using a token to communicate between the controllers, the controller gets the token and it can send messages or receive messages, right. And that's all well and good. That's how BACnet mstp works. Because of that we're typically limited to some slower communication rates, which are baud rates.

Phil Zito 3:45
You would say similar to modem speed baud rates, right? 56k somewhere. Normally, it's like 38, six to 76 may not be memorizing those precisely. But as I say, in all my podcasts, I'm not going to memorize something that I can Google, I'm not going to put it into my brain when I can just google BACnet mstp baud rates and get a table. There's no reason for you to memorize that. There's no reason for me to memorize that. So mstp like I said, it goes and communicates across the controllers and they can have a run, you know, some of the sites are going to come to yours are going to say 128 nodes that it can be no, no, no, no, no, no, it could be 96. If you're following the RS 45 standard across three segments at 3300 feet or more. anything more than that you're not guaranteed to get the results no matter what your OEM tells you because you're violating the RS 45 standard on which mstp is dependent upon. So just be cognizant of that. Also polarity comes into play you know if you cross wires because it is volts DC communicating, so if you cross wires that could be bad. If you don't punch down properly that could be bad on the controllers. And you could have issues with n Vline. You can have issues with interference, etc, right? But at the end of the day, it's pretty stupid simple to set up. You just run the wires, you connect the controllers. Ideally, you address the controllers using MAC addresses that are in series. So that's what you would do. And then, right, once you've done that, once you've address the controllers, you turn them on and they should all communicate, you just discover them should be good, right? Pretty simple. And simplicity is king. In today's market, where we have a lot of unskilled labor, because we have a labor shortage, and we have so much backlog that we're putting people out there to do work, and we need that simplicity. Then on the other side, yeah, BACnet IP, right BACnet IP, it uses IP addressing to communicate, and you go and you discover using a who is I am discovery message, map a man. And as long as everything's on the same subnet, pretty good. When things get off on the different subnets, you need things like BB MDS and bdts. I'll put some links into my back net resources in case you don't know what a BB MD and BB BDT are. But suffice to say, back net IP, it's gonna be a little faster and have some better communication.

Phil Zito 6:28
It can in some cases be more reliable. In other cases, it can be less reliable. Some cases it can be easier to troubleshoot In other cases, it can be harder to troubleshoot. In some cases, it can be faster. In other cases, it can be slower, and you'll be like what I've never heard slower. In some cases, it can cost more in some cases, it can cost less. So therein lies the rub. Everything you see out there about IP, not everything, most of what you see about IP is going to be pushing you to IP controllers. Why? Because that's what they're selling. They're selling IP controllers, they want you to buy IP controllers, they need you to pay off their r&d costs associated with IP controllers. At the end of the day, Now, that's not to say that IP controllers are not better. There are many ways that they're better. But there comes to a point of diminishing returns. If you are getting a contractor, or someone who's advising you to do all of your VA v boxes with IP enabled controllers. I feel like what, really why? Because what I can download programs Faster How many times in my downloading programs, because I can have IP supervisory device enabled capabilities like graphics and all sorts of stuff in my controllers, their VA v box controllers, people, they don't need to be that fancy. So let's start to list out the pros and cons and this is in no particular order. We're going to go IP first we're gonna go pros, then we're going to go cons and then we're going to go mstp we're going to go pros, and we're gonna go cons and now I'm going to give you my closing thoughts. Okay, so IP controllers, pros, they are faster. They are definitely faster. Average IP controller is anywhere from 10 megabit to 100 megabit, typically, that is significantly faster than mstp controllers, which are going to be anywhere from you know, 36,000 to 76,000. baud, which baud is different than bits. Just be cognizant, baud is the state change of a bit, where as bits were just talking, and when we're talking about Ethernet, we're talking about bits transfers, whereas BOD is state change, signal change. So it's not a direct comparison, anyone who tells you 76k is a direct comparison to the megabit, or kilobit on an Ethernet side doesn't know what they're talking about. They are not parody, okay. But suffice to say, Ethernet IP is significantly faster. Alright, it means that you're going to be able to send data faster, you're gonna be able to download programs faster, but you will also be able to send more data, which means that you can send graphics, you can send alarm data, all sorts of stuff. I'll talk about data packets and data sizes and why this isn't that big of a deal. But the really thing about IP that it enables you to do is it enables you to use higher level protocols like HTTP or HTTPS. So you can do Web Services, you could do things like that you can use SNMP, you could do trapping, all sorts of stuff that you really can't do over mstp, not because of the baud rate, but rather because of how it works, how it's a serial communication using tokens. And it's not meant to support IP traffic, which is layer three TCP traffic, which we need for HTTP, which is layer four, and HTTP traffic, which is a layer seven protocol, right? So we can't support those things with the serial networks. Now, some folks will argue that IP is more scalable, because you can go and put, you know, 256 controllers on a slash 24 network, you could do, potentially, and I don't know why you would do this. But you could do like 500. And what was 256, that'd be 512. Minus three rights. That'd be 509 controllers on a slash 23. Network, I don't know why you would do that. That would be a very unwieldy subnet, be very difficult to troubleshoot all that traffic, but you could. So in theory, you can have these ginormous subnets, filled with controllers, and these IP addresses DHCP. And everything can be working really nice and good, right. So it's scalable, you can just keep expanding it, you're not tied necessarily to a mstp trunk, and it's 96, not 128 96 node limit,

