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IP and Optical Convergence: Use Cases and Technical Requirements

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Objective This is a non-proprietary white paper authored by network operators.

The key objective for this white paper is to outline the benefits, enablers and challenges for IP and Optical convergence and the rationale for encouraging an international collaboration to accelerate development and deployment of interoperable solutions based on high volume industry standard data and control plane solutions.

Status and Version: Final

Date of issue: 31.01.2014

Distribution: Public

Author(s): Company Name

Principal Editor Telefonica Juan Pedro Fernandez-Palacios

Editors and contributors

AXTEL Mexico Francisco Javier Rios

Bouygues Telecom Gregory Cauchie, Nicolas Lemonnier

BT Russell Davey, Rob Shakir, Andrew Lord

China Unicom Wang Guangquan，Zhou Xiaoxia

Colt Nicolas Fischbach, Valéry Augais

Deutsche Telekom Matthias Gunkel, Arnold Mattheus

KDDI Takehiro Tsuritani

Korea Telecom Kwang-koog Lee

Orange Julien Meuric, Olivier Renais, Thierry Marcot, Patrice Robert

Telecom Italia Marco Schiano, Alessandro D’Alessandro, Alessandro Capello

Telefonica Victor Lopez, Oscar Gonzalez, Felipe Jimenez, Pablo Aguilar

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Table of Contents

1 Executive Summary 3

2 Introduction 5

2.1 Definitions 5

2.2 Challenges to be addressed 7

3 Use cases for IP/Optical Convergence 9

3.1 Packet and Optical data plane integration 9

3.2 Packet and OTN integration in the Core 11

3.2.1 LSR switching-enabled optical core 11

3.2.2 Ethernet switching-enabled optical core 12

3.2.3 LSR router by-pass 13

3.3 Multilayer Control and Resilience 13

3.3.1 Automated IP/DWDM network operation 13

3.3.2 Multilayer resilience 15

3.4 Multilayer Planning and Management 18

4 Technology Enablers for IP and Optical Convergence 19

4.1 Pluggable Optics 19

4.2 Black Link 20

4.3 Control plane 21

4.4 SDN 22

4.5 Hybrid switching matrix 22

5 Recommendations /Call for action 23

6 Acronyms 24

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1 Executive Summary

The main goal of this white paper is to identify the most relevant use cases and technical requirements for IP&OC (IP and Optical Convergence). IP&OC can be achieved through multiple angles: data plane integration (colored interfaces), multilayer control and resilience, multilayer planning and management.

All of these pieces are not necessarily put in place at once. A network operator, making its way to IP&OC, does not need to deploy these capabilities all at once. The network type, topology and size, the network operation processes, the network life cycle (in place, to be replaced, new deployment) and the network migration steps will have a clear influence on the need for one, several or all of these capabilities. At the end of this document, a table provides the interest level per contributing network operator for each of the identified use cases.

Carriers are at a crossroad with their IP and Optical access, aggregation and core networks. Beyond the need to bring new services and service models faster to the market, they need to cope with the steady growth of traffic coming from IP services and content-centric applications. This is done using easier to manage infrastructures that radically reduce the operational complexity. Minimizing CAPEX and OPEX for these infrastructures is another point of emphasis for the operators. Additional influences include cultural changes related to convergent technologies and architectures within operators’ organizations. Technological advances enable more flexible and service-aware networking (e.g. SDN & NFV) beyond the static connectivity models of the past.

Next-generation multi-service networks have to provide high bandwidth to interconnect data centers, while, at the same time, providing for simplified operations and easing capacity upgrades. Beyond the common approach to overprovision the network by increasing capacity and installing more forwarding capacity, new ways of optimizing the design are required to better accommodate traffic growth.

Most of today’s existing Core and Backhaul transport networks rely on an optical transport layer based on WDM. Thanks to optical technology evolution, we are migrating towards an agile transparent WDM infrastructure based on ROADM. IP/MPLS network stands out as the main client layer of this flexible optical infrastructure.

Depending on different business and service models, there are two main core network architectures all around the world:

• Packet over DWDM networks where OTN is exclusively used for framing purposes.

• Packet/OTN/DWDM networks where transit traffic is mainly groomed/switched by OTN multiplexing/switching network elements.

In both cases enhanced control, planning and management mechanisms shall enable a better coordination between the transmission layer and its client layers (mainly IP), improving network efficiency, thus contributing to TCO reduction. In particular, multilayer resilience schemes are expected to minimize packet and optical back-up resources.

Data plane integration (i.e. colored optical transceivers in routers and packet switches) will also be a major step towards higher network efficiency in Packet over DWDM networks.

All network operators signing this document, independently of their particular core network architectures, declare their interest in IP and Optical convergence, including optimized network control and planning.

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Different use cases for both data and control plane multilayer integration are described in this document. However, current commercial solutions for IP and optical convergence, in both data and control planes, present several shortcomings in terms of multivendor interoperability which are currently limiting their application to single vendor networks.

This paper presents a set of technology enablers which would allow network operators to overcome these shortcomings and allow a widespread introduction of integrated data and control plane solutions in multivendor networks:

Black Link:

The existing standard ensures interoperability up to 10Gbit/s. For higher data rates, standardized application codes (ITU-T G.698.2) are still missing. Multi-vendor interoperability for 100G is less a technical issue (first interoperability tests have already been successfully carried out); it is a question of willingness of vendors and operators to move forward towards a new paradigm operating carrier networks. It is acknowledged that the achievable distance is smaller for a multi-vendor interoperable interface as compared to a proprietary interface. However, the target distance for a standardized interface should not be too small from the very beginning. Black Link standardization and implementation enables data plane integration in IP/OTN/DWDM networks.

