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Expert’s Guide to Optical Transport Networks:

Optical Transport Networkingby Paul Littlewood Fady Masoud with Earl Follis

Optical Transport NetworkingPublished byCiena7035 Ridge Rd.Hanover, MD 21076

Copyright © 2014 by Ciena Corporation. All Rights Reserved.

No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, without the prior written permission of Ciena Cor-poration. For information regarding permission, write to: Ciena Experts Books 7035 Ridge Rd Hanover, MD 21076.

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Contents

Executive Summary ....................................................................................... 7

Introduction: OTN Fundamentals ................................................................ 9

What Makes OTN Essential? ...................................................................... 11

Key OTN Benefits ........................................................................................ 11

Key Drivers in the Transition to OTN ......................................................... 13

OTN as the Successor to SONET and SDH .............................................. 14

OTN Values .................................................................................................. 15

OTN Architecture ........................................................................................ 16

OTN Bit Rates .............................................................................................. 20

OTN Multiplexing Hierarchy ....................................................................... 21

Forward Error Correction (FEC) .................................................................. 22

OTN Network Fit ......................................................................................... 22

Transforming Network Economics with OTN ............................................ 23

Control Plane Compatibility and Features ................................................ 28

OTN Market Acceptance ............................................................................ 32

Use Cases ..................................................................................................... 33

Use Case 1: Bandwidth Grooming (Sub-wavelength) on 40G/100G Backbones ................................................................................. 33

Use Case 2: Network Path Optimization ................................................... 33

Use Case 3: Core Router Offload ............................................................... 34

Real-World OTN Selection Case ................................................................ 34

Conclusion.................................................................................................... 36

Why Ciena? .................................................................................................. 36

OTN Glossary of Acronyms ........................................................................ 39

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Executive Summary

The adoption of Optical Transport Network (OTN) technology continues to gain momentum in the market. This is attributable to the significant leap forward in optical network technology that OTN represents and the waning fortunes of SONET/SDH networking. Though this Expert’s Guide is an in-depth look at the technical underpinnings and architecture of OTN networks, it’s important to remember that OTN technology can solve business challenges for Ciena’s customers by increasing the perfor-mance of their networks while saving money, lowering latency, increasing network manageability and paving the way for the network to embrace Cloud and Software Defined Networking. These aspects are described in this guide.

Advantages of OTN

OTN offers a number of advantages over legacy transport networks, and this guide details on these advantages in describing how they can be leveraged to provide carriers and service providers with top-performance optical networking, reduced costs and a broader service catalog. Benefits include:

• Reduction in transport costs• Efficient use of optical spectrum• Determinism • Virtualized network operations • Flexibility in network architecture, design and performance• Inherent security • Robust yet simple operations

What’s Driving the Adoption of OTN?

When SONET/SDH was originally architected in the early 1990s, data and voice networks were designed and built separately. But almost immediately, SONET/SDH was being used to combine data and voice traffic onto a single transport network, with data network elements adopting voice transport protocols and interfaces. Adaptations were developed to map data traffic over SONET/SDH frames so carriers could use SONET/SDH networks, but this proved increasingly inefficient, because voice and data payloads are constructed at significantly different rates. The industry learned that OTN must be designed to

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provide data transport in a format native to data networking. This meant fixed frame sizes instead of the fixed frame rates inherent in SONET/SDH. This fundamental change helps IP-based traffic to map into OTN much more efficiently than SONET/SDH. This tight integration of Internet Protocol (IP) and OTN via Ethernet is much more appropriate to the modern mix of networking protocols and traffic. The 40 Gigabits per second (Gb/s) line rate cap of SONET/SDH is no longer a barrier to data rate increases.

Network Modernization and Migration

OTN represents both a technical leap forward in optical networking and a business opportunity for carriers and service providers. OTN allows carriers and service providers to evolve to a mesh overlay combining SONET/SDH, Ethernet and OTN payloads, providing an effective means to build a modernized infrastructure but still carry legacy traffic. This architectural flexibility preserves existing investments in legacy transport while providing SONET/SDH access to 100 Gb/s lines and beyond. Selective upgrading, or capping and growing, allows service providers to evolve their networks in stages to avoid a costly disruption to core services or ‘all-at-once’ upgrade challenges.

Competitive Advantages of OTN

Opportunities abound for overcoming bandwidth, latency, and management hurdles by implementing converged networks of OTN and SONET/SDH. However, the real competitive advantage for Ciena’s customers is the adoption of OTN to seamlessly handle Ethernet and data center protocols through the network edges and cores, optimizing existing investments in routing interfaces, eliminating router hops, and minimizing network latency. OTN is the technology platform upon which Ciena delivers connection-oriented Ethernet traffic to ensure consistent, high-throughput, low-latency delivery at the most economical price point of any optical networking technology.

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Introduction: OTN Fundamentals

Telecommunications industry and service provider networks are quickly evolving to deal with an explosion of digital traffic driven by multimedia services, mobile applications, social media, Voice-over-Internet Protocol (VoIP), and cloud computing, and an ever-growing array of bandwidth-hungry applications. For decades, service provider network traffic was dominated by voice calls, in which traffic was carried over circuit-based networks in a predictable network connection between pairs of endpoints. Most network traffic today is packet-based, generated by a multitude of services and applications in bursty, unpredictable traffic patterns with widely varying demands on bandwidth and data transmission performance. Service provider networks that were once optimized for voice traffic are now in need of a new transport technology that can handle modern network traffic patterns and content.

Previous-generation transport technologies, such as Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH), were not designed for packet-dominated, high-capacity services requiring transmission capacities of 40 Gb/s and above. With this in mind, visionaries in the telecommunications industry created OTN, Optical Transport Network, which is standardized by the International Telecommunications Union (ITU) as G.709.

Networks employing OTN technology are designed and optimized to support current applications employing massive network capacity, and OTN is increasingly recognized as the transport standard of choice to meet the growing demand for network capacity. The ITU Telecommunication Standardization Sector (ITU-T) defines OTN in a set of standards, with the G.709 specification acting as the core technology definition. The ITU-T standards cover the encapsulation format, multiplexing, switching, management, supervision, and survivability of optical channels carrying client payloads. OTN also provides the ability to measure network performance across multiple service providers’ domains and to provide seamless, end-to-end monitored services.