Phil Zito 11:48
then we come to troubleshooting. Now, I will agree that troubleshooting IP is more simple than troubleshooting mstp to a point, if you're running a star pattern, which is an end run from a switch to a host device, it's a single run, it's pretty easy to troubleshoot. It's either up or it's down, troubleshooting your IP packets, they're either malformed or they are not. It becomes simpler to troubleshoot. So from that perspective, there is a benefit. supervisory capabilities. A lot of when you hear me advocate for IP controllers, it's going to be on air handlers and central utility plants. Because of the supervisory standalone capabilities that come with most IP controllers, where they have graphics built into them, they have trending alarming, all sorts of more advanced capabilities so that it could run as a standalone controller, if your connection to your supervisory device were to go down for whatever reason, you could effectively run that air handler, and its sub devices off of that advanced application controller. Alright, so then what are the cons of IP controls? Well, price, they do cost more, that cost is coming more to parity with non IP controllers. And eventually, you're going to be forced to use IP because they're going to phase out mstp, eventually, at least at the central utility and major air handling unit controller level. So your large capacity controllers eventually will be IP only, it's just a matter of time. So cost, the actual cost of the wires, it does cost more, you will be told that you can run IP controllers and you can run the cat five cable cat six cable for less, because it's extra low voltage. But that's not true, you're gonna have to in a lot of unionized cities and Metropolitan, you're gonna have to pay the same Sparky the same rate to run that wire as you did for your 22 three. And now you're gonna probably have to put it in an actual cable tray versus j hooking. You can run Ethernet over j hooks, it's not preferred. Some people will say that you it's easier to terminate, right because you go and you have to terminate the rj 45 heads. I would argue that it is the same level of difficulty whether you're terminating three to four wires onto a terminal strip or you're putting eight wires into an RJ 45 head and crimping it down. Either way, you're terminating. Either way, you can mess it up, I would argue that terminating rj 45 heads is going to be more difficult. Do not buy pre terminated cables, just do yourself a favor. But it's going to be more difficult because there's eight wires you can mess up versus three to four wires that you can mix up and you're doing this in the plenum and it's going to be confusing and you're going to potentially mess it up. Now cost also you Have a switch now that you have to pay for it. If you're doing star pattern, you could be paying 10s to hundreds of dollars to switch port per year to have access to that switchboard. Now granted, there are things like the bus pattern. And there are things like the ring pattern. And they enable you to have wires. Basically, the bus pattern is a daisy chain pattern. And that enables you to run a series of controllers and daisy chain from one to another. The problem is that unlike with mstp, where things are, electrically just the signals going across the wire, and if the controller loses power, the signal will continue across the wire. With a lot of IP controllers, they use network interface cards inside them that are not electrically bridged. So if one of those controllers powers down everything downstream from it dies, thus we came out with the ring architecture where you have one ring that is open one port that's open, and the other port that is closed, also known as a blocking port rapid spanning tree or Spanning Tree Protocol. And when it senses that the open port is down, it opens the blocked port, thus switched us. And that enables you to have communication up to the point of the dead controller, but you still will have a dead controller potentially blocking your ability to communicate. Now, a lot of manufacturers are working through this. They're solving the electrical issue. But be cognizant that it is something that still occurs. Let's talk about mstp mstp is tried and true. It's simple. It is easy to use, oh, and about IP security.