Pluggable OTN transponders:

The integration of OTN framing, FEC and digital signal processing (DSP) into pluggable optics would enable multivendor interoperability (e.g. compatible pluggable optics integrated in different packet vendor nodes) and to extend data plane integration to long reach deployments. This technology in combination with the Black Link approach could enable network operators to have full interoperability vendor maps.

Multilayer control plane:

Multilayer operation, optimization and resilience mechanisms do not depend on data plane integration but require multilayer control support. Most packet and optical system providers are including basic UNI implementations in their control plane features. However, these implementations are almost useless unless they are complemented with additional standard control plane features enabling the use cases proposed in this document: multilayer resilience, automatic network provisioning, alien wavelength restoration, etc.

Multivendor SDN:

SDN can help operators to reduce the CAPEX and OPEX in the networks, allowing greater network flexibility, optimization of resources and the reduction of complexity in network operation. However, SDN solutions currently in development are still rather monolithic, and not well adapted to heterogeneous network environments in service provider networks. There is a need for modular SDN architectures, based on open and standardized interfaces between different SDN modules, allowing for a free choice of components and suppliers. Open and standardized interfaces allow removing or reducing the dependency on proprietary element management systems, and solving the problem of vendor lock-in for the operators.

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2 Introduction

Main technical aspects addressed in this paper are

1. Packet and optical data plane integration by the use of fixed/tunable colored DWDM interfaces into the IP routers and switches.

2. Multilayer control and resilience: enabling automated interworking between both IP and optical network control functionalities (e.g. resilience mechanisms). In the case of packet-optical integration, for example, the multi-layer control plane allows to automatically select the wavelength used by the integrated transponder.

3. Multilayer planning and management to handle both IP and optical layers as a seamless network where services are planned with the right path across layers (optimizing the resources used, the cost and the latency…) and with the right level of end-to-end recovery (optimizing SLA conformance).

2.1 Definitions

Packet and Optical Data Plane Integration

Packet and optical data plane integration is achieved by integrating DWDM or colored interfaces into the IP routers and switches. The transponder is moved from the optical system to the IP/packet device, eliminating the grey interfaces in both the packet and the transport equipment, thus reducing the number of transport elements (see Figure 1). In this way IP/packet devices can monitor the optical path and implement OTN framing and FEC.

In this case, the wavelength generated from the colored interface of the IP router and switch, transparently passes through the optical network, that may encompass amplifiers, filters and (R) OADMs. In terms of optical specifications such as optical max/min power, spectrum bandwidth and so forth, the multi-vendor optical interoperability between the colored transponders is required.

Figure 1: Packet and Optical Data Plane Integration

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Multilayer Control Plane

The control plane is the set of functions that are automatically performed by the network devices themselves. This automation allows to reduce the number of manual interventions, as well as to reduce the complexity of the network management. The functionality is aimed at simplifying the network creation process and providing self-recovery mechanisms.

Nowadays, IP and optical networks are operated independently, and the control plane mechanisms, if any, are not coordinated, leading to longer provisioning times, longer time to market, and less resiliency. The multi-layer control plane is the set of functions that allows to provision connections spanning through several network layers and to take coordinated actions in the recovery against failures.

In the case of packet-optical integration, for example, the multi-layer control plane allows to automatically select the wavelength used by the integrated transponder.

In case of no DP integration, a proper network design and operation allows a coordinated multi-layer control and recovery. E.g. a close coordination of IP recovery mechanisms with photonic recovery (e.g. restoration) might already achieve a minimization of packet and optical back-up resources. Thus DP integration is not a prerequisite for improving network efficiency. There are multiple approaches to operate networks with several layers and domains. E.g. the peer modelputs packet and optical nodes within a common IGP area, thus rapidly facing some scalability issues (IP routing in optical controllers?). The overlay model is based on the premise that the exchange of information between client and server networks is low due to confidentiality, trustiness and scalability issues, thus typically limited to signaling. Different augmented models stand between them: e.g., the border model extends the overlay by including packet border nodes within the optical IGP, thus addressing the concerns of the peer model.

Multilayer Management

Management relates to many aspects ranging from element, network and business management. Depending on the adopted management model, configuration, control and supervision of the network may be different. Data plane integration and multilayer control/SDN and Management are therefore strictly correlated and they influence each other.

In this document, multilayer management must be intended as management in a network with Packet/Optical data plane integration and/or with Multilayer Control/SDN.

A Multilayer Management model may offer carriers the opportunity to unify the management aspects of different technologies and at the same time provide more effective network control and supervision. The level of integration depends a lot from the availability of standard models/architectures/interfaces/functional specifications and from the cost of that integration in terms of systems changes and integration and from the cost of changes in carriers’ organization models.

Multilayer planning

With the IP layer being the main client of the optical network, the optimization of one layer independently of the other layer is no longer viable if network operators want to achieve a global optimization. Today, this multi-layer optimization is done rather manually based on extraction of data from each layer and by using tools with limited scope (single layer, single vendor).

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IP&OC would help network operator to handle both layers as a seamless network, where services are planned with the right path across layers (optimizing the resources used, the cost and the latency…) and with the right level of end-to-end recovery (optimizing SLA conformance). Tools with an entire view on both layers would also help in running fault simulation scenario and analysis on a global context.

