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
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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.
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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]
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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%
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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]
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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]
