INTERNET-DRAFT
     Document: draft-ietf-ipo-carrier-requirements-03.txt draft-ietf-ipo-carrier-requirements-04.txt             Yong Xue
     Category: Informational                                          (Editor)
     Expiration Date: December, 2002 May, 2003                                  WorldCom, Inc

                                                                  Monica Lazer
                                                                Jennifer Yates
                                                                  Dongmei Wang
                                                                          AT&T

                                                              Ananth Nagarajan
                                                                        Sprint

                                                            Hirokazu Ishimatsu
                                                        Japan Telecom Co., LTD

                                                                 Olga Aparicio
                                                       Cable & Wireless Global

                                                                 Steven Wright
                                                                     Bellsouth

                                                                         June

                                                                 November 2002

                    Carrier Optical Services Service Requirements

     Status of This Memo
     This document is an Internet-Draft and is in full conformance with
     all provisions of Section 10 of RFC2026. Internet-Drafts are working
     documents of the Internet Engineering Task Force (IETF), its areas,
     and its working groups.  Note that other groups may also distribute
     working documents as Internet-Drafts.

     Internet-Drafts are draft documents valid for a maximum of six months
     and may be updated, replaced, or rendered obsolete by other documents
     at any time. It is inappropriate to use Internet-Drafts as reference
     material or to cite them other than as "work in progress."

     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt.

     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.

     Abstract
     This Internet Draft describes the major carrier's optical service requirements
     for the
     automatic switched optical networks Automatically Switched Optical Networks (ASON) from both an end-user's
     as well as an operator's perspectives. Its focus is on the description of the
     service building blocks and service-related control plane functional
     requirements. The management functions for the optical services and their
     underlying networks are beyond the scope of this document and will be addressed
     in a separate document.

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     Table of Contents
        1. Introduction                                         3
         1.1 Justification                                      4
         1.2 Conventions used in this document                  4
         1.3 Value Statement                                    4
         1.4 Scope of This Document                             5
        2. Abbreviations                                        6
        3. General Requirements                                 7
         3.1 Separation of Networking Functions                 7
         3.2 Separation of Call and Connection Control          8
         3.3 Network and Service Scalability                    9
         3.4 Transport Network Technology                       9
         3.5 Service Building Blocks                           10
        4. Service Models and Applications                     10
         4.1 Service and Connection Types                      10
         4.2 Examples of Common Service Models                 11
        5. Network Reference Model                             12
         5.1 Optical Networks and Subnetworks                  13
         5.2 Network Interfaces                                13
         5.3 Intra-Carrier Network Model                       15
         5.4 Inter-Carrier Network Model                       16
         5.5 Implied Control Constraints                       16
        6. Optical Service User Requirements                   17
         6.1 Common Optical Services                           17
         6.2 Bearer Interface Types                            18
         6.3 Optical Service Invocation                        18
         6.4 Optical Connection Granularity                    20
         6.5 Other Service Parameters and Requirements         21
        7. Optical Service Provider Requirements               22
         7.1 Access Methods to Optical Networks                22
         7.2 Dual Homing and Network Interconnections          22
         7.3 Inter-domain connectivity                         23
         7.4 Names and Address Management                      23
         7.5 Policy-Based Service Management Framework         24
        8. Control Plane Functional Requirements for Optical
           Services                                            25
         8.1 Control Plane Capabilities and Functions          25
         8.2 Control Message Transport Network                 27
         8.3 Control Plane Interface to Data Plane             28
         8.4 Management Plane Interface to Data Plane          28
         8.5 Control Plane Interface to Management Plane       29
         8.6 IP and Optical Control Plane Interconnection      29
        9. Requirements for Signaling, Routing and Discovery   30
         9.1 Requirements for information sharing over UNI,
             I-NNI and E-NNI                                   30
         9.2 Signaling Functions                               30
         9.3 Routing Functions                                 31
         9.4 Requirements for path selection                   32
         9.5 Discovery Functions                               33
        10. Requirements for service and control plane
            resiliency                                         34
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            resiliency                                         34
         10.1 Service resiliency                               35
         10.2 Control plane resiliency                         37
        11. Security Considerations                            37
         11.1 Optical Network Security Concerns                37
         11.2 Service Access Control                           39
        12. Acknowledgements                                   39
        13. References                                         39
        Authors' Addresses                                     41
        Appendix: Interconnection of Control Planes            42

     1. Introduction

     Optical transport networks are evolving from the current TDM-based SONET/SDH
     optical networks as defined by ANSI T1.105 and ITU Rec. G.803 [itu-sdh] G.803[ansi-sonet, itu-
     sdh] to
     the emerging WDM-based optical transport networks (OTN) as defined by
     the ITU
     Rec. G.872 in [itu-otn]. Therefore in the near future, carrier optical transport
     networks will are expected to consist of a mixture of the SONET/SDH-based sub-networks sub-
     networks and the WDM-based wavelength or fiber switched OTN sub-networks. The
     OTN networks can be either transparent or opaque depending upon if O-E-O
     functions are utilized within the
     sub-networks. optical networks. Optical networking
     encompasses the functionalities for the establishment, transmission, multiplexing,
     multiplexing and switching of optical connections carrying a wide range of user
     signals of varying formats and bit rate. The optical connections in this
     document include switched optical path using TDM channel, WADM wavelength or
     fiber links.

     Some of the challenges for the carriers are efficient bandwidth management and
     fast service provisioning in such a multi-technology and possibly multi-vendor
     networking environment. The emerging and rapidly evolving automatic
     switched optical networks or ASON Automatically Switched
     Optical Network (ASON) technology [itu-astn, itu-ason] is aimed at providing
     optical networks with intelligent networking functions and capabilities in its
     control plane to enable rapid optical connection provisioning, dynamic rerouting
     as well as multiplexing and switching at different granularity level, levels, including
     fiber, wavelength and TDM time slots. channel. The ASON control plane should not only enable
     the new networking functions and capabilities for the emerging OTN networks, but
     significantly enhance the service provisioning capabilities for the existing
     SONET/SDH networks as well.

     The ultimate goals should be to allow the carriers to automate network resource
     and topology discovery, to quickly and dynamically provision network resources
     and circuits,  and to support assorted network survivability using ring and
     mesh-based protection and restoration techniques. The carriers see that this new
     networking platform will create tremendous business opportunities for the
     network operators and service providers to offer new services to the market, and
     in the long run to reduce their network operation efficiency cost (OpEx saving), and to
     improve their network utilization efficiency (CapEx saving).

     1.1. Justification
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     The charter of the IPO WG calls for a document on "Carrier Optical
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     Services Service
     Requirements" for IP over Optical networks. This document addresses that aspect
     of the IPO WG charter. Furthermore, this document was accepted as an IPO WG
     document by unanimous agreement at the IPO WG meeting held on March 19, 2001, in
     Minneapolis, MN, USA. It presents a carrier and as well as an end-user perspective
     on optical network services and requirements.

     1.2. Conventions used in this document

     The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
     "SHOULD", NOT","SHOULD",
     "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
     interpreted as described in RFC 2119.

     1.3. Value Statement

     By deploying ASON technology, a carrier expects to achieve the following
     benefits from both technical and business perspectives:
     -
     Automated Discovery: ASON technology will enable automatic network
     inventory,  Inventory
     management, topology and resource discovery and maintenance which eliminates the manual or semi-manual semi-
     manual process for maintaining the network information database that exist in
     most carrier environment.

     -

     Rapid Circuit Provisioning: ASON technology will enable the dynamic end-to-end
     provisioning of the optical connections across the optical network by using
     standard routing and signaling protocols.

     -

     Enhanced Survivability: Protection and Restoration: ASON technology will enable the network to
     dynamically reroute an optical connection in case of a failure using mesh-based
     network protection and restoration techniques, which greatly improves the cost-effectiveness cost-
     effectiveness compared to the current line and ring protection schemes in the
     SONET/SDH network.

     - Service Flexibility: ASON technology will support provisioning of
     an assortment of existing and new services such as protocol and bit-
     rate independent transparent network services, and bandwidth-on-
     demand services.

     - Enhanced Interoperability: ASON technology will use a control plane
     utilizing industry and international standards standards-based architecture and
     protocols, which facilitate the interoperability of the optical
     network equipment from different vendors.

     In addition, the introduction of a standards-based ASON control plane
     offers may offer the following potential
     value-added benefits:

     - Reactive traffic engineering at optical layer that allows network
     resources to be dynamically allocated to traffic flow.

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     - Reduce the need for service providers to develop new operational
     support systems (OSS) software for the network control and new service
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     provisioning on the optical network, thus speeding up the deployment
     of the optical network technology and reducing the software
     development and maintenance cost.

     - Potential development of a unified control plane that can be used
     for different transport technologies including OTN, SONET/SDH, ATM
     and PDH.

     1.4.  Scope of this document

     This document is intended to provide, from the carriers perspective,
     a service framework and some associated requirements in relation to
     the optical transport services to be offered in the next generation optical
     transport networking environment and their service control and
     management functions.  As such, this document concentrates on the
     requirements driving the work towards realization of the automatic
     switched optical networks.  This document is intended to be protocol-
     neutral, but the specific goals include providing the requirements to
     guide the control protocol development and enhancement within IETF in
     terms of reuse of IP-centric control protocols in the optical
     transport network.

     Every carrier's needs are different. The objective of this document
     is NOT to define some specific service models. Instead, some major
     service building blocks are identified that will enable the carriers
     to use them in order to create the best service platform most
     suitable to their business model. These building blocks include
     generic service types, service enabling control mechanisms and
     service control and management functions.

