WAN Equipment

Ownership: the two parties

I'm not going to talk too much about the equipment that we have been covering and that you're already very familiar with. Instead, there are a few other topics that I want to cover. One of the things is ownership. There's some equipment that a business would own, and there's some equipment that the internet service provider would own, and there's a point at which the business needs to maintain the internal infrastructure and the internet service provider maintains the other part of this infrastructure.

There are really two parties involved here. One of them is the company, or subscriber — that's the entity or party that's paying for the services. Then there's the service provider, the one who is providing the services, the company that's providing the services.

Now, if this company is paying for an internet connection, the service provider is what's known as an ISP, or internet service provider. But that's not the only scenario here. A company could be paying for a connection between two of its sites. It could be a factory and the headquarters, or headquarters and a branch office, or possibly between two branch offices. They're going to pay for a service to connect these two different sites, or pay for an internet connection.

Defining responsibility

So we have the service provider and the company or subscriber. Now with this, we have to define who's responsible for what. When something goes wrong, we need to say, well, that's your responsibility, or that's our responsibility. There needs to be a defined ownership of what one entity is going to be in charge of and what the other entity is in charge of.

As an example, the company has an internal infrastructure, cables running through their building, through their network, and the internet service provider really has no access to that, has no real idea what that network looks like, and so that's the company's responsibility. Same thing with the internet service provider: it has a network, and lots of networks, this service provider network that it has, that creates all these different connections. So this service provider has this different network that it's obviously in charge of.

The demarcation point

But the problem is there's this gray area in between of, well, what is the responsibility of the subscriber and what is the responsibility of the service provider, and that is where this demarcation point comes into play. The demarcation point is the point at which it says this service provider is in charge of all of this side of the network, and the company or subscriber is in charge of all of this side of the network.

It could be as simple as just a little jack that is inside the network closet. A lot of these companies will have some sort of network closet, or some sort of what's called an MDF, a main distribution frame, and within there then there would be just a little jack, and that could be what you connect into. Or maybe it's a switch — it could look different — but a lot of them are just a little jack. Everything on one side is the responsibility of the service provider, everything on the other side is the company or subscriber.

This actual network box right here, you can actually find this on your home too. So if you go onto your home, there's a demarcation point, and anything from that point inside your house, that's all your responsibility, and from outside of the house, then that's the company's responsibility. In fact, there's a little special connection that you can open up to break the connection between the two different networks and plug in equipment right directly into there. What the service provider will do, if you're having connectivity issues, is they'll plug into that jack right there, they'll see if there's an issue right there at that jack. If there is an issue, they'll say it's our responsibility, we'll figure it out, we'll fix it. If there's no issue up to that point, then they'll say, well, this is ours, our side of this is working just fine, so it must be something on your side. So that's the point of demarcation.

CPE, DTE, DCE and the local loop

Anything that's on the left side here is the customer premises equipment, so any equipment that you have on that side is called the CPE, customer premise equipment. Then you have a data terminal equipment and a data communication equipment. An example of the data termination equipment is this router; a data communication equipment is this modem that we have right here.

Then we have the local loop. The local loop is that connection from that demarcation point to the central office. We also can call this the last mile. There's lots of discussions and lots of technologies with this last mile, and it can be very expensive. Although there's a huge cost to this backbone network, to the service provider network — there's a huge cost to that — but it's shared amongst thousands or hundreds of thousands or millions of subscribers here, so the cost per subscriber is actually pretty low. But to do this to every individual home or every individual company or every individual subscriber can be very expensive. So there is lots of discussion around this local loop, or this last mile.

That is a little bit about the ownership, with who's responsible for the different pieces of equipment and different components of this connectivity.

What runs across the local loop

Now, the service provider is going to provide your service to this demarcation point through the local loop, and that local loop could be a cable that comes into your home from a cable company, it could be fiber optics that comes into your home, it could be the public switch telephone network cables, copper cables, that are coming into your home or your business or whatever the subscriber is. So that is coming into the subscriber, the place where you are that the service provider is providing the service to.

It is some sort of media, and it has some sort of protocols, layer one protocols, that it's going to need to communicate across there, and so that layer one needs to make establishment between the service provider and the subscriber. So that's where this data communication equipment comes into play. It's going to provide some sort of timing, where it's going to communicate across this media using whatever signaling goes across that. And the key to this is it's layer one here that's going across this local loop right here. So the data communication equipment makes that connection and establishes that connection.

An example of this would be a voice band modem, so like a dial-up modem, a DSL or cable modem, a CSU/DSU, some sort of optical converter. So that is going to be what sits here on the customer premise, this data communication equipment.

Then you have a data termination equipment, and that's going to be like your router, so that's a layer 3 right there. Your router will take that functionality.

All-in-one devices and bridge mode

Now, in a lot of these cases, like for a home network, sometimes the service provider will provide you with a modem slash router slash wireless access point slash switch. It's all in one, you just plug it in, so this DTE and DCE is all wrapped up into one device and you don't need to worry about it. But there are times when we actually go out and buy a separate modem, we put it onto our network, and this DCE then is a separate piece of equipment, and then we need to set up our router to carry the layer 2 and up signaling between these. So the DCE will make the connection and then pass off the layer 2 and above to this router right here.

An example of that would be, let's say you have a DSL connection and you set up a DSL modem, and then you get into that DSL modem, because a lot of them have router functionalities, and you say, I don't want you to carry on the router functionalities, I want you to actually do point-to-point over ethernet and pass this off to the router. Go into what's called bridge mode and pass this off to the router, and the router will take care of it.

Now, there are some times I've seen where people will take that and not make that connection, not pass it off to their home router, and so now they're doing double routing, and it can cause some issues and some latency problems if you do this double routing. So you have to go into that DSL modem and say, I want to go into bridge mode and pass this on to my router, because I purchased a separate router.

The central office

One thing that I haven't mentioned here yet is this is called the central office. The central office is where, like the public switch telephone networks, the cables actually come into the central office, and then that's where all of those get terminated on the other side.

So that is some of the equipment that you will see for your different companies, for the different subscribers, and even for your homes. When it comes down to equipment, there's certain equipment that's owned by the subscriber, and then there's certain equipment that's owned by the service provider. So we just have to understand the difference between the two, and that there is a point at which the ownership takes place: if there's a problem, the service provider should take care of it, and then on the other side of that, if there's a problem, then the company or the subscriber should take care of it.