Although it’s now common to link OTN and Ethernet technologies, OTN was not originally created to work specifically with Ethernet. In fact, OTN was developed to manage Wavelength Division Multiplexing (WDM) wavelengths with SONET/SDH as the client payload, given the wide deployment of SONET/SDH at the time. OTN was also intended

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to support a manageable wholesaled wavelength infrastructure. It is this original use case from which the capability of full payload transparency originated. By 2009, it was clear that the majority of traffic carried by OTN would be Ethernet-based, so OTN standards were enhanced to closely align with Ethernet traffic characteristics.

Often referred to as a ‘digital wrapper,’ OTN allows one or more different services to be transparently carried over a wavelength, each with its own full set of monitoring capabilities. Initially standardized in 1998, the adoption of OTN has steadily grown in the telecommunications carrier market. OTN initially provided an optical backbone for transparent carriage of SONET and SDH payloads; extended SONET/SDH-like Operations, Administration, and Maintenance (OAM); as well as Fault, Configuration, Accounting, Performance, and Security (FCAPS) capabilities to client payloads such as Ethernet, Fibre Channel (FC), ESCON, and digital video. OTN provides robust OAM features for WDM networks, including performance monitoring, fault detection, Forward Error Correction (FEC), embedded communications channels, latency measuring, and a standard mapping structure for multiplexing low-rate signals onto high-speed payloads.

In the 2009 update, G.709 was enhanced to more tightly integrate with Ethernet data rates and packet formats. As a result, OTN and Ethernet are now inseparable in most networks. This symbiotic relationship makes OTN the ideal protocol for transport of Ethernet over Dense Wavelength Division Multiplexing (DWDM) networks.

Industry observers anticipate strong OTN growth in the next few years. According to Infonetics Research,1 a respected analyst firm in the telecommunications industry, the OTN market was approximately $8 billion in 2013 and is expected to grow to $13 billion by 2017. That’s a 13 percent compound annual growth rate—faster than the projected growth in the general optical networking market. Infonetics further expects OTN switching to eventually become a de facto standard for WDM networks: 89 percent of carriers surveyed have implemented or intend to implement OTN switching by 2016.

1 Infonetics Research, OTN and Packet-Optical Hardware - Biannual Worldwide Market Share, Size, and Forecasts, March 2014

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What Makes OTN Essential?

When it comes to network infrastructures capable of carrying diverse and data-rich traffic, OTN delivers the high-speed, high-bandwidth networking and intelligence that carriers and their customers must have for optimum efficiency. OTN is recognized as the only optical technology defined to encapsulate the high-capacity payloads needed by packet-network entities such as Ethernet switches and routers. Critically, OTN is also the only optical transport protocol that currently scales beyond 40 Gb/s.

To keep pace with a continually growing demand for high-performance networks, organizations increasingly realize they must work to modernize and transform network operations. For the foreseeable future, bandwidth growth is unlikely to subside. In long-haul networks, the current highest OTN container (OTU4) can accommodate 100 Gigabit Ethernet (100GbE). The IEEE has already started to define rates for Ethernet above 100 Gb/s, and it is expected that OTN capable of carrying 400 Gb/s payloads will be required sometime in the 2015 timeframe, with 1 terabit per second (Tb/s) payloads projected to be in use before 2020.

OTN offers specific benefits in backbone and metro core networks, thanks to the complementary nature of IP and OTN. OTN-based IP backbones and metro cores offer significant advantages over traditional WDM-based networks, including increased efficiency, reliability around 99.999 percent, and wavelength–based private services. The combination of IP over OTN also offers better management and monitoring, reduced hops, protection of services, and reduced costs for equipment acquisition. In addition to scaling the network to 100G and beyond, OTN plays a key role in making the network an open and programmable platform, making it possible for transport to become as important as computing and storage in intelligent data center networking.

Key OTN Benefits

OTN wraps each client payload transparently into a container for transport across optical networks, preserving the client’s native structure, timing information, and management information. This means that any client, storage device, mainframe, digital video, Ethernet, SONET/SDH, OTN, wavelength, full-rate 10GbE, and more can be mapped onto an OTN wavelength.

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This technological adaptability makes OTN a fitting platform upon which organizations modernize their networks. By supporting legacy technologies such as SONET or SDH running concurrently with other clients on the same network infrastructure, organizations can gracefully transition to OTN in phases, without requiring wholesale replacement of the underlying optical network infrastructure.

Primary advantages of OTN include:

• Reduction in transport costs: By allowing multiple clients to be transported on a single wavelength, OTN provides an economical mechanism to fill optical network wavelengths.

• Efficient use of optical spectrum: OTN facilitates efficient use of DWDM capacity by ensuring fill rates are maintained across a network using OTN switches at fiber junctions.

• Determinism: OTN dedicates specific and configurable bandwidth to each service, group of services, or each network partition. This means that network capacity and managed performance (throughput, latency, jitter, and availability) are guaranteed for each client, and there is no contention between concurrent services or users.

• Virtualize network operations: The ability to partition an OTN-switched network into private network partitions, also referred to as Optical Virtual Private Networks (O-VPNs), provides a dedicated set of network resources to a client, independent of the rest of the network. Each network tenant sees only the resources associated with that tenant’s private partition. Other resources associated with other tenants will not be visible. O-VPNs also ease network evolution because network upgrades can be tested or introduced in a protected network partition or ‘sandbox,’ without the risk of impacting day-to-day network operations in production partitions.

• Flexibility: OTN networks give operators the ability to employ the technologies needed now to support transport demands while enabling operators to adopt new technologies as business requirements dictate.

• Secure by design: OTN networks ensure a high level of privacy and security through hard partitioning of traffic onto dedicated circuits. This segregation of network traffic makes it difficult to intercept data transferred between nodes over OTN-channelized links. And because OTN-switched networks keep all applications

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and tenants separate, organizations can effectively stop hackers who access one part of the network from gaining access to other parts of the network.

• Robust yet simple operations: OTN network management data is carried on a separate channel, completely isolated from user application data. This means OTN network settings are much more difficult to access and modify by gaining admittance through a client interface port.

No other technological solution allows operators to turn up new services faster and more efficiently while removing the cost of uncertainty from the future traffic mix. The advent of billions of network–connected consumer devices, and advances in the way content is delivered to users around the world, are generating demand for OTN solutions that makes this technology essential for next-generation networks.

