Posting a reply here to @dproffer post in Zigbee Connectivity in my house sucks 😢 - #24 by dproffer (which perhaps went a little too much off on a tangent) as it so not to hijack the topic thread by @mombro even though the subject questions and problems posted there are also indirectly related so should be in his interest to read as well. Thought this discussion might fit better in this thread with the title “a random collection of Zigbee trivia”.
Firstly, I am not saying that Zigbee is an overall bad protocol, it does work very well for its intended purpose if you set it up correctl, and I have been promoting Zigbee devices to IoT beginners and those on a smaller budget for years because it does have a few benefits over other home automation wireless IoT protocols used for products; with those primarily that practically all Zigbee products made for home automation uses the same 2.4 GHz radio frequency spectrum throughout the world (making it possible to sell the same products worldwide), and the cheap price of Zigbee devices due to cost of the chips being inexpensive and include license fees (with even the certification fees and royalty rights to use the official trademarked Zigbee logo on products is not expensive).
Secondly, a little background is that Zigbee technology/protocol is relatively old compared to most other wireless IoT protocol standards so some of its limitations are due to that, (Zigbee was conceived in 1998, standardized in 2003, and Zigbee Pro which we use for home automation devices was finalized in 2007, but while the specification has it has been revised with extensions and improvements since then it is still backwards compatible so carries legacy burdens).
Thirdly, all wireless IoT protocols have common limitations, problems, and challenges that device product manufacturers and end-users need to accept or work around. They also all have some common benefits, like being wireless (which all in all usually makes for a simpler installation).
So if we limit the scope to only comparing Zigbee, Z-Wave, Thread, and Bluetooth as those are currently or will soon dominate the market then the fact is that Zigbee technology, protocol and gateway + device implementations do have several limitations, I like to highlight these important key points for example, which some other protocols share too but those have different implementations with ways to work around.
Disclaimer: I do not think that it is fair at all to compare Zigbee with Wi-Fi for many reasons, and I do not see those two as competing protocols as they are intended for very different purposes. WiFi is not low-power nor low-bandwidth/low-datarate like Zigbee, and in the case of home automation products those serving a single purpose while WiFi is used for general wireless networking), however, that is a whole separate discussion, but let us just say that Zigbee has many limitations/problem that WiFi does not, and the current WiFi specification can almost not be used for battery-operated products (at least not as well and not without large and expensive batteries). 802.15.4 (Zigbee/Thread) and Z-Wave radios also have very tight constraints on power and bandwidth compared to Wi-Fi. 802.15.4 (Zigbee/Thread) and Z-Wave were purposely designed with long battery life requirements and from the start meant to utilize mesh network.technology function to extend range and coverage.
Now to two major downsides to Zigbee and the major benefit of competing protocols for one of those:
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A Zigbee network can only have a single Zigbee Coordinator which not only means it is a SPOF (Single-Point-Of-Failure) but that is also the only point of ingress to the Zigbee gateway application layer which also means that all Zigbee communication messages must be routed to the same Zigbee Coordinator.
- Thread protocol allows you you have active-active Thread Border Routers so it does not have a SPOF, and you can have several Thread Border Routers on the same Thread network, allowing you to have multiple points of ingress.They do this by featuring a technique called TREL (Thread Radio Encapsulation Link) which can tunnel Thread traffic over other IP-based networks (i.e.LAN and WiFi) and load load-balanced the traffic between all your Thread Border Routers in your home. So you can spread Thread Border Routers around your house in a single Thread network for a rock-solid setup
- Z-Wave protocol does support multiple Z-Wave controllers on a single Z-Wave network, meaning that you can at least have two (or more) Z-Wave controllers on a single Z-Wave network to avoid SPOF, (though the Z-Wave JS implementation does not yet support adding a second Z-Wave controller on the same Z-Wave network). However you can only have one primary controller per network, but any second or third controller, etc. are “active-standby” mode so ready to take over if the primary controller should fail.
