E

3

5

ISDN

Kinds of ISDN electrical interfaces

4

There are two interfaces an ISDN user needs to know about. The phone companies install a two-wire interface called a “U” interface. Many consumer devices connect directly to this interface, but you need to ask which interface it has. If you want to connect more than one device to your BRI, there are two solutions. If you want to use the BRI for voice and data, the simplest solution is to buy a data interface device that has Plain Old Telephone Service (POTS)/Analog ports on it. These devices, either Terminal Adapters (TAs) or Routers (see below for trade-off), can have an ordinary analog phone plugged into the back. The other solution is more costly, and requires a device (a Network Termination 1 or NT1) to convert the U interface into an S (four-wire) bus that multiple devices can connect to. The NT1 will cost about $100 and only ISDN phone sets (expensive) can plug into the S interface, so the first solution is the most cost effective. What you should take away from this section is that ISDN interfaces come in two flavors, and you have to know which you’re buying. You probably want to buy a U interface device, because it avoids the cost of a separate NT1, and if you want to use the BRI for calls as well as data, you need to buy a data device with POTS ports (usually 2). A U interface serves only one device, but that device can be used for data or two telephones if you buy the right kind.

Central office Switch

Network Termination 1 BRI U (2wire) Interface

BRI S/T (4 wire) Interface

Figure 5-1. U versus S/T BRI Interfaces

What else do you need to know about ISDN?

5

There are a lot of options for setting up a BRI line on the telephone company side. The best way to handle this is to know what BRI device you’re going to buy before you order the BRI line, and

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tell the phone company what it is when you order. They’ll know what to do. If they ask, make sure you get two numbers and two Service Point Identifiers (SPID’s). When they install the line, they’ll give you the phone numbers and the SPID’s. You may need both to set up your device, so keep them.

Types of devices used with ISDN

6

Four types of devices will typically be used in SOHO applications. All four are appropriate for a single device/single user situation. For more than one user or device use a BRI router, item 4. 1. External ISDN Terminal Adapters (TA’s), also known as “digital modems,” are a one-for-one replacement for modems. They connect to a the PC with a serial cable, like a modem, and are configured in the same way, including potential use of AT commands. TA manufacturers usually include a Microsoft® Windows interface to simplify configuration. They are subject to a maximum transfer rate set by the serial channel (115.2 kbps); furthermore, the use of start and stop bits on this line reduces raw throughput aside from compression to about 90 kbps. A few TA’s can do bandwidth on demand. 2. Internal TA’s or BRI boards bypass the serial channel and therefore may be able to use most of the raw 128 kbps available in an ISDN Basic Rate Interface. Some internal TAs are configured like modems, and some are configured like network interrface cards. 3. PCMCIA BRI cards are smaller and more convenient than external TAs, but are subject to the same bit rate limit as external TAs because of the internal use of the serial channel. 4. BRI routers connect to PCs and other devices via an Ethernet interface and either an Ethernet cross-over cable (for one device) or a small hub for more than one device. Many BRI routers currently offer bandwidth-on-demand (section 2.0 item 5), while only a few TA’s offer BWOD. An advantage of BRI routers in that they can support more devices without turning your PC into a router. A disadvantage is that they are somewhat more difficult to configure.

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ISDN service offered by AT&T VPN Service

7

The AT&T VPN Service ISDN offering is via AT&T Toll Free Multimedia service. Any login that works with Basic IP or Closed User Group will also work with the 800 service, as long as the login is presented in the correct style. For those using the AT&T client, a new version of the client will be required for ISDN access. The ISDN service can be accessed without the AT&T client by entering the correct 8XX number and the correct username and password in a standard client, e.g. Windows 95 dial-up networking. Scripting and post-dial windows cannot be used with our ISDN service. ISDN minutes will be charged at a higher rate than local modem access. Using the service with a BRI router requires specific configuration information that is different for each router. The router will have to support address translation so that it can use pool IP addresses assigned from AT&T. Routers that support address translation include Ascend Pipelines, Cisco 7XXs, Cisco 2503 (and any other IOS router), and the Netopia 630.

NOTE: As the present time, the AT&T VPN Service Proxy Radius Option is not available with the AT&T WorldNet VPN Service ISDN offering.

Ordering and configuring an ISDN device to connect to the AT&T VPN Service 8

The short answer is read the instructions that come with your device, but there are some general rules that apply to all devices. As described in the previous section there are two main categories of devices, Terminal Adapters and BRI routers. Terminal Adapters normally require installation of software on your PC and only connect one PC to the dial-up network. TA’s come in the three varieties described in the previous section, external (a.k.a. ISDN Modems), internal boards for desktop or tower PCs, and PCMCIA cards (a.k.a. PC cards) for laptops. The second category, ISDN BRI1 routers, connect to the PC (or multiple PCs) via a LAN, and route IP packets from the LAN to the BRI.2

1

BRI is short for Basic Rate Interface, the smaller of two ISDN line types, and the one a small user or Small Office/Home Office user will want.

2

Routers may come with software for convenient configuration of the router, but the software is not required for operation. Routers can be configured via a terminal port or telnet.

