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When you get started with automating your home, you quickly find out that many devices need a hub or bridge to function correctly. For example, the Philips Hue bulbs need a bridge, August Smart Locks need a different bridge, and some people also buy hubs like the SmartThings hub or the Vera hub.

There are lots of people who don't seem to be sure whether they need a hub when they start automating their home, but often the explanations aren't clear.

Why might I need a hub or bridge instead of just connecting all my devices straight to my home network?

For example, if I have some Philips Hue bulbs, an Amazon Echo and an ecobee3, how can I figure out if I need a hub? Is there a methodology that will help me to determine which hub is best?

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Technically, different devices will communicate using protocols that are not internet-based, protocols that are proprietary, and tied together with different administration tools.

The reality is, particularly in consumer IoT, that you are witnessing an important battle between vendors that have an interest in dominating the consumer IoT (or home automation) market. Vendors of chipsets will promote their chosen radio network, vendors of products will promote their management tools, and others will position themselves as the one hub to rule them all. People, and minnow tech companies, fed up with this try and promote standards, which often get co-opted by major players. You will see this where every 'standard' has an 'alliance' page, which is the source of their ability to produce a standard.

There is no single 'hub', as there is no single vendor. People need to commit to an ecosystem (or two) and hope for the best. In much the same way that people will commit to the Apple or Android mobile ecosystem, they will commit to a 'smart home' ecosystem. Samsung wants to be the 'Apple of IoT', so does Philips, so do many others.

While there are efforts to standardise, because of the frustrations that you are questioning, it is unlikely that any standard will emerge soon, and even more unlikely that it will be a truly open standard.

This answer may seem cynical, and more opinion than fact, but IoT is a new market with huge rewards for vendors that dominate. Current users of IoT are early adopters that will be frustrated while the battle of technology giants is played out. Understanding the current state of the market is important to adjust your expectations while evaluating the technology.

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Generally, you need a smart hub when some of your devices don't use Wi-Fi and can't communicate with your home network directly. Quite a lot of devices, especially sensors and actuators (like door locks and motors), use other protocols such as ZigBee, Z-Wave, Bluetooth and Thread, so they can't 'speak' directly with your Wi-Fi router. The hub acts as a translator, being able to communicate with both Wi-Fi networks and other protocols (almost always ZigBee and Z-Wave, but sometimes others too).

What's the difference between Wi-Fi and these other protocols?

Wi-Fi works well for applications where you're transmitting a lot of data, throughout your house. For example, if you're streaming a video across your house, you'll have no problems at all using Wi-Fi. But, as explained by Time, Wi-Fi isn't perfect for every use case:

"Wi-Fi is a whole-home network,” says Chris Coley, principle engineer and architect with Logitech. Primarily used for media streaming, browsing the web, and other data-heavy activities, it’s a high-bandwidth network that’s power-intensive — just watch how fast your laptop battery dies when you’re watching a video on Netflix.

Many smart home products eschew Wi-Fi-connectivity because it would require their devices to have a dedicated power source or a long-lasting battery.

It'd be very costly if every networked device in your home used Wi-Fi, and your shiny new LED bulbs might use even more power than old, incandescent light bulbs, so devices like this turn to other protocols, such as ZigBee or Z-Wave. Philips Hue bulbs, for example, use ZigBee, which is why the bridge is needed to 'translate' back to Wi-Fi so all the other devices can interface with it.

You can see how ZigBee and Bluetooth compare on page 51 of A Comparative Study of Wireless Protocols: Bluetooth, UWB, ZigBee, and Wi-Fi; in Figure 6, you can see that Wi-Fi consumes far less power per megabit. So, why don't we use Wi-Fi for everything? If you look at Figure 5, you can see that each Wi-Fi transmission uses far more power than ZigBee (Wi-Fi uses about 700mW, compared to ZigBee's power usage of less than 100mW).

For your light bulb, or thermostat, Wi-Fi doesn't make a lot of sense. If your device is just sending a few bytes worth of data (e.g. just a number), why waste loads of power on each transmission?

