Francois Le Faucheur, Editor
Thomas Nadeau
Cisco Systems, Inc.
Jim Boyle
PDNets
Kireeti Kompella
Juniper Networks
William Townsend
Tenor Networks
Darek Skalecki
Nortel Networks
IETF Internet Draft
Expires: December, 2002
Document: draft-ietf-tewg-diff-te-proto-01.txt June, 2002
Protocol extensions for support of
Diff-Serv-aware MPLS Traffic Engineering
Status of this Memo
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all provisions of Section 10 of RFC2026. Internet-Drafts are
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Abstract
This document specifies the IGP and signaling extensions and
procedures (beyond those already specified for existing MPLS Traffic
Engineering) for support of Diff-Serv-aware MPLS Traffic Engineering.
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A default Bandwidth Constraints model for Diff-Serv-aware Traffic
Engineering (the Russian Dolls model) is also specified.
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.
This document specifies:
- the IGP and signaling extensions and procedures (beyond those
already specified for existing MPLS Traffic Engineering
[OSPF-TE][ISIS-TE][RSVP-TE][CR-LDP]) for support of the DS-TE
requirements [DSTE-REQ] in environments relying on
distributed Constraint Based Routing (i.e. path computation
involving Head-end LSRs).
- A default Bandwidth Constraint Model for DS-TE called the
Russian Dolls model. While DS-TE implementations may support
other Bandwidth Constraints model, they must all support the
Russian Dolls model to ensure interoperability across all
implementations.
2. Definitions
[DSTE-REQ] discusses how a Head-end LSR may split the set of Ordered
Aggregates from the traffic to a given Tail-end into multiple Traffic
Trunks. Each Traffic Trunk is transported over a separate LSP which
is Constraint Based Routed individually.
For readability a number of definitions from [DSTE-REQ] are repeated
here:
Traffic Trunk: an aggregation of traffic flows of the same class
[i.e. which are to be treated equivalently from the DS-TE
perspective] which are placed inside a Label Switched Path.
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. 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.
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3. Configurable Parameters
This section only discusses the differences with the configurable
parameters supported for MPLS Traffic Engineering as per [TE-REQ],
[ISIS-TE], [OSPF-TE], [RSVP-TE] and [CR-LDP]. All other parameters
are unchanged.
3.1. Link Parameters
3.1.1. Bandwidth Constraints (BCs)
[DSTE-REQTS] states that "Regardless of the Bandwidth Constraint
Model, the DS-TE solution must allow support for up to 8 BCs."
For DS-TE, the existing "Maximum Reservable link bandwidth" parameter
is retained but its semantic is generalized and interpreted as BC0.
Additionally, on every link, a DS-TE implementation MUST provide for
configuration of up to 7 additional link parameters which are the
seven other potential Bandwidth Constraints i.e. BC1, BC2 , ... BC7.
The LSR MUST interpret these Bandwidth Constraints in accordance with
the supported Bandwidth Constraint Model (i.e. what bandwidth
constraint applies to what Class-Type and how).
Where the Bandwidth Constraint Model imposes some relationship among
the values to be configured for these Bandwidth Constraints, the LSR
MUST enforce those at configuration time. For example, with the
"Russian Doll" Bandwidth Constraints Model defined below in section
9, the LSR must ensure that BCi is configured smaller or equal to
BCj, where i is greater than j.
3.1.2. per-CT Local Overbooking Multipliers (LOMs)
DS-TE enables a network administrator to apply different overbooking
(or underbooking) ratios for different CTs.
The principal method to achieve this is the same as historically used
in existing TE deployment, which is :
(i) to take into account the over-booking/underbooking ratio
appropriate for the OA/CT associated with the considered LSP
at the time of establishing the bandwidth size of a given
LSP, AND/OR
(ii) to take into account the overbooking/underbooking ratio at
the time of configuring the Maximum Reservable
Bandwidth/Bandwidth Constraints and/or the Maximum Link
Bandwidth (which effectively controls the maximum size of an
individual LSP) and use values which are larger(overbooking)
or smaller(underbooking) than the actual link.
We refer to this method as the "LSP/link size overbooking" method.
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The "LSP/link size overbooking" method is expected to be often
sufficient in many DS-TE environments and requires no additional
configurable parameters.
However, in the particular DS-TE environments where, for a given CT,
the overbooking ratio needs to be tweaked differently on different
links and where a very fine accounting of overbooking cross-effect
across Class-Types is required, a DS-TE implementation MAY optionally
support the "local overbooking" method as a complement to the
"LSP/link size overbooking" method. The "local overbooking" method
relies on optional "per-CT Local Overbooking Multipliers" (LOMs)
which are configurable, on every link, for every CT. The per-CT Local
Overbooking Multiplier effectively allows the network operator to
increase/decrease", on some links, the overbooking ratio already
enforced by the "LSP/link size overbooking" method. This is achieved
by factoring the per-CT LOM in all local bandwidth accounting for the
purposes of admission control and IGP advertisement of unreserved
bandwidths. Exact details on how the LOMs need to be factored in
depend on the Bandwidth Constraints model. This is discussed for the
Russian Dolls model in section 9.
Since the per-CT Local Overbooking Multipliers are factored in the
IGP advertisement of unreserved bandwidth by the local LSR, a remote
LSR computing a path for a DS-TE tunnel need not be aware that local
overbooking is used on the considered link. In fact, the remote LSR
does not even need to support the optional local overbooking method.
In any case, the remote LSR will compute a path that effectively
takes into account the LOMs on the considered link because it bases
its computation on advertised unreserved bandwidth which do factor in
the LOMs for that link.
3.2. LSR Parameters
3.2.1. TE-Class Mapping
In line with [DSTE-REQ], the preemption attributes defined in [TE-
REQ] are retained with DS-TE and applicable across all Class Types.
The preemption attributes of setup priority and holding priority
retain existing semantics, and in particular these semantics are not
affected by the Ordered Aggregate transported by the LSP or by the
LSP's Class Type. This means that if LSP1 contends with LSP2 for
resources, LSP1 may preempt LSP2 if LSP1 has a higher set-up
preemption priority (i.e. lower numerical priority value) than LSP2's
holding preemption priority regardless of LSP1's OA/CT and LSP2's
OA/CT.
For DS-TE, LSRs MUST allow configuration of a TE-Class mapping
whereby the Class-Type and preemption level are configured for each
of (up to) 8 TE-Classes.
This mapping is referred to as :
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TE-Class[i] <--> < CTc , preemption p >
Where 0 <= i <= 7, 0 <= c <= 7, 0 <= p <= 7
Two TE-Classes must not be identical (i.e. have both the same Class-
Type and the same preemption priority).
Where the network administrator uses less than 8 TE-Classes, the DS-
TE LSR MUST allow remaining ones to be configured as "Unused".
There are no other restrictions on how any of the 8 Class-Types can
be paired up with any of the 8 preemption priorities to form a TE-
class. In particular, one given preemption priority can be paired up
with two (or more) different Class-Types to form two (or more) TE-
classes. Similarly, one Class-Type can be paired up with two (or
more) different preemption priorities to form two (or more) TE-
Classes. Also, there is no mandatory ordering relationship between
the TE-Class index (i.e. "i" above) and the Class-Type (i.e. "c"
above) or the preemption priority (i.e. "p" above) of the TE-Class.
To ensure coherent DS-TE operation, the network administrator MUST
configure exactly the same TE-Class Mapping on all LSRs of the DS-TE
domain.
When the TE-class mapping needs to be modified in the DS-TE domain,
care must be exercised during the transient period of reconfiguration
during which some DS-TE LSRs may be configured with the new TE-class
mapping while others are still configured with the old TE-class
mapping. It is recommended that active tunnels do not use any of the
TE-classes which are being modified during such a transient
reconfiguration period.
3.3. LSP Parameters
3.3.1. Class-Type
With DS-TE, LSRs MUST support, for every LSP, an additional
configurable parameter which indicates the Class-Type of the Traffic
Trunk transported by the LSP.
There is one and only one Class-Type configured per LSP.
The configured Class-Type indicates, in accordance with the supported
Bandwidth Constraint Model, what are the Bandwidth Constraints
applicable to that LSP.
3.3.2. Setup and Holding Preemption Priorities
As per existing TE, DS-TE assumes that every DS-TE LSP is configured
with a setup and holding priority, each with a value between 0 and 7.
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3.3.3. Class-Type/Preemption Relationship
With DS-TE, the preemption priority configured for the setup priority
of a given LSP and the Class-Type configured for that LSP must be
such that, together, they form one of the (up to) 8 TE-Classes
configured in the TE-Class Mapping specified is section 3.2.1 above.
