Francois Le Faucheur
Liwen Wu
Bruce Davie
Cisco Systems
Shahram Davari
PMC-Sierra Inc.
Pasi Vaananen
Nokia
Ram Krishnan
Lucent Technologies
Pierrick Cheval
Alcatel
Juha Heinanen
Telia Finland
IETF Internet Draft
Expires: August, 2001
Document: draft-ietf-mpls-diff-ext-08.txt February, 2001
MPLS Support of Differentiated Services
Status of this Memo
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Le Faucheur, et. al 1
MPLS Support of Diff-Serv February 2001
Abstract
This document defines a flexible solution for support of
Differentiated Services (Diff-Serv) over Multi-Protocol Label
Switching (MPLS) networks.
This solution allows the MPLS network administrator to select how
Diff-Serv Behavior Aggregates (BAs) are mapped onto Label Switched
Paths (LSPs) so that he/she can best match the Diff-Serv, Traffic
Engineering and protection objectives within his/her particular
network. For instance, this solution allows the network
administrator to decide whether different sets of BAs are to be
mapped onto the same LSP or mapped onto separate LSPs.
This solution relies on combined use of two types of LSPs:
- LSPs which can transport multiple Ordered Aggregates, so that
the EXP field of the MPLS Shim Header conveys to the LSR the PHB
to be applied to the packet (covering both information about the
packet's scheduling treatment and its drop precedence).
- LSPs which only transport a single Ordered Aggregate, so that
the packet's scheduling treatment is inferred by the LSR
exclusively from the packet's label value while the packet's
drop precedence is conveyed in the EXP field of the MPLS Shim
Header or in the encapsulating link layer specific selective
drop mechanism (ATM, Frame Relay, 802.1).
1. Introduction
In an MPLS domain [MPLS_ARCH], when a stream of data traverses a
common path, a Label Switched Path (LSP) can be established using
MPLS signaling protocols. At the ingress Label Switch Router (LSR),
each packet is assigned a label and is transmitted downstream. At
each LSR along the LSP, the label is used to forward the packet to
the next hop.
In a Differentiated Service (Diff-Serv) domain [DIFF_ARCH] all the
IP packets crossing a link and requiring the same Diff-Serv behavior
are said to constitute a Behavior Aggregate (BA). At the ingress
node of the Diff-Serv domain the packets are classified and marked
with a Diff-Serv Code Point (DSCP) which corresponds to their
Behavior Aggregate. At each transit node, the DSCP is used to select
the Per Hop Behavior (PHB) that determines the scheduling treatment
and, in some cases, drop probability for each packet.
This document specifies a solution for supporting the Diff-Serv
Behavior Aggregates whose corresponding PHBs are currently defined
(in [DIFF_HEADER], [DIFF_AF], [DIFF_EF]) over an MPLS network. This
solution also offers flexibility for easy support of PHBs that may
be defined in the future.
As mentioned in [DIFF_HEADER], "Service providers are not required
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MPLS Support of Diff-Serv February 2001
to use the same node mechanisms or configurations to enable service
differentiation within their networks, and are free to configure the
node parameters in whatever way that is appropriate for their
service offerings and traffic engineering objectives". Thus, the
solution defined in this document gives Service Providers
flexibility in selecting how Diff-Serv classes of service are Routed
or Traffic Engineered within their domain (e.g. separate classes of
services supported via separate LSPs and Routed separately, all
classes of service supported on the same LSP and Routed together).
Because MPLS is path-oriented it can potentially provide faster and
more predictable protection and restoration capabilities in the face
of topology changes than conventional hop by hop routed IP systems.
In this document we refer to such capabilities as "MPLS protection".
Although such capabilities and associated mechanisms are outside the
scope of this specification, we note that they may offer different
levels of protection to different LSPs. Since the solution presented
here allow Service Providers to choose how Diff-Serv classes of
services are mapped onto LSPs, the solution also gives Service
Providers flexibility in the level of protection provided to
different Diff-Serv classes of service (e.g. some classes of service
can be supported by LSPs which are protected while some other
classes of service are supported by LSPs which are not protected).
Furthermore, the solution specified in this document achieves label
space conservation and reduces the volume of label set-up/tear-down
signaling where possible by only resorting to multiple LSPs for a
given Forwarding Equivalent Class (FEC) [MPLS_ARCH] when useful or
required.
This specification allows support of Differentiated Services for
both IPv4 and IPv6 traffic transported over an MPLS network.
This document only describes operations for unicast. Multicast
support is for future study.
The solution described in this document does not preclude the
signaled or configured use of the EXP bits to support Explicit
Congestion Notification [ECN] simultaneously with Diff-Serv over
MPLS. However, techniques for supporting ECN in an MPLS environment
are outside the scope of this document.
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119.
The reader is assumed to be familiar with the terminology of
[MPLS_ARCH], [MPLS_ENCAPS], [MPLS_ATM] and [MPLS_FR] including the
following:
EXP EXPerimental (bits)
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MPLS Support of Diff-Serv February 2001
FEC Forwarding Equivalency Class
FTN FEC-To-NHLFE Map
ILM Incoming Label Map
LC-ATM Label Switching Controlled-ATM (interface)
LC-FR Label Switching Controlled-Frame Relay (interface)
LSP Label Switched Path
LSR Label Switch Router
MPLS Multi-Protocol Label Switching
NHLFE Next Hop Label Forwarding Entry
The reader is assumed to be familiar with the terminology of
[DIFF_ARCH], [DIFF_HEADER], [DIFF_AF] and [DIFF_EF] including the
following:
AF Assured Forwarding
BA Behavior Aggregate
CS Class Selector
DF Default Forwarding
DSCP Differentiated Services Code Point
EF Expedited Forwarding
PHB Per Hop Behavior
The reader is assumed to be familiar with the terminology of
[DIFF_NEW] including the following:
OA Ordered Aggregate. The set of Behavior Aggregates which
share an ordering constraint.
PSC PHB Scheduling Class. The set of one or more PHB(s) that
are applied to the Behavior Aggregate(s) belonging to a
given OA. For example, AF1x is a PSC comprising the
AF11, AF12 and AF13 PHBs. EF is an example of PSC
comprising a single PHB, the EF PHB.
The following acronyms are also used:
CLP Cell Loss Priority
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MPLS Support of Diff-Serv February 2001
DE Discard Eligibility
SNMP Simple Network Management Protocol
Finally, the following acronyms are defined in this specification:
E-LSP EXP-Inferred-PSC LSP
L-LSP Label-Only-Inferred-PSC LSP
1.2 EXP-Inferred-PSC LSPs (E-LSP)
A single LSP can be used to support up to eight BAs of a given FEC,
regardless of how many OAs these BAs span. With such LSPs, the EXP
field of the MPLS Shim Header is used by the LSR to determine the
PHB to be applied to the packet. This includes both the PSC and the
drop preference.
We refer to such LSPs as "EXP-inferred-PSC LSPs" (E-LSP), since the
PSC of a packet transported on this LSP depends on the EXP field
value for that packet.
The mapping from EXP field to PHB (ie to PSC and drop precedence)
for a given such LSP, is either explicitly signaled at label set-up
or relies on a pre-configured mapping.
Detailed operations of E-LSPs are specified in section 3 below.
1.3 Label-Only-Inferred-PSC LSPs (L-LSP)
A separate LSP can be established for a single <FEC, OA> pair.
With such LSPs, the PSC is explicitly signaled at label
establishment time so that, after label establishment, the LSR can
infer exclusively from the label value the PSC to be applied to a
labeled packet. When the Shim Header is used, the Drop Precedence to
be applied by the LSR to the labeled packet, is conveyed inside the
labeled packet MPLS Shim Header using the EXP field. When the Shim
Header is not used (e.g. MPLS Over ATM), the Drop Precedence to be
applied by the LSR to the labeled packet is conveyed inside the link
layer header encapsulation using link layer specific drop precedence
fields (e.g. ATM CLP).
We refer to such LSPs as "Label-Only-Inferred-PSC LSPs" (L-LSP)
since the PSC can be fully inferred from the label without any other
information (e.g. regardless of the EXP field value). Detailed
operations of L-LSPs are specified in section 4 below.
1.4 Overall Operations
For a given FEC, and unless media specific restrictions apply as
identified in the sections 7, 8 and 9 below, this specification
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MPLS Support of Diff-Serv February 2001
allows any one of the following combinations within an MPLS Diff-
Serv domain:
- zero or any number of E-LSPs, and
- zero or any number of L-LSPs.
The network administrator selects the actual combination of LSPs
from the set of allowed combinations and selects how the Behavior
Aggregates are actually transported over this combination of LSPs,
in order to best match his/her environment and objectives in terms
of Diff-Serv support, Traffic Engineering and MPLS Protection.
Criteria for selecting such a combination are outside the scope of
this specification.
For a given FEC, there may be more than one LSP carrying the same
OA, for example for purposes of load balancing of the OA; However in
order to respect ordering constraints, all packets of a given
microflow, possibly spanning multiple BAs of a given Ordered
Aggregate, MUST be transported over the same LSP. Conversely, each
LSP MUST be capable of supporting all the (active) BAs of a given
OA.
Examples of deployment scenarios are provided for information in
APPENPIX A.
1.5 Relationship between Label and FEC
[MPLS_ARCH] states in section `2.1. Overview' that:
`Some routers analyze a packet's network layer header not merely to
choose the packet's next hop, but also to determine a packet's
"precedence" or "class of service". They may then apply different
discard thresholds or scheduling disciplines to different packets.
MPLS allows (but does not require) the precedence or class of
service to be fully or partially inferred from the label. In this
case, one may say that the label represents the combination of a FEC
and a precedence or class of service.'
In line with this, we observe that:
- With E-LSPs, the label represents the combination of a FEC and
the set of BAs transported over the E-LSP). Where all the
supported BAs are transported over an E-LSP, the label then
represents the complete FEC.
- With L-LSPs, the label represents the combination of a FEC and
an OA.
1.6 Bandwidth Reservation for E-LSPs and L-LSPs
Regardless of which label binding protocol is used, E-LSPs and
L-LSPs may be established without bandwidth reservation or with
bandwidth reservation.
Establishing an E-LSP or L-LSP with bandwidth reservation means that
bandwidth requirements for the LSP are signaled at LSP establishment
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MPLS Support of Diff-Serv February 2001
time. Such signaled bandwidth requirements may be used by LSRs at
establishment time to perform admission control of the signaled LSP
over the Diff-Serv resources provisioned (e.g. via configuration,
SNMP or policy protocols) for the relevant PSC(s). Such signaled
bandwidth requirements may also be used by LSRs at establishment
time to perform adjustment to the Diff-Serv resources associated
with the relevant PSC(s) (e.g. adjust PSC scheduling weight).
Note that establishing an E-LSP or L-LSP with bandwidth reservation
does not mean that per-LSP scheduling is necessarily required. Since
E-LSPs and L-LSPs are specified in this document for support of
Differentiated Services, the required forwarding treatment
(scheduling and drop policy) is defined by the appropriate Diff-Serv
PHB. This forwarding treatment MUST be applied by the LSR at the
granularity of the BA and MUST be compliant with the relevant PHB
specification.
When bandwidth requirements are signaled at establishment of an
L-LSP, the signaled bandwidth is obviously associated with the
L-LSP's PSC. Thus, LSRs which use the signaled bandwidth to perform
admission control may perform admission control over Diff-Serv
resources which are dedicated to the PSC (e.g. over the bandwidth
guaranteed to the PSC through its scheduling weight).
When bandwidth requirements are signaled at establishment of an
E-LSP, the signaled bandwidth is associated collectively to the
whole LSP and therefore to the set of transported PSCs. Thus, LSRs
which use the signaled bandwidth to perform admission control may
perform admission control over global resources which are shared by
the set of PSCs (e.g. over the total bandwidth of the link).
Examples of scenarios where bandwidth reservation is not used and
scenarios where bandwidth reservation is used are provided for
information in APPENDIX B.
2. Label Forwarding Model for Diff-Serv LSRs and Tunneling Models
2.1 Label Forwarding Model for Diff-Serv LSRs
Since different Ordered Aggregates of a given FEC may be transported
over different LSPs, the label swapping decision of a Diff-Serv LSR
clearly depends on the forwarded packet's Behavior Aggregate. Also,
since the IP DS field of a forwarded packet may not be directly
visible to an LSR, the way to determine the PHB to be applied to a
received packet and to encode the PHB into a transmitted packet is
different than a non-MPLS Diff-Serv Router.
Thus, in order to describe Label Forwarding by Diff-Serv LSRs, we
model the LSR Diff-Serv label switching behavior as comprising four
stages:
- Incoming PHB Determination (A)
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MPLS Support of Diff-Serv February 2001
- Outgoing PHB Determination with Optional Traffic Conditioning(B)
- Label Forwarding (C)
- Encoding of Diff-Serv information into Encapsulation Layer (EXP,
CLP, DE, User_Priority) (D)
Each stage is described in more details in the following sections.
Obviously, to enforce the Diff-Serv service differentiation the LSR
MUST also apply the forwarding treatment corresponding to the
Outgoing PHB.
