[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02

Network Working Group                                      G. Bernstein
Internet Draft                                        Grotto-Networking
Expiration Date: August 2003                             B. Rajagopalan
Document: draft-ietf-ipo-optical-inter-domain-02.txt      D. Pendarakis
                                                                Tellium
                                                            Angela Chiu
                                                            John Strand
                                                                   AT&T
                                                              V. Sharma
                                                               Metanoia
                                                             Dean Cheng
                                                                Polaris
                                                          Rauf Izmailov
                                                                    NEC
                                                             Lyndon Ong
                                                                  Ciena
                                                    Sudheer Dharanikota
                                                           Frank Hujber

                                                          February 2003


              Optical Inter Domain Routing Considerations


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   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 obsoleted 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 draft investigates the requirements for general inter-domain
   and inter-area routing in optical networks and reviews the
   applicability of existing route protocols in various optical routing
   applications.

   Table of Contents:
   1    Introduction    2
   1.1  Specification of Requirements   3
   1.2  Abbreviations   3

Bernstein, G.                                                 [Page 1]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   2    Background      3
   2.1  Basic Concept of Domains and Network Partitioning       3
   2.2  Major Differences between Optical and IP datagram Routing
        6
   2.3  Differences between MPLS and Optical Circuit routing    7
   2.4  Diversity in Optical Routing    7
   2.4.1        Generalizing Link Diversity     9
   2.4.2        Generalizing Node Diversity     9
   2.5  Routing Information Categorization      10
   2.5.1        Link and Topology Related Information   10
   2.5.2        Domain and Node Related Information     11
   3    Applications of Inter Domain Optical Routing    12
   3.1  Intra Carrier Applications of Optical Inter Domain Routing
        12
   3.1.1        Intra-Carrier Scalability       12
   3.1.2        Intra-Carrier Inter-vendor      13
   3.1.3        Inter-Layer Partitioning        16
   3.1.4        Interaction with IP Layer Routing       17
   3.1.5        Inter-Business Unit     18
   3.2  Inter-Carrier Inter-Domain Optical Routing      19
   3.3  Multi-Domain Connection Control 21
   4    Multiple Layers of Optical Routing      22
   5    Conclusion      24
   6    Security Considerations 24
   6.1.1        24
   7    References      25
   8    Acknowledgments 26
   9    Author's Addresses      26

NOTE: This draft has been updated with more current author contact
information and references, but is otherwise unchanged from the
previous version.

1  Introduction

   Multi Protocol Label Switching (MPLS) has received much attention
   recently for use as a control plane for non-packet switched
   technologies.  In particular, optical technologies have a need to
   upgrade their control plane as reviewed in reference [2]. Many
   different optical switching and multiplexing technologies exist and
   more are sure to come.  For the purposes of this draft we only
   consider non-packet (i.e. circuit switching) forms of optical
   switching.
   As the requirements for and extensions to interior gateway protocols
   such as OSPF and IS-IS have begun to be investigated in the single
   area case, e.g., reference [3], we consider the requirements that
   optical networking and switching impose in the inter-domain case.

   First we explore the definition of a control domain and its use in
   optical and transport networking. This is explored again later in
   the document when we consider a number of important applications,
   networking scenarios, where the notions of inter-control domain
   routing are important. We review the various differences between
   routing in the datagram case, the virtual circuit case and the
   (real) optical circuit case.  Then we look at the optical path
   selection/computation needs to provide for path diversity, switching

 Bernstein, G.                                                [Page 2]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   capabilities, transport capabilities and impairments, and
   bandwidth/resource status reporting.

   To add to the concreteness of these considerations we try to
   illustrate them with one or more specific examples from a particular
   optical networking layer or technology. This is not to reduce the
   generality of the requirement but to facilitate the understanding of
   the requirement or concept.

1.1 Specification of Requirements

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

1.2 Abbreviations

   LSP        Label Switched Path (MPLS terminology)
   LSR        Label Switched Router (MPLS terminology)
   MPLS       Multiprotocol Label Switching
   SDH        Synchronous Digital Hierarchy (ITU standard)
   SONET      Synchronous Optical NETwork (ANSI standard)
   STM(-N)    Synchronous Transport Module (-N)
   STS(-N)    Synchronous Transport Signal-Level N (SONET)
   TU-n       Tributary Unit-n (SDH)
   TUG(-n)    Tributary Unit Group (-n) (SDH)
   VC-n       Virtual Container-n (SDH)
   VTn        Virtual Tributary-n (SONET)

2  Background

2.1 Basic Concept of Domains and Network Partitioning

   In this draft we use the term domain in a general sense, i.e.,
   beyond the BGP interpretation of an Autonomous System.  In this
   draft we will consider domains as the result of partitioning of a
   network into subnetworks, as shown in the network of Figure 1. A
   network may be partitioned for a variety of reasons, such as:
   *    Administrative boundaries
   *    Scalability of routing or signaling
   *    Isolation of partitions for security or reliability reasons
   *    Technology differences in the systems in different domains

                       /------------------------------------\
                      /                                      \
                     /             /-\                        \
                     |  Domain    |NE2|<--Internal Node       |
                     |    B       /\-/\                        |
                     |           /     \                       |
                     |       /-\/       \/-\                   |


 Bernstein, G.                                                [Page 3]


                draft-ipo-optical-inter-domain-02.txt   February 2003


                     |      |NE1|-------|NE3|                  /
                     \+------\-/         \-/                  /
                     /\       |           |                  /
                    /  \------+-----------+-----------------/
                   /           |           |<--- Inter-Domain Links
                  /     /------+-----------+-----------------\
                 |     /       |           |                  \
                 |    /        |    /-\    |          /-\      \
                 |    | Domain |   |NE2|---+---------|NE3|      |
                 |    |   A    |   /\-/\   |   ------/\-/       |
                 |    |        |  /     \  |  /        |        |
                 |    |       /-\/       \/-\/         |        |
                 |    |      |NE1|-------|NE5|----     |        /
                 |    \    -- \-/         \-/     \   /-\      /
                 |     \  /    |           |       --|NE4|    /
                 |      \/     |           |          \-/    /
                 |      /\-----+-----------+----------------/
            Border Nodes       |           |<--- Inter-Domain Links
                       \       |<----------+---- (External Links)
                       /\------+-----------+-----------------\
                      /  \     |           |                  \
                     /    \   /-\       /-\                   |
                     |     --|NE1|-----|NE2|                  |
                     |        \-/       \-/                   |
                     | Domain  |         |<--- Intra-Domain   |
                     |    C    |         |     Links (Internal|
                     |        /-\       /-\    Links)         |
                     |       |NE3|-----|NE3|                  |
                     |        \-/       \-/                   |
                      \                                      /
                       \------------------------------------/

              Figure 1.  Partitioning a network into domains.

   The Inter-Domain interface is likely to have different
   characteristics than the Intra-Domain interface as the domain
   boundary exists for the purpose of hiding some aspect within the
   domain from the outside world.

   For the remainder of this draft we will be concerned with "control
   domains" that is a control domain will be hiding the internal
   details of its control plane from other control domains. This
   definition has a number of important ramifications when we consider
   inter-domain protocols for routing or signaling.

   1. Inter-control domain routing or signaling is required to be
      independent of a control domainËs internal signaling or route
      protocol or lack of either a signaling or routing protocol. This
      is sometimes referred to as the "domain independence" property.