The LSR MUST enforce this rule at configuration time.
The preemption priority configured for the holding priority of a
given LSP and the Class-Type configured for that LSP must also be
such that, together, they form one of the (up to) 8 TE-Classes
configured in the TE-Class Mapping specified is section 3.2.1 above.
The LSR MUST enforce this rule at configuration time.
3.4. Examples of Parameters Configuration
For illustrative purposes, we now present a few examples of how these
configurable parameters may be used. All these examples assume that
different bandwidth constraints need to be enforced for different
sets of Traffic Trunks (e.g. for Voice and for Data) so that two, or
more, Class-Types must be used.
3.4.1. Example 1
The Network Administrator of a first network using two Class Types
(CT1 for Voice and CT0 for Data), may elect to configure the
following TE-Class Mapping to ensure that Voice LSPs are never driven
away from their shortest path because of Data LSPs:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT0 , preemption 1 >
TE-Class[i] <--> unused, for 2 <= i <= 7
Voice LSPs would then be configured with:
- CT=CT1, set-up priority =0, holding priority=0
Data LSPs would then be configured with:
- CT=CT0, set-up priority =1, holding priority=1
A new Voice LSP would then be able to preempt an existing Data LSP in
case they contend for resources. A Data LSP would never preempt a
Voice LSP. A Voice LSP would never preempt another Voice LSP. A Data
LSP would never preempt another Data LSP.
3.4.2. Example 2
The Network Administrator of another network may elect to configure
the following TE-Class Mapping in order to optimize global network
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resource utilization by favoring placement of large LSPs closer to
their shortest path:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT0 , preemption 1 >
TE-Class[2] <--> < CT1 , preemption 2 >
TE-Class[3] <--> < CT0 , preemption 3 >
TE-Class[i] <--> unused, for 4 <= i <= 7
Large size Voice LSPs could be configured with:
- CT=CT1, set-up priority =0, holding priority=0
Large size Data LSPs could be configured with:
- CT=CT0, set-up priority = 1, holding priority=1
Small size Voice LSPs could be configured with:
- CT=CT1, set-up priority = 2, holding priority=2
Small size Data LSPs could be configured with:
- CT=CT0, set-up priority = 3, holding priority=3.
A new large size Voice LSP would then be able to preempt a small size
Voice LSP or any Data LSP in case they contend for resources.
A new large size Data LSP would then be able to preempt a small size
Data LSP or a small size Voice LSP in case they contend for
resources, but it would not be able to preempt a large size Voice
LSP.
3.4.3. Example 3
The Network Administrator of another network may elect to configure
the following TE-Class Mapping in order to ensure that Voice LSPs are
never driven away from their shortest path because of Data LSPs while
also achieving some optimization of global network resource
utilization by favoring placement of large LSPs closer to their
shortest path:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT1 , preemption 1 >
TE-Class[2] <--> < CT0 , preemption 2 >
TE-Class[3] <--> < CT0 , preemption 3 >
TE-Class[i] <--> unused, for 4 <= i <= 7
Large size Voice LSPs could be configured with:
- CT=CT1, set-up priority = 0, holding priority=0.
Small size Voice LSPs could be configured with:
- CT=CT1, set-up priority = 1, holding priority=1.
Large size Data LSPs could be configured with:
- CT=CT0, set-up priority = 2, holding priority=2.
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Small size Data LSPs could be configured with:
- CT=CT0, set-up priority = 3, holding priority=3.
A Voice LSP could preempt a Data LSP if they contend for resources. A
Data LSP would never preempt a Voice LSP. A Large size Voice LSP
could preempt a small size Voice LSP if they contend for resources. A
Large size Data LSP could preempt a small size Data LSP if they
contend for resources.
3.4.4. Example 4
The Network Administrator of another network may elect to configure
the following TE-Class Mapping in order to ensure that no preemption
occurs in the DS-TE domain:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT0 , preemption 0 >
TE-Class[i] <--> unused, for 2 <= i <= 7
Voice LSPs would then be configured with:
- CT=CT1, set-up priority =0, holding priority=0
Data LSPs would then be configured with:
- CT=CT0, set-up priority =0, holding priority=0
No LSP would then be able to preempt any other LSP.
3.4.5. Example 5
The Network Administrator of another network may elect to configure
the following TE-Class Mapping in view of increased network stability
through a more limited use of preemption:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT1 , preemption 1 >
TE-Class[2] <--> < CT0 , preemption 1 >
TE-Class[3] <--> < CT0 , preemption 2 >
TE-Class[i] <--> unused, for 4 <= i <= 7
Large size Voice LSPs could be configured with:
- CT=CT1, set-up priority = 0, holding priority=0.
Small size Voice LSPs could be configured with:
- CT=CT1, set-up priority = 1, holding priority=0.
Large size Data LSPs could be configured with:
- CT=CT0, set-up priority = 2, holding priority=1.
Small size Data LSPs could be configured with:
- CT=CT0, set-up priority = 2, holding priority=2.
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A new large size Voice LSP would be able to preempt a Data LSP in
case they contend for resources, but it would not be able to preempt
any Voice LSP even a small size Voice LSP.
A new small size Voice LSP would be able to preempt a small size Data
LSP in case they contend for resources, but it would not be able to
preempt a large size Data LSP or any Voice LSP.
A Data LSP would not be able to preempt any other LSP.
4. IGP Advertisement
This section only discusses the differences with the IGP
advertisement supported for MPLS Traffic Engineering as per [OSPF-TE]
and [ISIS-TE]. The rest of the IGP advertisement is unchanged.
4.1. Bandwidth Constraints
As detailed above in section 3.1.1, up to 8 Bandwidth Constraints (
BCb, 0 <= b <= 7) are configurable on any given link.
With DS-TE, the existing "Maximum Reservable Bw" sub-TLV is retained
with a generalized semantic so that it is now interpreted as
Bandwidth Constraint 0 (BC0).
DS-TE also defines the following optional sub-TLV to advertise the
eight potential Bandwidth Constraints (BC0 to BC7):
"Bandwidth Constraints" sub-TLV:
TBD - Bandwidth Constraint Model Id (1 octet)
- Bandwidth Constraints (Nx4 octets)
Where:
- Bandwidth Constraint Model Id: 1 octet identifier for the
Bandwidth Constraints Model currently in use by the LSR
initiating the IGP advertisement.
Values 0 to 127 are to be allocated by the TEWG to identify
Bandwidth Constraints Models defined in the TEWG. Value 0
identifies the Russian Doll Bandwidth Constraint Model
defined in section 9.
Values 128 to 255 are for experimental use.
- Bandwidth Constraints: contains BC0, BC1,... BCN-1.
Each Bandwidth Constraint is encoded in 32 bits in IEEE
floating point format. The units are bytes (not bits!) per
second. It is recommended that only the Bandwidth Constraints
corresponding to active CTs be advertised in order to
minimize the impact on IGP scalability.
A DS-TE LSR MAY optionally advertise Bandwidth Constraints.
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A DS-TE LSR which does advertise Bandwidth Constraints MUST use the
new "Bandwidth Constraints" sub-TLV to do so. For example, where a
Service Provider deploys DS-TE with two active CTs, only two
Bandwidth Constraints per link would be meaningful (assuming, for
instance, the Russian Doll Bandwidth Constraint Model defined in
section 9). A DS-TE LSR which does advertise Bandwidth Constraint
would include the "Bandwidth Constraints" sub-TLV in the IGP
advertisement and this should contain BC0 and BC1.
A DS-TE LSR which does advertise Bandwidth Constraints, MAY also
include the existing "Maximum Reservable Bw" sub-TLV. This may be
useful in migration situations where some LSRs in the network are not
DS-TE capable (see Appendix G) and thus do not understand the new
"Bandwidth Constraints" sub-TLV. IN that case, the DS-TE LSR MUST set
the value of the "Maximum Reservable Bw" sub-TLV to the same value as
the one for BC0 encoded in the "Bandwidth Constraints" sub-TLV.
A DS-TE LSR receiving both the old "Maximum Reservable Bw" sub-TLV
and the new "Bandwidth Constraints" sub-TLV for a given link MAY
ignore the "Maximum Reservable Bw" sub-TLV.
A DS-TE LSR receiving the "Bandwidth Constraints" sub-TLV with a
Bandwidth Constraint Model Id which does not match the Bandwidth
Constraint Model it currently uses, MAY generate a warning to the
operator reporting the inconsistency between Bandwidth Constraint
Models used on different links. If the DS-TE LSR does not support the
Bandwidth Constraint Model designated by the Bandwidth Constraint
Model Id, or if the DS-TE LSR does not support operations with
multiple simultaneous Bandwidth Constraint Models, the DS-TE LSR MAY
ignore the corresponding TLV.
