PCE Working Group H. Chen, Ed.
Internet-Draft Futurewei
Intended status: Standards Track Y. Zhuang, Ed.
Expires: January 8, 2020 Q. Wu
Huawei
D. Ceccarelli
Ericsson
July 7, 2019
PCEP Extensions for LSP scheduling with stateful PCE
draft-ietf-pce-stateful-pce-lsp-scheduling-08
Abstract
This document defines a set of extensions needed to the stateful Path
Computation Element (PCE) communication Protocol (PCEP), so as to
enable Labeled Switched Path (LSP) scheduling for path computation
and LSP setup/deletion based on the actual network resource usage and
the duration of a traffic service in a centralized network
environment as stated in RFC 8413.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on January 8, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation and Objectives . . . . . . . . . . . . . . . . . . 5
4. Procedures and Mechanisms . . . . . . . . . . . . . . . . . . 5
4.1. LSP Scheduling Overview . . . . . . . . . . . . . . . . . 5
4.2. Support of LSP Scheduling . . . . . . . . . . . . . . . . 7
4.2.1. LSP Scheduling . . . . . . . . . . . . . . . . . . . 7
4.2.2. Periodical LSP Scheduling . . . . . . . . . . . . . . 7
4.3. Scheduled LSP creation . . . . . . . . . . . . . . . . . 9
4.4. Scheduled LSP Modifications . . . . . . . . . . . . . . . 10
4.5. Scheduled LSP activation and deletion . . . . . . . . . . 10
5. PCEP Objects and TLVs . . . . . . . . . . . . . . . . . . . . 11
5.1. Stateful PCE Capability TLV . . . . . . . . . . . . . . . 11
5.2. LSP Object . . . . . . . . . . . . . . . . . . . . . . . 12
5.2.1. SCHED-LSP-ATTRIBUTE TLV . . . . . . . . . . . . . . . 12
5.2.2. SCHED-PD-LSP-ATTRIBUTE TLV . . . . . . . . . . . . . 14
6. The PCEP Messages . . . . . . . . . . . . . . . . . . . . . . 16
6.1. The PCRpt Message . . . . . . . . . . . . . . . . . . . . 16
6.2. The PCUpd Message . . . . . . . . . . . . . . . . . . . . 16
6.3. The PCInitiate Message . . . . . . . . . . . . . . . . . 16
6.4. The PCReq message . . . . . . . . . . . . . . . . . . . . 16
6.5. The PCRep Message . . . . . . . . . . . . . . . . . . . . 17
6.6. The PCErr Message . . . . . . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Manageability Consideration . . . . . . . . . . . . . . . . . 18
8.1. Control of Function and Policy . . . . . . . . . . . . . 18
8.2. Information and Data Models . . . . . . . . . . . . . . . 18
8.3. Liveness Detection and Monitoring . . . . . . . . . . . . 18
8.4. Verify Correct Operations . . . . . . . . . . . . . . . . 18
8.5. Requirements On Other Protocols . . . . . . . . . . . . . 19
8.6. Impact On Network Operations . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9.1. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 19
9.2. STATEFUL-PCE-CAPABILITY TLV Flag field . . . . . . . . . 19
9.3. Schedule TLVs Flag Field . . . . . . . . . . . . . . . . 20
9.4. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 20
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
11.1. Normative References . . . . . . . . . . . . . . . . . . 21
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11.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Contributor Addresses . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
The Path Computation Element Protocol (PCEP) defined in [RFC5440] is
used between a Path Computation Element (PCE) and a Path Computation
Client (PCC) (or other PCE) to enable path computation of Multi-
protocol Label Switching (MPLS) Traffic Engineering Label Switched
Paths (TE LSPs).
[RFC8231] describes a set of extensions to PCEP to provide stateful
control. A stateful PCE has access to not only the information
carried by the network's Interior Gateway Protocol (IGP) but also the
set of active paths and their reserved resources for its
computations. The additional state allows the PCE to compute
constrained paths while considering individual LSPs and their
interactions.
Traditionally, the usage and allocation of network resources,
especially bandwidth, can be supported by a Network Management System
(NMS) operation such as path pre-establishment. However, this does
not provide efficient network usage since the established paths
exclude the possibility of being used by other services even when
they are not used for undertaking any service. [RFC8413] then
provides a framework that describes and discusses the problem, and
defines an appropriate architecture for the scheduled reservation of
TE resources.
The scheduled reservation of TE resources allows network operators to
reserve resources in advance according to the agreements with their
customers, and allows them to transmit data about scheduling such as
a specified start time and duration, for example for a scheduled bulk
data replication between data centers. It enables the activation of
bandwidth usage at the time the service really being used while
letting other services use it when this service is not using it. The
requirement of scheduled LSP provision is mentioned in [RFC8231] and
[RFC7399], so as to provide more efficient network resource usage for
traffic engineering, which hasn't been solved yet. Also, for
deterministic networks [I-D.ietf-detnet-architecture], the scheduled
LSP or temporal LSP can provide a better network resource usage for
guaranteed links. This idea can also be applied in segment routing
[RFC8402] to schedule the network resources over the whole network in
a centralized manner as well.
