Internet DRAFT - draft-dimitri-ccamp-gmpls-ason-routing-eval


CCAMP Working Group                                John Drake (Boeing) 
Internet Draft                                     Chris Hopps (Cisco) 
Category: Informational                             Lyndon Ong (Ciena) 
                                       Dimitri Papadimitriou (Alcatel) 
Expiration Date: September 2005              Jonathan Sadler (Tellabs) 
                                                 Stephen Shew (Nortel) 
                                                     Dave Ward (Cisco) 
                                                            March 2005 
                 Evaluation of existing Routing Protocols 
                     against ASON routing requirements 
Status of this Memo 
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   and any of which I become aware will be disclosed, in accordance 
   with RFC 3668. 
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Copyright Notice 
   Copyright (C) The Internet Society (2004). All Rights Reserved. 
   The Generalized MPLS (GMPLS) suite of protocols has been defined to 
   control different switching technologies as well as different 
   applications. These include support for requesting TDM connections 
   including SONET/SDH and Optical Transport Networks (OTNs). 

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   This document provides an evaluation of the IETF Routing Protocols 
   against the routing requirements for an Automatically Switched 
   Optical Network (ASON) as defined by ITU-T.  
1. Contributors 
   This document is the result of the CCAMP Working Group ASON Routing 
   Solution design team joint effort.  
2. Conventions used in this document 
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   document are to be interpreted as described in RFC 2119 [RFC2119]. 
3. Introduction 
   There are certain capabilities that are needed to support the ITU-T 
   Automatically Switched Optical Network (ASON) control plane 
   architecture as defined in [G.8080].  
   [ASON-RR] details the routing requirements for the GMPLS routing 
   suite of protocols to support the capabilities and functionality of 
   ASON control planes identified in [G.7715] and in [G.7715.1]. The 
   ASON routing architecture provides for a conceptual reference 
   architecture, with definition of functional components and common 
   information elements to enable end-to-end routing in the case of 
   protocol heterogeneity and facilitate management of ASON networks. 
   This description is only conceptual: no physical partitioning of 
   these functions is implied. 
   However, [ASON-RR] does not address GMPLS routing protocol 
   applicability or capabilities. This document evaluates the IETF 
   Routing Protocols against the requirements identified in [ASON-RR]. 
   The result of this evaluation is detailed in Section 5. Close 
   examination of applicability scenarios and the result of the 
   evaluation of these scenarios are provided in Section 6. 
   ASON (Routing) terminology sections are provided in Appendix 1 and 2. 
4. Requirements - Overview 
   The following functionality is expected from GMPLS routing protocol 
   to instantiate the ASON hierarchical routing architecture realization 
   (see [G.7715] and [G.7715.1]): 
   - Routing Areas (RAs) shall be uniquely identifiable within a  
     carrier's network, each having a unique RA Identifier (RA ID)  
     within the carrier's network. 
   - Within a RA (one level), the routing protocol shall support  
     dissemination of hierarchical routing information (including  
     summarized routing information for other levels) in support of an  
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     architecture of multiple hierarchical levels of RAs; the number of  
     hierarchical RA levels to be supported by a routing protocol is  
     implementation specific. 
   - The routing protocol shall support routing information based on a  
     common set of information elements as defined in [G.7715] and  
     [G.7715.1], divided between attributes pertaining to links and  
     abstract nodes (each representing either a sub-network or simply a  
     node). [G.7715] recognizes that the manner in which the routing  
     information is represented and exchanged will vary with the  
     routing protocol used. 
   - The routing protocol shall converge such that the distributed  
     Routing DataBases (RDB) become synchronized after a period of  
   To support dissemination of hierarchical routing information, the 
   routing protocol must deliver: 
   - Processing of routing information exchanged between adjacent  
     levels of the hierarchy (i.e. Level N+1 and N) including  
     reachability and upon policy decision summarized topology  
   - Self-consistent information at the receiving level resulting from 
     any transformation (filter, summarize, etc.) and forwarding of 
     information from one Routing Controller (RC) to RC(s) at different  
     levels when multiple RCs bound to a single RA. 