-3Virtual Private Network Service Company Point of Contact (CPOC) Guide 3.0 AT&T Proprietary

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Steps that apply to both TA’s and routers:

9

1. Select an ISDN device. If you haven’t ordered a device yet, decide which type of device is best for you. If you have only one PC to attach to the BRI, a TA will work well. If you have more than one PC you want to attach, consider a BRI router. Consult reviews of various devices and select one. If you decide on a BRI router, make sure you get one that can accept an assigned IP address from the ISP, not all do. If you are only going to attach one ISDN device to your line, get a product with a U interface (integrated NT1). It’s less expensive and simpler to install. 2. Order your BRI. If you haven’t ordered your BRI, order it after you have selected the device. Tell the telephone company order-taker the make and model of your device. ISDN Product Manuals often provide a section on the information required to provision your line. Many ISDN Vendors include an ISDN Ordering Code to provide to your telephone company. The code represents all of the necessary information for your device in configuring your ISDN line. If unsure about anything, check up on it before completing the order. If your device has an S interface, they may offer you an NT1 as an option. You probably want a device with a U interface in the US. If your device has an S interface, you will need an NT1. 3. Make sure you get your BRI line description. After the order is processed, the telephone company will schedule an ISDN installation date. Either before or during the installation you will receive information about your ISDN line that you need to configure your ISDN equipment; the phone numbers and SPIDs for the line (usually two of each), the switch type (5ESS, DMS, or Siemens), and the ISDN line type usually NI-1. If you complete steps 4 and 5 before the technician arrives, you can test the circuit with your equipment before the technician leaves. You will need the toll free number for AT&T VPN Service ISDN service to test the line. The number is 1-888-ATT-ISDN. 4. Install the configuration software that comes with the device. Follow directions that come with your device. Use instructions for connecting to an Internet Service Provider. The configuration software will include entries for your BRI telephone numbers, SPIDs, and switch manufacturer and/or ISDN line type (from previous step). 5. Connect the BRI to your device. Warning - Check port names, some connectors fit in more than one place on your device - damage might occur if you connect the BRI to the wrong port. After you set the BRI parameters (see your TA or router instructions to see how to do this) see if the BRI synchs up with the BRI line. For every device, there is both an LED indication and a software control panel indication as to whether the BRI has synched up with the device. See your instructions to see how to check for BRI sync, and what to do if it doesn’t sync up. If you can’t sync up, don’t go any further, nothing else will work. If your device does not sync up, first read instructions, then call your TA or router vendor’s help line. AT&T cannot debug your wires, BRI line, or device configuration. 6. Try a test call. If it does synch up, try a test call. Most devices have a test call option, usually the box uses one channel on your BRI to call the other. This tests everything you’ve done so far.

-4Virtual Private Network Service Company Point of Contact (CPOC) Guide 3.0 AT&T Proprietary

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7. Keep at it. Do not get frustrated, everybody has a few initial problems with BRI devices. The key is to use the debugging procedures that come with the product, and after those have been exhausted, use the vendor help lines. All BRI device vendors provide free support for BRI device setup. You paid for it when you bought the product. No one understands your device better than the vendor’s help personnel. 8. Set idle time out. Usually default time-outs are short, but select one that suits your needs. Failing to set the idle time-out may lead to excessive line-charges. 9. Use the correct login type. AT&T VPN Service Dial Network Tunneling logins do not work with AT&T VPN Service ISDN.3 Basic IP and CUG logins will work. ISDN does not have to be individually authorized, all Basic IP and Closed User Group/Dial Destination Restricted logins will work with ISDN, either with a TA or a router. Multilink PPP (using both channels on a BRI for one logical connection) only works with Closed User Group/Dial Destination Restricted logins; it will not work with Basic IP logins. Attempting Multilink PPP for Basic IP will delay connection. See table below. 10. Turn off Toll-miser or Data over Voice. these calls will be refused by AT&T. 11. Your Terminal adapter or router must be able to do CHAP. (Challenge Handshake Authentication Protocol) for authentication, and be set to do CHAP rather than PAP (Password Authentication Protocol). PAP authentication will not succeed. Login Type ê

Access Type è

Basic IP Closed User Group Dial Destination Restricted Tunneling

ISDN Synchronous PPP and V.120 Single channel Yes Yes

ISDN Synchronous PPP Multilink PPP (2 channels) No Yes

No

No

10

Additional suggestions for TAs, internal boards, and PCMCIA cards: 11

1. Turn off any protocols except IP and MP. If using Windows 95 Dial-Up Networking (DUN), unselect all settings under Properties-Servers except TCP/IP and Enable Software Compression.. If your TA supports compression directly, unselect Enable Software Compression as well. Extra protocols may slow down the connect process. Compressing twice (on the PC and the TA) will slow down transmission and not gain you anything. 2. Turn Multilink PPP on or off. - Multilink PPP (using both channels on a BRI for one logical connection) must be explicitly enabled on most devices, either by an at command string setting, or under Properties-Multilink for Windows 95 DUN 1.1 or 1.2. Your manual will tell you how to do it. Start with Multilink off and use it only after everything else works. Multilink PPP only works with Closed User Group/Dial Destination Restricted logins; it will not work with Basic IP logins. 3. Use the right AT&T client. - If you are using the AT&T client, you will need version 2.4.1 in order to support ISDN.

