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Mutually Exclusive Link Group (MELG)
draft-beeram-ccamp-melg-01

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Document Type This is an older version of an Internet-Draft whose latest revision is Expired
Authors Vishnu Pavan Beeram , Igor Bryskin
Last updated 2013-07-15
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draft-beeram-ccamp-melg-01
CCAMP Working Group                            Vishnu Pavan Beeram (Ed) 
 Internet Draft                                         Juniper Networks 
 Intended status: Standards Track                      Igor Bryskin (Ed) 
                                                 ADVA Optical Networking 
      
 Expires: January 15, 2013                                 July 15, 2013 
                                         
      
                                          
                    Mutually Exclusive Link Group (MELG) 
                       draft-beeram-ccamp-melg-01.txt 

 
 Status of this Memo 

 
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    Copyright (c) 2013 IETF Trust and the persons identified as the 
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    Section 4.e of the Trust Legal Provisions and are provided without 
    warranty as described in the Simplified BSD License. 
          
 Abstract 

    This document introduces the concept of MELG ("Mutually Exclusive 
    Link Group") and discusses its usage in the context of mutually 
    exclusive Virtual TE Links. 

 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. Mutually Exclusive Virtual TE Links............................3 
    3. Mutually Exclusive Link Group..................................6 
    4. Protocol Extensions............................................6 
       4.1. OSPF......................................................6 
       4.2. ISIS......................................................7 
    5. Security Considerations........................................9 
    6. IANA Considerations............................................9 
       6.1. OSPF......................................................9 
       6.2. ISIS......................................................9 
    7. Normative References...........................................9 
    8. Acknowledgments................................................9 
        
 1. Introduction 

    A Virtual TE Link (as defined in [RFC6001]) advertised into a Client 
    Network Domain represents a potentiality to setup an LSP in the 
    Server Network Domain to support the advertised TE link. The Virtual 
    TE Link gets advertised like any other TE link and follows exactly 
    the same rules that are defined for the advertising, processing and 
    use of regular TE links [RFC4202]. However, "mutual exclusivity" is 
    one attribute that is specific to Virtual TE links. This document 
    discusses the need to advertise this information and the means to do 
    so. 

      
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 2. Mutually Exclusive Virtual TE Links 

    Consider the network topology depicted in Figure 1a. This is a 
    typical packet optical transport deployment scenario where the WDM 
    layer network domain serves as a Server Network Domain providing 
    transport connectivity to the packet layer network Domain (Client 
    Network Domain).   
                                   | 
                                   | +---+            /-\ 
                                   | |   | Router    (   ) WDM  
                                   | +---+ Node       \-/  node 
                                   |________________________________ 
                                      
      +---+        /-\          /-\           /-\          +---+ 
      | B |-------( E )--------( G )---------( J )---------| C | 
      +---+        \-/          \-/           \-/          +---+ 
                               /   \         /   \ 
                              /     \       /     \ 
                             /       \     /       \ 
                            /         \   /         \ 
                           /           \ /           \ 
          +---+          /-\           /-\           /-\          +---+ 
          | A |---------( F )---------( H )---------( I )---------| D | 
          +---+          \-/           \-/           \-/          +---+ 

                         Figure 1a: Sample topology  

          -------------                        |  [ ] Client TE Node 
          | Client TE |                        |  +++ Client TE Link 
          | DataBase  |                        |_____________________                 
          ------------- 
             [B] ++++++++ [E]                  [J] +++++++++ [C] 
                        
                                       
                             
             [A] ++++++++ [F]                  [I] +++++++++ [D]  
              

                          Figure 1b: Client TE Database 

      
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    Nodes A, B, C and D are IP routers that are connected to an Optical 
    WDM transport network. E, F, G, H, I and J are WDM nodes that 
    constitute the Server Network Domain. The border nodes (E, F, I and 
    J) operate in both the server and client domains. Figure 1b depicts 
    how the Client Network Domain TE topology looks like when there are 
    no Client TE Links provisioned across the optical domain. 

 
                                 | *****  F-J WDM Path (lambda 192000)              
                                 | @@@@@  E-I WDM Path (lambda 192000) 
                                 |________________________________ 
                                      
  +---+        /-\ @@@@@@@@ /-\           /-\          +---+ 
  | B |-------( E )--------( G )---------( J )---------| C | 
  +---+        \-/         *\-/*@       @*\-/@         +---+ 
                          */   \*@     @*/   \@ 
                         */     \*@   @*/     \@ 
                        */       \*@ @*/       \@ 
                       */         \*@*/         \@ 
                      */           \*/           \@ 
      +---+          /-\           /-\           /-\          +---+ 
      | A |---------( F )---------( H )---------( I )---------| D | 
      +---+          \-/           \-/           \-/          +---+ 

   
         Figure 2a: Mutually Exclusive potential WDM paths 

       ------------   |  TE-Links E-I and F-J are mutually exclusive   
       | Client-TE|   |  Advertised with MELG-ID - 25/192000 
       | Database |   |  [SRLG-ID 25; Shared Resource ID 192000]    
       ------------   |_____________________________________________   
            
         [B] ++++++++ [E]                      [J] +++++++++ [C] 
                          ++++            +++++  
                              +++      +++         
                                 ++++++     
                              +++      +++ 
                          ++++            +++++ 
         [A] ++++++++ [F]                      [I] +++++++++ [D]  
              

 Figure 2b: Client TE Database - Mutually Exclusive Virtual TE Links 

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    Now consider augmenting the Client TE topology by creating a couple 
    of Virtual TE Links across the optical domain. The potential paths 
    in the WDM network catering to these two virtual TE links are as 
    shown in Fig 2a and the corresponding augmented Client TE topology 
    is as illustrated in Fig 2b. 
         