2.2 Challenges to be addressed

Data Plane

1) Line-side standardization

Solutions ensuring data plane integration are available and deployable; however, higher speeds and longer reaches usually require specific, joint engineering efforts. Vendors offer colored interfaces today, but using proprietary technologies. To ensure interoperability it is indispensable to standardize the line-side of the optical transport network domain.

2) Operational issues

In many carrier networks two different organizations are responsible for IP and the optical transport domain by using different management solutions with less interaction. The integration of colored interfaces in IP routers would reduce the number of FCAPS information on the optical domain. The information which is needed on the transport domain and the additional information needed on the IP domain must be exchanged. There are different ways to exchange this information some of which has been specified at the IETF.

3) Physical integration vs. virtual integration

In some cases it could be beneficial if a separate interface shelf is used and the interfaces are virtually integrated. This issue occurs when new technologies enter the market and this point tackles mainly the core nodes of the network equipped with the latest technology. Normally you can see a shrinking of the form factor towards pluggable modules after time.

A from the management point of view logically integrated interface shelf must fulfill the first two points as well.

Control plane

IP link provisioning over optical networks is a basic operation which typically requires long operational workflows (see Figure 2).

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Figure 2: IP link provisioning workflow

Currently, when a new IP link is activated between two different locations interconnected by an optical network, the IP department identifies one free interface at each location and requests an optical channel between them. If the optical capacity exists, the transport department configures optical equipment and sets up such connection. When the IP department receives the setup acknowledgement, the IP routers are configured accordingly. This configuration process may take days to complete, even when network elements are already set up in the network.

In order to solve this problem, most packet and optical system providers are including GMPLS UNI in their control plane features. GMPLS UNI, as defined in RFC4208 allows specifying the explicit route of the path. That is, the packet router can include the details of the route. However, how does the packet node know the details of the route to be requested is not standardized yet. Thus, with basic standard UNI either the end points (source and destination) are specified, or a route (obtained by external means) is provided. There is no way to include additional constraints in the UNI request.

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3 Use cases for IP/Optical Convergence

3.1 Packet and Optical data plane integration

1.-Ring/Bus based optical infrastructure with metro/provincial scope

Replacement of 10Gbps/100Gbps connections between switches/routers connected through grey interfaces to a Ring/Bus compensated network with an End to End light path between colored pluggable modules inserted into the switches/routers. This corresponds to point-to-point and ring configurations of small distances, avoiding regeneration, where L1/L2 grooming and/or switching (electric level) at the intermediate nodes is not needed and when interworking between WDM interfaces in routers and legacy WDM is not present or limited (assuming alien wavelength support). Brownfield environment or metro network of limited perimeter could be others candidate scenarios considering completely port agnostic passive WDM system. Solutions based on simple pluggable optics (no OTN framing) for “multipurpose” boards (i.e. for 10Gbps those supporting any MSA compliant XFP) could be deployed according to different scenarios.

A potential alternative for the same segment (Metro Ethernet support) could be based on pluggable optics including OTN framing and FEC. This would allow extending the IPoWDM solution to every potential deployment. It would also allow mixed colored/grey scenarios where one of the light path endpoints is a colored pluggable while the other is a regular optical system transponder with a grey interface towards the router. This would imply the use of GFEC (for interoperability between the vendors) and will limit the maximum reach, but will not probably be an issue considering a metro/regional scope.

2.-Optical bus infrastructure with regional/national scope, no control plane

In order to provide future-proof and cloud-ready infrastructures, an evolutionary network architecture concept enables to cope with upcoming trends and requirements that affect carrier networks as well as the mode of operation of such kind of networks.

A first issue is the huge success of OTT (over the top) service providers addressing billions of customers without any complex network infrastructure. The second trend is the consolidation of suppliers of carrier-grade network equipment. To address these points together with the goal to reduce the transport costs, the following high level design criteria are to be covered:

� Simplification of design, reduction of internal interfaces and operational touch points

� Reduce the amount of technologies

� Integrate optical networks and IP networks as much as possible

� Use a common network for all services

� Cloud centric network architecture based on new SDN related management paradigm

Figure 3 shows the network scenario based on optical fiber rings to interconnect between Aggregation exchange Routers (AXR) and Packet Core Routers (PCR). AXRs aggregate business and residential customers using 100GBit/s interfaces towards the main PoP-Locations.

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EDFA

Coupler/

Splitter

EDFA

EDFA

Coupler/

Splitter

EDFA

DWDM

EDFA

Coupler/

Splitter

Data Centers

PCR

PCR’AXR’

EDFA

Coupler/

Splitter

Access

Network

AXR

Figure 3: Passive optical bus infrastructure based on splitters/couplers providing connectivity to data centers

Integrated colored interfaces are used in the aggregation/regional network to interconnect routers to data centers, using DWDM. The use of DWDM interfaces to connect Access Nodes is optional. The network design enables to reduce layers, and reduce OEO conversions by the use of colored interfaces.

The interconnection between the AXR and PCR routers will be established by using a plain WDM layer. Routers use coherent colored interfaces while each AXR is connected via point-to-point WDM links to two distinct PCR routers located at different sites.

There are 2 deployment models for the optical infrastructure that come into consideration:

1) Passive optical transport infrastructure working with power splitters/couplers or wavelength splitters/couplers following the optical “drop and waste” paradigm based on an open ring topology.

2) Using active OADMs or ROADMs to add and drop wavelengths to/from the system. Using OADMs/ROADMs allows increasing the mesh character of such kind of network, if required.