 Bernstein, G.                                                [Page 4]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   2. Inter-control domain routing or signaling can not count on
      specific protocols being implemented within the domain.
   3. Inter-control domain routing or signaling can not require that a
      network element participate in the internal protocols of two
      different control domains. This is sometimes refered to as
      "boundary on the wire" property.
   4. The Inter-control domain routing or signaling protocol does not
      require that the control domains be interconnected in any
      particular fashion (except for general graph connectivity).


   Example #1 (inter-control domain routing)
   Consider a collection of BGP Autonomous Systems (AS).  Each of these
   may run their own internal IGP. Of these internal IGPs, OSPFv2 and
   IS-IS are very popular but also incompatible with each other.
   BGP does not rely on the Autonomous Systems running a particular
   IGP, i.e., OSPF or IS-IS.  Hence it meets the definition of an
   inter-control domain routing protocol. Note that nothing prevents
   BGP from being used within an ISP to glue together islands of
   incompatible IGPs. In fact, the availability of private AS numbers
   can help in this situation.


   Example #2 (OSPF Areas)
   An OSPF Area, on the other hand, is a mechanism within OSPF for
   providing scalability. It assumes that within each OSPF area that
   OSPF is being run in addition it requires that all border routers
   participate in both the backbone area and one or more other their
   own areas.  Hence OSPF with its area concept equated with a control
   domain doesn't meet the definition of an inter-control domain
   routing protocol in two ways. It would require OSPF to run within
   the domains and it requires that a network element (router)
   participate in the internal routing protocol of two separate
   domains.

   Example #3 (PNNI routing Peer Groups)
   With ATM's PNNI routing hierarchy the concept of a peer group is
   introduced. PNNI with peer groups does not meet the definition of an
   a inter-control domain routing protocol since it, like OSPF,
   requires that within a peer group ATM PNNI routing is running.
   However, it doesnËt require that border members of a peer group at a
   given level in the hierarchy participate in the internal protocols
   of both peer groups. In other words PNNI's hierarchical routing
   allows for a "boundary on the wire" model.




 Bernstein, G.                                                [Page 5]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   The domain concept as used here is orthogonal to the transport
   network concept of layering.  When the term layer is used with
   respect to the transport network we are not referring to the 7-
   layer OSI model which includes application, presentation, etc.,
   layers.  With regard to this model all the optical transport layers
   would lie at the "physical layer".  In the transport network, layers
   are used for multiplexing, performance monitoring and fault
   management purposes. Layers tend to be very technology specific.  At
   some point an optical routing protocol must include information
   particular to the technology layer for which it is being used to
   acquire/disseminate topology and resource status information.  For
   more information on layering and domain concepts see ITU-T
   recommendation G.805 [14].

2.2 Major Differences between Optical and IP datagram Routing

   Let us first review the major difference between routing for optical
   (circuit switched networks) and IP datagram networks.  In IP
   datagram networks packet forwarding is done on a hop-by-hop basis
   for each packet(no connection established ahead of time), while in
   circuit switched optical networks end-to-end connections must be
   explicitly established based on network topology and resource status
   information.  This topology and resource status information can be
   obtained via routing protocols. Note that the routing protocols in
   the circuit switch case are not involved with data (or bit)
   forwarding, i.e., they are not "service impacting", while in the IP
   datagram case the routing protocols are explicitly involved with
   data plane forwarding decisions and hence are very much service
   impacting. Note that signaling or label distribution protocols that
   set up or tear down the virtual or real circuits are service
   impacting.

   This does not imply routing is unimportant in the optical case, only
   that its service impacting effect is secondary.  For example,
   topology and resource status inaccuracies will affect whether a new
   connection can be established (or a restoration connection can be
   established) but will not (and should not) cause an existing
   connection to be torn down.

   This tends to lead to a slightly different view towards
   incorporating new information fields (objects, LSA, etc.) into
   optical routing protocols versus IP routing protocols.  In the
   optical circuit case, any information that can potentially aid in
   route computations or be used in service differentiation may be
   incorporated into the route protocol, as either a standard element
   or a vendor specific extension.  Whether a route computation
   algorithm uses this information and whether two route computation
   algorithms use this information in the same way doesnËt matter since
   the optical connections are explicitly routed (although perhaps
   loosely).


 Bernstein, G.                                                [Page 6]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   Path selection or route computation in transport case may be based
   on a different criteria or combination of criteria on a per path
   basis.  For example one connection may requests the lowest economic
   cost available path while another may request the highest
   reliability path. One important evaluation criteria for any proposed
   inter-domain optical routing protocol is the variety of path
   selection criteria with which it may work.

2.3 Differences between MPLS and Optical Circuit routing

   The bandwidth accounting needed in optical circuit-switched networks
   is also different than in packet networks. In packet networks using
   either ATM QoS or MPLS-TE, complex statistical measures are used to
   characterize the load on a link, often with varying degrees of
   accuracy.  The inexactness of such measures and the
   ††compressibilityËË of statistically multiplexed traffic imply that a
   small percentage change in link utilization can usually be absorbed
   by the network.

   By contrast, if an OC-192 link has just one STS-1 path occupied
   (less than 1% of the link bandwidth), it cannot accommodate an STS-
   192c path. Due to the relatively simple finite multiplex structures
   currently use in optical networks tracking bandwidth resources is
   much easier than packet switched networks,  however much stricter
   bandwidth accounting is required on circuit switched links. In
   particular, it is expected that an individual optical circuit
   switched link can be fully utilized, while due to queuing effects a
   packet switched link on average can never be run at full capacity
   and is typically run at less then 80% of capacity.  This also
   affects how protection (or restoration) bandwidth can be committed.
   In a packet-based network, while the protection path can be
   preconfigured, resources along it are not used until a failure
   occurs.  In circuit-based networks, a protection path generally
   implies a committed resource. Such basic differences restrict the
   direct applicability of some of the traffic engineering mechanisms
   used in packet-switched networks to circuit-switched networks.


2.4 Diversity in Optical Routing

   There are two basic demands that drive the need to discover diverse
   routes for establishing optical paths:
        1. Reliability/Robustness
        2. Bandwidth capacity.

   Many times multiple optical connections are set up between the same
   end points. An important constraint on these connections is that
   they must be diversely routed in some way [4].  In particular they
   could be routed over paths that are link diverse, i.e., two
   connections do not share any common link. Or the more stringent
   constraint that the two paths should be node diverse, i.e., the two
   paths do not traverse any common node.


 Bernstein, G.                                                [Page 7]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   Additionally, insufficient bandwidth may exist to set up all the
   desired connection across the same path (set of links) and hence we
   need to know about alternative (diverse) ways of reaching the
   destination that may still have unused capacity.

   "Diversity" is a relationship between lightpaths. Two lightpaths are
   said to be diverse if they have no single point of failure. In
   traditional telephony the dominant transport failure mode is a
   failure in the interoffice plant, such as a fiber cut inflicted by a
   backhoe.

   Data network operators have relied on their private line providers
   to ensure diversity and so IP routing protocols have not had to deal
   directly with the problem. GMPLS makes the complexities handled by
   the private line provisioning process, including diversity, part of
   the common control plane and so visible to all.