4.2. Unreserved Bandwidth
With DS-TE, the existing "Unreserved Bandwidth" sub-TLV is retained
as the only vehicle to advertise dynamic bandwidth information
necessary for Constraint Based Routing on Head-ends, except that it
is used with a generalized semantic. The Unreserved Bandwidth sub-TLV
still carries eight bandwidth values but they now correspond to the
unreserved bandwidth for each of the TE-Class (instead of for each
preemption as per existing TE).
More precisely, a DS-TE LSR MUST support the Unreserved Bandwidth
sub-TLV with a definition which is generalized into the following:
The Unreserved Bandwidth sub-TLV specifies the amount of bandwidth
not yet reserved for each of the eight TE-classes, in IEEE floating
point format arranged in increasing order of TE-Class index, with
unreserved bandwidth for TE-Class [0] occurring at the start of the
sub-TLV, and unreserved bandwidth for TE-Class [7] at the end of the
sub-TLV. The unreserved bandwidth value for TE-Class [i] ( 0 <= i <=
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7) is referred to as "Unreserved TE-Class [i]". It indicates the
bandwidth that is available, for reservation, to an LSP which :
- transports a Traffic Trunk from the Class-Type of TE-
Class[i], and
- has a setup priority corresponding to the preemption priority
of TE-Class[i].
The units are bytes per second.
Since the bandwidth values are now ordered by TE-class index and thus
can relate to different CTs with different bandwidth constraints and
can relate to any arbitrary preemption priority, a DS-TE LSR MUST NOT
assume any ordered relationship among these bandwidth.
With existing TE, since all preemption priorities reflect the same
(and only) bandwidth constraints and since bandwidth values are
advertised in preemption priority order, the following relationship
is always true, and is often assumed by TE implementations:
If i < j , then "Unreserved Bw [i]" >= "Unreserved Bw [j]"
With DS-TE, no relationship is to be assumed so that:
If i < j , then
"Unreserved TE-Class [i]" = "Unreserved TE-Class [j]"
OR
"Unreserved TE-Class [i]" > "Unreserved TE-Class [j]"
OR
"Unreserved TE-Class [i]" < "Unreserved TE-Class [j]".
Since some Bandwidth Constraints Models are such that a given Class-
Type is constrained by multiple Bandwidth Constraints (as in the case
of the Russian Doll Bandwidth Constraint Model specified in section
9), the value to be advertised by the IGP in "Unreserved TE-Class
[i]" MUST reflect all of the Bandwidth Constraints relevant to the CT
associated with TE-Class [i].
If TE-Class[i] is unused, the value advertised by the IGP in
"Unreserved TE-Class [i]" MUST be set to zero.
4.3. Local Overbooking Multiplier
The following additional optional sub-TLV is defined for DS-TE:
"Local Overbooking Multiplier" sub-TLV:
TBD - per-CT Local Overbooking Multipliers (N x 2 octets).
Each LOM is encoded as an integer in the range
[ 0 , (2^16 -1) ] that represents LOM expressed in
percentage. For example, a LOM of 1 (i.e. 100%) is encoded
as 100, and represents no overbooking/underbooking. A LOM
of 2 (i.e. 200%) is encoded as 200, and represents an
overbooking of 2. A LOM of 0.5 (i.e. 50%) is encoded as 50
and represents an underbooking of 2.
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where N is the number of per-CT Local Overbooking Multipliers
actually advertised. It is recommended that only the LOMs
corresponding to active CTs be included, in order to minimize the
impact on IGP scalability.
A DS-TE LSR supporting the optional local overbooking method MAY
optionally advertise LOMs. A DS-TE LSR which does advertise LOMs MUST
use the "Local Overbooking Multiplier" sub-TLV to do so.
For example, where a Service Provider only deploys DS-TE with two CTs
and makes use of the Local Overbooking method, the "Local Overbooking
Multiplier" sub-TLV may optionally be used and would then contain
only LOM[0] and LOM[1.
Note that the use of this sub-TLV is only optional even when the
optional Local Overbooking method is actually used (and thus when the
Local Overbooking Multipliers parameters are actually configured
locally on some or all links). Its use may assist in head-end
prediction of network response to LSP establishment.
5. LSP Signaling
This section only describes the signaling extensions beyond those
already specified for MPLS Traffic Engineering as per [RSVP-TE] and
[CR-LDP] and for Diff-Serv over MPLS as per [DIFF-MPLS].
The Class-Type of the LSP is signaled in RSVP-TE and CR-LDP for DS-TE
in order for LSRs to enforce the appropriate bandwidth constraint(s)
for admission control and bandwidth accounting.
Protocol and procedure extensions for signaling of the Class-Type are
specified in details in Appendix A and B respectively for RSVP-TE and
CR-LDP.
A DS-TE implementation based on RSVP-TE MUST support the protocol and
procedure extensions specified in Appendix A.
A DS-TE implementation based on CR-LDP MUST support the protocol and
procedure extensions specified in Appendix B.
6. Constraint Based Routing
Let us consider the case where a path needs to be computed for an LSP
whose Class-Type is configured to CTc and whose set-up preemption
priority is configured to p.
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Then the pair of CTc and p will map to one of the TE-Classes defined
in the TE-Class mapping. Let us assume that this is the i-th TE-Class
i.e. TE-Class[i].
The Constraint Based Routing algorithm of a DS-TE LSR is still only
required to perform path computation satisfying a single bandwidth
constraint which is to fit in "Unreserved TE-Class [i]" as advertised
by the IGP for every link. Thus, no changes are required to the
existing TE Constraint Based Routing algorithm itself.
The Constraint Based Routing algorithm MAY also optionally take into
account, when used, the optional information advertised in IGP which
are the Bandwidth Constraints and the Local Overbooking Multipliers.
As an example, the Bandwidth Constraints MIGHT be used as a tie-
breaker criteria in situations where multiple paths, otherwise
equally attractive, are possible.
7. Diff-Serv scheduling
The Class-Type signaled at LSP establishment MAY optionally be used
by DS-TE LSRs to dynamically adjust the resources allocated to the
Class-Type by the Diff-Serv scheduler. In addition, the Diff-Serv
information (i.e. the PSC) signaled by the TE-LSP signaling protocols
as specified in [DIFF-MPLS], if used, MAY optionally be used by DS-TE
LSRs to dynamically adjust the resources allocated to a PSC/OA within
a Class Type by the Diff-Serv scheduler.
8. Existing TE as a Particular Case of DS-TE
We observe that existing TE can be viewed as a particular case of DS-
TE where:
(i) a single Class-Type is used, all 8 preemption priorities
are allowed for that Class-Type and the following TE-Class
Mapping is used:
TE-Class[i] <--> < CT0 , preemption i >
Where 0 <= i <= 7.
(ii) optional per-CT Local Overbooking Multipliers are not
used.
In that case, DS-TE behaves as existing TE.
As with existing TE, the IGP advertises:
- Unreserved Bandwidth for each of the 8 preemption priorities
- Max Link Bandwidth
As with existing TE, the IGP may also optionally advertise BC0 =
Maximum Reservable Bandwidth.
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Note that, unlike with existing TE, the IGP will also advertise the
Bandwidth Constraint sub-TLV (which will contain BC0).
Since all LSPs transport traffic from CT0, LSP Signaling is done
without explicit signaling of the Class-Type (which is only used for
other Class-Types than CT0 as explained in Appendix A and B).
9. Russian Doll Bandwidth Constraints Model
9.1. Definition
[DSTE-REQ] introduces the concept of Bandwidth Constraints Models to
characterize the Bandwidth Constraints associated with CTs, but it
does not actually select one particular Model.
[DSTE-REQ] also requires that a default Bandwidth Constraints Model
be specified. The purpose of such a default Model is to ensure that
there is at least one common Bandwidth Constraints model supported
across all DS-TE implementations to allow for easier deployment of
DS-TE.
This section specifies a default Bandwidth Constraints Model which is
referred to as the "Russian Dolls" Bandwidth Constraints model. DS-TE
implementations MUST support the Russian Dolls models and MAY also
optionally support other Bandwidth Constraints Models.