This model is illustrated below:
--Inc_label(s)(*)------------------------>I===I--Outg_label(s)(&)-->
\ I I \
\---->I===I I C I \-->I===I--Encaps->
I A I I===I--Outg_PHB->I===I I D I (&)
-Encaps->I===I--Inc_PHB->I B I \ /->I===I
(*) I===I \--------+
\----Forwarding-->
Treatment
(PHB)
"Encaps" designates the Diff-Serv related information encoded in the
MPLS Encapsulation layer (eg EXP field, ATM CLP, Frame Relay DE,
802.1 User_Priority)
(*) when the LSR behaves as an MPLS ingress node, the incoming
packet may be received unlabelled.
(&) when the LSR behaves as an MPLS egress node, the outgoing packet
may be transmitted unlabelled.
This model is presented here to describe the functional operations
of Diff-Serv LSRs and does not constrain actual implementation.
2.2 Incoming PHB Determination
This stage determines which Behavior Aggregate the received packet
belongs to.
2.2.1 Incoming PHB Determination Considering a Label Stack Entry
Sections 3.3 and 4.3 provide the details on how to perform incoming
PHB Determination considering a given received label stack entry
and/or received incoming MPLS encapsulation information depending on
the incoming LSP type and depending on the incoming MPLS
encapsulation.
Section 2.6 provides the details of which label stack entry to
consider for the Incoming PHB Determination depending on the
supported Diff-Serv tunneling mode.
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2.2.2 Incoming PHB Determination Considering IP Header
Section 2.6 provides the details of when the IP Header is to be
considered for incoming PHB determination depending on the supported
Diff-Serv tunneling model. In those cases where the IP header is to
be used, this stage operates exactly as with a non-MPLS IP Diff-Serv
Router and uses the DS field to determine incoming PHB.
2.3 Outgoing PHB Determination With Optional Traffic Conditioning
The traffic conditioning stage is optional and may be used on an LSR
to perform traffic conditioning including Behavior Aggregate
demotion or promotion. It is outside the scope of this
specification. For the purpose of specifying Diff-Serv over MPLS
forwarding, we simply note that the PHB to be actually enforced, and
conveyed to downstream LSRs, by an LSR (referred to as "outgoing
PHB") may be different to the PHB which had been associated with the
packet by the previous LSR (referred to as "incoming PHB").
When the traffic conditioning stage is not present, the "outgoing
PHB" is simply identical to the "incoming PHB".
2.4 Label Forwarding
[MPLS_ARCH] describes how label swapping is performed by LSRs on
incoming labeled packets using an Incoming Label Map (ILM), where
each incoming label is mapped to one or multiple NHLFEs. [MPLS_ARCH]
also describes how label imposition is performed by LSRs on incoming
unlabelled packets using a FEC-to-NHLFEs Map (FTN), where each
incoming FEC is mapped to one or multiple NHLFEs.
A Diff-Serv Context for a label is defined as comprising:
- `LSP type (ie E-LSP or L-LSP)'
- `supported PHBs'
- `Encaps-->PHB mapping' for an incoming label
- `Set of PHB-->Encaps mappings' for an outgoing label
The present specification defines that a Diff-Serv Context is stored
in the ILM for each incoming label.
[MPLS_ARCH] states that the `NHLFE may also contain any other
information needed in order to properly dispose of the packet'. In
accordance with this, the present specification defines that a Diff-
Serv Context is stored in the NHLFE for each outgoing label which is
swapped or pushed.
This Diff-Serv Context information is populated into the ILM and the
FTN at label establishment time.
If the label corresponds to an E-LSP for which no EXP<-->PHB mapping
has been explicitly signaled at LSP setup, the `supported PHBs' is
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MPLS Support of Diff-Serv February 2001
populated with the set of PHBs of the preconfigured
EXP<-->PHB Mapping, which is discussed below in section 3.2.1.
If the label corresponds to an E-LSP for which an EXP<-->PHB mapping
has been explicitly signaled at LSP setup, the `supported PHBs' is
populated with the set of PHBs of the signaled EXP<-->PHB mapping.
If the label corresponds to an L-LSP, the `supported PHBs' is
populated with the set of PHBs forming the PSC that is signaled at
LSP set-up.
The details of how the `Encaps-->PHB mapping' or `Set of
PHB-->Encaps mappings' are populated are defined below in sections 3
and 4.
[MPLS_ARCH] also states that:
"If the ILM [respectively, FTN] maps a particular label to a set of
NHLFEs that contains more than one element, exactly one element of
the set must be chosen before the packet is forwarded. The
procedures for choosing an element from the set are beyond the scope
of this document. Having the ILM [respectively, FTN] map a label
[respectively, a FEC] to a set containing more than one NHLFE may be
useful if, e.g., it is desired to do load balancing over multiple
equal-cost paths."
In accordance with this, the present specification allows that an
incoming label [respectively FEC] may be mapped, for Diff-Serv
purposes, to multiple NHLFEs (for instance where different NHLFEs
correspond to egress labels supporting different sets of PHBs). When
a label [respectively FEC] maps to multiple NHLFEs, the Diff-Serv
LSR MUST choose one of the NHLFEs whose Diff-Serv Context indicates
that it supports the Outgoing PHB of the forwarded packet.
When a label [respectively FEC] maps to multiple NHLFEs which
supports the Outgoing PHB, the procedure for choosing one among
those is outside the scope of this document. This situation may be
encountered where it is desired to do load balancing of a Behavior
Aggregate over multiple LSPs. In such situations, in order to
respect ordering constraints, all packets of a given microflow MUST
be transported over the same LSP.
2.5 Encoding Diff-Serv Information Into Encapsulation Layer
This stage determines how to encode the fields which convey Diff-
Serv information in the transmitted packet (e.g. MPLS Shim EXP, ATM
CLP, Frame Relay DE, 802.1 User_Priority).
2.5.1 Encoding Diff-Serv Information Into Transmitted Label Entry
Sections 3.5 and 4.5 provide the details on how to perform Diff-Serv
information encoding into a given transmitted label stack entry
and/or transmitted MPLS encapsulation information depending on the
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MPLS Support of Diff-Serv February 2001
corresponding outgoing LSP type and depending on the MPLS
encapsulation.
Section 2.6 provides the details of which label stack entry to
perform Diff-Serv information encoding into depending on the
supported Diff-Serv tunneling mode.
2.5.2 Encoding Diff-Serv Information Into Transmitted IP Header
To perform Diff-Serv Information Encoding into the transmitted
packet IP header, this stage operates exactly as with a non-MPLS IP
Diff-Serv Router and encodes the DSCP of the Outgoing PHB into the
DS field.
Section 2.6 provides the details of when Diff-Serv Information
Encoding is to be performed into transmitted IP header depending on
the supported Diff-Serv tunneling mode.
2.6 Diff-Serv Tunneling Models over MPLS
2.6.1 Diff-Serv Tunneling Models
[DIFF_TUNNEL] considers the interaction of Differentiated Services
with IP tunnels of various forms. MPLS LSPs are not a form of "IP
tunnels" since the MPLS encapsulating header does not contain an IP
header and thus MPLS LSPs are not considered in [DIFF_TUNNEL].
However, although not a form of "IP tunnel", MPLS LSPs are a form of
"tunnel".
From the Diff-Serv standpoint, LSPs share a lot of characteristics
with IP Tunnels:
- Intermediate nodes (i.e. Nodes somewhere along the LSP span)
only see and operate on the "outer" Diff-Serv information.
- LSPs are unidirectional.
- The "outer" Diff-Serv information can be modified at any
intermediate nodes.
However, from the Diff-Serv standpoint, LSPs also have a
distinctive property compared to IP Tunnels:
- There is generally no behavior analogous to Penultimate Hop
Popping (PHP) used with IP Tunnels. Furthermore, PHP results in
the "outer" Diff-Serv information associated with the LSP not
being visible to the LSP egress. In situations where this
information is not meaningful at the LSP Egress, this is
obviously not an issue at all. In situations where this
information is meaningful at the LSP Egress, then it must
somehow be carried in some other means.
The two conceptual models for Diff-Serv tunneling over IP Tunnels
defined in [DIFF_TUNNEL] are applicable and useful to Diff-Serv over
MPLS but their respective detailed operations is somewhat different
over MPLS. These two models are the Pipe Model and the Uniform
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MPLS Support of Diff-Serv February 2001
Model. Their operations over MPLS are specified in the following
sections. Discussion and definition of alternative tunneling models
are outside the scope of this specification.
2.6.2 Pipe Model
With the Pipe Model, MPLS tunnels (aka LSPs) are used to hide the
intermediate MPLS nodes between LSP Ingress and Egress from the
Diff-Serv perspective.
In this model, tunneled packets must convey two meaningful pieces of
Diff-Serv information:
- the Diff-Serv information which is meaningful to intermediate
nodes along the LSP span including the LSP Egress (which we
refer to as the "LSP Diff-Serv Information"). This LSP Diff-Serv
Information is not meaningful beyond the LSP Egress: Whether
Traffic Conditioning at intermediate nodes on the LSP span
affects the LSP Diff-Serv information or not, this updated Diff-
Serv information is not considered meaningful beyond the LSP
Egress and is ignored.
- the Diff-Serv information which is meaningful beyond the LSP
Egress (which we refer to as the "Tunneled Diff-Serv
Information"). This information is to be conveyed by the LSP
Ingress to the LSP Egress. This Diff-Serv information is not
meaningful to the intermediate nodes on the LSP span.
Operation of the Pipe Model without PHP is illustrated below:
========== LSP =============================>
---Swap--(M)--...--Swap--(M)--Swap----
/ (outer header) \
(M) (M)
/ \
>--(m)-Push.................(m).....................Pop--(m)-->
I (inner header) E (M*)
(M) represents the "LSP Diff-Serv information"
(m) represents the "Tunneled Diff-Serv information"
(*) The LSP Egress considers the LSP Diff-Serv information received
in the outer header (i.e. before the pop) in order to apply its
Diff-Serv forwarding treatment (i.e. actual PHB)
I represents the LSP ingress node
E represents the LSP egress node
With the Pipe Model, the "LSP Diff-Serv Information" needs to be
conveyed to LSP Egress so that it applies its forwarding treatment
based on it. The "Tunneled Diff-Serv information" also needs to be
conveyed to the LSP Egress so it can be conveyed further downstream.
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Since both Diff-Serv information need to be conveyed to the LSP
Egress, the Pipe Model operates only without PHP.
The Pipe Model is particularly appropriate to environments in which:
- the cloud upstream of the incoming interface of the LSP Ingress
and the cloud downstream of the outgoing interface of the LSP
Egress are in Diff-Serv domains which use a common set of Diff-
Serv service provisioning policies and PHB definitions, while
the LSP spans one (or more) Diff-Serv domain(s) which use(s) a
different set of Diff-Serv service provisioning policies and PHB
definitions
- the outgoing interface of the LSP Egress is in the (last) Diff-
Serv domain spanned by the LSP.
As an example, consider the case where a service provider is
offering an MPLS VPN service (see [MPLS_VPN] for an example of MPLS
VPN architecture) including Diff-Serv differentiation. Say that a
collection of sites are interconnected via such an MPLS VPN service.
Now say that this collection of sites are managed under a common
administration and are also supporting Diff-Serv service
differentiation. If the VPN site administration and the Service
Provider are not sharing the exact same Diff-Serv policy (for
instance not supporting the same number of PHBs), then operation of
Diff-Serv in the Pipe Model over the MPLS VPN service would allow
the VPN Sites Diff-Serv policy to operate consistently throughout
the ingress VPN Site and Egress VPN Site and transparently over the
Service Provider Diff-Serv domain. It may be useful to view such
LSPs as linking the Diff-Serv domains at their endpoints into a
single Diff-Serv region by making these endpoints virtually
contiguous even though they may be physically separated by
intermediate network nodes.
The Pipe Model MUST be supported.
For support of the Pipe Model over a given LSP without PHP, an LSR
performs the Incoming PHB Determination and the Diff-Serv
information Encoding in the following manner:
- when receiving an unlabelled packet, the LSR performs Incoming
PHB Determination considering the received IP Header.
- when receiving a labeled packet, the LSR performs Incoming PHB
Determination considering the outer label entry in the received
label stack. In particular, when a pop operation is to be
performed for the considered LSP, the LSR performs Incoming PHB
Determination BEFORE the pop.
- when performing a push operation for the considered LSP, the
LSR:
o encodes Diff-Serv Information corresponding to the
OUTGOING PHB in the transmitted label entry corresponding
to the pushed label.
o encodes Diff-Serv Information corresponding to the
INCOMING PHB in the encapsulated header (swapped label
entry or IP header).
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MPLS Support of Diff-Serv February 2001
- when performing a swap-only operation for the considered LSP,
the LSR encodes Diff-Serv Information in the transmitted label
entry that contains the swapped label
- when performing a pop operation for the considered LSP, the LSR
does not perform Encoding of Diff-Serv Information into the
header exposed by the pop operation (i.e. the LSR leaves the
exposed header "as is").