The first deployment model is suitable for small and medium-sized networks, while active optical elements can be added for large scale infrastructures. Both cases can be operated by the classic, centralized network management approach, or with an SDN management approach, without any additional control plane functionality in the optical transport network. The optical transport network infrastructure could be managed by a separate team or by common management staff.

In both cases colored coherent or un-coherent interfaces will be used to setup the wavelength channels between AXR and the PCRs.

OTN Framing will be used to ensure interoperability and the application of an enhanced FEC (eFEC) to successfully span national distances up to 1000 km. The FEC that will be used is expected to be widely available, and thus to be standardized, and/or based on an industry multi-source agreement supported by major suppliers.

Interoperability of integrated colored interfaces with a defined set of parameters is a major step towards integration. The agreement of a common paradigm on how to deploy and

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operate networks will foster the integration on the control and management perspective as well.

3.2 Packet and OTN integration in the Core

3.2.1 LSR switching-enabled optical core

In today’s metro core node architecture, connectivity to remote locations in distant cities is achieved through the use of two complementary platforms that are completely physically and logically separate:

- The long-haul optical platform in charge of switching wavelengths in the optical domain (ROADM function) as well as circuits in the electrical domain (OTN cross-connect function)

- The core packet platform in charge of switching MPLS-labeled packets also in the electrical domain (Label Switch Router function)

In the 2 to 3 year future we envision that these two platforms will collapse into one single platform with the optical platform being enhanced to also support MPLS switching.

On the OTN function it is likely that OTN switching, as opposed to the simpler OTN multiplexing, will be required for some time. This is due to the need to efficiently deal with high-speed leased line services (e.g. 10Gbps today) that the MPLS packet transport layer will not be able to transport because of scaling limit, even when considering the statistical multiplexing benefit.

Figure 4 shows metro areas connecting to the long-haul optical core enhanced with LSR packet switching capability.

L2 access &aggregation

(metro A)

L2 service

L3 service

L2 service

L2 CPE

L2 CPE

LSR-enabledoptical core

L2/L3 PE LSR/P

• Multi-layer switching platform– WDM (colourless, directionless)

– OTN

– Packet

• OTN switching– Fill-in the high speed waves

• Packet switching– MPLS switching (LSR)

– No LER (VPN, VPLS, GRE, MC), no BGP

– CP protocols (IS-IS, OSPF, TE, LDP, RSVP)

(metro C)

(metro B)

Figure 4 – Packet and Optical Switching Integration in the Core

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In terms of expected benefits, reducing the number & types of physical platforms and simplifying the overall service architecture shall make the operations easier; improve the various lead times to deliver and maintain the services; reduce the service unit costs; reduce the operational and capital expenditure costs.

Another side benefit envisaged with packet and optical switching integration in the core is the multi-layer integration of the control plane itself. The physical integration of optical and packet switching functions will enable a true multi-layer control plane (single IGP protocol, single optical & packet GMPLS provisioning protocol, etc.) that will also results in simplified operations.

3.2.2 Ethernet switching-enabled optical core

The described IPoDWDM solution in section 3.1 achieves cost reduction by eliminating the grey optics and the transponder used in separate router and DWDM systems. On the other hand, another approach called POTN/WDM (packet and optical transport network) is also interesting for operators who require more flexible migration in terms of IP and TDM services.

With the ability to accommodate multiple services (both IP and TDM) in a single integrated platform, the POTN/WDM solution transforms separated traditional WDM transport and IP core networks into a single integrated transport core with multilayer switching and services. The POTN/WDM basically consists of three layers PTN, OTN, and WDM, and provides scalable and flexible cross-connection of high-performance PTN/OTN switching through its universal switching fabric. First, the PTN (packet transport network) layer implementing MPLS-TP, PBB-TE, or pure Ethernet supports grooming IP services at port or sub-port level (e.g., VLAN) with its standard OAM and protection mechanisms. Additionally, its carrier-Ethernet capabilities support a wide range of services such as E-Line, E-Tree, E-LAN and E-Access based on the MEF (Metro Ethernet Forum) Carrier Ethernet certifications. On the other hand, the OTN (optical transport network) layer efficiently multiplexes both packet and TDM services with higher client signal rates (1G, 2.5G, 10G, 40G, 100G…). With more enhanced OAM and protection schemes than legacy SONET/SDH, OTN provides sub-lambda grooming for maximizing wavelength utilization and greater flexibility. Finally, the WDM (wavelength division multiplexing) layer offers high bandwidth capacity to meet traffic growth with its reconfigurable optical add-drop multiplexing (ROADM) technology where client service can be transported over any wavelength in any direction. The highly efficient photonic layer enables operators to lower transport network costs by eliminating unnecessary optical-to-electrical-to-optical (OEO) conversions.

One addresses that the multi-layer integration of the POTN/WDM approach is somewhat complicate by the multi-layer architecture compared to other IP and optical integration solutions such as IPoDWDM. However, the POTN/WDM has the flexibility to support both packet and TDM services with abundant OAM and protection schemes provided at each layer. Actually, the integrated universal switch fabric does not separate OTN and PTN switching. Rather, it is capable of performing native packet and circuit switching

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simultaneously based on cell switching technology using a multipurpose centralized switching fabric.

In summary, the POTN/WDM integrates both packet and optical capabilities including carrier-Ethernet, OTN, ROADM, and DWDM all in a single box. This multi-layer integration effectively reduces TCO (total cost of ownership) compared to traditional multi-box core network designs and increases revenue opportunities by offering customers more flexible network services.

