Section 4

ISDN to Multiple Target Rooms, New Wiring

4.0 Introduction

Providing ISDN service to more than one target room will require new wiring. With the exception of multiple rooms, some of the basic requirements involved with a new wiring application are mentioned in Section 3. It is recommended that Section 3 be read first, before proceeding into this section. This will aid the reader in understanding new wiring concepts.

The wiring method recommended in this section is based on EIA/TIA-570. As previously mentioned in Section 3, adding new wire carries an expense. However, adhering to EIA/TIA standards will help ensure added value and less likelihood of troubleshooting cable faults (see Section 3, paragraph 3.1 for a summary of wiring standards). New wiring in the home (old or new) will support future needs such as POTS, 10BaseT, alarm systems, etc. Once the new wiring is in place, with the correct distribution device installed, the customer can choose the target rooms which will have ISDN service. If changes are required later, then the versatility exists for the customer to move the ISDN Terminal Equipment from one location to another with ease.


4.1 Requirements

This wiring configuration requires the following components:

€ Four pair (8 wire) UTP cable, Category 3 cable or better.

€ A distribution device that provides at least 4 pair cable input and several outputs per input cable. The number of outputs will depend on your ISDN service requirements or the number of rooms to be cabled for ISDN ( refer to Section 1.A.2.4 for detailed information regarding distribution devices).

€ 8 position Modular Jacks that conform to T568A or T568B standards, and are rated Category 3 or better. The standard recommends matching the cable and jack categories, however a category 3 jack used with a higher category cable will provide improved performance for ISDN over a category 3 cable and allows for easier system upgrade.

NOTE: Polarity integrity must be maintained on the S/T Interface wiring. The terminal equipment will not operate if there is incorrect polarity or pair reversal.


4.2 Star Configuration

When multiple service outlets are "home run" to a centralized distribution point, the configuration is referred to as "star wiring" (see Figure 1.A.11b). The actual term for this is an ISDN Passive Bus (also referred to as Branched Multipoint) using a star configuration. The Star Configuration allows the NT1 to be placed in a central location with the termination of individual cable runs. Unlike POTS wiring, ISDN wiring is subject to certain considerations and sometimes limitations. These considerations or limitations apply to the multiple target room scenario, therefore the following rules are recommended for installation of this wiring scheme:

€ a maximum of 3 or 4 Active Service Outlets (depending on the equipment manufacturer's recommendations). There is no limit on the total number of Connected Service Outlets. A Connected Service Outlet is an outlet that is wired to the distribution device but not necessarily connected to the NT1. An Active Service Outlet is a Connected Service Outlet that is wired to the NT1.

€ a maximum branch length of 295 feet

€ 50 ohm termination at the NT1

€ no termination on the Terminal Equipment

4.3 Task - Locate the NT1 and Distribution Device

The NT1 should be centrally located in order to minimize the length of both Active and Connected Service Outlets. The distance from the NT1 to the Demarc connected point is not critical.

Also remember that the NT1 will require an external power supply to operate. Keep in mind that an electrical outlet should be near the placement of the NT1, assuming you are using the local powering method. Once the NT1 has been located, the distribution device should be collocated within 10 feet.

This figure illustrates an NT1 centrally located, with all cable runs being routed to the same location. With the use of this distribution method, ISDN service can be moved from one target room to another. Currently the figure shows ISDN service connected to bedroom one, den and bonus rooms.

4.4 Task - Wire the Service Outlets

Install 4 pair cable from the Distribution Device to each Service Outlet. Terminate all 4 pairs on a modular jack that conforms to T568A or T568B standards (8 pins w/8 conductors). Be sure to use the same standard on all jacks. The jacks should have the same Category rating (or better) than the cable being used. Once these jacks have been installed, they should be labeled "ISDN S/T" to prevent accidental connection (Refer to section 1.B for wiring jacks).

4.5 Task - Select a Powering Method

ISDN terminal equipment requires power for operation. There are different methods for powering which will differ according to the application. See section 1.C ISDN Powering Considerations for detailed information.

€ Local Power - Some terminal equipment and NT1s may come with a local power supply. This is a power supply co-located with the device utilizing that supply. See figure 1.C.5.

