Network Working Group                                     Xian Zhang
Internet-Draft                                             Young Lee
Intended status: Standards Track                              Huawei
                                                      Ramon Casellas
                                              Oscar Gonzalez de Dios
                                                      Telefonica I+D

Expires: July 16, 2013                             February 17, 2013

Stateful Path Computation Element (PCE) for Time-based Scheduling


Status of this Memo

This Internet-Draft is submitted to IETF in full conformance with
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Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on July 16, 2013.


This document presents the architecture and procedures for stateful
PCE to support time-based scheduling application and also provides
PCEP extensions needed.

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Conventions used in this document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
document are to be interpreted as described in RFC-2119 [RFC2119].

Table of Contents

1. Introduction ................................................ 2
2. Architecture ................................................ 3
   2.1. Terms and Definitions................................... 3
   2.2. Network Architecture.................................... 3
3. PCEP Extensions ............................................. 5
   3.1. New Object ............................................. 6
   3.2. Procedure .............................................. 6
4. IANA Considerations ......................................... 9
5. Manageability Considerations................................ 10
   5.1. Requirements on Other Protocols........................ 10
6. Security Considerations..................................... 10
7. Acknowledgement ............................................ 10
8. References ................................................. 10
   8.1. Normative References................................... 10
   8.2. Informative References................................. 11
9. Contributors' Address....................................... 11
10. Authors' Addresses ........................................ 12

1. Introduction

As described in [stateful-app], stateful PCE are helpful in a
variety of applications. One of the applications is time-based
scheduling, which books network resources in advance. A simple
utilization example of the time-based scheduling application is to
support scheduled data transmission between data centers or servers.

To support this without a PCE, network operators need to reserve
resources in advance according to customers' requests with specified
starting time and duration. This can be supported by NMS operation
through path pre-establishment and activation on the agreed starting
time. 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 due
to the lack of a time-based mechanism. It can also be accomplished
through GMPLS protocol extensions by carrying the related request
information (e.g., starting time and duration) across the network.

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Nevertheless, this method inevitably increases the complexity of
signaling and routing process.

Since a stateful PCE collects LSP related information for the whole
network, it can support this service with resource usage flexibility
(i.e., only excluding the time slots reserved for time-based
scheduling requests). Moreover, it can avoid the need to add
complexity on network elements in this regard.

The fundamental PCEP extensions are covered in [stateful-pcep],
[stateful-pcep-mpls] and [stateful-pcep-gmpls]. This document
complements these documents by elaborating issues related to the
time-based scheduling application as well as providing the
extensions needed. Note that the time synchronization required for
time-based scheduling does not need a precise one and can be in a
coarser scale as long as it does not impact its operation.

2. Architecture

2.1. Terms and Definitions

Following the definitions provided in [PCE-Q&A], a stateful PCE is
defined as a PCE with the ability to maintain LSP related
information and take advantage of such information to facilitate
computing better paths. It is also referred as a passive PCE. On the
other hand, an active PCE is defined as a PCE with ability to
provide "provisioning suggestions" to the network. The "provisioning
suggestions" include both modification of existing LSPs and creation
of new LSPs. In this document, a PCE is assumed to have the stateful
ability. So, the aforementioned two categories can also be referred
as an active PCE with LSP delegation and an active PCE with LSP
initiation ability, respectively.

2.2. Network Architecture

The figure below shows the network architecture for deploying time-
based scheduling application. The network shown is an example.

The NMS can issues resource scheduling requests to a stateful PCE.
Alternatively, it can enquire a stateful PCE whether the network has
the ability to undertaken any upcoming service requests. In this
document, it is assumed that the PCE system will be a stateful one.
It should have access to the database(s) including the following

o network TE information: this can be obtained via IGP protocols or

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o In-use LSPs information: this denotes the LSPs that are currently
taking network resource. They are helpful for a PCE to better
schedule network resource for resource booking requests with
constraints related to existing LSPs;

o Scheduled LSP information: this denotes the LSPs that are yet to
be activated. A stateful PCE should take this information into
consideration when allocating resources upon resource booking
requests to avoid double-booking.

The last two types of information are LSPs related and they can be
obtained via LSP state update/report messages as defined in
[stateful-pcep]. Extensions are needed and are explained later in
this document.

|          NMS            |
+----------------------+     +-----------------+
|                      |     |  Databases:     |
|     Stateful PCE     |-----|  TE info        |
|                      |     |  In-use LSPs    |
+----------------------+     |  Scheduled LSPs |
            |                +-----------------+
|          +--+   +--+   +--+   +--+   +--+   +--+              |
|          |N1+---+N2+---+N3+---+N7+---+N8+---+N9|              |
|          +-++   +--+   +-++   +-++   +--+   +-++              |
|            |             |      |             |               |
|            |             |      |             |               |
|          +-++   +--+   +-++   +-+-+        +--++              |
|          |N4+---+N5+---+N6+---+N10+--------+N11|              |
|          +--+   +--+   +--+   +---+        +---+              |
Figure 1: Stateful PCE for Deploying Time-based Scheduling

Depending on the ability of a stateful PCE, there are three
available modes for deploying time-based scheduling application.

o Passive stateful PCE and PCC cooperating mode

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In this case, PCCs are responsible for the creation, activation and
deletion of the scheduled LSPs. With the network level view of
resource usage and booking, the stateful PCE can help efficiently
allocate network resource upon receiving resource booking requests
from PCCs.