3

This results from a limitation of the protocols, not a limitation of AT&T WorldNet Virtual Private Network Service. Future tunneling options will address this limitation. You also may be able to use client to server tunneling options, and Network Address Translation, or router to router tunneling to solve the problems addressed by TCP tunneling (unregistered addresses and non-IP protocols).

-5Virtual Private Network Service Company Point of Contact (CPOC) Guide 3.0 AT&T Proprietary

AT&T PROPRIETARY

Additional suggestions for BRI routers:

12

1. The router must support and be configured for a downloaded (assigned) IP address. Follow instructions for using downloaded or assigned pool IP addresses. on BRI routers. On some routers this requires using a feature called Network Address Translation (Port Address Translation on Cisco 7XX). If this is not a choice, and you find no mention of using assigned or downloaded addresses, you may need an upgrade (or a different router). Consult your router vendor for upgrades and for instructions on how to configure your router to accept assigned IP addresses. 2. Set IP addresses on the PC(s) and router to be consistent. The PC(s) and BRI router must be using IP addresses on the same IP (sub)network, and the default gateway IP address on the PC(s) must be the router’s IP address. These addresses can be anything as far as AT&T is concerned, since the router is using address translation to convert these to the assigned pool IP address (see previous step), but your PC(s) and router must be consistent with each other. Make sure you can ping the router from the PC(s) and vice versa. 3. Turn off any protocols except IP and MP. Extra protocols will delay the connection setup, and won’t work anyway, unless you tunnel them through IP. 4. Turn off RIP. - Turn all forms of RIP off for the BRI connection. RIP will not help, and will keep the link up when otherwise idle, leading to excess connect charges. 5. Beware of unwanted connects. Windows 95 or NT using NETBIOS, also known as Client for Microsoft Networks, will bring up a router every 15 minutes to make NETBIOS and DNS name queries. To stop the calls either turn off the protocol or consult your router vendor for a filter that will prevent the calls. 6. Enter the correct 800 number. The number can be obtained from your company’s AT&T contact. 7. Set authentication type. Select CHAP as the authentication protocol if a choice is required. On Cisco devices, follow instructions for connecting to an ISP. The default authentication setting on Cisco devices is only correct when calling another Cisco device with two-way authentication; this setting must be changed to authenticate with AT&T services. See your device manual or quick-start instructions to see how to change this setting. 8. Turn Multilink PPP on or off. Multilink PPP (using both channels on a BRI for one logical connection) must be explicitly enabled on most devices. Multilink PPP only works with Closed User Group/Dial Destination Restricted logins; it will not work with Basic IP logins.

-6Virtual Private Network Service Company Point of Contact (CPOC) Guide 3.0 AT&T Proprietary

AT&T PROPRIETARY

Definition of Terms

13

B-Channels

Bearer channels, the two 64 kbps channels in a BRI (or the 23 or 30 in a PRI). Each one of these is the ISDN equivalent of a single voice channel.

BRI

Basic Rate Interface - the type of ISDN interface most people will get. Two 64 kbps channels plus a separate 16 kbps signaling channel. An existing analog line can generally be converted into a BRI without any rewiring.

BWOD

Bandwidth on demand - in the context of ISDN this means bringing 1 or 2 bearer channels up in response to demand, and dropping them when they are not needed.

D-Channel

The signaling channel in any ISDN line. It carries the information used for call setup and tear down, among other things.

DUN

Windows 95 Dial-up Networking

IP

Internet Protocol - the data protocol for the Internet (and lots of other places)

ISDN

Integrated Services Digital Network (integrated = voice + data)

LAN

Local area network - a way for a community of users to share data easily.

MP

Multilink Protocol - also called MPPP or MLPPP - protocol for using two B channels for one data transmission.

NT1

Network Termination 1 - converts U to S

PCMCIA

Credit card size peripherals for laptops, also called PC cards.

POTS

Plain old telephone service - jargon for analog phone service, the usual kind

PPP

Point-to-Point Protocol - used to set up a dial-up data connections - important parts are Authentication, IP Control Protocol, and Multilink Protocol

PRI

Primary Rate Interface - 23 or 30 B channels plus a 64 kbps D channel

S-Interface

The four wire interface - standard around the world. Pertains to ISDN.

SOHO

Small office / home office

SPID

Service Point Identifier - Used to direct calls to multiple devices on an S interface

TA

Terminal Adapter - The equivalent of a modem for ISDN – sometimes called a digital modem

U-Interface

The two wire interface installed by telephone companies - varies by country. Pertains to ISDN.

WWW

World Wide Web - also known as The Web - The world wide Internet

-7Virtual Private Network Service Company Point of Contact (CPOC) Guide 3.0 AT&T Proprietary