   - A mechanism to prevent re-introduction of information propagated 
     into the Level N RA's RC back to the adjacent level RA's RC from 
     which this information has been initially received. 
   Note: the number of hierarchical levels to be supported is routing 
   protocol specific and reflects a containment relationship. 
   Reachability information may be advertised either as a set of UNI 
   Transport Resource address prefixes, or a set of associated 
   Subnetwork Point Pool (SNPP) link IDs/SNPP link ID prefixes, assigned 
   and selected consistently in their applicability scope. The formats 
   of the control plane identifiers in a protocol realization are 
   implementation specific. Use of a routing protocol within a RA should 
   not restrict the choice of routing protocols for use in other RAs 
   (child or parent). 
   As ASON does not restrict the control plane architecture choice used, 
   either a co-located architecture or a physically separated 
   architecture may be used. A collection of links and nodes such as a 
   sub-network or RA must be able to represent itself to the wider 
   network as a single logical entity with only its external links 
   visible to the topology database. 
5. Evaluation 
   This section evaluates support of existing IETF routing protocols 
   with respect to the requirements summarized from [ASON-RR] in Section 

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   4. Candidate routing protocols are IGP (OSPF and IS-IS) and BGP. The 
   latter in not addressed in the current version of this document. 
5.1 Terminology and Identification 
   - Pi is a physical node (bearer/data/transport plane) node  
   - Li is a logical control plane identifier that is associated to a  
     single data plane (abstract) node i.e., the Logical Node ID 
   - TE Router_ID: control plane identifier that refers to the 
     . RFC 3630: Router_Address (top level) TLV of the Type 1 TE LSA 
     . RFC 3784: Traffic Engineering Router ID TLV (Type 134) 
     Note: both [RFC3630] and [RFC3784] make use of a single stable    
     address to populate this identifier. 
   - Ri is a logical control plane identifier that is associated to a  
     control plane "router" e.g. (advertising) Router_ID i.e.  
     . RFC 2328: Router ID (32-bit)  
     . RFC 1195: IS-IS System ID (48-bit)  
     The Router_ID, represented by Ri and that corresponds to the RC_ID  
     [ASON-REQ], does not enter into the identification of the logical  
     entities representing the data plane resources such as links. The  
     Routing DataBase (RDB) is associated to the Ri. Note that, in the  
     ASON context, arrangement considering multiple Ri's announcing  
     routing information related to a single Li is under evaluation. 
   Aside from the Li/Pi mappings, these identifiers are not assumed to 
   be in a particular entity relationship, e.g., an Ri may have 
   multiple Li in its scope. 
   Note: Si is a control plane signaling function associated with one 
   or more Li. 
5.2 RA Identification 
   G.7715.1 notes some necessary characteristics for RA identifiers, 
   e.g., that they may provide scope for the Ri, and that they must be 
   provisioned to be unique within an administrative domain. The RA ID 
   format itself is allowed to be derived from any global address space. 
   Provisioning of RA IDs for uniqueness is outside the scope of this 
   Under these conditions, GMPLS link state routing protocols provide 
   the capability for RA Identification.  
5.3 Routing Information Exchange 
   We focus on routing information exchange between Ri entities 
   (through routing adjacencies) within single hierarchical level. 
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   Routing information mapping between levels may require specific 
   The control plane does not transport Pi information as these are 
   data plane addresses for which the Li/Pi mapping is kept (link) 
   local - see for instance the transport LMP document [LMP-T] where 
   such exchange is described. Example: the transport plane identifier 
   is the Pi (the identifier assigned to the physical element) which 
   could be for instance "666B.F999.AF10.222C", whereas the control 
   plane identifier is the Li (the identifier assigned by the control 
   plane), which could be for instance "".  
