OSPF-TE Extensions for General Network Element Constraints
draft-ietf-ccamp-gmpls-general-constraints-ospf-te-02

Network work group                                           Fatai Zhang 
Internet Draft                                                 Young Lee 
Intended status: Standards Track                             Jianrui Han 
                                                                  Huawei 
                                                            G. Bernstein 
                                                       Grotto Networking 
                                                               Yunbin Xu 
                                                                    CATR 
Expires: March 22, 2012                               September 22, 2011 
                                      

                                      
         OSPF-TE Extensions for General Network Element Constraints 

                                      
         draft-ietf-ccamp-gmpls-general-constraints-ospf-te-02.txt 

Status of this Memo 

   This Internet-Draft is submitted to IETF in full conformance with   
   the provisions of BCP 78 and BCP 79. 

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   This Internet-Draft will expire on March 22, 2012. 

    

Abstract 

   Generalized Multiprotocol Label Switching can be used to control a 
   wide variety of technologies including packet switching (e.g., MPLS), 
   time-division (e.g., SONET/SDH, OTN), wavelength (lambdas), and 
 
 
 
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   spatial switching (e.g., incoming port or fiber to outgoing port or 
   fiber). In some of these technologies network elements and links may 
   impose additional routing constraints such as asymmetric switch 
   connectivity, non-local label assignment, and label range limitations 
   on links. This document describes OSPF routing protocol extensions to 
   support these kinds of constraints under the control of Generalized 
   MPLS (GMPLS). 

Conventions used in this document 

   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 [RFC2119]. 

Table of Contents 

    
   1. Introduction ................................................ 2 
   2. Node Information ............................................ 3 
      2.1. Connectivity Matrix..................................... 4 
   3. Link Information ............................................ 4 
      3.1. Port Label Restrictions................................. 5 
      3.2. Available Labels........................................ 5 
      3.3. Shared Backup Labels.................................... 6 
   4. Routing Procedures .......................................... 6 
   5. Scalability and Timeliness................................... 7 
      5.1. Different Sub-TLVs into Multiple LSAs ...................7 
      5.2. Decomposing a Connectivity Matrix into Multiple Matrices.8 
   6. Security Considerations...................................... 8 
   7. IANA Considerations ......................................... 8 
      7.1. Node Information........................................ 8 
      7.2. Link Information........................................ 9 
   8. References .................................................. 9 
      8.1. Normative References.................................... 9 
      8.2. Informative References................................. 10 
   9. Authors' Addresses.......................................... 10 
   Acknowledgment ................................................ 12 
    
    

1. Introduction 

   Some data plane technologies that wish to make use of a GMPLS control 
   plane contain additional constraints on switching capability and 
   label assignment. In addition, some of these technologies should be 
   capable of performing non-local label assignment based on the nature 
   of the technology, e.g., wavelength continuity constraint in WSON 
 
 
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   [RFC6163]. Such constraints can lead to the requirement for link by 
   link label availability in path computation and label assignment. 

   [GEN-Encode] provides efficient encodings of information needed by 
   the routing and label assignment process in technologies such as WSON 
   and are potentially applicable to a wider range of technologies. 

   This document defines extensions to the OSPF routing protocol based 
   on [GEN-Encode] to enhance the Traffic Engineering (TE) properties of 
   GMPLS TE which are defined in [RFC3630], [RFC4202], and [RFC4203]. 
   The enhancements to the Traffic Engineering (TE) properties of GMPLS 
   TE links can be announced in OSPF TE LSAs. The TE LSA, which is an 
   opaque LSA with area flooding scope [RFC3630], has only one top-level 
   Type/Length/Value (TLV) triplet and has one or more nested sub-TLVs 
   for extensibility. The top-level TLV can take one of three values (1) 
   Router Address [RFC3630], (2) Link [RFC3630], (3) Generic Node 
   Attribute defined in Section 2. In this document, we enhance the sub-
   TLVs for the Link TLV and define a new top-level TLV (Generic Node 
   Attribute TLV) in support of the general network element constraints 
   under the control of GMPLS.  

