Evolution of the Transport Network

Transcription

1 Evolution of the Transport Network Deirdre Doherty, Thomas Müller, Newman Wilson W H I T E P A P E R OPTICAL NETWORKING GROUP

2 INTRODUCTION In today's telecommunications environment, change is rapid and pervasive: traffic is growing exponentially, fuelled by both consumer and business demands; new optical technologies are allowing capacity to keep pace with demand, and are enabling new services; the regulatory environment is changing almost daily; and competition is intensifying on all fronts. In such an environment, choosing the right transport network, and the proper evolutionary path toward realising it, becomes a difficult and perilous proposition, as there are many variables to weigh, and substantial risks to consider. In this paper, we discuss the key factors affecting the evolution of the transport network, and provide guidance for future-ready the transport infrastructure. We begin by viewing traffic growth as the key driver behind the evolution of the transport network, and optical technology as the key enabler of transport evolution. We then present three transport architecture alternatives and consider the merits of each relative to future extension. Finally, we describe the needs of the transport network, and the elements of Lucent's transport network vision and evolution. We show that the benefits accruing to service-provider customers include flexible capacity management and a transport infrastructure that is truly futureready. TRAFFIC DEMAND GROWTH Figure 1 shows the projected growth in data-traffic demand over a four-year period beginning with the year Note that by the year 2002, growth in traffic demand is projected to increase by a factor of 16. This exponential growth assumes, of course, that the applications fuelling demand (voice, data, web, , file transfer, video, video conferencing, multimedia) will change and evolve over the next several years, as will the network protocols that must efficiently support them. The other half of the demand equation is, of course, a transport network of sufficient capacity and flexibility to accommodate exponential growth and near-limitless change. Transport infrastructure must evolve, therefore, in such a way as to provide reliable, flexible, manageable networks that interoperate among themselves, and that support longterm traffic growth independent of particular applications or protocols. TRANSPORT CAPACITY GROWTH The rate of growth in optical-transport capacity is expected to exceed the growth rate in data-traffic demand over the next several years, and also to surpass the rate of growth in switch/router capability (see Figure 2). The following scenarios support this outlook. We can extrapolate the actual growth rates in optical transport by taking the commercial release of the first 2.5 Gbps systems in 1991, and the first 400 Gbps systems in 1998, as the basis for the extrapolation. Doing this yields a growth rate of about 73% per year. We can then compare this growth rate to Moore's Law, which governs the growth of Routers and Switches. Moore's Law Year Figure 1: Data Traffic Demand Growth Multiplication Factor 2 LUCENT TECHNOLOGIES OPTICAL NETWORKING

3 Transport Element Switch/Router Year Figure 2: Transport Network Capacity Growth Multiplication Factor states that the number of transistors on a chip doubles every 18 months, thus yielding a growth rate of 46% per year. Other studies estimate the optical growth rate at 130% per year through Year 2001, and estimate the switch/router capacity growth rate at 20 to 50% per year 1. A Ryan Hankin and Kent (RHK) report on WDM 2 forecasts optical-capacity growth exceeding the switch/router capability growth. This report also shows the reduction in the cost of WDM-based transport. The extraordinary growth in transport capacity suggested above will continue to be achieved by a combination of electrical and wavelength multiplexing technologies. TRANSPORT NETWORK EVOLUTION ARCHITECTURE Evolution of the optical transport network necessarily involves evolution of the underlying architecture. There are three primary options for evolving the optical-transport architecture: Present Mode Operation Transport Layer Networking Client Layer Networking These options are illustrated in Figure 3. The Present Mode Operation option (CL, SDH, Optical) allows for evolving functionality and features in the three network layers independently. The SDH/SONET layer in this approach follows Present Mode Operation (Separate layer for SDH/SONET Functionality) Transport Layer Networking (SDH/SONET functionality integrated with optical layer) Client Layer Networking (Reduced SDH/SONET functionality integrated with client layer) Client Layers (CL) Client Layers (CL) Client Layers (CL) SDH/SONET SDH/SONET SDH/SONET Optical (WDM) Optical (WDM) Optical (WDM) Figure 3: Transport Network Architecture Options 1 VISIBIS WORKSHOP "IP OVER DWDM", JULY 1999, GENEVA, SWITZERLAND. 2 RHK REPORT "WDM AND OPTICAL NETWORKS: TECHNOLOGY AND MARKETS", LUCENT TECHNOLOGIES OPTICAL NETWORKING 3