   The control plane exchanges the control plane identifier information 
   but not the transport plane identifier information (i.e. not 
   "666B.F999.AF10.222C" but only ""). The mapping Li/Pi is kept  
   local. So, when the Si receives a control plane message requesting 
   the use of "", Si knows locally that this information refers 
   to the data plane entity identified by the transport plane 
   identifier "666B.F999.AF10.222C".  
   The control plane carries:  
   1) its view of the data plane link end-points and other link 
   connection end-points      
   2) the identifiers scoped by the Li's i.e. referred to as an 
   associated IPv4/IPv6 addressing space  
   3) when using OSPF or ISIS as the IGP in support of traffic 
   engineering, RFC 3477 RECOMMENDS that the Li value (referred to the 
   "LSR Router ID") to be set to the TE Router ID value. Note that in 
   the ASON context, there may be cases where this is not desirable. 
   These cases are under evaluation. 
5.3.1 Link Attributes 
   From the list of link attributes and characteristics (detailed in 
   [ASON-RR], the Local Adaptation support information is missing as TE 
   link attribute. GMPLS routing does not currently consider the use of 
   dedicated TE link attribute(s) to describe the cross/inter-layer 
   relationships. All other TE link attributes and characteristics are 
   currently covered (see Table 1.) 
   However, the representation of bandwidth requires further analysis 
   i.e. GMPLS Routing defines an Interface Switching Capability 
   Descriptor (ISCD) that delivers information about the (maximum/ 
   minimum) bandwidth per priority an LSP can make use of. In the ASON 
   context, other representations are possible, e.g., in terms of a set 
   of tuples <signal_type; number of unallocated timeslots>. The latter 
   also may require definition of additional signal types (from those 
   defined in [RFC 3496]) to represent contiguous concatenation i.e. 
   STS-(3xN)c SPE / VC-4-Nc, N = 4, 16, 64, 256.  
   The method proposed in [GMPLS-RTG] is the most straightforward 
   without requiring any bandwidth accounting change from an LSR 
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   perspective. However, it introduces some lost of information. This 
   lost of information affects the number of signals that can be used 
   but not the range they cover. On the other hand, if additional 
   technology specific information (such as capabilities) are 
   advertised a finer grained resource countdown and accounting can be 
   performed allowing for network wide resource allocation in Sonet/SDH 
   Link Characteristics     GMPLS OSPF  
   -----------------------  ---------- 
   Local SNPP link ID       Link local part of the TE link identifier 
                            sub-TLV [GMPLS-OSPF]          
   Remote SNPP link ID      Link remote part of the TE link identifier 
                            sub-TLV [GMPLS-OSPF]                 
   Signal Type              Technology specific part of the Interface 
                            Switching Capability Descriptor sub-TLV    
   Link Weight              TE metric sub-TLV [RFC3630] 
   Resource Class           Administrative Group sub-TLV [RFC3630] 
   Local Connection Types   Switching Capability field part of the 
                            Interface Switching Capability Descriptor 
                            sub-TLV [GMPLS-OSPF] 
   Link Capacity            Unreserved bandwidth sub-TLV [RFC3630]
                            Max LSP Bandwidth part of the Interface 
                            Switching Capability Descriptor sub-TLV    
   Link Availability        Link Protection sub-TLV [GMPLS-OSPF] 
   Diversity Support        SRLG sub-TLV [GMPLS-OSPF] 
   Local Adaptation support see above 
   Link Characteristics     GMPLS IS-IS  
   -----------------------  ----------- 
   Local SNPP link ID       Link local part of the TE link identifier 
                            sub-TLV [GMPLS-ISIS]          
   Remote SNPP link ID      Link remote part of the TE link identifier 
                            sub-TLV [GMPLS-ISIS]         
   Signal Type              Technology specific part of the Interface 
                            Switching Capability Descriptor sub-TLV    
   Link Weight              TE Default metric [RFC3784] 
   Resource Class           Administrative Group sub-TLV [RFC3784] 
   Local Connection Types   Switching Capability field part of the 
                            Interface Switching Capability Descriptor 
                            sub-TLV [GMPLS-ISIS] 
   Link Capacity            Unreserved bandwidth sub-TLV [RFC3784]
                            Max LSP Bandwidth part of the Interface 
                            Switching Capability Descriptor sub-TLV    
   Link Availability        Link Protection sub-TLV [GMPLS-ISIS] 
   Diversity Support        SRLG sub-TLV [GMPLS-ISIS] 
   Local Adaptation support see above 
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      Table 1. TE link Attribute in GMPLS OSPF-TE and GMPLS IS-IS-TE, 
5.3.2 Node Attributes 
   Nodes attributes include the "Logical Node ID" (as detailed in 
   Section 5.1) and the reachability information as described in 
   Section 5.3.3. 