2.6.2.1 Short Pipe Model
The Short Pipe Model is an optional variation over the Pipe Model
described above. The only difference is that, with the Short Pipe
Model, the Diff-Serv forwarding treatment at the LSP Egress is
applied based on the "Tunneled Diff-Serv Information" (i.e. Diff-
Serv information conveyed in the encapsulated header) rather than on
the "LSP Diff-Serv information" (i.e. Diff-Serv information conveyed
in the encapsulating header).
Operation of the Short Pipe Model without PHP is illustrated below:
========== LSP =============================>
---Swap--(M)--...--Swap--(M)--Swap----
/ (outer header) \
(M) (M)
/ \
>--(m)-Push.................(m).....................Pop--(m)-->
I (inner header) E
(M) represents the "LSP Diff-Serv information"
(m) represents the "Tunneled Diff-Serv information"
I represents the LSP ingress node
E represents the LSP egress node
Since the LSP Egress applies its forwarding treatment based on the
"Tunneled Diff-Serv Information", the "LSP Diff-Serv information"
does not need to be conveyed by the penultimate node to the LSP
Egress. Thus the Short Pipe Model can also operate with PHP.
Operation of the Short Pipe Model with PHP is illustrated below:
=========== LSP ============================>
---Swap--(M)--...--Swap------
/ (outer header) \
(M) (M)
/ \
>--(m)-Push.................(m).............Pop-(m)--E--(m)-->
I (inner header) P (M*)
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MPLS Support of Diff-Serv February 2001
(M) represents the "LSP Diff-Serv information"
(m) represents the "Tunneled Diff-Serv information"
(*) The Penultimate LSR considers the LSP Diff-Serv information
received in the outer header (i.e. before the pop) in order to
apply its Diff-Serv forwarding treatment (i.e. actual PHB)
I represents the LSP ingress node
P represents the LSP penultimate node
E represents the LSP egress node
The Short Pipe Model is particularly appropriate to environments in
which:
- the cloud upstream of the incoming interface of the LSP Ingress
and the cloud downstream of the outgoing interface of the LSP
Egress are in Diff-Serv domains which use a common set of Diff-
Serv service provisioning policies and PHB definitions, while
the LSP spans one (or more) Diff-Serv domain(s) which use(s) a
different set of Diff-Serv service provisioning policies and PHB
definitions
- the outgoing interface of the LSP Egress is in the same Diff-
Serv domain as the cloud downstream of it.
Since each outgoing interface of the LSP Egress is in the same Diff-
Serv domain as the cloud downstream of it, each outgoing interface
may potentially be in a different Diff-Serv domain, and the LSP
Egress needs to be configured with awareness of every corresponding
Diff-Serv policy. This operational overhead is justified in some
situations where the respective downstream Diff-Serv policies are
better suited to offering service differentiation over each egress
interface than the common Diff-Serv policy used on the LSP span. An
example of such a situation is where a Service Provider offers an
MPLS VPN service and where some VPN users request that their own VPN
Diff-Serv policy be applied to control service differentiation on
the dedicated link from the LSP Egress to the destination VPN site,
rather than the Service Provider's Diff-Serv policy.
The Short Pipe Model MAY be supported.
For support of the Short Pipe Model over a given LSP without PHP, an
LSR performs the Incoming PHB Determination and the Diff-Serv
information Encoding in the same manner as with the Pipe Model with
the following exception:
- when receiving a labeled packet, the LSR performs Incoming PHB
Determination considering the header (label entry or IP header)
which is used to do the actual forwarding. In particular, when a
pop operation is to be performed for the considered LSP, the LSR
performs Incoming PHB Determination AFTER the pop.
For support of the Short Pipe Model over a given LSP with PHP, an
LSR performs Incoming PHB Determination and Diff-Serv information
Encoding in the same manner as without PHP with the following
exceptions:
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MPLS Support of Diff-Serv February 2001
- the Penultimate LSR performs Incoming PHB Determination
considering the outer label entry in the received label stack.
In other words, when a pop operation is to be performed for the
considered LSP, the Penultimate LSR performs Incoming PHB
Determination BEFORE the pop.
Note that the behavior of the Penultimate LSR in the Short Pipe Mode
with PHP, is identical to the behavior of the LSP Egress in the Pipe
Mode (necessarily without PHP).
2.6.3 Uniform Model
With the Uniform Model, MPLS tunnels (aka LSPs) are viewed as
artifacts of the end-to-end path from the Diff-Serv standpoint. MPLS
Tunnels may be used for forwarding purposes but have no significant
impact on Diff-Serv. In this model, any packet contains exactly one
piece of Diff-Serv information which is meaningful and is always
encoded in the outer most label entry (or in the IP DSCP where the
IP packet is transmitted unlabelled for instance at the egress of
the LSP). Any Diff-Serv information encoded somewhere else (e.g. in
deeper label entries) is of no significance to intermediate nodes or
to the tunnel egress and is ignored. If Traffic Conditioning at
intermediate nodes on the LSP span affects the "outer" Diff-Serv
information, the updated Diff-Serv information is the one considered
meaningful at the egress of the LSP.
Operation of the Uniform Model without PHP is illustrated below:
========== LSP =============================>
---Swap--(M)--...-Swap--(M)--Swap----
/ (outer header) \
(M) (M)
/ \
>--(M)--Push...............(x).......................Pop--(M)->
I (inner header) E
(M) represents the Meaningful Diff-Serv information encoded in the
corresponding header.
(x) represents non-meaningful Diff-Serv information.
I represents the LSP ingress node
E represents the LSP egress node
Operation of the Uniform Model with PHP is illustrated below :
========== LSP =========================>
---Swap-(M)-...-Swap------
/ (outer header) \
(M) (M)
/ \
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MPLS Support of Diff-Serv February 2001
>--(M)--Push..............(x)............Pop-(M)--E--(M)->
I (inner header) P
(M) represents the Meaningful Diff-Serv information encoded in the
corresponding header.
(x) represents non-meaningful Diff-Serv information.
I represents the LSP ingress node
P represents the LSP penultimate node
E represents the LSP egress node
The Uniform Model for Diff-Serv over MPLS is such that, from the
Diff-Serv perspective, operations are exactly identical to the
operations if MPLS was not used. In other words, MPLS is entirely
transparent to the Diff-Serv operations.
Use of the Uniform Model allows LSPs to span Diff-Serv domain
boundaries without any other measure in place than an inter-domain
Traffic Conditioning Agreement at the physical boundary between the
Diff-Serv domains and operating exclusively on the "outer" header,
since the meaningful Diff-Serv information is always visible and
modifiable in the outmost label entry.
The Uniform Model MAY be supported.
For support of the Uniform Model over a given LSP, an LSR performs
Incoming PHB Determination and Diff-Serv information Encoding in the
following manner:
- when receiving an unlabelled packet, the LSR performs Incoming
PHB Determination considering the received IP Header.
- when receiving a labeled packet, the LSR performs Incoming PHB
Determination considering the outer label entry in the received
label stack. In particular, when a pop operation is to be
performed for the considered LSP, the LSR performs Incoming PHB
Determination BEFORE the pop.
- when performing a push operation for the considered LSP, the LSR
encodes Diff-Serv Information in the transmitted label entry
corresponding to the pushed label. The Diff-Serv Information
encoded in the encapsulated header (swapped label entry or IP
Header) is of no importance.
- when performing a swap-only operation for the considered LSP,
the LSR encodes Diff-Serv Information in the transmitted label
entry that contains the swapped label.
- when PHP is used, the Penultimate LSR needs to be aware of the
"Set of PHB-->Encaps mappings" for the label corresponding to
the exposed header (or the PHB-->DSCP mapping) in order to
perform Diff-Serv Information Encoding. Methods for providing
this mapping awareness are outside the scope of this
specification. As an example, the "PHB-->DSCP mapping" may be
locally configured. As another example, in some environments, it
may be appropriate for the Penultimate LSR to assume that the
"Set of PHB-->Encaps mappings" to be used for the outgoing label
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MPLS Support of Diff-Serv February 2001
in the exposed header is the "Set of PHB-->Encaps mappings" that
would be used by the LSR if the LSR was not doing PHP.
Note also that this specification assumes that the Penultimate
LSR does not perform label swapping over the label entry exposed
by the pop operation (and in fact that it does not even look at
the exposed label). Consequently, restrictions may apply to the
Diff-Serv Information Encoding that can be performed by the
Penultimate LSR. For example, this specification does not allow
situations where the Penultimate LSR pops a label corresponding
to an E-LSP supporting two PSCs, while the header exposed by the
pop contains label values for two L-LSPs each supporting one
PSC, since the Diff-Serv Information Encoding would require
selecting one label or the other.
Note that LSR behaviors for the Pipe , the Short Pipe and the
Uniform Model only differ when doing a push or a pop. Thus,
Intermediate LSRs which perform swap only operations for an LSP,
behave exactly in the same way regardless of whether they are
behaving in the Pipe, Short Pipe or the Uniform model. With a Diff-
Serv implementation supporting multiple Tunneling Models, only LSRs
behaving as LSP Ingress, Penultimate LSR or LSP Egress need to be
configured to operate in a particular Model. Signaling to associate
a Diff-Serv tunneling model on a per-LSP basis is out of the scope
of this specification.
2.6.4 Hierarchy
Through the label stack mechanism, MPLS allows LSP tunneling to nest
to any depth. We observe that with such nesting, the push of level
N+1 takes place on a subsequent (or the same) LSR to the LSR doing
the push for level N, while the pop of level N+1 takes place on a
previous (or the same) LSR to the LSR doing the pop of level N. For
a given level N LSP, the Ingress LSR doing the push and the LSR
doing the pop (Penultimate LSR or LSP Egress) must operate in the
same Tunneling Model (i.e. Pipe, Short Pipe or Uniform). However,
there is no requirement for consistent tunneling models across
levels so that LSPs at different levels may be operating in
different Tunneling Models.
Hierarchical operations is illustrated below in the case of two
levels of tunnels:
+--------Swap--...---+
/ (outmost header) \
/ \
Push(2).................(2)Pop
/ (outer header) \
/ \
>>---Push(1)........................(1)Pop-->>
(inner header)
(1) Tunneling Model 1
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MPLS Support of Diff-Serv February 2001
(2) Tunneling Model 2
Tunneling Model 2 may be the same as or may be different to
Tunneling Model 1.
For a given LSP of level N, the LSR must perform the Incoming PHB
Determination and the Diff-Serv information Encoding as specified in
section 2.6.2, 2.6.2.1 and 2.6.3 according to the Tunneling Model of
this level N LSP and independently of the Tunneling Model of other
level LSPs.
3. Detailed Operations of E-LSPs
3.1 E-LSP Definition
E-LSPs are defined in section 1.2.
Within a given MPLS Diff-Serv domain, all the E-LSPs relying on the
pre-configured mapping are capable of transporting the same common
set of 8, or fewer, BAs. Each of those E-LSPs may actually transport
this full set of BAs or any arbitrary subset of it.
For a given FEC, two given E-LSPs using signaled EXP<-->PHB mapping
can support the same or different sets of Ordered Aggregates.
3.2 Populating the `Encaps-->PHB mapping' for an incoming E-LSP
This section defines how the `Encaps-->PHB mapping' of the Diff-Serv
Context is populated for an incoming E-LSP in order to allow
Incoming PHB determination.
The `Encaps-->PHB mapping' for an E-LSP is always of the form
`EXP-->PHB mapping'.
If the label corresponds to an E-LSP for which no EXP<-->PHB mapping
has been explicitly signaled at LSP setup, the `EXP-->PHB mapping'
is populated based on the Preconfigured EXP<-->PHB Mapping which is
discussed below in section 3.2.1.
If the label corresponds to an E-LSP for which an EXP<-->PHB mapping
has been explicitly signaled at LSP setup, the `EXP-->PHB mapping'
is populated as per the signaled EXP<-->PHB mapping.
3.2.1 Preconfigured EXP<-->PHB mapping
LSRs supporting E-LSPs which use the preconfigured EXP<-->PHB
mapping must allow local configuration of this EXP<-->PHB mapping.
This mapping applies to all the E-LSPs established on this LSR
without a mapping explicitly signaled at set-up time.
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MPLS Support of Diff-Serv February 2001
The preconfigured EXP<-->PHB mapping must either be consistent at
every E-LSP hop throughout the MPLS Diff-Serv domain spanned by the
LSP or appropriate remarking of the EXP field must be performed by
the LSR whenever a different preconfigured mapping is used on the
ingress and egress interfaces.
In case, the preconfigured EXP<-->PHB mapping has not actually been
configured by the Network Administrator, the LSR should use a
default preconfigured EXP<-->PHB mapping which maps all EXP values
to the Default PHB.
3.3 Incoming PHB Determination On Incoming E-LSP
This section defines how Incoming PHB Determination is carried out
when the considered label entry in the received label stack
corresponds to an E-LSP. This requires that the `Encaps-->PHB
mapping' is populated as defined in section 3.2.
