ISDN

Low cost, high-speed data communications

ISDN (Integrated Services Digital Network) is a high-quality, switched digital communications service that gives your standard phone line the ability to transmit voice, data, and packet data simultaneously at a relatively low-cost. With ISDN, you can have multiple digital channels over your phone jack. There are two types of ISDN service: Basic Rate Interface (BRI), which is good for small businesses, and Primary Rate Interface (PRI) for larger businesses.

ISDN provides:

• Integrated access - One connection can be used for multiple services, multiple devices, and multiple destinations.
• End-to-end digital connections - ISDN gives you digital speed from start to finish.
• Standard interfaces - Standard interfaces ensure easy installation.
• Message-oriented signaling - ISDN won't distort or lose your information like analog data transmission.
• Customer control - With ISDN, you can dynamically specify what voice, video, and data services you want to use

Benefits
Applications
How It Works
ISDN BRI
ISDN PRI
Equipment
Availability
Ordering

Benefits
ISDN brings you a wide range of benefits, including:

• Reduced Network Management/Maintenance-uses the public switched network for voice, data and packet switching
• Communications Cost Savings-Reduced retransmissions over analog dial-up, saving time and money
• Easy Network Connectivity and Expansion-Bandwidth-on-demand and Expanded availability to support growing digital data applications
• Flexibility-Widely available dial-up services for voice and data
• Low Cost-Usage is charged at standard business voice rates for voice and data transmission.

Applications
ISDN supports the following applications:

• Internet access
• Video
• LAN/WAN interconnectivity
• EDI
• High-resolution imaging
• Private line backup
• Telecommuting host access

For Internet Service Providers, ISDN PRI (AT&T Enhanced Multipath Service) can provide a high-speed link between our central office switch and your ISP access server. Using the dial-up capabilities of ISDN PRI and the public network, you can connect a large number of remote users to an access server in a very cost-effective manner. And when your remote users dial in from several adjacent local-calling areas, this capability really becomes important. By placing your ISDN PRI connection in a central location, your users can dial in with just a local call.

How It Works
A regular telephone line transmits analog signals over copper wires. ISDN uses multi-channel protocol to combine separate data signals together on one digital facility so that they can be decoded at their destination. Since the line is digital, it's easier to keep out noise and interference. ISDN adds capabilities you won't find in standard phone service. Instead of sending a ring voltage (analog) signal to your phone, it sends a digital package that tells you who's calling, what type of call it is (voice or data), and what number was dialed (if multiple numbers, such as fax, are used for a single line). ISDN phone equipment can then decide how to answer the call, and if it's a data call, it makes the connection instantaneously, so you don't have to wait a long time for large graphics files to download.

Both BRI and PRI use channels called "B" or Bearer channels and a "D" or Delta channel. The B channels provide a transmission path for user information, such as voice and data, while the D Channel carries signaling information, such as call setup and packet data. Each B channel is a 64 Kbps clear channel connection. With BRI, the D channel is a 16 Kbps packet channel that is used to send and receive call set-up and signaling messages to the terminal equipment. The D channel with PRI is 64 Kbps.

ISDN BRI
ISDN BRI is known as Digital Enhancer in AT&T Connecticut. ISDN BRI is known as DigiLine Service^SM in Missouri, Texas, Oklahoma, Arkansas, and Kansas. ISDN BRI is known as ISDN Direct in Illinois, Indiana, Michigan, Ohio, and Wisconsin. ISDN BRI is known as Business ISDN in California and Nevada.

ISDN BRI gives you an affordable yet reliable form of high-speed, digital data communications. If you have a wide range of data transmission needs, AT&T ISDN BRI service will give you a low-cost way to transmit high-speed data and high-quality voice over a single telephone line at the same time.

ISDN BRI converts your regular telephone wires into three signaling channels. Two 64 Kbps Bearer (B) channels each carry user information (voice and data), while one 16 Kbps Data (D) channel carries call set-up and signaling information, giving you a maximum capability of 144 Kbps. The D Channel also enables X.25 packet applications such as credit card authorizations, automatic teller machine transactions and other short bursty messages that would needlessly tie up a connection over the regular circuit-switched network. The two B channels can be combined in one call for high-bandwidth applications such as Internet access and videoconferencing, for a total of 128 Kbps bandwidth.

ISDN PRI
AT&T Connecticut markets it's PRI service as Enhanced Multipath Service. ISDN PRI provides 24 individually controlled, software-defined channels for your voice, data, and video communications. Each channel has a 64 Kbps capacity, enabling a total transmission speed of up to 1.54 Mbps. ISDN PRI is served over a DS1, DS3, or SONET transport facility for flexibility and scalability. Out-of-band signaling allows you to carry 20% - 30% more traffic than analog trunks. And call setup is quick compared to analog trunks, for extra efficiency. With ISDN PRI, you can predefine the number of channels used for specific types of calls. So whether it's voice, data, or video, ISDN PRI can help maximize your network's efficiency.

ISDN-PRI provides you with:

• Channels that can be used for voice, video, or data on a call by call basis
• Clearer transmission of your voice communications
• Faster connects and disconnects, which save time and money
• Flexible trunk assignments for incoming and outgoing calls
• The same capacity over fewer trunks
• Higher bandwidth, which enables faster transmissions
• Greater protection from outages for your voice network
• Support for channel bonding CPE

Equipment
Depending on the applications you need to support, you may require some or all of the following ISDN equipment:

• Network Termination 1 (NT1) - Connects a basic two-wire BRI line to the eight-wire cables necessary for ISDN equipment.
• Network Termination 2 (NT2) - Concentrates multiple lines in addition to performing the functions of an NT1. An example of an NT2 device is a PBX equipped for ISDN.
• Terminal Equipment 1 (TE1) - any ISDN-compatible device.
• Terminal Equipment 2 (TE2) - any ISDN incompatible device, such as a plain telephone, an asynchronous terminal, a 3270 terminal, or a FAX machine.
• Terminal Adapter (TA) - provides ISDN connectivity to a TE2. A TA is one type of TE1.
• PRI Multiplexer, Router, Bridge or Hub - which interfaces between the ISDN PRI network and your terminal equipment.

Availability
ISDN uses existing infrastructure, so most homes and businesses are ISDN-ready right now. Certain conditions apply.

Ordering
If you are interested in AT&T ISDN service, contact your AT&T Sales Representative who can provide more detailed information on service features and help you place your order. You may also contact us for assistance using the following telephone numbers:

• For Calls within Illinois, Indiana, Michigan, Ohio, Wisconsin: 1-800-552-8647
  
• For calls within California and Nevada: 1-800-472-4736
  
• For calls within Missouri, Texas, Oklahoma, Arkansas, Kansas: 1-800-792-4736
  
• For calls within Connecticut: 1-888-718-7638

Note
Services not available in some areas. ISDN terminal adapter and network termination devices required. Applicable installation, inside wire, and jack charges apply. Compatible customer premises equipment required. The digital transport facility is not included and must be provided separately. PRI is available only where equipment and operating conditions permit. Variations in switching and control equipment used may cause differences in the operation or availability of certain features. Individual B-channels can transmit and receive voice and/or data calls up to 64 Kbps within a PRI serving arrangement or PRI network serving arrangement. Calls placed to or from outside the PRI, or over the public switched network where Signaling System 7 (SS7) and/or 64Kbps Clear Channel are not deployed, will be limited to 56 Kbps throughout.