Why did you place the DSLAM at the cross-connect box rather than at the SLC (remote terminal)?

A visitor asks:

You connected your DSLAM right next to the cross-connect box. Could I use that same setup, except connecting a DSLAM directly to the SLC [remote terminal on Badger Road]? Or does it need to be the cross-connect box?

To be able to answer your question, one needs to know about the availability of spare pairs in various parts of the system, and about the availability of locations where to put the DSLAM.

If we choose to put the DSLAM somewhere, then we need to supply electric power to it. And we need to be able to put the DSLAM into a place where it won't get rained on. And we need the permission of whoever owns the land at that location, to put the DSLAM there.

In our case, the barn had the advantage that there was already electric power there. So we were able to plug it in. The barn also had the advantage that our Metropolitan District was willing to give us permission to put the DSLAM there, and was willing to let us use the electric power (72 watts) without paying for it. And the barn had plenty of room for the DSLAM and its cabinet, so that the DSLAM would not get rained on.

Many SLCs are "full," that is, they are already filled with equipment and there is no space in it for anything else such as a DSLAM. If your SLC were full, then you would have to find some other place to put the DSLAM. (Under most interconnect agreements, you could ask the ILEC to build another cabinet for you to house the DSLAM, but the price charged by the ILEC would likely be more than the price of a house.)

I suppose you might get lucky and there would be extra room in the SLC. (Supposedly, we are told, there is extra room in our SLC box.) Then you could put the DSLAM there. But with Qwest, as we understand it, such a move would have increased Qwest's demand for insurance by a factor of eleven. Instead of a ridiculous one-million-dollar insurance policy naming Qwest as beneficiary, Qwest would have demanded that we purchase a ridiculous eleven-million dollar policy naming Qwest as beneficiary. Instead of a thousand-dollar annual premium, we would have to pay an eleven-thousand-dollar annual premium. As we have only around twelve subscribers, this would mean an extra thousand dollars per subscriber per year that would have to be charged to subscribers. Maybe with another year of litigation against Qwest we could get that insurance demand knocked down to a tolerable level. It's not something we would enjoy.

A third approach would be to find some helpful nearby property owner who will provide a place to put the DSLAM, and run a cable from there to the SLC box. The pairs from the SLC box to the cross-box are called F1s. There would need to be a way to connect the DSLAM pairs to the F1s, what the telco would call a "cross-connect field." In our SLC box we are told there isn't room for a cross-connect field. We are told the F1s are spliced directly to line-card positions in the SLC box and that the splice vault space within the SLC box is already filled with splices. Thus it might be a challenge even working out how to splice pairs of the DSLAM cable into pairs of the F1s.

This third approach assumes that there is a nearby helpful property owner. And it assumes that electric power can be found at that nearby location. And it assumes that some structure exists, or can be built, to keep the DSLAM out of the rain. And the DSLAM will have some limits of ambient temperature. The structure that exists or is to be built would need to control the ambient temperature so that the DSLAM does not get too hot or too cold.

Still another issue (for some SLCs) would be the question of whether there would be spare F1s from the SLC box to the crossbox. In our case there are some 80 spares, definitely enough to carry DSL signals to our maximum number of sixty homes. But some some SLCs it might turn out that the number of spare F1s would not be enough to accommodate the number of homes.

Still another issue is how to get the connection-to-the-Internet-backbone (in our case, a frame relay T1 line) to the DSLAM. Whatever location you select for the DSLAM, you need to get the T1 to the DSLAM. This may be no problem for you, but for some people who are trying to set up DSL systems, it might turn out that it's not possible to get the T1 line to the desired location.

Still another issue is loop lengths. As you can see at http://www.coppermountain.com/library/datasheets/pdf/10101ds.pdf, loop lengths can affect the speed of the connection to a subscriber location. In our case, since we are using one of the ports of the DSLAM as our connection to our T1 line, we want that port to be as fast as possible.

Our longest loop from the crossbox to the most remote home (that is, our longest F2) is about 7600 feet of 24-gauge cable. As you can see from the SDSL spec sheet, this means we can pass a full T1 speed (1.54M bits per second) to that home (and to any nearer home).

But the F1s are each about 7000 feet long. So if we were to put the DSLAM at (or near) the SLC box rather than at the crossbox, we would be adding some 7000 feet to each loop. This would make the loops as long as 14,000 feet. Depending on wire gauges and other conditions (e.g. bridge taps) we could end up with data rates as slow as 384K.

A further problem is loading coils. We got lucky in that there are no loading coils anywhere in our F2s. There are, however, loading coils in some of our F1s. That would make the DSL impossible on such F1s unless we were to pay Qwest's exorbitant price for removal of loading coils.

Back to your original question. Could you put your DSLAM at your remote terminal (SLC) location? Yes, if the loops don't get too long, and if you can find electric power, and if you can get the T1 there, and if there are enough spare F1s, and if you can find space for splicing, and so on.