With this in mind, this document defines a set of extensions needed
to PCEP used for stateful PCEs so as to enable LSP scheduling for
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path computation and LSP setup/deletion based on the actual network
resource usage duration of a traffic service. A scheduled LSP is
characterized by a starting time and a duration. When the end of the
LSP life is reached, it is deleted to free up the resources for other
LSPs (scheduled or not).
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.1. Terminology
The following terminologies are re-used from existing PCE documents.
o Active Stateful PCE [RFC8231];
o Passive Stateful PCE [RFC8231];
o Delegation [RFC8231];
o PCE-Initiated LSP [RFC8281];
o PCC [RFC5440], [RFC8231];
o PCE [RFC5440], [RFC8231];
o TE LSP [RFC5440], [RFC8231];
o TED [RFC5440], [RFC8231];
o LSP-DB [RFC8231];
In addition, this document defines the following terminologies.
Scheduled TE LSP (or Scheduled LSP for short): an LSP with the
scheduling attributes, that carries traffic flow demand at a
starting time and lasts for a certain duration (or from a starting
time to an ending time, where the ending time is the starting time
plus the duration). A scheduled LSP is also called a temporal
LSP. The PCE operates path computation per LSP availability for
the required time and duration.
Scheduled LSP-DB: a database of scheduled LSPs.
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Scheduled TED: Traffic engineering database with the awareness of
scheduled resources for TE. This database is generated by the PCE
from the information in TED and scheduled LSP-DB and allows
knowing, at any time, the amount of available resources (does not
include failures in the future).
Starting time (start-time): This value indicates when the scheduled
LSP is used and the corresponding LSP must be setup and active.
In other time (i.e., before the starting time or after the
starting time plus Duration), the LSP can be inactive to include
the possibility of the resources being used by other services.
Duration: This value indicates the time duration that the LSP is
undertaken by a traffic flow and the corresponding LSP must be
setup and active. At the end of which, the LSP is torn down and
removed from the data base.
3. Motivation and Objectives
A stateful PCE [RFC8231] can support better efficiency by using LSP
scheduling described in the use case of [RFC8051]. This requires the
PCE to maintain the scheduled LSPs and their associated resource
usage, e.g. bandwidth for Packet-switched network, as well as have
the ability to trigger signaling for the LSP setup/tear-down at the
correct time.
Note that existing configuration tools can be used for LSP
scheduling, but as highlighted in section 3.1.3 of [RFC8231] as well
as discussions in [RFC8413], doing this as a part of PCEP in a
centralized manner, has obvious advantages.
This document provides a set of extensions to PCEP to enable LSP
scheduling for LSP creation/deletion under the stateful control of a
PCE and according to traffic service requests from customers, so as
to improve the usage of network resources.
4. Procedures and Mechanisms
4.1. LSP Scheduling Overview
The LSP scheduling allows PCEs and PCCs to provide scheduled LSP for
customers' traffic services at its actual usage time, so as to
improve the network resource efficient utilization.
For stateful PCE supporting LSP scheduling, there are two types of
LSP databases used in this document. One is the LSP-DB defined in
PCEP [RFC8231], while the other is the scheduled LSP database (SLSP-
DB, see section 6). The SLSP-DB records scheduled LSPs and is used
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in conjunction with the TED and LSP-DB. Note that the two types of
LSP databases can be implemented in one physical database or two
different databases. This is an implementation matter and this
document does not state any preference.
Furthermore, a scheduled TED can be generated from the scheduled LSP-
DB, LSP-DB and TED to indicate the network links and nodes with
resource availability information for now and future. The scheduled
TED should be maintained by all PCEs within the network environment.
In case of implementing PCC-initiated scheduled LSPs, before a PCC
delegates a scheduled LSP, it MAY use the PCReq/PCRep messages to
learn the path for the scheduled LSP. A PCC MUST delegate a
scheduled LSP with information of its scheduling parameters,
including the starting time and the duration using PCRpt message.
Since the LSP is not yet signaled, at the time of delegation the LSP
would be in down state. Upon receiving the delegation of the
scheduled LSP, a stateful PCE SHALL check the scheduled TED for the
network resource availability on network nodes and computes a path
for the LSP with the scheduling information and update to the PCC as
per the active stateful PCE techniques [RFC8231].
Note that the active stateful PCE can update to the PCC with the path
for the scheduled LSP at any time. However, the PCC should not
signal the LSP over the path on receiving these messages since the
path is not active yet; PCC signals the LSP at the starting time.
