wdiff draft-ietf-pce-disco-proto-isis-01.txt draft-ietf-pce-disco-proto-isis-02.txt

Network Working Group J.L. Le Roux (Editor)
Internet Draft France Telecom
Category: Standard Track
Expires: June August 2007 J.P. Vasseur (Editor)
Cisco System Inc.

Yuichi Ikejiri
NTT Communications

Raymond Zhang
BT Infonet

December 2006

February 2007

IS-IS protocol extensions for Path Computation Element (PCE) Discovery

draft-ietf-pce-disco-proto-isis-01.txt

draft-ietf-pce-disco-proto-isis-02.txt

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Abstract

There are various circumstances where it is highly desirable for a
Path Computation Client (PCC) to be able to dynamically and
automatically discover a set of Path Computation Element(s) Elements (PCE),
along with some of information that can be used for PCE selection.
When the PCE is a Label Switch Switching Router (LSR) participating to in the IGP,
Interior Gateway Protocol (IGP), or even a server participating
passively to in the IGP, a simple and efficient way for PCE discovery to discover PCEs
consists of relying on using IGP flooding. For that purpose this document
defines IS-IS extensions to the Intermediate System to Intermediate System
(IS-IS) routing protocol for the advertisement of PCE Discovery
information within an IS-IS area or within the entire IS-IS routing
domain.

Conventions used in this document

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.

Table of Contents

1. Note (to be removed before publication).....................3
2. Terminology.................................................3
3.
2. Introduction................................................4
4.
3. Overview....................................................5
4.1.
3.1. PCE Information.............................................5
4.1.1.
3.1.1. PCE Discovery Information...................................5
4.1.2.
3.1.2. PCE Status Information......................................6
4.2.
3.2. Flooding scope..............................................6
5.
4. IS-IS extensions............................................6
5.1.
4.1. The IS-IS PCED TLV format.......................................6
5.1.1. TLV..........................................6
4.1.1. PCE-ADDRESS sub-TLV.........................................7
5.1.2.
4.1.2. The PATH-SCOPE sub-TLV......................................8
5.1.3.
4.1.3. PCE-DOMAINS sub-TLV........................................10
5.1.3.1.
4.1.3.1. Area ID DOMAIN sub-TLV...................................10
5.1.3.2.
4.1.3.2. AS Number DOMAIN sub-TLV.................................10
5.1.4. PCE-DEST-DOMAINS sub-TLV.................................11
4.1.4. PCE-NEIG-DOMAINS sub-TLV...................................11
5.1.5. GENERAL-CAP sub-TLV........................................11
5.1.6. The PATH-COMP-CAP sub-TLV..................................12
5.1.6.1. Objective Functions sub-TLV..............................13
5.1.6.2. Opaque Objective Function sub-TLV........................14
5.1.6.3. Switch Caps sub-TLV......................................14
5.2. The IS-IS PCES sub-TLV.....................................15
5.2.1.
4.1.5. PCE-CAP-FLAGS sub-TLV......................................11
4.1.6. The CONGESTION sub-TLV.....................................15
6. sub-TLV.....................................12
5. Elements of Procedure......................................16
6.1.1. PCES TLV Procedure......................................13
5.1.1. CONGESTION sub-TLV specific procedure................................17
7. procedures.....................14
6. Backward compatibility.....................................17
8. compatibility.....................................15
7. IANA considerations........................................18
8.1. considerations........................................15
7.1. IS-IS sub-TLVs.............................................18
8.2. sub-TLV..............................................15
7.2. PCED sub-TLVs registry.....................................15
7.3. PCE Capability bits............................................19
9. Flags registry..............................16
8. Security Considerations....................................19
10. Considerations....................................16
9. Manageability Considerations...............................20 Considerations...............................17
9.1. Control of Policy and Functions............................17
9.2. Information and Data Model.................................17
9.3. Liveness Detection and Monitoring..........................17
9.4. Verify Correct Operations..................................17
9.5. Requirements on Other Protocols and Functional
Components...............................................17
9.6. Impact on network operations...............................18
10. Acknowledgments............................................18
11. Acknowledgments............................................20
12. References.................................................20
12.1. References.................................................18
11.1. Normative references.......................................20
12.2. references.......................................18
11.2. Informative references.....................................21
13. references.....................................19
12. Editors' Addresses:........................................21
14. Addresses:........................................19
13. Contributors' Adresses:....................................21
15. Adresses:....................................19
14. Intellectual Property Statement............................21 Statement............................20

1. Note (to be removed before publication)

This document specifies sub-TLVs to be carried within the IS-IS
Router Capability TLV ([IS-IS-CAP]). Because this document does not
introduce any new IS-IS element of procedure it will be discussed
within the PCE Working Group with a review of the IS-IS Working
Group.

2. Terminology

Terminology used in this document

ABR: IGP Area Border Router (L1L2 router).

AS: Autonomous System.

Domain: any collection of network elements within a common sphere
of address management or path computational responsibility.
Examples of domains include IGP areas and Autonomous Systems.

IGP: Interior Gateway Protocol. Either of the two routing
protocols Open Shortest Path First (OSPF) or Intermediate System
to Intermediate system (IS-IS).

Intra-area TE LSP: A TE LSP whose path does not cross IGP area
boundaries.

Intra-AS TE LSP: A TE LSP whose path does not cross AS boundaries.

Inter-area TE LSP: A TE LSP whose path transits through two or
more IGP areas. That is a TE-LSP that crosses at least one IGP
area boundary.

Inter-AS TE LSP: A TE LSP whose path transits through two or more
ASes or sub-ASes (BGP confederations). That is a TE-LSP that
crosses at least one AS boundary.