   The detailed encoding of OSPF extensions are not defined in this 
   document. [GEN-Encode] provides encoding detail.  

2. Node Information 

   According to [GEN-Encode], the additional node information 
   representing node switching asymmetry constraints includes Node ID, 
   connectivity matrix. Except for the Node ID which should comply with 
   Routing Address described in [RFC3630], the other pieces of 
   information are defined in this document. 

   This document defines a new top TLV named the Generic Node Attribute 
   TLV which carries attributes related to a general network element. 
   This Generic Node Attribute TLV contains one or more sub-TLVs 

   Per [GEN-Encode], we have identified the following new Sub-TLVs to 
   the Generic Node Attribute TLV. Detail description for each newly 
   defined Sub-TLV is provided in subsequent sections:  

      Sub-TLV Type    Length         Name 

         TBD          variable    Connectivity Matrix 

   In some specific technologies, e.g., WSON networks, Connectivity 
   Matrix sub-TLV may be optional, which depends on the control plane 
   implementations. Usually, for example, in WSON networks, Connectivity 
 
 
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   Matrix sub-TLV may appear in the LSAs because WSON switches are 
   asymmetric at present. It is assumed that the switches are symmetric 
   switching, if there is no Connectivity Matrix sub-TLV in the LSAs.  

2.1. Connectivity Matrix 

   It is necessary to identify which ingress ports and labels can be 
   switched to some specific labels on a specific egress port, if the 
   switching devices in some technology are highly asymmetric. 

   The Connectivity Matrix is used to identify these restrictions, which 
   can represent either the potential connectivity matrix for asymmetric 
   switches (e.g. ROADMs and such) or fixed connectivity for an 
   asymmetric device such as a multiplexer as defined in [WSON-Info]. 

   The Connectivity Matrix is a sub-TLV (the type is TBD by IANA) of the 
   Generic Node Attribute TLV. The length is the length of value field 
   in octets. The meaning and format of this sub-TLV are defined in 
   Section 5.3 of [GEN-Encode]. One sub-TLV contains one matrix. The 
   Connectivity Matrix sub-TLV may occur more than once to contain 
   multi-matrices within the Generic Node Attribute TLV. In addition a 
   large connectivity matrix can be decomposed into smaller separate 
   matrices for transmission in multiple LSAs as described in Section 5.  

3. Link Information 

   The most common link sub-TLVs nested to link top-level TLV are 
   already defined in [RFC3630], [RFC4203]. For example, Link ID, 
   Administrative Group, Interface Switching Capability Descriptor 
   (ISCD), Link Protection Type, Shared Risk Link Group Information 
   (SRLG), and Traffic Engineering Metric are among the typical link 
   sub-TLVs.  

   Per [GEN-Encode], we add the following additional link sub-TLVs to 
   the link-TLV in this document. 

      Sub-TLV Type    Length         Name 

         TBD          variable    Port Label Restrictions 

         TBD          variable    Available Labels 

         TBD          variable    Shared Backup Labels 

   Generally all the sub-TLVs above are optional, which depends on the 
   control plane implementations. If it is default no restrictions on 
   labels, Port Label Restrictions sub-TLV may not appear in the LSAs. 
 
 
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   In order to be able to compute label assignment, Available Labels 
   sub-TLV may appear in the LSAs. For example, in WSON networks, 
   without available wavelength information, path computation need guess 
   what lambdas may be available (high blocking probability or 
   distributed wavelength assignment may be used).  

3.1. Port Label Restrictions 

   Port label restrictions describe the label restrictions that the 
   network element (node) and link may impose on a port. These 
   restrictions represent what labels may or may not be used on a link 
   and are intended to be relatively static. More dynamic information is 
   contained in the information on available labels. Port label 
   restrictions are specified relative to the port in general or to a 
   specific connectivity matrix for increased modeling flexibility.  