Key Drivers in the Transition to OTN

Networks continually evolve, transforming to meet ever-growing bandwidth and service requirements. The introduction of SONET and SDH standards in the early 1990s enabled robust and efficient transport of voice traffic over long distances, along with greater interoperability among carriers. WDM further increased network capacity by allowing multiple wavelengths to be carried on the same fiber. The reliability, capacity, and efficiency of SONET/SDH optical networks have set the standard since then.

By the mid-1990s, operators started to use SONET/SDH networks to carry data services such as Ethernet and Asynchronous Transfer Mode (ATM), primarily to avoid the need to operate two separate networks—one dedicated to voice and another dedicated to data. Transport network elements introduced technologies to map data traffic over SONET/SDH frames. Ethernet Inverse Multiplexing (mapping 10Base-T traffic into VT 1.5s) and Packet-over-SONET (mapping GbE over an OC-48/STM-16), among other solutions, became available. More protocols were introduced, such as Contiguous Concatenation (CCAT) and Virtual Concatenation (VCAT), which allow service providers to carry large–capacity data payloads distributed over smaller SONET/SDH containers (STS-1/VC-4). VCAT provides for greater flexibility, enabling SONET/SDH containers to be transported or routed independently.

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Since then, network traffic has increased exponentially, outgrowing the capacities of SONET and SDH.

After nearly 25 years since the introduction of SONET and SDH, the evolution of SONET and SDH standards has ceased, and the majority of SONET/SDH equipment is reaching its planned end of life. Considering the limited future usefulness of SONET and SDH hardware, most optical networking vendors have ceased major platform investments in SONET/SDH products. Support contracts between service providers and equipment vendors are becoming difficult to renew because many component parts have been discontinued by the manufacturers. Moreover, SONET/SDH is increasingly cumbersome. Client line rates continue to rise while technical limitations in the SONET/SDH standards have capped network capacity at 40 Gb/s (OC-768/STM-256).

Modern applications place increasing demands on the network and are becoming much more sophisticated and network dependent. High levels of performance, manifested as fast protection switching, low/zero packet loss, and other features, are key to ensuring the proper functioning of critical applications. Payloads such as Ethernet between data centers, native video between production centers, and synchronous storage traffic need careful treatment and typically very high capacity and robustness in the network.

Along with stringent performance demands, high availability is also crucial to many applications and the industries they serve. The current business climate simultaneously puts a significant amount of pressure on service providers to increase top-line revenue while reducing capital and operational expenses. And fierce competition is shaping service providers’ strategies in their quest to increase customer loyalty, tap into new revenue streams, and optimize day-to-day operations.

OTN as the Successor to SONET and SDH

Although OTN and SONET/SDH have similarities, there are also some significant design differences (see Table 1). Perhaps the biggest difference is that SONET was defined with fixed frame rates, while OTN was defined with fixed frame sizes.

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The G.709 standard defines client payload encapsulation, OAM overhead, FEC, and a multiplexing hierarchy. These functions deliver optical transport capabilities as robust and manageable as SONET/SDH, but with greater suitability for current traffic demands, and data center interconnection circuits in particular.

OTN is asynchronous and thus does not require the complex and costly timing distribution and verification of SONET/SDH. Instead, OTN includes per-service timing adjustments to carry both asynchronous (GbE, ESCON) and synchronous (OC-3/12/48, STM-1/4/16, SDI) services. OTN can additionally multiplex these services into a common wavelength.

Like SONET/SDH, OTN also offers comprehensive OAM, but with standardized FEC. OAM is used to efficiently manage network resources and services. FEC enables service providers to extend the distance between optical repeaters, reducing expenses and simplifying network operations.

OTN Values

There are practical and technical drivers behind customer migrations from SONET/SDH to OTN. OTN is the logical choice for a

OTN SONET/SDH

Asynchronous mapping of payloads Synchronous mapping of payloads

Timing distribution not required Requires tight timing distribution across networks

Designed to operate on multiple wavelengths (DWDM)

Designed to operate on multiple wavelengths

Scales to 100 Gb/s (and beyond) Scales to a maximum of 40 Gb/s

Performs single-stage multiplexing Performs multi-stage multiplexing

Uses a variable frame size and increases the frame size as client size increases

Uses a fixed frame rate for a given line rate and increases frame size (or uses concatenation of multiple frames) as client size increases

FEC sized for error correction to correct 16 blocks per frame

Not applicable (no standardized FEC)

Table 1: Comparison of SONET and OTN

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next-generation optical network that offers 100 Gb/s speeds today, while maintaining support for legacy SONET/SDH devices during the transition period. Other technical advantages of OTN include:

• OTN provides ‘deterministic’ and simple service delivery: Stringent service requirements cannot be met without ensuring deterministic service delivery. OTN builds a guaranteed delivery infrastructure in which every bit that enters a network is delivered according to a contracted Service Level Agreement (SLA). Premium services can be supplied and monitored using a simple operational model over a survivable OTN-switched network.

• OTN provides private, highly secured network services: OTN offers dedicated and secure connectivity over direct links or virtual networks by physically isolating each customer’s mission-critical traffic from the rest of the network. OTN links can also be encrypted at wire-speed for further protection from intruders. When coupled with a control plane, OTN enables self-healing restoration and the ability to survive multiple simultaneous failures, thus preventing massive and widespread service outages in the aftermath of network disruptions or natural disasters.

OTN Architecture

The OTN wrapper is made up of several components that constitute the hierarchy depicted in Figure 1 for overhead communication between network nodes. The Optical Transport Module (OTM) is the structure transported across the optical line interface. It has two parts: a digital section and an analog section.

The Optical channel Payload Unit (OPU) contains the payload frames. The ‘service layer’ represents the end-user services such as GbE, SONET, SDH, FC, or any other protocol. For transparently mapped services such as ESCON, GbE, or FC, the service is passed through a Generic Framing Procedure (GFP) mapper.