When considering a label entry corresponding to an incoming E-LSP
for Incoming PHB Determination, the LSR:
- determines the EXP-->PHB mapping by looking up the
`Encaps-->PHB mapping' of the Diff-Serv Context associated in
the ILM with the considered incoming E-LSP label.
- determines the incoming PHB by looking up the EXP field of the
considered label entry in the EXP-->PHB mapping table.
3.4 Populating the `Set of PHB-->Encaps mappings' for an outgoing E-LSP
This section defines how the `Set of PHB-->Encaps mappings' of the
Diff-Serv Context is populated at label setup for an outgoing E-LSP
in order to allow Encoding of Diff-Serv information in the
Encapsulation Layer.
3.4.1 `PHB-->EXP mapping'
An outgoing E-LSP must always have a `PHB-->EXP mapping' as part of
the `Set of PHB-->Encaps mappings' of its Diff-Serv Context.
If the label corresponds to an E-LSP for which no EXP<-->PHB mapping
has been explicitly signaled at LSP setup, this `PHB-->EXP mapping'
is populated based on the Preconfigured EXP<-->PHB Mapping which is
discussed above in section 3.2.1.
If the label corresponds to an E-LSP for which an EXP<-->PHB mapping
has been explicitly signaled at LSP setup, the `PHB-->EXP mapping'
is populated as per the signaled EXP<-->PHB mapping.
3.4.2 `PHB-->CLP mapping'
If the LSP is egressing over an ATM interface which is not label
switching controlled, then one `PHB-->CLP mapping' is added to the
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MPLS Support of Diff-Serv February 2001
`Set of PHB-->Encaps mappings' for this outgoing LSP. This
`PHB-->CLP mapping' is populated in the following way:
- it is a function of the PHBs supported on this LSP, and may use
the relevant mapping entries for these PHBs from the
Default PHB-->CLP Mapping defined in section 3.4.2.1. Other
mappings than the one defined in section 3.4.2.1 may be used. In
particular, if a mapping from PHBs to CLP is standardized in the
future for operations of Diff-Serv over ATM, such standardized
mapping may then be used.
For example if the outgoing label corresponds to an LSP supporting
the AF1 PSC , then the `PHB-->CLP mapping' may be populated with:
PHB CLP Field
AF11 ----> 0
AF12 ----> 1
AF13 ----> 1
EF ----> 0
Notice that in this case the `Set of PHB-->Encaps mappings' contains
both a `PHB-->EXP mapping' and a `PHB-->CLP mapping'.
3.4.2.1 Default PHB-->CLP Mapping
PHB CLP Bit
DF ----> 0
CSn ----> 0
AFn1 ----> 0
AFn2 ----> 1
AFn3 ----> 1
EF ----> 0
3.4.3 `PHB-->DE mapping'
If the LSP is egressing over a Frame Relay interface which is not
label switching controlled, one `PHB-->DE mapping' is added to the
`Set of PHB-->Encaps mappings' for this outgoing LSP and is
populated in the following way:
- it is a function of the PHBs supported on this LSP, and may use
the relevant mapping entries for these PHBs from the Default
PHB-->DE Mapping defined in section 3.4.3.1. Other mappings than
the one defined in section 3.4.3.1 may be used. In particular,
if a mapping from PHBs to DE is standardized in the future for
operations of Diff-Serv over Frame Relay, such standardized
mapping may then be used.
Notice that in this case the `Set of PHB-->Encaps mappings' contains
both a `PHB-->EXP mapping' and a `PHB-->DE mapping'.
3.4.3.1 Default PHB-->DE Mapping
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MPLS Support of Diff-Serv February 2001
PHB DE Bit
DF ----> 0
CSn ----> 0
AFn1 ----> 0
AFn2 ----> 1
AFn3 ----> 1
EF ----> 0
3.4.4 `PHB-->802.1 mapping'
If the LSP is egressing over a LAN interface on which multiple 802.1
Traffic Classes are supported as per [IEEE_802.1], then one
`PHB-->802.1 mapping' is added to the `Set of PHB-->Encaps mappings'
for this outgoing LSP. This `PHB-->802.1 mapping' is populated in
the following way:
- it is a function of the PHBs supported on this LSP, an uses the
relevant mapping entries for these PHBs from the Preconfigured
PHB-->802.1 Mapping defined in section 3.4.4.1.
Notice that the `Set of PHB-->Encaps mappings' then contains both a
`PHB-->EXP mapping' and a `PHB-->802.1 mapping'.
3.4.4.1 Preconfigured `PHB-->802.1 Mapping'
At the time of producing this specification, there are no
standardized mapping from PHBs to 802.1 Traffic Classes.
Consequently, an LSR supporting multiple 802.1 Traffic Classes over
LAN interfaces must allow local configuration of a `PHB-->802.1
Mapping'. This mapping applies to all the outgoing LSPs established
by the LSR on such LAN interfaces.
3.5 Encoding Diff-Serv information into Encapsulation Layer On Outgoing
E-LSP
This section defines how to encode Diff-Serv information into the
MPLS encapsulation Layer for a given transmitted label entry
corresponding to an outgoing E-LSP. This requires that the `Set of
PHB-->Encaps mappings' is populated as defined in section 3.4.
The LSR first determines the `Set of PHB-->Encaps mappings' of the
Diff-Serv Context associated with the corresponding label in the
NHLFE.
3.5.1 `PHB-->EXP mapping'
If the `Set of PHB-->Encaps mappings' contains a mapping of the form
`PHB-->EXP mapping', then the LSR:
- determines the value to be written in the EXP field of the
corresponding level label entry by looking up the "outgoing PHB"
in this PHB-->EXP mapping table.
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3.5.2 `PHB-->CLP mapping'
If the `Set of PHB-->Encaps mappings' contains a mapping of the form
`PHB-->CLP mapping', then the LSR:
- determines the value to be written in the CLP field of the ATM
encapsulation header, by looking up the "outgoing PHB" in this
PHB-->CLP mapping table.
3.5.3 `PHB-->DE mapping'
If the `Set of PHB-->Encaps mappings' contains a mapping of the form
`PHB-->DE mapping', then the LSR:
- determines the value to be written in the DE field of the Frame
Relay encapsulation header, by looking up the "outgoing PHB" in
this PHB-->DE mapping table.
3.5.4 `PHB-->802.1 mapping'
If the `Set of PHB-->Encaps mappings' contains a mapping of the form
`PHB-->802.1 mapping', then the LSR:
- determines the value to be written in the User_Priority field of
the Tag Control Information of the 802.1 encapsulation header
[IEEE_802.1], by looking up the "outgoing PHB" in this
PHB-->802.1 mapping table.
3.6 E-LSP Merging
In an MPLS domain, two or more LSPs can be merged into one LSP at
one LSR. E-LSPs are compatible with LSP Merging under the following
condition:
E-LSPs can only be merged into one LSP if they support the
exact same set of BAs.
For E-LSPs using signaled EXP<-->PHB mapping, the above merge
condition MUST be enforced by LSRs through explicit checking at
label setup that the exact same set of PHBs is supported on the
merged LSPs.
For E-LSPs using the preconfigured EXP<-->PHB mapping, since the
PHBs supported over an E-LSP is not signaled at establishment time,
an LSR can not rely on signaling information to enforce the above
merge. However all E-LSPs using the preconfigured EXP<-->PHB mapping
are required to support the same set of Behavior Aggregates within a
given MPLS Diff-Serv domain. Thus, merging of E-LSPs using the
preconfigured EXP<-->PHB mapping is allowed within a given MPLS
Diff-Serv domain.
4. Detailed Operation of L-LSPs
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4.1 L-LSP Definition
L-LSPs are defined in section 1.3.
4.2 Populating the `Encaps-->PHB mapping' for an incoming L-LSP
This section defines how the `Encaps-->PHB mapping' of the Diff-Serv
Context is populated at label setup for an incoming L-LSP in order
to allow Incoming PHB determination.
4.2.1 `EXP-->PHB mapping'
If the LSR terminates the MPLS Shim Layer over this incoming L-LSP
and the L-LSP ingresses on an interface which is not ATM nor Frame
Relay, then the `Encaps-->PHB mapping' is populated in the following
way:
- it is actually a `EXP-->PHB mapping'
- this mapping is a function of the PSC which is carried on this
LSP, and must use the relevant mapping entries for this PSC from
the Mandatory EXP/PSC-->PHB Mapping defined in Section 4.2.1.1.
For example if the incoming label corresponds to an L-LSP supporting
the AF1 PSC, then the `Encaps-->PHB mapping' will be populated with:
EXP Field PHB
000 ----> AF11
001 ----> AF12
011 ----> AF13
An LSR supporting L-LSPs over PPP interfaces and LAN interfaces is
an example of LSR terminating the Shim layer over ingress interfaces
which are not ATM nor Frame Relay.
If the LSR terminates the MPLS Shim Layer over this incoming L-LSP
and the L-LSP ingresses on an ATM or Frame Relay interface, then the
`Encaps-->PHB mapping' is populated in the following way:
- it should actually be a `EXP-->PHB mapping'. Alternative
optional ways of populating the `Encaps-->PHB mapping' might be
defined in the future (e.g., using a 'CLP/EXP--> PHB mapping' or
a 'DE/EXP-->PHB mapping') but are outside the scope of this
document.
- when the `Encaps-->PHB mapping' is an `EXP-->PHB mapping', this
`EXP-->PHB mapping' mapping is a function of the PSC which is
carried on the L-LSP, and must use the relevant mapping entries
for this PSC from the Mandatory EXP/PSC-->PHB Mapping defined in
Section 4.2.1.1.
An Edge-LSR of an ATM-MPLS domain or of a FR-MPLS domain is an
example of LSR terminating the shim layer over an ingress ATM/FR
interface.
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4.2.1.1 Mandatory EXP/PSC --> PHB mapping
EXP Field PSC PHB
000 DF ----> DF
000 CSn ----> CSn
000 AFn ----> AFn1
001 AFn ----> AFn2
011 AFn ----> AFn3
000 EF ----> EF
4.2.2 `CLP-->PHB mapping'
If the LSR does not terminate an MPLS Shim Layer over this incoming
label and uses ATM encapsulation (i.e. it is an ATM-LSR), then the
`Encaps-->PHB mapping' for this incoming L-LSP is populated in the
following way:
- it is actually a `CLP-->PHB mapping'
- the mapping is a function of the PSC which is carried on this
LSP, and should use the relevant mapping entries for this PSC
from the Default CLP/PSC-->PHB Mapping defined in Section
4.2.2.1.
For example if the incoming label corresponds to an L-LSP supporting
the AF1 PSC, then the `Encaps-->PHB mapping' should be populated
with:
CLP Field PHB
0 ----> AF11
1 ----> AF12
4.2.2.1 Default CLP/PSC --> PHB Mapping
CLP Bit PSC PHB
0 DF ----> DF
0 CSn ----> CSn
0 AFn ----> AFn1
1 AFn ----> AFn2
0 EF ----> EF
4.2.3 `DE-->PHB mapping'
If the LSR does not terminate an MPLS Shim Layer over this incoming
label and uses Frame Relay encapsulation (i.e. it is a FR-LSR), then
the `Encaps-->PHB mapping' for this incoming L-LSP is populated in
the following way:
- it is actually a `DE-->PHB mapping'
- the mapping is a function of the PSC which is carried on this
LSP, and should use the relevant mapping entries for this PSC
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from the Default DE/PSC-->PHB Mapping defined in Section
4.2.3.1.
4.2.3.1 Default DE/PSC --> PHB Mapping
DE Bit PSC PHB
0 DF ----> DF
0 CSn ----> CSn
0 AFn ----> AFn1
1 AFn ----> AFn2
0 EF ----> EF
4.3 Incoming PHB Determination On Incoming L-LSP
This section defines how Incoming PHB determination is carried out
when the considered label entry in the received label stack
corresponds to an L-LSP. This requires that the `Encaps-->PHB
mapping' is populated as defined in section 4.2.
When considering a label entry corresponding to an incoming L-LSP
for Incoming PHB Determination, the LSR first determines the
`Encaps-->PHB mapping' associated with -corresponding label.
4.3.1 `EXP-->PHB mapping'
If the `Encaps-->PHB mapping' is of the form `EXP-->PHB mapping',
then the LSR:
- determines the incoming PHB by looking at the EXP field of the
considered label entry and by using the EXP-->PHB mapping.
4.3.2 `CLP-->PHB mapping'
If the `Encaps-->PHB mapping' is of the form `CLP-->PHB mapping',
then the LSR:
- determines the incoming PHB by looking at the CLP field of the
ATM Layer encapsulation and by using the CLP-->PHB mapping.
4.3.3 `DE-->PHB mapping'
If the `Encaps-->PHB mapping' is of the form `DE-->PHB mapping',
then the LSR:
- determines the incoming PHB by looking at the DE field of the
Frame Relay encapsulation and by using the DE-->PHB mapping.
4.4 Populating the `Set of PHB-->Encaps mappings' for an outgoing L-LSP
This section defines how the `Set of PHB-->Encaps mappings' of the
Diff-Serv Context is populated at label setup for an outgoing L-LSP
in order to allow Encoding of Diff-Serv Information.