    In this particular example, the potential paths in the WDM layer 
    network supporting the Virtual TE Links not only intersect, but also 
    require the usage of the same resource (lambda channel 192000) on 
    the intersection. Because the Virtual TE Links depend on the same 
    uncommitted network resource, only one of them could get activated 
    at any given time. In other words they are mutually exclusive. This 
    scenario is encountered when the potential paths depend on any 
    common physical resource (e.g. transponder, regenerator, wavelength 
    converter, etc.) that could be used by only one Server Network 
    Domain LSP at a time.  
         
    For a Client Network Domain path computation function (especially a 
    centralized one) that is capable of concurrent computation of 
    multiple paths, it is important to know the existence of mutually 
    exclusive relationship between Virtual TE Links. Absent this 
    information, there exists the risk of yielding erroneous concurrent 
    path computation results where only a subset of the computed paths 
    can get successfully provisioned. This document introduces the 
    concept of Mutually Exclusive Link Group to address this problem. 
         
    The Virtual TE Link mutual exclusivity attribute can be either (a) 
    Static or (b) Dynamic.  
        
    In case (a), the Virtual TE Link mutual exclusivity exists 
    permanently within a given network configuration. This type of 
    mutual exclusivity comes into play when two or more Virtual TE Links 
    depend on a Server Network Domain resource that could be used in its 
    entirety by only one Virtual TE Link (when committed). 
         
    In case (b), the Virtual TE Link mutual exclusivity exists 
    temporarily within a given network configuration. This type of 
    mutual exclusivity comes into play when two or more Virtual TE Links 
    depend on a Server Network Domain resource that could be shared 
    simultaneously in some limited capacity by several Virtual TE Links 
    (when committed). Consider, for example, a situation when three 
    Virtual TE Links depend on a Server Domain WDM link that currently 
    has two lambda channels available. Consider further that each 
    Virtual TE Link (in order to be committed) requires one lambda 
    channel to be allocated on said WDM link. Obviously, under these 
    conditions only two out of three Virtual TE Links could be 
 
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    concurrently committed. Such Virtual TE Link mutual exclusivity is 
    dynamic and temporary because as soon as additional lambda channels 
    become available on the WDM link, the Virtual TE Link mutual 
    exclusivity will cease to exist - it will become possible to commit 
    all three Virtual TE Links concurrently. 
         
    This revision of the draft discusses only the Static Virtual TE Link 
    mutual exclusivity. Dynamic Virtual TE Link mutual exclusivity will 
    be addressed in later revisions. 
         
 3. Mutually Exclusive Link Group 

    The Mutually Exclusive Link Group (MELG) construct defined in this 
    document has 2 purposes 
         
    - To indicate via a separate network unique number (MELG ID) an 
      element or a situation that makes the advertised Virtual TE Link 
      belong to one or more Mutually Exclusive Link Groups. Path 
      computing element will be able to decide on whether two or more 
      Virtual TE Links are mutually exclusive or not by finding an 
      overlap of advertised MELGs (similar to deciding on whether two or 
      more TE links share fate or not by finding common SRLGs) 
           
    - To indicate whether the advertised Virtual TE Link is committed or 
      not at the moment of the advertising. Such information is 
      important for a path computation element: Committing new Virtual 
      TE links (vs. re-using already committed ones) has a consequence 
      of allocating more server layer resources and disabling other 
      Virtual TE Links that have common MELGs with newly committed 
      Virtual TE Links; Committing a new Virtual TE Link also means a 
      longer setup time for the Client LSP and higher risk of setup-
      failure.  
      
 4. Protocol Extensions
 4.1. OSPF

    The MELG is a sub-TLV of the top level TE Link TLV. It may occur at 
    most once within the Link TLV. The format of the MELGs sub-TLV is 
    defined as follows: 

    Name: MELG 
    Type: TBD 
    Length: Variable 
       
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    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 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    |            Sub-TLV Type       |            Sub-TLV Length     | 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    |    VTE-Flags (16 bits)     |U |  Number of MELGs (16 bits)    | 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    |                 MELGID1 (64 bits)                             | 
    |                 MELGID2 (64 bits)                             | 
    |                ........................                       | 
    |                 MELGIDn (64 bits)                             | 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         
    Number of MELGs:              number of MELGS advertised for the  
                                  Virtual TE Link; 
    VTE-Flags:                    Virtual TE Link specific flags; 
    MELGID1,MELGID2,...,MELGIDn:  64-bit network domain unique numbers  
                                  associated with each of the advertised  
                                  MELGs    
    Currently defined Virtual TE Link specific flags are: 
       U bit (bit 1): Uncommitted - if set, the Virtual TE Link is 
       uncommitted at the time of the advertising (i.e. the server layer
       network LSP is not set up); if cleared, the Virtual TE Link is 
       committed (i.e. the server layer LSP is fully provisioned and 
       functioning). All other bits of the "VTE-Flags" field are 
       reserved for future use and MUST be cleared. 