The "Russian Dolls" model is defined in the following manner
(assuming that the optional per-CT Local Overbooking Multipliers are
not used - i.e. LOM[c]=1 , 0<=c<=7 ):
o Maximum Number of Bandwidth Constraints (MaxBC)= Maximum
Number of Class-Types (MaxCT) = 8
o All LSPs supporting Traffic Trunks from CTc (with
b<=c<=7) use no more than BCb i.e.:
- 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
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
Le Faucheur et. al 14
Protocols for Diff-Serv-aware TE June 2002
I-----BC2------>
I----------------------BC1------>
I---------------------------------------------BC0------>
While simpler or, conversely, more flexible/sophisticated Bandwidth
Constraints models can be defined, the Russian Dolls model is an
attractive trade-off for the following reasons:
- Network administrators generally find it superior to the most
basic model of a single independent BC per CT (which, in
typical deployment scenarios, results in either capacity
wastage, low priority Traffic Trunk starvation and/or
degradation of QoS objectives)
- network administrators generally find it sufficient for the
real life deployments currently anticipated (e.g. it
addresses all the scenarios described in [DSTE-REQ])
- it remains simple and only requires limited protocol
extensions, while more sophisticated Bandwidth Constraints
model may require more complex extensions.
More details on the properties of the Russian Dolls model can be
found in [RUSSIAN] and [BCMODEL].
As an 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 = 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).
Another (or other) Bandwidth Constraints Model(s) may be specified in
another (or other) document(s) to address other potential
requirements which may emerge from Service Providers real life
deployment and which cannot be efficiently addressed by the Russian
Dolls model. This is outside the scope of the current specification.
The Russian Doll Bandwidth Constraints Model can be supported with
the extensions defined earlier in this document for DS-TE. Note that
a number of other Bandwidth Constraints could also be supported with
these same extensions. Note also that not all Bandwidth Constraints
models could be supported with these extensions and some may require
additional or different extensions. Both of these situations are
beyond the scope of this specification.
Note that as per [DSTE-REQTS], while deployment of DS-TE is expected
to be easier when a single Bandwidth Constraints Model is used on all
the DS-TE LSRs of a DS-TE domain, the DS-TE solution itself does not
prevent a network operator to activate different Bandwidth
Constraints models on different links in a network, if he/she wishes
to do so and if the particular DS-TE LSR implementations allow this.
9.2. Computing "Unreserved TE-Class [i]"
Le Faucheur et. al 15
Protocols for Diff-Serv-aware TE June 2002
We first observe that, for existing TE, details on admission control
algorithms for TE LSPs, and consequently details on formulas for
computing the unreserved bandwidth, are outside the scope of the
current IETF work. This is left for vendor differentiation. Note that
this does not compromise interoperability across various
implementations since the TE schemes rely on LSRs to advertise their
local view of the world in terms of Unreserved Bw to other LSRs. This
way, regardless of the actual local admission control algorithm used
on one given LSR, Constraint Based Routing on other LSRs can rely on
advertised information to determine whether an additional LSP will be
accepted or rejected by the given LSR. The only requirement is that
an LSR advertises unreserved bandwidth values which are consistent
with its specific local admission control algorithm and take into
account the holding preemption priority of established LSPs.
In the context of DS-TE, again, details on admission control
algorithms are left for vendor differentiation and formulas for
computing the unreserved bandwidth for TE-Class[i] are outside the
scope of this specification. However, DS-TE places the additional
requirement on the LSR that the unreserved bandwidth values
advertised MUST reflect all of the Bandwidth Constraints relevant to
the CT associated with TE-Class[i], as discussed in section 4.2.
As with existing TE, DS-TE assumes that the holding preemption
priority of established LSPs is the one considered (as opposed to
their set-up preemption priority) for the purpose of computing the
unreserved bandwidth for TE-Class [i].
Example formulas for computing "Unreserved TE-Class [i]" are provided
in Appendix C.
9.3. Admission Control Rules
A DS-TE LSR MUST support the following admission control rule:
Regardless of how the admission control algorithm actually computes
the unreserved bandwidth for TE-Class[i] for one of its local link,
an LSP of bandwidth B, of set-up preemption priority p and of Class-
Type CTc is admissible on that link iff:
B <= unreserved bandwidth for TE-Class[i], AND
B <= Max Link Bandwidth
Where
- TE-Class [i] maps to < CTc , p > in the LSR's configured TE-
Class mapping
- Max Link Bandwidth is the maximum link bandwidth configured
on the link and advertised in IGP.
Le Faucheur et. al 16
Protocols for Diff-Serv-aware TE June 2002
Note that this admission control rule assumes that the optional per-
CT Local Overbooking Multipliers are not used (i.e. LOM[c]=1,
0<=c<= 7 ).
9.4. Support of Optional Local Overbooking Method
We remind the reader that, as discussed in section 3.1.2, the "LSP/link
size overbooking" method (which does not use the Local Overbooking
Multipliers) is expected to be sufficient in many DS-TE environments.
It is expected that the optional Local Overbooking method (and LOMs)
would only be used in specific environments, in particular where
different overbooking ratios need to be enforced on different links of
the DS-TE domain and cross-effect of overbooking across CTs needs to be
accounted for very accurately.
This section discusses the impact of the optional local overbooking
method on the Russian Dolls model and associated rules and formula.
This is only applicable in the cases where the optional local
overbooking method is indeed supported by the DS-TE LSRs and actually
deployed.
9.4.1. Russian Dolls Model Definition
Let us define "Reserved(CTc)" as the sum of the bandwidth reserved by
all established LSPs which belong to CTc.
Let us define "Normalised(CTc)" as "Reserved(CTc)/LOM(c)".
When the optional Local Overbooking method is supported, the "Russian
Doll" model definition MUST be extended in the following manner:
- Maximum Number of Bandwidth Constraints (MaxBC)= Maximum
Number of Class-Types (MaxCT) = 8
- SUM [ Normalised(CTc), for b<=c<=7 ] <= BCb i.e.:
o [ Normalised(CT7) ] <= BC7
o [ Normalised(CT6) + Normalised(CT7) ] <= BC6
o [ Normalised(CT5) + Normalised(CT6) +
Normalised(CT7) ] <= BC5
o etc.
o [ Normalised(CT0) + Normalised(CT1) +
...
Normalised(CT6) + Normalised(CT7) ] <= BC0
Purely for illustration purposes, the diagram below represents the
Russian Doll Bandwidth Constraints model in a pictorial manner when 3
Class-Types are active and the local overbooking method is used:
I--------------------------------------------------------------I
I-----------------------------------------I Normalised(CT2) I
I--------------------I Normalised(CT2) I + I
I Normalised(CT2) I + I Normalised(CT1) I
I--------------------I Normalised(CT1) I + I
I-----------------------------------------I Normalised(CT0) I
Le Faucheur et. al 17
Protocols for Diff-Serv-aware TE June 2002
I--------------------------------------------------------------I
I--------BC2--------->
I-------------------------BC1------------->
I-----------------------------------------------BC0------------>
9.4.2. Bandwidth Constraints
When the optional Local Overbooking method is supported, the
relationship among the Bandwidth Constraints values to be enforced by
the LSR is not modified. The LSR MUST still ensure that BCi is
configured smaller or equal to BCj, where i is greater than j.
When the Bandwidth Constraints are optionally advertised in the
Bandwidth Constraints sub-TLV, the values advertised are the BC
values as configured (i.e. LOMs do not affect the advertisement of
BCs).
9.4.3. Computing "Unreserved TE-Class [i]"
As discussed in section 9.2, details on formulas for computing the
unreserved bandwidth, are outside the scope of the current IETF work.
However, when the Local Overbooking method is supported, the
advertised unreserved bandwidth values MUST reflect the per-CT Local
Overbooking Multipliers. This MUST be consistent with how the LOMs
are taken into account in the specific local admission control
algorithm.
Note that this may result in the Unreserved Bandwidth values
advertised for a particular CT being larger than one or more of the
BCs relevant to this CT (since BCs are not affected by LOMs).
Example formulas for computing "Unreserved TE-Class [i]" when local
overbooking is supported are provided in section 2 of Appendix C.
9.4.4. Max Link Bandwidth
The Max Link bandwidth parameter effectively controls the maximum
size of a single LSP. The value advertised in the Max Link Bandwidth
sub-TLV is the value as configured locally (i.e. LOMs do not affect
the advertisement of the Max Link Bandwidth).
9.4.5. Admission Control Rules
When the optional Local Overbooking method is supported, the DS-TE
LSR MUST support the same admission control rules as without LOM:
Regardless of how the admission control algorithm actually computes
the unreserved bandwidth for TE-Class[i] for one of its local link,
Le Faucheur et. al 18
Protocols for Diff-Serv-aware TE June 2002
an LSP of bandwidth B, of set-up preemption priority p and of Class-
Type CTc is admissible on that link iff:
(i) B <= unreserved bandwidth for TE-Class[i], AND
(ii) B <= Max Link Bandwidth
Where
- TE-Class [i] maps to < CTc , p > in the LSR's configured TE-
Class mapping
- Max Link Bandwidth is the maximum link bandwidth configured
on the link and advertised in IGP.