The Optical channel Data Unit (ODUk, where k = 1/2/2e/3/3e2/4) contains the OPU plus overhead such as BIP8, GCC1, TCM, and so on. The Optical Transport Unit (OTUk, where k = 1/2/2e/3/3e2/4) contains the ODU, provides the section-level overhead such as BIP8, and

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OTN Values in a Nutshell

OTN allows the network to be an open and programmable platform:

• Enables a smooth transition from circuit to packet–based services

• Underpins emerging and high-performance network-level applications

OTN reduces the cost of network operations:

• Improves wavelength efficiency up to 78 percent to minimize WAN link requirements

• Simplifies planning for IT upgrades/changes• Decreases dependence on specialized technical skills

OTN improves network application performance:

• Provides dedicated bandwidth to eliminate contention• Minimizes latency and jitter• Uses carrier-grade Performance Monitoring (PM) to

guarantee delivery per service specification

OTN supports integration of multiple applications:

• Carries any combination of service types on single or multiple wavelengths

• Seamlessly interfaces with any client device (router, Ethernet switch, SAN Director, SONET terminal, and others)

OTN supports business continuity:

• Circuit performance for data and storage clients• Comprehensive PM to ensure adherence to SLA

requirements across nested networks

OTN easily integrates geographically dispersed locations:

• Service-level grooming, which allows per-service add/drop at any location

• Broadcasting centralized application instance to multiple locations, using drop-and-continue

• Single-ended management from a remote Network Operations Center (NOC)

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supports the General Communication Channel (GCC) bytes for overhead communication between network nodes. The GCC is used for OAM functions such as performance monitoring, fault detection, and signaling and maintenance commands in support of protection switching, fault sectionalization, service-level reporting, and control plane communications. The physical layer maps the OTU into a wavelength and the Optical Channel (OCh), which runs across the optical line. Figure 1 shows the OTM hierarchy for overhead communication between

network nodes.

An Optical Multiplex Section (OMS) sits between two devices and can multiplex wavelengths onto a fiber, as shown in Figure 2. An Optical Transmission Section (OTS) consists of the fiber between anything that performs an optical function on the signal. An Erbium-Doped Fiber Amplifier (EDFA) counts as ‘line amplifying’ equipment. OTN offers six levels of tandem connection monitoring that enable a network operator to monitor a signal as it passes through other operators’ networks. This functional breakdown aids in fault management, as OTN overhead is rigorously aligned with these points.

Figure 1: Optical Transport Module (OTM)

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Figure 3 illustrates how different services are mapped onto common wavelengths (an OCh always contains a single OTU), thereby providing for sub-wavelength bandwidth management and decoupling of service rates from the line rate. OTN includes per-service timing adjustments to carry both asynchronous and synchronous (OC-3/12/48, STM-1/4/16, SDI) services, which may share a common wavelength.

Figure 2: OTN Line Structure Breakdown

Figure 3: OTN Supports Different Types of Services over the Same Wavelength

OCH

OMS

OTS OTS OTSWDM

Mux/Demux

fiber

10GbE

SONET/SDH

SONET/SDH10GbE

Video Video

1GbE

1GbE

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A cornerstone of OTN is transparency. Transparent payloads, a transparent multiplex hierarchy, and transparent timing are all inherent OTN features. OTN’s transparency enables the transport of any service without interfering with the client payload, OAM, or timing. This is important when offering wholesale services for third-party providers and for connecting equipment that may utilize the client OAM for overhead communications. Note that OTN is a single global standard adopted without modification worldwide.

OTN Bit Rates

OTN rates are equal to or higher than the bit rates of the client traffic. There are basically two types of mappings into an ODU: transparent and non-transparent. Transparent maps the complete client payload into an ODU (so the OTN rate is higher than the client rate), whereas non-transparent mapping removes some of the client signal overhead to conserve network capacity. More ODUs can be mapped into an OTU using this mapping strategy. Some key OTN line rates defined by the G.709 standard are listed in Table 2, and Table 3 lists the standardized ODUk rates of G.709. Additional rates are in development in the ITU for more clients and faster lines.

Signal Approximate data rate (Gb/s)

Optimized for

OTU1 2.66 SONET OC-48 or SDH STM-16 signal transport

OTU2 10.70 SONET OC-192 or SDH STM-64 or 10GbE Wide Area Network (WAN) physical layer (PHY) transport

OTU2e 11.09 10GbE Local Area Network (LAN) PHY transport (for IP/Ethernet switches/routers ports) at full line rate (10.3 Gb/s)

OTU3 43.01 SONET OC-768 or SDH STM-256 or 40GbE signal transport

OTU3e2 44.58 Transport of up to four OTU2e signals

ODU4 112 100GbE signal transport

Table 2: Standard OTN Line Rates

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OTN Multiplexing Hierarchy

OTN supports single- and multi-step multiplexing into higher containers at the ODU level, as depicted in Figure 4, which shows an abridged hierarchical view. For example, four ODU1s can be multiplexed into an OPU2. An OPU3 can contain a multiplexing of four ODU2s, 16 ODU1s, or a mixture of ODU1s and ODU2s. Figure 4 also shows that OTN supports both Low Order (LO) and High Order (HO) mapping. LO is

Signal Data rate (Gb/s) Optimized for

ODU0 1.24416 Transport of a timing transparent transcoded (compressed) 1000BASE-X signal or packets over GFP

ODU1 2.49877512605042 Transport of two ODU0 signals or a STS-48/STM-16 signal or packets over GFP

ODU2 10.0372739240506 Transport of up to eight ODU0 signals or up to four ODU1 signals or a STS-192/STM-64 signal or a WAN PHY or packets over GFP

ODU2e 10.3995253164557 Transport of a 10GbE signal or a timing transparent transcoded (compressed) 10G Fibre Channel Signal

ODU3 40.3192189830509 Transport of up to 32 ODU0 signals or up to 16 ODU1 signals or up to four ODU2 signals or a STS-768/STM-256 signal or a timing transparent transcoded 40GbE signal or packets over GFP

ODU3e2 41.7859685595012 Transport of up to four ODU2e signals

ODU4 104.794445814978 Transport of up to 80 ODU0 signals or up to 40 ODU1 signals or up to ten ODU2 signals or up to two ODU3 signals or a 100GbE signal

ODUflex (CBR) 239/238 x client bit rate Transport of a constant bitrate signal such as Fibre Channel 8 GFC or Infiniband or video

ODUflex (GFP) Any configured rate Transport of packets over GFP

Table 3: Standard ODUk Rates

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used when a client signal does not need further aggregation within the optical carrier (wavelength), and HO is used when sub-wavelength grooming and/or multiplexing is required. Note that 10G refers to a line rate, regardless of the type of traffic being transported, while 10GbE refers to Ethernet traffic operating at 10Gb/s.