4 well-established standards. Conforming to these standards helps fulfil the interoperability needs of embedded-base equipment, and the interconnection granularity (E1, E3, etc.) needs for a large fraction of leased-line capacity. In the Transport Layer Networking option, the lower two network layers are integrated, while keeping standards and interoperability requirements intact. The client-layer equipment (switches/routers) implements the SDH/WDM/optical interfaces functionality (to connect to the transport-layer network), but does not provide transport-layer networking functionality. By integrating functions in common equipment, there is potential in the near term for both equipment and operations cost savings. In the long term, functionality to can evolve in a unified infrastructure. Note that the investment at the physical layer (involving buried cables and associated equipment) tends to have a much longer life, during which there can be many life-cycle changes in the upperlayer protocols, the applications, and the corresponding upper-layer equipment. In the unified physical infrastructure, an integrated management approach is possible, which affords many key benefits, including provisioning flexibility; improved reliability, availability, and network efficiency (stemming from an integrated approach to fault detection); protection switching; and restoration. In the Client Layer Networking option, the upper-layer equipment (routers and switches) incorporates part of the functionality provided at the SDH/SONET layer, including protection switching in dual-ring architectures. Using this approach alone limits service-provider networks to ring implementations, but with cost reductions comparable to those in Transport Layer Networking equipment integrations, as the two implementations are very similar. The reduced functionality, however, can limit full interoperability as well as the flexibility associated with complete standards-based equipment. While it is possible to incorporate additional features to integrate protection functions with other features (associated with Upper Layer Protocol), such implementations tend to be proprietary, and do not lend themselves to operations in a multi-vendor, multi-service environment. In addition, there are concerns about this solution's scalability to large service-provider networks. As mentioned previously, the life-cycle of the client-layer (router) equipment is shorter, and the SDH functionality in the combined equipment may face premature retirement. In addition, there are additional costs associated with equipment swap-out operations. Table 1: Transport Architecture Comparison Present Mode Transport Layer Client Layer Operation Networking Networking Current Follows well- Aimed at retention and Reduced functionality standards- established SDH extension of SDH- (line-card type based standards for full analogous features in implementation) & functionality flexibility & inter- Optical/WDM restricted interworking operability Standards Independent evolution Integrated functionality Proprietary extensions functionality of functionality in all in a unified for a ring architecture extension layers infrastructure Life-cycle cost Separate long time- Separate long time- Pre-mature SDH swap containment scale infrastructure scale infrastructure out along with equipment equipment switch/router Operations/ Flexibility in Potential operations Operations efficiency upgrades (incremental) capacity efficiency but swap-out upgradeallocation related costs Standards Standardised Standardised Proprietary -based inter- switch/router (SDH) switch/router (SDH) implementations in networking interfaces employed interfaces employed switch/router interfaces Scalability for Proven in large Scalable to large Scalability concerns large networks networks networks exist 4 LUCENT TECHNOLOGIES OPTICAL NETWORKING

5 The three architecture options outlined above are compared in Table 1. LONG-TERM REQUIREMENTS This section identifies and briefly discusses the long-term requirements of the optical transport network: Open multi-service platform. Flexibility. Protection and restoration. Scalability. Management and supervision. Open Multi-Service Platform Next Generation Networks will need to provide a platform for an ever-growing number of different service types, today's existing and currentlydeveloping services as well as all future services. These new networks will need to allow both large and small companies to develop network applications and to offer associated services on the public network (Programmable Networks). The concept of Programmable Networks will leverage the creativity of new enterprises, and will be one of the sources of the anticipated exponential traffic growth. In order to support a large variety of services and applications, and Programmable Networks, the underlying infrastructure will need to be highly flexible, and will require easy adaptations to an ever-changing environment. Therefore, the infrastructure of the Next Generation Network must be open, and must support a large variety of different services. Exponential traffic growth, together with exploding service variety, will affect optical-network architectures at the client layer. The protocols involved will likely need to undergo significant change; the various network elements required will certainly need to be adapted to higher traffic loads; and even the client-layer logical topologies themselves will likely need to undergo significant change. In addition, because advancement in optical-networking technology is so rapid and radical, and because Programmable Networks will provide such an extensive variety of new applications, new client layers based on technologies not yet known will need to be developed and implemented. However, service providers cannot afford to supplant existing transport infrastructure in order to accommodate changes at the client layer. Hence, an Open Multi-Service Platform inevitably requires an optical-transport infrastructure that is independent of changes at the client layer, and that provides a pool of types of shared functionality; in other words, it requires Optical Transport Layer Networking. There is also an economical advantage to providing an Open Multi-Service Platform by way of Optical Transport Layer Networking: A transport layer in a network allows different services to share raw bandwidth. Even in the case where bandwidth requirements of different services might justify separate transport infrastructures, the savings in operations for a common basic transport infrastructure would make a common transport infrastructure far superior. Flexibility There will be continued need to manage capacities in transport networks. This need is induced by the fact that different services may have different peak times, certain capacities may be leased for limited periods, and main traffic relations may change over time. An example for the latter would be trade fairs creating - during different times of the year - temporary traffic peaks in different parts of a network (Figure 4). In this example, a rearrangement of the existing transport capacity could increase capacity use and defer adding new capacity to the network. Also, operations, upgrades, and repairs of portions of the network would require temporary rearrangement of traffic and hence some network flexibility. Key to implementing flexibility into an optical network is the eventual introduction of optical cross-connects and flexible add-drop multiplexers, as well as associated network management. In sum, optical transport networks will eventually require flexibility similar to today's transport networks. In order for optical transport networks to be shared among a variety of client layers and services, a clear separation must be made between the optical-transport layer and the client layer. This approach increases the overall efficiency of the network. LUCENT TECHNOLOGIES OPTICAL NETWORKING 5