Condition (i) above applies to B [and not B/LOM(c) ] because the LOM
is already factored in the unreserved bandwidth values.
Condition (ii) above also applies to B [and not B/LOM(c) ]. Condition
(ii) controls the maximum bandwidth that a single LSP can grab on its
own, by limiting it to the Maximum Link Bandwidth. Since
"overbooking" is usually only (fully) achievable when a sufficient
number of LSPs share the Link Bandwidth, it is not appropriate to
factor in the LOM when assessing the maximum bandwidth that a single
LSP can grab on a link.
9.4.6. Example Usage of LOM
To illustrate usage of the local overbooking method, let's consider a
DS-TE deployment where two CTs (CT0 for data and CT1 for voice) and a
single preemption priority are used.
The TE-Class mapping is the following:
TE-Class <--> CT, preemption
==============================
0 CT0, 0
1 CT1, 0
rest unused
Let's assume that on a given link, BCs and LOMs are configured in the
following way:
BC0 = 200
BC1 = 100
LOM(0) = 4 (i.e. = 400%)
LOM(1) = 2 (i.e. = 200%)
Let's further assume that the DS-TE LSR uses the example formulas
presented in section 2 of Appendix C for computing unreserved
bandwidth values.
If there is no established LSP on the considered link, the LSR will
advertise for that link in IGP :
Unreserved TE-Class [0] = 4 x (200 - 0/4 - 0/2 )= 800
Unreserved TE-Class [1] = 2 x (100- 0/2) = 200
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Protocols for Diff-Serv-aware TE June 2002
Note again that these values advertised for Unreserved Bandwidth are
larger than BC1 and BC0.
If there is only a single established LSP, with CT=CT0 and BW=100,
the LSR will advertise:
Unreserved TE-Class [0] = 4 x (200 - 100/4 - 0/2 )=700
Unreserved TE-Class [1] = 2 x (100- 0/2) = 200
If there is only a single established LSP, with CT=CT1 and BW=100,
the LSR will advertise:
Unreserved TE-Class [0] = 4 x (200 - 0/4 - 100/2 )= 600
Unreserved TE-Class [1] = 2 x (100- 100/2) = 100
Note that the impact of an LSP on the unreserved bandwidth of a CT
does not depend only on the LOM for that CT: it also depends on the
LOM for the CT of the LSP. This can be seen in our example. A BW=100
tunnel affects Unreserved
CT0 twice as much if it is a CT1 tunnel, than if it is a CT0 tunnel.
It reduces Unreserved CTO by 200 (800->600) rather than by 100
(800->700). This is because LOM(1) is half as big as LOM(0). This
illustrates why the local overbooking method allows very fine
accounting of cross-effect of overbooking across CTs, as compared
with the LSP/link size overbooking method.
If there are two established LSPs, one with CT=CT1 and BW=100 and one
with CT=CT0 and BW=100, the LSR will advertise:
Unreserved TE-Class [0] = 4 x (200 - 100/4 - 100/2) = 500
Unreserved TE-Class [1] = 2 x (100 - 100/2) = 100
If there are two LSPs established, one with CT=CT1 and BW=100, and
one with CT=CT0 and BW=480, the LSR will advertise:
Unreserved TE-Class [0] = 4 x (200 - 480/4 - 100/2) = 120
Unreserved TE-Class [1] = 2 x MIN [ (200 - 480/4 - 100/2),
(100 - 100/2) ]
= 2 x MIN [ 30, 50 ]
= 60
10. Security Considerations
The solution is not expected to add specific security requirements
beyond those of Diff-Serv and existing TE. The security mechanisms
currently used with Diff-Serv and existing TE can be used with this
solution.
11. Acknowledgments
We thank Martin Tatham, Angela Chiu and Pete Hicks for their earlier
contribution in this work. We also thank Sanjaya Choudhury for his
thorough reviews and numerous suggestions.
Le Faucheur et. al 20
Protocols for Diff-Serv-aware TE June 2002
References
[DSTE-REQ] Le Faucheur et al, Requirements for support of Diff-Serv-
aware MPLS Traffic Engineering, draft-ietf-tewg-diff-te-reqts-05.txt,
June 2002.
[OSPF-TE] Katz, Yeung, Traffic Engineering Extensions to OSPF, draft-
katz-yeung-ospf-traffic-06.txt, October 2001.
[ISIS-TE] Smit, Li, IS-IS extensions for Traffic Engineering, draft-
ietf-isis-traffic-04.txt, August 2001.
[RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[CR-LDP] Jamoussi et al, "Constraint-Based LSP Setup using LDP", RFC
3212, January 2002.
[DIFF-MPLS] Le Faucheur et al, "MPLS Support of Diff-Serv", RFC3270,
May 2002.
[RUSSIAN] Le Faucheur, "Considerations on Bandwidth Constraints Model
for DS-TE", draft-lefaucheur-tewg-russian-dolls-00.txt, June 2002.
[BCMODEL] Lai, "Bandwidth Constraints Models for DS-TE",
draft-wlai-tewg-bcmodel-00.txt, June 2002.
Authors' 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
Jim Boyle
Protocol Driven Networks
1381 Kildaire Farm Road #288
Cary, NC 27511
Phone: +1 919 852-5160
Email: jboyle@pdnets.com
Kireeti Kompella
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94099
Email: kireeti@juniper.net
Le Faucheur et. al 21
Protocols for Diff-Serv-aware TE June 2002
William Townsend
Tenor Networks
100 Nagog Park
Acton, MA 01720
Phone: +1-978-264-4900
Email: btownsend@tenornetworks.com
Thomas D. Nadeau
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
Phone: +1-978-244-3051
Email: tnadeau@cisco.com
Darek Skalecki
Nortel Networks
3500 Carling Ave,
Nepean K2H 8E9
Phone: +1-613-765-2252
Email: dareks@nortelnetworks.com
Appendix A - RSVP Extensions for Diff-Serv-aware TE
In this section we describe extensions to RSVP for support of
Diff-Serv-aware MPLS Traffic Engineering. These extensions are in
addition to the extensions to RSVP defined in [RSVP-TE] for support
of (aggregate) MPLS Traffic Engineering and to the extensions to RSVP
defined in [DIFF-MPLS] for support of Diff-Serv over MPLS.
1. Diff-Serv-aware TE related RSVP Messages Format
One new RSVP Object is defined in this document: the CLASSTYPE
Object. Detailed description of this Object is provided below. This
new Object is applicable to Path messages. This specification only
defines the use of the CLASSTYPE Object in Path messages used to
establish LSP Tunnels in accordance with [RSVP-TE] and thus
containing a Session Object with a C-Type equal to LSP_TUNNEL_IPv4
and containing a LABEL_REQUEST object.
Restrictions defined in [RSVP-TE] for support of establishment of LSP
Tunnels via RSVP are also applicable to the establishment of LSP
Tunnels supporting Diff-Serv-aware Traffic Engineering. For instance,
only unicast LSPs are supported and Multicast LSPs are for further
study.
This new CLASSTYPE object is optional with respect to RSVP so that
general RSVP implementations not concerned with MPLS LSP set up do
not have to support this object.
An LSR supporting Diff-Serv-aware Traffic Engineering in compliance
with this specification MUST support the CLASSTYPE Object.
Le Faucheur et. al 22
Protocols for Diff-Serv-aware TE June 2002
1.1. Path Message Format
The format of the Path message is as follows:
<Path Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <EXPLICIT_ROUTE> ]
<LABEL_REQUEST>
[ <SESSION_ATTRIBUTE> ]
[ <DIFFSERV> ]
[ <CLASSTYPE> ]
[ <POLICY_DATA> ... ]
[ <sender descriptor> ]
<sender descriptor> ::= <SENDER_TEMPLATE> [ <SENDER_TSPEC> ]
[ <ADSPEC> ]
[ <RECORD_ROUTE> ]
2. CLASSTYPE Object
The CLASSTYPE object format is shown below.
2.1. CLASSTYPE object
class = TBD, C_Type = 1 (need to get an official class num from the
IANA with the form 0bbbbbbb)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | CT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved : 29 bits
This field is reserved. It must be set to zero on transmission
and must be ignored on receipt.
CT : 3 bits
Indicates the Class-Type. Values currently allowed are 1, 2, ...
, 7.