     OIF carrier group has developed a comprehensive set of control plane
     requirements for both UNI and NNI [oif-carrier, oif-nnireq] and they
     have been used as the base line input to this document.

     The fundamental principles and basic set of requirements for the
     control plane of the automatic switched optical networks have been
     provided in a series of ITU Recommendations under the umbrella of the
     ITU ASTN/ASON architectural and functional requirements as listed
     below:

     Architecture:
     - ITU-T Rec. G.8070/Y.1301 (2001), Requirements for the Automatic
     Switched Transport Network (ASTN)[itu-astn]

      - ITU-T Rec. G.8080/Y.1304  (2001), Architecture of the Automatic
     Switched Optical Network (ASON)[itu-ason]

     Signaling:

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     - ITU-T Rec.  G.7713/Y.1704 (2001), Distributed Call and Connection
     Management (DCM)[itu-dcm]
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     Routing:
     - ITU-T Draft Rec. G.7715/Y.1706 (2002), Architecture and Requirements for
     Routing in the Automatically Switched Optical Network [itu-rtg]

     Discovery:
     - ITU-T Rec. G.7714/Y.1705 (2001), Generalized Automatic Discovery
     [itu-disc]

     Link Management:
     - ITU-T Rec. G.7716/Y.1707 (2003), Link Resource Management for ASON
     (work in progress)[itu-lm]

     Signaling Communication Network:
     - ITU-T Rec. G.7712/Y.1703 (2001), Architecture and Specification of
     Data Communication Network [itu-dcn]

     This document provides further detailed requirements based on this the ASTN/ASON
     framework. In addition, even though for IP over Optical we consider IP as a
     major client to the optical network in this document, the same requirements
     and principles should be equally applicable to non-IP clients such as
     SONET/SDH, ATM, ITU G.709, Ethernet, etc. The general architecture for IP over
     Optical is described in the IP over Optical framework document [ipo-frame]

     2. Abbreviations

      ASON     Automatic Switched Optical Networking
      ASTN     Automatic Switched Transport Network
      CAC      Connection Admission Control
      NNI      Node-to-Node Interface
      UNI      User-to-Network Interface
      I-NNI    Internal NNI
      E-NNI    External NNI
      NE       Network Element
      OTN      Optical Transport Network
      CNE      Customer/Client Network Element
      ONE      Optical Network Element
      OLS      Optical Line System
      PI       Physical Interface
      SLA      Service Level Agreement
      SCN      Signaling Communication Network

     3. General Requirements
     In this section, a number of generic requirements related order to provide the
     service control carriers with flexibility and management functions control of the optical
     networks, the following set of architectural requirements are discussed. essential.

     3.1. Separation of Networking Functions
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     A fundamental architectural principle of the ASON network
     is to segregate the networking functions within
     each layer network into three logical functional planes: control
     plane, data plane and management plane. They are responsible for
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     providing network control functions, data transmission functions and
     network management functions respectively. The crux of the ASON
     network is the networking intelligence that contains automatic
     routing, signaling and discovery functions to automate the network
     control functions.

     Control Plane: includes the functions related to networking control
     capabilities such as routing, signaling, and policy control, as well
     as resource and service discovery. These functions are automated.

     Data Plane (transport plane): (Transport Plane): includes the functions related to
     bearer channels and signal transmission.

     Management Plane: includes the functions related to the management
     functions of network element, networks and network resources and
     services. These functions are less automated as compared to control
     plane functions.

     Each plane consists of a set of interconnected functional or control
     entities, physical or logical, responsible for providing the
     networking or control functions defined for that network layer.

     Each plane has clearly defined functional responsibilities. However, the
     management plane is responsible for the management of both control and data
     planes, thus playing an authoritative role in overall control and management
     functions as discussed in Section 8.

     The separation of the control plane from both the data and management
     plane is beneficial to the carriers in that it:

     - Allows equipment vendors to have a modular system design that will
     be more reliable and maintainable thus reducing the overall systems
     ownership and operation cost. maintainable.

     - Allows carriers to have the flexibility to choose a third party
     vendor control plane software systems as its the control plane solution
     for its switched optical network.

     - Allows carriers to deploy a unified control plane and
     OSS/management systems to manage and control different types of
     transport networks it owns.

     - Allows carriers to use a separate control network specially
     designed and engineered for the control plane communications.

     The separation of control, management and transport function is
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     required and it shall accommodate both logical and physical level
     separation. The logical separation refers to functional separation while
     physical separation refers to the case where the control, management and
     transport functions physically reside in different equipment or locations.

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     Note that it is in contrast to the IP network where the control
     messages and user traffic are routed and switched based on the same
     network topology due to the associated in-band signaling nature of
     the IP network.

     When the physical separation is allowed between the control and data plane, a
     standardized interface and control protocol (e.g. GSMP [ietf-gsmp]) should be
     supported.

     3.2. Separation of call and connection control

     To support many enhanced optical services, such as scheduled
     bandwidth on demand, diversity diverse circuit provisioning and bundled connections, a
     call model based on the separation of the, all call control and connection control is
     essential.

     The call control is responsible for the end-to-end session
     negotiation, call admission control and call state maintenance while
     connection control is responsible for setting up the connections
     associated with a call across the network. A call can correspond to
     zero, one or more connections depending upon the number of
     connections needed to support the call.

     The existence of the connection depends upon the existence of its
     associated call session and connection can be deleted and re-
     established while still keeping the call session up.

     The call control shall be provided at an ingress port or gateway port
     to the network such as UNI and E-NNI [ see Section 5 for definition].
     The connection control is provided at the originating node of the circuit as
     well as on each link along the path.

     The control plane shall support the separation of the call control
     from the connection control.

     The control plane shall support call  admission control on call setup
     and connection admission control on connection setup.

     3.3.  Network and Service Scalability

     Although some specific applications or networks may be on a small
     scale, the control plane protocol and functional capabilities shall
     support large-scale networks.

     In terms of the scale and complexity of the future optical network,
     the following assumption can be made when considering the scalability
     and performance that are required of the optical control and
     management functions.

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     - There may be up to thousands of OXC nodes and the same or higher
     order of magnitude of OADMs per carrier network.

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     - There may be up to thousands of terminating ports/wavelength per
     OXC node.

     - There may be up to hundreds of parallel fibers between a pair of
     OXC nodes.

     - There may be up to hundreds of wavelength channels transmitted on
     each fiber.

     In relation to

     As for the frequency and duration of the optical connections:

     - The expected end-to-end connection setup/teardown time should be in
     the order of seconds, preferably less.

     - The expected connection holding times should be in the order of
     minutes or greater.

     - There may be up to millions of simultaneous optical connections
     switched across a single carrier network.

     3.4. Transport Network Technology

     Optical services can be offered over different types of underlying
     optical transport technologies including both TDM-based SONET/SDH
     network and WDM-based OTN networks.

     For this document, standards-based transport technologies SONET/SDH
     as defined in the ITU Rec. G.803 and OTN implementation framing as
     defined in ITU Rec. G.709 [itu-g709] shall be supported.

     Note that the service characteristics such as bandwidth granularity
     and signaling framing hierarchy to a large degree will be determined
     by the capabilities and constraints of the server layer network.

     3.5.  Service Building Blocks

     The primary goal of this document is to identify a set of basic
     service building blocks the carriers can use to create the best
     suitable service models that serve their business needs.

     The service building blocks are comprised of a well-defined set of
     capabilities and a basic set of control and management functions.
     These capabilities and functions should support a basic set of
     services and enable a carrier to build enhanced services through
     extensions and customizations. Examples of the building blocks
     include the connection types, provisioning methods, control
     interfaces, policy control functions, and domain internetworking
     mechanisms, etc.

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     4.  Service Model and Applications
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     A carrier's optical network supports multiple types of service
     models. Each service model may have its own service operations,
     target markets, and service management requirements.

     4.1.  Service and Connection Types

     The optical network is primarily offering optical paths that are
     fixed bandwidth connections between two client network elements, such
     as IP routers or ATM switches, established across the optical
     network. A connection is also defined by its demarcation from ingress
     access point, across the optical network, to egress access point of
     the optical network.

     The following connection capability topologies must be supported:

     - Bi-directional point-to-point connection

     - Uni-directional point-to-point connection

     - Uni-directional point-to-multipoint connection

     The point-to-point connections are the primary concerns of the carriers. In this
     case, the following three types of network
     connections based on different connection set-up control methods
     shall be supported:

     - Permanent connection (PC): Established hop-by-hop directly on each
     ONE along a specified path without relying on the network routing and
     signaling capability. The connection has two fixed end-points and
     fixed cross-connect configuration along the path and will stays
     permanently until it is deleted. This is similar to the concept of
     PVC in ATM. ATM and there is no automatic re-routing capability.

     - Switched connection (SC): Established through UNI signaling
     interface and the connection is dynamically established by network
     using the network routing and signaling functions. This is similar to the
     concept of SVC in ATM.

     - Soft permanent connection (SPC): Established by specifying two PC
     at end-points and let the network dynamically establishes a SC
     connection in between. This is similar to the SPVC concept in ATM.

     The PC and SPC connections should be provisioned via management plane
     to control interface and the SC connection should be provisioned via
     signaled UNI interface.

     Note that even though automated rapid optical connection provisioning
     is required, the carriers expect the majority of provisioned
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     circuits, at least in short term, to have a long lifespan ranging
     from months to years.

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     In terms of service provisioning, some carriers may choose to perform
     testing prior to turning over to the customer.

     4.2.  Examples of Common Service Models

     Each carrier may define its own service model based on it business
     strategy and environment. The following are three example service
     models that carriers may use.