IS-IS LSP: Link State PDU

LSR: Label Switch Switching Router.

PCC: Path Computation Client: any Any client application requesting a
path computation to be performed by a Path Computation Element.

PCE: Path Computation Element: an An entity (component, application,
or network node) that is capable of computing a network path or
route based on a network graph, and applying computational
constraints.

PCEP: Path Computation Element communication Protocol.

TE LSP: Traffic Engineered Label Switched Path.

2. Introduction

[RFC4655] describes the motivations and architecture for a Path
Computation Element (PCE)-based path computation model for Multi
Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic
Engineered Label Switched Paths (TE-LSPs). The model allows for the
separation of the PCE from a PCC (also referred to as a non co-located co-
located PCE) and allows for cooperation between PCEs. This relies on
a communication protocol between PCC and PCE, and between PCEs. The
requirements for such a communication protocol can be found in
[RFC4657] and the communication protocol is defined in [PCEP].

The PCE architecture requires, of course, requires that a PCC be aware of the location of
one or more PCEs in its domain, and also potentially of some PCEs in
other domains, e.g. in case of inter-domain TE LSP computation.

A network may comprise contain a large number of PCEs with potentially
distinct capabilities. In such a context it is highly desirable to
have a mechanism for automatic and dynamic PCE discovery, which
allows PCCs to automatically discover a set of PCEs, along with
additional information about each PCE that may be required for the
PCC to perform PCE selection, and selection. Additionally, it is valuable for a PCC
to dynamically detect new PCEs or any modification of the PCE
information. Detailed requirements for such a PCE discovery mechanism
are described provided in [RFC4674].

Moreover, it may also be useful to discover when a PCE experiences
some
processing congestion state and when it exits such a state, in order for
the PCCs to take some appropriate actions (e.g. redirect their
requests to another PCE). Note that the PCE selection algorithm
applied by a PCC is out of the scope of this document.

When PCCs are LSRs participating to in the IGP (OSPF, IS-IS), and PCEs
are either LSRs or a servers also participating to in the IGP, an efficient
effective mechanism for PCE discovery within an IGP routing domain
consists of
relying on utilizing IGP advertisements.

This document defines IS-IS extensions allowing to allow a PCE participating
to the in an IS-IS
routing domain to advertise its location along with some information
useful to a PCC for PCE selection, so as to satisfy dynamic PCE
discovery requirements set forth in [RFC4674]. This document also
defines extensions allowing a PCE participating to the in an IS-IS routing domain to
advertise its potential processing congestion state.

Generic capability advertisement mechanisms for IS-IS have been are defined in [IS-IS-
CAP] the purpose of which is to
[IS-IS-CAP]. These allow a router to advertise its
capability capabilities
within an IS-IS area or an entire IS-IS routing domain.
Such IS-IS extensions This document
leverages this generic capability advertisement mechanism to fully
satisfy the aforementioned dynamic PCE discovery requirements.

This document defines two a new sub-TLVs sub-TLV (named the PCE Discovery (PCED) TLV and the PCE Status (PCES) TLV) for IS-IS,
to be carried within the IS-IS Router Capability TLV ([IS-IS-CAP]).

The PCE information advertised is detailed in section 4. 3. Protocol
extensions and procedures are defined in section 5 4 and 6. 5.

This document does not define any new IS-IS element elements of procedure but
how the procedure.
The procedures defined in [IS-IS-CAP] should be used.

The routing IS-IS extensions defined in this document allow for PCE discovery
within an IS-IS Routing domain. Solutions for PCE discovery across AS
boundaries are beyond the scope of this document, and for further
study.

This document defines a set of sub-TLVs that are nested within each
other. When the degree of nesting TLVs is 2 (a TLV is carried within
another TLV) the TLV carried within a TLV is called a sub-TLV.
Strictly speaking, when the degree of nesting is 3, a subsub-TLV is
carried within a sub-TLV that is itself carried within a TLV. For the
sake of terminology simplicity, we refer to sub-TLV, a TLV carried
within a TLV regardless of the degree of nesting.

3. Overview

4.1.

3.1. PCE Information

The PCE information advertised via IS-IS falls into two categories:
PCE Discovery Information information and PCE Status information.

4.1.1.

3.1.1. PCE Discovery Information

The PCE Discovery information is comprised of:

- The PCE location: an IPv4 and/or IPv6 address that must be is used to reach
the PCE. It is RECOMMENDED to use addresses an address that is always
reachable;

- The PCE inter-domain functions: PCE path computation scope (i.e.
inter-area, inter-AS, inter-layer�);

- The PCE domain(s): set of one or more domain(s) where into which the PCE
has visibility and can compute paths;

- The PCE Destination neighbor domain(s): set of one or more destination neighbor domain(s)
towards which a PCE can compute paths;

- A set of general PCEP communication capabilities (e.g. support for
request prioritization) and path computation specific capabilities
(e.g. supported constraints, supported objective functions). constraints).

Optional elements to describe more complex capabilities may also be
advertised.

PCE Discovery information is by nature fairly static and does not
change with PCE activity. Changes in PCE Discovery information may
occur as a result of PCE configuration updates, PCE
deployment/activation, PCE deactivation/suppression deactivation/suppression, or PCE failure.
Hence, this information is not expected to change frequently.

4.1.2.

3.1.2. PCE Status Information

The PCE Status is optional and can be used to report a PCE PCE's
processing
congested congestion state along with an estimated congestion
duration. This is a dynamic information, which may change with PCE
activity.

Procedures for a PCE to move from a processing congested congestion state to a
non-congested
non-congestion state are beyond the scope of this document, but the
rate at which a PCE Status change is advertised MUST not NOT impact by
any mean means the IGP scalability. Particular attention should be given
on procedures to avoid state oscillations.