   Diversity is discussed in the IPO WG document [5]. A key associated
   concept, "Shared Risk Link Groups", is discussed in a number of
   other IETF (refs) and OIF (refs) documents.  Some implications for
   routing that are drawn in [5] are:
     . Dealing with diversity is an unavoidable requirement for
        routing in the optical layer.  It requires dealing with
        constraints in the routing process but most importantly
        requires additional state information -- the SRLG relationships
        and also the routings of any existing circuits from which the
        new circuit is to be diverse -- to be available to the routing process.

     . At present SRLG information cannot be self-discovered. Indeed,
        in a large network it is very difficult to maintain accurate
        SRLG information. The problem becomes particularly daunting
        whenever multiple administrative domains are involved, for
        instance after the acquisition of one network by another,
        because there normally is a likelihood that there are diversity
        violations between the domains. It is very unlikely that
        diversity relationships between carriers will be known any time
        in the near future.

    - Considerable variation in what different customers will mean by
   acceptable diversity should be anticipated. Consequently we suggest
   that an SRLG should be defined as follows: (i) It is a relationship
   between two or more links, and (ii) it is characterized by two
   parameters, the type of compromise (shared conduit, shared ROW,
   shared optical ring, etc.) and the extent of the compromise (e.g.,
   the number of miles over which the compromise persisted). This will
   allow the SRLGËs appropriate to a particular routing request to be
   easily identified.




 Bernstein, G.                                                [Page 8]


                draft-ipo-optical-inter-domain-02.txt   February 2003


2.4.1   Generalizing Link Diversity

   Optical networks may posses a number of hierarchical signaling
   layers.  For example two routers interconnected across an optical
   network may communicate with IP packets encapsulated within an STS-
   48c SONET path layer signal.  Within the optical network this STS-
   48c signal may be multiplexed at the SONET line layer into an OC-192
   line layer signal.  In addition this OC-192 may be wavelength
   division multiplexed onto a fiber with other OC-192 signals at
   different wavelengths (lambdas).  These WDM signals can then be
   either lambda switched, wave band switched or fiber switched.  Hence
   when we talk about diversity we need to specify the layer to which
   we are referring.  In the previous example we can talk about
   diversity with respect to the SONET line layer, wave bands, and/or
   optical fibers.  A similar situation arises when we consider the
   definition of node diversity.  For example are we talking with
   respect to a SONET path layer switch or an optical switch or
   multiplexer?

     The Shared Risk Link Group concept in reference [6] generalizes
   the notion of link diversity (general list of numbers).  First it's
   useful with respect to major outages (cable cuts, natural disasters)
   to have a few more types of diversity defined:

        1. Cable (conduit) diversity (allows us to know which fibers
           are in the same cable (conduit).  This helps avoid sending
           signals over routes that are most vulnerable to "ordinary"
           cable cuts (technically known as backhoe fades).

        2. Right of Way (ROW) diversity.  This helps avoid sending
           signals over routes that are subject to larger scale
           disasters such as ship anchor drags, train derailments, etc.

        3. Geographic Route diversity. This type of diversity can help
           one avoid sending signals over routes that are subject to
           various larger scale disasters such as earthquakes, floods,
           tornadoes, hurricanes, etc.  A route could be approximately
           described by a piecewise set of latitude/longitude or UTM
           coordinate pairs.

   We also have a form of link abstraction/summarization via the link
   bundling concept [7].

2.4.2   Generalizing Node Diversity

   The concept of a node abstraction associated with GMPLS appears in
   reference [11] where it is used to generalize the concept of an
   explicitly routed path.  In this case an abstract node can be a set
   of IP addresses or an AS number. From the point of view of node
   diverse routing specific concepts of interest include:
     1. Nodes, i.e., individual switching elements.
     2. Switching centers, i.e., a central office or exchange site.
     3. Cities, or towns that contain more that one switching center.

 Bernstein, G.                                                [Page 9]


                draft-ipo-optical-inter-domain-02.txt   February 2003


     4. Metro areas, or counties
     5. States,
     6. Countries, or
     7. Geographic Regions

2.5 Routing Information Categorization
   Different applications of inter-domain optical routing call for
   different types of information to be shared or hidden between
   domains. In the following we decompose the information that can be
   transferred via a routing protocol broadly into link/topology
   information and node/domain information. We further subdivide these
   categories and will use this taxonomy of routing information when
   discussing the routing applications.

2.5.1   Link and Topology Related Information
   -Internal topology- information is information concerning the nodes
   and links and their connectivity within a domain. This type of
   information is traditionally shared within a domain via an intra-
   domain (interior gateway) routing protocol such as OSPF or IS-IS
   within a single area. For example the existence of nodes that only
   have links to other nodes within the domain, i.e., do not have links
   to other domains, would be strictly internal topology information.
   These nodes are known as internal nodes, while nodes with links to
   other domains are known as border nodes. Also included in this
   information is link/port property information such as whether the
   link is protected and what type of protection is being used, e.g.,
   linear 1+1, linear 1:N, or some type of ring such as a 4F-BLSR [cite
   T1 document].

   -Internal Resource- Information is concerned with the bandwidth
   available on links within a domain and possibly other resource
   related information. This information plays an important role in
   path selection within a domain.

   -Inter-Domain Topology- Information is concerned with how the
   domains are interconnected. This information can be key in inter-
   domain path selection, for example, in determining diverse routes.
   For the network in Figure 1 this information would let us know that
   domain A has two distinct links to domain B, domain A has two
   distinct links to domain C, but that domains B and C are not
   directly connected via any links.

   -Inter-Domain Resource- Information is concerned with the available
   bandwidth on inter-domain links. This information is important for
   inter-domain path selection and inter-domain traffic engineering
   purposes. For example in Figure 1 this information would give us
   some kind of bandwidth or capacity measure on the links between

 Bernstein, G.                                               [Page 10]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   domain A and domain B, and the links between domains A and C.  The
   exact nature of this information may be application/context
   dependent.

2.5.2   Domain and Node Related Information
   -Reachability- information tells us what addresses are directly
   reachable via a particular domain. These systems can be end systems
   (clients) to the network or nodes within the network depending upon
   the application/context.  Suppose in domain B of Figure 1 each of
   the network elements, NE1-NE3, have subtending end systems, and that
   NE1-NE3 do not represent a valid final destination for a path. Under
   this assumption the collection of the addresses of all these
   subtending end systems would form the reachability information for
   domain B.
   -Subnetwork Capability- information is concerned with the
   capabilities or features offered by the domain as a whole. This
   information is used in some applications where sharing the internal
   topology and resource information is inappropriate. This information
   can include: (a) Switching capabilities, (b) Protection
   capabilities, (c) Some kind of overall available capacity measure,
   (d) Reliability measures.
   Examples:
   1.   For example, in the SONET realm, one subnetwork may switch down
        to an STS-3c granularity while another switches down to an STS-
        1 granularity.  Understanding what types of signals within a
        SDH/SONET multiplex structure can be switched by a subnetwork
        is important.  Similar examples of granularity in switching
        apply to the waveband case.
   2.   Some networking technologies, particularly SONET/SDH, provide a
        wide range of standardized protection technologies. But not all
        domains will offer all protection options.  For example, a 2/4-
        F BLSR based subnetwork could offer extra data traffic, ring
        protected traffic and non-preemptible unprotected traffic,
        (NUT)[8], while a mesh network might offer shared SONET line
        layer linear protection and some form of mesh protection.
   3.   Some domains may be in locations that have lower incidences of
        link failure.  Such information could be helpful in computing
        routes to statistically "share the pain".