   For example, Port Label Restrictions describes the wavelength 
   restrictions that the link and various optical devices such as OXCs, 
   ROADMs, and waveband multiplexers may impose on a port in WSON. These 
   restrictions represent what wavelength may or may not be used on a 
   link and are relatively static. The detailed information about Port 
   label restrictions is described in [WSON-Info]. 

   The Port Label Restrictions is a sub-TLV (the type is TBD by IANA) of 
   the Link TLV. The length is the length of value field in octets. The 
   meaning and format of this sub-TLV are defined in Section 5.4 of 
   [GEN-Encode]. The Port Label Restrictions sub-TLV may occur more than 
   once to specify a complex port constraint within the link TLV. 

3.2. Available Labels 

   Available Labels indicates the labels available for use on a link as 
   described in [GEN-Encode]. The Available Labels is a sub-TLV (the 
   type is TBD by IANA) of the Link TLV. The length is the length of 
   value field in octets. The meaning and format of this sub-TLV are 
   defined in Section 5.1 of [GEN-Encode]. The Available Labels sub-TLV 
   may occur at most once within the link TLV. 

   Note that there are five approaches for Label Set which is used to 
   represent the Available Labels described in [GEN-Encode]. Usually, it 
   depends on the implementation to one of the approaches. In WSON 
   networks, considering that the continuity of the available or 
   unavailable wavelength set can be scattered for the dynamic 
   wavelength availability, so it may burden the routing to reorganize 
   the wavelength set information when the Inclusive (/Exclusive) List 
   (/Range) approaches are used to represent Available Wavelengths 

 
 
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   information. Therefore, it is RECOMMENDED that only the Bitmap Set be 
   used for representation Available Wavelengths information.  

   The "Base Label" and "Last Label" in label set defined in [GEN-Encode] 
   corresponds to base wavelength label and last wavelength label in 
   WSON, the format of which is described as follows: 

       0                   1                   2                   3 
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |Grid |  C.S. |      Reserved   |    n                          | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    

   The detailed information related to wavelength label can be referred 
   to [RFC6205]. 

3.3. Shared Backup Labels 

   Shared Backup Labels indicates the labels available for shared backup 
   use on a link as described in [GEN-Encode]. 

   The Shared Backup Labels is a sub-TLV (the type is TBD by IANA) of 
   the Link TLV. The length is the length of value field in octets. The 
   meaning and format of this sub-TLV are defined in Section 5.2 of 
   [GEN-Encode]. The Shared Backup Labels sub-TLV may occur at most once 
   within the link TLV. 

4. Routing Procedures  

   All the sub-TLVs are nested to top-level TLV(s) and contained in 
   Opaque LSAs. The flooding of Opaque LSAs must follow the rules 
   specified in [RFC2328], [RFC5250], [RFC3630], [RFC4203]. 

   Considering the routing scalability issues in some cases, the routing 
   protocol should be capable of supporting the separation of dynamic 
   information from relatively static information to avoid unnecessary 
   updates of static information when dynamic information is changed. A 
   standard-compliant approach is to separate the dynamic information 
   sub-TLVs from the static information sub-TLVs, each nested to top-
   level TLV ([RFC3630 and RFC5876]), and advertise them in the separate 
   OSPF TE LSAs. 

   For node information, since the Connectivity Matrix information is 
   static, the LSA containing the Generic Node Attribute TLV can be 
   updated with a lower frequency to avoid unnecessary updates. 

 
 
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   For link information, a mechanism MAY be applied such that static 
   information and dynamic information of one TE link are contained in 
   separate Opaque LSAs. For example, the Port Label Restrictions 
   information sub-TLV and Available Labels information sub-TLV can be 
   nested to the top level link TLVs and advertised in the separate LSAs. 

   Note that as with other TE information, an implementation SHOULD take 
   measures to avoid rapid and frequent updates of routing information 
   that could cause the routing network to become swamped. A threshold 
   mechanism MAY be applied such that updates are only flooded when a 
   number of changes have been made to the label availability  
   information (e.g., wavelength availability) within a specific time. 
   Such mechanisms MUST be configurable if they are implemented. 

