Russian Dolls Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering
draft-ietf-tewg-diff-te-russian-07

TEWG                                                                 
   Internet Draft                                  Francois Le Faucheur 
                                                                 Editor 
   draft-ietf-tewg-diff-te-russian-07.txt                Cisco Systems, 
                                                                   Inc. 
   Expires: June 2005                                     December 2004 
    
    
             Russian Dolls Bandwidth Constraints Model for   
                 Diff-Serv-aware MPLS Traffic Engineering 
    
    
Status of this Memo 
    
   This document is an Internet-Draft and is subject to all provisions 
   of section 3 of RFC 3667. By submitting this Internet-Draft, each 
   author represents that any applicable patent or other IPR claims of 
   which he or she is aware have been or will be disclosed, and any of 
   which he or she become aware will be disclosed, in accordance with 
   RFC 3668. 
    
   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. 
    
   This Internet-Draft will expire on June 13, 2005. 
    
    
Copyright Notice 
    
   Copyright (C) The Internet Society (2004).  All Rights Reserved. 
    
    
Abstract 
    

 
 
Le Faucheur, et al.                                           [Page 1] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
   This document provides specification for one Bandwidth Constraints 
   Model for Diff-Serv-aware MPLS Traffic Engineering, which is referred 
   to as the Russian Dolls Model. 
 
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 [RFC2119]. 
    
    
Table of Contents 
    
   1. Introduction...................................................2 
   2. Contributing Authors...........................................3 
   3. Definitions....................................................3 
   4. Russian Dolls Model Definition.................................4 
   5. Example Formulas for Computing "Unreserved TE-Class [i]" with 
   Russian Dolls Model...............................................6 
   6. Receiving both Maximum Reservable Bandwidth and Bandwidth 
   Constraints sub-TLVs..............................................7 
   7. Security Considerations........................................8 
   8. Acknowledgments................................................8 
   9. IANA Considerations............................................8 
   10. Normative References..........................................8 
   11. Informative References........................................9 
   12. Intellectual Property Considerations.........................10 
   13. Editor's Address:............................................10 
   14. Full Copyright Statement.....................................10 
   Appendix A - Addressing [DSTE-REQ] Scenarios.....................11 
   Disclaimer of Validity...........................................12 
   Copyright Statement..............................................13 
   Acknowledgment...................................................13 
    
    
1.Introduction 
 
   [DSTE-REQ] presents the Service Providers requirements for support of 
   Diff-Serv-aware MPLS Traffic Engineering (DS-TE). This includes the 
   fundamental requirement to be able to enforce different Bandwidth 
   Constraints for different classes of traffic. 
    
   [DSTE-REQ] also defines the concept of Bandwidth Constraints Model 
   for DS-TE and states that "The DS-TE technical solution MUST specify 
   at least one Bandwidth Constraints Model and MAY specify multiple 
   Bandwidth Constraints Models." 
    

 
 
Le Faucheur, et al.                                           [Page 2] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
   This document provides a detailed description of one particular 
   Bandwidth Constraints Model for DS-TE which is introduced in [DSTE-
   REQ] and called the Russian Dolls Model (RDM).  
    
   [DSTE-PROTO] specifies the IGP and RSVP-TE signaling extensions for 
   support of DS-TE. These extensions support RDM. 
    
    
2.Contributing Authors 
    
   This document was the collective work of several. The text and 
   content of this document was contributed by the editor and the co-
   authors listed below. (The contact information for the editor appears 
   in Section 11, and is not repeated below.) 
    
