Volume One, Issue Two, Phile 6 of 9
Toward Universal Information Services Via ISDN
by Taran King
From PROTO newsletter of AT&T Bell Laboratories
Phase one, the Present.
The local network of today, although still largely
voice-oriented, is already on the path to Universal
Information Services. Lightguide fiber is dramatically
expanding the capacity of local networks, helping to lower
the costs and increase the demand for high-band width,
Information Age services. And public networks are
increasingly digital and geared for data and special
services. For example:
Today's public networks consist of multiple or
overlay networks. The public switched network, or circuit
network, mainly for voice, is the base network. Two kinds of
overlay networks provide special services. Channel networks
carry private lines leased by large customers and transmit
much of today's data and image traffic; they also handle
traffic for network operations support. Packet networks
carry data communications, while packet switching is used
internally to public networks for common channel signaling to
set up, route and take down calls, or to give customers
- The AT&T Network Systems 5ESS (TM ) switch,
designed by Bell Laboratories, can serve as the hub of a
local deployment of remote modules at locations up to 100
miles from a host central office.
- The Integrated Special Services Network (ISSN) is a channel
network that provides special services, customer control
options and digital private lines rearrangeable under
software control. The ISSN incorporates digital carrier
terminating equipment such as the D4 Channel Bank, D5 Digital
Terminal System and Digital Access and Cross-connect System
- The New Centrex is bringing greater levels of customer
control, improved services and a broad range of data
capabilities to the business customer.
"Overlay networks help telecommunications companies
efficiently meet growing demand for digital transmission and
special services," says Stan Johnston, Market Planning
Manager, Network Systems Evolution, in AT&T Network Systems.
"Their integration into a single network, however, would be
still more effective."
Phase two, the Integrated Services Digital Network (ISDN).
The ISDN is a concept to which AT&T is committed - and it's
the foundation for Universal Information Services. The
central idea of ISDN, as AT&T Network Systems sees it, is to
provide an individual user a link to the local central office
of generous band-width - a digital subscriber line that can
carry 144,000 bits per second (sure beats 2400 baud!). The
band-width is subdivided into two 64,000-bit channels, which
may carry voice or data or both, and one 16,000-bit channel
for packetized signaling information or data transport. Such
a link provides convenient "integrated" network access by
accommodating voice, data and signaling over a single line.
The ISDN will make it easier for a customer to get
varied services from public and private networks. More
bandwidth for big customers will be available through another
ISDN access standard, the extended digital subscriber line,
which provides 1.5 billion bits per second as 24 channels of
64,000 bits each.
In 1986, new software from Bell Labs will enable the
5ESS switch to accommodate ISDN-sized 144,000-bit channels
that standardize and simplify subscribers' use of local
networks. AT&T is committed to future products that will
also be ISDN-compatible. Other vendors, too, some of whom
already plan to build premises, terminal, and other
equipment to ISDN standards, will make ISDN a cooperative
By providing integrated digital access to networks,
ISDN will make important progress toward the goal of
Universal Information Services. But overlay networks will
continue to divvy up the transport job. And messages needing
less than 144,000 bits per second will not fill their
allotted bandwidth, leaving capacity underutilized.
Phase three, Universal Information Services.
Rooted in the fertile ground of 5ESS switches, ISDN equipment
and technologies such as wideband packet transport, Universal
Information Services will bear fruit during the 1990s. From
a single kind of network will hang services as different as
apples, oranges and pears. Just as network access was
integrated in ISDN, transport functions will increasingly be
integrated by powerful new network equipment evolved from
equipment developed for the ISDN. Where customers once got
standard-sized ISDN channels, they'll get big bandwidth for
large jobs, little bandwitdh for small jobs.