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Cable Modems Technology Overview

Another long Editorial by Thomas (Bouncer) Blakely
2000-05-25 (updated: 2014-08-17) by

(Get some coffee, you're gonna need it.. Go to the bathroom. This is going to  be loooong. Get me a donut while yer up.)

A couple of months ago, I posted an "xDSL Opinion" (in the Cable/DSL Forum) which talked about xDSL service, and it's marketing. I didn't pull a lot of punches, and got some people pretty darn mad.

Today, it's cable's turn.

Why is it, that cable modem service seems so unreliable, in both bandwidth, and actual experience? Why do some people get great experiences and lots of bandwidth, while others have truly horrid experiences and bandwidth that could be better described as a trickle?

The answer is kinda simple and kinda complex, so let's take a minute, and start at the beginning.

Your cable TV works, because each channel in the line, has it's own frequency. Channel two might be two megahertz, channel three three megahertz, and so on. (This is a simplistic explanation, but makes the point). An analogy, might be the travel lanes on a highway. A three lane highway, would give you three channels. Make sense? Now imagine sixty lanes. So what if I took a couple of those lanes, and dedicated them to data flow up and down?

Introducing the cable modem. In short, the cable modem takes certain frequencies (lanes) from the cable spectrum (highway), and sends and receives data using those frequencies.

The primary problem, is NOT the technology, which is sheer genius, but rather the application of it on a local basis.

Standby for a LOT of background info. It's unavoidable. Sorry.

Now Cable companies, are in the business of selling you TV. Data access, is something they don't really want to futz around with. It's not that cost effective for them to try and do it all themselves on a local basis. Think about it for a minute. Going into the ISP business is NOT cheap. Not only do you have to buy your own multiple broadband connections, but also a 24 hour X 365 day support staff, a Network Operations Center, and lots of expensive routers, switches, servers and other gear. It's LOTS more cost efficient to simply let someone else do all that, and split the profits, right?

As a consequence, local cable companies usually contract to one of a couple (@Home and RoadRunner are two of the largest) of Internet Service Providers (ISPs), who supply some of the equipment and broadband connections and take care of all the network issues. The local cable company is responsible for local cable support, installation issues, and that's about it. From their perspective, it's very cost efficient. The primary cable runs are already there, and this is simply a new way of generating revenue off of them. Remember as well, that these runs tend to be permanent fixtures, so while it might be expensive to run a new line to your house, that line might stay in place for DECADES. It's long term cost effective to run that line. Plus they might start offering other services (like phone service) over those lines as well one again, it's cost justified for future expansion purposes. Finally, they have an excuse to get the cable into your house, so you might as well sign up for 500 channels for 60 bucks a month right? MARKETING, people. It's here to stay. :)

The problem though, is this. Local cable companies, because they AREN'T really responsible for much beyond the physical connections, don't have any real motivation to do more than jam as many people as they can into one node or area. They can do this, because network traffic is generally "bursty". I'll spend over an hour writing all this, but the amount of time it'll take to upload will be less than a second. So no one user is likely to be using most of the bandwidth at any given time. It therefore makes good economic sense to get lots of people on one headend connection. The more people they can pack in, the greater their profit margin. In addition, the local cable company frequently doesn't have their own network operations center, and honestly has little or no real idea how the network with THEIR NAME on it is performing.

As well, almost ALL cable Companies are regulated monopolies, because your local government doesn't want cable running all over the place with no way to track who is responsible for what, as well as other regulatory reasons. (In most places, cable access is treated more as a utility than as a don't see competing sewer or power lines, now do you?) So there's only ONE option for the user, and that's the local monopoly.

Okay, whew, that's a lot of background info. But I had to tell you all that, to tell you this. :)

Let's take a look at why there's such a diversity in cable modem performance.

We have a situation, where you effectively have a HUGE PRIVATE LAN/WAN, with multiple sub-groups each being run by some local contractor. This sub-contractor frequently has no direct responsibility or ability to react to local network problems besides cable cuts etc. In short, local physical problems.

In the case of RoadRunner, for instance, Network Operations / Administration is run out of Tampa, Florida. Their presence extends all the way to Richmond, VA where I live and beyond. This means that even though I have a local cable company who's name is on the service, all the real admin and monitoring is being done over a thousand miles away from me. That's a long distance, and a lot of places where problems can occur. But wait, there's more. Many of these cable companies are interconnected, so it's not as if I go directly from Richmond to Tampa. I go through multiple other franchises and links, some of which might be owned by Smitty and Co. in Backwoodsville, who are using two overworked hamsters to power their entire system. I have to go through all of this before I ever hit the backbone links to the internet.