     4.2.1.  Provisioned Bandwidth Service (PBS)

     The PBS model provides enhanced leased/private line services
     provisioned via service management interface (MI)  using either PC or
     SPC type of connection. The provisioning can be real-time or near
     real-time. It has the following characteristics:

     - Connection request goes through a well-defined management interface

     - Client/Server relationship between clients and optical network.

     - Clients have no optical network visibility and depend on network
     intelligence or operator for optical connection setup.

     4.2.2.  Bandwidth on Demand Service (BDS)

     The BDS model provides bandwidth-on-demand dynamic connection
     services via signaled user-network interface (UNI). The provisioning
     is real-time and is using SC type of optical connection. It has the
     following characteristics:

     - Signaled connection request via UNI directly from the user or its
     proxy.

     - Customer has no or limited network visibility depending upon the
     control interconnection model used and network administrative policy.

     - Relies on network or client intelligence for connection set-up
     depending upon the control plane interconnection model used.

     4.2.3.  Optical Virtual Private Network (OVPN)

     The OVPN model provides virtual private network at the optical layer
     between a specified set of user sites.  It has the following
     characteristics:

     - Customers contract for specific set of network resources such as
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     optical connection ports, wavelengths, etc.

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     - Closed User Group (CUG) concept is supported as in normal VPN.

     - Optical connection can be of PC, SPC or SC type depending upon the
     provisioning method used.

     - An OVPN site can request dynamic reconfiguration of the connections
     between sites within the same CUG.

     - A customer may have visibility and control of network resources up
     to the extent allowed by the customer service contract.

     At a minimum, the PBS, BDS and OVPN service models described above
     shall be supported by the control functions.

     5.  Network Reference Model

     This section discusses major architectural and functional components
     of a generic carrier optical network, which will provide a reference
     model for describing the requirements for the control and management
     of carrier optical services.

     5.1.  Optical Networks and Subnetworks Sub-networks

     As mentioned before, there are two main types of optical networks
     that are currently under consideration: SDH/SONET network as defined
     in ITU Rec. G.803, and OTN as defined in ITU Rec. G.872.

     In the current SONET/SDH-based optical network, digital cross-connects (DXC) and
     add-drop multiplexer (ADM) and line multiplexer terminal (LMT) are connected in
     ring or linear topology. Similarly, we assume an OTN is composed of a set of
     optical cross-connects (OXC) and optical add-drop multiplexer (OADM) which are is
     interconnected in a general mesh topology using DWDM optical line systems (OLS).

     It is often convenient for easy discussion and description to treat
     an optical network as an subnetwork sub-network cloud, in which the details of
     the network become less important, instead focus is on the function
     and the interfaces the optical network provides. In general, a
     subnetwork can be defined as a set of access points on the network
     boundary and a set of point-to-point optical connections between
     those access points.

     5.2.  Network Control Domains and Interfaces
     A generic carrier network reference model describes a multi-carrier
     network environment. Each individual carrier network can be further
     partitioned into domains or sub-networks or administrative domains based on administrative,
     technological or architectural reasons. This partition can be recursive.
     Similarly, a network can be partitioned into control domains that match the
     administrative domains and are controlled by a single administrative policy.
     The control domains can be recursively divided into sub-domains to form control
     hierarchy for scalability. The control domain concept can be applied to routing,
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     signaling and protection & restoration to form an autonomous control function
     domain.

     The demarcation between
     (sub)networks domains can be either logical or physical and consists
     of a set of reference points identifiable in the optical network. From >From the
     control plane perspective, these reference points define a set of
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     control interfaces in terms of optical control and management
     functionality. The figure 1 is an illustrative diagram for this.

                                    +---------------------------------------+
                                    |   single carrier network              |
             +--------------+       |                                       |
            |
             |Customer      |       |  +------------+       +------------+  |
             |IP            |       |  |            |       |            |  |
             |Network       +--UNI  |       +--UNI--+  +  Optical   +--UNI--+ Carrier IP |   +--UNI--+CarrierĂs IP|  |
             |              |       |  | Subnetwork |       |  network   |  |
             +--------------+       |  | (Domain A) +--+    |            |  |
                                    |  +------+-----+  |    +------+-----+  |
                                    |         |        |           |        |
                                    |       I-NNI    E-NNI        UNI       |
             +--------------+       |         |        |           |        |
             |
             |Customer      |       |  +------+-----+  |    +------+-----+  |
             |IP            +--UNI  |            +--UNI--+  +            |  +----+            |  |
             |Network       |       |  | Optical    |       |  Optical   |  |
             |              |       |  | Subnetwork +-E-NNI-+ Subnetwork |  |
             +--------------+       |  | (Domain A) |       | (Domain B) |  |
                                    |  +------+-----+       +------+-----+  |
                                    |         |                    |        |
                                    +---------------------------------------+
                                             UNI                 E-NNI
                                              |                    |
                                       +------+-------+    +-------+--------+
                                       |              |    |                |
                                       | Other Client |    |  Other Carrier |
                                       |Network       |    | Network        |
                                       | (ATM/SONET)  |    |                |
                                       +--------------+    +----------------+

            Figure 1 Generic Carrier Network Reference Model

     A network can be partitioned into control domains that match the administrative
     domains and is controlled under a single administrative policy.  The control
     domains can be recursively divided into sub-domains to form control hierarchy
     for scalability. The control domain concept can be applied to routing, signaling
     and protection & restoration to form an autonomous control function domain.

     The network interfaces encompass two aspects of the networking
     functions: user data plane interface and control plane interface. The
     former concerns about user data transmission across the physical
     network interface and the latter concerns about the control message
     exchange across the network interface such as signaling, routing,
     etc. We call the former physical interface (PI) and the latter
     control interface. Unless otherwise stated, the control
     interface is assumed in the remaining of this document.

     5.2.1.  Control Plane Interfaces
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     Control interface defines a relationship between two connected
     network entities on both sides of the interface. For each control
     interface, we need to define the architectural function that each side
     plays and a controlled set of information that can be exchanged
     across the interface. The information flowing over this logical
     interface may include, but not limited to:

     - Endpoint Interface endpoint name and address

     - Reachability/summarized network address information

     - Topology/routing information

     - Authentication and connection admission control information

     - Connection management signaling messages

     - Network resource control information

     Different types of the interfaces can be defined for the network
     control and architectural purposes and can be used as the network
     reference points in the control plane. In this document, the
     following set of interfaces are is defined as shown in Figure 1. The
     User-Network Interface (UNI) (UNI): is a bi-directional control interface
     between service requester and service provider control entities. The
     service request control entity resides outside the carrier network
     control domain.

     The

     Network-Network/Node-Node Interface  (NNI) (NNI): is a bi-directional signaling
     interface between two optical network elements or sub-networks.

     We differentiate between internal NNI (I-NNI) and external NNI (E-NNI) as
     follows:

     - E-NNI: A NNI interface between two control plane entities belonging
     to different control domains.

     - I-NNI: A NNI interface between two control plane entities within
     the same control domain in the carrier network.

     It should be noted that it is quite common to use I-NNI between two
     sub-networks within the same carrier network if they belong to
     different control domains.

     Different types of interface, internal vs. external, have different implied
     trust relationship for security and access control purposes. The trust
     relationship is not binary, instead a policy-based control mechanism need to be
     in place to restrict the type and amount of information that can flow cross each
     type of interfaces depending the carrier's service and business requirements.
     Generally, two networks have a fully trusted relationship if they belong to
     the same administrative domain, in this case, the control information exchange
     across the control interface between them should be unlimited. Otherwise, the
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     type and amount of the control information that can go across the information
     should be constrained by the administrative policy.

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     An example of fully trusted interface is an I-NNI between two optical
     network elements in a single control domain. Non-trusted interface
     examples include an E-NNI between two different carriers or a UNI
     interface between a carrier optical network and its customers. The trust level
     can be different for the non-trusted UNI or E-NNI interface depending upon if it
     within the carrier or not.  In general, intra-carrier E-NNI has higher trust
     level than inter-carrier E-NNI; similarly UNI internal to the carrier (private
     UNI) has higher trust level than UNI external to the carrier (public UNI). E-NNI.

     The control plane shall support the UNI and NNI interface described
     above and the interfaces shall be configurable in terms of the type
     and amount of control information exchange and their behavior shall
     be consistent with the configuration (i.e., external versus internal
     interfaces).

     5.3. Intra-Carrier Network Model

     Intra-carrier network model concerns the network service control and
     management issues within networks owned by a single carrier.

     5.3.1. Multiple Sub-networks

     Without loss of generality, the optical network owned by a carrier
     service operator can be depicted as consisting of one or more optical
     sub-networks interconnected by direct optical links. There may be
     many different reasons for more than one optical sub-networks sub-network. It may
     be the result of using hierarchical layering, different technologies
     across access, metro and long haul (as discussed below), or a result
     of business mergers and acquisitions or incremental optical network
     technology deployment by the carrier using different vendors or
     technologies.

     A sub-network may be a single vendor and single technology network.
     But in general, the carrier's optical network is heterogeneous in
     terms of equipment vendor and the technology utilized in each sub-
     network.

     5.3.2.  Access, Metro and Long-haul networks

     Few carriers have end-to-end ownership of the optical networks. Even
     if they do, access, metro and long-haul networks often belong to
     different administrative divisions as separate optical sub-networks.
     Therefore Inter-(sub)-networks interconnection is essential in terms
     of supporting the end-to-end optical service provisioning and
     management. The access, metro and long-haul networks may use
     different technologies and architectures, and as such may have
     different network properties.