3. Handling CLASSTYPE Object
To establish an LSP tunnel with RSVP, the sender LSR creates a Path
message with a session type of LSP_Tunnel_IPv4 and with a
LABEL_REQUEST object as per [RSVP-TE]. The sender LSR may also
include the DIFFSERV object as per [DIFF-MPLS].
Le Faucheur et. al 23
Protocols for Diff-Serv-aware TE June 2002
If the LSP is associated with Class-Type 0, the sender LSR MUST NOT
include the CLASSTYPE object in the Path message.
If the LSP is associated with Class-Type N (1 <= N <=7), the sender
LSR MUST include the CLASSTYPE object in the Path message with the
Class-Type (CT) field set to N.
If a path message contains multiple CLASSTYPE objects, only the first
one is meaningful; subsequent CLASSTYPE object(s) MUST be ignored and
MUST not be forwarded.
Each LSR along the path MUST record the CLASSTYPE object, when
present, in its path state block.
If the CLASSTYPE object is not present in the Path message, the LSR
MUST associate the Class-Type 0 to the LSP.
The destination LSR responding to the Path message by sending a Resv
message MUST NOT include a CLASSTYPE object in the Resv message
(whether the Path message contained a CLASSTYPE object or not).
During establishment of an LSP corresponding to the Class-Type N, the
LSR MUST perform admission control over the bandwidth available for
that particular Class-Type.
An LSR that recognizes the CLASSTYPE object and that receives a path
message which contains the CLASSTYPE object but which does not
contain a LABEL_REQUEST object or which does not have a session type
of LSP_Tunnel_IPv4, MUST send a PathErr towards the sender with the
error code 'Diff-Serv-aware TE Error' and an error value of
'Unexpected CLASSTYPE object'. Those are defined below in section 5.
An LSR receiving a Path message with the CLASSTYPE object, which
recognizes the CLASSTYPE object but does not support the particular
Class-Type, MUST send a PathErr towards the sender with the error
code 'Diff-Serv-aware TE Error' and an error value of 'Unsupported
Class-Type'. Those are defined below in section 5.
An LSR receiving a Path message with the CLASSTYPE object, which
recognizes the CLASSTYPE object but determines that the Class-Type
value is not valid (i.e. Class-Type value 0), MUST send a PathErr
towards the sender with the error code 'Diff-Serv-aware TE Error' and
an error value of 'Invalid Class-Type value'. Those are defined below
in section 5.
An LSR receiving a Path message with the CLASSTYPE object, which:
- recognizes the CLASSTYPE object,
- supports the particular Class-Type, but
- determines that the tuple formed by (i) this Class-Type and
(ii) the set-up priority signaled in the same Path message,
is not one of the eight TE-classes configured in the TE-class
mapping,
Le Faucheur et. al 24
Protocols for Diff-Serv-aware TE June 2002
MUST send a PathErr towards the sender with the error code 'Diff-
Serv-aware TE Error' and an error value of 'CT and setup priority do
not form a configured TE-Class'. Those are defined below in section
5.
An LSR receiving a Path message with the CLASSTYPE object, which:
- recognizes the CLASSTYPE object,
- supports the particular Class-Type, but
- determines that the tuple formed by (i) this Class-Type and
(ii) the holding priority signaled in the same Path message,
is not one of the eight TE-classes configured in the TE-class
mapping,
MUST send a PathErr towards the sender with the error code 'Diff-
Serv-aware TE Error' and an error value of 'CT and holding priority
do not form a configured TE-Class'. Those are defined below in
section 5.
An LSR receiving a Path message with the CLASSTYPE object and with
the DIFFSERV object for an L-LSP, which:
- recognizes the CLASSTYPE object,
- has local knowledge of the relationship between Class-Types
and PSC (e.g. via configuration)
- based on this local knowledge, determines that the PSC
signaled in the DIFFSERV object is inconsistent with the
Class-Type signaled in the CLASSTYPE object,
MUST send a PathErr towards the sender with the error code 'Diff-
Serv-aware TE Error' and an error value of 'Inconsistency between
signaled PSC and signaled CT'. Those are defined below in section 5.
An LSR receiving a Path message with the CLASSTYPE object and with
the DIFFSERV object for an E-LSP, which:
- recognizes the CLASSTYPE object,
- has local knowledge of the relationship between Class-Types
and PHBs (e.g. via configuration)
- based on this local knowledge, determines that the PHBs
signaled in the MAP entries of the DIFFSERV object are
inconsistent with the Class-Type signaled in the CLASSTYPE
object,
MUST send a PathErr towards the sender with the error code 'Diff-
Serv-aware TE Error' and an error value of 'Inconsistency between
signaled PHBs and signaled CT'. Those are defined below in section 5.
An LSR MUST handle the situations where the LSP can not be accepted
for other reasons than those already discussed in this section, in
accordance with [RSVP-TE] and [DIFF-MPLS] (e.g. a reservation is
rejected by admission control, a label can not be associated).
4. Non-support of the CLASSTYPE Object
An LSR that does not recognize the CLASSTYPE object Class-Num MUST
behave in accordance with the procedures specified in [RSVP] for an
unknown Class-Num whose format is 0bbbbbbb (i.e. it must send a
Le Faucheur et. al 25
Protocols for Diff-Serv-aware TE June 2002
PathErr with the error code 'Unknown object class' toward the
sender).
An LSR that recognizes the CLASSTYPE object Class-Num but does not
recognize the CLASSTYPE object C-Type, MUST behave in accordance with
the procedures specified in [RSVP] for an unknown C-type (i.e. it
must send a PathErr with the error code 'Unknown object C-Type'
toward the sender).
In both situations, this causes the path set-up to fail. The sender
SHOULD notify management that a LSP cannot be established and
possibly might take action to retry reservation establishment without
the CLASSTYPE object.
5. Error Codes For Diff-Serv-aware TE
In the procedures described above, certain errors must be reported as
a 'Diff-Serv-aware TE Error'. The value of the 'Diff-Serv-aware TE
Error' error code is (TBD).
The following defines error values for the Diff-Serv-aware TE Error:
Value Error
1 Unexpected CLASSTYPE object
2 Unsupported Class-Type
3 Invalid Class-Type value
4 CT and setup priority do not form a configured TE-Class
5 CT and holding priority do not form a configured
TE-Class
6 Inconsistency between signaled PSC and signaled CT
7 Inconsistency between signaled PHBs and signaled CT
Appendix B - CR-LDP Extensions for Diff-Serv-aware TE
CR-LDP, defined in [CR-LDP], is an extension to LDP, defined in
[LDP], for support of (aggregate) MPLS Traffic Engineering. In this
section we describe extensions to CR-LDP for support of Diff-Serv-
aware MPLS Traffic Engineering. These extensions are in addition to
the extensions to LDP defined in [DIFF-MPLS] for support of Diff-Serv
over MPLS. They closely resemble the extensions to RSVP defined in
the previous section.
Note that extensions of this section for support of Diff-Serv-aware
Traffic Engineering are not applicable to LDP due to the fact that
LDP does not support MPLS Traffic Engineering and bandwidth
reservation in particular.
1. Diff-Serv-aware TE related CR-LDP Messages Encoding
One new CR-LDP TLV is defined in this document: the Class Type TLV.
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Protocols for Diff-Serv-aware TE June 2002
Detailed description of this TLV is provided below. This new TLV is
applicable to Label Request messages.
Restrictions defined in [CR-LDP] for support of establishment of LSPs
via CR-LDP are also applicable to the establishment of LSPs
supporting Diff-Serv-aware Traffic Engineering: for instance, only
unicast LSPs are supported and multicast LSPs are for further study.
This new Class Type TLV is optional with respect to CR-LDP so that
general CR-LDP implementations not concerned with Diff-Serv-aware
Traffic Engineering are not required to support this TLV.
An LSR supporting Diff-Serv-aware Traffic Engineering in compliance
with this specification MUST support the Class Type TLV.
1.1. Label Request Message Encoding
The encoding for the CR-LDP Label Request message is extended as
follows, to optionally include the Class Type 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diff-Serv TLV (LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Class Type TLV (CR-LDP optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Other CR-LDP TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The extension is based on a related LDP extension, defined in [DIFF-
MPLS], for support of Diff-Serv TLV but further extended for CR-LDP
with CR-LDP TLVs.
2. Class Type TLV
The Class Type TLV has the following form:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Class Type TLV | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | CT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Le Faucheur et. al 27
Protocols for Diff-Serv-aware TE June 2002
Reserved : 29 bits
This field is reserved. It must be set to zero on transmission
and must be ignored on receipt.