For a multiple PCE environment, a PCE MUST synchronize to other PCEs
within the network, so as to keep their scheduling information
synchronized. There are many ways that this could be achieved: one
such mechanism is described in [I-D.litkowski-pce-state-sync]. Which
way is used to achieve this is out of scope for this document. The
scheduled TED can be determined from the synchronized SLSP-DB. The
PCE with delegation for the scheduled LSP would report the scheduled
LSP to other PCEs, any future update to the scheduled LSP is also
updated to other PCEs. This way the state of all scheduled LSPs are
synchronized among the PCEs. [RFC7399] discusses some
synchronization issues and considerations, that are also applicable
to the scheduled databases.
The scheduled LSP can also be initiated by PCE itself. In case of
implementing PCE-initiated scheduled LSP, the stateful PCE shall
check the network resource availability for the traffic and computes
a path for the scheduled LSP and initiate a scheduled LSP at the PCC
and synchronize the scheduled LSP to other PCEs. Note that, the PCC
could be notified immediately or at the starting time of the
scheduled LSP based on the local policy. In case of former SCHED-
LSP-ATTRIBUTE TLV (see Section 5.2.1) MUST be included in the message
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where as for the latter SCHED-LSP-ATTRIBUTE TLV SHOULD NOT be
included. Either way the synchronization to other PCEs should be
done when the scheduled LSP is created.
In both modes, for activation of scheduled LSPs, the PCC could
initiate the setup of scheduled LSP at the start time by itself or
wait for the PCE to update the PCC to initiate the setup of LSP.
Similarly on the scheduling usage expires, the PCC could initiate the
removal by itself or wait for the PCE to request the removal of the
LSP. This is based on the Flag set in SCHED-LSP-ATTRIBUTE TLV.
4.2. Support of LSP Scheduling
4.2.1. LSP Scheduling
For a scheduled LSP, a user configures it with an arbitrary
scheduling duration from time Ta to time Tb, which may be represented
as [Ta, Tb].
When an LSP is configured with arbitrary scheduling duration [Ta,
Tb], a path satisfying the constraints for the LSP in the scheduling
duration is computed and the LSP along the path is set up to carry
traffic from time Ta to time Tb.
4.2.2. Periodical LSP Scheduling
In addition to LSP Scheduling at an arbitrary time period, there are
also periodical LSP Scheduling.
A periodical LSP Scheduling represents Scheduling LSP every time
interval. It has a scheduling duration such as [Ta, Tb], a number of
repeats such as 10 (repeats 10 times), and a repeat cycle/time
interval such as a week (repeats every week). The scheduling
interval: "[Ta, Tb] repeats n times with repeat cycle C" represents
n+1 scheduling intervals as follows:
[Ta, Tb], [Ta+C, Tb+C], [Ta+2C, Tb+2C], ..., [Ta+nC, Tb+nC]
When an LSP is configured with a scheduling interval such as "[Ta,
Tb] repeats 10 times with a repeat cycle a week" (representing 11
scheduling intervals), a path satisfying the constraints for the LSP
in each of the scheduling intervals represented by the periodical
scheduling interval is computed and the LSP along the path is set up
to carry traffic in each of the scheduling intervals.
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4.2.2.1. Elastic Time LSP Scheduling
In addition to the basic LSP scheduling at an arbitrary time period,
another option is elastic time intervals, which is represented as
within -P and Q, where P and Q is an amount of time such as 300
seconds. P is called elastic range lower bound and Q is called
elastic range upper bound.
For a simple time interval such as [Ta, Tb] with an elastic range,
elastic time interval: "[Ta, Tb] within -P and Q" means a time period
from (Ta+X) to (Tb+X), where -P <= X <= Q. Note that both Ta and Tb
is shifted by the same 'X'.
When an LSP is configured with elastic time interval "[Ta, Tb] within
-P and Q", a path is computed such that the path satisfies the
constraints for the LSP in the time period from (Ta+X) to (Tb+X)
and |X| is the minimum value from 0 to max(P, Q). That is, [Ta+X,
Tb+X] is the time interval closest to time interval [Ta, Tb] within
the elastic range. The LSP along the path is set up to carry traffic
in the time period from (Ta+X) to (Tb+X).
Similarly, for a recurrent time interval with an elastic range,
elastic time interval: "[Ta, Tb] repeats n times with repeat cycle C
within -P and Q" represents n+1 simple elastic time intervals as
follows:
[Ta+X0, Tb+X0], [Ta+C+X1, Tb+C+X1], ..., [Ta+nC+Xn, Tb+nC+Xn]
where -P <= Xi <= Q, i = 0, 1, 2, ..., n.
If a user wants to keep the same repeat cycle between any two
adjacent time intervals, elastic time interval: "[Ta, Tb] repeats n
times with repeat cycle C within -P and Q SYNC" may be used, which
represents n+1 simple elastic time intervals as follows:
[Ta+X, Tb+X], [Ta+C+X, Tb+C+X], ..., [Ta+nC+X, Tb+nC+X]
where -P <= X <= Q.