3.2.3 LSR router by-pass

Another potential use of the packet and OTN integration in the Core is the possibility to transform the OTN+WDM network as a “P router”. If a transmission network is used as a “P router”, then direct PE-to-PE connectivity can be achieved. This “full-mesh” per say provides minimum RTT on PE-to-PE connectivity while minimizing the CAPEX on the transmission network since there is no need to deploy “nation-wide” lambda (for PE-P-PE connectivity) to interconnect two adjacent region PEs.

3.3 Multilayer Control and Resilience

Multi-layer control plane does not require integration in the data plane. Data plane integration may add more restrictions to control plane technologies, but if integration happens it can be an enabler of multi-layer control plane solutions. However, but multi-layer control plane can exist without the integration of data plane.

3.3.1 Automated IP/DWDM network operation

A multi-layer Control Plane allows a better coordination between the transmission layer and its client layers (mainly IP), improving network efficiency, thus contributing to TCO reduction. For instance, with this coordination, the IP layer can request optical bandwidth between 2 network points and this bandwidth can be released (and even switched-off for energy savings) when it is no more needed. The bandwidth resources can then be re-used by another client. It implies to use a flexible transport layer, based on flexible WDM to enhance end to end provisioning, routing and troubleshooting, with the ability to rely on innovative recovery schemes involving coordination of IP recovery mechanisms with photonic recovery (e.g. restoration).

The dynamic and autonomous setting of new adjacencies by the IP layer through a multilayer control plane can be considered through different use cases. We present in the following section a non-exhaustive list of some of the most interesting implementations we foresee in the coming years.

Automated link provisioning

Nowadays, operation of the IP/DWDM network is done via manual intervention of two different departments. This process is slow and very costly from multiple aspects. Automated link provision via control plane enables facilitating the interaction between the

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IP and optical layer, so the network operator can configure the network in a faster way and reduce the costs of this process.

Dynamic adjustment of adjacencies to face traffic evolution:

Considering that a free spare resource pool is in place (unsaturated links, production advance, shared resources for restoration…), the network has the ability to adjust the capacity of existing adjacencies, configure and set automatically some new adjacencies to face sporadic traffic evolution.

If this capability seems attractive to face unpredictable changes of traffic distribution, involved transport resources (router interfaces and transponders), which represent the main cost contribution, must be in place at day one. In the absence of flexibility point that interconnects several client layers to the transport interfaces (such as an OTN cross connect), resource sharing amounts to nothing more than the bandwidth available on the WDM link. The WDM link in itself (MUX, ROADM, Amplifiers) does not represent the main cost contribution of the global transport infrastructure, which limits the economic benefits of such approach. If the architecture includes a flexibility point, the free resource pool could rely on a part of interfaces that are used for shared protection purposes.

In this use case, convergence brings an improved scalability and flexibility according to traffic distribution changes, and allows faster / automated provisioning. It also provides the ability to handle specific events.

Low cost automatic re-attachment after disaster

In a standard flavor of disaster recovery services, access is provided in different sites that interconnect to a Data Center. This Data center is backed up in a distant location, so that all sites of the customer are dual homed to the 2 geographically dispersed data center sites. During normal operation, data are replicated between the two data centers.

We consider here the ability to reconfigure network connectivity thanks to dynamic setup/change of IP adjacencies and transmission resources. In case of a disaster (connection lost with the main data center), transport connections are modified to allow the connection of remote sites to the second data center site. Rather than configuring permanent dual homed connections, and provision all the associated interfaces in both the remote and the 2 data center sites, the interfaces normally used between the two data center for replication could be reused to provide the connection of the remote site to the second data center, leveraging on NG WDM flexibility (directionless colorless configuration).

In this use case, convergence allows proposing Dual Homing at a lower cost with non permanent connections, using photonic rerouting to redirect connections at no cost (provided that wavelength resources are available on the links).

Transport bandwidth auto-adjustment in the context of BoD services

Considering that the WDM layer could embed some OTN switching functions

In this use case, BoD services include Business services that can be adjusted to customer bandwidth needs, as well as transport services for operator internal needs offered to higher client layers. In the last case, transmission resources are available for several L2/L3 networks sharing the same transport network, each of them possibly having different temporal traffic distributions.

If BoD services rely on an OTN transport network with L2/L3 Function (Policing, shaping) bandwidth adjustment can be provided with an ODU0 granularity to the higher layer. One

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shall note that the required OTN switching function can be embedded in the WDM Platform. The bandwidth used on the transport network can be adjusted dynamically with no traffic hit thanks to Hitless Adjustment of ODUflex (HAO), through IP and transport Control plane interactions.

Convergence in this case improves flexibility, and provides transmission bandwidth sharing through different clients (higher layer / Business customers).

3.3.2 Multilayer resilience

Differentiated resilience mechanisms in multiservice core networks

In a meshed based optical infrastructure with national scope, we consider an advantageous architecture with an agile L0/photonic ROADM network interworking with an L3/router client network. The purpose of the agility of the photonic layer is to recover from failures in the optical domain and, by this, to reduce the number of optical interfaces as explained below. In the long run, the glue between the two interacting layers is a photonic control plane; as a short-term solution, the network might be operated mainly manually. Dedicated L1/L2 switching devices are not necessary and consequently are not considered in this use case.