   Jim Boyle                            Kireeti Kompella 
   Protocol Driven Networks, Inc.       Juniper Networks, Inc. 
   1381 Kildaire Farm Road #288         1194 N. Mathilda Ave. 
   Cary, NC 27511, USA                  Sunnyvale, CA 94099 
   Phone: (919) 852-5160                Email: kireeti@juniper.net 
   Email: jboyle@pdnets.com              
                                         
   William Townsend                     Thomas D. Nadeau 
   Tenor Networks                       Cisco Systems, Inc. 
   100 Nagog Park                       250 Apollo Drive 
   Acton, MA 01720                      Chelmsford, MA 01824 
   Phone: +1-978-264-4900               Phone: +1-978-244-3051 
   Email:                               Email: tnadeau@cisco.com 
   btownsend@tenornetworks.com 
                                         
   Darek Skalecki                        
   Nortel Networks                       
   3500 Carling Ave,                     
   Nepean K2H 8E9                        
   Phone: +1-613-765-2252                
   Email: dareks@nortelnetworks.com      
                                         
    
    
3.Definitions 
    
   For readability a number of definitions from [DSTE-REQ] are repeated 
   here: 
    
   Class-Type (CT): the set of Traffic Trunks crossing a link that is 
   governed by a specific set of Bandwidth Constraints. CT is used for 
   the purposes of link bandwidth allocation, constraint based routing 
   and admission control. A given Traffic Trunk belongs to the same CT 
   on all links.  
 
 
Le Faucheur, et al.                                           [Page 3] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
    
   TE-Class: A pair of: 
             i. a Class-Type 
            ii. a preemption priority allowed for that Class-Type. This 
                means that an LSP transporting a Traffic Trunk from 
                that Class-Type can use that preemption priority as the 
                set-up priority, as the holding priority or both. 
    
   A number of recovery mechanisms under investigation or specification 
   in the IETF take advantage of the concept of bandwidth sharing across 
   particular sets of LSPs. "Shared Mesh Restoration" in [GMPLS-RECOV] 
   and "Facility-based Computation Model" in [MPLS-BACKUP] are example 
   mechanisms which increase bandwidth efficiency by sharing bandwidth 
   across backup LSPs protecting against independent failures. To ensure 
   that the notion of "Reserved (CTc)" introduced in [DSTE-REQ] is 
   compatible with such a concept of bandwidth sharing across multiple 
   LSPs, the wording of the "Reserved (CTc)" definition provided in 
   [DSTE-REQ] is generalized into the following:  
    
   Reserved (CTc): For a given Class-Type CTc ( 0 <= c <= MaxCT ) ,let 
   us define "Reserved(CTc)" as the total amount of the bandwidth 
   reserved by all the established LSPs which belong to CTc. 
    
   With this generalization, the Russian Dolls Model definition provided 
   in this document is compatible with Shared Mesh Restoration defined 
   in [GMPLS-RECOV], so that DS-TE and Shared Mesh Protection can 
   operate simultaneously, under the assumption that Shared Mesh 
   Restoration operates independently within each DS-TE Class-Type and 
   does not operate across Class-Types (for example back up 
   LSPs protecting Primary LSPs of CTx need to also belong to CTx; 
   Excess Traffic LSPs sharing bandwidth with Backup LSPs of CTx need to 
   also belong to CTx). 
    
   We also introduce the following definition: 
    
   Reserved(CTb,q) : let us define "Reserved(CTb,q)" as the total amount 
   of the bandwidth reserved by all the established LSPs which belong to 
   CTb and have a holding priority of q. Note that if q and CTb do not 
   form one of the 8 possible configured TE-Classes, then there can not 
   be any established LSP which belong to CTb and have a holding 
   priority of q, so in that case, Reserved(CTb,q)=0. 
    
 
4.Russian Dolls Model Definition 
    
   RDM is defined in the following manner: 
             o Maximum Number of Bandwidth Constraints (MaxBC)=  
               Maximum Number of Class-Types (MaxCT) = 8 
             o for each value of b in the range 0 <= b <= (MaxCT - 1): 
 
 
Le Faucheur, et al.                                           [Page 4] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
                     SUM (Reserved (CTc)) <= BCb, 
                     Where the SUM is across all values of c in the 
                     range b <= c <= (MaxCT - 1) 
            o BC0= Maximum Reservable Bandwidth, so that 
                    SUM (Reserved(CTc)) <= Max-Reservable-Bw,    
                     where the SUM is across all values of c in the  
                     range  0 <= c <= (MaxCT - 1) 
    
   A DS-TE LSR implementing RDM MUST support enforcement of Bandwidth 
   Constraints in compliance with this definition. 
    
   Both preemption within a Class-Type and across Class-Types is 
   allowed. 
    