4.2.2.2. Grace Periods
Besides the stated time scheduling, a user may want to have some
grace periods for each or some of the time intervals for the LSP.
Two grace periods may be configured for a time interval. One is the
grace period before the time interval, called grace-before, which
extends the lifetime of the LSP for grace-before (such as 30 seconds)
before the time interval. The other is the one after the time
interval, called grace-after, which extends the lifetime of the LSP
for grace-after (such as 60 seconds) after the time interval.
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When an LSP is configured with a simple time interval such as [Ta,
Tb] with grace periods such as grace-before GB and grace-after GA, a
path is computed such that the path satisfies the constraints for the
LSP in the time period from Ta to Tb. The LSP along the path is set
up to carry traffic in the time period from (Ta-GB) to (Tb+GA).
During grace periods from (Ta-GB) to Ta and from Tb to (Tb+GA), the
LSP is up to carry traffic (maybe in best effort).
4.3. Scheduled LSP creation
In order to realize PCC-Initiated scheduled LSPs in a centralized
network environment, a PCC has to separate the setup of an LSP into
two steps. The first step is to request/delegate and get an LSP but
not signal it over the network. The second step is to signal the
scheduled LSP over the LSRs (Label Switching Router) at its starting
time.
For PCC-Initiated scheduled LSPs, a PCC can delegate the scheduled
LSP by sending a path computation report (PCRpt) message by including
its demanded resources with the scheduling information to a stateful
PCE. Note the PCC MAY use the PCReq/PCRep with scheduling
information before delegating.
Upon receiving the delegation via PCRpt message, the stateful PCE
computes the path for the scheduled LSP per its starting time and
duration based on the network resource availability stored in
scheduled TED (see Section 4.1).
The stateful PCE will send a PCUpd message with the scheduled path
information as well as the scheduled resource information for the
scheduled LSP to the PCC. The PCE SHOULD add the scheduled LSP into
its scheduled LSP-DB and update its scheduled TED.
For PCE-Initiated Scheduled LSP, the stateful PCE can compute a path
for the scheduled LSP per requests from network management systems
automatically based on the network resource availability in the
scheduled TED, send a PCInitiate message with the path information
back to the PCC. Based on the local policy, the PCInitiate message
could be sent immediately to ask PCC to create a scheduled LSP (as
per this document) or the PCInitiate message could be sent at the
start time to the PCC to create a normal LSP (as per [RFC8281]).
In both modes:
o The stateful PCE is required to update its local scheduled LSP-DB
and scheduled TED with the scheduled LSP. Besides, it shall send
a PCRpt message with the scheduled LSP to other PCEs within the
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network, so as to achieve the scheduling traffic engineering
information synchronization.
o Upon receiving the PCUpd message or PCInitiate message for the
scheduled LSP from PCEs with a found path, the PCC knows that it
is a scheduled path for the LSP and does not trigger signaling for
the LSP setup on LSRs immediately.
o The stateful PCE can update the Scheduled LSP parameters on any
network events using the PCUpd message to PCC. These changes are
also synchronized to other PCEs.
o Based on the configuration (and the C flag in scheduled TLVs),
when it is time (i.e., at the start time) for the LSP to be set
up, either the PCC triggers the LSP to be signaled or the
delegated PCE sends a PCUpd message to the head end LSR providing
the updated path to be signaled (with A flag set to indicate LSP
activation).
4.4. Scheduled LSP Modifications
After a scheduled LSP is configured, a user may change its parameters
including the requested time as well as the bandwidth.
In PCC-Initiated case, the PCC can send a PCRpt message for the
scheduled LSP with updated parameters as well as scheduled
information included in the SCHED-LSP-ATTRIBUTE TLV (see
Section 5.2.1) or SCHED-PD-LSP-ATTRIBUTE TLV (see Section 5.2.2)
carried in the LSP Object. The PCE would take the updated resources
and schedule into considerations and update the new path for the
scheduled LSP to the PCC as well as synchronize to other PCEs in the
network. In case path cannot be set based on new requirements the
same should be conveyed by the use of empty ERO in the PCEP messages.
In PCE-Initiated case, the Stateful PCE would recompute the path
based on updated parameters as well as scheduled information. In
case it has already conveyed to the PCC this information by sending a
PCInitiate message, it should update the path and other scheduling
and resource information by sending a PCUpd message.
4.5. Scheduled LSP activation and deletion
In PCC-Initiated case, based on the configuration (and the C flag in
scheduled TLVs), when it is time (i.e., at the start time) for the
LSP to be set up, either the PCC triggers the LSP to be signaled or
the delegated PCE sends a PCUpd message to the head end LSR providing
the updated path to be signaled (with A flag set to indicate LSP
activation). The PCC would report the status of the active LSP as
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per the procedures in [RFC8231] and at this time the LSP MUST be
considered as part of the LSP-DB. The A flag MUST be set in the
scheduled TLVs to indicate that the LSP is active now. After the
scheduled duration expires, based on the C flag, the PCC triggers the
LSP deletion on itself or the delegated PCE sends a PCUpd message to
the PCC to delete the LSP as per the procedures in [RFC8231].