4.2.

3.2. Flooding scope

The flooding scope for PCE Discovery Information information advertised through IS-IS can
be limited to one or more IS-IS areas the PCE belongs to to, or can be
extended across the entire IS-IS routing domain.
Note that some PCEs may belong to multiple areas, in which case the
flooding scope may comprise these areas. This could be the case of for a
L1L2 router for instance advertising its PCE information within the
L2 level area and/or a subset of its attached L1 area(s).

4. IS-IS extensions

5.1.

4.1. The IS-IS PCED TLV format

The IS-IS PCED TLV is made of various a set of non ordered sub-TLVs.

The format of the IS-IS PCED TLV and its sub-TLVs is the same as identical to
the TLV format used by the Traffic Engineering Extensions to IS-IS
[RFC3784]. That is, the TLV is composed of 1 octet for the type, 1
octet specifying the TLV length length, and a value field. The Length field
defines the length of the value portion in octets.

The IS-IS PCED TLV has the following format:

TYPE: To be assigned by IANA (suggested value = 5)
LENGTH: Variable
VALUE: set of sub-TLVs

Sub-TLVs types are under IANA control.

Currently five six sub-TLVs are defined (suggested type values to be
assigned by IANA):
Sub-TLV type Length Name
1 variable PCE-ADDRESS sub-TLV
2 3 PATH-SCOPE sub-TLV
3 variable PCE-DOMAINS sub-TLV
4 variable PCE-DEST-DOMAINS PCE-NEIG-DOMAINS sub-TLV
5 variable GENERAL-CAP PCE-CA-FLAGS sub-TLV
6 variable PATH-COMP-CAP 1 CONGESTION sub-TLV

The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within
the PCED TLV.

The PCE-DOMAINS and PCE-DEST-DOMAINS PCE-NEIG-DOMAINS sub-TLVs are optional. They may
be present in the PCED TLV to facilitate selection of inter-domain
PCEs.

The GENERAL-CAP and PATH-COMP-CAP PCE-CAP-FLAGS sub-TLVs are optional and MAY be present in the
PCED TLV to facilitate the PCE selection process.

The CONGESTION sub-TLV is optional and MAY be present in the PCED
TLV, to indicate a PCE's processing congestion state.

Any non recognized sub-TLV MUST be silently ignored.

Additional sub-TLVs could be added in the future to advertise
additional PCE information.

The PCED TLV is carried within an IS-IS CAPABILITY TLV defined in
[IS-IS-CAP], whose S bit is determined by the desired flooding scope.

5.1.1.
[IS-IS-CAP].

4.1.1. PCE-ADDRESS sub-TLV

The PCE-ADDRESS sub-TLV specifies the IP address that MUST can be
used to reach the PCE. It is RECOMMENDED to make use of an address
that is always reachable, provided the PCE is alive.

The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the
PCED TLV. It MAY appear twice, when the PCE has both an IPv4 and
IPv6 address. It MUST NOT appear more than once for the same address
type.

The PCE-ADDRESS sub-TLV has the following format:

TYPE: To be assigned by IANA (Suggested value =1)
LENGTH: 5 for IPv4 address and 17 for IPv6 address
VALUE: This comprises one octet indicating the address-type and 4
or 16 octets encoding the IPv4 or IPv6 address to be used
to reach the PCE

Address-type:
1 IPv4
2 IPv6

5.1.2.

4.1.2. The PATH-SCOPE sub-TLV

The PATH-SCOPE sub-TLV indicates the PCE path computation scope scope,
which refers to the PCE PCE's ability to compute or take part into in the
computation of intra-area, inter-area, inter-AS inter-AS, or inter-layer_TE
LSP(s).

The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the
PCED TLV. There MUST be exactly one instance of the PATH-SCOPE sub-
TLV within each PCED TLV.

The PATH-SCOPE sub-TLV contains a set of bit flags indicating the
supported path scopes (intra-area, inter-area, inter-AS, inter-layer) scopes, and four fields indicating PCE preferences.

The PATH-SCOPE sub-TLV has the following format:

TYPE: To be assigned by IANA (Suggested value =2)
LENGTH: 3
VALUE: This comprises a one-byte flag of bits flags field where each bit flag
represents a supported path scope, followed by a 2-bytes
preferences field indicating PCE preferences.

Here is the structure of the bits flag:

+-+-+-+-+-+-+-+-+
|0|1|2|3|4|5|Res|
+-+-+-+-+-+-+-+-+

Bit Path Scope

0 L bit: Can compute intra-area path
1 R bit: Can act as PCE for inter-area TE LSPs LSP computation
2 Rd bit: Can act as a default PCE for inter-area TE LSPs LSP
computation
3 S bit: Can act as PCE for inter-AS TE LSPs LSP computation
4 Sd bit: Can act as a default PCE for inter-AS TE LSPs
computation

5 Y bit: Can compute or take part into the computation of
paths across layers
6-7 Reserved for future usage.

Here is the structure of the preferences field

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PrefL|PrefR|PrefS|PrefY| Res |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Res: Reserved for future usage.

Pref-L field: PCE's preference for intra-area TE LSPs computation.

Pref-R field: PCE�s PCE's preference for inter-area TE LSPs computation.

Pref-S field: PCE�s PCE's preference for inter-AS TE LSPs computation.

Pref-Y field: PCE's preference for inter-layer TE LSPs computation.

Res: Reserved for future usage.

The bits L, R, S S, and Y bits are set when the PCE can act as a PCE
for intra-area, inter-area, inter-AS and or inter-layer TE LSPs
computation respectively. These bits are non mutually exclusive. non-exclusive.

