
    In Perspective
   
                           HEADING TOWARD THE LIGHT
                                       
  AS BANDWIDTH DEMANDS INCREASE, THE BENEFITS OF SONET WILL MOVE TO END-USERS.
  
   
   
   Take a look at the telecom manager's wish list.
   
   An ideal telecommunications environment would allow voice and data to
   be mixed, would support "bandwidth-on-demand" for data-intense
   applications, would provide network robustness and resiliency and
   would offer a more flexible service mix and faster service
   provisioning.
   
   SONET, which stands for Synchronous Optical Network, is poised to help
   businesses and carriers alike realize that ideal.
   
  A SONET PRIMER
  
   
   
   SONET is an international optical transmission standard, parts of
   which have been under development since 1984. Interest in SONET, both
   among telecommunications service providers and - more recently -
   end-users, has been exploding. This demand stems from incremental
   growth in voice traffic, from new data communication applications
   requiring substantial bandwidth (such as LAN interconnection or
   medical imaging) and from existing data applications that are
   significantly increasing communications traffic.
   
   Traditional transmission standards are based on the digital signal
   (DS) hierarchy, which includes DS0 (64 kilobits per second), DS1
   (1.544 megabits per second) and DS3 (approximately 45 megabits per
   second) circuits. DS transmission relies on electrical interfaces to
   transmit information. The maximum-speed interface is DS3 or 45 Mbps.
   The DS hierarchy is asynchronous, meaning that extra bits must be
   inserted into digital signal streams to bring them up to a common
   speed.
   
   SONET, however, extends the standard electrical interfaces to optical
   signals, which are transmitted using laser-light pulses. SONET is
   "synchronous," meaning it uses external timing to make sure all
   fiber-optical equipment is timed to the frequency. And like a larger
   water hose that lets more water flow through, Sonet provides increased
   bandwidth. It comes in 155-megabit increments that can be easily
   aggregated to create 600 Mbps or larger signals.
   
   For carriers as well as end-users, SONET also simplifies provisioning
   and enhances operational flexibility through robust fractional
   services. SONET improves reliability and management of the network,
   too, because it requires fewer network cross-connects and provides
   more information about the quality of the network.
   
  GROWING BANDWIDTH DEMAND
  
   
   
   For end-users to ever connect directly to SONET services, SONET must
   be offered by local-exchange carriers. A forecast of SONET penetration
   in the local loop and the local interoffice telephone network by
   Technology Futures, Inc., of Austin, Texas, identifies the next six
   years as a period of great growth.
   
   The development of high-speed data applications in conjunction with
   LAN interconnection - though still limited today - are drivers of
   early demand for SONET capacity. Increasingly widespread business use
   of these and other high-bandwidth applications during the remainder of
   the 90s is expected to accelerate SONET penetration of the telco
   infrastructure.
   
   Traditionally, high-band-width demand has been satisfied by dedicated
   or leased lines, typically T1 or T3 circuits. Use of these circuits,
   which support data transfer rates of 1.544 megabits per second (Mbps)
   and 44.736 Mbps respectively, has its drawbacks. For end-users, moving
   up to T-services often requires more in-house technical and management
   expertise, particularly when mixing voice and data.
   
   However, the truth is that most end-users today just don't need the
   bandwidth supplied by SONET. It is a technology that is being deployed
   in local networks to prepare for expected future growth in bandwidth
   demand.
   
   "Practically speaking, this high-bandwidth market doesn't exist yet,"
   notes LDDS WorldCom Vice-president of Engineering Russ Ray. Once the
   capability is available, I think we're going to see requests for
   bandwidth that will be used in new ways."
   
   As an example, Ray points to businesses that today extensively use
   frame-relay services - high-speed (64 Kbps to 1.544 Mbps) packet-based
   data communications.
   
   "I can envision a customer using electronic data interchange (EDI) to
   communicate with its 2,000 suppliers," Ray says. "But that business
   doesn't want hundreds or thousands of 'pipes' coming in to its
   facility. I can see [that business] wanting one large Asynchronous
   Transfer Mode (ATM) pipe, perhaps an OC-3 level SONET interface, with
   those 2,000 remote locations on frame relay."
   
   This approach simplifies the communications system substantially,
   easing system management and enhancing network reliability through
   sheer reduction of components.
   
  SELF-HEALING NETWORKS
  
   
   
   Reliability and network-management capabilities are other important
   benefits of SONET. The SONET standard provides for end-to-end
   monitoring of the communications network. This makes identification
   and repair of faulty network elements both more straightforward and
   faster. Further, it means that carriers can guarantee transmission
   performance and that users can readily verify compliance without
   resorting to network test equipment and off-line testing. For network
   managers, SONET's features mean earlier and faster problem
   identification as well as enhanced network maintainability.
   