In PCE-Initiated case, based on the local policy, if the scheduled
LSP is already conveyed to the PCC at the time of creation, the
handling of LSP activation and deletion is handled in the same way as
PCC-Initiated case as per the setting of C flag. In other case, the
PCE would send the PCInitiate message at the start time to the PCC to
create a normal LSP without the scheduled TLVs and remove the LSP
after the duration expires as per [RFC8281].
5. PCEP Objects and TLVs
5.1. Stateful PCE Capability TLV
After a TCP connection for a PCEP session has been established, a PCC
and a PCE indicates its ability to support LSP scheduling during the
PCEP session establishment phase. For a multiple-PCE environment,
the PCEs should also establish PCEP session and indicate its ability
to support LSP scheduling among PCEP peers. The Open Object in the
Open message contains the STATEFUL-PCE-CAPABILITY TLV defined in
[RFC8231]. Note that the STATEFUL-PCE-CAPABILITY TLV is defined in
[RFC8231] and updated in [RFC8281] and [RFC8232]". In this document,
we define a new flag bit B (SCHED-LSP-CAPABLITY) flag for the
STATEFUL-PCE-CAPABILITY TLV to indicate the support of LSP scheduling
and another flag bit PD (PD-LSP-CAPABLITY) to indicate the support of
LSP periodical scheduling.
B (LSP-SCHEDULING-CAPABILITY - 1 bit) [Bit Position - TBD3]: If set
to 1 by a PCC, the B Flag indicates that the PCC allows LSP
scheduling; if set to 1 by a PCE, the B Flag indicates that the
PCE is capable of LSP scheduling. The B bit MUST be set by both
PCEP peers in order to support LSP scheduling for path
computation.
PD (PD-LSP-CAPABLITY - 1 bit): [Bit Position - TBD4] If set to 1 by
a PCC, the PD Flag indicates that the PCC allows LSP scheduling
periodically; if set to 1 by a PCE, the PD Flag indicates that the
PCE is capable of periodical LSP scheduling. The PD bit MUST be
set by both PCEP peers in order to support periodical LSP
scheduling for path computation.
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5.2. LSP Object
The LSP object is defined in [RFC8231]. This document adds an
optional SCHED-LSP-ATTRIBUTE TLV for normal LSP scheduling and an
optional SCHED-PD-LSP-ATTRIBUTE TLV for periodical LSP scheduling.
The presence of SCHED-LSP-ATTRIBUTE TLV in the LSP object indicates
that this LSP is requesting scheduled parameters while the SCHED-PD-
LSP-ATTRIBUTE TLV indicates that this scheduled LSP is periodical.
The scheduled LSP attribute TLV MUST be present in LSP Object for
each scheduled LSP carried in the PCEP messages. For periodical
LSPs, the SCHED-PD-LSP-ATTRIBUTE TLV can be used in LSP Object for
each periodic scheduled LSP carried in the PCEP messages.
Only one of these TLV SHOULD be present in the LSP object. In case
more than one scheduling TLV is found, the first instance is
processed and others ignored.
5.2.1. SCHED-LSP-ATTRIBUTE TLV
The SCHED-LSP-ATTRIBUTE TLV MAY be included as an optional TLV within
the LSP object for LSP scheduling for the requesting traffic service.
This TLV SHOULD NOT be included unless both PCEP peers have set the B
(LSP-SCHEDULING-CAPABILITY bit) in STATEFUL-PCE-CAPABILITY TLV
carried in the Open message.
The format of the SCHED-LSP-ATTRIBUTE TLV is shown in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|C|A| Flags | Reserved (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start-Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GrB | GrA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Elastic-Lower-Bound | Elastic-Upper-Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SCHED-LSP-ATTRIBUTE TLV
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The type of the TLV is [TBD1] and the TLV has a fixed length of 20
octets.
The fields in the format are:
Flags (8 bits): Following flags are defined in this document
R (1 bit): Set to 1 to indicate the Start-Time is a relative
time, which is relative to the current time; set to 0 to
indicate that the 32-bit Start-Time is an absolute time, which
is the number of seconds since the epoch. The epoch is 1
January 1900 at 00:00 UTC. It wraps around every 2^32 seconds,
which is roughly 136 years. The next wraparound will occur in
the year 2036.
C (1 bit): Set to 1 to indicate the PCC is responsible to setup
and remove the scheduled LSP based on the Start-Time and
duration.
A (1 bit): Set to 1 to indicate the scheduled LSP has been
activated and should be considered as part of LSP-DB (instead
of Scheduled LSP-DB).
Reserved (24 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Start-Time (32 bits): This value in seconds, indicates when the
scheduled LSP is used to carry traffic and the corresponding LSP
must be setup and activated.
