How Much Bandwidth Do You Need?
Written by Doug Houseman
How can knowing what bandwidth you need help plan your backhaul network?
Bandwidth has been the limiting factor in what data we can retrieve from equipment in the field and how often it can be retrieved. Most deployed meters operate on a record every 30 seconds or 1 minute but aggregate that to 15 minute or 60-minute reads and send those reads 1 to 6 times a day. In many cases voltage and demand are not sent, even though they are measured, because of bandwidth issues. That was perfectly fine for a billing purpose, but not so good for operations, especially when we start to look at also metering rooftop (and other generation), vehicle chargers and responsive loads. Residential storage is another item to not only monitor but manage as well.
In a smart grid/smart city many items want bandwidth. But you may be asking: What is bandwidth and why do those things want it?
Bandwidth is the maximum rate of data transfer across a given path, including in this case the overhead that the network must move the data. Overhead can be space between packets of data, addressing headers, error correction information, routing inefficiencies and other items that take away from a network’s raw bandwidth. Bandwidth allows data to flow from the internet or a person’s phone or field device to wherever it needs to go. Too many devices asking for bandwidth can clog up a network with extra overhead and slow everything down. Sometimes, like traffic cameras, without enough bandwidth the system drops some data, and it may be lost forever.
Extra bandwidth can also help solve latency issues, by allowing traffic to clear faster, so that the network does not drop packets and must ask for retries, adding to the network overhead and potential congestion. By removing this overhead, latency issues are less likely to appear.
So, what are we monitoring?
- Water, natural gas, and electric meters are typically seen on every building.
- Decorative streetlights are typically 10-15 feet tall and are spaced every 30-45 feet.
- Some utilities are putting reclosers every mile and distributed capacitor banks, voltage regulators, and remotely monitored switches on about the same spacing.
- Electric Vehicle chargers can be on every streetlight or in every home, and rooftop solar has the potential to be on each and every roof.
But this won’t necessarily help you plan your network. Different devices are deployed in different fashions and can vary by region and country. Just using another city’s bandwidth plan may not be useful for your applications.
Now that bandwidth is defined, let’s look at some of the device classes and the bandwidth they require.
In rural areas, your may be asked to carry customer broadband on your network. The lowest requirement in the United States is 25 Megabits per second (Mbps) from the internet to the premise and 3 Mbps back to the internet. In Europe the broadband requirements are 100 Mbps download speed. It is not unusual for people to expect broadband to be 100 Mbps or even 2 gigabits per second (Gbps). In suburban locations the premise requirements may already be taken care of by another provider. In the residential areas of older cities, the rural requirements may again surface to support neighborhood needs.
Businesses can easily consume several Gbps each and are not the focus of this article. Typically, separate communications channels are used for businesses.
Video cameras have a lot of different device classes, with different resolutions and bandwidth requirements.
At the lowest end are black-and-white “steady-state” devices that only send differences between one frame and the next. They point in a single direction, don’t move and are of a low frame rate, typically 3 to 5 frames per second (typical video is 30). They have a bandwidth need of as little as 0.005 Mbps.
At the highest end are 4K (4,000 pixel) 32-bit color (millions of shades), 30 frames per second, full refresh cameras that need 25 megabits per second or more.
Typical “street” cameras are in the range of 2 Mbps (1K, 10 frames per second).
For rough calculations to define an initial network carrying video, 4 Mbps camera is reasonable. This can be adjusted up or down as needed.
Water meters are a low bandwidth user of the network, typically averaging less than 0.0002 Mbps per water meter.
Electric meters use more than water meters, but not much more. Residential meters can be assumed to use 0.001 Mbps, and large industrial meters tend to use 0.02 Mbps.
Reclosers and other distribution devices demand a bit more bandwidth, averaging 0.003 Mbps.
Substations depending on size and instrumentation can require up to 2 Mbps without physical security equipment and up to 20 Mbps with physical security equipment. The largest substations with the highest priority can require up to 200 Mbps during times of high alert.
Residential photovoltaics and storage use bandwidth at a rate similar to commercial meters at 0.01 Mbps.
Because of their different uses, smart streetlights range from less than 0.01 Mbps to as much as 40 Mbps. Components include security cameras (0.005 to 25 Mbps), sound detectors (0.01 Mbps), vehicle chargers (0.01 Mbps), LED billboards (0.1 Mbps), LED Help panels (1.0 Mbps), Wi-Fi hotspots (1.0 Mbps/up to typically 16 users), and traffic or crossing signals (0.003 Mbps).
When looking up bandwidth, do not assume the first number you find on the internet is accurate. Look at several sites and try to find at least two not associated with a vendor to get a reasonable number. Be conservative in your estimating. It is cheaper to put in more than is needed so there is room to grow than to put in just enough and find out what was installed is too little and what you have installed has to be replaced.
While the bandwidth of many devices is increasing, it may require replacing the version of the device you have in your backhaul network to achieve that higher bandwidth you need. Some devices can have compression algorithms applied to the data to reduce bandwidth needs, but never assume that you can make up for too little by running compression.
If installed well, your network infrastructure will probably last 15 to 30 years. In 1990, Digital Subscriber Lines (DSL) at 8 Mbps were fast, expensive, and seldom installed. Today no one wants them because they are too slow. Today the standard is at least 100 Mbps, and the demand for more bandwidth is growing. Smart Grid devices have seen bandwidth expectation grow by a factor of 8 since 1990 and will probably see that expansion again by 2050. Consider this growth per device and growth in numbers of devices when planning your network.
This article edited by Jorge Angarita
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