5.3.3 Reachability Information 
   Advertisement of reachability can be achieved using the techniques 
   described in [OSPF-NODE] where the set of local addresses are 
   carried in a OSPF TE LSA node attribute TLV (a specific sub-TLV is 
   defined per address family, e.g., IPv4 and IPv6). However, [OSPF-
   NODE] restricts to advertisement of Host addresses and not prefixes, 
   and therefore requires enhancement (see below). 
   A similar mechanism does not exist for IS-IS as the Extended IP 
   Reachability TLV [RFC3784] focuses on IP reachable end-points 
   (terminating points), as its name indicates.   
   In order to advertise blocks of reachable address prefixes a 
   summarization mechanism is additionally required. This mechanism may 
   take the form of an prefix length (that indicates the number of 
   significant bits in the prefix) or a network mask. 
5.4 Routing Information Abstraction  
   G.7715.1 describes both static and dynamic methods for abstraction of 
   routing information for advertisement at a different level of the 
   routing hierarchy. However, the information that is advertised 
   continues to be in the form of link and node advertisements 
   consistent with the link state routing protocol used at that level, 
   hence no specific capabilities are added to the routing protocol 
   beyond the ability to locally identify when routing information 
   originates outside of a particular RA.   
   The methods used for abstraction of routing information are outside 
   the scope of GMPLS routing protocols. 
5.5 Dissemination of routing information in support of multiple 
hierarchical levels of RAs 
   G.7715.1 does not define specific mechanisms to support multiple 
   hierarchical levels of RAs, beyond the ability to support abstraction 
   as discussed above. However, if RCs bound to adjacent levels of the 
   RA hierarchy were allowed to redistribute routing information in 
   both directions between adjacent levels of the hierarchy without any 
   additional mechanisms, they would not be able to determine looping 
   of routing information.   
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   To prevent this looping of routing information between levels, IS-IS 
   [RFC1195] allows only advertising routing information upward in the 
   level hierarchy, and disallow the advertising of routing information 
   downward in the hierarchy. [RFC2966] defines the up/down bit to 
   allow advertising downward in the hierarchy the "IP Internal 
   Reachability Information" TLV (Type 128) and "IP External 
   Reachability Information" TLV (Type 130). [RFC3784] extends its 
   applicability for the "Extended IP Reachability" TLV (Type 135). 
   Using this mechanism, the up/down bit is set to 0 when routing 
   information is first injected into IS-IS. If routing information is 
   advertised from a higher level to a lower level, the up/down bit is 
   set to 1, indicating that it has traveled down the hierarchy. 
   Routing information that have the up/down bit set to 1 may only be 
   advertised down the hierarchy, i.e. to lower levels. This mechanisms 
   applies independently of the number of levels. However, this 
   mechanism does not apply to the "Extended IS Reachability" TLV (Type 
   22) used to propagate the summarized topology (see Section 5.3), 
   traffic engineering information as listed in Table 1, as well as 
   reachability information (see Section 5.3.3). 