Duration (32 bits): The value in seconds, indicates the duration
that the LSP is undertaken by a traffic flow and the corresponding
LSP must be up to carry traffic. At the expiry of this duration,
the LSP is torn down and deleted.
The Start-Time indicates a calendar time (e.g.,2018/12/13 8:29:58),
at or before which the scheduled LSP must be set up. The value of
the Start-Time represents the number of seconds since 00:00 hours,Jan
1, 1970 UTC when R bit is set to 0. When R bit is set to 1, it
represents the number of seconds from the current time.
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In addition, it contains an non zero grace-before and grace-after if
grace periods are configured. It includes an non zero elastic range
lower bound and upper bound if there is an elastic range configured.
o GrB (Grace-Before -16 bits): The grace period time length in
seconds before the starting time.
o GrA (Grace-After -16 bits): The grace period time length in
seconds after time interval [starting time, starting time +
duration].
o Elastic-Lower-Bound (16 bits): The maximum amount of time in
seconds that time interval can shift to lower/left.
o Elastic-Upper-Bound (16 bits): The maximum amount of time in
seconds that time interval can shift to upper/right.
5.2.2. SCHED-PD-LSP-ATTRIBUTE TLV
The periodical LSP is a special case of LSP scheduling. The traffic
service happens in a series of repeated time intervals. The SCHED-
PD-LSP-ATTRIBUTE TLV can be included as an optional TLV within the
LSP object for this periodical LSP scheduling.
This TLV SHOULD NOT be included unless both PCEP peers have set the B
(LSP-SCHEDULING-CAPABILITY bit) and PD (PD-LSP-CAPABLITY bit) in
STATEFUL-PCE-CAPABILITY TLV carried in open message.
The format of the SCHED-PD-LSP-ATTRIBUTE TLV is shown in Figure 2.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|C|A| Flags | Opt | NR | Reserved (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start-Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Repeat-time-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GrB | GrA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Elastic-Lower-Bound | Elastic-Upper-Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SCHED-PD-LSP-ATTRIBUTE TLV
The type of the TLV is [TBD2] and the TLV has a fixed length of 24
octets. The description, format and meaning of the Flags (R, C and A
bit), Start-Time, Duration, GrB, GrA, Elastic-Lower-Bound and
Elastic-Upper-Bound fields remains same as SCHED-LSP-ATTRIBUTE TLV.
The following fields are new :
Opt: (4 bits) Indicates options to repeat.
Options = 1: repeat every day;
Options = 2: repeat every week;
Options = 3: repeat every month;
Options = 4: repeat every year;
Options = 5: repeat every Repeat-time-length.
NR: (12 bits) The number of repeats. In each of repeats, LSP
carries traffic.
Reserved (8 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Repeat-time-length: (32 bits) The time length in seconds after which
LSP starts to carry traffic again for the Duration.
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6. The PCEP Messages
6.1. The PCRpt Message
Path Computation State Report (PCRpt) is a PCEP message sent by a PCC
to a PCE to report the status of one or more LSPs as per [RFC8231].
Each LSP State Report in a PCRpt message contains the actual LSP's
path, bandwidth, operational and administrative status, etc. An LSP
Status Report carried on a PCRpt message is also used in delegation
or revocation of control of an LSP to/from a PCE. In case of
scheduled LSP, the scheduled TLVs MUST be carried in the LSP object
and the ERO conveys the intended path for the scheduled LSP. The
scheduled LSP MUST be delegated to a PCE. This message is also used
to synchronize the scheduled LSPs to other PCE as described in
[RFC8231]
6.2. The PCUpd Message
Path Computation Update Request (PCUpd) is a PCEP message sent by a
PCE to a PCC to update LSP parameters, on one or more LSPs as per
[RFC8231]. Each LSP Update Request on a PCUpd message contains all
LSP parameters that a PCE wishes to be set for a given LSP. In case
of scheduled LSP, the scheduled TLVs MUST be carried in the LSP
object and the ERO conveys the intended path for the scheduled LSP.
In case no path can be found, an empty ERO is used. The A bit is
used in PCUpd message to indicate the activation of the scheduled LSP
in case the PCE is responsible for the activation (as per the C bit).
6.3. The PCInitiate Message
An LSP Initiate Request (PCInitiate) message is a PCEP message sent
by a PCE to a PCC to trigger LSP instantiation or deletion as per
[RFC8281]. In case of scheduled LSP, based on the local policy, PCE
MAY convey the scheduled LSP to the PCC by including the scheduled
TLVs in the LSP object. Or the PCE would initiate the LSP only at
the start time of the scheduled LSP as per the [RFC8281] without the
use of scheduled TLVs.
