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. Cerzán 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 an individual case basis or in a packaged
offering as Cerzán 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
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 Cerzán
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
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 at Cerzán will look like this: NPA NXXXXXX1111
where NPA is your area code, NXXXXXX is your prefix (NXX)
and telephone number (XXXX) - e.g. 65155512341111.
Why a Service Profile Identifier?
Because 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
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, but 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 over
the loop facility from the customer’s premises to the
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.