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How Sonet is coming to customer premises.

There is perhaps no other change affecting data communications as dramatic as the tremendous amount of fiber cable deployed throughout North America over the past decade. But because of the proprietary nature of fiber implementation, its bandwidth capacity has yet to be fully exploited for digital transmission.

The emerging Synchronous Optical Network (Sonet) has only recently become standardized, but will eventually allow the full potential of fiber optics to be realized.

In addition to specifying a standard fiber-optic interface, worldwide Sonet standards currently specify transmission rates that start at 51.84 Mb/s and reach to 2.488 Gb/s. The long-term ramifications of this standard are far-reaching: Throughout this decade, Sonet will gradually replace the asynchronous networks of today.

With essentially the same fiber cable that supports asynchronous networks, transmission capacity can be increased a thousandfold by using end-to-end Sonet equipment. Sonet also offers:

* Standard optical interface. Currently the conversions between electrical and optical signals are proprietary and vary among vendors. This limits product selection and configuration flexibility, while increasing dependence on a single vendor. Sonet changes all that.

* Network management. Bandwidth may be managed to the DSO (64 kb/s) level to provide maximum control of bandwidth, regardless of carrier.

* Functional support. Complies with B8ZS and ESF signaling formats to ensure optimal network performance.

The basic building blocks of a Sonet-compliant private network node include a terminal multiplexer, an add-drop multiplexer and fiber transmission modules connected to a Sonet-equipped T1 multiplexer under the control of a sophisticated transport management system (TMS).

This configuration is exemplified by General DataComm's Megamux-S/TMS, an intelligent networking T1 multiplexer equipped with Sonet-compliant interfaces. The configuration provides a smooth migration path from the T1 world into the Sonet world--without prematurely antiquating the installed base of customer premises equipment.

Configuration scenario

When the multi-node private network outgrows its T1 (1.544 MB/s) boundaries, the terminal multiplexer becomes the first gateway into the Sonet world.

In a typical point-to-point configuration, a terminal multiplexer at the telephone company central office is paired with a terminal multiplexer at the customer premises. This provides a transparent Sonet interface for T1 nodes, placing up to 28 DS1 signals in the Sonet payload at 51.84 MB/s. For further networking flexibility, the terminar multiplexer can be combined with the add-drop multiplexer to form a multipoint transmission system that can add or drop DS1 and/or DS0 bundles from the T1 multiplexer nodes along the route.

The add-drop multiplexer shares high- and low-speed port capabilities with the terminal multiplexer, but can be equipped to perform DS0 as well as DS1 grooming. This means the add-drop multiplexer can act as a digital cross-connect system, separating lower-speed signals from the Sonet payload.

With the fiber transmission system, users can prepare for bandwidth requirements higher than OC-1. Depending on the fiber transmission system used, it can transport any combination of up to three STS-1 (Synchronous Transport Signal, Level 1) or DS3 signals at an OC-3 (Optical Carrier, Level 3) line rate of 155.52 Mb/s, or it can transport up to 12 STS-1 or DS3 signals at an optical OC-12 line rate of 622.08 Mb/s.

Monitoring and control are handled via an integrated network management system which provides access to all Sonet overhead functions, as well as other network management capabilities. These capabilities include trouble ticket administration, customer report generation, multi-level operator security and system utilities.

Users: plan now for Sonet

Businesses must approach Sonet the way they approach their entry into new markets--with a well defined forecast and positioning strategy. Planning the level of commitment and the timing for Sonet should be as carefully thought out as any new business initiative.

As an international standard, Sonet permits truly global networking that is virtually insensitive to distance and time. High speeds cut network delays to a minimum and greatly expand the scope of long-haul transport.

Sonet's frame structure lets signals pass with equal ease through both public and private networks, supporting services based on FDDI and IEEE 802.6/DQDB, as well as proprietary "fast packet" and industry-standard frame relay architectures.

As Sonet becomes more widely available and the promised efficiencies and cost savings materialize, the way networks are designed, operated and managed will change. For carriers, timely and effective deployment of Sonet will determine the types of broadband services they can offer. For corporations, planning for Sonet will determine how the emerging broadband services will support new applications, how these applications can be integrated into various business operations and within what timeframes.

Clearly, the extent to which corporations can plan for Sonet deployment will impact their competitive position in the 1990s and beyond.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

Article Details
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Title Annotation:Fiber-Optic Networks; Synchronous Optical Network
Author:Davidson, Robert P.; Muller, Nathan J.
Publication:Communications News
Date:Dec 1, 1991
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