Cable vs. DSL > That's utterly fascinating...

reply to floydb1982

Re: That's utterly fascinating...

I have to correct you here. I have been an engineer for both cable companies and DSL providers. The major difference, in fact the only difference, is the deliverance to the subscriber.


First, you are correct that cable companies still have distance limitations. Cable does not use two copper wires like DSL. Cable uses a coax cable and fiber optics, not twisted pair like the phone company, on the infrastructure. The hybrid network is what allows cable to provide service further out then DSL. Both DSL and cable use RF, and RF signal degrades. The rate of the decay in the signal is different for DSL and cable due to the differences in the cabling used to carry that signal. To boost this distance covered, most cable companies run fiber from the headend to the service area and then do the conversion to RF, thus negating the loss of signal quality due to distance. The trade off is that all cable modems in a given area utilize the same bandwidth in the cable plant. This is where plant design kicks in. The cable company needs to design the plant to support the numbers of subscribers at a given rate of speed. That process might include creating new nodes, or service areas, to limit the number of subscribers in any given grouping of equipment. What you need to understand is that the bandwidth available in the system is greater then the bandwidth available to any one subscriber, but not to all of them added together. This is what leads to the slow down in service when many users are online in an area and is a symptom of a service area that needs to be reengineered by the cable company.


Now, on to DSL. There are several major differences. First, every line in DSL is independent to the customer, as opposed to the shared service that cable uses. So, if you and your neighbor both order DSL his line is a distinctly separate line from his house to the CO then yours. It is also twisted pair all the way from the house to the CO. If there is a SLIC (fiber optic connection in phone wiring) DSL will not work. This inability to utilize fiber in the connection is what limits DSL’s distance. Physical medium is also a factor. The size of the cable used in telephony is smaller then that of the coax cable in cable service. This limits the frequencies that can be carried and/or the distance that you can carry these frequencies before they become to degraded to utilize. That is why the cable company uses the larger coax cable instead of twisted pair cable, more room to move more frequencies. Also, the nature of the service, where every line is independent, makes it more difficult to move the equipment closer to the subscriber. We introduce the term “wire mile” here. Just because you have phone lines to your house, and your neighbor has phone lines to his house, does not mean that those phone lines run the same way down the street. That is correct, over the years the phone company has run wires all over the place. So, you would have to rewire all the connections in an organized manner and essentially rebuild the phone telephone infrastructure.


The shared nature of the cable network is what in the end makes it more able to change and allow for newer technologies. There is less equipment, closer to the customer, and that makes it easier to provide these technologies that we all love. On the flip side, the independent nature of the phone system is what allows for your neighbor’s service to fail and yours to continue working. It is also what makes it more difficult to upgrade and allow for newer uses.

reply to knightmb

reply to kahunanull

Yes, both use fiber at different portions of their network. Cable companies get the fiber connection closer to the subscriber then the phone companies do though. The nature of the infrastructure allows for the cable companies to do so since they have less individual equipment impacted due to the architecure of a cable plant. Also, remote terminal is not the correct term in DSL. It is a DSLAM (digital subscriber line access multiplexer) and the DSLAMs are located in the CO of the telco. A CO is designed such that from the CO out to the subscriber is all twisted pair. This creates a huge difference in the distance that can be covered by the DSL signal. Since you cannot just up and rewire a whole city to add a CO, you cannot really reduce the "wire mile" from a CO to a residence without serious re-engineering of a telco line. In the cable world, you just add a new fiber run, and either add a new area of split an existing one. Far less change in cabling is needed to allow for new subscriber areas, or to reduce the size of any given subscriber area since all you need to add/change is the trunk run to the headend, not every single line to every subscribers house.

I understand the point that you were trying to make, and appreciate it. There are many advantages and disadvantages to both means of access, and I tried to point them out. I simply saw a few errors in the information and sought to correct them, while providing some additional information along the way.

reply to xygor

reply to kahunanull
I agree with some of what you have said but not all. Of course things may vary from region to region, state to state. From most of what I have heard... and from a friend or two on the East Coast the DSL on there is behind the curve. So that may account for some of the statements here.

Here in Cali (at least the area I live and work in) we have fiber to RT (SLAM) which is usually with in a mile (but can be as many as three to five miles) of the prem... if we are talking rural areas. We have a small farming community some eight miles outside of town which has fiber fed DSL. Ask them if they can get cable modem service. Or even cable TV service out there... or if they even want it.

In my area ComCast cable is behind... way behind. We are putting a huge hurt on them. Our 1536/384 DSL is $12.95 for the year with free equipment and free activation. And we have fiber to the RT feeding 75% of the people who are not within two miles of the CO. With only one area of town not yet covered by a SLAM (RT) int eh field.

DSL does not slow down at peak hour usage... that is the
internet. Cable on the other hand does. One conductor for an entire neighborhood. Not so with DSL.

We also have fiber to the prem for all new neighborhoods. Each house has 37mb per fiber to the prem. One fiber at the RT feeds twelve houses. Try that with cable. Only downfall so far is it is newer technology and some bugs are still present on occasion.

We are even rolling out fiber to the NOD here and hopefully will begin offering the major networks to our fiber to the prem customers soon.

I get the new at&t Yahoo elite package for $27.95 (plus taxes). Which is 6016/768. No slower speeds during peak usage. No faster speeds when the neighbors finally go to bed. I get over 600 kbps if the download server can handle it.

Though I am not knocking cable. I would have it in a heart beat if DSL wasn't available. :P

reply to kahunanull
Remote Terminal is the correct term. BellSouth uses a Central Office and Remote Terminals. Remote Terminals are 2-3 miles away from the CO. The Remote Terminals are nothing more than a box that contains a DSLAM. There is one that is 1 mile from my house, and it serves our area...if you are a BellSouth customer, which I am not anymore.
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