€ Remote Power - Remote power, also referred to as Central Bulk Power is a power supply which is found in an alternate location, other than where the NT1 or terminal equipment is located (see figure 1.C.6). For example, a power supply co-located with the terminal equipment can provide power to a remotely located NT1 on pins 7 and 8 of the S/T interface. See section 1.C.6.5.

€ Distributed Power - Distributed power is defined as any combination of local and remote power sources. The terminal equipment may or may not be co-located with the NT1. See section 1.C.4.

4.6 Task - Connect Your ISDN Service

Verify that the service provider has connected and activated your ISDN service. The service provider may have identified the connection points for ISDN on the Demarc device. The identification will often be a notation of the phone number(s) assigned to your ISDN line next to one of the Demarc connecting points. Connect the ISDN pair from the NT1 to the connecting points of the Demarc identified for your ISDN service. Be sure the pigtail (if one exists) for the ISDN Demarc is plugged in.
Caution should be observed when at the Demarc. Please refer to Section 1.A Appendix A.

4.7 Task - Connect Your NT1

Proper selection of NT1 timing and terminating resistors are very important for satisfactory ISDN service. For the wiring configuration recommended in this section, option the NT1 so that it provides a 50 ohm termination resistance. This 50 ohm termination can be provided in many ways depending upon the design of the NT1; some vendors provide a 50 ohm terminating resistor, others may provide a combination of terminators that achieves a 50 ohm termination. See the manufacturer's instructions for proper optioning of your equipment.

If your NT1 has an option for fixed or adaptive timing, use the default timing option. See the manufacturer's instructions for additional optioning information of your equipment.

Plug the NT1 power supply into a wall outlet and follow the instructions provided to you from the manufacturer. Depending on the power configuration you've chosen, this task will be more involved for power verification, (e.g. remote powering using "Back Feed" method). You may need another modular cord to connect the power supply to the NT1 (some manufacturer's provide the necessary cables). Again, consult the power supply and NT1 instructions on the type of cable and where it should be connected. Once the NT1 is connected to the power supply, you may notice indicators lighting to show the NT1 and ISDN line status (see manufacturer's operation manual).

4.8 Task - Connect Your ISDN Terminal Equipment

Connect the ISDN terminal equipment directly to the ISDN service outlets unless local power is required. The instructions for your ISDN TE will provide information on cables, power supplies, and (possible) terminating resistor options. In the wiring configuration discussed here, the proper option for terminating resistors in your ISDN TE is "off or none". Use the straight through 8 pin modular cord provided with your TE to connect to the NT1 (if one is not provided, see section 1.A.2.6). Program your ISDN TE with the appropriate parameters (e.g. DNs, SPID, etc.) following the manufacturer's instructions. Certain parameters (e.g., DNs, SPID) are provided by your service provider. You should now be able to make a call from your ISDN TE.


4.9 Task - Troubleshooting

If your ISDN service is not working, you may need to troubleshoot your configuration:

- Is everything plugged in as it is supposed to be?
- Do status indicators on your ISDN equipment appear OK?
- Is your ISDN set programmed with a SPID(s) and other required parameters?
- Are the terminating resistors optioned correctly in the NT1 (50 ohms) and the ISDN set (off or none)?
- Does your ISDN equipment pass its own self test?
- Is the problem eliminated if you connect your ISDN equipment (NT1 plus ISDN set) directly into the Demarc? If it is, recheck your in house wiring.

4.9.1 Troubleshooting - Verify In-House Wiring

If your service appears to operate properly at the Demarc, but a problem still exists at the service outlets, then you should verify your in-house wiring. ISDN S/T interface wiring is polarity sensitive.

Step 1 - If the distribution device is not co-located with the Demarc, connect the NT1 and TE at the distribution device, to verify the wiring between the distribution device and the Demarc.

Step 2 - Leave the NT1 connected at the distribution device. Connect the TE to each of the active service outlets to verify the wiring between the distribution device and each active service outlet. For service outlets that fail this step, first verify that they are cross connected at the Demarc. Then check wiring continuity as shown in Figure 4.3.


The above figure shows a simple way to test for continuity on suspect cable pairs. A craftsperson may have other tools or test equipment designed specifically for the troubleshooting application.


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Copyright 1996 - 2001 by AHK & Associates, Inc

Saturday, December 22, 2001