4.4.1 `PHB-->EXP mapping'
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If the LSR uses an MPLS Shim Layer over this outgoing L-LSP, then
one `PHB-->EXP mapping' is added to the `Set of
PHB-->Encaps mappings' for this outgoing
L-LSP. This `PHB-->EXP mapping' is populated in the following way:
- it is a function of the PSC supported on this LSP, and must use
the mapping entries relevant for this PSC from the Mandatory
PHB-->EXP Mapping defined in section 4.4.1.1.
For example if the outgoing label corresponds to an L-LSP supporting
the AF1 PSC, then the following `PHB-->EXP mapping' is added into
the `Set of PHB-->Encaps mappings':
PHB EXP Field
AF11 ----> 000
AF12 ----> 001
AF13 ----> 011
4.4.1.1 Mandatory PHB-->EXP Mapping
PHB EXP Field
DF ----> 000
CSn ----> 000
AFn1 ----> 000
AFn2 ----> 001
AFn3 ----> 011
EF ----> 000
4.4.2 `PHB-->CLP mapping'
If the L-LSP is egressing on an ATM interface (i.e. it is an ATM-LSR
or it is a frame-based LSR sending packets on an LC-ATM interface or
on an ATM interface which is not label switching controlled), then
one `PHB-->CLP mapping' is added to the `Set of PHB-->Encaps
mappings' for this outgoing L-LSP.
If the L-LSP is egressing over an ATM interface which is not label-
controlled, the `PHB-->CLP mapping' is populated as per section
3.4.2.
If the L-LSP is egressing over an LC-ATM interface, the `PHB-->CLP
mapping' is populated in the following way:
- it is a function of the PSC supported on this LSP, and should
use the relevant mapping entries for this PSC from the Default
PHB-->CLP Mapping defined in section 3.4.2.1.
Notice that if the LSR is a frame-based LSR supporting an L-LSP
egressing over an ATM interface, then the `Set of PHB-->Encaps
mappings' contains both a `PHB-->EXP mapping' and a `PHB-->CLP
Le Faucheur et. al 27
MPLS Support of Diff-Serv February 2001
mapping'. If the LSR is an ATM-LSR supporting an L-LSP, then the
`Set of PHB-->Encaps mappings' only contains a `PHB-->CLP mapping'.
4.4.3 `PHB-->DE mapping'
If the L-LSP is egressing over a Frame Relay interface (i.e. it is
an LSR sending packets on an LC-FR interface or on a Frame Relay
interface which is not label switching controlled), one `PHB-->DE
mapping' is added to the `Set of PHB-->Encaps mappings' for this
outgoing L-LSP.
If the L-LSP is egressing over a FR interface which is not label
switching controlled, the `PHB-->DE mapping' is populated as per
section 3.4.3.
If the L-LSP is egressing over an LC-FR interface, the `PHB-->DE
mapping' is populated in the following way:
- it is a function of the PSC supported on this LSP, and should
use the relevant mapping entries for this PSC from the Default
PHB-->DE Mapping defined in section 3.4.3.1.
Notice that if the LSR is an Edge-LSR supporting an L-LSP egressing
over a LC-FR interface, then the `Set of PHB-->Encaps mappings'
contains both a `PHB-->EXP mapping' and a `PHB-->DE mapping'. If the
LSR is a FR-LSR supporting an L-LSP, then the `Set of PHB-->Encaps
mappings' only contains a `PHB-->DE mapping'.
4.4.4 `PHB-->802.1 mapping'
If the LSP is egressing over a LAN interface on which multiple 802.1
Traffic Classes are supported as defined in [IEEE_802.1], then one
`PHB-->802.1 mapping' is added as per section 3.4.4.
4.5 Encoding Diff-Serv Information into Encapsulation Layer on Outgoing
L-LSP
This section defines how to encode Diff-Serv information into the
MPLS encapsulation Layer for a transmitted label entry corresponding
to an outgoing L-LSP. This requires that the `Set of PHB-->Encaps
mappings' is populated as defined in section 4.4.
The LSR first determines the `Set of PHB-->Encaps mappings' of the
Diff-Serv Context associated with the corresponding label in the
NHLFE and then performs corresponding encoding as specified in
sections 3.5.1, 3.5.2, 3.5.3 and 3.5.4.
4.6 L-LSP Merging
In an MPLS domain, two or more LSPs can be merged into one LSP at
one LSR. L-LSPs are compatible with LSP Merging under the following
condition:
Le Faucheur et. al 28
MPLS Support of Diff-Serv February 2001
L-LSPs can only be merged into one L-LSP if they support the
same PSC.
The above merge condition MUST be enforced by LSRs through explicit
checking at label setup that the same PSC is supported on the merged
LSPs.
Note that when L-LSPs merge, the bandwidth that is available for the
PSC downstream of the merge point must be sufficient to carry the
sum of the merged traffic. This is particularly important in the
case of EF traffic. This can be ensured in multiple ways (for
instance via provisioning, or via bandwidth signaling and explicit
admission control).
5. RSVP Extension for Diff-Serv Support
The MPLS architecture does not assume a single label distribution
protocol. [RSVP_MPLS_TE] defines the extension to RSVP for
establishing label switched paths (LSPs) in MPLS networks. This
section specifies the extensions to RSVP, beyond those defined in
[RSVP_MPLS_TE], to establish label switched path (LSPs) supporting
Differentiated Services in MPLS networks.
5.1 Diff-Serv related RSVP Messages Format
One new RSVP Object is defined in this document: the DIFFSERV
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 DIFFSERV Object in Path messages used to
establish LSP Tunnels in accordance with [RSVP_MPLS_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_MPLS_TE] for support of establishment
of LSP Tunnels via RSVP are also applicable to the establishment of
LSP Tunnels supporting Diff-Serv: for instance, only unicast LSPs
are supported and Multicast LSPs are for further study.
This new DIFFSERV 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.
The DIFFSERV Object is optional for support of LSP Tunnels as
defined in [RSVP_MPLS_TE]. A Diff-Serv capable LSR supporting E-LSPs
using the preconfigured EXP<-->PHB mapping in compliance with this
specification MAY support the DIFFSERV Object. A Diff-Serv capable
LSR supporting E-LSPs using a signaled EXP<-->PHB mapping in
compliance with this specification MUST support the DIFFSERV Object.
A Diff-Serv capable LSR supporting L-LSPs in compliance with this
specification MUST support the DIFFSERV Object.
Le Faucheur et. al 29
MPLS Support of Diff-Serv February 2001
5.1.1 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> ]
[ <POLICY_DATA> ... ]
[ <sender descriptor> ]
<sender descriptor> ::= <SENDER_TEMPLATE> [ <SENDER_TSPEC> ]
[ <ADSPEC> ]
[ <RECORD_ROUTE> ]
5.2 DIFFSERV Object
The DIFFSERV object formats are shown below. Currently there are two
possible C_Types. Type 1 is a DIFFSERV object for an E-LSP. Type 2
is a DIFFSERV object for an L-LSP.
5.2.1. DIFFSERV object for an E-LSP:
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 | MAPnb |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAP (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// ... //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAP (MAPnb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved : 28 bits
This field is reserved. It must be set to zero on transmission
and must be ignored on receipt.
MAPnb : 4 bits
Indicates the number of MAP entries included in the DIFFSERV
Object. This can be set to any value from 0 to 8.
MAP : 32 bits
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MPLS Support of Diff-Serv February 2001
Each MAP entry defines the mapping between one EXP field value
and one PHB. The MAP entry has the following format:
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 | EXP | PHBID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved : 13 bits
This field is reserved. It must be set to zero on
transmission and must be ignored on receipt.
EXP : 3 bits
This field contains the value of the EXP field for the
EXP<-->PHB mapping defined in this MAP entry.
PHBID : 16 bits
This field contains the PHBID of the PHB for the
EXP<-->PHB mapping defined in this MAP entry. The PHBID
is encoded as specified in section 2 of [PHBID].
5.2.2 DIFFSERV object for an L-LSP:
class = TBD, C_Type = 2 (class num is the same as DIFFSERV object
for E-LSP))
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 | PSC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved : 16 bits
This field is reserved. It must be set to zero on transmission
and must be ignored on receipt.
PSC : 16 bits
The PSC indicates a PHB Scheduling Class to be supported by the
LSP. The PSC is encoded as specified in section 2 of [PHBID]:
- Where the PSC comprises a single PHB defined by standards
action, the encoding for the PSC is the encoding for this
single PHB. It is the recommended DSCP value for that PHB,
left-justified in the 16-bit field, with bits 6 through 15 set
to zero.
- Where the PSC comprises multiple PHBs defined by standards
action, the PSC encoding is the encoding for this set of PHB.
It is the smallest numerical value of the recommended DSCP for
the various PHBs in the PSC, left-justified in the 16 bit
field, with bits 6 through 13 and bit 15 set to zero and with
bit 14 set to one.
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MPLS Support of Diff-Serv February 2001
For instance, the encoding of the EF PSC is :
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 0 1 1 1 0|0 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For instance, the encoding of the AF1 PSC is :
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 1 0 1 0|0 0 0 0 0 0 0 0 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.3 Handling DIFFSERV Object
To establish an LSP tunnel with RSVP, the sender creates a Path
message with a session type of LSP_Tunnel_IPv4 and with a
LABEL_REQUEST object as per [RSVP_MPLS_TE].
To establish with RSVP an E-LSP tunnel which uses the Preconfigured
EXP<-->PHB mapping, the sender creates a Path message:
- with a session type of LSP_Tunnel_IPv4,
- with the LABEL_REQUEST object, and
- without the DIFFSERV object.
To establish with RSVP an E-LSP tunnel which uses the Preconfigured
EXP<-->PHB mapping, the sender MAY alternatively create a Path
message:
- with a session type of LSP_Tunnel_IPv4,
- with the LABEL_REQUEST object, and
- with the DIFFSERV object for an E-LSP containing no MAP entries.
To establish with RSVP an E-LSP tunnel which uses a signaled EXP<--
>PHB mapping, the sender creates a Path message :
- with a session type of LSP_Tunnel_IPv4,
- with the LABEL_REQUEST object,
- with the DIFFSERV object for an E-LSP containing one MAP entry
for each EXP value to be supported on this E-LSP.
To establish with RSVP an L-LSP tunnel, the sender creates a Path
message:
- with a session type of LSP_Tunnel_IPv4,
- with the LABEL_REQUEST object,
- with the DIFFSERV object for an L-LSP containing the PHB
Scheduling Class (PSC) supported on this L-LSP.
If a path message contains multiple DIFFSERV objects, only the first
one is meaningful; subsequent DIFFSERV object(s) must be ignored and
not forwarded.
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MPLS Support of Diff-Serv February 2001
Each LSR along the path records the DIFFSERV object, when present,
in its path state block.
If a DIFFSERV object is not present in the Path message, the LSR
SHOULD interpret this as a request for an E-LSP using the
Preconfigured EXP<-->PHB Mapping. However, for backward
compatibility purposes with other non-Diff-Serv Quality of Service
options allowed by [RSVP_MPLS_TE] such as Integrated Services
Controlled Load or Guaranteed Services, the LSR MAY support a
configurable "override option". When this "override option" is
configured, the LSR interprets a path message without a Diff-Serv
object as a request for an LSP with such non-Diff-Serv Quality of
Service.
If a DIFFSERV object for an E-LSP containing no MAP entry is present
in the Path message, the LSR MUST interpret this as a request for an
E-LSP using the Preconfigured EXP<-->PHB Mapping. In particular,
this allows an LSR with the "override option" configured to support
E-LSPs with Preconfigured EXP<-->PHB Mapping simultaneously with
LSPs with non-Diff-Serv Quality of Service.
If a DIFFSERV object for an E-LSP containing at least one MAP entry
is present in the Path message, the LSR MUST interpret this as a
request for an E-LSP with signaled EXP<-->PHB Mapping.
If a DIFFSERV object for an L-LSP is present in the Path message,
the LSR MUST interpret this as a request for an L-LSP.
The destination LSR of an E-LSP or L-LSP responds to the Path
message containing the LABEL_REQUEST object by sending a Resv
message:
- with the LABEL object
- without a DIFFSERV object.
Assuming the label request is accepted and a label is allocated, the
Diff-Serv LSRs (sender, destination, intermediate nodes) must:
- update the Diff-Serv Context associated with the established
LSPs in their ILM/FTN as specified in previous sections
(incoming and outgoing label),
- install the required Diff-Serv forwarding treatment (scheduling
and dropping behavior) for this NHLFE (outgoing label).
An LSR that recognizes the DIFFSERV object and that receives a path
message which contains the DIFFSERV object but which does not
contain a LABEL_REQUEST object or which does not have a session type
of LSP_Tunnel_IPv4, sends a PathErr towards the sender with the
error code `Diff-Serv Error' and an error value of `Unexpected
DIFFSERV object'. Those are defined below in section 5.5.
