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DWDM Network Transport Systems with Digital Tributaries for Use in Metropolitan Area Applications: Common Generic Criteria

Document Number GR-2918
Issue Number 06
Issue Date Jan 2003

    ABSTRACT: Issue 6 of GR-2918, DWDM Network Transport Systems with Digital Tributaries for Use in Metropolitan Area Applications: Common Generic Criteria, replaces Issue 5.

    This GR provides the Telcordia view of generic requirements for the physical layer of transversely compatible Dense Wavelength Division Multiplexing (DWDM) systems operating in the 1550 nm region. Generic OAM&P requirements for such systems are also addressed. Specifically, this GR covers physical layer parameters necessary for interoperability in DWDM networks of various topologies that provide optical layer transport of digital signals in the range of nominally 45 Mb/s (e.g., DS3 signals) to nominally 2.67 Gb/s (e.g., SONET OC-48 and ITU-T OTU1 bit-rates). The transport of analog signals as well as the transport of nominally 10 Gb/s signals (e.g., SONET OC-192 signals) is beyond the scope of this issue of the GR. However, some aspects of 10 Gb/s interfaces have been introduced in this issue. It is possible that future issues of this GR will cover these systems more extensively.

    For the physical layer requirements, this document focuses on specifications of the physical layer parameters that describe the interface between Optical Network Elements (ONEs). For the OAM&P requirements, the document focuses on issues that apply to DWDM networks and optical network elements and are common across all ONEs.

    This document applies to a number of different optical network architectures that are realizable in the near term (3 to 5 years). A point-to-point architecture refers to the case where optical transport is provided between two network nodes, with all optical tributaries being terminated at these two nodes. The term optical tributary (OT) is used in this GR to denote one of the optical carrier signals in a multiplex of optical carrier signals. Point-to-Point architectures use Optical Terminal Multiplexers (OTMs) and could also use Optical Line Amplifiers (OLAs). Linear architectures refer to cases where specific OTs are terminated at different points in a chain of ONEs. This architecture is realized through a combination of OTMs, Optical Add-Drop Multiplexers and could use OLAs. The OADM is capable of terminating certain OTs and passing through other OTs to the next node on the chain without requiring any Electrical to Optical (E/O) or Optical to Electrical (O/E) conversion for the pass-through OTs. Such optical pass-through of OTs is a fundamental characteristic for the DWDM applications developed in this GR. This feature avoids the cost of O/E/O conversion for passed-through OTs. Ring topologies involve OADMs (and possibly OLAs) connected in a ring configuration so that all traffic travels between two OADMs on the ring. Ring topologies provide cost advantages to network operators because redundant optical paths can be provided with fewer optical fibers. Finally, Optical Cross-connects may be used to interconnect OTs carried over various optical fibers connected to various OXC ports. Each optical fiber will typically carry multiple OTs.

    Telecommunications service providers are experiencing exploding demand for bandwidth in their networks. The explosive growth of data traffic, primarily fueled by the increased use of data networking and of the Internet by businesses and homes, has caused increasing demands for network bandwidth.

    Faced with this increased demand for bandwidth, service providers have three main choices:
    (1) deploy additional fiber
    (2) increase the capacity of their Time Division Multiplexed (TDM) systems (e.g., their SONET systems) or
    (3) deploy DWDM systems.

    Because of the high cost and long lead times involved in deployment of new fibers, most service providers are relying on maximizing the amount of traffic that can be transported within their existing fiber networks. DWDM technology can be a cost-effective way to significantly increase the transport capacity of existing fiber networks, particularly those that are relatively long or have needs for high capacity. In these circumstances, DWDM technology can provide larger transport capacity increases than currently available TDM based technology with a reduced impact of fiber impairments that can be prevalent in high bit-rate TDM systems. Because the individual signal is limited to lower bit-rates such as SONET OC-48 and ITU-T OTU1, the impact of fiber impairments such as dispersion are reduced.

    Issue 6 completely supersedes Issue 5. The primary reason for this reissue is to align with the relevant aspects of recently approved ITU-T Recommendations on optical layer networks (OLNs) and optical transport networks (OTNs). In addition, Issue 6 incorporates comments received from the industry as well as internally within Telcordia on the criteria described in the previous issue. Because of the relative immaturity of the technology, the criteria contained in this document are subject to changes predicated by technology changes, standards developments, and further input from the industry.

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