   OSPFv2 prevents that inter-area routes which are learned from area 0 
   are not passed back to area 0. However, GMPLS makes use of Type 10 
   (area-local scope) LSA to propagate TE information [RFC3630], [GMPLS-
   RTG]. Type 10 Opaque LSAs are not flooded beyond the borders of 
   their associated area. It is therefore necessary to have a means by 
   which Type 10 Opaque LSA may carry the information that a particular 
   routing information has been learned from a higher level RC when 
   propagated to a lower level RC. Any downward RC from this level 
   which receives an LSA with this information would omit the 
   information in this LSA and thus not re-introduce this information 
   back into an higher level RC.  
5.6 Routing Protocol Convergence 
   Link state protocols have been designed to detect topological 
   changes (such as interface failures, link attributes modification). 
   Convergence period is short and involves a minimum of routing 
   information exchange. 
   Therefore, existing routing protocol convergence mechanisms are 
   sufficient for ASON applications. 
6. Evaluation Scenarios 
   The evaluation scenarios are the following: referred to as 
   respectively case 1), 2), 3) and 4). Additional base scenarios 
   (being not combinations or decomposition of entities) may further 
   complete this set in a future revision of this document. 
   In the below Figure 1:  
   - R3 represents an LSR with all components collocated.  
   - R2 shows how the "router" component may be disjoint from the node  
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   - R1 shows how a single "router" may manage multiple nodes  
                -------------------     -------  
               |R1                 |   |R2     |  
               |                   |   |       |    ------  
               |  L1    L2    L3   |   |   L4  |   |R3    |  
               |   :     :     :   |   |   :   |   |      |  
               |   :     :     :   |   |   :   |   |  L5  |  
   Control      ---+-----+-----+---     ---+---    |   :  |  
   Plane           :     :     :           :       |   :  |  
   Data            :     :     :           :       |   :  |  
   Plane          --     :    --          --       |  --  |  
                  -- \   :  / --          --       |  --  |  
                      \ -- /                       |      |  
                       |P2|                         ------  
   Case 1) as represented refers either to direct links between edges 
   or "logical links" as per below figure (or any combination of them)  
                   ------                        ------  
                  |      |                      |      |  
                  |  L1  |                      |  L2  |  
                  |  :   |                      |  :   |  
                  |  : R1|                      |  : R2|  
   Control Plane   --+---                        --+---  
   Elements          :                             :  
   Data Plane        :                             :  
   Elements          :                             :  
                |    :                             :     |  
                |   ---            ---            ---    |  
                |  |   |----------| P |----------|   |   |  
             ---+--|   |           ---           |   |---+---  
                |  |   |                         |   |   |  
                |  | P1|-------------------------| P2|   |  
                |   ---                           ---    |  
   Another case (referred to as Case 4) is constituted by the Abstract 
   Node as represented in the below figure. There is no internal 
   structure associated (externally) to the abstract node.  
                      |R4            |  
                      |              |  
                      |      L6      |  
                      |       :      |  
                      |    ......    |  
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   Control Plane          :      :  
   Data Plane             :      :  
                      |P8 :      :   |  
                      |  --      --  |  
                    --+-|P |----|P |-+--  
                      |  --      --  |  
   Note: the "signaling function" i.e. the control plane entity that  
   processes the signaling messages (referred to as Si) is not 
   represented in these Figures. More than one Si can be associated to 
   one Ri (N:1 relationship, N >= 1) and make use of the path 
   computation function associated to the Ri.   
7. Acknowledgements 
   The authors would like to thank Adrian Farrel for having initiated 
   the proposal of an ASON Routing Solution Design Team and the ITU-T 
   SG15/Q14 for their careful review and input. 
8. References 
8.1 Normative References 
   [GMPLS-RTG]  Kompella, K. (Editor) et al., "Routing Extensions in  
                Support of Generalized MPLS," Internet Draft (work in  
                progress), draft-ietf-ccamp-gmpls-routing-09.txt,  
                October 2003. 
   [LMP-T]      D.Fedyk et al., "A Transport Network View of LMP," 
                Internet Draft (work in progress), draft-ietf-ccamp-
                transport-lmp-01, February 2005. 