6 Figure 4: Example of Network Flexibility Protection and Restoration Protection or restoration mechanisms can be implemented either in the client network or in the transport network 3. At first glance, it might seem preferable to leave protection to the client layer, because doing this would allow protection to be customised around different services. However, there are more advantages to implementing protection/restoration mechanisms in the transport layer: Protection bandwidth can be shared between different applications (for example, between Optical Shared Protection Rings and Optical restoration), thereby providing more-efficient bandwidth usage (Figure 5). Unified protection mechanisms provide operational advantages; for example, personnel and the network management system do not need to deal with an otherwise excessive variety of different protection mechanisms Leased-capacity services require that links with a specified level of reliability be written down in a service-level agreement. This in turn requires protection mechanisms in the optical layer. Scalability Scalability is fundamentally important for planning and deploying new technologies. Scalability is a measure of a network's ability to grow in number of users, number of network nodes, geographic reach, and total bandwidth. The challenge is to achieve scalability within the confines of other network requirements, especially those pertaining to cost, performance, and reliability. Consider the network example in Figure 6. The operator has deployed a client-layer transport architecture, and certain nodes experience sudden spikes in demand; for example, a major new customer comes on line. In Figure 6, to handle the increased capacity, the entire network must be expanded. This expansion includes adding intermediate client-layer nodes to provide 3 FOR A MORE DETAILED DISCUSSION OF PROTECTION OPTIONS, PLEASE REFER TO THE WHITE PAPER "MULTI-LAYER SURVIVABILITY" BY JOHAN MEIJEN, EVE VARMA, REN WU, AND YUFEI WANG. 6 LUCENT TECHNOLOGIES OPTICAL NETWORKING

7 Figure 5: Protection Sharing between Different Applications transport-like bandwidth management and survivability functions for the engineered routes. The problem is that the client-layer logical topology becomes tied to the network's physical-link topology. Our analysis shows that this coupling leads the more complex and expensive client layer to become de-optimised. At a time when there is so much growth and churn in new services, network operators cannot afford this kind of deoptimisation Transport networking provides a better solution, as shown in Figure 7. By implementing networking, bandwidth management, and survivability for aggregated traffic in the most efficient way, the client layer is freed to grow and operate in the most effective manner possible. Under this approach, expensive, client-layer upgrades are made only when they are absolutely required, while the reliable transmission achieved - provided by transport networking between service endpoints - makes it easier to ensure Quality of Service. Management and Supervision In the context of the evolving transport network, the optical network will need to assume more and more of the functions currently provided by SDH/SONET networks. This is certainly true of protection mechanisms, as we discussed previously, but is perhaps especially true of network management functions. For example, the parameters of Quality and Service Level Agreements will need to be monitored and controlled, not just at the edges, but also in different sections of the network. In addition, multi-vendor environments and high connectivity Demand spikes All routers must upgrade to handle more through traffic Client Layer Client Layer (a) Figure 6: Scalability Problems with Client Layer Transport Architecture (b) LUCENT TECHNOLOGIES OPTICAL NETWORKING 7