When set the Rd bit indicates that the PCE can act as a default PCE
for inter-area TE LSPs LSP computation (the (that is the PCE can compute a path for
towards any
destination neighbor area). Similarly, when set set, the Sd bit indicates
that the PCE can act as a default PCE for inter-AS TE LSPs LSP computation
(the PCE can compute a path for towards any destination neighbor AS).

When the Rd bit is set, the PCE-DEST-DOMAIN PCE-NEIG-DOMAIN TLV (see 5.1.4) does not MUST NOT
contain any Area ID DOMAIN sub-TLV. sub-TLVs.

Similarly, when the Sd bit is set, the PCE-DEST-DOMAIN PCE-NEIG-DOMAIN TLV does not MUST NOT
contain any AS-DOMAIN sub-TLV. sub-TLVs.

When the R/S bit is cleared, the RD/Sd bit SHOULD be cleared and MUST
be ignored.

The PrefL, PrefR, PrefS and PrefY fields are 3-bit each three bits long and
allow the PCE to specify a preference for each computation scope,
where 7 reflects the highest preference. Such preference can be used
for weighted load balancing of requests. An operator may decide to
configure a preference for each computation scope to each PCE so as
to balance the path computation load among them, with respect to their respective CPU
capacity. them. The algorithms used
by a PCC to balance its path computation requests according to such PCE�s
PCE preference are out of the scope of this document. Same document and is a matter
for local or network wide policy. The same or distinct preferences
may be used for different each scopes. For instance an operator that wants a
PCE capable of both inter-area and inter-AS computation to be used
preferably for inter-AS computation may configure a PrefS higher than
the PrefR.

When the PrefL, PrefR, PRefS or PrefY is cleared, this
indicates an absence of preference.

When the L bit, R bit, S bit or Y bit are cleared the PrefL, PrefR,
PrefS, PrefY fields MUST SHOULD respectively be set to 0.

5.1.3. 0 and MUST be
ignored.

Both reserved fields SHOULD be set to zero on transmission and MUST
be ignored on receipt.

4.1.3. PCE-DOMAINS sub-TLV

The PCE-DOMAINS sub-TLV specifies the set of domains (areas or AS) and/or
ASes) where the PCE has topology visibility and through which the PCE
can compute paths. It contains a set of one or more sub-TLVs where
each sub-TLV identifies a domain.

The PCE-DOMAINS sub-TLV MUST MAY be present when PCE domains cannot be
inferred by other IGP information, for instance when the PCE is
inter-domain capable (i.e. when the R bit or S bit is set) and the
flooding scope is the entire routing domain. domain (see section 5 for a
discussion of how the flooding scope is set and interpreted).

The PCE-DOMAINS sub-TLV has the following format:

TYPE: To be assigned by IANA (Suggested value =2) =3)
LENGTH: Variable
VALUE: This comprises a set of one or more DOMAIN sub-TLVs where
each DOMAIN sub-TLV identifies a domain where the PCE has
topology visibility and can compute paths

DOMAIN sub-TLVs types are under IANA control.

Currently two paths.

Two DOMAIN sub-TLVs are defined (suggested type values to
be assigned by IANA):

Sub-TLV type Length Name
1 variable Variable Area ID sub-TLV
2 4 AS number sub-TLV

At least one DOMAIN sub-TLV MUST be present in the PCE-DOMAINS sub-
TLV. Note than when the PCE visibility is an entire AS, the PCE-
DOMAINS sub-TLV MUST uniquely include exactly one AS number sub-TLV, and MUST
not contain an area-ID sub-TLV.

5.1.3.1.

4.1.3.1. Area ID DOMAIN sub-TLV

This sub-TLV carries an IS-IS area ID. It has the following format

TYPE: To be assigned by IANA (Suggested value =1) 1
LENGTH: Variable
VALUE: This comprises a variable length IS-IS area ID. This is the
combination of an Initial Domain Part (IDP) and High Order
part of the Domain Specific part (HO-DSP)

5.1.3.2.

4.1.3.2. AS Number DOMAIN sub-TLV

The AS Number sub-TLV carries an AS number. It has the following
format:

TYPE: To be assigned by IANA (Suggested value =2) 2
LENGTH: 4
VALUE: AS number identifying an AS. When coded on in two
bytes (which is the current defined format as the
time of writing this document), the AS Number field
MUST have its left two bytes set to 0.

5.1.4. PCE-DEST-DOMAINS

4.1.4. PCE-NEIG-DOMAINS sub-TLV

The PCE-DEST-DOMAINS PCE-NEIG-DOMAINS sub-TLV specifies the set of destination neighbour domains
(areas, AS) ASes) toward which a PCE can compute paths. It means that the
PCE can compute or take part in the computation of inter-domain TE
LSPs whose destinations are located within path transits one of these domains. It contains a set of
one or more DOMAIN sub-TLVs where each DOMAIN sub-
TLV sub-TLV identifies a
domain.

The PCE-DEST-DOMAINS PCE-NEIG-DOMAINS sub-TLV has the following format:

TYPE: To be assigned by IANA (Suggested value =3) =4)
LENGTH: Variable
VALUE: This comprises a set of one or more area or/and AS DOMAIN sub-
TLVs where each sub-TLV identifies a destination neighbour domain toward
which a PCE can compute path.

The PCE-DEST-DOMAINS PCE-NEIG-DOMAINS sub-TLV MUST be present if the R bit is set and
the Rd bit is cleared, and/or, if the S bit is set and the Sd bit is
cleared.

