Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1999-03-31
2003-06-17
Vincent, David (Department: 2661)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S376000
Reexamination Certificate
active
06580709
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for flexible SONET access and transmission; and, in particular, to an apparatus for flexible SONET access and transmission which flexibly and economically supports services from voice frequency (POTS) to OC 48 (2488 Mbit/s) with the potential for value added services, mixed ATM and STM multiplexing; and capable of modular system growth.
2. Description of the Related Art
Optical fibers provide a high bandwidth medium for data transmission. Consequently, optical fibers have found applications in many computer networks, including those used in digital telephone systems. To allow a uniform interface for voice and computer equipment on an integrated voice and computer network using optical fibers, American National Standards, Inc. adopted a standard, known as SONET (Synchronous Optical Network). The SONET standard is described in “American National Standard for Telecommunications-Digital Hierarchy-Optical Interface Rates and Formats Specification (SONET)” (“SONET document”), which is hereby incorporated by reference in its entirety. The SONET document defines a hierarchy of data formats to support a layered communication architecture, which comprises the photonic, section, line and path layers. A schematic model of the layered architecture is provided in FIG.
12
. Each of these layers, except the photonic layer, builds on services provided by the next lower layer.
The basic data unit of the SONET standard is represented by a frame, called the STS-1 frame, consisting of 90 “columns” and 9 “rows” of 8-bit bytes. The STS-1 frame is shown graphically in FIG.
13
. Under the fixed transmission rate, the STS-1 frame is transmitted in 125 microseconds. Under the SONET standard, as shown in
FIG. 13
, data of an STS-1 frame is transmitted row by row, and from left to right. In each byte, the most significant bit is transmitted first.
To support the layered architecture, the first three columns of the STS-1 frame are used for carrying transport overhead information, and the remaining 87 columns of the frame, known as the STS-1 Synchronous Payload Envelope (SPE), carry the data to be transported. Path layer overhead are also carried in the STS-1.
FIG. 14
shows the allocation of the transport and path overheads in the STS-1 frame. A description of each of the overhead bytes is provided in the SONET document and is therefore omitted from this discussion.
The SONET standard also defines (i) data formats which are each smaller than an STS-1 frame and transported within the STS-1 SPE, called virtual tributaries (VT); and (ii) data formats, designated as STS-N frames (where N is an integer), which are each larger than a STS-1 frame. An STS-N frame is formed by byte inter-leaving N STS-1 frames. The counterparts of the STS-1 and STS-N data formats in the optical fibers are called CO-1 and OC-N (optical carrier level
1
and optical carrier level N) respectively. CO-1 and OC-N are obtained by optical conversions of the respective STS signals after scrambling.
A rough description for each of the layers in the SONET architecture is provided here to facilitate understanding of the present invention. The photonic layer provides transport of bits at a fixed bit rate (N×51.84 megabits/second, where N is an integer) across the physical medium, i.e. the optical fibers. The main function of the photonic layer is the conversion between the STS signals and the OC signals.
The section layer deals with the transport of an STS-N frame across the physical medium. In this layer, framing, scrambling, section error monitoring are provided. Equipment which terminates in the section layer reads, interprets and modifies the section overhead bytes of the STS-1 frame.
The line layer deals with the reliable transport of the path layer payload. A path is a basic unit of logical point-to-point connection between equipment providing a service on the network. More than one path layer payload, each typically having a data rate less than the STS-1 basic data rate, can share an STS-SPE. The line layer synchronizes and multiplexes for the path layer. The overhead bytes for the line layer includes overhead involved in maintenance and protection (i.e. error recovery and redundancy) purposes. Equipment which terminates in the line layer reads, interprets and modifies the line layer overhead bytes of the STS-1 frame.
The path layer deals with the transport of services between path terminating equipment. Examples of such services include synchronous and asynchronous DS-1 services and video signals. The main function of the path layer is to map the services into the format required by the line layer.
Previous generation SONET equipment had one or more of the following limitations. The locations in which different types of tributary interface units (e.g., DS1, DS3, or optical interface units) was typically restricted. This lead to inefficiencies in using all of the unit slots in a shelf for different service mixes. Those few systems that allowed a more universal slot usage did not allow for small incremental growth of the lower-rate tributary interfaces. For example, placing 14 DS1s on a working unit and using an identical unit for 1:1 protection. Previous equipment lacked a modular manner in which to increase the capacity of a single shelf system without duplicating all of the common units in the additional shelf. In most cases, the additional shelf had to be a separate network element within the SONET network. Previous generation equipment also typically required many different types of common units to perform such functions as system control, external maintenance LAN network interface, high-speed optical interface, system timing generation, time slot interchange (TSI), and intermediate SONET signal processing. Previous systems used dedicated buses for synchronous transfer mode (STM) and asynchronous transfer mode (ATM) PCM signals with no sharing of the two formats within the same STS-N high-speed multiplexed signal. Typically, ATM and STM signals have been processed in separate, unique shelves. Previous systems did not allow for units to use the tributary interface slots to provide a common processing function across part or all of the system's PCM data without using add/drop time slots on the PCM buses. Also, previous generation equipment had no provision for a local area network among the tributary interface units that allows for packet processing (e.g., IP store and forward) of data packets within the tributary PCM data. Lastly, typical systems of the prior art terminated dropped paths from both directions of a ring configuration on a single unit and also on its protection partner unit, thus requiring twice as much termination circuitry as necessary.
What is needed is an architecture which allows a more universal SONET access and transmission system that can economically serve both small and large bandwidth applications with an extremely wide range of services and which has the potential for value-added services wherein all high-speed interface and TSI functions are combined onto the same unit (in conjunction with the system backplane).
SUMMARY OF THE INVENTION
The present invention provides hardware architecture for a flexible transmission and access platform. The primary high speed interfaces can be SONET STS-1 (52 Mb/s), OC-3 (155 Mb/s), OC-12 (622 Mb/s), or OC-48 (2488 Mb/s). For OC-3, OC-12, and OC-48, line terminal, linear add/drop multiplex, and unidirectional path switched ring network topologies are supported. On the tributary input side, services between voice frequency plain-old telephone service (POTS) and OC-3 can be supported.
The time slot interchange function is performed on the backplane so that the system can simultaneously and economically support STM time slot interchange (TSI) of channels from 16 kb/s through 51 Mb/s as well as ATM cell multiplexing. Systems using an integrated circuit for all TSI and cell multiplex functions typically require a different, costly device for narrowband services (16
Brooks Robert Wesley
Gorshe Steven Scott
NEC America Inc.
Scully Scott Murphy & Presser
Vincent David
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