Part 2: Understanding Cellular Connectivity for Real Time Camera Streaming
Learn how bandwidth effects video quality, reliability, latency, and cost.
May 21, 2021
In my last article (Part 1) I laid out the considerations for cybersecurity as it relates to cellular connected IP cameras. In this article, I’m going to focus on bandwidth.
Bandwidth has a large impact on several factors, namely video quality, reliability, latency, and the biggest factor of all cost. Cost is such a big factor that I’m going to reserve that topic for my last article of this series. Because cost is directly related to data utilization and data utilization is directly related to bandwidth, there will be some overlap but I will try to keep that overlap to a minimum.
When we think of bandwidth we think in bits or bytes per second or the capacity of the internet connection we are using to push data through. How this translates to video is a matter of simple math. I’m not going to go into the gory details of this simple math but if you would like a refresher course, IPVM has a great breakdown of it here.
Upload vs. download speeds
The most common mistake is overlooking “upload” bandwidth capacity. When we think of internet speeds we often hear about the download speed. However, when connecting a camera to a cellular connection it is all about upload speeds. Most internet service providers will tune their services to cater to download speeds over upload speeds. This is often because most people are downloading content with minimal upload. Makes sense. Therefore, it is common to see download speeds above 100Mbps while upload speeds are less than 10Mbps.
Cellular is not immune to this bandwidth steering, but worse is the effect of radio frequency (RF) signals on cellular bandwidth (especially upload speeds). As a rule of thumb, the RF signal coming from the cell tower to the cell modem is going to be stronger than the signal from the cell modem back to the cell tower. Just because you have four bars of signal showing on your cellular modem doesn’t mean the tower is receiving four bars of signal back from the cellular modem. Speaking simplistically, download speeds will be faster because of this stronger RF signal than upload speeds. So, don’t be surprised if you have great download speeds but your upload speeds are poor.
The “multiplier effect”
The important thing to keep in mind as it relates to cameras transmitting data over cellular connections is what I like to call the “multiplier effect.” What is the “multiplier effect?” This is the subtle yet very impactful nuance that is often overlooked when multiple video streams can and often are pulled from a camera simultaneously. For example, if you have a camera that is recording to a Network Video Recorder (NVR), it is pulling a video stream from the camera. If a user is watching a live video stream, they too are pulling a video stream from the camera. You now have two video streams pulling from the camera simultaneously. If an additional user begins to watch a live video stream from the camera, you now have three simultaneous video streams coming from the camera. The more systems or people watching video from the camera, the more video streams are being pulled from the camera simultaneously. To illustrate the problem using math—if a single video stream is averaging 1Mbps per video stream and there are three people or systems consuming video streams, then you are consuming 3Mbps in bandwidth. Making matters worse—the data is sent in time slices that add more latency as more simultaneous streams need to be transmitted.
Now, some of you smart people out there may be yelling out, “Steve, that isn’t necessarily true because the cameras could be streaming multicast and not unicast, silly!” To that I would respond, “You’re right! These could be multicast streams.” However, multicast over internet connections are not a trivial setup and most people have no idea how to do it. Most likely they are not using multicast to stream their cameras. Instead, they are most likely using unicast over HTTP(S) directly from the camera or RTSP into a VMS system and/or VMS clients. So, simultaneous streams it is and the more a camera has to support the worse things are going to get for everyone.
Multiple cameras per cell modem
This should be assumed, but I will mention it just in case. Connecting multiple cameras to a single cellular modem behaves similar to the “multiplier effect” above. So, be just as careful streaming multiple cameras simultaneously if you need to connect multiple cameras to a single cellular modem.
“Stadium effect” cell tower congestion
Cell tower congestion has dashed the dreams of more cellular based camera streamers than Tom Brady did when he married Gisele Bündchen. Cell tower congestion is the unanticipated disrupter of cellular bandwidth and often comes without warning. Cell towers are engineered under the assumption that a limited number of cell phone users will be simultaneously connected to the tower at any given time. Often cellular users are driving in their cars or passing through as they travel through a geographical area a specific cell tower covers. However, when a large number of cell users are congregated around a single cell tower, let's say at a parade or a sporting event or even a traffic jam, the cell tower can be overloaded causing everyone’s cell service to essentially become inoperable.
Under these conditions there is little to nothing that can be done. If you are a first responder you have the option of signing up for an AT&T FirstNet account or Verizon Frontline account which has its own cellular RF frequency spectrum and data backhaul separate from the public networks the rest of us use. In some cases, only a specific carrier may be struggling with the congestion and if this is the case, a multi-carrier SIM option would allow you to switch to a different carrier when another carrier’s service becomes degraded. The key to this situation is controlling upload consumption and thereby ensuring that the camera(s) are transmitting as little data as possible (reducing resolution and framerate while spacing out I-frames and using variable bit rates).
Summary on bandwidth
In summary, there are many things to consider when thinking about the bandwidth required to livestream cameras over cellular networks. Things that you have control over and things that you don’t have control over. Utilizing a cloud-based VMS can help considerably with these issues by providing increased security, bandwidth management, and scale.
In Part 3 of “Understanding Cellular Connectivity for Real Time Camera Streaming,” I will cover the aspects of costs associated with cellular connected camera systems.