   Where 8 Class-Types are active, the RDM Bandwidth Constraints can 
   also be expressed in the following way: 
        - All LSPs from CT7 use no more than BC7 
        - All LSPs from CT6 and CT7 use no more than BC6 
        - All LSPs from CT5, CT6 and CT7 use no more than BC5 
        - etc. 
        - All LSPs from CT0, CT1,... CT7 use no more than  
          BC0 = "Maximum Reservable Bandwidth" 
    
   Purely for illustration purposes, the diagram below represents the 
   Russian Dolls Bandwidth Constraints Model in a pictorial manner when 
   3 Class-Types are active: 
    
   I------------------------------------------------------I 
   I-------------------------------I                      I 
   I--------------I                I                      I 
   I    CT2       I    CT2+CT1     I      CT2+CT1+CT0     I 
   I--------------I                I                      I 
   I-------------------------------I                      I 
   I------------------------------------------------------I 
    
   I-----BC2------> 
   I----------------------BC1------> 
   I------------------------------BC0=Max Reservable Bw---> 
    
    
   While simpler Bandwidth Constraints models or, conversely, more 
   flexible/sophisticated Bandwidth Constraints models can be defined, 
   the Russian Dolls Model is attractive in some DS-TE environments for 
   the following reasons: 
       - Although a little less intuitive than the Maximum Allocation 
          Model (see[DSTE-MAM]), RDM is still a simple model to 
          conceptualize. 

 
 
Le Faucheur, et al.                                           [Page 5] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
       - RDM can be used to simultaneously ensure bandwidth efficiency 
          and protection against QoS degradation of all Class-Types, 
          whether preemption is used or not. 
       - RDM can be used in conjunction with preemption to  
          simultaneously achieve isolation across Class-Types (so that 
          each Class-Type is guaranteed its share of bandwidth no 
          matter the level of contention by other classes), bandwidth 
          efficiency and protection against QoS degradation of all 
          Class-Types.  
       - RDM only requires limited protocol extensions such as the 
          ones defined in [DSTE-PROTO]. 
    
   RDM may not be attractive in some DS-TE environments for the 
   following reasons: 
       - if the usage of preemption is precluded for some 
          administrative reason, while RDM can still ensure bandwidth 
          efficiency and protection against QoS degradation of all CTs, 
          RDM cannot guarantee isolation across Class-Types. 
    
   Additional considerations on the properties of RDM can be found in 
   [BC-CONS] and [BC-MODEL]. 
    
   As a simple example usage of the "Russian Dolls" Bandwidth 
   Constraints Model, a network administrator using one CT for Voice 
   (CT1) and one CT for data (CT0) might configure on a given link: 
        - BC0 = Max-Reservable-Bw= 2.5 Gb/s (i.e. Voice + Data is 
          limited to 2.5 Gb/s) 
        - BC1= 1.5 Gb/s (i.e. Voice is limited to 1.5 Gb/s). 
 
    
5.Example Formulas for Computing "Unreserved TE-Class [i]" with Russian 
   Dolls Model 
    
   As specified in [DSTE-PROTO], formulas for computing "Unreserved TE-
   Class [i]" MUST reflect all of the Bandwidth Constraints relevant to 
   the CT associated with TE-Class[i], and thus, depend on the Bandwidth 
   Constraints Model. Thus, a DS-TE LSR implementing RDM MUST reflect 
   the RDM Bandwidth Constraints defined in section 4 above when 
   computing "Unreserved TE-Class [i]". 
    
   Keeping in mind, as explained in [DSTE-PROTO], that details of 
   admission control algorithms as well as formulas for computing 
   "Unreserved TE-Class [i]" are outside the scope of the IETF work, we 
   provide in this section, for illustration purposes, an example of how 
   values for the unreserved bandwidth for TE-Class[i] might be computed 
   with RDM, assuming the basic admission control algorithm which simply 
   deducts the exact bandwidth of any established LSP from all of the 
   Bandwidth Constraints relevant to the CT associated with that LSP. 
    
 
 
Le Faucheur, et al.                                           [Page 6] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
   We assume that: 
        TE-Class [i] <--> < CTc , preemption p> 
   in the configured TE-Class mapping. 
    