   -End System Capabilities- information: While properties of the
   subnetwork are very important when trying to decide which domain to
   use to access a system (in the case of multi-homing), end systems
   also posses a wide variety of capabilities. Throwing end system
   capabilities such as a system's ability to support SONET/SDH virtual
   concatenation for distribution into a routing protocol may not be
   that advantageous since it somewhat counters the ability to


 Bernstein, G.                                               [Page 11]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   summarize reachability information.  Detailed end-system information
   may alternatively be obtained via a directory service or some type
   of direct query between the end systems.

3  Applications of Inter Domain Optical Routing

   In this section we review some of the main applications of optical
   inter-control domain routing. We also review which aspects of the
   definition of control domain is most relevant to the application.

3.1 Intra Carrier Applications of Optical Inter Domain Routing

   Intra Carrier inter domain routing refers to a situation where the
   network that is to be partitioned into areas is under the control of
   one administrative entity. The main reasons for this partitioning in
   optical networks stem from scalability, inter-vendor
   interoperability, legacy equipment interoperability, and inter-layer
   partitioning.

3.1.1   Intra-Carrier Scalability
   As networks grow it is useful to partition a carriers network into
   separate optical routing domains which share limited or summarized
   information amongst each other. This reduces the overhead of
   information exchange across the network as a whole, and reduces the
   convergence time of routing protocols within a particular area.
   Hence we see in the inter-carrier scalability application that we
   will hide or summarize internal topology and resource information,
   while completely sharing inter-domain topology and resources
   information so that diverse paths can still be calculated. Note that
   general domain capabilities/capacity as well as reachability
   information would tend to be shared as completely as possible. For
   example the network shown in Figure 1 can be approximately
   represented as shown in Figure 2. This summarized network topology
   only has 4 links whose state need to be advertised in a routing
   protocol versus 17 links in the original network. Note that we may
   also advertise the capabilities of the three domains in Figure 2 as
   opposed to the 12 nodes of Figure 1. In Note that this partitioning
   into domains can recurse, i.e., we can have multiple levels of
   routing hierarchy to permit larger and larger networks.  Such was
   the motivation behind the extensive hierarchical routing capability
   within ATM's PNNI routing protocol.  The trade off to partitioning
   into domains for scalability is that less information is available
   for use in the route selection process, which can lead to
   inefficient utilization of network resources.  On the other hand
   frequently this partitioning occurs on somewhat "natural" boundaries
   and as such the potential inefficiencies can be minimized.

            --------                  ------


 Bernstein, G.                                               [Page 12]


                draft-ipo-optical-inter-domain-02.txt   February 2003


          /-        -\              /-      -\              -----
        //       NE 3 \mmmmmm     //          \\           /     \
       /         Port 2 \    mmmmm NE 3   NE 5  \         /NE 3   \
      /                  \      / Port 4  Port 6 \    mmmmmPort 17  \
     |                    |     |                mmmmm   |         |
     |                    |    |                  |      |         |
    |                      |   |     Domain A     |     | Domain C  |
    |       Domain B       |   |                  |     |           |
    |                      |   | NE 2     NE 1    |      |         |
     |                    |     |Port 5   Port 2 mmmmmmmmmNE 1     |
     |                        mmm                /       \Port 21  /
      \          NE 1    /mmmm   \              /         \       /
       \         Port 7 mm        \\          //           \     /
        \\            //            \-      -/              -----
          \-        -/                ------
            --------
        Figure 2.  Summarized topology for the network of Figure 1.

   Also in Figure 2 we show the end points of the links between being
   identified by the triple of (domain, NE address, NE port number).
   This information is available via the discovery process. Though not
   strictly necessary including the identification of border nodes in a
   domain, allowing other nodes to understand whether these links
   terminate on the same or different nodes is valuable in setting up
   diverse inter-domain paths.
   In current intra-domain IP routing protocols, such as OSPF's, a
   multiple area capability provides for intra-carrier scalability.
   However, this is currently done by sharing reachability information
   and using a distance-vector method to obtain routes.  This does not
   discover and propagate inter-domain topology information and hence
   insufficient information is available for diverse route
   calculations. In addition OSPF areas are required to be assembled in
   a particular fashion with all areas bordering on a single backbone
   area.
   When the topology within the domain is approximated or hidden then
   signaling and call processing at the domain border will receive an
   approximated (loose) route and the border node or signaling entity
   must then translate this to a precise route through the domain.
   Hence there is some linkage between multi-domain connection control
   and inter-area/inter-domain routing.

3.1.2   Intra-Carrier Inter-vendor
   An important application of intra-carrier optical routing is the
   intra-carrier inter-vendor scenario. From a carrierËs perspective,
   the use of domains provides a clean way to isolate clouds of



 Bernstein, G.                                               [Page 13]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   equipment belonging to different vendors, while at the same time
   allowing for interoperability between the vendors.
   An advantage of this method is that it allows the vendors complete
   freedom to use any combination of routing protocols or traditional
   management-based methods to propagate topology and resources
   internal to their domains. In other words, the routing entity in
   each domain could obtain this information either by participating in
   a routing protocol like OSPF, or by querying each NE via an EMS, or
   by simply having the required information manually configured into
   it. Here the "domain independence" and "boundary on the wire"
   properties of an inter-control domain routing protocol are being
   stressed.

   Note that the routing entity shown in each vendorËs cloud in Figure
   3 is in reality an abstract representation of the routing
   intelligence within the vendor cloud. This intelligence may either
   be implemented in a distributed way, by having a routing protocol
   running at each NE, or in a centralized way, through the use of an
   intelligent, centralized routing entity that communicates with the
   individual NEËs (either via a protocol or by querying individual
   elements) to retrieve connectivity and resource information that it
   uses to build a complete topology and resource map of the domain.
   Therefore, vendors may use different protocols as the primary option
   between their own devices, adding specialized features or optimizing
   their performance based on their choice of protocol.
                    /------------------------------------\
                   /            /-\                       \
                  /  Domain B  |NE3|          +-------+    \
                  | (Vendor 2) /\-/\          |Routing|    |
                  |           /     \         |Entity |    |
                  |       /-\/       \/-\     +-------+    |
                  \      |NE1|-------|NE2|       @         /
                   \      \-/:        \-/        @        /
                    \------+-:---------+---------@-------/
     Neighbor discovery    | :         |         @ Exchange of routing
     Between NEs in the    | :         |         @ information between
     same domain.    ----> | :         |         @ the domains routing
                           | :         |         @ entities.
                    /------+-:---------+---------@-------\
                   /       | :         |         @        \
                  /        /-\       /-\      +-------+    \
                  |       |NE1|-----|NE2|     |Routing|     |
                  |        \-/\     /\-/      |Entity |     |
                  |            \/-\/          +-------+     |
                  |  Domain A  |NE3|                        |
                  | (Vendor 1)  \-/                        /
                   \                                      /
                    \------------------------------------/


 Bernstein, G.                                               [Page 14]


                draft-ipo-optical-inter-domain-02.txt   February 2003


            Figure 3.  Intra-Carrier Inter-vendor routing domains
   Even if it is a centralized entity, the routing entity could still
   be run on a given NE in the vendor cloud. In other words, these
   entities could be distributed, or centralized onto a single node, or
   independent of any of the nodes.  In ATM's PNNI protocol, for
   example, this was centralized on a node elected as the  "peer group
   leader".  In the inter-vendor case, it can be particularly
   advantageous to centralize this so that the flow of information can
   be monitored.  A centralized routing entity could apply flooding and
   summarization mechanisms as if it is a switching system.  Since this
   is optical rather than IP routing, signaling would be carried by a
   control channel between the routing entity and the neighboring
   system, rather than being carried over the data links. The functions
   of the routing entity include:  (a) direct reachability exchange
   (that is, which NEËs can be directly reached from this domain, (b)
   verification of area connectedness (that is, understanding how the
   two domains are interconnected), (c) area/domain topology (possibly
   summarized) exchange and updates, and (d) topology updates
   concerning other domains/areas.