In traditional packet networks, it is the IP layer who reacts to a failure. Following the traditional approach of having reactive resilience exclusively on the packet layer causes comparably badly utilization of both, router interfaces as well as transponders equivalent to lambdas on the optical layer. Though packet traffic is statistically multiplexed onto lambdas, those lambdas may be filled only up to 50 per cent in the maximum. The remaining capacity is reserved for backup if a failure occurs. Without any dynamic countermeasure on the DWDM layer, optical robustness is conventionally assured by the creation of a second 1+1 disjoint backup path. This comes along with a second transponder interface leading to more wavelengths and more links in the overall network. Directly related to these intrinsic inefficiencies are high capital expenditures inhibiting overall network profitability.

With a recently proposed converged transport network architecture (in the sense of an integration of packet layer devices and optical transport equipment), operators aim at building a network that comprises automated multi-layer resilience enabling considerably higher interface utilization. By treating different service classes unequally, capacity for best effort class traffic is optically recovered after a short delay, while high-priority traffic maintains priority and is served in the same way as today. The concept relies on an agile photonic layer where switching on the lambda layer is related with the least cost. Several studies proofed the feasibility and techno-economic superiority of this architecture.

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Figure 5: Example topology of a national backbone comprising of a meshed optical ROADM network (serving layer) and an IP router plane (client layer)

One peculiarity exists for backbone networks, which is not often mentioned but nevertheless is an important property and in practice often applied by operators. In reality the network infrastructure, as shown in Figure 5 above, is physically implemented twice in order to guarantee failure robustness. That means for resilience purposes the operator builds a so-called A and a B variant of the IP core network which mutually protect each other. As a consequence, every given IP PoP consists of an A and a B site. For example, the doubling strategy has an impact on working and backup paths. In case of a link failure in the ‘A’ network, there always exists a straightforward backup route in the B network. Both paths have to be mutually disjoint, though they follow similar geographical routes through the country. Therefore, also latency is usually similar.

This network architecture requires three main ingredients at least:

• Firstly, an agile DWDM layer with colourless and directionless, ROADMs provides faster service provisioning. Those photonic devices are also used for resilience switching at the physical layer (L0).

• Secondly, an integrated multi-layer packet-optical control plane offers a software-based flexibility including path selection in case of a network failure and signalling functionalities. An efficient integrated CP solution also comprises just the right amount of information exchange between the packet and optical layer. In the early days of the network, operators tend to run some processes manually in order to gain experience before migrating towards a fully automated control as the final goal.

• Thirdly, a standard interface allows configuring all IP routers using the same protocol. The advent of multi-layer control plane may ease the configuration of the MPLS and the GMPLS equipment. IP layer services also require configurations that go beyond control plane functionalities. After a failure, adding new routes or changing the metrics in the IP layer can help to optimize the IP topology.

Multilayer shared restoration mechanisms

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Considering interactions between IP and transmission CP, higher layer has the possibility to set up automatically some adjacencies in case of network failures, providing automated network reconfiguration. This use case potentially applies to any IP network relying on a flexible WDM / OTN network.

User-to-Network Interfaces (UNI) between IP and optical networks enable requesting for connections on demand, after a failure happens in the IP layer. This allows minimizing the number of IP resources for backup purposes.

Figure 6: Multi-layer IP-port resilient mechanism.

In traditional hierarchical IP networks where protection is handled through parities, the network dimensioning savings we can expect from such approach is limited to the interfaces that interconnect the routers of the 2 parities. Photonic restoration (and possibly 1: N protection of the interfaces) does not really help saving interfaces on the routers since we still need to protect them against equipment failures (duplicated redundant configurations). Such approach implies to continuously monitor the state of the network in order to plan the upgrades that might be required by the traffic growth, as network resources can be used autonomously with potentially no human confirmation.

On the other hand, multilayer resilience mechanisms could enable network operators to optimize IP back up resources since just a free IP port would be required in each node to recover any port failure in the router.

A main drawback of these multilayer resilience schemes is the recovery time since the whole service can not be restored until the light-path is established. According to it, this kind of restoration mechanism could only be applied to best-effort traffic without strict recovery times. On the other hand, a combination of 1+1 and multilayer resilience could enable network operators to extend the time to repair a failure in the IP layer [references].

Alien wavelength monitoring and restoration

Optical restoration is a feature given by the GMPLS control plane. This feature may be an optical layer problem, but when transponders are integrated in the IP cards it becomes a control plane issue involving network nodes of different layers. When a link is established using an integrated transponder, IP and optical nodes must have the mechanisms to

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support an optical restoration when there is a failure in any segment of the transport network.

router vendor

B

router vendor

B T

x

R

x

Vendor B

R

x

T

x

Vendor B

IP Node 1 IP Node 2

Figure 7: Multi-layer IP-port resilient mechanism.

3.4 Multilayer Planning and Management

When data plane integration is introduced and the overall network architecture is based on different vendors for the IP and DWDM systems, it is clear that management approach at both element and network level of the two sub-networks (the IP and the optical one) significantly changes with respect to the legacy approach.

The management system of the DWDM network is required to have visibility of the “optical interfaces” integrated into the IP devices that in turns must be able to expose in a standard way all the parameters that are required for a correct configuration by the DWDM management system. The demarcation between the two networks seems to be softening because the optical parameters of the same interface may be required to be visible also to the IP system for the evaluation of many aspects including server layer status and for the feasibility of the calculated path. The characterization of the interface between the layer 0/1 and the upper layers of the integrated interface may be subject to standardization work to evaluate the need to clear defines parameters and their manipulation from the two management systems.