The problem starts to take shape then. The local cable company has the area franchise, and has sold or contracted data access to @home or RR, or whomever; you, the user, are stuck with the local connection equipment being operated and maintained by people who have no direct interest in whether or not it runs well. More to the point, the cable company has experience in TV operations, and not data operations. You are also connected to other possibly independent cable operations who might have even LESS interest than your local company in this whole data business stuff.

As a result, we see headend systems (where all the cable modems come together at their side of the local connection) that aren't even plugged into UPSs! This was a KNOWN condition in at least one headend facility. It's absolutely unthinkable for any normal ISP to run their primary equipment without redundant protected power supplies. But this kind of thing IS happening with cable modem access.

In this case, what can happen then, is every time there's a power blip, all the headend gear loses power for a split second, faster than you can blink. This causes it to reboot or more accurately, "recycle". When the devices recycle, all the users are cut off. Some of them come back, some don't, and the phone calls start pouring in. To the support center. Located in another state. Which has no IDEA what the problem REALLY is.

Another example from real life: Until very recently ALL the cable modem authentication for one particular service EVERYWHERE IN THE US was being handled by a SINGLE server. When that server recycles or has a problem, this can affect TENS OF THOUSANDS of users simultaneously.

Again the calls pour in, tying up the lines. Frustrated users vent on poor tech support staff. The staff (many of whom are pretty woefully undertrained and WAY overworked) has to begin walking them through the baby steps of troubleshooting, because the little book they were handed with their logo'd shirt says they must do this. I feel bad for these people, because they ARE overworked, ARE underpaid, and ARE receiving the full anger of hundreds or thousands of people daily. AND they have no REAL way of telling what the problem is OR solving it. I'd be a pepto-bismal freak after one week of that.

In any case, the server has gone down, and has begun rebooting. They've walked ten thousand people through the "illustrated cartoon book o' troubleshooting". By this time, the server has finished rebooting. All those modems have re-authenticated. However, the tech support has the user reboot their machine, and they're back on the network without ANYONE having a CLUE as to what the real long term problem is.

This cycle repeats itself, over, and over, and over.

In sum, the real problem is NOT the technology. It's simply that most local cable company franchises do not have the staff or possibly even the equipment to support a network that has their name plastered all over it, and are interconnected to some other operators who could best be described as "fly-by-night". This problem will continue to grow and get worse until open access is mandated.

I can hear people groaning already about AOLers flocking onto their system. Just think about it for a second though, before you start calling for me to be summarily executed with a large pointy stick.

Open access means that multiple ISPs can be at the cable headend, and puts competitive pressure on the local cable co's to hire some of their own, LOCAL network support staff. It also means that the cable company, if they desire, can get more or less completely out of the ISP business (which many don't want to be in in the first place), and simply be the medium supplier. Leaving the choice up to the USER as to which service they want to subscribe to. It also means that more infrastructure will be invested in at the headend, which means most probably less users per node per service. It means in many cases a, faster, more direct connection to the internet backbones. With lower latency, and higher throughput. It will be a more complex set up at the headend facility, but in the end, I believe it will be worth it.

I would also remind people that xDSL as a technology has been around for DECADES, but it wasn't until the open access for phone service was mandated that you started to see xDSL for residential service. Before that, ISDN was pretty much ALL you could get, and it was tres' expensive! Because the local TelCo had a monopoly on the line, and no interest in spending money provisioning equipment and lines in order to bring you a better service when they could sell you an expensive service they already had equipment for.

Open access, boys and girls, has been VERY good for the consumer there. It's also brought in scammers and snake-oil companies, but the net effect has been positive.

I want to stress a couple of things very clearly near the end of this lengthy opinion piece. One, I am NOT against cable modem access. I use it myself. Two, I have NOTHING against RoadRunner or @home as ISPs. I think they both catch the brunt of what may legitimately be local problems. Three, there are many fine, diligent cable companies out there that DO try and pay attention to what's going on.

However, in the end, until we have more options, we're stuck in a situation where we have centralized management but regional implementation. Kinda like trying to run Ford Germany from Michigan. It simply doesn't work as well as it could by instituting management closer to the actual physical operations sites. There's NO way around that. Open access is going to mean more ISPs, and more users. But it'll also mean more redundant connections, and more options for the consumer. That is a good thing.

As always, your mileage may vary. This is a general overview, and not meant to be specific to your cable franchise or area. Trying to do THAT, would turn this long winded piece into an epic. :)


Thomas (Bouncer) Blakely, CCNA, CCDA

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