Forward Error Correction (FEC)

One of the key advantages of OTN is its support of FEC in the OTU frame, which is standardized in ITU G.975. This overhead is added to the last part of the frame before it gets scrambled for transmission. FEC has proved to be efficient in correcting a very high number of errors in transmission due to noise or other impairments present in high-capacity transmissions. The standard FEC uses a Reed-Solomon RS (255/239) coding technique, in which 239 bytes are required to compute a 16-byte parity check. Allowing service providers to extend the distance between optical repeaters, FEC helps reduce both capital and operational expenses while simplifying the network topography by being able to skip amplifier sites.

OTN Network Fit

Figure 5 highlights where OTN fits hierarchically in network infrastructures. Depending on the specified service, some IP and IT services require routing. The output from the router layer is passed to

Figure 4: OTN Mapping Hierarchy

100G

40G

10GbE LANPHY

10G, 10GbEWAN PHY

Any bit rate

1GbE~1.25Gb/s

~2.7Gb/s

~10.7Gb/s

~11.1Gb/s

~43.0Gb/s

~111.8Gb/s

ODUflex: an interger number of tributary slotsof an OPUk (OPU2, OPU3, OPU4)

~104Gb/s

EncapsulationContainer

LineContainer

OC-48/STM-16

ODU0

ODU1ODU1

OTU1

ODUflex

ODU2 OTU2ODU2

ODU2e OTU2e

ODU3 OTU3ODU3

ODU4 OTU4ODU4

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the transport infrastructure to improve transport efficiency, as described previously. Other services not requiring routing, such as the private services in the figure, pass directly to the transport switching layer for carriage directly across the OTN infrastructure. The core function of each layer in the hierarchy is highlighted on the right side of the figure.

Transforming Network Economics with OTN

The key capabilities OTN delivers can be used to reshape the economics of high-capacity networks. Some significant use cases and applications of OTN are described as follows:

• Private line connection: One of the main contributors to a service provider’s top line is high-capacity private lines (OC-192, wavelength). They are well established, highly profitable, and, most importantly, they remain solid, growing network performers. Recent studies from Infonetics and Insight Research estimate these services are growing at a double-digit Compound Annual Growth Rate (CAGR) and accounted for $98 billion in 2013. OTN matches the SLA requirements of these services and lowers the cost of transporting high-capacity private line services through efficient bandwidth utilization. Many private line clients may be transported on the same wavelength if capacity allows.

Figure 5: OTN Fit with Other Network Layers

Ro

utin

gP

hoto

nic

Swit

chin

g

IP-based consumer &enterprise services

IP Internetworking

MPLS (optional)

Private connectivityservices

Service routing –forwarding based on global IP address

Sub-lambda bandwidthmanagement – agilevirtual wavelength layer,decouples service ratesfrom line rates

Agile Photonic Layer

Ethernet Encapsulation OTN Encapsulation

Serv

ices

High-bandwidth agile photonic connections

MPLS-TP OTNCarrierEthernet

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• Multiplexing/switching for 40G/100G lines: For years, service providers have used OTN dedicated wavelength point-to-point links to interconnect client equipment. These have employed either transponder- or muxponder-based network elements. Despite the simplicity of this approach, it can prematurely exhaust network resources (ports, bandwidth, fiber, and so on) because of sub-optimal capacity fill across a network. After periods of service churn or network upgrade, it might also lead to bandwidth fragmentation, resulting in even lower network utilization. Introduction of OTN switches into networks can improve wavelength fill and periodically be used to reduce fragmentation through grooming of OTN payloads at key locations across networks.

Adding OTN switching to an existing OTN transport network is a relatively smooth process that offers a quick return on investment. When OTN switching is added, organizations can stop using manual fiber connections for capacity grooming; bandwidth management is more efficient and less costly in a switch.

Increasingly, customers are buying services such as 10GbE private lines, which are clearly less than the capacity of 100 Gb/s lines. These services have been typically fulfilled using transponders or muxponders connected to a dedicated optical line using a single wavelength or multiple wavelengths. Muxponders are deployed on a service-pair (demand-pair) basis, as shown in Figure 6.

Because the optical lines are dedicated, the service is inflexible and results in underutilized hardware and stranded bandwidth. These hard-wired connections are extremely labor-intensive for engineering and operations, and often require truck rolls for maintenance or circuit changes.

By utilizing OTN switching at hub sites, as shown in Figure 7, back-to-back multiplexers can be eliminated while reducing the number of wavelengths required. The introduction of OTN switching at Reconfigurable Optical Add/Drop Multiplexer (ROADM) locations enables automated grooming of services and a reduction in the number of required wavelengths due to sharing of common capacity.

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OTN switching also allows for efficient bandwidth utilization by eliminating fragmentation, and it maintains higher wavelength fill under traffic churn. Because the wavelengths are highly utilized, the DWDM line systems are optimized, deferring premature network over-builds, as

Figure 6: Transponder/Muxponder Architecture

Figure 7: Introduction of OTN Switching at ROADM Locations

Back-to-back transponders

Physical connection Wavelength connection Muxponder endpoint

OTN switching at hub sites toeliminate back-to-back muxponders

Physical connection Wavelength connection Muxponder endpoint

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shown in Figure 8. Bandwidth optimization is mandatory as wavelength rates progress beyond 100G to 400G and 1 Tb/s.

• Increased network capacity: OTN provides managed growth to 100 Gb/s and beyond. This allows service providers to scale their networks or expand their service offerings without network re-engineering or massive capital investments. With 40 Gb/s and 100 Gb/s links, service providers can turn up services faster, reduce the cost per bit of service delivery, and provide relief to bandwidth-constrained fiber spans.

• Enhanced end-to-end service monitoring: OTN includes traffic monitoring solutions native to the protocol, with features such as Tandem Connection Monitoring (TCM), which allows end-to-end service monitoring across multiple domains (see Figure 9).

• Efficient and lossless switched core: The deterministic nature of OTN ensures there is no degradation of traffic across the network. This allows service providers to implement an inherently lossless packet core. Packet aggregation, with or without over-subscription, can be performed at the edge as necessary (see Figure 10). Once sufficient fill is achieved, traffic is mapped to OTN and carried across the core to its destination at the lowest possible cost.