   When a carrier partitions its network for inter-vendor
   interoperability as described above, it may still share information
   about the internal topology of the domains in some standardized form
   that has been agreed upon between the vendors. Although one option
   is to force both vendors to adopt a new common protocol, another is
   to require that only a minimum subset of reachability/topology
   information be shared between the vendor clouds. The latter option
   helps during fault situations, by providing fault isolation at the
   domain boundaries. It prevents an outage in a domain composed of one
   vendorËs equipment from causing a reaction in an adjacent domain
   composed of another vendorËs equipment, thus preventing a situation
   that would typically degenerate into a process known as ††finger
   pointingËË between the two vendors.

   The setup described above takes into account the three most
   important sub-cases of inter-carrier inter-vendor partitioning:
        a. The first is where both vendor domains run distributed
        routing protocols. This is the most flexible case, and is the
        situation when new equipment capable of running such protocols
        is deployed.

        b. The second is where the optical subnetworks or domains
        (which includes a large number of existing installations) do
        not run any internal routing protocol (because the NEËs are not
        capable of doing so), relying instead on EMS-based topology
        discovery/resource management. In this case, interoperability

 Bernstein, G.                                               [Page 15]


                draft-ipo-optical-inter-domain-02.txt   February 2003


        with other vendor clouds can be realized by having the routing
        entity run as a separate software entity with access to the
        appropriate information. These entities may exchange routing
        proxy addresses through the neighbor discovery protocol, and
        then exchange routing information (proxying for the entire
        domain) with each other. The basic advantage here is that even
        though the vendor specific element management system (EMS)
        knows the topology of its subnetwork, it is far easier to get
        an inter-domain routing protocol to share information than
        trying to get the separate vendors management systems to
        communicate.
        c.  The third is where one domain has a centralized routing
        entity, while the other runs a distributed routing protocol.
        Once again, the neighbor discovery process between the area
        border NEËs could be used to advertise the address of the
        routing entity.

3.1.3   Inter-Layer Partitioning
   In transport networks layering is a part of the multiplex and OA&M
   structure of the signals, playing a role in multiplexing, monitoring
   and general link management.  Layering in the transport network is
   defined in fairly abstract terms in [G.805] and the concepts are
   applied to SDH in [G.803].  As explained in a recent ITU SG15
   document (WD45 Q.14/15) not all the layers in the transport network
   are of interest to the control plane, or to routing in particular.
   Some layers may not contain active switching elements, however this
   does not mean that information flow concerning a non-switching layer
   is not valuable in routing. For example in [GB-WDM-SRLG] static WDM
   layer information was used to set the SRLGs for SONET lines (i.e.,
   information passed around by a link state protocol operating at the
   SONET line layer). It should be noted that much of the information
   available from non-switching layers relates to performance
   monitoring and fault management.

   In this situation the network is partitioned into sub-networks that
   operate at different switching layers. One reason for doing this is
   that not all the information from one layer is necessary or relevant
   to another layer.  For example, between transparent optical switches
   and SDH/SONET path (VC) layer switches, the optical switches have no
   direct use for the SONET layer information. In addition optical
   networks may keep a lot more physical layer information (such as the
   properties of every optical amplifier on a WDM span) that is of no
   use to the SONET layer.  One again this promotes scalability, but
   also simplifies the implementation by reducing inter-layer
   information transfer to that which is actually useful.



 Bernstein, G.                                               [Page 16]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   Now in network planning it is very useful to have a view of the
   current higher layer traffic matrix [9] being satisfied and higher
   layer traffic trend measurements over time.  Although we can
   somewhat see this in higher layer resource status changes over time,
   this represents a link level view when we really desire the trend
   (change in time) of the traffic matrices between sites.  How this
   information gets distributed is an open issue. Currently individual
   nodes in a GMPLS network know only about connections that they
   source or sink. Network planning is generally a longer time horizon
   process than even traffic engineering hence it is an open question
   as to whether this would ever be a useful function to incorporate
   into a network element.

   Now looking the other way is initially simpler, i.e., it is easier
   to ask: what can a higher layer use for path selection/computation
   from a lower layer. The first item that springs to mind is diversity
   information. For example in setting up a SONET STS-1 path we can use
   information from a WDM system concerning which  SONET lines share
   the same WDM fiber.  This is information, however, is already
   abstracted into routing protocols via SRLG concept. Other
   information from a lower layer is of questionable value since it
   tends to be technology specific and puts more and more burden on the
   upper layer to be able to effectively understand and use this
   information.

3.1.4   Interaction with IP Layer Routing
   The applicability of IP-based routing protocols has, over the years,
   been constantly expanded to increasingly more circuit-oriented
   layers. The community began with pure datagram routing, gradually
   expanded to cover virtual-circuit switched packet routing (for e.g.,
   MPLS), and is finally looking at the application of routing
   protocols to real circuit switching, e.g. the optical layer.

   However, as pointed out earlier in this document, it is not clear
   that the different layers should necessarily share the same instance
   of the routing protocols. Indeed, there may be significant reasons
   for not doing so and many carrier tend to partition their networks
   along switching layer boundaries. For example, IP-layer reachability
   information is not particularly useful for the optical layer, so it
   seems an overkill to burden the optical equipment with storing and
   distributing that information. (It is an extra expense on memory and
   processing for information that the optical layer does not really
   care about, so there is little incentive for a vendor to want to do
   so.) Likewise, information on physical plant (fibers, conduits,
   ducts) diversity, which is crucial at the optical transport layer,
   is very unlikely to be used directly by the IP layer. So, it would


 Bernstein, G.                                               [Page 17]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   be quite wasteful of resources to burden the IP layer routing with
   distributing and manipulating this information. Thus, the extent of
   interaction or integration with IP layer routing (if any) requires
   careful consideration.

3.1.5   Inter-Business Unit

   A slightly different but interesting application of intra-carrier
   optical routing occurs in the intra-carrier inter-business unit
   scenario. This arises because a carrier often has multiple
   administrative domains, with groups of administrative domains being
   under the purview of independent BUËs within the carrier.

