Why is my internet connection slowing down?

Latency is nothing more than the time it takes to get a reply. That's different than the speed of your connection.

Since electricity travels at roughly the speed of light, the time it takes to get a response in the most ideal set of circumstances would be:

• The time it takes to send a request packet at whatever your upload line speed is.

• ... plus the time it takes for the remote server to "act" on that request.

• ... plus the time it takes to send a response packet at whatever your download line speed is.

The problem is that there are typically several pieces of equipment between you and the remote server, and each must receive, act on, and then send the request or the response on to the next step in the communications chain.

In addition, those connections aren't just carrying your requests, but also the internet traffic for others, so even in the best situations there are minor delays added as your packet of data waits for other data to be transmitted along the same connection.

The most common cause for the kinds of slowdown you're describing is that one or more of the connections between devices in that chain is "full". By that I mean that there's more data wanting to be sent than that line has the ability to keep up with. In a case like that, the devices along the way often have to receive a packet, and then wait until the connection that the packet is supposed to go out on next has room.

So what causes one of these lines to be "full"?

This is where your neighbors come in. As I said, it's not just your data on those connections.

In the morning, it might be just you and a couple of other people surfing the net and doing things. The amount of data that you're sending and requesting is, for lack of a better term, "average", and within the capacity of you cable system's infrastructure to deliver relatively quickly.

In the evening, however, things get more crowded. More neighbors come home from work and start surfing, the kids are home from school and doing their homework or playing games online. Perhaps folks are downloading larger files like YouTube videos and the like. More people making more requests using more of your cable company's infrastructure.

In addition, the sheer volume of spam being transmitted around the internet contributes, and as of late, peer-to-peer file sharing networks are also having a significant impact on the network's ability to handle other traffic.

Somewhere "upstream" from your internet connection, one of the connections that connects you and your neighbors to the internet is saturated - it's trying to carry more traffic than it has capacity.

The result is significantly increased latency. In other words, things get slow.

As I understand it, this is more common with cable internet than it is with some of the alternatives. At the "head end" you mentioned the internet connection you share with your neighbors via your cable comes together with other neighbors connected to the same head end into a single network connection back to the cable company's office. How many neighbors? Who knows? How fast is the connection between the head end and the office? Again, we don't know, but it's most certainly not big enough to handle you and all of your neighbors trying to fully use the internet at once.

In fact, as I understand it, the reason that cable tends to suffer from this more so than some other technologies is that the choke point, be it the cable you share to the head end, or the head end's own connection back to the office, is "closer" to the average cable subscriber, and thus it takes less total traffic to cause congestion.

Naturally good ISPs are continually working to keep up and improve the capacity of their infrastructure, whatever the technology might be.

Since things seem to have gotten worse when the cable company played with the head end you're connected to, it's natural that suspicion would rest squarely there.

The problem is that I can't really see a way to convince the cable company of that.

I can sympathize with their position slightly. Of the speed complaints that they probably get, the vast majority are more than likely problems with individual computers and not the internet connection itself. Viruses, spyware, old systems, and "messy" systems all slow down - and many people blame the ISP. So it's natural that the ISP would respond by saying "it's not our problem" when 99% of the time they're exactly right.

In your case, assuming everything else is the same on your machine morning and evening (i.e. your machine is basically the same in terms of programs running and the like) the fact that evenings are slower than mornings is, to me, a large indication that the problem is not your machine but rather traffic congestion upstream with your ISP.

If I were in your shoes, I would start by recording internet speed test results periodically throughout the day for a few days. If they consistently show major differences between morning and evening, and particularly if the morning results are reasonable, then I would begin hounding the cable company.

Or I'd start looking at alternative ISPs.