ROADM Towards a Fully Flexible DWDM Network

ROADM Towards a Fully Flexible DWDM Network

Tel:+44 (0)1242 530630 Fax: +44 (0) 1242 530660 E-Mail [email protected] www.horsebridge.net

Horsebridge Network Systems Ltd, 1 Pate Court, North Place, Cheltenham, GL50 4DY England.

ROADM Towards a Fully Flexible DWDM Network White Paper December, 2008

© Copyright by ECI Telecom, 2008. All rights reserved worldwide.

The information contained in the documentation and/or disk is proprietary and is subject to all relevant copyright, patent, and other laws protecting intellectual property, as well as any specific agreement protecting ECI Telecom's rights in the aforesaid information. Neither this document nor the information contained in the documentation and/or disk may be published, reproduced, copied, modified or disclosed to third parties, in whole or in part, without the express prior written permission of ECI Telecom. In addition, any use of this document, the documentation and/or the disk, or the information contained therein for any purposes other than those for which it was disclosed, is strictly forbidden. ALL RIGHTS NOT EXPRESSLY GRANTED ARE RESERVED BY ECI TELECOM.

Any representation(s) in the documentation and/or disk concerning performance of ECI Telecom product(s) are for informational purposes only and are not warranties of product performance or otherwise, either express or implied. ECI Telecom's standard limited warranty, stated in its sales contract or order confirmation form, is the only warranty offered by ECI Telecom.

The documentation and/or disk is provided “AS IS” and may contain flaws, omissions, or typesetting errors. No warranty is granted nor liability assumed in relation thereto, unless specifically undertaken in ECI Telecom's sales contract or order confirmation. Information contained in the documentation and in the disk is periodically updated, and changes will be incorporated in subsequent editions. If you have encountered an error, please notify ECI Telecom. All specifications are subject to change without prior notice.

CONTENTS

ECI Telecom Ltd. Proprietary iii

Contents

Introduction...................................................................................................................... 5 ROADM Overview............................................................................................................ 6 ROADM Technologies Primer ....................................................................................... 7

Pluggable ROADM .................................................................................................. 7 Remotely Reconfigurable ROADM....................................................................... 8

Broadcast and Select............................................................................ 8 PLC ......................................................................................................... 9

Dynamic Reconfigurable ROADM ........................................................................ 9 Wavelength Selective Switch............................................................... 9

ECI Telecom ROADM Value Proposition ................................................................... 11 Cost-Optimized ROADM Solutions.....................................................................11

Third-Generation WSS ROADM ......................................................... 11 B&S-Based ROADM............................................................................ 12 Pluggable ROADM .............................................................................. 12

Conclusion .....................................................................................................................13 About ECI Telecom .......................................................................................................14

CONTENTS

iv ECI Telecom Ltd. Proprietary

List of Figures

Figure 1: Pluggable ROADM block diagram in standby and active modes .................... 7 Figure 2: WB-based ROADM ........................................................................................... 8 Figure 3: PLC based ROADM .......................................................................................... 9 Figure 4: WSS-based ROADM architecture...................................................................10 Figure 5: Typical WSS ROADM application................................................................... 12

INTRODUCTION

ECI Telecom Ltd. Proprietary 5

Introduction

Over the last decade, DWDM technology has gained wider acceptance in long-haul and metro networks, despite the lack of cost-effective flexible wavelength management capabilities.

Fixed filter technology has been used to implement wavelength provisioning methods. Wavelength connection is accomplished by using wavelength-specific filters, typically adding and dropping up to four random channels or groups of four adjacent channels. Changes to the connectivity pattern can become extremely complicated and labor-intensive, resulting in extensive capital layout. In addition, the manual reconfiguration process is often traffic-affecting, requiring field technicians to be dispatched at all hours of the day and night. In extreme situations when networks operate close to their technological limitations, long and expensive re-engineering of the entire network is often necessary.

Clearly, when used in applications like typical metro networks where traffic patterns and growth rates fluctuate, the fixed filter architecture is very costly to provision, deploy, and maintain.

A fully flexible DWDM network is the solution and this is now possible due to Reconfigurable Optical Add/Drop Multiplexer (ROADM) technology. Although ROADM prices were prohibitive when they first hit the market, the components have matured and proliferated to a point where implementation is not only a valuable enhancement but significantly more affordable.

This paper surveys various ROADM technologies and network architectures (including general requirement and planning considerations for service providers), and highlights the ECI Telecom approach to implementing a fully flexible DWDM network.

ROADM OVERVIEW

6 ECI Telecom Ltd. Proprietary

ROADM Overview

The introduction of ROADM technologies offers service providers greater flexibility by providing any wavelength to any node connectivity (known as "any-to-any") without the need to predefine traffic demands. In addition, unlimited changes can be made to already deployed wavelengths. As a result, service providers now benefit from:

Simplified network design and implementation with lower operating expenses

Limitless wavelength deployment for faster setup of wavelength services

Simple reconfiguration of operating wavelengths to meet changes in traffic demands

Reduced cost of inventory management

Reconfigurable DWDM networks use one of the following ROADM technologies:

Pluggable ROADM - this technology uses fixed OADM filters and optical switches to enable remote activation and deactivation of predefined wavelengths. Single or four-wavelength modules set the operating lambdas. As traffic demands change, they can be replaced by the operator without affecting the express traffic. This extremely low cost technology is optimal for sites that are not likely to change often during the network life cycle.