Figure 8: Reduction in Wavelength Consumption Using OTN Switching

0

200

400

600

800

1000

1200

1400 Point-to-Pointmuxponders

FragmentedBandwidth

DefragmentedBandwidth

Dep

loye

d W

avel

eng

ths

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100G

40G

10G

40%reduction

Recovered 40%of the bandwidth

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Figure 9: Tandem Connection Monitoring (TCM) Provides Management Visibility

at Multiple (Nested) Levels

Figure 10: Efficient and Lossless Switched Core with OTN

OTN Core

Lossless Core(with dedicated OTN links)

Packet Aggregation (with or without over-subscription)

Packet Aggregation (with or without over-subscription)

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• Network modernization: OTN is recognized by a majority of carriers as the evolutionary path for their SONET/SDH networks. OTN provides SONET/SDH access to 100 Gb/s lines and acts as a gateway for legacy transport networks. By selectively upgrading or capping and growing, service providers can evolve their networks over multiple stages to avoid any disruption to core services. An example evolution from inefficient ring interconnect to mesh overlay to intelligent mesh is shown in Figure 11.

• Core IP router express connection: Many operators are already aware of the much higher cost of switching traffic on a router as compared to an OTN or Ethernet switch. The extra cost is attributed to the additional sophistication of router traffic processing and its management and operations complexity. Because IP traffic is packet-based, many operators believe Multi-Protocol Label Switching (MPLS) routers are necessary everywhere in the network, regardless of traffic patterns. OTN allows the offload of transit IP traffic from core routers, thus reducing the number of router ports and overall network cost. This offloading of transit IP can also help providers delay capacity upgrades. Customer case studies have shown capital cost reductions of 20 to 60 percent, achieving cash-flow breakeven within nine months. OTN also lowers Ethernet service delivery costs through expressing traffic around edge routers while enhancing service performance and network availability.

Control Plane Compatibility and Features

The value of OTN is multiplied significantly when combined with an Automatically Switched Optical Network (ASON) or a Generalized MPLS

Figure 11: Ring-to-Mesh Network Modernization Scenario

SONET/SDHRing

SONET/SDHRing

Baseline

Inefficient ringinterconnect

*EOL/MDequipment

*End of Life/Manufacturer Discontinued equipment

“Expensive”capacitygrowth

SONET/SDHRing

SONET/SDHRing

OTNMesh

Step 1Step 2

Improve spaceand power footprint

OTN meshoverlay for

high-capicitycircuits

Add newOADMlocation

Replacing failingequipment and

“recover” spares

Add new linksto extend mesh

Evolution toOTN/Packet-enabled

intelligent mesh

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(GMPLs) control plane. The control plane automates many network operations such as service turn-up, modification, and tear down; maintenance planning and execution; and automatic discovery of the network including network extensions. The control plane also provides automatic restoration and routing of impacted traffic without human intervention. Service feature sets can be expanded to support many options, including various levels of service availability and dynamic services.

An intelligent mesh solution can reduce service provisioning time from months to less than an hour. A control plane also makes the network much more resilient by handling multiple simultaneous failures, which can raise network availability to the level of six-9’s (99.9999 percent).

Some of the key capabilities of the control plane are described as follows:

• Automated network operations: The control plane provides the intelligence needed to streamline operations by automating many network operations, leading to faster service turn-up, better management, and significantly faster service restoration. The primary functions of the control plane include:

° Automated connection management

° Automated self-inventory and maintenance

° Automated discovery

° Automated restoration

• Tiered availability: Service providers can now design customized, tiered service classes from a rich set of available building blocks, as shown in Figure 12. Options can be constructed such as restoration time (50ms, 250ms, 500ms), the number of failures protected against (one or many), and provision of minimal or no protection for low-priority traffic. Offering flexible, tiered services helps expand the capability of OTN to meet the needs of an increasing customer base while also meeting the requirements of sophisticated applications.

• Real-time latency measurement: Complying with a maximum latency SLA is a key factor in many OTN applications such as data center interconnection. Latency measurements are native to OTN and can be used to ensure SLA compliance.

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• Dynamic infrastructure: OTN and the control plane allow the network to become dynamic and responsive to upper-layer applications in real time. Emerging services, such as on-demand or scheduled cloud interconnections in which the control plane negotiates with the cloud operating system, are possible. The network operates as a partner with cloud servers and storage to support new high-value applications, actively providing and releasing capacity upon the command of the Application layer, as depicted in Figure 13.

Figure 12: Increase Network Survivability with OTN and Control Plane

Figure 13: OTN and Control Plane as a Dynamic Pool of Resources for the Cloud

Extra Bandwidth

CloudApplicationsand Services

✓ the network becomes dynamic pool of resources

Intelligent Network

New Connections Self-healing Proactive Network Monitoring

“Client-Server”Interaction

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• Optical Virtual Private Networks (O-VPNs): O-VPNs enable service providers to virtually partition their networks by allowing specific links, wavelengths, sub-wavelengths, or even nodes to be dedicated for use by a single customer, such as an enterprise. As shown in Figure 14, virtual network partitions provide all of the bandwidth, manageability, and security required, but without the expense and inflexibility of building a completely separate dedicated service infrastructure. O-VPNs provide a secure, high-bandwidth private network that connects end-user sites with a flexible, managed virtual infrastructure over fractional, single, or multiple transparent optical wavelength connections. This is done with a wide variety of client interfaces, including Ethernet, OTN, SONET, SDH, Storage Area Networks (SANs), and video. In addition, O-VPNs provide a virtual infrastructure for end users to manage their own site-to-site connections, bandwidth allocation, and circuit protection options within the O-VPN domain.

In Figure 14, as a way to illustrate virtualization, the Enterprise A partition could provide high-availability mesh-protected connections to support mission-critical applications for a variety of packet and storage protocols. The Enterprise B partition may be established to support cloud services in which customers can schedule large data transfers required for storage mobility or virtual machine migrations.