The PCE-DEST-DOMAINS PCE-NEIG-DOMAINS sub-TLV MUST include at least one DOMAIN sub-
TLV. It MUST include at least one area Area ID sub-TLV, if the R bit of
the PATH-SCOPE TLV is set and the Rd bit of the PATH-SCOPE TLV is
cleared. Similarly, it MUST include at least one AS number sub-TLV if
the S bit of the PATH-SCOPE TLV is set and the Sd bit of the PATH-
SCOPE TLV is cleared.

5.1.5. GENERAL-CAP

4.1.5. PCE-CAP-FLAGS sub-TLV

The GENERAL-CAP PCE-CAP-FLAGs sub-TLV is an optional TLV used to indicate PCEP
related capabilities. It carries a 32-bit flag, where each bit
corresponds to a general PCE capability. It MAY also include optional
sub-TLVs to encode more complex capabilities.

The GENERAL-CAP sub-TLV has the following format:

TYPE: To be assigned by IANA (Suggested value =4)
LENGTH: Variable
VALUE: This comprises a 32-bit General Capabilities flag where
each bit corresponds to a general PCE capability, and
optional sub-TLVs that may present within the PCED TLV. It MUST
NOT be defined to specify present more
complex capabilities. Currently no sub-TLVs are defined. than once.

The following bits in the General Capabilities 32-bit flag are to be
assigned by IANA:

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

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P|M| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Bit Capabilities

0 P bit: Support for Request prioritization.
1 M bit: Support for multiple requests within value field of the same
request message.

2-31 Reserved for future assignments by IANA.

5.1.6. The PATH-COMP-CAP sub-TLV

The PATH-COMP-CAP PCE-CAP-FLAGS sub-TLV is made up of an optional TLV used to indicate path
computation specific capabilities array
of a PCE.
It comprises a 32-bit flag, units of 32 bit flags numbered from the most significant as bit
zero, where each bit corresponds to a path
computation represents one PCE capability. It MAY also include optional sub-TLVs to
encode more complex capabilities.

The PATH-COMP-CAP GENERAL-CAP sub-TLV has the following format:

TYPE: To be assigned by IANA (suggested (Suggested value = 5) =4)
LENGTH: Variable Multiple of 4
VALUE: This comprises one contains an array of units of 32 bit Path Computation Capabilities
Flag, flags numbered
from the most significant as bit zero, where each bit corresponds to a path computation
capability, and optional sub-TLVs that may be defined
represents one PCE capability.

IANA is requested to
specify more complex capabilities. Three optional sub-TLVs
are currently defined. manage the space of the PCE Capability Flags

The following bits in the Path Computation Capabilities 32-bit Flag are to be assigned by IANA:

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

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G|B|D|L|S|0|P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Bit Capabilities

0 G bit: Capability to handle GMPLS link contraints constraints
1 B bit: Capability to compute bidirectional paths
2 D bit: Capability to compute PSC path
3 Capability to compute a TDM path
4 Capability to compute a LSC path
5 Capability to compute a FSC path

6 Capability to compute link/node/SRLG diverse paths
3 L bit:
7 Capability to compute load-balanced paths
4 S bit:
8 Capability to compute a set of paths in a
synchronized Manner
5 O bit:
9 Support for multiple objective functions
6 P bit:
10 Capability to handle path constraints (e.g. max hop count, metric bound)

7-31
max path metric)
11 Support for Request prioritization.
12 Support for multiple requests within the same
request message.

13-31 Reserved for future assignments by IANA.

The G, B, D, L, S, O and P

Reserved bits are not exclusive.

Three optional sub-TLVs are currently defined for the PATH-COMP-CAP
TLV:
- The Objective Functions sub-TLV (type to be defined, suggested
value =1) that carries a list of supported objective functions,
where each objective function is identified by a 16 bit integer.
- The Opaque Objective Function sub-TLV (type to be defined,
suggested value =2) that allows the user to encode a specific
objective function in any appropriate language.
- The Switch Caps sub-TLV (type to be defined, suggested value =3)
that carries a list of supported switching capabilities. This
means that the PCE can compute paths for the listed switching
capabilities.

5.1.6.1. Objective Functions sub-TLV

The format of the Objective Functions sub-TLV is as follows:
TYPE: To be defined by IANA (suggested value =1)
LENGTH: Variable (N*2)
VALUE: This comprises a set of one or more 16 bit function
ids, where each function id identifies a supported
objective functions.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| function 1 | function 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| function N | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Objectives functions and their identification will be defined in a
separate document.

The Objective Functions sub-TLV is optional. It MAY be present within
the PATH-COMP-CAP TLV. When present it MUST be present only once in
the PATH-COMP-CAP TLV.

5.1.6.2. Opaque Objective Function sub-TLV

The format of the Opaque Objective Function sub-TLV is as follows:

TYPE: To be defined by IANA (suggested value =2)
LENGTH: Variable
VALUE: This encodes a specific objective function in any
appropriate language.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque objective function |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Opaque Objective function sub-TLV is optional. The PATH-COMP-CAP TLV
MAY comprise 0, one or more Opaque Objective Functions.

5.1.6.3. Switch Caps sub-TLV

The format of the Switch Caps sub-TLV is as follows:

TYPE To be defined by IANA (suggested value =3)
LENGTH Variable = N, where N is the number of supported
switching capabilities
VALUE This comprises a set of one or more 8-bit switching
types, where each switching types identifies a
supported switching capability.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SC type | SC type | SC type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Switching type values are defined in [RFC4205].

The Switch Caps sub-TLV is optional. It MAY be present in the PATH-COMP-
CAP TLV. When present it MUST be present only once in the PATH-COMP-CAP
TLV.