CT : 3 bits
Indicates the Class-Type. Values currently allowed are 1, 2, ...
, 7.
3. Handling Class Type TLV
To establish an LSP using CR-LDP, an ingress LSR generates a Label
Request message as per [CR-LDP]. This Label Request may optionally
include the Diff-Serv TLV as defined in [DIFF-MPLS] for LDP but
extended to CR-LDP.
If the LSP is associated with Class-Type 0, the ingress LSR MUST NOT
include the Class Type TLV in the Label Request message.
If the LSP is associated with Class-Type N (1 <= N <= 7), the ingress
LSR MUST include the Class Type TLV in the Label Request message with
the Class-Type (CT) field set to N.
If a Label Request message contains multiple Class Type TLVs, only
the first one is meaningful; subsequent Class Type TLV(s) MUST be
ignored and not forwarded.
If the Class Type TLV is not present in the Label Request message, an
LSR MUST associate the Class-Type 0 to the LSP.
A downstream LSR sending a Label Mapping message in response to a
Label Request message MUST NOT include the Class-Type TLV (whether
the Class-Type TLV was included in the Label Request message or not).
During establishment of an LSP corresponding to the Class-Type N, an
LSR MUST perform admission control over the bandwidth available for
that particular Class-Type.
An LSR that recognizes the Class Type TLV and receives a Label
Request message which contains the Class Type TLV but which does not
contain any of the CR-LDP TLVs, MUST reject the label request by
sending upstream a Notification message which includes the Status TLV
with a Status Code of 'Unexpected Class-Type TLV'. This is defined
below in section 4. This error can only occur when an LDP LSP as
opposed to CR-LDP LSP is being established. As was already mentioned,
Class Type TLV extension for Diff-Serv-aware Traffic Engineering is
not applicable to LDP.
An LSR receiving a Label Request message with the Class Type TLV,
which recognizes the Class Type TLV but does not support the
particular Class-Type, MUST reject the label request by sending
upstream a Notification message which includes the Status TLV with a
Le Faucheur et. al 28
Protocols for Diff-Serv-aware TE June 2002
Status Code of 'Unsupported Class-Type'. This is defined below in
section 4.
An LSR receiving a Label Request message with the Class Type TLV,
which recognizes the Class Type TLV but determines that the Class-
Type value is not valid (i.e. Class-Type value 0), MUST reject the
label request by sending upstream a Notification message which
includes the Status TLV with a Status Code of 'Invalid Class-Type
value'. This is defined below in section 4.
An LSR receiving a Label Request message with the Class Type TLV,
which:
- recognizes the Class Type TLV,
- supports the particular Class-Type, but
- determines that the tuple formed by (i) this Class-Type and
(ii) the set-up priority signaled in the same Label Request
message, is not one of the eight TE-classes configured in
the TE-class mapping,
MUST reject the label request by sending upstream a Notification
message which includes the Status TLV with a Status Code of 'CT and
setup priority do not form a configured TE-Class'. This is defined
below in section 4.
An LSR receiving a Label Request message with the Class Type TLV,
which:
- recognizes the Class Type TLV,
- supports the particular Class-Type, but
- determines that the tuple formed by (i) this Class-Type and
(ii) the holding priority signaled in the same Label Request
message, is not one of the eight TE-classes configured in
the TE-class mapping,
MUST reject the label request by sending upstream a Notification
message which includes the Status TLV with a Status Code of 'CT and
holding priority do not form a configured TE-Class'. This is defined
below in section 4.
An LSR receiving a Label Request message with the Class Type TLV and
with the Diff-Serv TLV for an L-LSP, which:
- recognizes the Class Type TLV,
- has local knowledge of the relationship between Class-Types
and PSC (e.g. via configuration)
- based on this local knowledge, determines that the PSC
signaled in the Diff-Serv TLV is inconsistent with the Class-
Type signaled in the Class-Type TLV,
MUST reject the label request by sending upstream a Notification
message which includes the Status TLV with a Status Code of
'Inconsistency between signaled PSC and signaled CT'. This is defined
below in section 4.
An LSR receiving a Label Request message with the Class Type TLV and
with the Diff-Serv TLV for an E-LSP, which:
- recognizes the Class Type TLV,
Le Faucheur et. al 29
Protocols for Diff-Serv-aware TE June 2002
- has local knowledge of the relationship between Class-Types
and PHBs (e.g. via configuration)
- based on this local knowledge, determines that the PHBs
signaled in the MAP entries of the Diff-Serv TLV are
inconsistent with the Class-Type signaled in the Class-Type
TLV,
MUST reject the label request by sending upstream a Notification
message which includes the Status TLV with a Status Code of
'Inconsistency between signaled PHBs and signaled CT'. This is
defined below in section 4.
An LSR MUST handle the situations where the LSP can not be accepted
for other reasons than those already discussed in this section, in
accordance with [CR-LDP], [LDP] and [DIFF-MPLS] (e.g. reservation
rejected by admission control, a label can not be associated).
4. Status Code Values for Diff-Serv-aware TE
In the procedures described above, certain errors must be reported.
The following values are defined for the Status Code field of the
Status TLV:
Status Code E Status Data
Unexpected Class Type TLV 0 TBD
Unsupported Class-Type 0 TBD
Invalid Class-Type value 0 TBD
CT and setup priority do not 0 TBD
form a configured TE-Class
CT and holding priority do not 0 TBD
form a configured TE-Class'
Inconsistency between signaled 0 TBD
PSC and signaled CT
Inconsistency between signaled 0 TBD
PHBs and signaled CT
Appendix C - Example Formulas for Computing "Unreserved TE-Class [i]"
1. Example Formulas Without Local Overbooking
Keeping in mind that details of admission control algorithms as well
as formulas for computing "Unreserved TE-Class [i]" are outside the
scope of this specification, we provide in this section, for
illustration purposes, an example of how values for the unreserved
bandwidth for TE-Class[i] might be computed, assuming:
- the Russian Doll Bandwidth Constraints Model is used
- 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 30
Protocols for Diff-Serv-aware TE June 2002
- the optional per-CT Local Overbooking Multipliers are not
used (.i.e. LOM[c]=1, 0<= c <=7).
We assume that:
TE-Class [i] <--> < CTc , preemption p>
in the configured TE-Class mapping.
Let us define "Reserved(CTb,q)" as the sum of the bandwidth reserved
by all 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.
For readability, formulas are first shown assuming only 4 CTs are
active. The formulas below can be extended trivially 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 <= 3
If CTc = CT1, then "Unreserved TE-Class [i]" =
MIN [
[ BC1 - SUM ( Reserved(CTb,q) ) ] for q <= p and 1 <= b <= 3,
[ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 3
]
If CTc = CT2, then "Unreserved TE-Class [i]" =
MIN [
[ BC2 - SUM ( Reserved(CTb,q) ) ] for q <= p and 2 <= b <= 3,
[ BC1 - SUM ( Reserved(CTb,q) ) ] for q <= p and 1 <= b <= 3,
[ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 3
]
If CTc = CT3, then "Unreserved TE-Class [i]" =
MIN [
[ BC3 - SUM ( Reserved(CTb,q) ) ] for q <= p and 3 <= b <= 3,
[ BC2 - SUM ( Reserved(CTb,q) ) ] for q <= p and 2 <= b <= 3,
[ BC1 - SUM ( Reserved(CTb,q) ) ] for q <= p and 1 <= b <= 3,
[ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 3
]
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,
Le Faucheur et. al 31
Protocols for Diff-Serv-aware TE June 2002
. . .
[ 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.
2. Example Formulas With Local Overbooking
When the optional local overbooking method is supported, the above
example generalized formula becomes:
"Unreserved TE-Class [i]" =
LOM(c) x MIN [
[ BCc - SUM ( Normalised(CTb,q) ) ] for q <= p and c <= b <= 7,
. . .
[ BC0 - SUM ( Normalised(CTb,q) ) ] for q <= p and 0 <= b <= 7,
]
where:
- TE-Class [i] <--> < CTc , preemption p>
in the configured TE-Class mapping.
- Normalised(CTb,q) = Reserved(CTb/q)/LOM(b)
Appendix D - Prediction for Multiple Path Computation
There are situations where a Head-End needs to compute paths for
multiple LSPs. There are potential advantages for the Head-end in
trying to predict the impact of the n-th LSP on the unreserved
bandwidth when computing the path for the (n+1)-th LSP, before
receiving updated IGP information. One example would be to perform
better load-distribution of the multiple LSPs across multiple paths.
Another example would be to avoid CAC rejection when the (n+1)-th LSP
would no longer fit on a link after establishment of the n-th LSP.