Figure 14: Optical Virtual Private Networks

O-VPN for EnterpriseEnterprise A

Headquarters Data Center

Enterprise B

Service Provider’sInfrastructure

Branch Office

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Despite O-VPNs being offered across a service provider’s network, they provide dedicated bandwidth to connect multiple end-user sites in a mesh configuration with multiple parallel line rates available, while maintaining full separation of user traffic and restoration bandwidth. Full visibility of the network and optional control over provisioning, protection, and bandwidth-on-demand may also be provided using a secure, Web-based customer portal.

OTN Market Acceptance

OTN has been deployed into networks with increasing scope since its inception in 1998. Hundreds of thousands of OTN ports have been deployed and are now carrying mission-critical traffic across a wide spectrum of applications.

In March 2014, Infonetics Research published a report titled OTN and Packet-Optical Hardware - Biannual Worldwide Market Share, Size, and Forecasts, in which 21 optical networking decision-makers were surveyed about their use of and plans for OTN. It is important to note that the respondent service providers represented 34 percent of the world’s telecom Capital Expenditures (CAPEX). The results presented in the Infonetics report underscore the fact that OTN is indeed gaining market adoption. Some highlights of this survey include:

• 58 percent of total optical equipment in 2012 was OTN switching and transport

• 66 percent expected growth of OTN switching and transport in 2013• 78 percent of optical equipment will be OTN switching and

transport in 2017• 22 percent is the potential CAGR growth of OTN switching

between 2012 and 2017• 80 percent growth of OTN switching from 1H12 to 1H13• 35 percent growth of OTN Switching market from 1H13 to 1H14

(versus 3% growth for OTN transport in the same period)• 3X North American spending on OTN switching 1H12 to 1H13• First wavelength (40G/100G) efficiency is one of the key applications for OTN switching

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The deployment of OTN is also expanding into new application landscapes. For example, industry experts see an expansion of OTN from the core of the network to its metro edge, thus extending the benefits of service transparency and efficiency directly to end-users for data services such as 1GbE and 10GbE. Meanwhile, the evolution of OTN is not restricted to dry land. Instead, it is expected that all sub-sea cable networks that currently operate over SDH will be migrating to OTN sometime in the near future, to gain the benefit of OTN’s higher bit rates (40 Gb/s and 100 Gb/s), latency awareness, and advanced management features.

Use Cases

Real deployment scenarios and numerous network studies have quantified the benefits of deploying OTN for transport and switching. The customer use cases included here highlight those benefits.

Use Case 1: Bandwidth Grooming (Sub-wavelength) on 40G/100G Backbones

This example took place on the national backbone of a Tier 1 service provider in the United States. Traffic consisted of a mix of 10G wavelengths, including OC-192 and 10GbE serving wholesale and retail private lines with approximately 3,000 10G circuits. An architectural comparison was made between using point-to-point muxponders only versus muxponders plus a switched OTN core for sub-wavelength grooming. The results revealed a 32-percent reduction in the number of deployed ‘lit’ wavelengths and 13-percent reduction in deployed capacity.

Use Case 2: Network Path Optimization

This example focuses on how a switched OTN architecture helped optimize a newly added path to the network, which was part of a planned expansion to address traffic growth requirements. The study revealed that OTN with control plane automation allowed for a periodic regrooming of traffic onto more efficient routes, reducing average path latency, recovering optical spectrum by grooming onto higher bit-rate

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wavelengths, and rebalancing traffic to avoid congestion. Key benefits realized include:

• 19 percent reduction in average path latency• Up to 30 percent reduction in bandwidth congestion on most

highly utilized links

Use Case 3: Core Router Offload

This example compares the CAPEX required for IP router interconnect over three different scenarios: IP over DWDM, IP over DWDM with some wavelength expressing between traffic-heavy nodes, and sub-wavelength interconnection using OTN switching. The study was performed on a 28-node network with a total of 47 links. The scenario with sub-wavelength interconnection using OTN proved to preserve 10G interconnect and topology with ODU2 virtual wavelengths, allowing for greater router capacity offload, in addition to extending the life of existing router port cards. This led to a 50-percent reduction in router CAPEX.

Real-world OTN Selection Case

OTN is ideally suited for carrier-class networks and high-bandwidth multi-tenant service providers transitioning from legacy technology, such as SONET and SDH, to packet-switching OTN-based networks. Native support for IP and Ethernet is intrinsic to OTN, making the transition to an OTN infrastructure relatively painless for customers with IP- and Ethernet-based services.

Many companies are deploying OTN as a means of leveraging their network investments via maximization of wavelength capacity while enjoying the increased network flexibility offered by OTN. A large proportion of Metro network traffic remains local to the point of origin, so moving OTN switching closer to the network edge increases overall network throughput by keeping traffic off Metro network cores.

The mesh topology of OTN and native support for IP/Ethernet traffic increases network efficiency, simplifies network architectures, and reduces latency. By supporting multiple service line rates on one common network, OTN provides a clear upgrade path for service

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providers who need their network infrastructure to easily scale along with their customers’ service requirements. To that end, OTN networks are designed to simultaneously support services with a variety of line rates from 1G to 10G to 40G and beyond. As a result, when a customer requests an increase in their contracted line rate, that rise can be implemented with just a few changes to the service provider’s network configuration, typically requiring no upgrade to network hardware, software, or applications. OTN-based providers can also allow for automated, dynamic expansion and contraction of line rates based on customer utilization or specific customer requests.

A large-scale service provider following this strategy selected Ciena’s OTN network hardware and software to ease the transition from their existing SONET/DS1/DS3-based network to a converged OTN network. The new network will support the company’s legacy networking infrastructure while offering a clear bridge to higher line rates, increased stability and efficiency, and native support for IP/Ethernet traffic. This provider expects their transition to OTN to grant them competitive advantage in the market space while reducing network and operations costs to deploy, maintain, and expand their optical networks as customer network demands increase. The ability to unite SONET/SDH devices with an OTN infrastructure is a key consideration for this service provider because the company still has a substantial investment in SONET/SDH that is no longer being upgraded or actively expanded as an optical transport standard. As their legacy devices near end of life in the coming years, the provider expects to gradually phase out legacy SONET/SDH and replace it with an entire OTN infrastructure. Clearly, this service provider believes strongly that OTN is the optical network of the future.