5. Scalability and Timeliness 

   This document has defined four sub-TLVs for describing generic 
   routing contraints. The examples given in [Gen-Encode] show that very 
   large systems, in terms of label count or ports can be very 
   efficiently encoded. However there has been concern expressed that 
   some possible systems may produce LSAs that exceed the IP Maximum 
   Transmission Unit (MTU) and that methods be given to allow for the 
   splitting of general constraint LSAs into smaller LSA that are under 
   the MTU limit. This section presents a set of techniques that can be 
   used for this purpose. 

   5.1. Different Sub-TLVs into Multiple LSAs 

   Four sub-TLVs are defined in this document: 

      1. Connectivity Matrix (Generic Node Attribute TLV) 
      2. Port Label Restrictions (Link TLV) 
      3. Available Labels (Link TLV) 
      4. Shared Backup Labels (Link TLV) 
 
   Except for the Connectivity Matrix all these are carried in an Link 
   TLV of which there can be at most one in an LSA [RFC3630]. Of these 
   sub-TLVs the Port Label Restrictions are relatively static, i.e., 
   only would change with hardware changes or significant system 
   reconfiguration. While the Available Labels and Shared Backup Labels 
   are dynamic, meaning that they may change with LSP setup or teardown 
   through the system. The most important technique for scalability and 
   OSPF bandwidth reduction is to separate the dynamic information sub-
   TLVs from the static information sub-TLVs and advertise them in 
   separate OSPF TE LSAs[RFC3630 and RFC5250]. 

 
 
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   5.2. Decomposing a Connectivity Matrix into Multiple Matrices 

   In the highly unlikely event that a Connectivity matrix sub-TLV by 
   itself would result in an LSA exceeding the MTU, a single large 
   matrix can be decomposed into sub-matrices. Per [GEN-Encode] a 
   connectivity matrix just consists of pairs of input and output ports 
   that can reach each other and hence such this decomposition would be 
   straightforward. Each of these sub-matrices would get a unique matrix 
   identifier per [GEN-Encode]. 

   From the point of view of a path computation process, prior to 
   receiving an LSA with a Connectivity Matrix sub-TLV, no connectivity 
   restrictions are assumed, i.e., the standard GMPLS assumption of any 
   port to any port reachability holds. Once a Connectivity Matrix sub-
   TLV is received then path computation would know that connectivity is 
   restricted and use the information from all Connectivity Matrix sub-
   TLVs received to understand the complete connectivity potential of 
   the system. Prior to receiving any Connectivity Matrix sub-TLVs path 
   computation may compute a path through the system when in fact no 
   path exists. In between the reception of an additional Connectivity 
   Matrix sub-TLV path computation may not be able to find a path 
   through the system when one actually exists. Both cases are currently 
   encountered and handled with existing GMPLS mechanisms. Due to the 
   reliability mechanisms in OSPF the phenomena of late or missing 
   Connectivity Matrix sub-TLVs would be relatively rare. 

6. Security Considerations 

   This document does not introduce any further security issues other 
   than those discussed in [RFC 3630], [RFC 4203]. 

7. IANA Considerations 

   [RFC3630] says that the top level Types in a TE LSA and Types for 
   sub-TLVs for each top level Types must be assigned by Expert Review, 
   and must be registered with IANA. 

   IANA is requested to allocate new Types for the TLV or sub-TLVs as 
   defined in Sections 2 and 3 as follows: 

7.1. Node Information 

   This document introduces a new Top Level Node TLV (Generic Node 
   Attribute TLV) under the OSPF TE LSA defined in [RFC3630]. 

      Value    TLV Type 

 
 
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      TBA      Generic Node Attribute 

   This document also introduces the following sub-TLVs of Generic Node 
   Attribute TLV: 

      Type     sub-TLV 

      TBD      Connectivity Matrix 

7.2. Link Information 

   This document introduces the following sub-TLVs of TE Link TLV (Value 
   2): 

      Type     sub-TLV 

      TBD      Port Label Restrictions 

      TBD      Available Labels 

      TBD      Shared Backup Labels 

8. References 

8.1. Normative References 

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 
             Requirement Levels", BCP 14, RFC 2119, March 1997. 