In short: Wi-Fi makes sense when you're sending large amounts of data across long distances. Your devices probably don't need to do that, so other protocols make far more sense.

What else do the hubs do?

Some hubs, like SmartThings, can run pre-programmed routines ('automations') and allow you to customise their behaviour. Often, devices provide IDEs or editors so that you can customise the rules.

You might be able to integrate with IFTTT with some hubs (particularly Wink and SmartThings), which might be the simplest way of linking services together if you're not able to program using your hubs.

Do I really need a hub?

This really depends on your personal setup. If all of your devices use Wi-Fi, then no, it's probably not necessary. One FAQ on Reddit has a concise explanation:

A close parallel can be drawn between a hub and a standard Wi-Fi router. In simple terms, both are boxes with radios and a little bit of smartness. Eventually, hubs and Wi-Fi routers may merge into one product (indeed, the Almond line of routers from Securify already do this), but currently most households will need to buy a hub because no other device in the house has the requisite radios to talk to the various switches and sensors. In addition, the hub must remain in the house so that automation can continue even when no person is there. This allows for presence simulation in “vacation mode” or pre-heating or pre-cooling the house before arrival.

In effect: lots of hubs don't just 'translate', they can also perform some processing and automate things that the manufacturer didn't provide by default. If you want the flexibility of customising how your devices work and interact, a hub is a great idea. If you're just planning to have a voice assistant (like a Google Home or Amazon Echo) and want to fetch the weather, there's probably no need just yet.

To figure out which hub you should pick, consider the following points:

  • Which protocols do your devices use?
    You should be able to search for hubs which are compatible with a specific protocol. For example, when I searched for "Z-Wave hubs", I found this list of products, so you can get some additional guidance.

  • Do your devices list specific integrations with a hub?
    For example, the ecobee3 specifically lists SmartThings and Wink as compatible; you should factor this into your decision.

  • Does the hub you're looking at allow you to automate things simply?
    Some hubs may use a programming language you're unfamiliar with. It's probably best to avoid them, otherwise you're stuck with a device you can't control!

So, if that was all too much to read:

  • Bridges generally just 'translate' from one protocol to another, and tend to only work with one device or manufacturer (e.g. the Hue bridge).

  • Hubs can both translate and run automation routines themselves, allowing your devices to interact in a more complex way.

  • For anything more complex than a trivial setup, you probably need a hub. Make sure you research to find out which one suits you!

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  • From this answer I can't quite figure out if those hubs act as Ethernet bridges simply transferring unmodified Ethernet frames from one medium to another, or if they act as IP routers, or maybe something entirely different. Does the packets exchanged with each individual device have Ethernet and/or IP headers?
    – kasperd
    Commented Feb 5, 2017 at 16:25
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    @kasperd: I believe it depends on the protocol. For example, 6LoWPAN, used by Thread, does allow direct forwarding to the Internet. For hubs like the SmartThings, I don't think that tends to be the case; instead, you send your commands to the hub, and the hub then converts that to the correct protocol (ZigBee, Z-Wave, etc) without directly forwarding any packets.
    – Aurora0001
    Commented Feb 5, 2017 at 16:29
  • @kasperd: That again depends on the protocol. You seem to know about the typical layered architecture of networking, so let me explain it this way: some of those protocols may be just different physical layers for standard Ethernet frames (similar to how WiFi is mostly compatible with the upper layers of Ethernet), then you'd just need a bridge, some may be completely different protocols which still transport IP, then you'd need a router, and some may be completely different protocols altogether, not based on Ethernet or IP, then you'd need a full-stack translation server.
    – Jörg W Mittag
    Commented Feb 5, 2017 at 21:07
  • E.g. I couldn't find anything in Z-Wave that indicates that it is using Ethernet or IP. And one protocol that is definitely not based on Ethernet or IP is X10. (Although technically speaking, any protocol that is not based on IP (the Internet Protocol) is not part of the Internet of Things, since it's not part of the Internet.)
    – Jörg W Mittag
    Commented Feb 5, 2017 at 21:08

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