Phil Zito 16:47
How do I address this because you all if you've listened to this podcast for any amount of time know my feelings about BACnet secure Connect, you know my feelings about security when it comes to controllers and the overkill that is, hey, the government God or major pharmaceutical said we're not secure. And we lost one job and our top salesperson complained about it to the products group. And the products group has now implemented this secure connect and is going to force it on everyone because you know we're gonna solve this small problem with a giant mallet. And not with like a precise needle point hammer. We're going to apply security to everything regardless of if there's even a threat that no, you know, basically means that we should have that level of security. And now we're going to put this new bastardized form of security on top of everyone. But this isn't me railing against BACnet. Se, if you want to listen to that, I'll put that episode in the show notes. And you can definitely go listen to me complain about BACnet SC for 30 minutes. You don't have to agree with me though, you know, take your own stance, I think it's a bad idea it's coming. whether I like it or not, everyone's gonna have to learn it, everyone's gonna have to do it because it is being forced into specs by people who don't know better. In my opinion, once again, that's my opinion. And yeah, take it as you will. But IP does enable a better layer of security because you can do Point to Point VPN, you can do IPsec, VPN, stuff like that already. Now let's talk about mstp mstp tried and true. Most people know how to use it. Pretty straightforward, pretty stupid, simple. It's got a lot going for it right? controllers are a little cheaper, the wire is pretty cheap, you just connect it to a supervisory device, you don't need a switch. So it's got some definite price benefits. It is reliable when properly set up. Your I've went to sites that had 1020 year installs. And they were running. They're running good because people actually numbered their MAC addresses sequentially kept their wires clean, good weren't t tap and weren't doing crazy things just follow the RS 485 standard. And it ran fast enough. Yes, it is a little slower when downloading initial firmware or downloading your programs. But when we're talking about read and write properties, which let's be honest, read and write properties is pretty much the only services we run with back net except for maybe a CSV service, then it's plenty fast. It's plenty fast. considering our poll times are normally a minute anyways, plenty fast update graphics. Speed of data reporting should not be your primary reason for going to bank that IP. mstp also has the ability to be troubleshot in my opinion pretty easily. There's only a handful of things that I can go wrong, and they're all usually electrical. Meaning that you can go and troubleshoot them with your meter and figure out most of what's going on without having to go into Wireshark. Without having to know how to read packet captures all sorts of stuff, you don't have to deal with it. That is a definite benefit, you don't have to deal with the IT group, you don't have to go and size switches, you don't have to wait for the FF and E budget to actually put switches in the building. So that you can commission You don't have to be carrying around industrial switches for temp switches, that way, you have, you know, a temporary switch, so you can commission the system, lot of benefits there. Now, let's get into the negatives BACnet mstp is slower, it is slower. And because it's mstp, because it's a layer two communication, it cannot go and communicate HTTP traffic. So you're not getting graphics over mstp not gonna be running SNMP traps over mstp, you're not gonna be doing the analytics, typically direct from the controller across mstp, you still collect the points in the supervisory device and run analytics, but you're not going to be doing it at the edge, which I mean, honestly doing analytics at the edge in the controller. And then like saying, Oh, well, there's so much traffic that we're going to do the analytics in the edge in the controller prior to sending it up, because that's like some big deal. Because somehow we haven't built computers that can process our miniscule amount of data that a building automation system produces. And let me be clear, even on the largest of large sites, VA s systems are miniscule in their data