5.2. The IS-IS PCES sub-TLV

The IS-IS PCE Status TLV (PCES sub-TLV) carries information related
to PCE processing congestion state. The PCES sub-TLV is carried
within an IS-IS Capability TLV which is defined in [IS-IS-CAP].

The IS-IS PCES sub-TLV has the following format:

TYPE: To SHOULD be assigned by IANA
LENGTH: Variable
VALUE: set of sub-TLVs

Sub-TLVs types are under IANA control.

Currently two sub-TLVs are defined (suggested type values to be
assigned by IANA):
Sub-TLV type Length Name
1 variable PCE-ADDRESS sub-TLV
2 3 CONGESTION sub-TLV

There MUST be exactly one occurrence of the PCE-ADDRESS and
CONGESTION sub-TLVs within a PCES sub-TLV. The PCE-ADDRESS sub-TLV is
defined in section 5.1.1. It carries one of the PCE IP addresses and
is used to identify the PCE experiencing a processing congestion
state. This is required as the PCES and PCED TLVs may be carried in
separate IS-IS Capability TLVs.
A PCE implementation MUST use the same IP address for the PCE-
ADDRESS sub-TLV carried within the PCED sub-TLV zero on transmission and the PCE-ADDRESS
sub-TLV carried within the PCES sub-TLV.

Any non recognized sub-TLV MUST be silently ignored.

Additional sub-TLVs could be added in the future to advertise
additional congestion information.

5.2.1.
ignored on receipt.

4.1.6. The CONGESTION sub-TLV

The CONGESTION sub-TLV is used to indicate whether a PCE PCE's experiences a
processing congestion state or not along with and may optionally the PCE include expected PCE
congestion duration.
The CONGESTION sub-TLV is mandatory. There MUST optional, it MAY be a single instance
of the CONGESTION sub-TLV carried within the PCES PCED
TLV. It MUST NOT be present more than once.

The format of the CONGESTION sub-TLV is as follows:

TYPE: To be assigned by IANA (Suggested value =2) =6)
LENGTH: 3
VALUE: This comprises a one-byte flag of bits bit flags indicating the
congestion status, followed by a 2-bytes field indicating the
congestion duration.

Here is the TLV structure

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| Reserved| Congestion Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Value
-C bit: When set this indicates that the PCE experiences is experiencing
congestion and cannot accept any new request. When
cleared this indicates that the PCE does is not
experience
experiencing congestion and can accept new requests.

-Congestion Duration: 2-bytes, the estimated PCE congestion
duration in seconds.

When C is set and the Congestion Duration field is equal to 0, this
means that the Congestion Duration is unknown.
When C is cleared the Congestion Duration MUST SHOULD be set to 0.

6. 0 and MUST
be ignored.

5. Elements of Procedure

The PCED and PCES TLV are carried is advertised within an IS-IS Router Capability TLV
defined in [IS-IS-CAP].

As PCES information A such, elements of procedures are inherited
from those defined in [IS-IS-CAP].

The flooding scope is likely to change more frequently than controlled by the PCED
information, it is RECOMMENDED to carry PCES and PCED TLVs S flag in
separate IS-IS Capability TLVs, so as not to carry all PCED
information each time the PCE status changes.

An IS-IS router MUST originate a new IS-IS LSP whenever the content
of any of the PCED TLV or PCES Router
Capability TLV changes or whenever required by
the regular IS-IS procedure (LSP refresh). (see [IS-IS-CAP]). When the scope of the PCED or PCES TLV is
area local it MUST be carried within an IS-IS CAPABILITY TLV having
the S bit cleared. When the scope of the PCED or PCES TLV is the entire IGP
domain, the
PCED TLV MUST itMUST be carried within an IS-IS CAPABILITY TLV having the S
bit set. When only the L bit of the PATH-SCOPE sub-TLV is set, the
flooding scope MUST be local.
Note that

A PCE MUST originate a new IS-IS LSP whenever the flooding scopes content
of any of the PCED and PCES TLVs may TLV changes or whenever required by the regular
IS-IS procedure.

When the PCE function is deactivated on a node, the node MUST
originate a new IS-IS LSP with no longer any PCED TLV. A PCC MUST be
distinct, in which case they are carried in distinct
able to detect that the PCED TLV has been removed from an IS-IS Capability
TLVs. LSP.

The PCE address, i.e. the address indicated within the PCE ADDRESS
sub-TLV, MUST be distributed as part of IS-IS routing; this allows
speeding up the detection of a PCE failure. Note that when the PCE
address is no longer reachable, this means that the PCE node has
failed or has been torn down, or that there is no longer IP
connectivity to the PCE node.

The PCED and PCES sub-TLVs are TLV is OPTIONAL. When an IS-IS LSP does not contain any PCED or PCES sub-TLV,
TLV, this means that the PCE information of that node is unknown.

A change in PCED or PCES information MUST not trigger any SPF computation. computation at
a receiving router.

The way PCEs retrieve their own determine the information they advertise is out of the
scope of this document. Some information may be configured (e.g. (e.g.,
address, preferences, scope) and other information may be
automatically
retrieved determined by the PCE (e.g. areas of visibility).

6.1.1. PCES TLV

5.1.1. CONGESTION sub-TLV specific procedure procedures

When a PCE enters into a processing congestion state, the conditions
of which are implementation dependent, it SHOULD MAY originate a new IS-
IS IS-IS
LSP with a Capability TLV carrying a PCES TLV CONGESTION sub-TLV with the C bit set and optionally a
non-null expected congestion duration.