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     In general, end-to-end optical connectivity may easily cross multiple
     sub-networks with the following possible scenarios:
     Access -- Metro -- Access
     Access - Metro -- Long Haul -- Metro - Access
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     5.4.  Inter-Carrier Network Model

     The inter-carrier model focuses on the service and control aspects
     between different carrier networks and describes the internetworking
     relationship between them.

     Inter-carrier interconnection provides for connectivity between
     optical network operators. To provide the global reach end-to-end
     optical services, optical service control and management between
     different carrier networks becomes essential. It is possible to
     support distributed peering within the IP client layer network where
     the connectivity between two distant IP routers can be achieved via
     an optical transport network.

     5.5. Implied Control Constraints

     The intra-carrier and inter-carrier models have different implied control
     constraints. For example, in the intra-carrier model, the address for routing
     and signaling only need to be unique with the carrier while the inter-carrier
     model requires the address to be globally unique.

     In the intra-carrier network model, the network itself forms the largest control
     domain within the carrier network. This domain is usually partitioned into
     multiple sub-domains, either flat or in hierarchy. The UNI and E-NNI interfaces
     are internal to the carrier network, therefore higher trust level is assumed.
     Because of this, direct signaling between domains and summarized topology and
     resource information exchanged can be allowed across the private internal UNI or intra-
     carrier E-NNI interfaces.

     In the inter-carrier network model, each carrier's optical network is
     a separate administrative domain. Both the UNI interface between the
     user and the carrier network and the NNI interface between two
     carrier's networks are crossing the carrier's administrative boundary
     and therefore are by definition external interfaces.

     In terms of control information exchange, the topology information
     shall not be allowed to cross both E-NNI and UNI interfaces.

     6.  Optical Service User Requirements

     This section describes the user requirements for optical services,
     which in turn impose the requirements on service control and
     management for the network operators. The user requirements reflect
     the perception of the optical service from a user's point of view.

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     6.1.  Common Optical Services

     The basic unit of an optical transport service is fixed-bandwidth
     optical connectivity between parties. applications. However different services are
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     created based on its supported signal characteristics (format, bit
     rate, etc), the service invocation methods and possibly the
     associated Service Level Agreement (SLA) provided by the service
     provider.

     At present, the following are the major optical services provided in
     the industry:

     - SONET/SDH, with different degrees of transparency

     - Optical wavelength services, transparent or opaque

     - Ethernet at 10Mbps, 100Mbps, 1 Gbps and 10 Gbps

     - Storage Area Networks (SANs) based on FICON, ESCON and Fiber
     Channel

     Optical Wavelength Service refers to transport services where signal
     framing is negotiated between the client and the network operator
     (framing and bit-rate dependent), and only the payload is carried
     transparently. SONET/SDH transport is most widely used for network-
     wide transport. Different levels of transparency can be achieved in
     the SONET/SDH transmission.

     Ethernet Services, specifically 1Gb/s and 10Gbs Ethernet services,
     are gaining more popularity due to the lower costs of the customers'
     premises equipment and its simplified management requirements
     (compared to SONET or SDH).

     Ethernet services may be carried over either SONET/SDH (GFP mapping)
     or WDM networks. The Ethernet service requests will require some
     service specific parameters: priority class, VLAN Id/Tag, traffic
     aggregation parameters.

     Storage Area Network (SAN) Services. ESCON and FICON are proprietary
     versions of the service, while Fiber Channel is the standard
     alternative. As is the case with Ethernet services, SAN services may
     be carried over either SONET/SDH (using GFP mapping) or WDM networks.

     The control plane shall provide the carrier with the capability
     functionality to provision, control and manage all the services
     listed above.

     6.2.  Bearer Interface Types

     All the bearer interfaces implemented in the ONE shall be supported
     by the control plane and associated signaling protocols.

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     The signaling shall support the following interface types shall be supported by the signaling
     protocol:
     - SDH/SONET
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     - 1 Gb Ethernet, 10 Gb Ethernet (WAN mode)
     - 10 M/100 M/1 G/10 Gb (LAN mode) Ethernet
     - FC-N (N= 12, 50, 100, or 200) for Fiber Channel services
     - OTN (G.709)
     - PDH
     - APON, E-PON APON and EPON
     - ESCON and FICON

     6.3.  Optical Service Invocation
     As mentioned earlier, the methods of service invocation play an
     important role in defining different services.

     6.3.1. Provider-Controlled Provider-Initiated Service Provisioning

     In this scenario, users forward their service request to the provider
     via a well-defined service management interface. All connection
     management operations, including set-up, release, query, or
     modification shall be invoked from the management plane. This provisioning
     method is for PC and SPC connections.

     6.3.2. User-Initiated Service Provisioning

     In this scenario, users forward their service request to the provider
     via a well-defined UNI interface in the control plane (including
     proxy signaling). All connection management operation requests,
     including set-up, release, query, or modification shall be invoked
     from directly connected user devices, or its signaling representative
     (such as a signaling proxy). proxy.
     This provisioning method is for SC connection.

     6.3.3. Call set-up requirements
     In summary the following requirements for the control plane have been
     identified:
     - The control plane shall support action result codes as responses to
     any requests over the control interfaces.

     - The control plane shall support requests for call set-up, subject
     to policies in effect between the user and the network.

     - The control plane shall support the destination client device's
     decision to accept or reject call set-up requests from the source
     client's device.

     - The control plane shall support requests for call set-up and
     deletion across multiple (sub)networks.

     - NNI signaling shall support requests for call set-up, subject to
     policies in effect between the (sub)networks.

     - Call set-up shall be supported for both uni-directional and bi-
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     directional connections.

     - Upon call request initiation, the control plane shall generate a
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     network unique Call-ID associated with the connection, to be used for
     information retrieval or other activities related to that connection.

     - CAC shall be provided as part of the call control functionality. It
     is the role of the CAC function to determine if the call can be
     allowed to proceed based on resource availability and authentication.

     - Negotiation for call set-up for multiple service level options
     shall be supported.

     - The policy management system must determine what kinds of call setup
     requests can be authorized.

     - The control plane elements need the ability to rate limit (or pace)
     call setup attempts into the network.

     - The control plane shall report to the management plane, the
     success/failures of a call request.

     - Upon a connection request failure, the control plane shall report
     to the management plane a cause code identifying the reason for the
     failure and all allocated resources shall be released. A negative
     acknowledgment shall be returned to the source.

     - Upon a connection request success a positive acknowledgment shall
     be returned to the source when a connection has been successfully
     established, the control plane shall be notified.
     established.

     - The control plane shall support requests for call release by Call-
     ID.

     - The control plane shall allow any end point or any intermediate
     node to initiate call release procedures.

     - Upon call release completion all resources associated with the call
     shall become available for access for new requests.

     - The management plane shall be able to release calls or connections
     established by the control plane both gracefully and forcibly on
     demand.

     - Partially deleted calls or connections shall not remain within the
     network.

     - End-to-end acknowledgments shall be used for connection deletion
     requests.

     - Connection deletion shall not result in either restoration or
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     protection being initiated.

     - The control plane shall support management plane and neighboring
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     device requests for status query.

     - The UNI shall support initial registration and updates of the UNI-C
     with the network via the control plane.

     6.4.  Optical Connection granularity

     The service granularity is determined by the specific technology,
     framing and bit rate of the physical interface between the ONE and
     the client at the edge and by the capabilities of the ONE. The
     control plane needs to support signaling and routing for all the
     services supported by the ONE. In general, there should not be a one-
     to-one correspondence imposed between the granularity of the service
     provided and the maximum capacity of the interface to the user.

     The control plane shall support the ITU Rec. G.709 connection
     granularity for the OTN network.

     The control plane shall support the SDH/SONET connection granularity.

     Sub-rate interfaces shall be supported by the

     The optical control plane shall support sub-rate interfaces
     such as VT /TU granularity (as low as 1.5 Mb/s).

     The following fiber channel interfaces shall be supported by the
     control plane if the given interfaces are available on the equipment:

     - FC-12
     - FC-50
     - FC-100
     - FC-200

     Encoding of service types in the protocols used shall be such that
     new service types can be added by adding new code point values or
     objects.

     6.5.  Other Service Parameters and Requirements

     6.5.1. Classes of Service

     We use "service level" to describe priority related characteristics
     of connections, such as holding priority, set-up priority, or
     restoration priority. The intent currently is to allow each carrier
     to define the actual service level in terms of priority, protection,
     and restoration options. Therefore, individual carriers will
     determine mapping of individual service levels to a specific set of
     quality features.

     The control plane shall be capable of mapping individual service
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     classes into specific priority or protection and restoration options.

     6.5.2.  Diverse Routing Attributes

     The diversity
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     Diversity refers to the fact that a disjoint set of network resources (links and
     nodes) is utilized to provision multiple parallel optical connections terminated
     between a pair of ingress and egress ports.  There are different levels of
     diversity based on link, node or administrative policy as described below. In
     the simple node and link diversity case:
       . Two optical connections are said to be node-disjoint diverse, if the two
          connections do not share any node along the path except the ingress and
          egress nodes.
       . Two optical connections are said to be link-disjoint diverse, if the two
          connections do not share any link along the path.

     A more general concept of diversity is the Shared Risk Group (SRG) that is based
     risk sharing
     on a risk-sharing model and allows the definition of administrative policy-based
     diversity.  A SRG is defined as a group of links or nodes that share a common
     risk component, whose failure can potentially cause the failure of all the links
     or nodes in the group. When the SRG is applied to the link resource, it is
     referred to as shared risk link group (SRLG). For example, all fiber links that
     go through a common conduit under the ground belong to the same SRLG group,
     because the conduit is a shared risk component whose failure, such as a cut, may
     cause all fibers in the conduit to break. Note that SRLG is a relation defined
     within a group of links based upon a specific risk factor that can be defined
     based on various technical or administrative grounds such as ˘sharing Šsharing a
     conduit÷, ˘within
     conduitĂ, Šwithin 10 miles of distance proximity÷ proximityĂ etc.  Please see ITU-T G.7715
     for more discussion [itu-rtg].

