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The NT 4.0 ISDN Connection

How to get on the Internet ­fast

The number of Internet users and the complexity of accessible services are growing rapidly. With the growth of the Web and its increased functionality, the access speeds of conventional modems aren't meeting user needs. As an alternative, many users are turning to Integrated Services Digital Network (ISDN) for faster, more cost-effective Internet access.

To successfully use ISDN to connect NT Server and NT Workstation to the Internet, you need to understand ISDN and you need step-by-step instructions. I'll explain how to use the US Robotics Sportster ISDN 128K adapter (ISDN requires an adapter instead of a modem), and this information applies to most ISDN adapters that use Remote Access Service (RAS) as a connection mechanism. (For information on available ISDN adapters and more information on ISDN, see Dan Kegel's ISDN page at

ISDN Primer
ISDN provides a subscriber with three separate digital channels that are carried over a standard two-wire telephone cable. These channels are 2B+D, which means two 64Kilobits-per-second (Kbps) bearer (B) channels and one 16Kbps data (D) channel. The B channels usually carry user data, and the D channel ordinarily transmits and receives call setup and control information. Some equipment can bond the two B channels through a protocol such as Multilink Point-to-Point Protocol (MPPP) to form one 128Kbps channel. (For detailed information on ISDN, see Mel Beckman, "ISDN and Windows NT," January 1996, and John Enck, "ISDN to the Rescue (But Who Will Rescue You?)," May 1996.)

Before you call your local phone company to order an ISDN line, you must obtain the required line- configuration information from your adapter's manufacturer. (Call the manufacturer or check the adapter's users manual.) In most places, an ISDN line takes longer to install than a standard telephone line--one to two weeks is common.

You also need to contact your Internet Service Provider (ISP) to find out the ISDN access phone number, your login and password, the authentication type (i.e., Challenge Handshake Authentication Protocol--CHAP--or Password Authentication Protocol--PAP), and your Domain Name System (DNS) server's TCP/IP address. (Your ISP can assign you a different TCP/IP address each time you log on; otherwise, you need to ask for a preassigned TCP/IP address.)

After you install the ISDN line, you need some information from your local telephone company. You need the telephone number and Service Profile Identifier (SPID) numbers for each B channel. If your line has only one telephone number, you have only one SPID.

Installation and Configuration
The hardware installation is straightforward. Make sure you know which I/O addresses are available for your adapter card. You can use NT Diagnostics to view the I/O addresses in use.

The Sportster ISDN 128K adapter comes from the factory ready to use a software-configurable I/O address. For NT, you need to change this setting and manually select an I/O address by adding one or two jumpers to the adapter. Select an I/O address not in use--300, 320, or 340--and put your system back together. Now you're ready to configure the software.

RAS Installation: The first step is to install RAS. Make sure you configure TCP/IP as the protocol RAS will use to dial out. RAS won't let you complete the installation until you select a device. For the time being, set RAS for a modem because you haven't installed the ISDN card drivers. If you don't have a modem, skip autodetection and tell RAS you have a generic modem on COM1.

ISDN Card Driver Installation: You install the drivers for the ISDN card just as you do a network board. Select Control Panel, Networks, Adapters, and Add to see a list of network adapters. Place your driver disk in your floppy drive, and click Have Disk and OK. After you install the drivers, you enter the adapter's configuration information. The I/O address must match the adapter settings. Then select an available interrupt. NT Diagnostics can show you which interrupts are in use.

Next, you need to provide the ISDN line information. Select the appropriate ISDN switch type and the number of terminals (one terminal for each ISDN telephone number). Then, enter the ISDN phone numbers and their associated SPID numbers. After selecting OK, you'll see the RAS configuration screen. Click Add, and select one of the newly created ISDN devices, as you see in Screen 1. (Repeat this step if you have two ISDN phone numbers.) Then, keep clicking OK until a prompt asks you to reboot the server; select Reboot Now.

After the server reboots, you can use the Line Monitor tool that comes with the Sportster to check the status of the adapter. If the L1, L2, and L3 lights are green, the adapter is working properly. If L1 is red, NT isn't recognizing the ISDN adapter. If L2 is red, the ISDN line is either not plugged in to the adapter or not functioning. If L3 is red, the phone numbers and SPIDs in the adapter setup don't match the telephone company's configuration.