When a PCE exists from the processing congestion state, the
conditions of which are implementation dependent, two cases are
considered:
- If the congestion duration in the previously originated PCES
TLV
CONGESTION sub-TLV was null, it SHOULD originate a PCES TLV CONGESTION sub-TLV
with the C bit cleared and a null congestion duration;
- If the congestion duration in the previously originated PCES
TLV
CONGESTION sub-TLV was non null, it MAY originate a PCES TLV. CONGESTION sub-
TLV with the C bit cleared. Note that in some particular cases it may
be desired to originate a PCES TLV with the C bit cleared if the
congestion duration was over estimated.

The congestion duration allows reducing a reduction in the amount of IS-IS
flooding, as only uncongested-to-congested state transitions are need
advertised.

A PCE implementation SHOULD support an appropriate dampening
algorithm so as to dampen IS-IS flooding in order to not impact the
IS-IS scalability. It is RECOMMENDED to introduce some hysteresis for
congestion state transition, so as to avoid state oscillations that
may impact IS-IS performances. performance. For instance two thresholds MAY be
configured: a resource congestion upper-threshold and a resource
congestion lower-threshold. An LSR enters the congested state when
the CPU load reaches the upper threshold and leaves the congested
state when the CPU load goes under the lower threshold.

Upon receipt of an updated PCES TLV CONGESTION sub-TLV a PCC should take
appropriate actions. In particular, the PCC SHOULD stop sending
requests to a congested PCE, and SHOULD gradually start sending again
requests to a PCE that is no longer congested PCE.

6. Backward compatibility

The PCED and PCES TLVs TLV defined in this document do does not introduce any
interoperability issue. issues.

An IS-IS router not supporting the PCED/PCES TLVs PCED TLV will just silently ignore
the TLV as specified in [IS-IS-CAP].

7. IANA considerations

8.1.

7.1. IS-IS sub-TLVs sub-TLV

Once a registry for the IS-IS Router Capability TLV defined in
[IS-IS-CAP] will have been assigned, IANA will assign two a new codepoints
TLV code-point for the PCED and PCES sub-TLVs TLV carried within the IS-IS CAPABILITY Router Capability
TLV.

Value Sub-TLV References
----- -------- ----------
5 PCED TLV defined in [IS-IS-CAP].

Type Description Reference

1 (this document)

7.2. PCED [IS-IS-CAP]
2 PCES [IS-IS-CAP]

8.1.1 Sub-TLVs of the sub-TLVs registry

The PCED sub-TLV TLV referenced above is constructed from sub-TLVs. Each sub-
TLV includes a 8-bit type identifier.

The IANA is requested to manage sub-TLV types for the PCED sub-TLV.

Five sub-TLVs types are defined for the PCED sub-TLV create a new registry and should be
assigned by IANA: manage TLV type
identifiers as follows:

- TLV Type Description
- TLV Name
- Reference

This document defines five TLVs as follows (suggested values):

Value TLV name References
----- -------- ----------
1 PCE-ADDRESS This document
2 PATH-SCOPE This document
3 PCE-DOMAINS This document
4 PCE-DEST-DOMAINS PCE-NEIG-DOMAINS This document
5 GENERAL-CAP PCE-CAP-FLAGS This document
6 PATH-COMP-CAP CONGESTION This document

Sub-TLVs of the PCE-DOMAINS and and PCE-DEST-DOMAINS sub-TLVs

Two sub-TLVs types are defined for the PCE-DOMAINS and PCE-DEST-
DOMAINS sub-TLVs and should

New TLV type values may be assigned allocated only by IANA:

Type Description Reference

1 Area ID This document
2 AS Number an IETF Consensus
action.

7.3. PCE Capability Flags registry

This document

Sub-TLV of the PATH-COMP-CAP sub-TLV

Three sub-TLV types provides new capability bit flags, which are defined for the PATH-COMP-CAP sub-TLV and
should be assigned by IANA:

Type Description Reference

1 Objective Functions This document
2 Opaque Objective Function This document
3 Switch Caps sub-TLV This document

8.1.2 Sub-TLVs of present
in the PCES sub-TLV PCE-CAP-FLAGS TLV referenced in section 4.1.5.

The IANA is requested to manage sub-TLV types for the PCES TLV.

Type Description Reference

1 PCE-ADDRESS This document
2 CONGESTION This document

8.2. Capability bits

IANA is requested create a new registry and to manage the
space of the General Capabilities
32-bit flag and the Path Computation Capabilities 32-bit flag defined
in this document, PCE capability bit flags numbering them in the usual IETF
notation starting at zero zero, and continuing at least through 31. 31, with
the most significant bit as bit zero.

The same registry is defined for OSPF based PCE discovery [PCED-OSPF].
A single registry must be defined for both protocols.

New bit numbers may be allocated only by an IETF Consensus action.

Each bit should be tracked with the following qualities:

- Bit number
- Defining RFC
- Name of bit

Currently two bits are defined in the General Capabilities flag. Here
are the suggested values:
-0: Support for Request prioritization.
-1: Support for multiple messages within the same request message

Currently seven Capability Description

Several bits are defined in the Path Computation Capabilities
flag. this document. Here are the suggested
values:

-0:

Bit Capability to handle Description

0 GMPLS Constraints
-1: Capability to compute bidirectional link constraints
1 Bidirectional paths
-2: Capability to compute link/node/SRLG diverse
2 PSC paths
-3: Capability to compute load-balanced
3 TDM paths
-4: Capability to compute a set of
4 LSC paths in a
synchronized Manner
-5: Support for multiple
5 FSC paths
6 Diverse paths
7 Load-balanced paths
8 Synchronized computation
9 Multiple objective function
-6: Capability to handle functions
10 Additive path constraints (e.g. max hop count, metric
bound)

9. count)
11 Request prioritization
12 Multiple requests per message

8. Security Considerations

Any new security issues raised by the procedures in this

This document
depend upon the opportunity defines IS-IS extensions for LSPs to be snooped, PCE discovery within an
administrative domain. Hence the
ease/difficulty security of which has not been altered. As the LSPs may now
contain additional information regarding PCE capabilities, this
new information would also become available. discovery relies
on the security of IS-IS.