6.4. The PCReq message
The Path Computation Request (PCReq) message is a PCEP message sent
by a PCC to a PCE to request a path computation [RFC5440] and it may
contain the LSP object [RFC8231] to identify the LSP for which the
path computation is requested. In case of scheduled LSP, the
scheduled TLVs MUST be carried in the LSP object in PCReq message to
request the path computation based on scheduled TED and LSP-DB. A
PCC MAY use PCReq message to obtain the scheduled path before
delegating the LSP.
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6.5. The PCRep Message
The Path Computation Reply (PCRep) message is a PCEP message sent by
a PCE to a PCC in reply to a path computation request [RFC5440] and
it may contain the LSP object [RFC8231] to identify the LSP for which
the path is computed. A PCRep message can contain either a set of
computed paths if the request can be satisfied, or a negative reply
if not. The negative reply may indicate the reason why no path could
be found. In case of scheduled LSP, the scheduled TLVs MUST be
carried in the LSP object in PCRep message to indicate the path
computation based on scheduled TED and LSP-DB. A PCC and PCE MAY use
PCReq and PCRep message to obtain the scheduled path before
delegating the LSP.
6.6. The PCErr Message
The Path Computation Error (PCErr) message is a PCEP message as
described in [RFC5440] for error reporting. The current document
defines new error values for several error types to cover failures
specific to scheduling and reuse the applicable error types and error
values of [RFC5440] and [RFC8231] wherever appropriate.
The PCEP extensions for scheduling MUST NOT be used if one or both
PCEP speakers have not set the corresponding bits in the STATEFUL-
PCE-CAPABILITY TLV in their respective OPEN message. If the PCEP
speaker supports the extensions of this specification but did not
advertise this capability, then upon receipt of LSP object with the
scheduled TLV, it MUST generate a PCEP Error (PCErr) with Error-
type=19 (Invalid Operation) and error-value TBD6 (Attempted LSP
Scheduling if the scheduling capability was not advertised), and it
SHOULD ignore the TLV. As per Section 7.1 of [RFC5440], a legacy
PCEP implementation that does not understand this specification,
would consider the scheduled TLVs as unknown and ignore them.
If the PCC decides that the scheduling parameters proposed in the
PCUpd/PCInitiate message are unacceptable, it MUST report this error
by including the LSP-ERROR-CODE TLV (Section 7.3.3) with LSP error-
value="Unacceptable parameters" in the LSP object (with scheduled
TLVs) in the PCRpt message to the PCE.
The scheduled TLVs MUST be included in the LSP object for the
scheduled LSPs, if the TLV is missing, the receiving PCEP speaker
MUST send a PCErr message with Error-type=6 (Mandatory Object
missing) and Error-value TBD5 (Scheduled TLV missing).
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7. Security Considerations
This document defines LSP-SCHEDULING-CAPABILITY TLV and SCHED-LSP-
ATTRIBUTE TLV, the security considerations discussed in [RFC5440],
[RFC8231], and [RFC8281] continue to apply. In some deployments the
scheduling information could provide details about the network
operations that could be deemed as extra sensitive. Additionally,
snooping of PCEP messages with such data or using PCEP messages for
network reconnaissance may give an attacker sensitive information
about the operations of the network. A single PCEP message can now
instruct a PCC to set up and tear down an LSP every second for a
number of times. That single message could have a significant effect
on the network. Thus, such deployment should employ suitable PCEP
security mechanisms like TCP Authentication Option (TCP-AO) [RFC5925]
or [RFC8253]. The procedure based on Transport Layer Security (TLS)
in [RFC8253] is considered a security enhancement and thus is much
better suited for the sensitive information. PCCs may also need to
apply some form of rate limit to the processing of scheduled LSPs.
8. Manageability Consideration
8.1. Control of Function and Policy
The LSP-Scheduling feature MUST BE controlled per tunnel by the
active stateful PCE, the values for parameters like starting time,
duration SHOULD BE configurable by customer applications and based on
the local policy at PCE.
8.2. Information and Data Models
An implementation SHOULD allow the operator to view the capability
defined in this document. To serve this purpose, the PCEP YANG
module [I-D.ietf-pce-pcep-yang] could be extended.
8.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
8.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440].
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8.5. Requirements On Other Protocols
Mechanisms defined in this document do not imply any new requirements
on other protocols.
8.6. Impact On Network Operations
Mechanisms defined in this document do not have any impact on network
operations in addition to those already listed in [RFC5440].
9. IANA Considerations
9.1. PCEP TLV Type Indicators
This document defines the following new PCEP TLV. IANA maintains a
sub-registry "PCEP TLV Type Indicators" in the "Path Computation
Element Protocol (PCEP) Numbers" registry. IANA is requested to make
the following allocations from this sub-registry.
Value Meaning Reference
TBD1 SCHED-LSP-ATTRIBUTE This document
TBD2 SCHED-PD-LSP-ATTRIBUTE This document
IANA is requested to create and maintain a new registry "Opt" under
SCHED-PD-LSP-ATTRIBUTE (TLV Type: TBD2). Initial values for the
registry are given below.