RAS Configuration: The next step is to configure RAS to dial your ISP. Select Dial-Up Networking, and create a new Phonebook entry. Enter a name for this entry, and select the Next button.

Screen 2 shows the Server screen, which provides three options: If you are connecting directly to the Internet, select the first option. To send your password as plain text, if that's the only method available or if you're not sure whether your ISP supports encrypted passwords, select the second option. If your ISP requires a terminal login or a preassigned address, select the third option.

Select Next, and enter your ISP's ISDN dial-up access phone number. Select Next to continue. If you selected the third option from the server screen (your ISP requires a terminal login or a preassigned address), you need to enter an IP address. If your ISP assigns a dynamic address, leave the IP address at, as in Screen 3. If your ISP gave you an address to use, enter it here. Next you need to provide your ISP's DNS server address. Then select Next and Finish.

Now you need to edit the Dial-Up Networking Phonebook entry you just created. Select More, and then select Edit entry and modem properties. On the Basic tab on the Dial using field, select an ISDN line. (To use both B channels bonded for a 128Kbps MPPP connection, set this field to Multiple Lines.)

On the Server tab are two options: Enable software compression and Enable PPP LCP Extension. Make sure these options are not selected for now. Also on the Server tab under TCP/IP settings, make sure Use default gateway on remote network is checked. (For information about default gateways, see Mark Minasi, "Unlock Your Gateway to the Internet," June 1996, and "Gateways Revisited," page 47.)

On the Script tab, select None if your ISP doesn't require a terminal login. If your ISP requires a terminal login, select Pop up a terminal window. You can automate your login later by choosing the third option on the server screen to run a script. Save your Phonebook entry changes.

Now you can try to connect to your ISP. Select Dial. A prompt will ask you to enter your login and password. Enter the name and password that your ISP gave you. If the remote system you are logging on to is not an NT system, leave the field for the domain name blank. After you click OK, the connection process will begin. If the login was unsuccessful, you may need to click Enable the PPP LCP Extensions in the Phonebook Server TCP/IP properties.

After you successfully connect to your ISP, you can run your favorite Internet application. Be prepared for a shocking increase in speed if you've been using a modem. Even one ISDN B channel can more than double the throughput of a 28.8Kbps modem.

Use NT as an IP Router
After you successfully connect NT to your ISP and access the Internet, you can configure NT as an Internet router. This capability is useful if you have workstations connected to your NT system and you want to let them access the Internet. (For more information about IP routers, see Mark Minasi, "NT Workstations Using an IP Router," May 1996.)

An ISP can require that you connect in various ways. One popular method is to give you a randomly assigned IP address when your NT system calls in and to provide addresses for your workstations. Suppose you have 14 workstations connected to your NT server. Your ISP might provide the addresses through with a subnet mask of

To connect in this manner, you have to configure TCP/IP on your server's network card using one of these 14 assigned addresses, for example, Make sure you assign the correct subnet mask (, and don't assign a default gateway. You also need to select Enable IP Forwarding on the Routing tab under Control Panel, Network, TCP/IP Properties and configure any other information, such as DNS servers (for more information about DNS, see Spyros Sakellariadis, "Configuring and Administering DNS," August 1996, and "Integrating and Administering DNS," September 1996) and domain name, from your ISP.

Now you need to add a new Registry entry. Run Registry Editor (regedt32. exe), and go to hkey_local_machine\system\currentcontrolset\services\rasarp\parameters. Select Add Value from the Edit menu to create a new value. Enter DisableOtherSrcPackets as the name of the value, and select a Data Type of dword. After selecting OK, enter 0 for the string value. Now the workstation packets will contain the correct source address after crossing the RAS connection from the NT machine.

Configure your workstations as if NT Server were a dedicated router. You need to use the addresses and subnet mask from your ISP to configure TCP/IP on each workstation. Each workstation must have a unique TCP/IP address. Configure the DNS servers and domain name the same way you did for NT Server. However, this time, instead of leaving the default gateway blank, enter the TCP/IP address you configured on NT Server ( in this example). For more information on configuring IP routers, see Ed Tittel and Mary Madden, "Easy Access to the Internet," July 1996.

Beware of Traffic Jams
As long as the server remains connected to the Internet, all your workstations will be able to access the Internet. Keep in mind though, that when several of your workstations access the Internet at the same time, the speed of the connection can drastically decrease.

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