This mode requires the least amount of PCE involvement.

o Active stateful PCE with LSP delegation mode

In this mode, PCCs are responsible for the creation of the scheduled
LSPs and they will delegate the LSP activation and deletion
capability to a stateful PCE prior to the LSP activation time. For
example, the delegation can happen at the same time when a PCC sends
path computation requests to a PCE. Thus, a stateful PCE is
responsible for the activation and/or deletion of LSPs.

o Active stateful PCE with LSP initiation mode

This requires the PCE has the ability to initiating LSPs. In this
mode, a PCC does not necessarily be aware of any scheduled LSP ahead
of time. The PCE is the entity that accepts such requirements
externally, such as Network Management System (NMS). So, an active
PCE will initiate the LSP creation/setup as well as its deletion. If
returning LSP delegation is allowed, then a PCC also can have the
ability to delete a LSP when its duration time ends up.

3. PCEP Extensions

The following lists a number of requirements for implementing time-
based scheduling using a stateful PCE.

o A Mechanism to maintain the time synchronization in certain scale,
such as in the order of minutes, are expected. In other words,
strict time synchronization among requesting PCCs and PCEs is not
required. It is assumed that the synchronization scale of the PCE is
made known, e.g. through configuration, to all its related PCCs. How
to achieve this is out of the scope of this document.

o The ability to exchange time-related information between a
stateful PCE and PCCs during path computation request/reply as well
as LSP state updates;

o Maintenance of a database storing the information related to the
booking service requests, including the time and resource usage

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Irrespective of the deployment mode, a database that stores all the
reserved information with time reference should be maintained. This
can be achieved either by maintaining a separate database or having
all the reserved information with time reference incorporated into
in-use LSP database (LSP-DB). The details of organizing time-based
scheduling related information are subject to network provider's
policy and administrative consideration and thus outside of the
scope of this document.

3.1. New Object

A SERVICE-TIME object is presented as follows to provide the
required information (i.e. service starting time and holding time).

The Object-Class is TBD and the Object-Type is 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
   |       Start-Year              |    Month      |     Day       |
   |     Hour      |    Minute     |    Second     |   Reserved    |
   |                       Duration (in seconds)                   |

     field      Length       range

      -----      ------     --------

     Start-Year  16 bit     0..65536

     Month       8 bit     1..12

     Day         8 bit     1..31

     Hour        8 bit     0..23

     Minute    8 bit     0..59

     Second      8 bit     0..59

3.2. Procedure

There are three fundamental actions required for deploying a time-
based scheduling application. They are resource allocation for a
scheduled service request, activation of the scheduled service and

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deletion of the scheduled service, respectively. For the three modes
explained in Section 2, the responsible components may differ. The
following elaborates them separately, together with PCEP extensions

4.1.1 Passive stateful PCE and PCC cooperating mode

Step 1: Resource Allocation

When a PCC requests to a stateful PCE for booking resource in
advance, the SERVICE-TIME object MUST be included in a PCEP request
as specified in the following manner:

<PCReq Message>::=<Common Header>




   [<svec-list>]::= <SVEC> [<svec-list>]


  <request >::=<RP>











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Upon receiving a path computation request with the <SERVICE-TIME>
object included, the stateful PCE should compute the path,
considering the constraints of the TED, LSP-DB as well as other
already scheduled service information. Then, it should return the
computed route back to the requesting PCC and add such information
into the scheduled LSP database. If no path can be found due to
insufficient resource, the stateful PCE should return an error
message specifying the reason "no resource available for this
scheduling request".

If there is any change/update with regard to a particular scheduled
LSP, LSP report message should be used to inform the stateful PCE of
the change, such as cancelation of the scheduled LSP, assignment of
LSP identifiers etc. If attributes such as bandwidth, starting time
or duration needs to be updated, a path computation request MAY need
to be issued and it is similar to the process of bandwidth
modification of an ordinary LSP.

[Editor's note: further extensions are needed, such as adding a
"cancellation" status bit etc.]

Step 2: Activation of a scheduled LSP

The PCC will keep track of the time and start the signaling process
when it is time to set up the scheduled LSP. The stateful PCE should
be informed of the status of the scheduled LSP. For a successful
setup of a scheduled LSP, the relevant information should be moved
from the scheduled database to the in-use database or the LSP record
should be marked in its correct state. If there is a setup error,
the PCC should inform the stateful PCE of this failure specifying
the reason. The resource may be released instantly to allow
acceptance of other requests.