   Note that different BUËs represent independent cost centers with
   their own profit objectives and sales targets. As a result, while
   the BUËs can profitably share topology information and would like to
   do so, they may not be so inclined to advertise the details of their
   resource usage into domains belonging to other BUs.  Since each BU
   has its own revenue targets, advertising detailed resource
   availability information to other, potentially competing, BUs can
   have a negative impact on a BUs revenue generation. This is because
   the knowledge of available resources in one BU may enable other BUs
   within the carrier to requisition capacity from this BU. This would
   force the BU in question to yield to their request, possibly at the
   expense of selling capacity to more profitable, external, revenue
   generating customers.
   Thus, this scenario is likely to have an additional dimension of
   information sharing, namely, policy-based information sharing, which
   does not apply to the other cases that we have discussed so far.

   Two examples where the inter-business unit scenario could become
   important are in the case of metro-core-metro networks within a
   given carrier, and in the case of regional networks within a
   carrier.

   In the metro-core-metro situation, such as the one depicted in
   resource sharing between them.

                       /------------------------------------\
                      /                                      \
                     /             /-\                        \
                     |  Domain    |NE2|                        |
        Metro BU     |    B       /\-/\<-- Metro Ring          |
        Network      |           /     \                       |
                     |       /-\/       \/-\                   |
                     |      |NE1|-------|NE3|                  /
                     \       \-/         \-/                  /
                      \       |           |                  /

 Bernstein, G.                                               [Page 18]


                draft-ipo-optical-inter-domain-02.txt   February 2003


                       \------+-----------+-----------------/
                              |           |
                       /------+-----------+-----------------\
                      /       |           |                  \
                     /        |    /-\    |          /-\      \
                     | Domain |   |NE2|---+---------|NE3|      |
         CORE BU     |   A    |   /\-/\   |   ------/\-/       |
         Network     |        |  /     \  |  /        |        |
                     |       /-\/       \/-\/         |<--Core |
                     |      |NE1|-------|NE5|----     |   Mesh /
                     \       \-/         \-/     \   /-\      /
                      \       |           |       --|NE4|    /
                       \      |           |          \-/    /
                        \-----+-----------+----------------/
                              |           |
                       /------+-----------+-----------------\
                      /       |           |                  \
                     /        /-\       /-\                   \
                     |       |NE1|-----|NE2|                  |
        Metro BU     | Domain \-/       \-/                   |
        Network      |   C     |         |<--- Metro Ring     |
                     |         |         |                    |
                     |        /-\       /-\                   |
                     |       |NE3|-----|NE3|                  |
                     |        \-/       \-/                   |
                      \                                      /
                       \------------------------------------/

   Figure 4, the metro network domains could be under the jurisdiction       Deleted   of one BU, while the core network domains belong to a different BU.
   In this case, for example, it is possible that the metro BU, armed
   with resource availability information about the core BUËs domains,
   could requisition capacity from the core network when needed. This
   may harm the core networkËs profit goals, because they may not be
   able to charge an internal customer the same rates that they could
   charge for the same capacity from an external customer, thus
   motivating the need for selective, policy-based resource sharing
   between them.

                       /------------------------------------\
                      /                                      \
                     /             /-\                        \
                     |  Domain    |NE2|                        |
        Metro BU     |    B       /\-/\<-- Metro Ring          |
        Network      |           /     \                       |
                     |       /-\/       \/-\                   |
                     |      |NE1|-------|NE3|                  /
                     \       \-/         \-/                  /
                      \       |           |                  /
                       \------+-----------+-----------------/
                              |           |
                       /------+-----------+-----------------\
                      /       |           |                  \

 Bernstein, G.                                               [Page 19]


                draft-ipo-optical-inter-domain-02.txt   February 2003


                     /        |    /-\    |          /-\      \
                     | Domain |   |NE2|---+---------|NE3|      |
         CORE BU     |   A    |   /\-/\   |   ------/\-/       |
         Network     |        |  /     \  |  /        |        |
                     |       /-\/       \/-\/         |<--Core |
                     |      |NE1|-------|NE5|----     |   Mesh /
                     \       \-/         \-/     \   /-\      /
                      \       |           |       --|NE4|    /
                       \      |           |          \-/    /
                        \-----+-----------+----------------/
                              |           |
                       /------+-----------+-----------------\
                      /       |           |                  \
                     /        /-\       /-\                   \
                     |       |NE1|-----|NE2|                  |
        Metro BU     | Domain \-/       \-/                   |
        Network      |   C     |         |<--- Metro Ring     |
                     |         |         |                    |
                     |        /-\       /-\                   |
                     |       |NE3|-----|NE3|                  |
                     |        \-/       \-/                   |
                      \                                      /
                       \------------------------------------/

       Figure 4. Intra-carrier inter-business unit routing domains.


3.2 Inter-Carrier Inter-Domain Optical Routing

   In this case we are talking about dealing with outside entities,
   i.e., between service providers.  There may be a range of levels of
   trust here; for example there might be some level of trust between
   two providers that have formed a marketing alliance or have some
   other form of business relationship. In general, however, trust can
   not be assumed. In this case, all the concerns of revealing too much
   information about one's network come into play.  However, not
   revealing enough, say about diversity capabilities may also lead
   customers elsewhere. Also there are some other security issues not
   seen before. For example, in route distribution one carrier might
   not be inclined to pass on routing information that could point the
   way to competitive alternatives. This impacts the methods for route
   updates, etc.

   With the interest in bandwidth trading [10] we can also look at this
   as an advertisement of network connectivity and capability with of
   course any "warts" covered up. This would include reliance on other
   carrier for fibers or lambdas.  Also a fair amount of details such
   as "unused capacity" would not be advertised since this maybe
   financially sensitive information.

   Private line pricing today is based primarily on the service itself
   (bandwidth, end-points, etc.) and the holding time, and there is no


 Bernstein, G.                                               [Page 20]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   reason to expect that this will change. When multiple service
   providers are involved the algorithm for dividing up the revenue
   stream (which can be quite large even for a single connection) must
   be explicit by connect time. This could be done off-line or could be
   done at connect time. In either case, the entity or entities doing
   the routing will need to take provider pricing structures into
   account whenever there is a choice between providers that needs to
   be made. The routing logic could do this explicitly if the prices
   are captured in the advertised metrics or some other advertised
   data; alternatively it could be done by some sort of policy control,
   as it is today by BGP.

   The essence of bandwidth trading is the existence of competing price
   structures that are known to the entity deciding which competitor to
   use.  It is possible to create plausible bandwidth trading scenarios
   involving the UNI, the NNI, or both. If the NNI is involved, these
   price structures will need to be established across it. The
   situation is further complicated by the fact that bandwidth trading
   could be realized using any one of a number of business models, each
   with its own information requirements. To give two examples: If an
   auction model were used the buyer might repeatedly broadcast the
   lowest bid received to date and solicit lower bids from the
   competing providers. On the other hand, if there were a more formal
   market the providers might post their asking prices in some public
   fashion and a buyer would be matched by some third party with the
   lowest offer.

   In the inter-carrier case notions of hierarchy seem rather
   sensitive, i.e., he who controls the summarization and advertisement
   may have an undue advantage over competitors.  In addition, a
   "bandwidth aggregator" may want to advertise capabilities that he
   has put together via deals with multiple carriers...

   Notes: We can attempt to extend the SRLG concept to links between
   ASs but we will need the two ASs to agree on the meaning and number
   of the list of 32 bit integers that comprise the SRLG, i.e.,
   previously the SRLG concept was one of AS scope.  And this is also
   where things get tricky since it may not be possible to distinguish
   diverse routes based upon differing path vectors (i.e., AS number
   traversal list).  The reason for this is due the fact that many
   carriers "fill out" their networks by renting either dark fiber or
   "lambdas" from a WDM system and hence although the path vectors may
   be AS diverse they may not even be fiber diverse.