   In conjunction with digitally switched networks, SONET supports
   software control of traffic. Combined with SONET's error tracking and
   reporting, dynamic routing allows network managers to design robust,
   error-detecting networks that can offer "self-healing" capabilities.
   And, because SONET networks rely on digital multiplexers, end-user
   services can be provisioned under software control.
   
   "When we want to turn up capacity on a circuit, we won't have to have
   someone go, for instance, to Kansas City to make a physical
   cross-connect. It can all be done remotely through software," says
   Ray.
   
   Because routing and bandwidth are under software control, service can
   be provisioned in hours or minutes, rather than the days or weeks many
   telecommunications managers have been accustomed to waiting. Further,
   because connections are digital and programmable, SONET provides the
   capability for automatic restoration of service when network problems
   do occur.
   
   Finally, SONET provides really big pipes - and it does so in 155 Mbps
   increments. So, SONET networks can be readily configured to support
   whatever bandwidth is required.
   
  MIXING AND MATCHING
  
   
   
    "Among [SONET's] many advantages is standardized optical and
   electrical interfaces that all suppliers will adhere to," notes
   Lawrence Vanston, president of Technology Futures. "Another benefit is
   that an individual information stream on a fiber channel can be
   efficiently separated from the rest of the information on the
   channel." Thus, a key strength of SONET is its ability to integrate
   and manage different types of traffic on a single fiber.
   
   Because it is an "open" standard, SONET invites competition between
   customer-premise-equipment (CPE) suppliers. With SONET, carriers (and
   eventually end-users) can mix-and-match circuit equipment because,
   unlike most systems today, different manufacturers' equipment will
   inter-operate. This provides operational and equipment savings, as
   well as creating more competition among equipment manufacturers.
   
   For end-users, this new degree of equipment compatibility means that
   inter-connecting network segments supported by different carriers will
   become simpler and faster and will result in more flexible and
   survivable networks.
   
  WHO NEEDS SONET?
  
   
   
    Today, the benefits of SONET primarily accrue to carriers. As SONET
   becomes more widely deployed, those benefits are expected to trickle
   down to end-users.
   
   "The question is, Will the carriers extend the attributes of SONET all
   the way into the local-area environment?" asks Joseph Baylock, vice
   president of the Gartner Group ENS Services. Baylock refers to SONET's
   transmission monitoring and control features, which support error
   detection and correction.
   
   In order to offer these kind of capabilities to end-users,
   interexchange carriers like LDDS WorldCom are busy making their own
   networks SONET-ready. In 1993, LDDS WorldCom SONET-enabled a portion
   of its telecommunications backbone, and by the close of '94, will have
   completed installation of its OC-48 system on about 75 percent of the
   network. The benefits of SONET - greater reliability, faster
   provisioning, enhanced flexibility, higher quality service and
   improved cost-containment - are already penetrating the LDDS WorldCom
   network. And when the time comes, LDDS WorldCom will be ready to
   provide its customers with SONET's primary benefit as much bandwidth
   as customers want, when they want it.
   
   "In terms of pass-through benefits from carriers implementing SONET, I
   think end-users will see reliability benefits in '94, and certain
   users will see cost benefits in '94. From a maintenance and
   mean-time-to-repair point of view, there are probably some benefits
   there also, but I'd have a tough time quantifying them," Baylock says.
   
   
   End-users trying to get SONET local loops today are facing slim
   pickings. Local-exchange carriers are generally reluctant to sell
   SONET loops because they don't perceive adequate demand. Broadband
   technologies like ATM and frame-relay can run adequately on
   traditional T1 or T3 circuits, and there are only a handful of large
   users who need the bandwidth provided by SONET.
   
   Indeed, LDDS WorldCom Senior Scientist Joseph Liu predicts SONET will
   never completely replace DS transmission at the local loop. "Some
   business customers won't ever need SONET local loops because they
   don't have mega data centers or other high-speed applications. The
   circuits are more expensive, and local-exchange carriers aren't being
   aggressive about offering them."
   
   That should change as bandwidth demands expand. The benefits of SONET
   will then move quickly from the carrier level to end-users.
   
   Library ISMAP
   In Perspective ISMAP
   
   Note: Comments and opinions presented in this article do not, unless
   otherwise noted, necessarily reflect the opinion of LDDS WorldCom.
    Copyright 1994, by LDDS WorldCom. All rights reserved. Reproduction
    in whole or part is available via written permission from LDDS
    WorldCom.
    Comments to Webmaster
