What is ISDN?
ISDN is an acronym for Integrated Services Digital Network.

What is 23B + D?
This a service configuration that provides 23 B channels and 1 D channel. The B channels carry user information such as voice calls, circuit-switched data, or video, while the D channel handles signaling information. When equipped, the D channel can control a maximum of 479 B channels. The B channel may be provisioned on the same facility as the D channel or on another Primary Rate Service T1 facility.

What is Primary Rate Service?
The basic Primary Rate Service (PRS) structure consists of 23 B channels and a D channel, for a total transmission rate of 1.544 Mbits/second, which is equivalent to a T1 facility. Each 64 Kbits/second B channel carries user information such as voice calls, circuit-switched data, or video. The D channel is a 64 Kbits/second channel that is used to carry the control or signaling information.

What is BRI or Basic Rate ISDN?
Basic rate ISDN is basic rate service. Qwest calls this service Single Line ISDN Service. It consists of up to three distinct channels on one pair of wires: one or two B (Bearer) channels and one D (Delta) channel. Basic rate ISDN is offered on either an individual case basis or in a packaged offering as Qwest Single Line ISDN Service.

What is Single Line ISDN Service?
Single Line ISDN Service (SLS) is a platform based switched digital service offering fast, flexible, highly reliable, and digitally clear connections with the simplicity of dialing a telephone. Based upon international communications standards, ISDN provides users access to the powerful capabilities of today's Public Telephone Network for communicating across town, or around the world.

With Single Line ISDN Service, the same pair of wires that now delivers one communication-at-a-time basic phone service to business or residence customers provides two primary, high speed (64 Kbps) communications channels that can be used simultaneously and independently to carry any combination of data, image, video, or voice calls.

By combining these channels, data transfer at up to 128 Kbps may be achieved. Single Line ISDN Service also provides a third, auxiliary channel for low to moderate speed data communications which is ideal for point of sale, remote monitoring or telemetry applications.

No special handling is required when voice calls are made between ISDN phones and conventional telephones -- the network manages the necessary conversions. When conducting data calls, in order to utilize the B Channels for digital communications, ISDN based equipment is required at both ends of the communications path; as is the case with conventional modem connections or fax machine transmissions. Certain ISDN equipment also allows for modem-to-modem communications, providing the ISDN subscriber the best of both worlds!

Single Line ISDN Service is the Qwest name for Basic Rate Service. Single Line ISDN Service includes a comprehensive 2B + D package. Contained in the standard package are numerous voice and data features. The standard features and functions support two terminals per basic rate service. Within the standard package there is limited flexibility for customization and various optional features can be added. Single Line ISDN Service does not offer B channel packet service capability.

What is a Service Profile Identifier?

A Service Profile Identifier (SPID ) is simple. It's your ten digit telephone number, with a suffix of four 1's that describe a specific ISDN device to the network. As an example, a typical SPID in Qwest Will look like this: NPA NXXXXXX1111 where NPA is your area code, NXXXXXX is your prefix (NXX) and telephone number (XXXX) e.g. 20655555551111.

Why a Service Profile Identifier?
Because since it's technically possible to attach up to eight different devices with some 64 separate telephone numbers to a single ISDN telephone line, there must be a way to identify each device to both local switch and world wide telephone network.

What about local calling areas and telephone numbers?
If a customer is provided service from a designated central office which is not the customer's normal serving office, the local calling area for the customer's Single Line ISDN Service will be that of the designated ISDN equipped central office.

Calling areas are subject to change as additional central offices become capable of directly providing ISDN services to the customer's own and nearby serving area. Changes to calling areas will affect customer telephone numbers.

What is the D Channel?
The D or Delta channel carries signaling and/or packet data information, at speeds up to 16 Kbits/second on basic rate service or Single Line ISDN Service, and signaling only information up to 64 Kbits/second for primary rate service, from the customer's premises to the central office. The D channel has both data and signaling functionality; it does not have voice capability.

What is B channel?
The B or Bearer channel carries circuit switched voice and/or data communications at speeds up to 64 kbits/second, from the customers premises, over the loop facility, to the central office.

What is B Channel Circuit-switched Data?
Circuit-switched data provides the capability of making data calls over the public switched network. Information is transmitted the same way as digitized voice. Like a voice call, a circuit-switched data call ties up network/system resources for the duration of the call. Similar to voice, calling line identification functionality is provided.

Access Codes to Activate ISDN Single Line Features (pdf)