   [OSPF-NODE]  R.Aggarwal, and K.Kompella, "Advertising a Router's 
                Local Addresses in OSPF TE Extensions," Internet Draft, 
                (work in progress), draft-ietf-ospf-te-node-addr-
                01.txt, July 2004. 
   [RFC2026]    S.Bradner, "The Internet Standards Process --          
                Revision 3", BCP 9, RFC 2026, October 1996.            
   [RFC2328]    J.Moy, "OSPF Version 2", RFC 2328, April 1998. 
   [RFC2119]    S.Bradner, "Key words for use in RFCs to Indicate      
                Requirement Levels", BCP 14, RFC 2119, March 1997.  
   [RFC3477]    K.Kompella et al. "Signalling Unnumbered Links in 
                Resource ReSerVation Protocol - Traffic Engineering 
                (RSVP-TE)", RFC 3477, January 2003. 
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   [RFC3630]    D.Katz et al. "Traffic Engineering (TE) Extensions to 
                OSPF Version 2", RFC 3630, September 2003. 
   [RFC3667]    S.Bradner, "IETF Rights in Contributions", BCP 78, 
                RFC 3667, February 2004. 
   [RFC3668]    S.Bradner, Ed., "Intellectual Property Rights in IETF 
                Technology", BCP 79, RFC 3668, February 2004.  
   [RFC3784]    H.Smit and T.Li, "Intermediate System to Intermediate 
                System (IS-IS) Extensions for Traffic Engineering (TE)," 
                RFC 3784, June 2004. 
   [RFC3946]    E.Mannie, and D.Papadimitriou, (Editors) et al.,  
                "Generalized Multi-Protocol Label Switching Extensions  
                for SONET and SDH Control," RFC 3946, October 2004.    
8.2 Informative References 
   [ASON-RR]    W.Alanqar et al. "Requirements for Generalized MPLS 
                (GMPLS) Routing for Automatically Switched Optical 
                Network (ASON)," Work in progress, draft-ietf-ccamp-
                gmpls-ason-routing-reqts-04.txt, May 2004. 
   For information on the availability of ITU Documents, please see 
   [G.7715]     ITU-T Rec. G.7715/Y.1306, "Architecture and    
                Requirements for the Automatically Switched Optical  
                Network (ASON)," June 2002. 
   [G.7715.1]   ITU-T Draft Rec. G.7715.1/Y.1706.1, "ASON Routing 
                Architecture and Requirements for Link State Protocols," 
                November 2003. 
   [G.8080]     ITU-T Rec. G.8080/Y.1304, "Architecture for the        
                Automatically Switched Optical Network (ASON),"        
                November 2001 (and Revision, January 2003). 
9. Author's Addresses (to be completed) 
   Lyndon Ong (Ciena Corporation)  
   PO Box 308   
   Cupertino, CA 95015 , USA  
   Phone: +1 408 705 2978  
   Dimitri Papadimitriou (Alcatel) 
   Francis Wellensplein 1,  
   B-2018 Antwerpen, Belgium 
   Phone: +32 3 2408491 
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   Jonathan Sadler 
   1415 W. Diehl Rd 
   Naperville, IL 60563 
   Stephen Shew (Nortel Networks) 
   PO Box 3511 Station C 
   Ottawa, Ontario, CANADA K1Y 4H7 
   Phone: +1 613 7632462 

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Appendix 1: ASON Terminology 
   This document makes use of the following terms: 
   Administrative domain: (see Recommendation G.805) for the purposes of 
   [G7715.1] an administrative domain represents the extent of resources 
   which belong to a single player such as a network operator, a service 
   provider, or an end-user. Administrative domains of different players 
   do not overlap amongst themselves. 
   Control plane: performs the call control and connection control 
   functions. Through signaling, the control plane sets up and releases 
   connections, and may restore a connection in case of a failure. 
   (Control) Domain: represents a collection of (control) entities that 
   are grouped for a particular purpose. The control plane is subdivided 
   into domains matching administrative domains. Within an 
   administrative domain, further subdivisions of the control plane are 
   recursively applied. A routing control domain is an abstract entity 
   that hides the details of the RC distribution. 