   [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. 

   [RFC5250] L. Berger, I. Bryskin, A. Zinin, R. Coltun "The OSPF Opaque 
             LSA Option", RFC 5250, July 2008. 

   [RFC3630] Katz, D., Kompella, K., and Yeung, D., "Traffic Engineering 
             (TE) Extensions to OSPF Version 2", RFC 3630, September 
             2003. 

   [RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing Extensions 
             in Support of Generalized Multi-Protocol Label Switching 
             (GMPLS)", RFC 4202, October 2005 

   [RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions in 
             Support of Generalized Multi-Protocol Label Switching 
             (GMPLS)", RFC 4203, October 2005. 

 
 
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   [GEN-Encode] G. Bernstein, Y. Lee, D. Li, W. Imajuku, " General 
             Network Element Constraint Encoding for GMPLS Controlled 
             Networks", work in progress: draft-ietf-ccamp-general-
             constraint-encode-05.txt, May 2011. 

   [RFC6205] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, " Generalized 
             Labels for Lambda-Switching Capable Label Switching 
             Routers", work in progress: draft-ietf-ccamp-gmpls-g-694-
             lambda-labels-11.txt, January 2011. 

    

8.2. Informative References 

   [RFC6163] Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS and 
             PCE Control of Wavelength Switched Optical Networks (WSON)", 
             work in progress: draft-ietf-ccamp-rwa-WSON-Framework-
             12.txt, February 2011. 

   [WSON-Info] Y. Lee, G. Bernstein, D. Li, W. Imajuku, "Routing and 
             Wavelength Assignment Information Model for Wavelength 
             Switched Optical Networks", work in progress: draft-ietf-
             ccamp-rwa-info-12.txt, September 2011. 

    

9. Authors' Addresses 

   Fatai Zhang
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China
    
   Phone: +86-755-28972912
   Email: zhangfatai@huawei.com
    
    
   Young Lee 
   Huawei Technologies 
   1700 Alma Drive, Suite 100 
   Plano, TX 75075 
   USA 
    
   Phone: (972) 509-5599 (x2240)
 
 
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   Email: ylee@huawei.com 
    
    
   Jianrui Han
   Huawei Technologies Co., Ltd.
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China
 
   Phone: +86-755-28977943
   Email: hanjianrui@huawei.com
 
 
   Greg Bernstein
   Grotto Networking
   Fremont CA, USA
 
   Phone: (510) 573-2237
   Email: gregb@grotto-networking.com
 
 
   Yunbin Xu
   China Academy of Telecommunication Research of MII
   11 Yue Tan Nan Jie Beijing, P.R.China
   Phone: +86-10-68094134
   Email: xuyunbin@mail.ritt.com.cn
 
 
   Guoying Zhang
   China Academy of Telecommunication Research of MII
   11 Yue Tan Nan Jie Beijing, P.R.China
   Phone: +86-10-68094272
   Email: zhangguoying@mail.ritt.com.cn
 
 
   Dan Li
   Huawei Technologies Co., Ltd.
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China
 
 
 
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   Phone: +86-755-28973237
   Email: danli@huawei.com
 
 
   Ming Chen
   European Research Center
   Huawei Technologies
   Riesstr. 25, 80992 Munchen, Germany
 
   Phone: 0049-89158834072
   Email: minc@huawei.com
 
 
   Yabin Ye
   European Research Center
   Huawei Technologies
   Riesstr. 25, 80992 Munchen, Germany
 
   Phone: 0049-89158834074
   Email: yabin.ye@huawei.com
 
    
Acknowledgment 

   We thank Ming Chen and Yabin Ye from DICONNET Project who provided 
   valuable information for this document.   

 
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