   For readability, formulas are first shown assuming only 3 CTs are 
   active. The formulas are then extended to cover the cases where more 
   CTs are used. 
    
   If CTc = CT0, then "Unreserved TE-Class [i]" = 
      [ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 2 
    
    
   If CTc = CT1, then "Unreserved TE-Class [i]" = 
      MIN  [ 
      [ BC1 - SUM ( Reserved(CTb,q) ) ] for q <= p and 1 <= b <= 2, 
      [ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 2 
             ] 
    
    
   If CTc = CT2, then "Unreserved TE-Class [i]" = 
      MIN  [ 
      [ BC2 - SUM ( Reserved(CTb,q) ) ] for q <= p and 2 <= b <= 2, 
      [ BC1 - SUM ( Reserved(CTb,q) ) ] for q <= p and 1 <= b <= 2, 
      [ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 2 
             ] 
    
    
   The formula can be generalized to 8 active CTs and expressed in a 
   more compact way in the following: 
    
     "Unreserved TE-Class [i]" = 
      MIN  [ 
    [ BCc - SUM ( Reserved(CTb,q) ) ] for q <= p and c <= b <= 7, 
    [ BC(c-1) - SUM ( Reserved(CTb,q) ) ] for q <= p and (c-1)<= b <= 7, 
        . . . 
    [ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 7, 
           ] 
      where: 
        TE-Class [i] <--> < CTc , preemption p> 
        in the configured TE-Class mapping. 
    
    
6.Receiving both Maximum Reservable Bandwidth and Bandwidth Constraints 
   sub-TLVs 
    
   [DSTE-PROTO] states that  
   " A DS-TE LSR which does advertise Bandwidth Constraints MUST use the 
   new "Bandwidth Constraints" sub-TLV (in addition to the existing 
   Maximum Reservable Bandwidth sub-TLV) to do so."  
 
 
Le Faucheur, et al.                                           [Page 7] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
    
   With RDM, BC0 is equal to the Maximum Reservable Bandwidth since they 
   both represent the aggregate constraint across all Class-Types. Thus, 
   a DS-TE LSR receiving both the "Maximum Reservable Bw" sub-TLV and 
   the new "Bandwidth Constraints" sub-TLV (which contains BC0) for a 
   given link where the RDM model is used, MAY ignore the "Maximum 
   Reservable Bw" sub-TLV. 
    
    
7.Security Considerations 
    
   Security considerations related to the use of DS-TE are discussed in 
   [DSTE-PROTO]. Those apply independently of the Bandwidth Constraints 
   Model, including RDM specified in this document. 
    
    
8.Acknowledgments 
    
   We thank Martin Tatham for his key contribution in this work. Tatiana 
   Renko is also warmly thanked for her instantiation of the Russian 
   Doll. 
    
    
9.IANA Considerations 
    
   [DSTE-PROTO] defines a new name space for "Bandwidth Constraints 
   Model Id". The guidelines for allocation of values in that name space 
   are detailed in section 14.1 of [DSTE-PROTO]. In accordance with 
   these guidelines, IANA was requested to assign a Bandwidth 
   Constraints Model Id for RDM from the range 0-127 (which is to be 
   managed as per the "Specification Required" policy defined in [IANA-
   CONS]). 
    
   Bandwidth Constraints Model Id = TBD was allocated by IANA to RDM. 
    
   <IANA-note> To be removed by the RFC editor at the time of 
   publication 
        We request IANA to assign value 0 for the RDM model. 
      Once the value has been assigned, please replace "TBD" above 
        by the assigned value. 
   </IANA-note> 
    
    
10.Normative References 
    
   [DSTE-REQ] Le Faucheur et al, Requirements for support of Diff-Serv-
   aware MPLS Traffic Engineering, RFC3564. 
    

 
 
Le Faucheur, et al.                                           [Page 8] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
   [DSTE-PROTO] Le Faucheur et al, Protocol extensions for support of 
   Diff-Serv-aware MPLS Traffic Engineering, draft-ietf-tewg-diff-te-
   proto-08.txt, work in progress. 
    
