One document matched: draft-ietf-tewg-diff-te-russian-04.txt
Differences from draft-ietf-tewg-diff-te-russian-03.txt
Francois Le Faucheur, Editor
Cisco Systems, Inc.
IETF Internet Draft
Expires: March, 2004
Document: draft-ietf-tewg-diff-te-russian-04.txt September, 2003
Russian Dolls Bandwidth Constraints Model for
Diff-Serv-aware MPLS Traffic Engineering
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are
Working documents of the Internet Engineering Task Force (IETF), its
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Abstract
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.
Summary for Sub-IP related Internet Drafts
RELATED DOCUMENTS:
draft-ietf-tewg-diff-te-reqts-07.txt
draft-ietf-tewg-diff-te-proto-04.txt
WHERE DOES IT FIT IN THE PICTURE OF THE SUB-IP WORK
This ID is a Working Group document of the TE Working Group.
WHY IS IT TARGETED AT THIS WG(s)
TEWG is responsible for specifying protocol extensions for support of
Diff-Serv-aware MPLS Traffic Engineering.
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Russian Dolls Model for DS-TE September 2003
JUSTIFICATION
The TEWG charter states that "This will entail verification and
review of the Diffserv requirements in the WG Framework document and
initial specification of how these requirements can be met through
use and potentially expansion of existing protocols."
In line with this, the TEWG is specifying bandwidth constraints model
for Diff-Serv-aware MPLS Traffic Engineering. This document describes
one particular bandwidth constraints 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].
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 Constraint Models
for DS-TE and states that "The DS-TE technical solution MUST specify
at least one bandwidth constraint model and MAY specify multiple
bandwidth constraint."
This document provides a detailed description of one particular
Bandwidth Constraint 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
Le Faucheur et. al 2
Russian Dolls Model for DS-TE September 2003
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.
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
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Russian Dolls Model for DS-TE September 2003
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 must also belong to CTx; Excess
Traffic LSPs sharing bandwidth with Backup LSPs of CTx must 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):
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"
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Russian Dolls Model for DS-TE September 2003
Purely for illustration purposes, the diagram below represents the
Russian Doll 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.
- 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 Doll" 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)
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Russian Dolls Model for DS-TE September 2003
- 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.
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:
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Russian Dolls Model for DS-TE September 2003
"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."
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. Normative References
[DSTE-REQ] Le Faucheur et al, Requirements for support of Diff-Serv-
aware MPLS Traffic Engineering, RFC3564.
[DSTE-PROTO] Le Faucheur et al, Protocol extensions for support of
Diff-Serv-aware MPLS Traffic Engineering, draft-ietf-tewg-diff-te-
proto-05.txt, September 2003.
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Russian Dolls Model for DS-TE September 2003
[RFC2119] S. Bradner, Key words for use in RFCs to Indicate
Requirement Levels, RFC2119, March 1997.
10. 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-00.txt, June 2002.
[DSTE-MAM] Le Faucheur, Lai, "Maximum Allocation Bandwidth
Constraints Model for Diff-Serv-aware MPLS Traffic Engineering",
draft-ietf-tewg-diff-tet-mam-01.txt, September 2003.
[DSTE-MAR] Ash, "Max Allocation with Reservation Bandwidth Constraint
Model for MPLS/DiffServ TE & Performance Comparisons", March 2003.
[OSPF-TE] Katz et al., "Traffic Engineering Extensions to OSPF",
draft-katz-yeung-ospf-traffic-10.txt, June 2003.
[ISIS-TE] Smit et al., "IS-IS extensions for Traffic Engineering",
draft-ietf-isis-traffic-05.txt, August 2003.
[RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[DIFF-MPLS] Le Faucheur et al, "MPLS Support of Diff-Serv", RFC3270,
May 2002.
[GMPLS-RECOV] Lang et al, "Generalized MPLS Recovery Functional
Specification", draft-ietf-ccamp-gmpls-recovery-functional-00.txt,
January 2003.
[MPLS-BACKUP] Vasseur et al, "MPLS Traffic Engineering Fast reroute:
bypass tunnel path computation for bandwidth protection", draft-
vasseur-mpls-backup-computation-02.txt, February 2003.
11. Intellectual Property Considerations
Cisco Systems, Inc. may seek patent or other intellectual property
protection for some of all of the technologies disclosed in this
document. If any standards arising from this document are or become
protected by one or more patents assigned to Cisco Systems, Cisco
Systems intends to disclose those patents and license them on
reasonable and non-discriminatory terms.
12. Editor's Address:
Le Faucheur et. al 8
Russian Dolls Model for DS-TE September 2003
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
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%
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
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Russian Dolls Model for DS-TE September 2003
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.
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| PAFTECH AB 2003-2026 | 2026-04-23 05:44:55 |