Tag Archives: chokepoint

Is Jitter the Problem?

Most people assume that when they have broadband issues they don’t have fast enough broadband speeds. But in many cases, problems are caused by high jitter and latency. Today, I’m looking at the impact of  jitter.

What is Jitter? Jitter happens when incoming data packets are delayed and don’t show up at the expected time or in the expected order. When data is transmitted over the Internet it is broken into small packets. A typical packet is approximately 1,000 bytes or 0.001 megabytes. This means a lot of packets are sent to your home computer for even basic web transactions.

Packets are created at the location originates a web signal. This might be a site that is streaming a video, sending a file, completing a voice over IP call, or letting you shop online. The packets are sent in the order that the original data stream is encoded. Each packet takes a separate path across the Internet. Some packets arrive quickly, while others are delayed for some reason. Measuring jitter means measuring the degree to which packets end up at your computer late or in the wrong order.

Why Does Jitter Matter? Jitter matters the most when you are receiving packets for a real-time transaction like a streaming video, a Zoom call, a voice over IP call, or a video connection with a classroom. Your home computer is going to do its best to deliver the transmissions on time, even if all the packets haven’t arrived. You’ll notice missing packets of data as pixelation or fuzziness in a video, or as poor sound quality on a voice call. If enough packets are late, you might drop a VoIP call or get kicked out of a Zoom session.

Jitter doesn’t matter as much for other kinds of data. Most people are not concerned if it takes slightly longer to download a data file or to receive an email. These transactions don’t show up as received on your computer until all (or mostly all) of the packets have been received.

What Causes Jitter? The primary cause of jitter is network congestion. This happens when places in the network between the sender and the receiver are sent more data packets than can be processed in real time.

Bandwidth constraints can occur anywhere in a network where there is a possibility of overloading the capacity of the electronics. The industry uses the word chokepoint to describe any place where data can be restricted. On an incoming data transmission, an ISP might not have enough bandwidth on the incoming backbone connection. Every piece of ISP network gear that routes traffic within an ISP network is a potential chokepoint – a common chokepoint is where data is handed off to a neighborhood. The final chokepoint is at the home if data is coming in faster than the home broadband connection can handle it.

A common cause of overloaded chokepoints is old or inadequate hardware. An ISP might have outdated or too-small switches in the network. The most common chokepoints at homes are outdated WiFi modems or older computers that can’t handle the volume of incoming data.

One of the biggest problems with network chokepoints is that any time that an electronics chokepoint gets too busy, packets can be dropped or lost. When that happens, your home computer or your ISP will request the missing packets be sent again. The higher the jitter, the more packets that are lost and must be sent multiple times, and the greater the total amount of data being sent through the network. With older and slower technologies like DSL, the network can get paralyzed if failed packets accumulate to the point of overwhelming the technology.

Contrary to popular belief, faster speeds don’t reduce jitter, and can actually increase it. If you have an old inadequate WiFi modem and upgrade to a faster technology like fiber, the WiFi model will be even more overwhelmed than it was with a slower bandwidth technology. The best solution to lowering jitter is for ISPs and customers to replace equipment that causes chokepoints. Fiber technology isn’t better just because it’s faster – it also includes technology that move packets quickly through chokepoints.

What’s the Truth About Netflix?

Polk County SignClearly a lot of customers around the country are having trouble with NetFlix. The latest round of finger pointing is going on between Verizon, Netflix and some intermediate transport providers.

Netflix uses adaptive streaming for its standard quality video and this only requires about 2 Mbps at the customer end to get the quality that Netflix intends for the video. HD videos require more bandwidth, but customers are complaining about standard video. A Netflix download requires a burst of data up front so that the movie can load ahead of the customer. But after that it stays steady at the 2 Mbps rate and the download even pauses when the customer pauses. It’s getting hard to find an urban ISP that doesn’t deliver at least that much speed, so one would assume that any customer who subscribes to at least 2 Mbps data speeds should not to be having trouble watching Netflix.

But they are. On their blog Verizon talks about a customer who has a 75 Mbps product and who was not getting good Netflix quality. On that blog Verizon says that it checked every bit of its own network for possible choke points and found none. For those not familiar with how networks operate, a choke point is any place in a network where the amount of data traffic passing through could be larger than the capacity at the choke point. In most networks there are generally several potential chokepoints between a customer and the outside world. In this blog Verizon swears that there is nothing in its network for this particular customer that would cause the slowdown. They claim that the only thing running slow is Netflix.

This is not to say that there are no overloaded chokepoints anywhere in Verizon networks. It’s a big company and with the growth of demand for data they are bound to have choke points pop up – every network does. But one would think that their fiber FiOS network would have few chokepoints and so it’s fairly easy to believe Verizon in this instance.

Verizon goes on to say that the problem with this Los Angeles customer is either Netflix or the transit providers who are carrying Netflix traffic to Verizon. Verizon is not the only one who thinks it’s the transit interface between the networks. Here is a long article from Peter Sevcik of NetForecast Inc. that shows what happened to the Netflix traffic at numerous carriers both before and after Netflix started peering directly with Comcast. This data shows that traffic got better for everybody else immediately upon the Comcast transition, which certainly indicates that the problem is somewhere in the transit between Netflix and the ISPs.

Verizon says the problem is that Netflix, or the intermediate carriers don’t want to buy enough bandwidth to eliminate chokepoints. Sounds like a reasonable explanation for the troubles, right? But then Dave Schaffer, the CEO of Cogent came forward and pointed the finger back at Verizon. He says that the problem is indeed in the interface between Cogent and Verizon. But Schaffer claims this is Verizon’s fault since they won’t turn up additional ports to relieve the traffic pressure.

So now we are back to square one. The problem is clearly in the interface between Verizon and carriers like Cogent. But they are blaming each other publicly. And none of us outside of this squabble are going to know the truth. Very likely this is a tug-of-war over money, and that would fall in line with complaints made by Level3, who says that Verizon is holding traffic hostage to extract more money from the transit carriers.

The FCC is looking into this and it will be interesting to see what they find. It wouldn’t be surprising if there is a little blame on both sides, which is often the case when network issues devolve into money issues. Carriers don’t always act altruistically and sometimes these kinds of fights almost seem personal at the higher levels of the respective companies. The shame from a network perspective is that a handful of good technicians could solve this problem in a few hours. But in this case even the technicians at Verizon and the transit carriers might not know the truth about the situation.