     Therefore, two optical connections are said to be SRG-disjoint diverse if the
     two connections do not have any links or nodes that belong to the same SRG along
     the path.

     The ability to route service paths diversely is a required control
     feature. Diverse routing is one of the connection parameters and is
     specified at the time of the connection creation.

     The control plane routing algorithms shall be able to route a single
     demand an optical
     connection diversely from N a previously routed demands connection in terms of link
     disjoint path, node disjoint path and SRLG SRG disjoint path.

     7.  Optical Service Provider Requirements

     This section discusses specific service control and management
     requirements from the service provider's point of view.

     7.1.  Service Access Methods to Optical Networks

     In order to have access to the optical network service, a customer needs to be
     physically connected to the service provider network on the transport plane. The
     control plane connection may or may not be required depending upon the service
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     invocation model provided to the customer: provisioned vs. signaled. For the
     signaled, either direct or indirect signaling methods can be used depending upon
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     if the UNI proxy is utilized on the client side. The detailed discussion on the
     UNI signaling methods is in [oif-uni].

     Multiple access methods blow shall be supported:

     - Cross-office access (CNE co-located with ONE)

     - Direct remote access (Dedicated links to the user)

     - Remote access via access sub-network (via a
     multiplexing/distribution sub-network)

     7.2.  Dual Homing and Network Interconnections

     Dual homing is a special case of the access network. Client devices
     can be dual homed to the same or different hub, the same or different
     access network, the same or different core networks, the same or
     different carriers.  The different levels of dual homing connectivity
     result in many different combinations of configurations. The main
     objective for dual homing is for enhanced survivability.

     Dual homing must be supported. Dual homing shall not require the use
     of multiple addresses for the same client device.

     7.3.  Inter-domain connectivity

     A domain is a portion of a network, or an entire network that is
     controlled by a single control plane entity.  This section discusses
     the various requirements for connecting domains.

     7.3.1.  Multi-Level Hierarchy

     Traditionally current transport networks are divided into core inter-
     city long haul networks, regional intra-city metro networks and
     access networks. Due to the differences in transmission technologies,
     service, and multiplexing needs, the three types of networks are
     served by different types of network elements and often have
     different capabilities.  The network hierarchy is usually implemented through
     the control domain hierarchy.

     When control domains exists for routing and signaling purpose, there will be
     intra-domain routing/signaling and inter-domain routing/signaling. In general,
     domain-based routing/signaling autonomy is desired and the intra-domain
     routing/signaling and the inter-domain routing/signaling should be agnostic to
     each other.

     Routing and signaling for multi-level hierarchies shall be supported
     to allow carriers to configure their networks as needed.

     7.3.2.  Network Interconnections
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     7.3.2.  Network Interconnections

     Subnetworks

     Sub-networks may have multiple points of inter-connections. All
     relevant NNI functions, such as routing, reachability information
     exchanges, and inter-connection topology discovery must recognize and
     support multiple points of inter-connections between subnetworks.
     Dual inter-connection is often used as a survivable architecture.

     The control plane shall provide support for routing and signaling for
     subnetworks having multiple points of interconnection.

     7.4.  Names and Address Management

     7.4.1.  Address Space Separation

     To ensure the scalability of and smooth migration toward to the
     optical switched network, the separation of three address spaces are
     required as discussed in [oif-addr]:

     - Internal transport network addresses: This is used for routing
     control plane messages within the transport network. For example,
     if GMPLS is used then IP address should be used.

     - Transport Network Assigned (TNA) address: This is a routable
     address in the optical transport network and is assigned by the
     network.

     - Client addresses: This address has significance in the client layer.
     For example, if the clients are ATM switches, the NSAP address can be used.
     If the clients are IP router, then IP address should be used.

     7.4.2.  Directory Services

     Directory Services shall support address resolution and translation
     between various user/client device names or address and the corresponding TNA
     addresses.  UNI shall use the user naming schemes for connection request. The
     directory service is essential for the implementation of overlay model.

     7.4.3.  Network element Identification

     Each control domain and each network element within a carrier network shall be
     uniquely identifiable. Similarly all the service access points shall be uniquely
     identifiable.

     7.5.  Policy-Based Service Management Framework

     The IPO optical service must be supported by a robust policy-based management
     system to be able to make important decisions.

     Examples of policy decisions include:

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     - What types of connections can be set up for a given UNI?
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     - What information can be shared and what information must be
     restricted in automatic discovery functions?

     - What are the security policies over signaling interfaces?

     - What routing policies should be applied in the path selection? E.g
     The definition of the link diversity.

     Requirements:
     - Service and network policies related to configuration and
     provisioning, admission control, and support of Service Level
     Agreements (SLAs) must be flexible, and at the same time simple and
     scalable.

     - The policy-based management framework must be based on standards-
     based policy systems (e.g., IETF COPS [rfc2784]).

     - In addition, the IPO service management system must support and be
     backwards compatible with legacy service management systems.

     8.  Control Plane Functional Requirements for Optical Services

     This section addresses the requirements for the optical control plane
     in support of service provisioning.

     The scope of the control plane include the control of the interfaces
     and network resources within an optical network and the interfaces
     between the optical network and its client networks. In other words,
     it should include both NNI and UNI aspects.

     8.1.  Control Plane Capabilities and Functions

     The control capabilities are supported by the underlying control
     functions and protocols built in the control plane.

     8.1.1.  Network Control Capabilities

     The following capabilities are required in the network control plane
     to successfully deliver automated provisioning for optical services:
     - Network resource discovery

     - Address assignment and resolution

     - Routing information propagation and dissemination

     - Path calculation and selection

     - Connection management
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     These capabilities may be supported by a combination of functions
     across the control and the management planes.

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     8.1.2.  Control Plane Functions for network control Network Control

     The following are essential functions needed to support network
     control capabilities:

     - Signaling
     - Routing
     - Automatic resource, service and neighbor discovery

     Specific requirements for signaling, routing and discovery are
     addressed in Section 9.

     The general requirements for the control plane functions to support
     optical networking and service functions include:

     - The control plane must have the capability to establish, teardown
     and maintain the end-to-end connection, and the hop-by-hop connection
     segments between any two end-points.

     - The control plane must have the capability to support optical traffic-
     engineering (e.g. wavelength management) requirements including resource
     discovery and dissemination, constraint-based routing and path computation.

     - The control plane shall support network status or action result
     code responses to any requests over the control interfaces.

     - The control plane shall support call admission control on UNI and
     connection-admission control on NNI.

     - The control plane shall support graceful release of network
     resources associated with the connection after a successful
     connection teardown or failed connection.

     - The control plane shall support management plane request for
     connection attributes/status query.

     - The control plane must have the capability to support various
     protection and restoration schemes.

     - Control plane failures shall not affect active connections and
     shall not adversely impact the transport and data planes.

     - The control plane should support separation of control function
     entities including routing, signaling and discovery and should allow
     different control distributions of those functionalities, including
     centralized, distributed or hybrid.

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     - The control plane should support physical separation of the control
     plane from the transport plane to support either tightly coupled or
     loosely coupled control plane solutions.

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     - The control plane should support the routing and signaling proxy to
     participate in the normal routing and signaling message exchange and
     processing.

     - Security and resilience are crucial issues for the control plane
     and will be addressed in Section 10 and 11 of this document.

     8.2.  Signaling Communication Network (SCN)

     The signaling communication network is a transport network for
     control plane messages and it consists of a set of control channels
     that interconnect interconnects the nodes within the control plane. Therefore, the
     signaling communication network must be accessible by each of the
     communicating nodes (e.g., OXCs). If an out-of-band IP-based control
     message transport network is an overlay network built on top of the
     IP data network using some tunneling technologies, these tunnels must
     be standards-based such as IPSec, GRE, etc.

     - The signaling communication network must terminate at each of the
     nodes in the transport plane.

     - The signaling communication network shall not be assumed to have
     the same topology as the data plane, nor shall the data plane and
     control plane traffic be assumed to be congruently routed.

     A control channel is the communication path for transporting control
     messages between network nodes, and over the UNI (i.e., between the
     UNI entity on the user side (UNI-C) and the UNI entity on the network
     side (UNI-N)). The control messages include signaling messages,
     routing information messages, and other control maintenance protocol
     messages such as neighbor and service discovery.

     The following three types of signaling in the control channel shall
     be supported:

     - In-band signaling: The signaling messages are carried over a
     logical communication channel embedded in the data-carrying optical
     link or channel. For example, using the overhead bytes in SONET data
     framing as a logical communication channel falls into the in-band
     signaling methods.

     - In fiber, Out-of-band signaling: The signaling messages are carried
     over a dedicated communication channel separate from the optical
     data-bearing channels, but within the same fiber. For example, a
     dedicated wavelength or TDM channel may be used within the same fiber
     as the data channels.

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     - Out-of-fiber signaling: The signaling messages are carried over a
     dedicated communication channel or path within different fibers to
     those used by the optical data-bearing channels. For example,
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     dedicated optical fiber links or communication path via separate and
     independent IP-based network infrastructure are both classified as
     out-of-fiber signaling.

     The UNI control channel and proxy signaling defined in the OIF UNI
     1.0 [oif-uni] shall be supported.