Value Name Definition
----- ---- ----------
0 Reserved
1 REPEAT-EVERY-DAY Section 5.2.2
2 REPEAT-EVERY-WEEK Section 5.2.2
3 REPEAT-EVERY-MONTH Section 5.2.2
4 REPEAT-EVERY-YEAR Section 5.2.2
5 REPEAT-EVERY-REPEAT-TIME-LENGTH Section 5.2.2
6-14 Unassigned
15 Reserved
9.2. STATEFUL-PCE-CAPABILITY TLV Flag field
This document defines new bits in the Flags field in the STATEFUL-
PCE-CAPABILITY TLV in the OPEN object. IANA maintains a sub-registry
"STATEFUL-PCE-CAPABILITY TLV Flag Field" in the "Path Computation
Element Protocol (PCEP) Numbers" registry. IANA is requested to make
the following allocations from this sub-registry.
The following values are defined in this document:
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Bit Description Reference
TBD3 LSP-SCHEDULING-CAPABILITY (B-bit) This document
TBD4 PD-LSP-CAPABLITY (PD-bit) This document
9.3. Schedule TLVs Flag Field
IANA is requested to create a new sub-registry, named "Schedule TLVs
Flag Field", within the "Path Computation Element Protocol (PCEP)
Numbers" registry to manage the Flag field in the SCHED-LSP-ATTRIBUTE
and SCHED-PD-LSP-ATTRIBUTE TLVs. New values are assigned by
Standards Action [RFC8126]. Each bit should be tracked with the
following qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability description
o Defining RFC
The following values are defined in this document:
Bit Description Reference
0 R-bit This document
1 C-bit This document
2 A-bit This document
9.4. PCEP-Error Object
IANA is requested to allocate the following new error types to the
existing error values within the "PCEP-ERROR Object Error Types and
Values" subregistry of the "Path Computation Element Protocol (PCEP)
Numbers" registry:
Error-Type Meaning
6 Mandatory Object missing
Error-value
TBD5: Scheduled TLV missing
19 Invalid Operation
Error-value
TBD6: Attempted LSP Scheduling if the scheduling
capability was not advertised
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10. Acknowledgments
The authors of this document would also like to thank Rafal Szarecki,
Adrian Farrel, Cyril Margaria for the review and comments.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
and D. Dhody, "Optimizations of Label Switched Path State
Synchronization Procedures for a Stateful PCE", RFC 8232,
DOI 10.17487/RFC8232, September 2017,
<https://www.rfc-editor.org/info/rfc8232>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
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11.2. Informative References
[I-D.ietf-detnet-architecture]
Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", draft-ietf-
detnet-architecture-13 (work in progress), May 2019.
[I-D.ietf-pce-pcep-yang]
Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", draft-ietf-pce-pcep-
yang-12 (work in progress), July 2019.
[I-D.litkowski-pce-state-sync]
Litkowski, S., Sivabalan, S., Li, C., and H. Zheng, "Inter
Stateful Path Computation Element (PCE) Communication
Procedures.", draft-litkowski-pce-state-sync-05 (work in
progress), March 2019.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC7399] Farrel, A. and D. King, "Unanswered Questions in the Path
Computation Element Architecture", RFC 7399,
DOI 10.17487/RFC7399, October 2014,
<https://www.rfc-editor.org/info/rfc7399>.
[RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
Stateful Path Computation Element (PCE)", RFC 8051,
DOI 10.17487/RFC8051, January 2017,
<https://www.rfc-editor.org/info/rfc8051>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8413] Zhuang, Y., Wu, Q., Chen, H., and A. Farrel, "Framework
for Scheduled Use of Resources", RFC 8413,
DOI 10.17487/RFC8413, July 2018,
<https://www.rfc-editor.org/info/rfc8413>.
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Appendix A. Contributor Addresses
Dhruv Dhody
Huawei
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Xufeng Liu
Ericsson
USA
Email: xliu@kuatrotech.com
Mehmet Toy
Verizon
USA
Email: mehmet.toy@verizon.com
Vic Liu
China Mobile
No.32 Xuanwumen West Street, Xicheng District
Beijing, 100053
China
Email: liu.cmri@gmail.com
Lei Liu
Fujitsu
USA
Email: lliu@us.fujitsu.com
Khuzema Pithewan
Infinera
Email: kpithewan@infinera.com
Zitao Wang
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: wangzitao@huawei.com
Xian Zhang
Huawei Technologies
Research Area F3-1B,
Huawei Industrial Base,
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Shenzhen, 518129, China
Email: zhang.xian@huawei.com
Authors' Addresses
Huaimo Chen (editor)
Futurewei
Boston, MA
USA
Email: huaimo.chen@futurewei.com
Yan Zhuang (editor)
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: zhuangyan.zhuang@huawei.com
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: bill.wu@huawei.com
Daniele Ceccarelli
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
Email: daniele.ceccarelli@ericsson.com
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