Tutorial

Because ISDN is such a flexible service, you'll need to understand a few more components than you would with an Internet connection over your standard phone line. This tutorial provides help getting started with ISDN and more technical details about ISDN.

You can click on the diagram below for more information.

Types Of Equipment

ISDN requires different equipment than analog dial-up or even digital leased line service. To connect to the Internet, your equipment should include:

Network Termination Device 1 (NT1) and Power Supply

• Network Termination Device 1 (NT1)
  The NT1 is a simple device that serves as an interface between the ISDN BRI line and your other ISDN equipment. It converts the physical wiring interface delivered by Pacific Bell to the wiring interface needed by your ISDN equipment, and also provides a testing point for troubleshooting.

  Many ISDN terminal adapters and some ISDN routers (see below) have the NT1 function built-in. This makes for an easier installation and also reduces the total cost of your ISDN setup. However, a separate NT1 is more flexible in that it can support multiple ISDN devices.

• Power Supply
  The power supply plugs into a standard wall outlet and provides power to the ISDN line. Unlike a standard phone line, Pacific Bell does not provide the power on the ISDN line. For this reason, we recommend that customers consider keeping their analog phone service as insurance for use during emergency power outages.

ISDN Routers

These devices perform a function similar to that of a standard router. Using an ISDN router, multiple computers on a LAN can share a single ISDN BRI connection. Because ISDN routers use Ethernet connections (typically 10 Mbps), they can take full advantage of ISDN's speed. Many of the most popular ISDN routers also support analog voice, modem, or fax applications, as well as sophisticated network management capabilities. ISDN routers are typically more than twice as expensive as TAs, but they are often worth the money since they allow multiple computers on a small LAN to leverage your ISDN investment.

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Physical Interfaces

The ISDN standard defines several physical wiring interfaces, but most users only need to be familiar with one or two.

• U-Interface
  The U-interface is the 2-wire interface your phone company delivers for connection to the NT1. Many of the newer ISDN networking devices, such as the 3Com Impact, include a built-in internal NT-1 and power supply, so they can connect directly to the U-interface. Manufacturers may describe this feature as a "built-in NT-1" or simply as a U-Interface ISDN TA.

• S/T Interface
  The S/T-interface is the 4-wire interface between the NT1 and the ISDN networking equipment such as an ISDN TA or router. An S/T interface is used when the NT1 is a separate device.

• Other interfaces
  The interface between your ISDN networking equipment and your computer is usually one of the standard industry interfaces. For example, an External TA will use the computer's serial COM port such as RS232. ISDN routers will use a standard Ethernet connection, either directly to a computer's NIC card or via an intermediary Ethernet hub.

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Configuring your ISDN Line and Equipment

You will need the following information to program your ISDN equipment. Make sure that you receive this information when you order your ISDN line.

Switch Type

The "engines" of the ISDN phone network are the complex network switches which deliver the service. There are two dominant switches that provide ISDN: Lucent Technology's (formerly a part of AT&T) 5ESS and Northern Telecom's DMS100. While those two switches provide the same basic features and functionality, they differ in how they interact with your ISDN equipment. The DMS100 will also vary according to which software version is being used. It is important that you find out which switch type and which software version will be providing you with ISDN service, so you can order your ISDN service and set your ISDN networking equipment parameters correctly.

In Pacific Bell territory, the possible switches and software versions are:

• Lucent Technology (formerly a part of AT&T) 5ESS - Custom ISDN software
• Northern Telecom DMS100 - Custom ISDN software
• Northern Telecom DMS100 - NI1 (National ISDN version 1) software

ISDN Phone Number (Directory Number)

Your ISDN phone line will be assigned a phone number just like a standard phone line. However, depending on which kind of switch you are served from and how you are going to use the ISDN service, you may get one phone number per ISDN line or one phone number for each ISDN B-channel. It is important for you to define how you plan to use your ISDN line so Pacific Bell can assign the correct number of phone numbers.