Step 3: Deletion of a scheduled LSP

After a PCC tears a scheduled LSP down, the information related to
this LSP should be deleted or marked as in a deleted state. If there
is any issue with tearing down a scheduled LSP, the failure reason
may be reported to the stateful PCE.

[Editor's note: Error codes to be added.]

4.1.2 Active stateful PCE with LSP delegation mode

In this mode, the resource allocation procedure is similar to that
of the first mode. The difference is that the PCC will report this
LSP state and set the "delegate" bit in the LSP report message into
1 [Stateful-pcep]. Thus, the stateful PCE obtains the control of

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this potential LSP. This mode gives the flexibility of a stateful
PCE to change the attributes of a potential LSP proactively. The PCC
needs to get informed of the change prior to the time when this LSP
needs to be activated. This can be done via LSP state update
messages sent by a stateful PCE to PCCs.

The activation and deletion of the scheduling LSP is the same as the
one described previously.

4.1.3 Active stateful PCE with LSP initiation mode

Step 1: Resource Allocation

The request may not come from a network element in the network, but
from other entities instead, such as an NMS.

Step 2 & 3: Activation and Deletion of a scheduled LSP

This mode allows the statful PCE to maintain the information in a
centralized way and initiates the activation and deletion of the
scheduled LSP. Thus, it does not necessarily need the coarse time
synchronization between PCCs and PCE.

This is not the case when a PCC is granted to be in charge of the
LSP deletion action. Furthermore, the active PCE may need to inform
any changes related to a scheduled LSP. This MAY requires including
carrying the time-related information in <attribute-list > of the
PCRpt message.

<attribute-list> ::= [<LSPA>]





      <metric-list>::= <METRIC>[<metric-list>]

4. IANA Considerations

IANA is requested to allocate new Types for the TLV/Object defined
in this document.

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5. Manageability Considerations

The manageability requirements listed in [RFC5440] and [stateful-
pcep] apply in this document. Additional considerations are
explained below:

5.1. Requirements on Other Protocols

It is expected that the time synchronization should be realized
using other protocols, such as Network Time Protocol to ensure the
correct operation of the application specified in this document.

[Editor's note: the loss of time synchronization between PCCs and
PCEs will impact the performance of the application specified in
this document and needs to be investigated further.]

6. Security Considerations

This document defines extensions to PCEP to enable time-based
scheduling application to deployed using stateful PCE. The security
issues and solutions provided in [RFC5440] and [stateful-pcep]
remain applicable to this document. The following issues should also
be considered in the context of this document. The following lists
other security issues incurred in the context of this document.

A malicious PCC may drain the resource usage of the network by
sending large bulks of resource booking requests. This can be
avoided by setting a limit to the number of booking requests a PCC
can issue or a policy configured on the PCE to reject some or all of
the booking requests by monitoring the frequency and amount of
resource required.

7. Acknowledgement

We would like to thank Robert Varga and Adrian Farrel for their
useful comments and discussions.

8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to indicate
          requirements levels", RFC 2119, March 1997.

[Stateful-pcep]Crabbe, E., Medved, J., Varga, R., Minei, I., "PCEP
          Extensions for Stateful PCE", draft-ietf-pce-stateful-pce,
          work in progress.

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[stateful-pcep-mpls] Crabbe, E., Medved, J., Varga, R., Minei, I.,
          "Stateful PCE extensions for MPLS-TE LSPs", draft-crabbe-
          pce-stateful-pce-mpls-te-00, work in progress.

[stateful-pcep-gmpls] Zhang, X., Lee, Y., Casellas, R., Gonzalez de
          Dios, O., " Path Computation Element (PCE) Protocol
          Extension for Stateful PCE Usage in GMPLS Networks",
          draft-zhang-pce-pcep-stateful-pce-gmpls, work in progress

8.2. Informative References

[Stateful-app] Zhang, F., Zhang, X., Lee, Y., Casellas, R., Gonzalez
          de Dios, O., "Applicability of Stateful Path Computation
          Element (PCE) ", draft-zhang-pce-stateful-pce-app, work in

[PCE-Q&A] Farrel, A., King, D., "Unanswered Questions in the Path
          Computation Element Architecture", draft-farrkingel-pce-
          questions-00, working in progress;

9. Contributors' Address

Dhruv Dhody
Huawei Technology
Leela Palace
Bangalore, Karnataka 560008


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10. Authors' Addresses

Xian Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China

Phone: +86-755-28972913

Young Lee
1700 Alma Drive, Suite 100
Plano, TX  75075

Phone: +1 972 509 5599 x2240
Fax:   +1 469 229 5397

Ramon Casellas
CTTC - Centre Tecnologic de Telecomunicacions de Catalunya
Av. Carl Friedrich Gauss n7
Castelldefels, Barcelona 08860


Oscar Gonzalez de Dios
Telefonica Investigacion y Desarrollo
Emilio Vargas 6
Madrid,   28045

Phone: +34 913374013

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