The evaluation of the feasibility of the calculated path is also not trivial because optical systems (including optics integrated into the IP devices) are often characterized by vendor proprietary features to boost performances and to manage the overall network such as, for example, enhanced FECs, mitigation of propagation impairments by means of digital signal processing, or pilot tones to provide enhanced optical performance monitoring. How to grant compatibility of these vendor proprietary features probably requires further standardization works to help multilayer management and the impact of new optical systems based on coherent optics could speed up such integration.

Another item to be considered is how to manage the information carried by the Optical Supervisory Channel (OSC), which is terminated at the optical system because it carries information about optical multiplexed channels and optical fibers sections (OMS and OTS), which are related to optical systems. Nevertheless, some information related to the single optical channel (OCH), such as for example the missing activation of an optical cross-connection along the OCH path, are also carried by OSC and could be used by the optical interfaces, eventually integrated into the IP device, to properly trigger consequent actions.

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When Multilayer Control is introduced new paradigms may be adopted in terms of circuit design depending on the adopted model (peer, overlay, border, augmented…) and the adoption of Packet/Optical data plane integration. The various combinations of control interconnection with data plane integration must be carefully evaluated to fully understand their impact on management aspects and how their behaviors impact on a carrier organization. E.g. if we consider the Border Multilayer Control model with Packet/Optical Data Plane Integration it is likely that layer 2/layer3 components of the IP device have all information required to route the light paths across the DWDM network. Depending on carrier specific requirements, the knowledge of routing must be provided to the DWDM management system that needs therefore to be able to access such information onto the IP device beyond the layer 0/layer 1 components.

A further level of management integration, not considered in this document, is related to the fully integration of the management systems of the two technologies (IP and DWDM) that can bring to a better overall manageability of the network. The complexity of this integration is quite high because the different paradigms this network operate and it is not clear how deep this integration can be pursued. From a practical point of view it should be carefully evaluated the impacts of likely increased OPEX in qualifying the overall integrated management system because traditionally the IP layer is faster changing. Some examples of proprietary integrated systems already exist on the marked but this implies to buy the overall system from the same vendor (the entire IP and optical networks) that can considerably impact the evolution of a carrier network. On the other hand, it is worth noting the benefits of an integrated management system that can speed up and simplify the provisioning process, the fault management and the planning process. A converged management system is expected to simplify end-to-end multi-layers operations reducing the global network TCO. Some manufactures have already in their offer management platforms that cover both IP and optics segments in a single vendor environment and the others are moving toward this solution. These unified platforms allow fast end-to-end service provisioning, improves the visibility of multi-layer network and reduce the time needed for troubleshooting. However this approach implies to use IP and transport platforms from the same manufacturer, creating dependencies that constrain network evolutions. Additionally, it brings a significant risk of increasing part of the OPEX, through the different upgrades and associated release qualifications since IP Routers implies a higher number of release updates than pure transport equipments.

Avoiding proprietary management system suite would favor the integration into a converged OSS benefiting from open interfaces to IP layer and more specifically today to transmission layer.

It is therefore recommended to start working on standard solutions to enable converged network management systems.

4 Technology Enablers for IP and Optical Convergence

4.1 Pluggable Optics

The introduction of OTN framing and FEC into pluggable optics would enable multivendor interoperability (e.g. compatible pluggable optics integrated in different packet vendor nodes) and to extend data plane integration to long reach deployments.

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It would also allow mixed colored/grey scenarios where one of the light-path endpoints is a colored pluggable while the other is a regular optical system transponder with a grey interface towards the router. This would imply the use of GFEC (for interoperability between the vendors) and may limit the maximum reach application scope to metro/regional networks.

4.2 Black Link

Data plane (DP) integration aims to implement the transport network functionalities within just a few integrated circuits as far as possible rather than distributing the transport functionalities over many devices and intermediate physical layer interfaces. The protocol stack shall be kept as simple as possible, unnecessary (say redundant) parts of the protocol stack shall be avoided, and the number of physical layer interfaces shall be minimized. Thus less equipment is needed resulting also in a smaller power consumption and hardware-induced failure rate. Consequently lower CAPEX/OPEX is enabled from a technological viewpoint.

However, one has to face some risks due to DP integration. One of the most severe ones is the risk to run into a vendor-lock. Physical layer interfaces are required as demarcation points between vendor domains. Less interfaces result in less modularity. Therefore one has to find a synergy between DP integration and sufficient flexibility/modularity and interoperability where different vendors can come into play.

Network Management / Control Plane (NM/CP)

Vendor A

SS RS

Vendor B Vendor C

λk λk

Router/Switch

E1

Eth-Phy

OTI(Optical

TransmitterInterface)

Router/Switch

E2

Eth-Phy

ORI(OpticalReceiverInterface)

LØ-ON(Layer-Ø

Optical Network)

OA OADMOADM

Figure 8: Interconnection of routers/switches with an optically transparent network

This synergy can be achieved by the concept indicated in Figure 8. Routers/switches are connected to a layer-Ø optical network (LØ-ON), i.e. to an optically transparent network composed of fibers, optical amplifiers, OADMs, etc. According to the “black-link” (BL) approach the line-side single channel DWDM optical interfaces SS and RS must be fully standardized thus enabling data plane integration (in particular the elimination of grey interfaces and related transponders) along with multi-vendor interoperability (because the routers and the LØ-ON can be provided by different vendors A, B, C). An open access to standardized reference points E1 at the ingress of the Optical Transmitter Interface (OTI) and E2 at the egress of the Optical Receiver Interface (ORI) must be requested by operators and ensured by the vendors in order to avoid a vendor-lock for integrated coloured interfaces. The corresponding Ethernet physical interfaces (Eth Phy) have already been standardized up to 100 GbE. The line-side BL optical interfaces SS and RS have already been standardized up to 10 Gbit/s data rate in ITU-T G.698.2. The definition plus specification of parameters for 100G BL application codes in G.698.2 is in progress.