• DMS100
  A DMS switch always assumes a multipoint configuration. If you are served from a DMS-100 switch, you should receive two phone numbers, one for each B-channel.

• 5ESS
  If you receive your ISDN service from a 5ESS switch, you need to choose either a "point-to-point" or "multipoint" configuration. If you only intend to connect a single device/application to your ISDN line, then you only need the point-to-point configuration. With the point-to-point configuration you are assigned a single phone number per ISDN line (not one for each B-channel). If you intend to connect multiple devices/applications, then you need the multipoint configuration. With multipoint configuration you are assigned a phone number for each device connected.

Service Profile Identifier (SPID)

A SPID is an additional identifier used to identify the ISDN device to the telephone network. A SPID looks like a telephone number with extra digits. However, depending on which kind of switch you are served from and how you are going to use the ISDN service, you may not need a SPID or you may need a SPID for each B-channel, or each device. It is important for you to define how you plan to use your ISDN line so Pacific Bell can assign the correct number of SPIDs.

• DMS100
  A DMS switch always assumes a multipoint configuration. If you are served from a DMS-100 switch, you should receive two SPIDs, one for each B-channel.

• 5ESS
  If you receive your ISDN service from a 5ESS switch, you need to choose either a "point-to-point" or "multipoint" configuration. If you only intend to connect a single device/application (such as the 3COM Impact) to your ISDN line, then you only need the point-to-point configuration and you are not assigned any SPIDs. If you intend to connect multiple devices/applications, then you need the multipoint configuration. For example, connecting the 3COM Impact's analog port to an analog phone would be a multipoint configuration. With the multipoint configuration you are assigned a SPID for each device connected.

Terminal Identifier (TID)

Specific to a National ISDN-1 BRI line from a DMS100 switch, is the need for a terminal identifier (TID). The TID is comprised of two additional digits used in conjunction with the SPID when initializing devices. The TID is intended for use on all non-initializing terminals. All terminals in use today are initializing terminals, and most do not require a specific TID. To minimize confusion, it is recommended that you use "00" on each terminal device, no matter how many terminal devices there are. For further clarification, you should check with your ISDN equipment vendor for their recommendation.

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Wiring your Location for ISDN

Inside Wiring

By regulation, Pacific Bell ISDN service ends at what is called the demarcation point ("demarc") usually just outside your residence or in an apartment building basement. You are responsible for the wiring from the demarcation point to your ISDN equipment including the wall jacks. You will want your ISDN phone jacks close to your ISDN equipment for the best performance. You can choose to have Pacific Bell install and maintain this "inside wiring" for an additional charge, or you can use an electrical contractor.

While some homes and offices may need to be re-wired for ISDN, most will not. The copper twisted pair wiring that currently provides standard analog phone service can be successfully used for ISDN. However, with the increasingly popularity of multiple lines you may not have spare wiring available for your ISDN service. Therefore, additional cabling may be necessary.

ISDN Phone Jacks

There are three types of jacks associated with ISDN. It is important to check your equipment documentation to verify which jacks you need and then order the correct jack. Most terminal adapters come with the necessary cabling to plug into regular RJ11 phone jacks.

• RJ11
  This is the standard analog phone jack, and is used to deliver 2-wire service. The phone company will often install this jack for ISDN unless otherwise requested. However, some NT1s required the wider RJ45 or SJA11C jack. The 3Com Impact phone cable has an RJ11 plug on one end to connect to a RJ11 wall jack.

• RJ45
  This jack is slightly wider than the RJ11, and has 8 pins but can still be used to deliver 2-wire service such as ISDN BRI. Again, some NT1s require this jack and their associated connecting cable with the RJ45 plug will not fit into an RJ11 jack. The 3Com Impact phone cable has an RJ45 plug on one end for the RJ45 jack on the back of the Impact unit itself.

• SJA11
  This is identical to the RJ45 jack, but is a non-regulated product and therefore is significantly less expensive than the RJ45. Specifically request this jack when ordering your ISDN service.

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