While there are also a number of conceivable scenarios where doing
such predictions might result in a worse situation, it is more likely
to improve the situation. As a matter of fact, a number of network
administrators have elected to use such predictions when deploying
existing TE.
Such predictions are local matters, are optional and are outside the
scope of this specification.
Where such predictions are not used, the optional Bandwidth
Constraint sub-TLV and the optional Local Overbooking Multiplier sub-
TLV need not be advertised in IGP since the information contained in
the Unreserved Bw sub-TLV is all that is required by Head-Ends to
perform Constraint Based Routing.
Le Faucheur et. al 32
Protocols for Diff-Serv-aware TE June 2002
Where such predictions are used on Head-Ends, the optional Bandwidth
Constraint sub-TLV (and the optional Local Overbooking Multiplier
sub-TLV if different overbooking ratios need to be supported on
different links) MAY be advertised in IGP. This is in order for the
Head-ends to predict as accurately as possible how an LSP affects
unreserved bandwidth values for subsequent LSPs.
Remembering that actual admission control algorithms are left for
vendor differentiation, we observe that predictions can only be
performed effectively when the Head-end LSR predictions are based on
the same (or a very close) admission control algorithm as used by
other LSRs.
Appendix E - Addressing [DSTE-REQ] Scenarios
This Appendix provides examples of how the DS-TE solution can be used
to support each of the scenario 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= Max Reservable Link Bandwidth = link capacity
By configuring:
- every CT1/Voice TE-LSP with preemption =0
- every CT0/Data TE-LSP with preemption =1
The proposed solution 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%
The proposed DS-TE solution 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. Optional automatic adjustment of Diff-Sev
scheduling configuration could be used for maintaining very strict
relationship between amount of established traffic of each Class Type
and corresponding Diff-Serv resources.
Le Faucheur et. al 33
Protocols for Diff-Serv-aware TE June 2002
3. Scenario 3: Guaranteed Bandwidth Services
By configuring on every link:
- BC1 for CT1 = "given" percentage of bandwidth (appropriate to
achieve the Guaranteed Bandwidth service's QoS objectives)
- BC0 for CT0+CT1 = 100%
The proposed DS-TE solution will ensure that the amount of Guaranteed
Bandwidth Trafic 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.
Appendix F - Solution Evaluation
1. Satisfying Detailed Requirements
This DS-TE Solution address all the scenarios presented in [DSTE-REQ]
as explained in Appendix E. It also satisfy all the detailed
requirements presented in [DSTE-REQ].
2. Flexibility
This DS-TE solution supports 8 CTs. It is entirely flexible as to how
Traffic Trunks are grouped together into a CT.
3. Extendibility
A maximum of 8 CTs is considered by the authors of this document as
more than comfortable. However, this solution could be extended to
support more CTs if deemed necessary in the future. However, this
would necessitate additional IGP extensions beyond those specified in
this document.
4. Scalability
This DS-TE solution is expected to have a very small scalability
impact compared to existing TE.
From an IGP viewpoint, the amount of mandatory information to be
advertised is identical to existing TE. Two additional sub-TLVs have
been specified, but their use is optional and those contained a
limited amount of static information (at most 8 Bandwidth Constraints
and 8 LOMs).
We expect no noticeable impact on LSP Path computation since, as with
existing TE, this solution only require CSPF to consider a single
unreserved bandwidth value for any given LSP.
Le Faucheur et. al 34
Protocols for Diff-Serv-aware TE June 2002
From a signaling viewpoint we expect no significant impact due to
this solution since it only requires processing of one additional
information (the Class-Type) and does not significantly increase the
likelihood of CAC rejection. Note that DS-TE has some inherent impact
on LSP signaling in the sense that it assumes that different classes
of traffic are split over different LSPs so that more LSPs need to be
signaled; but this is due to the DS-TE concept itself and not to the
actual DS-TE solution discussed here.
5. Backward Compatibility/Migration
This solution is expected to allow smooth migration from existing TE
to DS-TE. This is because existing TE can be supported exactly as
today as a particular configuration of DS-TE. This means that an
"upgraded" LSR with a DS-TE implementation can directly interwork
with an "old" LSR supporting existing TE only.
This solution is expected to allow smooth migration when increasing
the number of CTs actually deployed since it only requires
configuration changes. however, these changes must be performed in a
coordinated manner across the DS-TE domain.
Appendix G - Interoperability with non DS-TE capable LSRs
This DSTE solution allows operations in a hybrid network where some
LSRs are DS-TE capable while some LSRs and not DS-TE capable, which
may occur during migration phases. This Appendix discusses the
constraints and operations in such hybrid networks.
We refer to the set of DS-TE capable LSRs as the DS-TE domain. We
refer to the set of non DS-TE capable (but TE capable) LSRs as the
TE-domain.
Hybrid operations requires that the TE-class mapping in the DS-TE
domain is configured so that:
- a TE-class exist for CT0 for every preemption priority
actually used in the TE domain
- the index in the TE-class mapping for each of these TE-
classes is equal to the preemption priority.
For example, imagine the TE domain uses preemption 2 and 3. Then, DS-
TE can be deployed in the same network by including the following TE-
classes in the TE-class mapping:
i <---> CT preemption
====================================
2 CT0 2
3 CT0 3
Another way to look at this is to say that, the whole TE-class
mapping does not have to be consistent with the TE domain, but the
Le Faucheur et. al 35
Protocols for Diff-Serv-aware TE June 2002
subset of this TE-Class mapping applicable to CT0 must effectively be
consistent with the TE domain.
In such hybrid networks :
- CT0 LSPs can be established by both DS-TE capable LSRs and
non-DSTE capable LSRs
- CT0 LSPs can transit via (or terminate at) both DS-TE capable
LSRs and non-DSTE capable LSRs
- LSPs from other CTs can only be established by DS-TE capable
LSRs
- LSPs from other CTs can only transit via (or terminate at)
DS-TE capable LSRs
Note that, for such hybrid operation, non DS-TE capable LSRs need to
be able to accept Unreserved Bw sub-TLVs containing non decreasing
bandwidth values (ie with Unreserved [p] < Unreserved [q] with p <q).
Also, the Bandwidth Constraints sub-TLV needs to be advertised in the
DS-TE domain and the Maximum Reservable Bandwidth sub-TLV needs to be
advertised in the TE-domain and the DS-TE domain.
Let us consider, the following example to illustrate operations:
LSR0--------LSR1----------LSR2
Link01 Link12
Where:
LSR0 is a non-DS-TE capable LSR
LSR1 and LSR2 are DS-TE capable LSRs
Let's assume again that preemption 2 and 3 are used in the TE-domain
and that the following TE-class mapping is configured on LSR1 and
LSR2:
i <---> CT preemption
====================================
0 CT1 0
1 CT1 1
2 CT0 2
3 CT0 3
rest unused
LSR0 is configured with a Max Reservable bandwidth=m for Link01.
LSR1 is configured with a BC0=x0 and a BC1=x1(possibly=0) for Link01.
LSR0 will advertise in IGP for Link01:
- Max Reservable Bw sub-TLV = <m>
- Unreserved Bw sub-TLV =
<CT0/0,CT0/1,CT0/2,CT0/3,CT0/4,CT0/5,CT0/6,CT0/7>
On receipt of such advertisement, LSR1 will:
- understand that LSR0 is not DS-TE capable because it
advertised a Max Reservable Bw sub-TLV and no Bandwidth
Constraint sub-TLV
Le Faucheur et. al 36
Protocols for Diff-Serv-aware TE June 2002
- conclude that only CT0 LSPs can transit via LSR0 and that
only the values CT0/2 and CT0/3 are meaningful in the
Unreserved Bw sub-TLV. LSR1 may effectively behave as if the
six other values contained in the Unreserved Bw sub-TLV were
set to zero.
LSR1 will advertise in IGP for Link01:
- Max Reservable Bw sub-TLV = <x0>
- Bandwidth Constraint sub-TLV = <BC Model ID=0, x0,x1>
- Unreserved Bw sub-TLV = <CT1/0,CT1/1,CT0/2,CT0/3,0,0,0,0>
On receipt of such advertisement, LSR0 will:
- Ignore the Bandwidth Constraint sub-TLV (unrecognized)
- Correctly process CT0/2 and CT0/3 in the Unreserved Bw sub-
TLV and use these values for CTO LSP establishment
- Incorrectly believe that the other values contained in the
Unreserved Bw sub-TLV relates to other preemption priorities
for CT0, but will actually never use those since we assume
that only preemption 2 and 3 are used in the TE domain.
Le Faucheur et. al 37
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