Remotely reconfigurable ROADM - this approach uses a first generation electromechanical switch, second generation wavelength blocker subsystems, or Planar Lightwave Circuit (PLC) subsystems in a Broadcast and Select (B&S) architecture, and offers access to each and every wavelength in the network. Ports are allocated for each specific wavelength. The operator is required to connect the colored transmit and receive interfaces of the transponders or colored line cards to specific ports that support the required wavelength. This ROADM technology is cost effective at sites with a large number of dropped wavelengths (typically 50% or more), and reserves Reshaping, Reamplification, and Retiming (3R) regeneration for express traffic.

Dynamic Reconfigurable ROADM (D-ROADM) - this advanced third-generation technology uses Wavelength Selective Switch (WSS) subsystems with four or eight add/drop ports. Each wavelength or combination of wavelengths can be dropped remotely at any port, enabling the operator to connect any service to any port. Apart from operating in ring topologies, D-ROADM supports multiring closure and hub and spoke configurations. D-ROADMs are cost optimal for sites with a small number of add/drop ports, typically four to eight, and are scalable to full DWDM capacity. WSS-based ROADMs can also provide solutions for full mesh networks.

ROADM TECHNOLOGIES PRIMER


ROADM Technologies Primer

Pluggable ROADM A pluggable ROADM can be programmed to operate in standby and in active modes. In standby mode, the “express switch” connects the line inputs to the outputs; in active mode, the switch connects the line interfaces via the OADM add/drop unit. The switch is operated remotely via the network management system. To prevent traffic failures triggered by accidental module extraction, the switch is automatically set to the bypass mode when the OADM module is not present.

Figure 1: Pluggable ROADM block diagram in standby and active modes

OADM units operate with predefined wavelengths (as do fixed OADMs) and support one channel, four random channels, and bands of four adjacent channels. This low-cost solution is most suitable for sites which drop a small number of wavelengths and are not likely to change often.

The main advantage of the pluggable ROADM solution is its extremely low 'day-one' costs, even when compared to fixed OADM solutions. The initial investment is just the low-cost basecard. The corresponding OADM unit is not purchased until the add/drop requirements are determined. At that point, the unit can be installed in the basecard and the optical switch can be changed to add/drop the channels via the management system. With the unique random OADM configuration, operators can choose any combination of channels to add/drop at the site, thus expanding wavelength connectivity between sites.



Remotely Reconfigurable ROADM

Broadcast and Select

The figure shows the block diagram of a typical B&S architecture using Wavelength Blocker (WB) technology for remote operation of the site. A demux unit that enables access to all wavelengths is connected to the DWDM line using a splitter at the input to the site. Each wavelength is dropped via a specific color-dependent port. The WB unit is remotely configured to block (attenuate) the specific wavelengths that are dropped at the site. The added channels are connected to a mux unit and back on to the line via the output coupler.

B&S architecture does not provide dynamic wavelength provisioning in that both drop and add channels are wavelength dependent. This limitation is sometimes overcome with an additional M x N optical switch (M = number of dropped channels; N = number of DWDM channels in the network). However, this capability induces additional cost and adds management complexity to the solution.

Figure 2: WB-based ROADM

Nonetheless, B&S architecture is optimal for sites with a large number of dropped channels, typically over 16. Its main benefit is that it saves 3R regeneration for express traffic at hub sites.

A WB-based ROADM should also provide optical power equalization and power monitoring. The WB is equipped with monitoring taps and a Variable Optical Attenuator (VOA) per channel, enabling the operator to monitor each express channel. Together with monitoring points and VOAs on added channels, full control over the optical power per channel is achieved.



PLC

An alternative technology for realizing the B&S architecture, PLC utilizes Array Waveguide Grating (AWG) multiplexers and demultiplexers and arrays of 2 x 2 switches to control the add/drop or pass-through wavelengths.

The following figure shows a block diagram of a typical PLC B&S architecture. An AWG demux unit is connected to the DWDM line at the input to the site. Each wavelength is connected to a remotely configured 2 x 2 switch that allows the channel either to pass through or to be added/dropped to specific input/output ports. The added channels are connected to an AWG mux and back on to the line via the output coupler. Built-in attenuators are remotely configured to allow equalization of the add channels.

Figure 3: PLC based ROADM

Dynamic Reconfigurable ROADM

Wavelength Selective Switch

In this architecture, the WSS ROADM is equipped with two line ports (line in and line out) and four or eight add/drop ports. This type of ROADM enables fully dynamic remote reconfiguration.

On the drop side, the WSS connects all wavelengths to the output (line) port. The operator can remotely switch any wavelength to any other port. Consequently, one or more wavelengths may be dropped at any given port and at any time. On the add side, wavelengths from all add ports and the line-in port are switched and multiplexed into the line-out port.