   External NNI (E-NNI): interfaces are located between protocol 
   controllers between control domains. 
   Internal NNI (I-NNI): interfaces are located between protocol 
   controllers within control domains. 
   Link: (see Recommendation G.805) a "topological component" which 
   describes a fixed relationship between a "subnetwork" or "access 
   group" and another "subnetwork" or "access group". Links are not 
   limited to being provided by a single server trail.  
   Management plane: performs management functions for the Transport 
   Plane, the control plane and the system as a whole. It also provides 
   coordination between all the planes. The following management 
   functional areas are performed in the management plane: performance, 
   fault, configuration, accounting and security management 
   Management domain: (see Recommendation G.805) a management domain 
   defines a collection of managed objects which are grouped to meet 
   organizational requirements according to geography, technology, 
   policy or other structure, and for a number of functional areas such 
   as configuration, security, (FCAPS), for the purpose of providing 
   control in a consistent manner. Management domains can be disjoint, 
   contained or overlapping. As such the resources within an 
   administrative domain can be distributed into several possible 
   overlapping management domains. The same resource can therefore 
   belong to several management domains simultaneously, but a management 
   domain shall not cross the border of an administrative domain. 
   Subnetwork Point (SNP): The SNP is a control plane abstraction that 
   represents an actual or potential transport plane resource. SNPs (in 
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   different subnetwork partitions) may represent the same transport 
   resource. A one-to-one correspondence should not be assumed. 
   Subnetwork Point Pool (SNPP): A set of SNPs that are grouped together 
   for the purposes of routing. 
   Termination Connection Point (TCP): A TCP represents the output of a 
   Trail Termination function or the input to a Trail Termination Sink 
   Transport plane: provides bi-directional or unidirectional transfer 
   of user information, from one location to another. It can also 
   provide transfer of some control and network management information. 
   The Transport Plane is layered; it is equivalent to the Transport 
   Network defined in G.805 Recommendation. 
   User Network Interface (UNI): interfaces are located between protocol 
   controllers between a user and a control domain. Note: there is no 
   routing function associated with a UNI reference point.  

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Appendix 2: ASON Routing Terminology 
   This document makes use of the following terms: 
   Routing Area (RA): a RA represents a partition of the data plane and 
   its identifier is used within the control plane as the representation 
   of this partition. Per [G.8080] a RA is defined by a set of sub-
   networks, the links that interconnect them, and the interfaces 
   representing the ends of the links exiting that RA. A RA may contain 
   smaller RAs inter-connected by links. The limit of subdivision 
   results in a RA that contains two sub-networks interconnected by a 
   single link. 
   Routing Database (RDB): repository for the local topology, network 
   topology, reachability, and other routing information that is updated 
   as part of the routing information exchange and may additionally 
   contain information that is configured. The RDB may contain routing 
   information for more than one Routing Area (RA). 
   Routing Components: ASON routing architecture functions. These 
   functions can be classified as protocol independent (Link Resource 
   Manager or LRM, Routing Controller or RC) and protocol specific 
   (Protocol Controller or PC).  
   Routing Controller (RC): handles (abstract) information needed for 
   routing and the routing information exchange with peering RCs by 
   operating on the RDB. The RC has access to a view of the RDB. The RC 
   is protocol independent. 
   Note: Since the RDB may contain routing information pertaining to 
   multiple RAs (and possibly to multiple layer networks), the RCs 
   accessing the RDB may share the routing information. 
   Link Resource Manager (LRM): supplies all the relevant component and 
   TE link information to the RC. It informs the RC about any state 
   changes of the link resources it controls. 
   Protocol Controller (PC): handles protocol specific message exchanges 
   according to the reference point over which the information is 
   exchanged (e.g. E-NNI, I-NNI), and internal exchanges with the RC. 
   The PC function is protocol dependent. 

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