   [RFC2119] S. Bradner, Key words for use in RFCs to Indicate 
   Requirement Levels, RFC2119, March 1997. 
    
   [IANA-CONS], T. Narten et al, "Guidelines for Writing an IANA 
   Considerations Section in RFCs", RFC2434. 
    
    
11.Informative References 
    
   [BC-CONS] Le Faucheur, "Considerations on Bandwidth Constraints Model 
   for DS-TE", draft-lefaucheur-tewg-russian-dolls-00.txt, June 2002. 
    
   [BC-MODEL] Lai, "Bandwidth Constraints Models for DS-TE",  
   draft-wlai-tewg-bcmodel-03.txt, work in progress. 
    
   [DSTE-MAM] Le Faucheur, Lai, "Maximum Allocation Bandwidth 
   Constraints Model for Diff-Serv-aware MPLS Traffic Engineering", 
   draft-ietf-tewg-diff-tet-mam-04.txt, work in progress. 
    
   [DSTE-MAR] Ash, "Max Allocation with Reservation Bandwidth 
   Constraints Model for MPLS/DiffServ TE & Performance Comparisons", 
   work in progress. 
    
   [OSPF-TE] Katz et al., "Traffic Engineering (TE) Extensions to OSPF 
   Version 2", RFC3630.  
    
   [ISIS-TE] Smit, Li, "Intermediate System to Intermediate System (IS-
   IS) extensions for Traffic Engineering (TE)", RFC 3784. 
    
   [RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP 
   Tunnels", RFC 3209. 
    
   [DIFF-MPLS] Le Faucheur et al, "MPLS Support of Diff-Serv", RFC3270. 
    
   [GMPLS-RECOV] Lang et al, "Generalized MPLS Recovery Functional 
   Specification", draft-ietf-ccamp-gmpls-recovery-functional-02.txt, 
   work in progress. 
    
   [MPLS-BACKUP] Vasseur et al, "MPLS Traffic Engineering Fast reroute: 
   bypass tunnel path computation for bandwidth protection", draft-
   vasseur-mpls-backup-computation-02.txt, work in progress. 
    
    

 
 
Le Faucheur, et al.                                           [Page 9] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
12.   Intellectual Property Considerations 
 
   The IETF takes no position regarding the validity or scope of any 
   Intellectual Property Rights or other rights that might be claimed to 
   pertain to the implementation or use of the technology described in 
   this document or the extent to which any license under such rights 
   might or might not be available; nor does it represent that it has 
   made any independent effort to identify any such rights. Information 
   on the procedures with respect to rights in RFC documents can be 
   found in BCP 78 and BCP 79. 
    
   Copies of IPR disclosures made to the IETF Secretariat and any 
   assurances of licenses to be made available, or the result of an 
   attempt made to obtain a general license or permission for the use of 
   such proprietary rights by implementers or users of this 
   specification can be obtained from the IETF on-line IPR repository at 
   http://www.ietf.org/ipr. 
    
   The IETF invites any interested party to bring to its attention any 
   copyrights, patents or patent applications, or other proprietary 
   rights that may cover technology that may be required to implement 
   this standard. Please address the information to the IETF at 
   ietf-ipr@ietf.org. 
    
    
13.Editor's Address: 
    
   Francois Le Faucheur 
   Cisco Systems, Inc. 
   Village d'Entreprise Green Side - Batiment T3 
   400, Avenue de Roumanille 
   06410 Biot-Sophia Antipolis 
   France 
   Phone: +33 4 97 23 26 19 
   Email: flefauch@cisco.com 
    
    
14.Full Copyright Statement 
    
   Copyright (C) The Internet Society (2004).  All Rights Reserved. 
    
   This document and translations of it may be copied and furnished to 
   others, and derivative works that comment on or otherwise explain it 
   or assist in its implementation may be prepared, copied, published 
   and distributed, in whole or in part, without restriction of any 
   kind, provided that the above copyright notice and this paragraph are 
   included on all such copies and derivative works.  However, this 
   document itself may not be modified in any way, such as by removing 

 
 
Le Faucheur, et al.                                          [Page 10] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
   the copyright notice or references to the Internet Society or other 
   Internet organizations, except as needed for the purpose of 
   developing Internet standards in which case the procedures for 
   copyrights defined in the Internet Standards process must be 
   followed, or as required to translate it into languages other than 
   English. 
    