WSS enables any service to be dropped at any port - hence the term “colorless” ports. Furthermore, as multiple wavelengths can be dropped via each port, WSS can connect subtending (access) rings to the core ring and drop multiple wavelengths at remote sites, including star or full mesh topologies.



Figure 4: WSS-based ROADM architecture

WSS is optimal for sites with a small number of services, typically four or eight. Its relatively high cost (compared to pluggable ROADM) positions it at sites that are likely to change often, or which have unpredictable day-one traffic.

WSS scalability for more than eight channels is achieved by cascading WSSs where a second WSS is connected to one of the drop ports on the first WSS.

ECI TELECOM ROADM VALUE PROPOSITION


ECI Telecom ROADM Value Proposition

The Optical Networks Division at ECI Telecom is a leading provider of intelligent multiservice metro transport and switching solutions. Well into its second decade of global optical networking experience, ECI Telecom offers advanced platforms that combine instant provisioning with on-demand network scalability.

The flagship XDM® family of products provides the building blocks for scalable intelligent optical networks using a single-architecture approach, and features a complete range of shelves, each optimized for the widest set of applications and configurations.

Cost-Optimized ROADM Solutions Fully flexible networks can save OPEX and simplify management and control, as well as shorten the provisioning time of new services. Nevertheless, operators are still hesitant to deploy advanced ROADMs. This is due to the seemingly substantial CAPEX outlay currently needed for their implementation.

With the first extensive deployments of ROADMs expected in 2006, economies of scale will reduce prices of ROADM components, further facilitating implementation of fully flexible DWDM networks.

The ECI Telecom approach is to supply a mix of ROADM solutions to provide operators with cost-optimized DWDM flexibility. This enhanced mix includes:

Software-reconfigurable ROADMs at critical sites, including:

Third-generation WSS ROADM

B&S-based ROADM

Pluggable ROADMs at most sites

Third-Generation WSS ROADM

WSS ROADM is the preferred technology to provide:

Colorless operation - any channel to any port

Full n-degree operation for multiple ring, subtended ring, star, and full mesh topologies

Low insertion loss for through channels

ECI TELECOM ROADM VALUE PROPOSITION


The following figure shows a typical WSS ROADM application providing full inter-ring connectivity between C/DWDM access rings and the metro DWDM backbone, plus local add/drops at the ROADM node.

Figure 5: Typical WSS ROADM application

The ECI Telecom WSS ROADM implementation is fully integrated in the XDM shelves with "all-range" regional and metro amplifiers, and provides operators with a complete managed and flexible DWDM, SDH/SONET, and Layer 1/Layer 2 solution. All channels are fully monitored and managed by the Lightsoft® network management software.

B&S-Based ROADM

The B&S-based ROADM is optimized for hub sites with a large number (maximum 40) of add/drop channels. Similar to the WSS, the B&S ROADM has built-in metro amplifiers or can be integrated with regional amplifiers.

Pluggable ROADM

Available for over two years and already deployed in many sites worldwide, the pluggable ROADM is the most cost-effective solution for sites requiring four to eight channel add/drops.

CONCLUSION


Conclusion

An increasing need for capacity and flexibility in DWDM networks experienced by operators is the main driver in the development and deployment of ROADM solutions. These systems provide full management of wavelength services while reducing OPEX. The fast implementation of new revenue-generating services thus becomes greatly simplified and cost-effective.

ECI Telecom provides a comprehensive suite of ROADM solutions tailored to operators' needs:

Third-generation WSS ROADM advanced technology for full inter-ring connectivity between access rings and the metro backbone

B&S ROADM optimized for hub sites

Pluggable ROADM - the solution for 4-8 channel OADM sites that gives the most value for the investment

Integrated in the XDM and fully managed by the Lightsoft network manager, the suite of ROADM options provides operators with the most cost-effective flexible multiservice optical solution available today for metro, regional, and long-haul networks.

ABOUT ECI TELECOM


About ECI Telecom

ECI Telecom is a leading global provider of intelligent infrastructure, offering platforms and solutions tailored to meet the escalating demands of tomorrow's services. Our comprehensive 1Net approach defines ECI’s total focus on optimal transition to Next-Generation Networks, through the unique combination of innovative and multi-functional network equipment, fully integrated solutions and all-around services.

For more information, please visit http://www.ecitele.com.

http://www.ecitele.com/

1Net defines ECI’s total focus on facilitating our customers' optimal transition

to Next-Generation Networks, through the unique combination of innovative and

multi-functional network equipment, fully integrated solutions and all-around services

Tel:+44 (0)1242 530630 Fax: +44 (0) 1242 530660 E-Mail [email protected] www.horsebridge.net

Horsebridge Network Systems Ltd, 1 Pate Court, North Place, Cheltenham, GL50 4DY England.

ROADM Towards a Fully Flexible DWDM Network

Documents

Transcript of ROADM Towards a Fully Flexible DWDM Network