		Toward Universal Information Services Via ISDN
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				 by Taran King
 
	 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:
 
	 o The AT&T Network Systems 5ESS (TM <riiiight>) 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.
 
	 o 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
	 (DACS).
 
	 o The New Centrex is bringing greater levels of customer
	 control, improved services and a broad range of data
	 capabilities to the business customer.
 
		 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
	 information.
		 "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).
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	 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
	 effort.
		 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.
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	 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.