An LSR receiving a Path message with the DIFFSERV object for E-LSP,
which recognizes the DIFFSERV object but does not support the
particular PHB encoded in one, or more, of the MAP entries, sends a
Le Faucheur et. al 33
MPLS Support of Diff-Serv February 2001
PathErr towards the sender with the error code `Diff-Serv Error' and
an error value of `Unsupported PHB'. Those are defined below in
section 5.5.
An LSR receiving a Path message with the DIFFSERV object for E-LSP,
which recognizes the DIFFSERV object but determines that the
signaled EXP<-->PHB mapping is invalid, sends a PathErr towards the
sender with the error code `Diff-Serv Error' and an error value of
`Invalid EXP<-->PHB mapping'. Those are defined below in section
5.5. The EXP<-->PHB mapping signaled in the DIFFSERV Object for an
E-LSP is invalid when:
- the MAPnb field is not within the range 0 to 8 or
- a given EXP value appears in more than one MAP entry, or
- the PHBID encoding is invalid.
An LSR receiving a Path message with the DIFFSERV object for L-LSP,
which recognizes the DIFFSERV object but does not support the
particular PSC encoded in the PSC field, sends a PathErr towards the
sender with the error code `Diff-Serv Error' and an error value of
`Unsupported PSC'. Those are defined below in section 5.5.
An LSR receiving a Path message with the DIFFSERV object, which
recognizes the DIFFSERV object but that is unable to allocate the
required per-LSP Diff-Serv context sends a PathErr with the error
code "Diff-Serv Error" and the error value "Per-LSP context
allocation failure". Those are defined below in section 5.5.
A Diff-Serv LSR MUST handle the situations where the label request
can not be accepted for other reasons than those already discussed
in this section, in accordance with [RSVP_MPLS_TE] (e.g. reservation
rejected by admission control, a label can not be associated).
5.4 Non-support of the DIFFSERV Object
An LSR that does not recognize the DIFFSERV 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
PathErr with the error code `Unknown object class' toward the
sender.
An LSR that recognize the DIFFSERV object Class-Num but does not
recognize the DIFFSERV 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 L-LSP cannot be established and
possibly take action to retry LSP establishment without the DIFFSERV
object (e.g. attempt to use E-LSPs with Preconfigured EXP<-->PHB
mapping as a fall-back strategy).
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MPLS Support of Diff-Serv February 2001
5.5 Error Codes For Diff-Serv
In the procedures described above, certain errors must be reported
as a `Diff-Serv Error'. The value of the `Diff-Serv Error' error
code is TBD (number to be allocated by IANA)).
The following defines error values for the Diff-Serv Error:
Value Error
1 Unexpected DIFFSERV object
2 Unsupported PHB
3 Invalid EXP<-->PHB mapping
4 Unsupported PSC
5 Per-LSP context allocation failure
5.6 Use of COS Service with E-LSPs and L-LSPs
Both E-LSPs and L-LSPs can be established with bandwidth reservation
or without bandwidth reservation.
To establish an E-LSP or an L-LSP with bandwidth reservation, Int-
Serv's Controlled Load service (or possibly Guaranteed Service) is
used and the bandwidth is signaled in the SENDER_TSPEC (respectively
FLOWSPEC) of the path (respectively Resv) message.
To establish an E-LSP or an L-LSP without bandwidth reservation, the
Class of Service service defined in [RSVP_MPLS_TE] is used.
Note that this specification defines usage of E-LSPs and L-LSPs
for support of the Diff-Serv service only. Regardless of whether the
signaling messages actually indicate an Int-Serv service of COS, GS
or CL and regardless of whether the signaling messages contain a
signaled bandwidth reservation or not, E-LSPs and L-LSPs are defined
here for support of Diff-Serv services. Support of Int-Serv services
over an MPLS Diff-Serv backbone is outside the scope of this
specification.
A Path message containing a COS SENDER_TSPEC and not containing a
DIFFSERV object indicates to a Diff-Serv capable LSR that the LSP to
be established is an E-LSP using the Preconfigured mapping and
without any bandwidth reservation.
A Path message containing a COS SENDER_TSPEC and containing a
DIFFSERV object for E-LSP indicates to a Diff-Serv capable LSR that
the LSP to be established is an E-LSP using a signaled mapping and
without any bandwidth reservation.
A Path message containing a COS SENDER_TSPEC and containing a
DIFFSERV object for L-LSP indicates to a Diff-Serv capable LSR that
the LSP to be established is an L-LSP without any bandwidth
reservation.
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MPLS Support of Diff-Serv February 2001
The above is summarized in the following table:
Path Message LSP type
Service DIFFSERV
Object
GS/CL No E-LSP + preconf mapping + bandw reservation
GS/CL Yes/E-LSP E-LSP + signaled mapping + bandw reservation
GS/CL Yes/L-LSP L-LSP + bandw reservation
COS No E-LSP + preconf mapping + no bandw reservation
COS Yes/E-LSP E-LSP + signaled mapping + no band reservation
COS Yes/L-LSP L-LSP + no bandw reservation
Where:
- GS stands for Guaranteed Service
- CL stands for Controlled Load
- COS stands for COS service
When processing a path (respectively Resv) message for an E-LSP or
an L-LSP using the COS service, a Diff-Serv capable LSR must ignore
the value of the COS field within a COS SENDER_TSPEC (respectively a
COS FLOWSPEC).
6. LDP Extensions for Diff-Serv Support
The MPLS architecture does not assume a single label distribution
protocol. [LDP] defines the Label Distribution Protocol and its
usage for establishment of label switched paths (LSPs) in MPLS
networks. This section specifies the extensions to LDP to establish
label switched path (LSPs) supporting Differentiated Services in
MPLS networks.
One new LDP TLV is defined in this document:
- the Diff-Serv TLV
Detailed description of this TLV is provided below.
The new Diff-Serv TLV is optional with respect to LDP. A Diff-Serv
capable LSR supporting E-LSPs which uses the Preconfigured
EXP<-->PHB mapping in compliance with this specification MAY support
the Diff-Serv TLV. A Diff-Serv capable LSR supporting E-LSPs which
uses the signaled EXP<-->PHB mapping in compliance with this
specification MUST support the Diff-Serv TLV. A Diff-Serv capable
LSR supporting L-LSPs in compliance with this specification MUST
support the Diff-Serv TLV.
6.1 Diff-Serv TLV
The Diff-Serv TLV has the following formats:
Diff-Serv TLV for an E-LSP:
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MPLS Support of Diff-Serv February 2001
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Diff-Serv (0x901) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T| Reserved | MAPnb |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAP (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAP (MAPnb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
T:1 bit
LSP Type. This is set to 0 for an E-LSP
Reserved : 27 bits
This field is reserved. It must be set to zero on transmission
and must be ignored on receipt.
MAPnb : 4 bits
Indicates the number of MAP entries included in the DIFFSERV
Object. This can be set to any value from 1 to 8.
MAP : 32 bits
Each MAP entry defines the mapping between one EXP field value
and one PHB. The MAP entry has the following format:
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 | EXP | PHBID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved : 13 bits
This field is reserved. It must be set to zero on
transmission and must be ignored on receipt.
EXP : 3 bits
This field contains the value of the EXP field for the
EXP<-->PHB mapping defined in this MAP entry.
PHBID : 16 bits
This field contains the PHBID of the PHB for the
EXP<-->PHB mapping defined in this MAP entry. The PHBID
is encoded as specified in section 2 of [PHBID].
Diff-Serv TLV for an L-LSP:
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MPLS Support of Diff-Serv February 2001
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type = PSC (0x901) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T| Reserved | PSC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
T:1 bit
LSP Type. This is set to 1 for an L-LSP
Reserved : 15 bits
This field is reserved. It must be set to zero on transmission
and must be ignored on receipt.
PSC : 16 bits
The PSC indicates a PHB Scheduling Class to be supported by the
LSP. The PSC is encoded as specified in section 2 of [PHBID]:
- Where the PSC comprises a single PHB defined by standards
action, the encoding for the PSC is the encoding for this
single PHB. It is the recommended DSCP value for that PHB,
left-justified in the 16-bit field, with bits 6 through 15 set
to zero.
- Where the PSC comprises multiple PHBs defined by standards
action, the PSC encoding is the encoding for this set of PHB.
It is the smallest numerical value of the recommended DSCP for
the various PHBs in the PSC, left-justified in the 16 bit
field, with bits 6 through 13 and bit 15 set to zero and with
bit 14 set to one.
For instance, the encoding of the EF PSC is :
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 0 1 1 1 0|0 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For instance, the encoding of the AF1 PSC is :
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 1 0 1 0|0 0 0 0 0 0 0 0 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.2 Diff-Serv Status Code Values
The following values are defined for the Status Code field of the
Status TLV:
Status Code E Status Data
Unexpected Diff-Serv TLV 0 0x01000001
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MPLS Support of Diff-Serv February 2001
Unsupported PHB 0 0x01000002
Invalid EXP<-->PHB mapping 0 0x01000003
Unsupported PSC 0 0x01000004
Per-LSP context allocation failure 0 0x01000005
6.3 Diff-Serv Related LDP Messages
6.3.1 Label Request Message
The format of the Label Request message is extended as follows, to
optionally include the Diff-Serv 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 (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.3.2 Label Mapping Message
The format of the Label Mapping message is extended as follows, to
optionally include the Diff-Serv 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 Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diff-Serv TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.3.3 Label Release Message
The format of the Label Release message is extended as follows, to
optionally include the Status 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 Release (0x0403) | Message Length |
Le Faucheur et. al 39
MPLS Support of Diff-Serv February 2001
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.3.4 Notification Message
The format of the Notification message is extended as follows, to
optionally include the Diff-Serv 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| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diff-Serv TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.4 Handling of the Diff-Serv TLV
6.4.1 Handling of the Diff-Serv TLV in Downstream Unsolicited Mode
This section describes operations when the Downstream Unsolicited
Mode is used.
When allocating a label for an E-LSP which is to use the
preconfigured EXP<-->PHB mapping, a downstream Diff-Serv LSR issues
a Label Mapping message without the Diff-Serv TLV.
When allocating a label for an E-LSP which is to use a signaled
EXP<-->PHB mapping, a downstream Diff-Serv LSR issues a Label
Mapping message with the Diff-Serv TLV for an E-LSP which contains
one MAP entry for each EXP value to be supported on this E-LSP.
When allocating a label for an L-LSP, a downstream Diff-Serv LSR
issues a Label Mapping message with the Diff-Serv TLV for an L-LSP
which contains the PHB Scheduling Class (PSC) to be supported on
this L-LSP.
Assuming the label set-up is successful, the downstream and upstream
LSRs must:
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MPLS Support of Diff-Serv February 2001
- update the Diff-Serv Context associated with the established
LSPs in their ILM/FTN as specified in previous sections
(incoming and outgoing label),
- install the required Diff-Serv forwarding treatment (scheduling
and dropping behavior) for this NHLFE (outgoing label).
An upstream Diff-Serv LSR receiving a Label Mapping message with
multiple Diff-Serv TLVs only considers the first one as meaningful.
The LSR must ignore and not forward the subsequent Diff-Serv TLV(s).
An upstream Diff-Serv LSR which receives a Label Mapping message
with the Diff-Serv TLV for an E-LSP and does not support the
particular PHB encoded in one, or more, of the MAP entries, must
reject the mapping by sending a Label Release message which includes
the Label TLV and the Status TLV with a Status Code of `Unsupported
PHB'.
An upstream Diff-Serv LSR receiving a Label Mapping message with the
Diff-Serv TLV for an E-LSP and determining that the signaled
EXP<-->PHB mapping is invalid, must reject the mapping by sending a
Label Release message which includes the Label TLV and the Status
TLV with a Status Code of `Invalid EXP<-->PHB Mapping'. The
EXP<-->PHB mapping signaled in the DIFFSERV Object for an E-LSP is
invalid when:
- the MAPnb field is not within the range 1 to 8, or
- a given EXP value appears in more than one MAP entry, or
- the PHBID encoding is invalid
An upstream Diff-Serv LSR receiving a Label Mapping message with the
Diff-Serv TLV for an L-LSP containing a PSC value which is not
supported, must reject the mapping by sending a Label Release
message which includes the Label TLV and the Status TLV with a
Status Code of `Unsupported PSC'.
6.4.2 Handling of the Diff-Serv TLV in Downstream on Demand Mode
This section describes operations when the Downstream on Demand Mode
is used.
When requesting a label for an E-LSP which is to use the
preconfigured EXP<-->PHB mapping, an upstream Diff-Serv LSR sends a
Label Request message without the Diff-Serv TLV.
When requesting a label for an E-LSP which is to use a signaled
EXP<-->PHB mapping, an upstream Diff-Serv LSR sends a Label Request
message with the Diff-Serv TLV for an E-LSP which contains one MAP
entry for each EXP value to be supported on this E-LSP.
When requesting a label for an L-LSP, an upstream Diff-Serv LSR
sends a Label Request message with the Diff-Serv TLV for an L-LSP
which contains the PSC to be supported on this L-LSP.
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MPLS Support of Diff-Serv February 2001
A downstream Diff-Serv LSR sending a Label Mapping message in
response to a Label Request message for an E-LSP or an L-LSP must
not include a Diff-Serv TLV in this Label Mapping message.