                                                 
    Note: A Virtual TE Link advertisement MAY include MELGs sub-TLV with 
    zero MELGs for the purpose of communicating to the TE domain whether 
    the Virtual TE Link is currently committed or not. 

 4.2. ISIS 

    The MELG TLV (of type TBD) contains a data structure consisting of: 

       6        octets of System ID 
       1        octet of Pseudonode Number 
       1        octet Flag 
       4        octets of IPv4 interface address or 4 octets of a Link  
                Local Identifier 
       4        octets of IPv4 neighbor address or 4 octets of a Link  
                Remote Identifier 
       2        octets MELG-Flags 

       
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       2        octets - Number of MELGs 
       variable List of MELG values, where each element in the list 
                    has 8 octets 
               
     The following illustrates encoding of the value field of the MELG
     TLV. 
         
         
     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 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    |                           System ID                           | 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    |        System ID (cont.)      |Pseudonode num |    Flags      | 
    +-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+ 
    |          Ipv4 interface address/Link Local Identifier         | 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    |          Ipv4 neighbor address/Link Remote Identifier         | 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    |    VTE-Flags (16 bits)     |U |  Number of MELGs (16 bits)    | 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    |                 MELGID1 (64 bits)                             | 
    |                 MELGID2 (64 bits)                             | 
    |                ........................                       | 
    |                 MELGIDn (64 bits)                             | 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
        
 The neighbor is identified by its System ID (6 octets), plus one octet 
 to indicate the pseudonode number if the neighbor is on a LAN 
 interface. 
         
 The least significant bit of the Flag octet indicates whether the   
 interface is numbered (set to 1) or unnumbered (set to 0). All other
 bits are reserved and should be set to 0. 
      
 The length of the TLV is 20 + 8 * (number of MELG values). 
      
 The semantics of "VTE-Flags", "Number of MELGs" and "MELGID Values" are 
 the same as the ones defined under OSPF extensions.  
      
 The MELG TLV MAY occur more than once within the IS-IS Link State 
 Protocol Data Units. 
  
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 5. Security Considerations 

    TBD 

 6. IANA Considerations 

 6.1. OSPF 

    IANA is requested to allocate a new sub-TLV type for MELG (as 
    defined in Section 4.1) under the top-level TE Link TLV. 

 6.2. ISIS 

    IANA is requested to allocate a new IS-IS TLV type for MELG (as 
    defined in Section 4.2). 

 7. Normative References 

    [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate 
                 Requirement Levels", BCP 14, RFC 2119, March 1997. 
        
    [RFC4202]    K.Kompella, Y.Rekhter, "Routing Extensions in Support 
                 of Generalized Multi-Protocol Label Switching (GMPLS)",  
                 RFC4202, October 2005. 
         
    [RFC6001]    D.Papadimitriou, M.Vigoureax, K.Shiomoto, D.Brungard  
                 and JL. Le Roux, "GMPLS Protocol Extensions for Multi- 
                 Layer and Multi-Region Networks", RFC 6001, October  
                 2010. 
         

 8. Acknowledgments

    Chris Bowers [cbowers@juniper.net] 
         
 Authors' Addresses 

    Vishnu Pavan Beeram 
    Juniper Networks 
    Email: vbeeram@juniper.net 
         
    Igor Bryskin 
    ADVA Optical Networking 
    Email: ibryskin@advaoptical.com 

       
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    John Drake 
    Juniper Networks 
    Email: jdrake@juniper.net 
         
    Gert Grammel 
    Juniper Networks 
    Email: ggrammel@juniper.net 
         
    Wes Doonan 
    ADVA Optical Networking 
    Email: wdoonan@advaoptical.com 
         
    Manuel Paul 
    Deutsche Telekom 
    Email: Manuel.Paul@telekom.de 
          
    Ruediger Kunze 
    Deutsche Telekom 
    Email: Ruediger.Kunze@telekom.de 
          
    Oscar Gonzalez de Dios  
    Telefonica 
    Email: ogondio@tid.es 
         
    Cyril Margaria 
    Coriant GmbH 
    Email: cyril.margaria@coriant.com 
         
    Friedrich Armbruster 
    Coriant GmbH
    Email: friedrich.armbruster@coriant.com 
          
    Daniele Ceccarelli 
    Ericsson 
    Email: daniele.ceccarelli@ericsson.com 
       
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