     The signaling communication network provides communication
     mechanisms between entities in the control plane.

     - The signaling communication network shall support reliable
     message transfer.

     - The signaling communication network shall have its own OAM mechanisms.

     - The signaling communication network shall use protocols that
     support congestion control mechanisms.

     In addition, the signaling communication network should support
     message priorities. Message prioritization allows time critical
     messages, such as those used for restoration, to have priority over
     other messages, such as other connection signaling messages and
     topology and resource discovery messages.

     The signaling communication network shall be highly reliable and
     implement failure recovery.

     8.3  Control Plane Interface to Data Plane

     In the situation where the control plane and data plane are decoupled, this
     interface needs to be standardized.
     Requirements for a standard control-data plane interface are under
     study. The specification of a control plane interface to the data
     plane is outside the scope of this document.

     Control plane should support a standards based interface to configure
     and
     switching fabrics and port functions. functions via the management plane.

     Data plane shall monitor and detect the failure (LOL, LOS, etc.) and
     quality degradation (high BER, etc.) of the signals and be able to
     provide signal-failure and signal-degrade alarms to the control plane
     accordingly to trigger proper mitigation actions in the control
     plane.

     8.4.  Management Plane Interface to Data Plane

     The management plane shall be responsible for the network resource
     management in the data plane. It should able to partition the network
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     resources and control the allocation and the deallocation of the
     resource for the use by the control plane.

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     Data plane shall monitor and detect the failure and quality
     degradation of the signals and be able to provide signal-failure and
     signal-degrade alarms plus associated detailed fault information to
     the management plane to trigger and enable the management for fault
     location and repair.

     Management plane failures shall not affect the normal operation of a
     configured and operational control plane or data plane.

     8.5.  Control Plane Interface to Management Plane

     The control plane is considered a managed entity within a network.
     Therefore, it is subject to management requirements just as other
     managed entities in the network are subject to such requirements.

     Control plane should be able to service the requests from the
     management plane for end-to-end connection provisioning (e.g. SPC
     connection) and control plane database information query (e.g.
     topology database)

     Control plane shall report all the control plane faults to the
     management plane with detailed fault information

     The control, management and transport plane each has its well-defined network
     functions. Those functions are orthogonal to each other. However, this does not
     total independency. Since the management plane is responsible for the management
     of both control plane and transport plane, the management plane plays an
     authoritative role

     In general, the management plane shall have authority over the
     control plane. Management plane should be able to configure the
     routing, signaling and discovery control parameters such as hold-down
     timers, hello-interval, etc. to effect affect the behavior of the control
     plane.

     In the case of network failure, both the management plane and
     the control plane need fault information at the same priority. The
     control plane shall be responsible for providing necessary statistic
     data such as call counts, traffic counts to the management plane.
     They should be available upon the query from the management plane.
     The management plane shall be able to tear down connections
     established by the control plane both gracefully and forcibly on
     demand.

     8.6.  IP and Optical Control Plane Interconnection

     The control plane interconnection model defines the way how two
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     control networks can be interconnected in terms of controlling
     relationship and control information flow allowed between them.
     There are three basic types of control plane network interconnection
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     models: overlay, peer and hybrid, which are defined in the IETF IPO
     WG document [ipo_frame]. See Appendix A for more discussion.

     Choosing the level of coupling depends upon a number of different
     factors, some of which are:

     - Variety of clients using the optical network

     - Relationship between the client and optical network

     - Operating model of the carrier

     Overlay model (UNI like model) shall be supported for client to
     optical control plane interconnection.

     Other models are optional for client to optical control plane
     interconnection.

     For optical to optical control plane interconnection all three models
     shall be supported. In general, the priority for support of
     interconnection models should be overlay, hybrid and peer, in
     decreasing order.

     9.  Requirements for Signaling, Routing and Discovery

     9.1.  Requirements for information sharing over UNI, I-NNI and E-NNI

     Different types of interfaces shall impose different requirements and
     functionality due to their different trust relationships.
     Specifically:

     -  Topology information shall not be exchanged across inter-carrier E-NNI and
     UNI.

     -  The control plane shall allow the carrier to configure the type
     and extent of control information exchange across various interfaces.

     -  Address resolution exchange over UNI is needed if an addressing
     directory service is not available.

     9.2.  Signaling Functions

     Call and connection control and management signaling messages are
     used for the establishment, modification, status query and release of
     an end-to-end optical connection.  Unless otherwise specified, the
     word "signaling" refers to both inter-domain and intra-domain
     signaling.

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     - The inter-domain signaling protocol shall be agnostic to the intra-
     domain signaling protocol for all the domains within the network.

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     - Signaling shall support both strict and loose routing.

     - Signaling shall support individual as well as groups of connection
     requests.

     - Signaling shall support fault notifications.

     - Inter-domain signaling shall support per connection, globally
     unique identifiers for all connection management primitives based on
     a well-defined naming scheme.

     - Inter-domain signaling shall support crank-back and rerouting.

     9.3.  Routing Functions

     Routing includes reachability information propagation, network
     topology/resource information dissemination and path computation.
     Network topology/resource information dissemination is to provide
     each node in the network with information about the carrier network
     such that a single node is able to support constraint-based path
     selection.  A mixture of hop-by-hop routing, explicit/source routing
     and hierarchical routing will likely be used within future transport
     networks.

     All three mechanisms (Hop-by-hop routing, explicit / source-based
     routing and hierarchical routing) must be supported.  Messages
     crossing untrusted boundaries must not contain information regarding
     the details of an internal network topology.

     Requirements for routing information dissemination:

     - The inter-domain routing protocol shall be agnostic to the intra-
     domain routing protocol within any of the domains within the network.

     - The exchange of the following types of information shall be
     supported by inter-domain routing protocols:
          - Inter-domain topology
          - Per-domain topology abstraction
          - Per domain reachability summarization

     Major concerns for routing protocol performance are scalability and
     stability, which impose the following requirement on the routing
     protocols:

     - The routing protocol shall scale with the size of the network

     The routing protocols shall support following requirements:

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     - Routing protocol shall support hierarchical routing information
     dissemination, including topology information aggregation and
     summarization.

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     - The routing protocol(s) shall minimize global information and keep
     information locally significant as much as possible.
     Over external interfaces only reachability information, next
     routing hop and service capability information should be exchanged.
     Any other network related information shall not leak out to other
     networks.

     - The routing protocol shall be able to minimize global information
     and keep information locally significant as much as possible (e.g.,
     information local to a node, a sub-network, a domain, etc). For
     example, a single optical node may have thousands of ports. The ports
     with common characteristics need not to be advertised individually.

     - The routing protocol shall distinguish static routing information
     and dynamic routing information. The routing protocol operation shall
     update dynamic and static routing information differently. Only
     dynamic
     routing information shall be updated in real time.

     - Routing protocol shall be able to control the dynamic information
     updating frequency through different types of thresholds. Two types
     of thresholds could be defined: absolute threshold and relative
     threshold.

     - The routing protocol shall support trigger-based and timeout-based
     information update.

     - Inter-domain routing protocol shall support policy-based routing
     information exchange.

     - The routing protocol shall be able to support different levels of
     protection/restoration and other resiliency requirements. These are
     discussed in Section 10.

     All the scalability techniques will impact the network resource
     representation accuracy. The tradeoff between accuracy of the routing
     information and the routing protocol scalability is an important
     consideration to be made by network operators.

     9.4.  Requirements for path selection

      The following are functional requirements for path selection:

     - Path selection shall support shortest path routing.

     - Path selection shall also support constraint-based routing.  At
     least the following constraints shall be supported:

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       - Cost
       - Link utilization
       - Diversity
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       - Service Class

     - Path selection shall be able to include/exclude some specific
     network resources, based on policy.

     - Path selection shall be able to support different levels of
     diversity, including node, link, SRLG and SRG.

     - Path selection algorithms shall provide carriers the ability to
     support a wide range of services and multiple levels of service
     classes. Parameters such as service type, transparency, bandwidth,
     latency, bit error rate, etc. may be relevant.

     Constraint-based routing in the optical network in significantly complex
     Compared to the IP network. There are many optical layer constraints to consider
     such as wavelength, diversity, optical layer impairments, etc.  A detailed
     discussion on the routing constraints at the optical layer is in [ietf-olr].

     9.5.  Discovery Functions
     The discovery functions include neighbor, resource and service
     discovery. The control plane shall support both manual configuration and
     automatic discovery

     9.5.1.  Neighbor discovery
     Neighbor Discovery can be described as an instance of auto-discovery
     that is used for associating two network entities within a layer
     network based on a specified adjacency relation.

     The control plane shall support the following neighbor discovery
     capabilities as described in [itu-disc]:

     - Physical media adjacency that detects and verifies the physical
     layer network connectivity between two connected network element
     ports.

     - Logical network adjacency that detects and verify the logical
     network layer connection above the physical layer between network
     layer specific ports.

     - Control adjacency that detect and verify the logical neighboring
     relation between two control entities associated with data plane
     network elements that form either physical or logical adjacency.

      The control plane shall support manual neighbor adjacency
     configuration to either overwrite or supplement the automatic
     neighbor discovery function.

     9.5.2. Resource Discovery
      Y. Xue et al

     Resource discovery is concerned with the ability to verify physical
     connectivity between two ports on adjacent network elements, improve
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     inventory management of network resources, detect configuration
     mismatches between adjacent ports, associating port characteristics
     of adjacent network elements, etc. Resource discovery shall be
     supported.

     Resource discovery can be achieved through either manual provisioning
     or automated procedures. The procedures are generic while the
     specific mechanisms and control information can be technology
     dependent.