Phil Zito 21:42
production, compared to other sites, that and other systems, let's just be real, we're talking about seconds, where we have changed value to minutes where we have changed the value. We're not talking nanoseconds, like stuff in the industrial world. Okay, a nother thing that we need to be clear about with negatives is going to be the fact that you do actually have to wire this stuff up, right, and that it has points of failure. Right? You can wire them up wrong, you can reverse polarity, you can go and Miss address stuff. You can go and not put dandelion in the right spot, you could do t taps, all sorts of stuff, it's kind of hard to do all that with IP, you can miss wire with IP, but you're not really going to miss address, and you're not going to do t taps and things like that. And then finally, we are losing the ability for security. Now, once again, I will argue that with mstp, if someone is up in your ceiling, hacking into your serial network with a rogue device, what is your real issue? Is it the lack of security at the mstp system? Or is it the lack of physical security that someone is literally in your ceiling or in your mechanical room breaking into your network, I would argue that you have a five sec problem, not a product problem. But it's easier to point the fingers and go and say that you have a product problem. It's just easier to do that plus it creates a problem to solve which means you've got to sell new hardware to fix that problem. You've got to go and say hey, you want BACnet secure Connect? Well guess what your controllers that are running it, they either are going to need this overlay gateway that we're going to sell you because your controllers can't be updated. Or you're going to have to update all your controllers so that they can support the firmware that runs at secure Connect. That's the only way you're going to do it. Can anyone say product sales? Yes. Repeat that with me product sales. Can you tell I'm a bit disappointed with BACnet Ms. s? c? Yes, I am. Alright. That being said, let's talk about my thoughts and my scenarios, because this is getting a little bit longer than our normal episodes. And I want to kind of close it up for you. My thoughts BACnet IP, definitely use it for central utility plants and major air handlers, especially if your controller line on the major air handlers has secondary mstp trunks and you can run that to the Associated v v boxes that are served by that air handler. That's a beautiful installation. It's kind of best of both worlds. And then you just pull those IP controllers from the air handlers. Ideally, those would be like a ring or a bus. I wouldn't do a star pattern on those. I do a ringer bus. And I would bring us unless it's critical then I would do a star pattern. And I would bring those to a switch right and then I would connect the supervisory devices switch and we'd map everything in IP and we call the day and then for the central utility plant I would do a star pattern. So direct end to end run from the switch to the central utility playing controller, that would be my approach, I would avoid terminal units, I would avoid fan coil units for IP controllers, it does not make sense to me to do those. And also, if you ever want to add someone else's controllers, everyone has an mstp line, not everyone has an IP line. So you can easily add mstp controllers, especially if you find some legacy controller somewhere. So that's my two cents. You don't have to agree with me. I encourage you not to agree with me. I'd like to know your thoughts. Why do you want to go and use BACnet IP over mstp What did I miss? What am I all wet on? So go to podcasts at smart buildings academy.com forward slash 280 once again that is podcast dot smart buildings khadem e comm forward slash 280. Let me know about what you think in regards to BACnet IP versus mstp. There you'll also find a link to our back net boot camp if you want to get up to speed on back net This is the best way for you to do that completely online completely fast and completely good. And also you can find my link to my back net SC episode, which got me a lot of heat, but I'm gonna always say what I think and like I said, don't believe it just because it comes from me. Question. Verify. Learn yourself and I look forward to talking to you on Wednesday. Take care

Phil Zito

Written by Phil Zito

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