What’s the issue with streaming capacity today?

Congestion in the ISP CORE NETWORK is the short answer.

Today, the idea of "television" has changed dramatically. Rather than receiving over-the-air (OTA) signals or even signals through a set-top box (STB), a good portion of television transmission has moved to the Internet. Recent data shows that by 2025, global internet traffic is expected to surpass 1200 Tbps, mainly driven by video streaming, which accounts for over 80% of all online traffic. But the "digitization" of television isn't the only difference. Broadcast works through multicast. That is, there is one signal that everyone "tunes" into. Streaming, though, works through unicast. That is, each person is provided their own stream which is a massive duplication of data.

To understand how this creates a capacity problem, you have to understand network capacity. There are three parts of the network for delivering content. The first mile, from the internet backbone to the ISP network, isn't usually an issue as the content is usually handed off to the ISP network by a CDN that is peered with the ISP in a Peering Fabric. Then, there is the middle mile. This is where the congestion really gets bad. All of those duplicative bits are backhauled by the ISP from the peering point to the end-user. So, the ISP's network gets jam packed with data which competes with all of their other data for services like phone, conferencing, etc. Finally, there's the last mile. This is from the edge of the ISP network to the subscriber's house. While there can be lots of capacity here (such as multi-gig fiber), it's not always consistent so it can add to the congestion issue.

So, there are two fundamental issues that impact the capacity available for streaming. First, is the method by which television is streamed (unicast) which fills up the middle mile of the ISP and makes everything run slower. This can increase the time it takes for a video to start playing or the number of buffering events, amongst other problems that can contribute to a poor viewing experience. Second is caching in the ISP network. While commercial CDNs help tremendously to avoid any first-mile issues (most commercial CDNs operate their own, private networks), the ISP still has to fetch it from the CDN caches (which are peered, so they are very close). If there were caches in the ISP network, really popular content might be available without having to backhaul it through the network. Still, for live events, even caches are of little help. Thankfully, really big content providers like Netflix and YouTube have worked out relationships with the big ISPs around the world to host their private CDN caches so at least the ISP doesn't have to backhaul their unicast content.

Unless the ISPs spend their own money to increase middle-mile capacity and install caches in their network, capacity for streaming is inherently limited. The problem with that? Demand for streaming is only getting greater. More people are watching higher bitrate content. Just consider what's required. For an HD stream, that might be 1.5Mbps to 3.0Mbps. For a 4K stream, that might increase to 15Mbps. And for VR? It might be even double. Traditional prime time viewing is now at the mercy of internet infrastructure as more people turn to streaming platforms to access their favorite shows and live events. And this problem is exacerbated by regional events where a spike in viewers, say for an exciting end to a sporting match, might overrun the network.