     After neighbor discovery, resource verification and monitoring must be
     performed periodically to verify physical attributes to ensure
     compatibility.

     9.5.3. Service Discovery

     Service Discovery can be described as an instance of auto-discovery
     that is used for verifying and exchanging service capabilities of a
     network. Service discovery can only happen after neighbor discovery.
     Since service capabilities of a network can dynamically change,
     service discovery may need to be repeated.

     Service discovery is required for all the optical services supported.

     10.  Requirements for service and control plane resiliency

     Resiliency is a network capability to continue its operations under
     the condition of failures within the network.  The automatic switched
     optical network assumes the separation of control plane and data
     plane. Therefore the failures in the network can be divided into
     those affecting the data plane and those affecting the control plane.
     To provide enhanced optical services, resiliency measures in both
     data plane and control plane should be implemented. The following
     failure handling
     Failure-handling principles shall be supported.

     The control plane shall provide optical service failure detection and
     recovery functions such that the failures in the data plane within
     the control plane coverage can be quickly mitigated.

     The failure of control plane shall not in any way adversely affect
     the normal functioning of existing optical connections in the data
     plane.

     In general, there shall be no single point of failure for all major
     control plane functions, including signaling, routing etc. The
     control plane shall provide reliable transfer of signaling messages
     and flow control mechanisms for easing any congestion within the
     control plane.

     10.1.  Service resiliency
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     10.1.  Service resiliency

     In circuit-switched transport networks, the quality and reliability
     of the established optical connections in the transport plane can be
     enhanced by the protection and restoration mechanisms provided by the
     control plane functions.  Rapid recovery is required by transport
     network providers to protect service and also to support stringent
     Service Level Agreements (SLAs) that dictate high reliability and
     availability for customer connectivity.

     Protection and restoration are closely related techniques for
     repairing network node and link failures. Protection is a collection
     of failure recovery techniques meant to rehabilitate failed
     connections by pre-provisioning dedicated protection network
     connections and switching to the protection circuit once the failure
     is detected.  Restoration is a collection of reactive techniques used
     to rehabilitate failed connections by dynamic rerouting the failed
     connection around the network failures using the shared network
     resources.

     The protection switching is characterized by shorter recovery time at
     the cost of the dedicated network resources while dynamic restoration
     is characterized by longer recover time with efficient resource
     sharing.  Furthermore, the protection and restoration can be
     performed either on a per link/span basis or on an end-to-end
     connection path basis. The former is called local repair initiated a
     node closest to the failure and the latter is called global repair
     initiated from the ingress node.

     The protection and restoration actions are usually in reaction to the
     failure in the networks. However, during the network maintenance
     affecting the protected connections, a network operator needs to
     proactively force the traffic on the protected connections to switch
     to its protection connection.

     The failure and signal degradation in the transport plane is usually
     technology specific and therefore shall be monitored and detected by
     the transport plane.

     The transport plane shall report both physical level failure and
     signal degradation to the control plane in the form of the signal
     failure alarm and signal degrade alarm.

     The control plane shall support both alarm-triggered and hold-down
     timers based protection switching and dynamic restoration for failure
     recovery.

     Clients will have different requirements for connection availability.
     These requirements can be expressed in terms of the "service level",
     which can be mapped to different restoration and protection options
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     and priority related connection characteristics, such as holding
     priority(e.g. pre-emptable or not), set-up priority, or restoration
     priority. However, how the mapping of individual service levels to a
      Y. Xue et al

     specific set of protection/restoration options and connection
     priorities will be determined by individual carriers.

     In order for the network to support multiple grades of service, the
     control plane must support differing protection and restoration
     options on a per connection basis.

     In order for the network to support multiple grades of service, the
     control plane must support setup priority, restoration priority and
     holding priority on a per connection basis.

     In general, the following protection schemes shall be considered for
     all protection cases within the network:
     - Dedicated protection: 1+1 and 1:1
     - Shared protection: 1:N and M:N.
     - Unprotected

     The control plane shall support "extra-traffic" capability, which
     allows unprotected traffic to be transmitted on the protection
     circuit.

     The control plane shall support both trunk-side and drop-side
     protection switching.

     The following restoration schemes should be supported:
     - Restorable
     - Un-restorable

     Protection and restoration can be done on an end-to-end basis per
     connection. It can also be done on a per span or link basis between
     two adjacent network nodes. These schemes should be supported.

     The protection and restoration actions are usually triggered by the
     failure in the networks. However, during the network maintenance
     affecting the protected connections, a network operator need to
     proactively force the traffic on the protected connections to switch
     to its protection connection. Therefore in order to support easy
     network maintenance, it is required that management initiated
     protection and restoration be supported.

     Protection and restoration configuration should be based on software
     only.

     The control plane shall allow the modification of protection and
     restoration attributes on a per-connection basis.

     The control plane shall support mechanisms for reserving bandwidth
     resources for restoration.

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     The control plane shall support mechanisms for normalizing connection
     routing (reversion) after failure repair.

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     Normal connection management operations (e.g., connection deletion)
     shall not result in protection/restoration being initiated.

     10.2.  Control plane resiliency

     The control plane may be affected by failures in signaling network
     connectivity and by software failures (e.g., signaling, topology and
     resource discovery modules).

     The signaling control plane should implement signaling message
     priorities to ensure that restoration messages receive preferential
     treatment, resulting in faster restoration.

     The optical control plane signal network shall support protection and
     restoration options to enable it to self-healing in case of failures
     within the control plane.

     Control network failure detection mechanisms shall distinguish
     between control channel and software process failures.

     The control plane failure shall only impact the capability to
     provision new services.

     Fault localization techniques for the isolation of failed control
     resources shall be supported.

     Recovery from control plane failures shall result in complete
     recovery and re-synchronization of the network.

     There shall not be a signal point of failure in the control plane systems
     design.

     Partial or total failure of the control plane shall not affect the existing
     established connections. It should only lose the capability to accept the new
     connection requests.

     11.  Security Considerations

     In this section, security considerations and requirements for optical
     services and associated control plane requirements are described.

     11.1.  Optical Network Security Concerns

     Since optical service is directly related to the physical network
     which is fundamental to a telecommunications infrastructure,
     stringent security assurance mechanism should be implemented in
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     optical networks.

     In terms of security, an optical connection consists of two aspects.

      Y. Xue et al

     One is security of the data plane where an optical connection itself
     belongs, and the other is security of the control plane.

     11.1.1.  Data Plane Security

     - Misconnection shall be avoided in order to keep the user's data
     confidential.  For enhancing integrity and confidentiality of data,
     it may be helpful to support scrambling of data at layer 2 or
     encryption of data at a higher layer.

     11.1.2.  Control Plane Security

     It is desirable to decouple the control plane from the data plane
     physically.

     Restoration shall not result in miss-connections (connections
     established to a destination other than that intended), even for
     short periods of time (e.g., during contention resolution). For
     example, signaling messages, used to restore connectivity after
     failure, should not be forwarded by a node before contention has been
     resolved.

     Additional security mechanisms should be provided to guard against
     intrusions on the signaling network. Some of these may be done with
     the help of the management plane.

     - Network information shall not be advertised across external
     interfaces (UNI or E-NNI). The advertisement of network information
     across the E-NNI shall be controlled and limited in a configurable
     policy based fashion. The advertisement of network information shall
     be isolated and managed separately by each administration.

     - The signaling network itself shall be secure, blocking all
     unauthorized access.  The signaling network topology and addresses
     shall not be advertised outside a carrier's domain of trust.

     - Identification, authentication and access control shall be
     rigorously used by network operators for providing access to the
     control plane.

     - Discovery information, including neighbor discovery, service
     discovery, resource discovery and reachability information should be
     exchanged in a secure way.

     - Information on security-relevant events occurring in the control
     plane or security-relevant operations performed or attempted in the
     control plane shall be logged in the management plane.

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     - The management plane shall be able to analyze and exploit logged
     data in order to check if they violate or threat security of the
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     control plane.

     - The control plane shall be able to generate alarm notifications
     about security related events to the management plane in an
     adjustable and selectable fashion.

     - The control plane shall support recovery from successful and
     attempted intrusion attacks.

     11.2.  Service Access Control

     From a security perspective, network resources should be protected
     from unauthorized accesses and should not be used by unauthorized
     entities. Service access control is the mechanism that limits and
     controls entities trying to access network resources. Especially on
     the UNI and E-NNI, Connection Admission Control (CAC) functions
     should also support the following security features:

     - CAC should be applied to any entity that tries to access network
     resources through the UNI (or E-NNI). CAC should include an
     authentication function of an entity in order to prevent masquerade
     (spoofing). Masquerade is fraudulent use of network resources by
     pretending to be a different entity. An authenticated entity should
     be given a service access level on a configurable policy basis.

     - The UNI and NNI should provide optional mechanisms to ensure origin
     authentication and message integrity for connection management
     requests such as set-up, tear-down and modify and connection
     signaling messages. This is important in order to prevent Denial of

     Service attacks. The UNI and E-NNI should also include mechanisms,
     such as usage-based billing based on CAC, to ensure non-repudiation
     of connection management messages.

     - Each entity should be authorized to use network resources according
     to the administrative policy set by the operator.

12.  Acknowledgements
The authors of this document would like to extend our special appreciation to John
Strand for his initial contributions to the carrier requirements. We also want to
acknowledge the valuable inputs from, Yangguang Xu, Zhiwei Lin,
           Eve Verma, Daniel Awduche, James Luciani, Deborah Brunhard and Lynn Neir,
     Wesam Alanqar, Tammy Ferris, Mark Jones.