   Hence there is a need for sharing of diversity information or
   constraints between ASs when setting up diverse connections across
   multiple ASs.  This gets us somewhat into a quandary over which
   information needs to be public and how to coordinate its
   distribution.  In this sense geographic link information may be the
   simplest and least contentious to get various players to disclose
   and standardize.



 Bernstein, G.                                               [Page 21]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   Notes:  (1) The real issue is consistency between the cloud/ASËs
   since in many cases they are sharing conduit, ROW, etc.  Getting
   this to happen could be very problematic. It would be preferable to
   see a diversity option that doesnËt require this. For example,
   ensure that there is diversity within each cloud and then do
   restoration separately within each cloud. (2)  See the definition of
   SRLG in the Carrier Requirements -- an equivalence class of links,
   the extent of violation, and the level. (3) Flexibility in defining
   the level of violation seems very desirable -- these historically
   have drifted in time. There are many others -- eg, if the shared
   resources are SPRING protected thatËs less of a problem than
   otherwise.

   Notes: Participation in the inter-domain network carries constraints
   on the carriers. First, in order to participate, each provider
   network MUST be willing to advertise the destinations that are
   reachable through his network at each entry point and advertise the
   formats available. Without providing such information, there is
   little motivation to participate since it is unlikely that others
   will be able to access services of which they are not aware. Second,
   every participating carriers MUST agree to fairly include the
   information made available by every other carrier so that each
   carrier has an equal opportunity to provide services. There may be
   specific exceptions, but the carrier claiming those exceptions MUST
   advertise the exceptions themselves. In this manner, other carriers
   that might otherwise be aware of distant services can be prompted to
   seek those services manually.  Note a combination of minimal
   required information transferred with deferral to the originating
   subnetwork along with some basic security mechanisms such as
   integrity and non-repudiation may be useful in helping organizations
   to "play nice".

3.3 Multi-Domain Connection Control

   MPLSË loose routing capability allows one to specify a route for an
   optical connection in terms of a sequence of optical AS numbers.
   This, for example, is handled via RSVP-TEËs abstract node concept
   [11]. Currently there is nothing in the GMPLS signaling
   specification that differentiates between intra AS boundaries, i.e.,
   between two neighbor optical LSRs in the same AS, and inter AS
   boundaries, i.e. between two neighbor optical LSRs in different ASs.
   Note that these same notions can apply to separate routing domains
   within an AS. There may, however, be some useful reasons for
   differentiating these two cases:

         1. Separation of signaling domains,
         2. Separation of protection domains.

   While routing protocols (used for their topology information) in the
   optical case are not "service impacting", signaling protocols most
   certainly are.  It is desirable to build some type of "wall" between
   optical ASs so that faults in one that lead to "signaling storms" do
   not get propagated to other ASs.  Note that the same motivation

 Bernstein, G.                                               [Page 22]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   applies for isolating other kinds of clouds, like vendors specific
   ones.

   The natural situation where "signaling storms" would be most likely
   to arise is during network restoration signaling, i.e., signaling to
   recover connections during major network outages, e.g., natural
   disasters etc. In this case it may be very advantageous to break up
   general source reroute forms of restoration into per domain segments
   or to start reroute at domain boundaries rather than all the way
   back at the originating node. Note that this has the advantage of
   reducing the need for globally consistent SRLGËs. (See earlier SRLG
   comment.) Such a capability requires some loose coordination between
   the local, intermediate and global protection mechanisms [12].  This
   is typically implemented via hold off timers, i.e., one layer of
   protection will not attempt restoration until a more fundamental
   (local) form has been given a chance to recover the connection [12].

   In other words, prevention of restoration related signaling storms
   may require the breaking up of a large network into multiple
   signaling (and hence routing) domains. These domains could be within
   the same AS.

4  Multiple Layers of Optical Routing

   As previously discussed, there are multiple layers of signals
   included in what in the IP model one would call the Physical Layer.
   One could separate the layers by creating sublayers in the Physical
   Layer.  For example, sublayers in the Physical Layer might be, top
   to bottom: SDH LOVCs, SDH HOVCs, and Lambdas. If a system supports
   only one of the three, then isolation of the sublayers is a given;
   it's geographical. But there are systems which will support more
   than one physical sublayer, therefore, it is necessary to establish
   whether or not there is a need to isolate the sublayers in the same
   manner. Or put another way is there a reason to "integrate" the
   sublayers for the purposes of routing (topology dissemination).

   If they are isolated, then there will be separate topological models
   for each sublayer: one mesh for the LOVC, one for the HOVC, one for
   the Lambda, and possibly others. The appropriate way to access a
   sublayer is via the use of sublayer SAPs (service access points).
   For example, in this way, one may find that use of Lambdas is more
   efficient because each sublayer can assess the availability of
   services at its own layer before searching for coarser-granularity
   services. On the other hand, the control plane must accommodate
   three separate routing protocols, or at least three separate
   instances of the same routing protocol, all operating at both intra
   and inter-domain level.

   Example (SDH multiplexing)
   For transport across an SDH network, the lower order signals must be
   multiplexed into a non-concatenated higher order signal. Hence LOVCs
   are not routed independently, but only as tributaries of HOVCs. In
   addition in the SDH hierarchy there is a signal, VC3, that can be

 Bernstein, G.                                               [Page 23]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   treated (multiplexed) as either a LOVC or a HOVC.  With this tight
   and somewhat confused coupling of these layers it may beneficial to
   sometimes combine them into the same route protocol instance.


   The alternative to separate routing protocols per sublayer is the
   original notion behind GMPLS routing and the forwarding adjaciency
   concept [13]. Rather than separating the route protocols into
   separate layers (or sublayers) with distinct topologies, each ONE
   would advertise the services it can provide, along with its topology
   information. For example, a ONE (optical network element) might
   advertise that it carries a route to node A with STS-N service and
   clear-channel lambda service and carries multiple routes to node B
   with STS-N service. It might, alternatively, advertise its entire
   network with summarized link capacity information for every included
   link. Neighboring carriers would, implicitly, be allowed to
   summarize that information for internal advertisement via its IGP.
   Further consideration could be given to a query service, where a
   carrier advertises the geographical area it serves without detailed
   reachability or capacity information. A second carrier desiring
   service could query the first carrier as to reachability for a
   specific destination, and the first carrier would respond with
   availability and capacity information.

   Integrating multiple layers into the same routing protocol instance
   leaves us fewer routing protocols to manage. The downside of this is
   that more information must be exchanged via this routing protocol
   and more network elements participate in this single instance of the
   routing protocol which can lead to scalability concerns. If the
   equipment working on the different sublayers comes from different
   vendors there would be little incentive to integrate multiple layers
   into the routing protocol for a single layer product.
   Regardless of whether multiple layers are integrated into the same
   routing protocol instance it can be very useful to share information
   between layers as illustrated by the following examples:


        o Drop side links between layers: Capabilities of the links
          that are between the (client and server) layers need to be
          propagated into the routing protocol.
        o Summarize link capabilities: Summarizing the server layer
          capabilities in the client layer will reduce the amount of
          information required for multi-layer constraint based path
          computation.
        o Send only that are required: Sending only the capabilities
          that are useful in the constraint path computation in the
          client layer.