- Bluetooth Low Energy (BLE) devices do not normally support or use the available Bluetooth Mesh technology and there is no unified network standard for it between products from different manufacturers, but at least users can partially work around the SPOF and by using multiple ESPHome Bluetooth Proxy → https://esphome.io/components/bluetooth_proxy.html
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Radio propagation of Zigbee low-energy signals is poor because Zigbee’s higher 2.4 GHz frequency radio waves have a shorter wavelength which translates into less penetration depth and passed through building materials or other obstructions that absorb medium frequency spectrum better than lower frequency spectrum, (e.i. compared to Z-Wave which uses Sub-GHz low frequency ranges that are better at passing through building materials and other obstructions). (This is by the way also why 2.4 GHz Wi-Fi have a longer range than 5GHz Wi-Fi signals).
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This radio propagation problem is compounded to produce more packet losses when the signals are low-energy and low-bandwidth as the messages are very short for Zigbee communication, so if a message does not go through then it needs to be re-send which can cause issues with battery-life of other Zigbee devices on the network so is only done a few times, hence causing messages to newer reach its intended target, however this problem is meant to be solved with mesh networking but that does not work if the users does not have enough Zigbee Router devices.
- 2.4 GHz radio frequency range is also prone to more EMF/EMI/RMI interference than Sub-GHz radio frequencies because there are a lot of other existing standards that intentionally use the 2.4 GHz radio frequency range precisely because it can be used globally. For example; Wi-Fi, Bluetooth, Thread, ISM band devices, security cameras, video senders, mobile phones, cordless phones, baby monitors, amateur radio, utility meters, etc… And there are also many appliances and other electronics that are electronically noisy and unintentionally emit EMF/EMI/RMI interference in the 2.4 GHz radio frequency range, like for example; USB 3.x/4.x devices, Thunderbolt, microwave ovens, computers, power-supplies, etc.
- This is why the CSA (formerly Zigbee Alliance) and chip manufacturers began developing Sub-GHz Dual-Band IEEE 802.15.4 radio chips for Zigbee and Thread. Manufacturers of 802.15.4 radio chips have measured 2-3 times better range performance of Sub-GHz Zigbee in indoor and suburban environments compared to 2.4GHz on average. The reason that Sub-GHz Zigbee products have not been viable before is that they have previously not been able to make chips for global (but now they have managed to make Sub-GHz chips that can digitally tune radio frequencies from 779MHz to 928MHz a single product can be shipped worldwide and not have to make chips and products specific for different RF regions. The downside to Sub-GHz Zigbee is that it is limited to 20-40 kbit/s datarate compared to 250 kbit/s datarate at 2.4GHz before packet overhead, (actual data throughput will be even less, however, that is a non-issue for most IoT devices that are not meant to transfer audio or video). For reference see → Alliance’s Zigbee Sub-GHz – The Power of Reliable Zigbee Mesh - CSA-IOT and https://www.silabs.com/documents/public/white-papers/Key-Priorities-for-Sub-GHz-Wireless-Deployments.pdf
- Sub-GHz radios can also offer longer battery life as lower frequencies take less energy to transmit and less packed-loss means the message to not need to be re-sent.
- These are facts in the physics of radio waves so should not be disputed unless just like to argue.
Hopefully, these limitations is something that will be addressed in future Zigbee revisions, (we can at least hope that they sooner or later will add support for multiple Zigbee Coordinators + that Zigbee sub-GHz Dual-Band radio chips will become readily available at lower costs and start to become used in popular home automation products). But even if so then it might just be to little and to late now that both the Matter standard and the Thread protocol specifications are finally evolving faster and faster as more companies are seeing it and its future versions/revisions as a larger merging market for profit growth.
Anyway, I do believe that manufacturers of home automation products will still continue to make Zigbee 3.0 variants of their popular products for many more years to come but eventually, (because you can use the same hardware to make Thread variant and a Zigbee variant of the same product, as it takes only a little effort to make a different firmware build and separate certifications), but when the Matter specification offers feature parity and has surpassed Zigbee then I think that manufacturers will slowly abandon the manufacturing of Zigbee in favour only making Thread based products. My guess is that it will only take 3-years or so before some companies who previously made Zigbee products will not bother making a Zigbee variant when they make a Thead variant of a new product, (as it is more economical to only maintain a single firmware variant even if the effort two make two variants is low).
PS: Not going to be answering any replies to this for at least a few weeks as plan to stay away from distractions during the holidays, but replies should not be needs as these are not secrets but facts that anyone can find easily if just do some basic research on those most popular wireless IoT protocols.