8 Controlled service layer upgrades Client Layer Transport Network Figure 7: Client Layer Scalability between separate networks will require monitoring of optical channels between different network islands. Also, leasing wavelengths will require usage of the entire network-management functionality currently used in SDH/SONET networks. This functionality can only be provided by the transport-network architecture. In addition, large transported bandwidths, representing high financial values, will need to be protected by sophisticated monitoring and measuring capabilities. In order to meet these requirements for network management, Lucent Technologies is developing a digital-wrapper technology, called WaveWrapper Technology, that provides optical-channel overhead independent of input-signal format. This overhead provides full network management capabilities in a virtually transparent network environment. See Figure 8. SHORT-TERM REQUIREMENTS Today, the SDH transport network provides the features of an open, integrated transport platform. The SDH transport infrastructure provides efficient capacity-sharing between different applications, highly flexible network elements like ADM and DXC, and reliable transport links. Also, SDH standards allow for extensive network management capabilities. In short, the great success of SDH networking is due to the fact that it provides the transport-networking functionalities for today's applications. Figure 8: Optical Channel "Digital Wrapper" 8 LUCENT TECHNOLOGIES OPTICAL NETWORKING

9 The high reliability and quality of service of leased lines provide a still booming market for SDH and SONET equipment. Both incumbent and new operators - even those operators determined to develop a completely IP-based infrastructure - offer leased-line services at SDH/SONET bit-rates today. Eventually, there will be more and more equipment that will interface to the transport layer at bit-rates matching the maximum SONET/SDH bit-rates. The SONET/SDH network will then move toward the edges of the transport network, and its functionality in the backbone and regional networks will be absorbed into the optical transport network. In the meantime, the advantages of an established SDH transport network and network-management environment should be exploited. CONCLUSION By the year 2002, growth in traffic demand is projected to increase by a factor of 16. Capacity growth in the transport layer is expected to be sufficient to accommodate this projected traffic growth. However, capacity growth in the client (switching/routing) layer is expected to lag far behind that of the transport layer. The network protocols needed to efficiently support various applications will evolve, and the client layer networking equipment will change accordingly. Hence, the infrastructure of the transport network must evolve in such a way as to provide reliable, flexible, manageable networks that inter-operate among themselves, and that support long-term traffic growth independent of particular applications or protocols. Transport-layer networking can provide a reliable, flexible, and manageable network sufficiently scalable to accommodate both near-exponential demand growth and near-limitless change. Transport-layer networking can support interoperability and long-term traffic growth independent of client applications and network protocols. Networking at the transport layer overcomes the serious architecture (and other) limitations of networking at the client layer. An efficient transport network infrastructure requires separation of the transport and client layers. Transport functionality should not be included in the client layers, because such integration leads to inefficiencies resulting from a lack of sharing between different applications. It also leads to a lack of scalability and higher operations costs. Today, transport-layer networking is provided by SDH/SONET standards-based networks. As transport networks evolve, transport-layer networking will migrate into the optical transport network. LUCENT TECHNOLOGIES OPTICAL NETWORKING 9

10 GLOSSARY Abbreviations Used: ATM Asynchronous Transfer Mode CL Client Layers DXC Digital Cross Connect DWDM Dense Wavelength Division Multiplexing FDDI Fiber Distributed Digital Interface FEC Forward Error Correction GbE Gigabit Ethernet Gbps Gigabits per second IP Internet Protocol OADM Optical Add/Drop Multiplexer OAM Operations, Administration, and Maintenance OCh Optical Channel OXC Optical Cross Connect PDH Plesiochronous Digital Hierarchy SDH Synchronous Digital Hierarchy SDL Simplified Data Link SONET Synchronous Optical NETwork WDM Wavelength Division Multiplexing 10 LUCENT TECHNOLOGIES OPTICAL NETWORKING

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12 This document is for planning purposes only, and is not intended to modify or supplement any Lucent Technologies specifications or warranties relating to these products or services. Performance figures and data quoted in this document are typical and must be specifically confirmed in writing by Lucent Technologies before they become applicable to any particular order or contract. The company reserves the right to make alterations or amendments to the detailed specifications at its discretion. The publication of information in this document does not imply freedom from patent or other protective rights of Lucent Technologies or others. WaveStar and AllMetro are trademarks of Lucent Technologies Inc. To learn more about our comprehensive portfolio and the new WaveStar ONG Series, please contact your Lucent Technologies Sales Representative or call LUCENT. Visit our web site at Copyright 1999 Lucent Technologies Inc. All rights reserved Printed in Holland / USA Lucent Technologies Inc. Marketing Communications Order Number: WP-009/ If you enjoyed this publication and are interested in our other White Papers, please visit the Optical Networking web site at for a complete listing of currently available titles.