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The approach indicated above is intended to satisfy the needs of all involved parties for the use cases under consideration. In cases where ultra-long transmission distances are required one may use just the interoperable interfaces E1 and E2 and connect there an OTI/ORI from any vendor which can be implemented in the most efficient way by the corresponding vendor. In cases of medium-reach distances coloured integrated BL interfaces (with standardized parameters at SS and RS) – without using transponders - are expected to be very efficient. The network management (NM) plus control plane (CP) must be sufficiently flexible to incorporate such different use cases and related implementations.

4.3 Control plane

The main enabler from the control plane point of view is the UNI. However, basic UNI just enables basic automated network provisioning features and it is not enough to support all use cases presented in this document. Following table presents the enablers for each use case with data plane separation and integration.

Use cases (Data plane Separation)

Basic UNI (set up tear down, no wavelength)

Basic automated network provisioning

Differentiated resilience (FRR+GMPLS)

Multilayer Shared Restoration

Alien Wavelength Restoration

Automated network

provisioning

Select service type (restoration)

UNI with wavelength (in ERO or Label Sets)

Collect SRLG information

Collect TE metrics

UNI with route exclusions

UNI with service constraints

PCEP from router

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4.4 SDN

Software Defined Networking (SDN) and network programmability are hoped to offer the ability to direct application service requests towards the IP/MPLS network, which may be converged with the optical layer. The claim of the SDN approach is to help operators to reduce the CAPEX and OPEX in the networks, thanks to the optimization of the resources and the reduction of the complexity in the operation of the network. However, the emerging SDN controllers in the market are based on OpenDayLight, which is not adapted to current heterogeneous network environments. Such SDN solutions are like “black-boxes” and their deployments would lead to different problems for the operator: vendor lock-in (solutions in the market are mono-vendor), lack of support with proprietary protocols, problems to support end to end multi-vendor path establishment... There is a need for modular SDN architectures based on standard interfaces between different SDN modules, which could be implemented by different vendors, in order to solve the problem of vendor lock-in for the operators.

4.5 Hybrid switching matrix

Co-locating the optical & packet switching functions into one single platform (as described by the use case in section 3.2) suggests such a platform features a switching matrix that is capable of handling in the electrical domain both OTN and MPLS switching.

This said it is likely that not just any base hybrid agnostic switching matrix will enable the use case. Performance objectives of the agnostic matrix will be required too. Indeed integration will prove very difficult if key performances such as latency and jitter don’t perform equally to non-integrated platforms.

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5 Recommendations /Call for action

Potential joint actions on standardization (IETF, BBF, ITU-T)

Problems to be solved

Technology enablers

Recommendations

Automated Operation

Adaptation to Traffic evolution

Low cost Disaster recovery

BW adjustment for BoD

Basic UNI is not enough

Basic UNI (set up tear down, no wavelength)

Select service type (restoration)

UNI with wavelength

Collect SRLG information

Collect TE metrics

UNI with route exclusions

UNI with service constraints

PCEP from router

Data Plane Integration

Bus/ring (Metro)

Bus wo CP (Core)

Extended reach

Multivendor interoperability

Pluggable optics including OTN and FEC

Black Link

Multilayer Management Operational complexity

Multivendor interoperability

Standard solutions to enable a converged management/SDN

Multilayer planning Single vendor solutions Multilayer optimization in multivendor networks

Multilayer Resilience


Multilayer shared resilience

Alien wavelength restoration

Basic UNI is not enough

Basic UNI and Select service type (restoration)

UNI with wavelength

Table below summarizes the specific interest across the different Proposed Use cases

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DT

KD

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Tele

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Tele

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Automated Operation

Adaptation to Traffic evolution

Low cost Disaster recovery

BW adjustment for BoD

+

+

+

+

++

+++

+

++

++

++ ++

+

++

Data Plane Integration

Bus/ring (Metro)

Bus wo CP (Core)

+

+

+++

++

++

+

+++

++

+

+

Multilayer Management + +++ ++ +++ +++ ++ ++ +

Multilayer planning ++ +++ ++ +++ +++ ++ ++ ++

Multilayer Resilience


Multilayer shared resilience

Alien wavelength restoration

+

-

+++

+++

++

++

+++

+++

++

+++

+++

+++

++

++

+

+

Packet and OTN integration in the core

LSR switching-enabled optical core

Ethernet switching-enabled optical core

LSR router by-pass

+

+

+

+++

6 Acronyms

DSP Digital Signal Processing

DWDM Dense wavelength Division Multiplexing

FCAPS Fault Configuration Accounting

Performance Security

FEC Forward Error Correction

IP&OC IP and Optical Convergence

IPoDWDM IP over DWDM (coloured interfaces in

routers

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MSA Measurement Systems Analysis

NFV Network Functions Virtualization

OAM Operations, Administration and

Management

OCH Optical Channel

ORI Optical Receiver Interface

OSC Optical Supervisory Channel

OTI Optical Transmitter Interface

OTN Optical Transport Network

POTN Portable OTN

ROADM Reconfigurable Optical Add-Drop

Multiplexer

SDN Software Defined Networking

SLA Service-Level Agreemen

TCO Total Cost of Ownership

WDM Wavelength Division Multiplexing

XFP 10 Gigabit Small Form Factor Pluggable

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