   The limited permissions granted above are perpetual and will not be 
   revoked by the Internet Society or its successors or assigns. 
    
   This document and the information contained herein is provided on an 
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 
    
    
Appendix A - Addressing [DSTE-REQ] Scenarios 
    
   This Appendix provides examples of how the Russian Dolls Bandwidth 
   Constraints Model can be used to support each of the scenarios 
   described in [DSTE-REQ]. 
    
1.   Scenario 1: Limiting Amount of Voice 
    
   By configuring on every link:  
        - Bandwidth Constraint 1 (for CT1=Voice) = "certain percentage" 
          of link capacity 
        - BC0 (for CT1=Voice + CT0= Data) =  link capacity 
    
   By configuring: 
        - every CT1/Voice TE-LSP with preemption =0  
        - every CT0/Data TE-LSP with preemption =1 
    
   DS-TE with the Russian Dolls Model will address all the requirements: 
        - amount of Voice traffic limited to desired percentage on 
          every link 
        - data traffic capable of using all remaining link capacity 
        - voice traffic capable of preempting other traffic 
    
2.   Scenario 2: Maintain Relative Proportion of Traffic Classes 
    
   By configuring on every link:  
        - BC2 (for CT2) = e.g. 45% 
        - BC1 (for CT1+CT2) = e.g. 80% 
        - BC0 (for CT0+CT1+CT2) = e.g.100% 
    

 
 
Le Faucheur, et al.                                          [Page 11] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
   DS-TE with the Russian Dolls Model will ensure that the amount of 
   traffic of each Class Type established on a link is within acceptable 
   levels as compared to the resources allocated to the corresponding 
   Diff-Serv PHBs regardless of which order the LSPs are routed in, 
   regardless of which preemption priorities are used by which LSPs and 
   regardless of failure situations.  
    
   By also configuring: 
        - every CT2/Voice TE-LSP with preemption =0  
        - every CT1/Premium Data TE-LSP with preemption =1  
        - every CT0/Best-Effort TE-LSP with preemption =2 
    
   DS-TE with the Russian Dolls Model will also ensure that: 
        - CT2 Voice LSPs always have first preemption priority in order 
          to use the CT2 capacity 
        - CT1 Premium Data LSPs always have second preemption priority 
          in order to use the CT1 capacity 
        - Best-Effort can use up to link capacity whatever is left by 
          CT2 and CT1.  
    
   Optional automatic adjustment of Diff-Serv scheduling configuration 
   could be used for maintaining very strict relationship between amount 
   of established traffic of each Class Type and corresponding Diff-Serv 
   resources. 
    
3.   Scenario 3: Guaranteed Bandwidth Services 
    
   By configuring on every link:  
        - BC1 (for CT1) = "given" percentage of link bandwidth 
          (appropriate to achieve the Guaranteed Bandwidth service's 
          QoS objectives) 
        - BC0 (for CT0+CT1) = 100% of link bandwidth 
    
   DS-TE with the Russian Dolls Model will ensure that the amount of 
   Guaranteed Bandwidth Traffic established on every link remains below 
   the given percentage so that it will always meet its QoS objectives. 
   At the same time it will allow traffic engineering of the rest of the 
   traffic such that links can be filled up.  
 
 
Disclaimer of Validity 
    
   This document and the information contained herein are provided on an 
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 
 
 
Le Faucheur, et al.                                          [Page 12] 

                    Russian Dolls Model for DS-TE       December 2005 
 
 
    
 
Copyright Statement 
    
   Copyright (C) The Internet Society (2004).  This document is subject 
   to the rights, licenses and restrictions contained in BCP 78, and 
   except as set forth therein, the authors retain all their rights. 
    
    
Acknowledgment 
    
   Funding for the RFC Editor function is currently provided by the 
   Internet Society. 
    

 
 
Le Faucheur, et al.                                          [Page 13]