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Conclusion

To summarize, the key benefits of deploying OTN include: • Key element in making the network an open and

programmable platform

• Service transparency

• End-to-end monitoring

• Built-in measurement for latency

• Efficient client multiplexing/switching for high-growth services

• Scalability to 100 Gb/s and beyond

• Increased network survivability

• The ability to underpin the delivery of emerging high-capacity services

For most organizations today, the goal is to lower costs and streamline network operations. Organizations are simultaneously seeking a solution that will set a new benchmark in service economics and turn the network into a dynamic and intelligent pool of resources. OTN offers a deterministic and simple service delivery model that complements packet networks and paves the way for an entirely new generation of services—one that is likely to reshape the way people communicate.

Why Ciena?

Ciena delivers many state-of-the-art features and capabilities to enhance OTN performance.

Ciena’s OneConnect intelligent control plane, provides a proven track record, it is:

• Being deployed in the world’s largest mesh network• The industry’s richest OTN control plane; refined over more than

a decade of real-world experience• Scalable to 1000+ nodes

Ciena also offers the broadest portfolio of OTN solutions, including:

• A complete family of OTN transport and switching platforms• Seamless portfolio interworking for SONET/SDH/OTN and

packet switching

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Ciena remains committed to OTN innovation, including: • Coherent optical processing

• Rich network design tools

• Agile photonic networking

• Unmatched scalability

Ciena’s Converged Packet Optical Portfolio includes:

• 6500 Packet-Optical Platform • Converge three comprehensive networking layers into a

single platform to provide customizable service delivery from the access edge, along the backbone core, and across ocean floors.

• Allows tuning the network toward packet and/or OTN, in any ratio, with these high-density fabric modules. Fabric-based switching complements blade-based switching, allowing service providers to tailor their network from low-capacity point-to-point to high-capacity mesh connectivity, as needed.

• 5400 Packet-Optical Platform • Offer the industry’s first fully modular and reconfigurable

switching platform. The 5400 enables practical transition to a converged OTN and Ethernet-based, service-enabling intelligent infrastructure to achieve unmatched CAPEX and OPEX reduction, rapid service delivery, and high network availability.

• SONET/SDH/OTN and Ethernet on the same platform • Multi–terabit switching

Ciena’s OTN solutions deliver the most economical and optimized network for transport enterprise application traffic. Ciena’s solutions give enterprises the flexibility to tunnel Ethernet and data center protocols directly through the intelligent OTN core, optimizing any investment in routing interfaces, eliminating router hops, and minimizing latency. And Ciena’s approach enables delivery of connection-oriented Ethernet that ensures consistent, high-throughput, low-latency data delivery.Based on key capabilities, including programmability and automated management, Ciena’s approach to optical networking offers low-cost implementation and operation of OTN networks, providing the scalability and flexibility to serve as adaptable foundations for enterprise networks for years to come.

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OTN Glossary of Acronyms

ADM: add-drop multiplexer

ASON: Automatically Switched Optical Network

ATM: Asynchronous Transfer Mode

bps: bits per second or b/s

CCAT: Contiguous Concatenation

DS1: Digital Signal 1

DS3: Digital Signal 3

DWDM: Dense Wave Division Multiplexing

EDFA: Erbium Doped Fiber Amplifier

Ethernet Inverse Multiplexing: maps 10Base-T traffic into VT 1.5

FCAPS: Fault, Configuration, Accounting, Performance, and Security

ESCON: Enterprise System Connection

FC: Fibre Channel

FEC: Forward Error Correction

G.709: ITU-T recommendation for interfaces for the OTN

GbE: Gigabit Ethernet (10GbE = 10 Gigabit Ethernet, 100GbE = 100 Gigabit Ethernet)

GbE/s: Gigabits per Second

GCC: General Communication Channel

GFP: Generic Framing Procedure

GMPLS: Generalized Multi-Protocol Label Switching

IP: Internet Protocol

ITU: International Telecommunications Union

MAN: Metropolitan Area Network

Mb/s: Megabits per second

MPLS: Multi-Protocol Label Switching

OAM: Operations, Administration, and Maintenance

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OC-n: Optical Carrier Level n (1, 3, 12, 48, 192, 768)

OCh: Optical Channel

OCC: Optical Carrier Channel

ODU: Optical Channel Data Unit

OMS: Optical Multiplex Section

OOS: OTM Overhead Signal

OPU: Optical channel Payload Unit

OTN: Optical Transport Networking (see G.709)

OTS: Optical Transmission Section

OTU: Optical Transport Unit

O-VPN: Optical Virtual Private Network

Packet-over-SONET: GbE over an OC-48/STM-16

ROADM: Reconfigurable optical add-drop multiplexer

SAN: Storage Area Network

SDH: Synchronous Digital Hierarchy

SLA: Service Level Agreement

SONET: Synchronous Optical Network

Tbps: Terabits per second

TCM: Tandem Connection Monitoring

VCAT: Virtual Concatenation

VLAN: Virtual Local Area Network

VOIP: Voice Over IP

WAN: Wide Area Network

WDM: Wavelength Division Multiplexing

Paul Littlewood

Principal, Network Architecture Office of the CTO

Paul Littlewood is a principal engineer in the CTO team at Ciena. His current areas of interest include network architecture evolution, metro network design, and multilayer networking.

During his career, Paul has led product management and engineering teams in optical transport and digital cross-connect projects, and was also a leader in the definition and development of Carrier Ethernet technologies, including Resilient Packet Rings.

Paul has seven patents granted and has written a number of papers on optical networking. He has an honors degree in pure physics from the University of Newcastle upon Tyne in Great Britain

Fady Masoud

Senior Advisor, Technical Marketing Ciena Portfolio Solutions

Fady Masoud is a senior advisor for Technical Marketing at the Ciena Portfolio Solutions group. His area of expertise focuses on the architecture and requirements of next-generation optical platforms.

During his more than 18 years in the telecommunications industry, Fady has held various positions in the optical networking domain at Nortel and now Ciena. He started as a hardware test engineer on the first OC-192 (10 Gbps) systems and then as a systems engineer on optical metropolitan products, all combined with hands-on experience.

Fady holds a bachelor’s degree in electrical engineering from Laval University (Quebec City, Canada) and a master’s degree in systems technology (simulation of optical networks) from the Superior School of Technology (Montreal, Canada). He has written publications on next-generation optical networking, including 40G, ROADMs, intelligent network evolution strategies and architecture, and on many other key topics.