Mechanisms defined to
secure ISIS Link State PDUs ensure authenticity and integrity of IS-IS LSPs
[RFC3567], and their TLVs, can be used to secure the PCED and PCES TLVs TLV as well.

10.

IS-IS provides no mechanism for protecting the privacy of LSAs, and
in particular the privacy PCE discovery information.

9. Manageability Considerations

Manageability considerations for PCE Discovery are addressed in
section 4.10 of [RFC4674].

11.

9.1. Control of Policy and Functions

Requirements on the configuration of PCE discovery parameters on PCCs
and PCEs are discussed in section 4.10.1 of [RFC4674].

Particularly, a PCE implementation SHOULD allow configuring the
following parameters on the PCE:
-The PCE IPv4/IPv6 address(es) (see section 4.1.1)
-The PCE Scope, including the inter-domain functions (inter-
area, inter-AS, inter-layer), the preferences, and whether the
PCE can act as default PCE (see section 4.1.2)
-The PCE domains (see section 4.1.3)
-The PCE neighbour domains (see section 4.1.4)
-The PCE capabilities (see section 4.1.5)

9.2. Information and Data Model

A MIB module for PCE Discovery is defined in [PCED-MIB].

9.3. Liveness Detection and Monitoring

PCE Discovery Protocol liveness detection relies upon OSPF liveness
detection. IS-IS already includes a liveness detection mechanism
(Hello PDUs), and PCE discovery does not require additional
capabilities.

Procedures defined in section 5 allow a PCC detecting when a PCE has
been deactivated, or is no longer reachable.

9.4. Verify Correct Operations

The correlation of information advertised against information
received can be achieved by comparing the PCED information in the PCC
and in the PCE, which is stored in the PCED MIB [PCED-MIB]. The
number of dropped, corrupt, and rejected information elements are
stored in the PCED MIB.

9.5. Requirements on Other Protocols and Functional Components

The IS-IS extensions defined in this documents does not imply any
requirement on other protocols.

9.6. Impact on network operations

Frequent changes in PCE information, and particularly in PCE
congestion information, may have a significant impact on IS-IS and
might destabilize the operation of the network by causing the PCCs to
swap between PCEs.

As discussed in section 5, a PCE implementation SHOULD support an
appropriate dampening algorithm so as to dampen IS-IS flooding in
order to not impact the IS-IS scalability.

Also, as discussed in section 4.10.4 of [RFC4674], it MUST be
possible to apply at least the following controls:

- Configurable limit on the rate of announcement of changed
parameters at a PCE.
- Control of the impact on PCCs such as through discovery messages
rate-limiting.
- Configurable control of triggers that cause a PCC to swap to
another PCE.

10. Acknowledgments

We would like to thank Lucy Wong and Adrian Farrel for their useful
comments and suggestions.

12.

11. References

12.1.

11.1. Normative references

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
3667, February 2004.

[BCP79] Bradner, S., "Intellectual Property Rights in IETF
Technology", RFC 3979, March 2005.

[IS-IS] "Intermediate System to Intermediate System Intra-Domain
Routing Exchange Protocol " ISO 10589.

[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.

[RFC3784] Li, T., Smit, H., "IS-IS extensions for Traffic
Engineering", RFC 3784, June 2004.

[IS-IS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising
router information", draft-ietf-isis-caps, work in progress.

[RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE)-based Architecture", RFC4655, august 2006.

[RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery",
RFC4674, October 2006.

[RFC4205] Kompella, Rekhter, " IS-IS Extensions in Support of
Generalized Multi-Protocol Label Switching (GMPLS)", RFC4205, October
2005.

[RFC3567] Li, T. and R. Atkinson, "Intermediate System to
Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567,
July 2003.

12.2.

11.2. Informative references

[RFC4657] Ash, J., Le Roux, J.L., " PCE Communication Protocol
Generic Requirements", RFC4657, September 2006.

[PCEP] Vasseur Vasseur, Le Roux, et al., "Path �Path Computation Element (PCE)
communication Protocol (PCEP) - Version 1", 1�, draft-ietf-pce-pcep, work
in progress.

13.

[PCED-MIB] Stephan, E., "Definitions of Managed Objects for Path
Computation Element Discovery", draft-ietf-pce-disc-mib-00, work in
progress.

[PCED-OSPF] Le Roux, Vasseur, "OSPF protocol extensions for Path
Computation Element (PCE) Discovery", draft-ietf-pce-disco-proto-
ospf, work in progress.

12. Editors' Addresses:

Jean-Louis Le Roux (Editor)
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: jeanlouis.leroux@orange-ftgroup.com

Jean-Philippe Vasseur (Editor)
Cisco Systems, Inc.
1414 Massachusetts avenue
Boxborough , MA - 01719
USA
Email: jpv@cisco.com

14.

13. Contributors' Adresses:

Yuichi Ikejiri
NTT Communications Corporation
1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo 100-8019
JAPAN
Email: y.ikejiri@ntt.com

Raymond Zhang
BT Infonet
2160 E. Grand Ave.
El Segundo, CA 90025
USA
Email: raymond_zhang@infonet.com

15. raymond_zhang@bt-infonet.com

14. Intellectual Property Statement

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pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
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made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
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such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.

Disclaimer of Validity

This document and the information contained herein are provided
on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
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Copyright (C) The IETF Trust (2006). (2007). This document is subject to the
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