     13. References

     [rfc2026] S. Bradner, "The Internet Standards Process -- Revision 3," BCP 9, RFC
     2026, IETF October 1996.

      Y. Xue et al

     [rfc2119] S. Bradner, ˘Ke y ˘Key words for use in RFC to indicate requirement levels÷,
     BCP 14, RFC 2119, 1997
      Y. Xue et al

     [itu-otn] ITU-T G.872 (2000) ű Architecture of Optical Transport Networks.

     [itu-g709] ITU-T G.709 (2001)ű Network Node Interface for the Optical Transport
     Network.

     [itu-sdh] ITU-T Rec. G.803 (2000), Architecture of Transport Networks based on
     the Synchronous Digital Hierarchy

     [ipo-frw] B. Rajagopalan, et. al ˘IP over Optical Networks: A Framework÷, work
     in progress, IETF 2002

     [oif-addr]  M. Lazer, "High Level Requirements on Optical Network Addressing",
     oif2001.196, 2001

     [oif-carrier] Y. Xue and M. Lazer, et al, ˘Carrier Optical Service Framework and
     Associated Requirements for UNI÷, OIF2000.155, 2000

     [oif-nnireq] M. Lazer et al, ˘Carrier NNI Requirements÷, OIF2002.229,  2002

     [ipo-olr]  A Chiu and J. Strand et al.,  "Impairments and Other Constraints on
     Optical Layer Routing", work in progress, IETF, 2002

     [ccamp-req] J. Jiang et al.,  "Common Control and Measurement Plane Framework
     and Requirements", work in progress, IETF, 2001

     [ietf-gsmp] A. Doria, et al ˘General Switch Management Protocol V3÷, work in
     progress, IETF, 2002

     [id-freeland]  D. Freeland, et al, ˘Consideration on the development of an
     optical control plane÷, Nov. 2000

     [rfc2748] D. Durham, et al, ˘The COPS (Common Open Policy Services) Protocol÷,
     RFC 2748, Jan. 2000

     [oif-uni] Optical Internetworking Forum (OIF), "UNI 1.0 Signaling
     Specification," December, 2001.

     [itu-astn] ITU-T Rec. G.8070/Y.1301 (2001), Requirements for the Automatic
     Switched Transport Network (ASTN).

     [itu-ason] ITU-T Rec. G.8080/Y.1304  (2001), Architecture of the Automatic
     Switched Optical Network (ASON).

     [itu-dcm] ITU-T Rec.  G.7713/Y.1704 (2001), Distributed Call and Connection
     Management (DCM).

      Y. Xue et al

     [itu-rtg] ITU-T Draft Rec. G.7715/Y.1706 (2002), Architecture and Requirements
     for Routing in the Automatic Switched Optical Networks.

      Y. Xue et al

     [itu-lm] ITU-T Draft Rec. G.7716/Y.1706 (2002), Link Resource Management for
     ASON Networks. (work in progress)

     [itu-disc] ITU-T Rec. G.7714/Y.1705 (2001), Generalized Automatic Discovery
     Techniques.

     [itu-dcn]ITU-T Rec. G.7712/Y.1703 (2001), Architecture and Specification of Data
     Communication Network.

     [ansi-sonet] ANSI T1.105-2001, Synchronous Optical Network (SONET) - Basic
     Description including Multiplex Structure, Rates and Formats

     14 Author's Addresses

     Yong Xue
     UUNET/WorldCom
     22001 Loudoun County Parkway
     Ashburn, VA 20147
     Email: yxue@ieee.org

     Monica Lazer
     AT&T
     900 ROUTE 202/206N PO BX 752
     BEDMINSTER, NJ  07921-0000
     mlazer@att.com

     Jennifer Yates,
     AT&T Labs
     180 PARK AVE, P.O. BOX 971
     FLORHAM PARK, NJ  07932-0000
     jyates@research.att.com

     Dongmei Wang
     AT&T Labs
     Room B180, Building 103
     180 Park Avenue
     Florham Park, NJ 07932
     mei@research.att.com

     Ananth Nagarajan
Sprint
     6220 Sprint Parkway
     Overland Park, KS 66251, USA
     Email: ananth.nagarajan@mail.sprint.com

     Hirokazu Ishimatsu
     Japan Telecom Co., LTD
     2-9-1 Hatchobori, Chuo-ku,
     Tokyo 104-0032 Japan
     Phone: +81 3 5540 8493
     Fax: +81 3 5540 8485
      Y. Xue et al

     EMail: hirokazu@japan-telecom.co.jp

     Olga Aparicio
     Cable & Wireless Global
     11700 Plaza America Drive
     Reston, VA 20191
     Phone: 703-292-2022
     Email: olga.aparicio@cwusa.com

     Steven Wright
     Science & Technology
     BellSouth Telecommunications
     41G70 BSC
     675 West Peachtree St. NE.
     Atlanta, GA 30375
     Phone +1 (404) 332-2194
     Email: steven.wright@snt.bellsouth.com

     Appendix A: Interconnection of Control Planes

     The interconnection of the IP router (client) and optical control
     planes can be realized in a number of ways depending on the required
     level of coupling.  The control planes can be loosely or tightly
     coupled.  Loose coupling is generally referred to as the overlay
     model and tight coupling is referred to as the peer model.
     Additionally there is the augmented model that is somewhat in between
     the other two models but more akin to the peer model.  The model
     selected determines the following:

     - The details of the topology, resource and reachability information
     advertised between the client and optical networks

     - The level of control IP routers can exercise in selecting paths
     across the optical network

     The next three sections discuss these models in more details and the
     last section describes the coupling requirements from a carrier's
     perspective.

      Peer Model (I-NNI like model)

     Under the peer model, the IP router clients act as peers of the
     optical transport network, such that single routing protocol instance
     runs over both the IP and optical domains.  In this regard the
     optical network elements are treated just like any other router as
     far as the control plane is concerned. The peer model, although not
     strictly an internal NNI, behaves like an I-NNI in the sense that
      Y. Xue et al

     there is sharing of resource and topology information.

     Presumably a common IGP such as OSPF or IS-IS, with appropriate
     extensions, will be used to distribute topology information.  One
     tacit assumption here is that a common addressing scheme will also be
     used for the optical and IP networks.  A common address space can be
     trivially realized by using IP addresses in both IP and optical
     domains.  Thus, the optical networks elements become IP addressable
     entities.

     The obvious advantage of the peer model is the seamless
     interconnection between the client and optical transport networks.
     The tradeoff is that the tight integration and the optical specific
     routing information that must be known to the IP clients.

     The discussion above has focused on the client to optical control
     plane inter-connection.  The discussion applies equally well to
     inter-connecting two optical control planes.

     Overlay (UNI-like model)

     Under the overlay model, the IP client routing, topology
     distribution, and signaling protocols are independent of the routing,
     topology distribution, and signaling protocols at the optical layer.
     This model is conceptually similar to the classical IP over ATM
     model, but applied to an optical sub-network directly.

     Though the overlay model dictates that the client and optical network
     are independent this still allows the optical network to re-use IP
     layer protocols to perform the routing and signaling functions.

     In addition to the protocols being independent the addressing scheme
     used between the client and optical network must be independent in
     the overlay model.  That is, the use of IP layer addressing in the
     clients must not place any specific requirement upon the addressing
     used within the optical control plane.

     The overlay model would provide a UNI to the client networks through
     which the clients could request to add, delete or modify optical
     connections.  The optical network would additionally provide
     reachability information to the clients but no topology information
     would be provided across the UNI.

     Augmented model (E-NNI like model)

     Under the augmented model, there are actually separate routing
     instances in the IP and optical domains, but information from one
     routing instance is passed through the other routing instance.  For
     example, external IP addresses could be carried within the optical
     routing protocols to allow reachability information to be passed to
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     IP clients.  A typical implementation would use BGP between the IP
     client and optical network.

     The augmented model, although not strictly an external NNI, behaves
     like an E-NNI in that there is limited sharing of information.

     Generally in a carrier environment there will be more than just IP
     routers connected to the optical network.  Some other examples of
     clients could be ATM switches or SONET ADM equipment.  This may drive
     the decision towards loose coupling to prevent undue burdens upon
     non-IP router clients.  Also, loose coupling would ensure that future
     clients are not hampered by legacy technologies.

     Additionally, a carrier may for business reasons want a separation
     between the client and optical networks.  For example, the ISP
     business unit may not want to be tightly coupled with the optical
     network business unit.  Another reason for separation might be just
     pure politics that play out in a large carrier.  That is, it would
     seem unlikely to force the optical transport network to run that same
     set of protocols as the IP router networks.  Also, by forcing the
     same set of protocols in both networks the evolution of the networks
     is directly tied together.  That is, it would seem you could not
     upgrade the optical transport network protocols without taking into
     consideration the impact on the IP router network (and vice versa).

     Operating models also play a role in deciding the level of coupling.
     [id-freeland] gives four main operating models envisioned for an optical
     transport network:
     Category 1: ISP owning all of its own infrastructure (i.e.,
     including fiber and duct to the customer premises)

     Category 2:  ISP leasing some or all of its capacity from a third party

     Category 3:  Carriers carrier providing layer 1 services

     Category 4:  Service provider offering multiple layer 1, 2, and 3 services over
     a common infrastructure

     Although relatively few, if any, ISPs fall into category 1 it would
     seem the mostly likely of the four to use the peer model.  The other
     operating models would lend themselves more likely to choose an
     overlay model.  Most carriers would fall into category 4 and thus
     would most likely choose an overlay model architecture.

     Full Copyright Statement

     Copyright (C) The Internet Society (2002).  All Rights Reserved.

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