Assuming the label set-up is successful, the downstream and upstream
LSRs must:
- update the Diff-Serv Context associated with the established
LSPs in their ILM/FTN as specified in previous sections
(incoming and outgoing label),
- install the required Diff-Serv forwarding treatment (scheduling
and dropping behavior) for this NHLFE (outgoing label).
An upstream Diff-Serv LSR receiving a Label Mapping message
containing a Diff-Serv TLV in response to its Label Request message,
must reject the label mapping by sending a Label Release message
which includes the Label TLV and the Status TLV with a Status Code
of `Unexpected Diff-Serv TLV'.
A downstream Diff-Serv LSR receiving a Label Request message with
multiple Diff-Serv TLVs only considers the first one as meaningful.
The LSR must ignore and not forward the subsequent Diff-Serv TLV(s).
A downstream Diff-Serv LSR which receives a Label Request message
with the Diff-Serv TLV for an E-LSP and does not support the
particular PHB encoded in one (or more) of the MAP entries, must
reject the request by sending a Notification message which includes
the Status TLV with a Status Code of `Unsupported PHB'.
A downstream Diff-Serv LSR receiving a Label Request message with
the Diff-Serv TLV for an E-LSP and determining that the signaled
EXP<-->PHB mapping is invalid, must reject the request by sending a
Notification message which includes the Status TLV with a Status
Code of `Invalid EXP<-->PHB Mapping'. The EXP<-->PHB mapping
signaled in the DIFFSERV TLV for an E-LSP is invalid when:
- the MAPnb field is not within the range 1 to 8, or
- a given EXP value appears in more than one MAP entry, or
- the PHBID encoding is invalid
A downstream Diff-Serv LSR receiving a Label Request message with
the Diff-Serv TLV for an L-LSP containing a PSC value which is not
supported, must reject the request by sending a Notification message
which includes the Status TLV with a Status Code of `Unsupported
PSC'.
A downstream Diff-Serv LSR that recognizes the Diff-Serv TLV Type in
a Label Request message but is unable to allocate the required
per-LSP context information, must reject the request sending a
Notification message which includes the Status TLV with a Status
Code of `Per-LSP context allocation failure'.
A downstream Diff-Serv LSR that recognizes the Diff-Serv TLV Type in
a Label Request message and supports the requested PSC but is not
able to satisfy the label request for other reasons (e.g. no label
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MPLS Support of Diff-Serv February 2001
available), must send a Notification message in accordance with
existing LDP procedures [LDP] (e.g. with a `No Label Resource'
Status Code). This Notification message must include the requested
Diff-Serv TLV.
6.5 Non-Handling of the Diff-Serv TLV
An LSR that does not recognize the Diff-Serv TLV Type, on receipt of
a Label Request message or a Label Mapping message containing the
Diff-Serv TLV, must behave in accordance with the procedures
specified in [LDP] for an unknown TLV whose U Bit and F Bit are set
to 0 i.e. it must ignore the message, return a Notification message
with `Unknown TLV' Status.
6.6 Bandwidth Information
Bandwidth information may also be signaled at establishment time of
E-LSP and L-LSP, for instance for the purpose of Traffic
Engineering, using the Traffic Parameters TLV as described in
[MPLS CR LDP].
7. MPLS Support of Diff-Serv over PPP, LAN, Non-LC-ATM and Non-LC-FR
Interfaces
The general operations for MPLS support of Diff-Serv, including
label forwarding and LSP setup operations are specified in the
previous sections. This section describes the specific operations
required for MPLS support of Diff-Serv over PPP interfaces, LAN
interfaces, ATM Interfaces which are not label controlled and Frame
Relay interfaces which are not label controlled.
On these interfaces, this specification allows any of the following
LSP combinations per FEC:
- Zero or any number of E-LSP, and
- Zero or any number of L-LSPs.
A Diff-Serv capable LSR MUST support E-LSPs which use pre-configured
EXP<-->PHB mapping over these interfaces.
A Diff-Serv capable LSR MAY support E-LSPs which use signaled
EXP<-->PHB mapping and L-LSPs over these interfaces.
8. MPLS Support of Diff-Serv over LC-ATM Interfaces
This section describes the specific operations required for MPLS
support of Diff-Serv over label switching controlled ATM (LC-ATM)
interfaces.
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MPLS Support of Diff-Serv February 2001
This document allows any number of L-LSPs per FEC within an MPLS ATM
Diff-Serv domain. E-LSPs are not supported over LC-ATM interfaces.
8.1 Use of ATM Traffic Classes and Traffic Management mechanisms
The use of the ATM traffic classes as specified by ITU-T and ATM-
Forum or of vendor specific ATM traffic classes is outside of the
scope of this specification. The only requirement for compliant
implementation is that the forwarding behavior experienced by a
Behavior Aggregate forwarded over an L-LSP by the ATM LSR MUST be
compliant with the corresponding Diff-Serv PHB specifications.
Since there is only one bit (CLP) for encoding the PHB drop
precedence value over ATM links, only two different drop precedence
levels are supported in ATM LSRs. Sections 4.2.2 and 4.4.2 define
how the three drop precedence levels of the AFn Ordered Aggregates
are mapped to these two ATM drop precedence levels. This mapping is
in accordance with the requirements specified in [DIFF_AF] for the
case when only two drop precedence levels are supported.
To avoid discarding parts of the packets, frame discard mechanisms,
such as Early Packet Discard (EPD) SHOULD be enabled in the ATM-LSRs
for all PHBs described in this document.
8.2 LSR Implementation With LC-ATM Interfaces
A Diff-Serv capable LSR MUST support L-LSPs over LC-ATM interfaces.
This specification assumes that Edge-LSRs of the ATM-LSR domain use
the "shim header" encapsulation method defined in [MPLS_ATM].
Operations without the "shim header" encapsulation is outside the
scope of this specification.
9. MPLS Support of Diff-Serv over LC-FR Interfaces
This section describes the specific operations required for MPLS
support of Diff-Serv over label switching controlled Frame Relay
(LC-FR) interfaces.
This document allows any number of L-LSPs per FEC within an MPLS
Frame Relay Diff-Serv domain. E-LSPs are not supported over LC-FR
interfaces.
9.1 Use of Frame Relay Traffic parameters and Traffic Management
mechanisms
The use of the Frame Relay traffic parameters as specified by ITU-T
and Frame Relay-Forum or of vendor specific Frame Relay traffic
management mechanisms is outside of the scope of this specification.
The only requirement for compliant implementation is that the
forwarding behavior experienced by a Behavior Aggregate forwarded
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MPLS Support of Diff-Serv February 2001
over an L-LSP by the Frame Relay LSR MUST be compliant with the
corresponding Diff-Serv PHB specifications.
Since there is only one bit (DE) for encoding the PHB drop
precedence value over Frame Relay links, only two different drop
precedence levels are supported in Frame Relay LSRs. Sections 4.2.3
and 4.4.3 define how the three drop precedence levels of the AFn
Ordered Aggregates are mapped to these two Frame Relay drop
precedence levels. This mapping is in accordance with the
requirements specified in [DIFF_AF] for the case when only two drop
precedence levels are supported.
9.2 LSR Implementation With LC-FR Interfaces
A Diff-Serv capable LSR MUST support L-LSPs over LC-Frame Relay
interfaces.
This specification assumes that Edge-LSRs of the FR-LSR domain use
the "generic encapsulation" method as recommended in [MPLS_FR].
Operations without the "generic encapsulation" is outside the scope
of this specification.
10. IANA Considerations.
This document defines a number of objects with implications for
IANA.
This document defines in section 5.2 a new RSVP object, the Diffserv
object. This object requires a number to be assigned from the space
defined in [RSVP] for those objects which, if not understood, cause
the entire RSVP message to be rejected with an error code of
"Unknown Object Class". Such objects are identified by a zero in the
most significant bit of the class number. Within that space, this
object should be assigned a number from the "IETF Consensus" space.
This document defines in section 5.5 a new RSVP error code,
"Diffserv Error". This error code should be assigned by IANA. This
document defines values 1 through 5 of the value field to be used
within the ERROR_SPEC object for this error code. Future allocations
of values in this space should be handled by IANA using the First
Come First Served policy defined in [IANA].
This document defines in section 6.1 a new LDP TLV, the Diffserv
TLV. The number for this TLV has been assigned by working group
consensus according to the policies defined in [LDP].
This document defines in section 6.2 five new LDP Status Code values
for Diffserv-related error conditions. The values for the Status
Code have been assigned by working group consensus according to the
policies defined in [LDP].
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MPLS Support of Diff-Serv February 2001
11. Security Considerations
This document does not introduce any new security issues beyond
those inherent in Diff-Serv, MPLS and RSVP, and may use the same
mechanisms proposed for those technologies.
12. Acknowledgments
This document has benefited from discussions with Eric Rosen, Angela
Chiu and Carol Iturralde. It has also borrowed from the work done by
D. Black regarding Diff-Serv and IP Tunnels interaction.
APPENDIX A. Example Deployment Scenarios
This section does not provide additional specification and is only
here to provide examples of how this flexible approach for Diff-Serv
support over MPLS may be deployed. Pros and cons of various
deployment options for particular environments are beyond the scope
of this document.
A.1 Scenario 1: 8 (or fewer) BAs, no Traffic Engineering, no MPLS
Protection
A Service Provider running 8 (or fewer) BAs over MPLS, not
performing Traffic engineering, not using MPLS protection and using
MPLS Shim Header encapsulation in his/her network, may elect to run
Diff-Serv over MPLS using a single E-LSP per FEC established via
LDP. Furthermore the Service Provider may elect to use the
preconfigured EXP<-->PHB mapping.
Operations can be summarized as follows:
- the Service Provider configures at every LSR the bi-directional
mapping between each PHB and a value of the EXP field
(e.g. 000<-->AF11, 001<-->AF12, 010<-->AF13)
- the Service Provider configures at every LSR, and for every
interface, the scheduling behavior for each PSC (eg bandwidth
allocated to AF1) and the dropping behavior for each PHB (e.g.
drop profile for AF11, AF12, AF13)
- LSRs signal establishment of a single E-LSP per FEC using LDP in
accordance with the specification above (i.e. no Diff-Serv TLV
in LDP Label Request/Label Mapping messages to implicitly
indicate that the LSP is an E-LSP and that it uses the
preconfigured mapping)
A.2 Scenario 2: More than 8 BAs, no Traffic Engineering, no MPLS
Protection
A Service Provider running more than 8 BAs over MPLS, not performing
Traffic Engineering, not using MPLS protection and using MPLS Shim
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MPLS Support of Diff-Serv February 2001
encapsulation in his/her network may elect to run Diff-Serv over
MPLS using for each FEC:
- one E-LSP established via LDP and using the preconfigured
mapping to support a set of 8 (or less) BAs, AND
- one L-LSP per <FEC,OA> established via LDP for support of the
other BAs.
Operations can be summarized as follows:
- the Service Provider configures at every LSR the bi-directional
mapping between each PHB and a value of the EXP field for the
BAs transported over the E-LSP
- the Service Provider configures at every LSR, and for every
interface, the scheduling behavior for each PSC supported over
the E-LSP and the dropping behavior for each corresponding PHB
- the Service Provider configures at every LSR, and for every
interface, the scheduling behavior for each PSC supported over
the L-LSPs and the dropping behavior for each corresponding PHB
- LSRs signal establishment of a single E-LSP per FEC for the set
of E-LSP transported BAs using LDP as specified above (i.e. no
Diff-Serv TLV in LDP Label Request/Label Mapping messages to
implicitly indicate that the LSP is an E-LSP and that it uses
the preconfigured mapping)
- LSRs signal establishment of one L-LSP per <FEC,OA> for the
other BAs using LDP as specified above (i.e. Diff-Serv TLV in
LDP Label Request/Label Mapping messages to indicate the L-LSP's
PSC).
A.3 Scenario 3: 8 (or fewer) BAs, Aggregate Traffic Engineering,
Aggregate MPLS Protection
A Service Provider running 8 (or fewer) BAs over MPLS, performing
aggregate Traffic Engineering (i.e. performing a single common path
selection for all BAs), using aggregate MPLS protection (i.e.
restoring service to all PSCs jointly) and using MPLS Shim Header
encapsulation in his/her network, may elect to run Diff-Serv over
MPLS using a single E-LSP per FEC established via RSVP
[RSVP_MPLS_TE] or CR-LDP [CR-LDP_MPLS_TE] and using the
preconfigured mapping.
Operations can be summarized as follows:
- the Service Provider configures at every LSR the bi-directional
mapping between each PHB and a value of the EXP field
(e.g. 000<-->AF11, 001<-->AF12, 010<-->AF13)
- the Service Provider configures at every LSR, and for every
interface, the scheduling behavior for each PSC (eg bandwidth
allocated to AF1) and the dropping behavior for each PHB (eg
drop profile for AF11, AF12, AF13)
- LSRs signal establishment of a single E-LSP per FEC which will
use the preconfigured mapping:
* using the RSVP protocol as specified above (i.e. no
DIFFSERV RSVP Object in the PATH message containing the
LABEL_REQUEST Object), OR
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MPLS Support of Diff-Serv February 2001
* using the CR-LDP protocol as specified above (i.e. no
Diff-Serv TLV in LDP Label Request/Label Mapping messages).