5  Conclusion




 Bernstein, G.                                               [Page 24]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   Key properties of optical control domains and an optical inter
   control domain routing protocol were reviewed. The stringent
   properties of "independence of internal domain control plane
   mechanisms" as well as support for "boundary on the wire" were shown
   to be crucial to the definition of control domain by showing their
   use in several mainstream optical inter-networking scenarios.

   Via examples we saw that BGP is the only existing IP routing
   protocol for which the "internal domain independence" and "boundary
   on the wire" property hold.  However, it was described how important
   the ability to diversely route optical connections is to the
   reliability and resilience of the optical network.  In addition it
   was pointed out that flexibility in choosing/computing paths can be
   very important to an optical network operator so that they can offer
   a range of differentiated services.  In this light BGP does not
   currently meet the needs of an optical inter control domain routing
   protocol.

   As of this writing we are therefore looking at two alternatives for
   an optical inter control domain routing protocol. (1) Extensions to
   a link state type protocol (such as OSPF, IS-IS or PNNI routing) to
   work at the control domain level rather than node to node level. Or
   (2) Extensions to a path vector type protocol (such as BGP) to
   provide diverse routing support and enhance path selection/network
   optimization.


6  Security Considerations

6.1.1

   Protection of the routing information exchanged across an optical
   inter-domain interface is of high importance; erroneous reachability
   or topology information may result in connection provisioning
   requests that either fail or are routed across sub-optimal paths. It
   is also possible that failed requests may consume significant
   control and transport resources for a transient amount of time. It
   follows that erroneous routing information could result in degraded
   carrier network operation, or even render a carrierËs network
   inoperable. Security requirements are expected to be of higher
   importance in interfaces between different administrative domains.
   Therefore, an optical inter-domain routing protocol should provide
   the following:

  1. Authenticate entities with which routing information is exchanged.
     For example, a carrier should authenticate the identity of other
     carriers it is connected to. The specific mechanisms used for
     authentication should provide protection against attacks; for
     example they should not be based on simple clear-text password
     authentication schemes.

  2. Guarantee the integrity of routing information (topology,
     reachability and resource status) exchanged across the interface.

 Bernstein, G.                                               [Page 25]


                draft-ipo-optical-inter-domain-02.txt   February 2003


     This requirement can be satisfied using security mechanisms at
     different layers. For example, each routing message could be
     individually authenticated using a keyed message digest, which is
     embedded in the message. Both OSPF and BGP provide such options.
     Alternatively, the two parties could establish a security
     association at the network layer using IPSEC, which could be used
     to provide security services to the optical inter-domain routing
     protocol.

   From the point of view of routing, information integrity is likely
   to be the most important requirement. However, in some cases it
   might be necessary to provide confidentiality of the routing
   information as well. A possible scenario for this is when a carrier
   would like to advertise information privately to another carrier,
   but does not wish to publicly disseminate this information, due to
   policy constraints.

   It should be noted than none of the known mechanisms that provide
   information integrity (such as keyed digests or IPSEC) can provide
   adequate protection against a compromised node participating in the
   inter-domain routing protocol. This is an item for further study.

7  References

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

   [2] G. Bernstein, J. Yates, D. Saha, "IP-Centric Control and
      Management of Optical Transport Networks", IEEE Communications
      Magazine, October 2000.

   [3] G. Bernstein, E. Mannie, V. Sharma, "Framework for MPLS-based
      Control of Optical SDH/SONET Networks", <draft-ietf-ccamp-
      sdhsonet-control-02.txt>, February 2003.

   [4] Ramesh Bhandari, Survivable Networks: Algorithms for Diverse
      Routing, Kluwer Academic Publishers,1999.

   [5] Strand, J. (ed.) "Impairments And Other Constraints On Optical
      Layer Routing", work in progress, draft-ietf-ipo-impairments-
      00.txt, May 2001.

   [6] Kompella, K., et. al. "IS-IS Extensions in Support of
      Generalized MPLS", Work in Progress, draft-ietf-isis-gmpls-
      extensions-16.txt, December 2002.

   [7]  K. Kompella, et. al. "Link Bundling in MPLS Traffic
      Engineering", Work in Progress, draft-ietf-mpls-bundle-
      04.txt, July 2002.





 Bernstein, G.                                               [Page 26]


                draft-ipo-optical-inter-domain-02.txt   February 2003



   [8]  ANSI T1.105.01-1995, Synchronous Optical Network (SONET)
      Automatic Protection Switching, American National Standards
      institute.

   [9]  Robert S. Cahn, Wide Area Network Design: Concepts and Tools
      for Optimization, Morgan Kaufmann Publishers, Inc., 1998.

   [10] Meghan Fuller, "Bandwidth trading no longer a case of 'if' but
      'when' says report", Lightwave, June 2001. (www.light-wave.com)

   [11] RFC 3209, "RSVP-TE: Extensions to RSVP for LSP
      Tunnels", December 2001.

   [12] K. Owens, V. Sharma, M. Oommen, "Network Survivability
      Considerations for Traffic Engineered IP Networks",  Work in
      Progress, draft-owens-te-network-survivability-03.txt, May 2002.

   [13]  K. Kompella and Y. Rekhter,  "LSP Hierarchy with MPLS TE",
      draft-ietf-mpls-lsp-hierarchy-08.txt, Internet Draft, Work in
      Progress, September 2002.
   [14] G.805, Generic Functional Architecture of Transport Networks,
      ITU-T, March 2000.



8  Acknowledgments

   The authors would like to thank Shezad Mirza of BT and Cheryl
   Sanchez of Calix for their help.


9  Author's Addresses

   Greg Bernstein
   Grotto-Networking
   Phone: (510) 573-2237
   Email: gregb@grotto-networking.com

   Lyndon Ong
   Ciena Corporation
   5965 Silver Creek Valley Road
   San Jose, CA 95015
   Phone: (408) 834-7894
   Email: lyong@ciena.com

   Bala Rajagopalan, Dimitrios Pendarakis
   Tellium, Inc
   2 Crescent Place
   Ocean Port, NJ 07757
   Email: braja@tellium.com, dpendarakis@Tellium.com

   Angela Chiu
   John Strand
   AT&T Labs

 Bernstein, G.                                               [Page 27]


                draft-ipo-optical-inter-domain-02.txt   February 2003


   200 Laurel Ave.
   Middletown, NJ 07748
   Phone:(732) 420-9061 Angela,  (732) 420-9036 John
   Email: chiu@research.att.com, jls@research.att.com

   Vishal Sharma
   Metanoia, Inc.
   335 Elan Village Lane, Unit 203
   San Jose, CA 95134
   Phone:  +1 408 943 1794
   Email: v.sharma@ieee.org

   Rauf Izmailov
   NEC USA, Inc.
   4 Independence Way
   Princeton, NJ 08540
   Email: rauf@nec-lab.com

   Dean Cheng
   Polaris Networks Inc.
   6810 Santa Teresa Bl.
   San Jose CA 95119
   Email: dcheng@polarinetworks.com

   Sudheer Dharanikota

   Frank Hujber















 Bernstein, G.                                               [Page 28]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/