Digital Subscriber Line

An Overview of Wiring Requirements to Support Residential DSL Service

Digital Subscriber Line (DSL) refers to a set of technologies used to provide broadband services via the existing copper cable plant. One variation of DSL is Asymmetric Digital Subscriber Line or ADSL, which has become very popular for residential internet access. ADSL can provide a subscriber receive speed approaching 1.5 Mbps and transmit speeds between 160 and 640 Kbps, which is more than adequate for most internet access applications. While there are numerous other variations of DSL (CDSL, HDSL, IDSL, RADSL, SDSL, and VDSL), ADSL has become so well known to the general public that it is often referred to as simply DSL.

Just for Information
CDSL = Consumer DSL (A.K.A. DSL-lite - lower speeds than ADSL - I don't expect to see this offered by many providers.)
HDSL = High-bit-rate DSL (Full 1.5 Mbps in both directions - requires two wire pairs - Not common for residential use.)
HDSL-2 = Newer version of HDSL (Full 1.5 Mbps in both directions using only one pair - Not common for residential use.)
IDSL = ISDN-Like DSL (Version of SDSL operating at 144 Kbps to transport a ISDN BRI - 2 64K B-chnl + 1 16K D-chnl)
RADSL = Rate-Adaptive DSL (Transmit and receive speeds vary with application and capacity of the copper path - Not common for residential use.)
SDSL = Symmetric DSL (1.5 Mbps in both directions for limited distance, normally operated at 768 Kbps or lower - Not common for residential use.)
VDSL = Very High Speed DSL (Short copper tail for fiber optic service with speeds up to 52 Mbps - Not common for residential use.)
ADSL2+ = Improved version of ADSL supporting speeds up 24 Mbps to for short distances (~8K ft) - Being used for "Video over DSL".
VDSL2 = New version of VDSL - theoretically capable of very high speeds for very short distances - Being used for "Video over DSL".

When seeking advice about your residential DSL installation, ensure that the information you obtain applies to ADSL.
When "DSL" appears on the rest of this page, it always refers to ADSL.

DSL service can use the same copper path as an existing telephone line. Because they operate at drastically different frequencies, the DSL service and telephone line can use the same path simultaneously, as long as the two signals are separated properly. However, if the two frequency bands are not separated properly, telephones and other equipment such as modems and fax machines can interfere with the DSL service. Theoretically, DSL service itself should never interfere with the phone service, but the wiring and equipment added to support use of the line for DSL may become the source of phone service problems.

Splitter or Filters ?

Separating the DSL signal from the telephone service requires either a splitter in or near the NID or filters at each telephone device. Ideally, the DSL service provider will install a DSL splitter module inside the NID or in a separate enclosure next to the NID and run a new cable to the DSL modem location. But many service providers will avoid the cost of sending a technician to install a splitter and instead will provide filters as part of a "self installation kit." In addition to the DSL modem or router and the cables to connect it to the line and to your computer or LAN, these kits include a few filters (also known as "microfilters") for your phones. The kit may also include a few duplex adapters to so that you can use one jack for both the DSL connection and a voice connection or one filter for several voice connections. Of course, there will probably be an additional charge for the filters and adapters.

Using filters isolates the DSL service at each individual telephone jack, but the DSL signal is present on all the jacks. That's an additional physical connection for each telephone device. Interference on any phone jack may impact DSL speeds or could cause DSL to stop functioning entirely. Because the filters are connected to the line cord for each device, their connections are subject to damage by someone just tugging on a phone line cord and a single damaged filter connection could result in problems with both your DSL and telephone services. If you're willing to replace all of your telephone jacks, there are filters available mounted in faceplates that replace standard telephone jacks. The cost of a few of these will pay for a splitter. Using a splitter completely isolates the DSL service from the telephone line, so the DSL signal is not present at each telephone jack. A splitter also limits how many connection changes are required to complete your DSL installation and is not normally subject to incidental physical damage. DSL signal from a splitter is much more isolated from sources of interference, resulting in optimal DSL speeds.

If filters are used instead of a splitter, a maximum of five or six telephone devices with filters can be used before they begin to excessively degrade the DSL signal. Remember that "telephone devices" include answering machines, fax machines, and satellite/cable receivers with phone line connections. Don't forget modems - you'll want to keep dialup as a backup capability and may need a modem to connect to the remote access at your office. If you're looking at this page, I'd wager you have more than six telephone devices. Even if you can limit your installation to five or six telephone devices, you'll probably have to buy more filters than will be included in a self installation kit. The cost of just the additional filters would probably pay for a splitter.

A splitter is really a better solution because it allows you to connect the voice side to multiple jacks, normally does a better job of separating the data and voice bandwidth, and helps prevent cross-talk problems. A splitter requires a different cable/pair be used for the voice and data. However, if you use a DSL splitter, your existing inside wiring can be used for voice with very little change and without filters at each phone.

If you have an alarm system, installing a DSL splitter has an additional advantage. An alarm system will require either a special filter for the connection to the RJ 31X jack for the alarm system or a splitter to separate the DSL service from the telephone line before it goes to the RJ 31X jack for the alarm system. A splitter is the preferred option by most alarm system companies.

Splitter - Where and How

Hopefully, all the information above has convinced you to install a splitter for your DSL service.
Now you need to know where and how!

If you are lucky enough to have a splitter installed in or near your NID by your DSL service provider, your only concern is to establish a separate cable path to a jack at the DSL modem/router location. Browse though the following and determine your best option of how to arrange the wiring for your home.

Old "JK" quad cable does not meet the minimum specification for DSL. It doesn't really make a lot of sense to pay $30 or more per month for DSL service and suffer low speeds due to using low quality cable for your inside wiring. If you already have quad cable installed in your home, you can try running DSL on it, but you should expect significantly lower speeds than would be achieved with CAT3 or CAT5. I would highly recommend running CAT5 cable for the DSL data and only using the quad cable for your telephone jacks. If you choose to use quad cable for DSL, expect your DSL provider to blame it for any complaints about low speeds.

If you are installing new inside wiring or making significant changes to your existing wiring, I recommend using a star topology with cables terminating on a hub/junction device such as a 66 block. For any new cabling, I recommend using four-pair CAT5 cable. CAT3 would be acceptable for telephone and would actually meet the minimum specification for DSL, but the cost for CAT5 is not significantly higher and it is much better cable.

If you have a ring, bus, or hybrid topology, it is probably most practical to locate the splitter near the NID and simply run a new cable from the splitter to the DSL modem location. You can use a splitter in a separate exterior enclosure or you can use a less expensive splitter without an exterior enclosure located inside the house at a protected location where the cable coming from the NID can be accessed before it goes to any jacks.

If you have a star topology, you have several other options for the location and type of splitter to install. You could locate the splitter at the hub/junction point or you could locate the splitter near the modem/router. Either of these options allow you to use a less expensive splitter without an exterior enclosure.

Even if you have a star topology, if you have an alarm system, you may find it preferable to use a splitter located near the NID, so that you don't have to reconfigure the connections to the RJ 31X jack. It is probably a better option to run a new cable for DSL from the splitter to your hub/junction and cross-connect to the cable to your DSL modem/router location, or you could run a cable directly from the splitter to a jack at the DSL modem/router location. Trying to splice a cable from the DSL modem/router into a spare pair in the cable between the NID and the RJ 31X jack is probably not worth the effort since there is a good probability that the splice would reduce your DSL speed and could result in a fault prone connection to the alarm system and to your phones.

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