- protection is activated on all the E-LSPs in order to achieve
MPLS protection via mechanisms outside the scope of this
document.
A.4 Scenario 4: per-OA Traffic Engineering/MPLS Protection
A Service Provider running any number of BAs over MPLS, performing
per-OA Traffic Engineering (i.e. performing a separate path
selection for each OA) and performing per-OA MPLS protection (i.e.
performing protection with potentially different levels of
protection for the different OAs) in his/her network, may elect to
run Diff-Serv over MPLS using one L-LSP per <FEC,OA> pair
established via RSVP or CR-LDP.
Operations can be summarized as follows:
- the Service Provider configures at every LSR, and for every
interface, the scheduling behavior for each PSC (eg bandwidth
allocated to AF1) and the dropping behavior for each PHB (eg
drop profile for AF11, AF12, AF13)
- LSRs signal establishment of one L-LSP per <FEC,OA>:
* using the RSVP as specified above to signal the
L-LSP's PSC (i.e. DIFFSERV RSVP Object in the PATH message
containing the LABEL_REQUEST), OR
* using the CR-LDP protocol as specified above to
signal the L-LSP PSC (i.e. Diff-Serv TLV in LDP Label
Request/Label Mapping messages).
- the appropriate level of protection is activated on the
different L-LSPs (potentially with a different level of
protection for each PSC)_via mechanisms outside the scope of
this document.
A.5 Scenario 5: 8 (or fewer) BAs, per-OA Traffic Engineering/MPLS
Protection
A Service Provider running 8 (or fewer) 8 BAs over MPLS, performing
per-OA Traffic Engineering (i.e. performing a separate path
selection for each OA) and performing per-OA MPLS protection (i.e.
performing protection with potentially different levels of
protection for the different OAs) in his/her network, may elect to
run Diff-Serv over MPLS using one E-LSP per <FEC,OA> pair
established via RSVP or CR-LDP. Furthermore, the Service Provider
may elect to use the preconfigured mapping on all the E-LSPs.
Operations can be summarized as follows:
- the Service Provider configures at every LSR the bi-directional
mapping between each PHB and a value of the EXP field
(e.g. 000<-->AF11, 001<-->AF12, 010<-->AF13)
- the Service Provider configures at every LSR, and for every
interface, the scheduling behavior for each PSC (eg bandwidth
Le Faucheur et. al 48
MPLS Support of Diff-Serv February 2001
allocated to AF1) and the dropping behavior for each PHB (eg
drop profile for AF11, AF12, AF13)
- LSRs signal establishment of one E-LSP per <FEC,OA>:
* using the RSVP protocol as specified above to signal
that the LSP is an E-LSP which uses the preconfigured mapping
(i.e. no DIFFSERV RSVP Object in the PATH message containing the
LABEL_REQUEST), OR
* using the CR-LDP protocol as specified above to
signal that the LSP is an E-LSP which uses the preconfigured
mapping (i.e. no Diff-Serv TLV in LDP Label Request/Label
Mapping messages)
- the Service Provider configures, for each E-LSP, at the head-end
of that E-LSP, a filtering/forwarding criteria so that only the
packets belonging to a given OA are forwarded on the E-LSP
established for the corresponding FEC and corresponding OA.
- the appropriate level of protection is activated on the
different E-LSPs (potentially with a different level of
protection depending on the PSC actually transported over each
E-LSP)_via mechanisms outside the scope of this document.
A.6 Scenario 6: no Traffic Engineering/MPLS Protection on 8 BAs, per-OA
Traffic Engineering/MPLS Protection on other BAs.
A Service Provider not performing Traffic Engineering/MPLS
Protection on 8 (or fewer) BAs, performing per-OA Traffic
Engineering/MPLS Protection on the other BAs (i.e. performing a
separate path selection for each OA corresponding to the other BAs
and performing MPLS Protection with a potentially different policy
for each of these OA) and using the MPLS Shim encapsulation in
his/her network may elect to run Diff-Serv over MPLS, using for each
FEC:
- one E-LSP using the preconfigured mapping established via LDP to
support the set of 8 (or fewer) non-traffic-engineered/non-
protected BAs, AND
- one L-LSP per <FEC,OA> pair established via RSVP or CR-LDP for
support of the other BAs.
Operations can be summarized as follows:
- the Service Provider configures at every LSR the bi-directional
mapping between each PHB and a value of the EXP field for the
BAs supported over the E-LSP
- the Service Provider configures at every LSR, and for every
interface, the scheduling behavior for each PSC supported over
the E-LSP and the dropping behavior for each corresponding PHB
- the Service Provider configures at every LSR, and for every
interface, the scheduling behavior for each PSC supported over
the L-LSPs and the dropping behavior for each corresponding PHB
- LSRs signal establishment of a single E-LSP per FEC for the non-
traffic engineered BAs using LDP as specified above (i.e. no
Diff-Serv TLV in LDP Label Request/Label Mapping messages)
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MPLS Support of Diff-Serv February 2001
- LSRs signal establishment of one L-LSP per <FEC,OA> for the
other BAs:
* using the RSVP protocol as specified above to signal
the L-LSP PSC (i.e. DIFFSERV RSVP Object in the PATH message
containing the LABEL_REQUEST Object), OR
* using the CR-LDP protocol as specified above to
signal the L-LSP PSC (i.e. Diff-Serv TLV in LDP Label
Request/Label Mapping messages).
- protection is not activated on the E-LSPs.
- the appropriate level of protection is activated on the
different L-LSPs (potentially with a different level of
protection depending on the L-LSP's PSC)_via mechanisms outside
the scope of this document.
A.7 Scenario 7: More than 8 BAs, no Traffic Engineering, no MPLS
Protection
A Service Provider running more than 8 BAs over MPLS, not performing
Traffic engineering, not performing MPLS protection and using MPLS
Shim Header encapsulation in his/her network, may elect to run Diff-
Serv over MPLS using two E-LSPs per FEC established via LDP and
using signaled EXP<-->PHB mapping.
Operations can be summarized as follows:
- the Service Provider configures at every LSR, and for every
interface, the scheduling behavior for each PSC (eg bandwidth
allocated to AF1) and the dropping behavior for each PHB (eg
drop profile for AF11, AF12, AF13)
- LSRs signal establishment of two E-LSPs per FEC using LDP in
accordance with the specification above (i.e. Diff-Serv TLV in
LDP Label Request/Label Mapping messages to explicitly indicate
that the LSP is an E-LSP and its EXP<--> mapping). The signaled
mapping will indicate the subset of 8 (or less) BAs to be
transported on each E-LSP and what EXP values are mapped to each
BA on each E-LSP.
APPENDIX B. Example Bandwidth Reservation Scenarios
B.1 Scenario 1: No Bandwidth Reservation
Consider the case where a network administrator elects to:
- have Diff-Serv resources entirely provisioned off-line (e.g. via
Command Line Interface, via SNMP, via COPS,...)
- have Shortest Path Routing used for all the Diff-Serv traffic.
This is the closest model to provisioned Diff-Serv over non-MPLS IP.
In that case, E-LSPs and/or L-LSPs would be established without
signaled bandwidth.
B.2 Scenario 2: Bandwidth Reservation for per-PSC Admission Control
Consider the case where a network administrator elects to:
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MPLS Support of Diff-Serv February 2001
- have Diff-Serv resources entirely provisioned off-line (e.g. via
Command Line Interface, via SNMP, via COPS,...)
- use L-LSPs
- have Constraint Based Routing performed separately for each PSC,
where one of the constraints is availability of bandwidth from
the bandwidth allocated to the relevant PSC.
In that case, L-LSPs would be established with signaled bandwidth.
The bandwidth signaled at L-LSP establishment would be used by LSRs
to perform admission control at every hop to ensure that the
constraint on availability of bandwidth for the relevant PSC is met.
B.3 Scenario 3: Bandwidth Reservation for per-PSC Admission Control and
per-PSC Resource Adjustment
Consider the case where a network administrator elects to:
- use L-LSPs
- have Constraint Based Routing performed separately for each PSC,
where one of the constraints is availability of bandwidth from
the bandwidth allocated to the relevant PSC.
- have Diff-Serv resources dynamically adjusted
In that case, L-LSPs would be established with signaled bandwidth.
The bandwidth signaled at L-LSP establishment would be used by LSRs
to attempt to adjust the resources allocated to the relevant PSC
(e.g. scheduling weight) and then perform admission control to
ensure that the constraint on availability of bandwidth for the
relevant PSC is met after the adjustment.
References
[MPLS_ARCH] Rosen et al., "Multiprotocol label switching
Architecture", RFC-3031, January 2001.
[MPLS_ENCAPS] Rosen et al., "MPLS Label Stack Encoding", RFC-3032,
January 2001.
[MPLS_ATM] Davie et al., "MPLS using LDP and ATM VC Switching", RFC-
3035, January 2001.
[MPLS_FR] Conta et al., "Use of Label Switching on Frame Relay
Networks Specification", RFC-3034, January 2001.
[DIFF_ARCH] Blake et al., "An architecture for Differentiated
Services", RFC-2475, December 1998.
[DIFF_AF] Heinanen et al., "Assured Forwarding PHB Group", RFC-2597,
June 1999.
[DIFF_EF] Jacobson et al., "An Expedited Forwarding PHB", RFC-2598,
June 1999.
Le Faucheur et. al 51
MPLS Support of Diff-Serv February 2001
[DIFF_HEADER] Nichols et al., "Definition of the Differentiated
Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC-2474,
December 1998.
[ECN] Ramakrishnan et al., "A Proposal to add Explicit Congestion
Notification (ECN) to IP", RFC-2481, January 1999.
[LDP] Andersson et al., "LDP Specification", RFC-3036, January 2001
[RSVP_MPLS_TE] Awduche et al, "Extensions to RSVP for LSP Tunnels",
work in progress, draft-ietf-mpls-rsvp-lsp-tunnel-07.txt, August
2000
[CR-LDP_MPLS_TE] Jamoussi et al., "Constraint-Based LSP Setup using
LDP", work in progress, draft-ietf-mpls-cr-ldp-04.txt, July 2000
[PHBID] Brim et al., "Per Hop Behavior Identification Codes"
RFC-2836, May 2000
[DIFF_NEW] Grossman, "New Terminology for Diffserv", work in
progress, draft-ietf-diffserv-new-terms-03.txt, August 2000
[IEEE_802.1] ISO/IEC 15802-3: 1998 ANSI/IEEE Std 802.1D, 1998
Edition (Revision and redesignation of ISO/IEC 10038:98
[ANSI/IEEE Std 802.1D, 1993 Edition], incorporating IEEE
supplements P802.1p, 802.1j-1996, 802.6k-1992, 802.11c-1998, and
P802.12e)
[DIFF_TUNNEL] Black, "Differentiated Services and Tunnels",
RFC-2983, October 2000.
[MPLS_VPN] Rosen et al., "BGP/MPLS VPNs", work in progress, draft-
rosen-rfc2547bis-02.txt, July 2000.
[RSVP] Braden et al., "Resource ReSerVation Protocol (RSVP) -
Version 1 Functional Specification", RFC-2205, September 1997.
[IANA] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, October 1998.
Authors' Address:
Francois Le Faucheur
Cisco Systems
Village d'Entreprise Green Side - Batiment T3
400, Avenue de Roumanille
06410 Biot-Sophia Antipolis
France
Phone: +33 4 97 23 26 19
Le Faucheur et. al 52
MPLS Support of Diff-Serv February 2001
Email: flefauch@cisco.com
Liwen Wu
Cisco Systems
250 Apollo Drive, Chelmsford, MA 01824,
USA
Phone: +1 (978) 244-3087
Email: liwwu@cisco.com
Bruce Davie
Cisco Systems
250 Apollo Drive, Chelmsford, MA 01824
USA
Phone: +1 (978) 244-8000
Email: bsd@cisco.com
Shahram Davari
PMC-Sierra Inc.
555 Legget drive,
Suit 834, Tower B,
Ottawa, ON K2K 2X3
Canada
Phone: +1 (613) 271-4018
Email: shahram_davari@pmc-sierra.com
Pasi Vaananen
Nokia
3 Burlington Woods Drive, Suit 250
Burlington, MA 01803
USA
Phone +1 (781) 238-4981
Email: pasi.vaananen@nokia.com
Ram Krishnan
Lucent Technologies
200 Nickerson Road,
Marlboro, MA 01752
USA
E-mail: ram64@lucent.com
Pierrick Cheval
Alcatel
5 rue Noel-Pons
92734 Nanterre Cedex
France
E-mail:pierrick.cheval@alcatel.fr
Juha Heinanen
Telia Finland
E-mail: jh@lohi.eng.telia.fi
Le Faucheur et. al 53
MPLS Support of Diff-Serv February 2001
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Le Faucheur et. al 54
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