Internet DRAFT - draft-gonzalezdedios-pce-reservation-state
draft-gonzalezdedios-pce-reservation-state
Network Working Group O. Gonzalez de Dios, Ed.
Internet-Draft Telefonica I+D
Intended status: Standards Track R. Casellas
Expires: September 10, 2012 CTTC
C. Margaria
Nokia Siemens Networks
Y. Lee
F. Zhang
Huawei
March 9, 2012
PCEP Extensions for Temporary Reservation of Computed Path Resources and
Support for Limited Context State in PCE
draft-gonzalezdedios-pce-reservation-state-01
Abstract
The Path Computation Element (PCE) provides path computation
functions in support of traffic engineering in Multi-Protocol Label
Switching (MPLS) and Generalized MPLS (GMPLS) networks.
A limited form of statefulness is useful to improve PCE functionality
in situations in which the local TED might not be up to date, or in
the case of concurrent requests where most of the LSPs are computed
before the end of the set-up of the LSPs, when the TED is updated.
The PCC is responsible to setup or not the TE-Path computed by the
PCE. By providing an indication that it intends to use the resources
on the TE-Path a PCC can help the PCE to get a more accurate dynamic
TED view and thus the PCE can avoid suggesting the use of the same
resources for subsequent TE LSPs.
This document proposes an extension to the PCEP protocol to allow the
PCC to indicate to the PCE to block or reserve the resources computed
in a path request of a TE LSP for subsequent requests for a certain
time and can help to reduce the number of crankbacks.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 10, 2012.
Copyright Notice
Copyright (c) 2012 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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. PCEP Requirements . . . . . . . . . . . . . . . . . . . . . . 6
3. PCEP Extensions (Encoding) . . . . . . . . . . . . . . . . . . 8
3.1. Requesting a Reservation of Resources . . . . . . . . . . 8
3.2. Replying a reservation status . . . . . . . . . . . . . . 10
3.3. Cancelling a Reservation . . . . . . . . . . . . . . . . . 10
3.4. RESERVATION object format . . . . . . . . . . . . . . . . 11
3.5. RESERVATION_CONF object format . . . . . . . . . . . . . . 12
3.6. RESERVATION_ID TLV . . . . . . . . . . . . . . . . . . . . 13
4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1. Multiple LSP restoration in a WSON network . . . . . . . . 14
5.2. Domain path selection . . . . . . . . . . . . . . . . . . 15
5.3. Multidomain path computation . . . . . . . . . . . . . . . 16
6. Manageability Considerations . . . . . . . . . . . . . . . . . 16
6.1. Control of Function and Policy . . . . . . . . . . . . . . 16
6.2. Information and Data Models . . . . . . . . . . . . . . . 16
6.3. Liveness Detection and Monitoring . . . . . . . . . . . . 17
6.4. Verifying Correct Operation . . . . . . . . . . . . . . . 17
6.5. Requirements for Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . . . . 17
6.6. Impact on Network Operation . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8.1. RESERVATION object . . . . . . . . . . . . . . . . . . . . 18
8.2. RESERVATION_CONF object . . . . . . . . . . . . . . . . . 18
8.3. RESERVATION_ID TLV . . . . . . . . . . . . . . . . . . . . 18
8.4. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 18
9. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 18
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
11. Normative References . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
According to [RFC4655], a PCE can be either stateful or stateless.
In the former case, there is a strict synchronization between the
PCE, the network state (in terms of topology and per link aggregated
resource information such as unreserved bandwidth), and also the set
of computed paths, active Label Switched Paths (LSPs) and resources
in use in the network.
In other words, a stateful PCE utilizes information from the TED as
well as information about existing paths (for example, TE LSPs) in
the network when processing new requests. However, the maintenance
and synchronization of a stateful LSP database (LSP-DB) can be non-
trivial, not only because it should verify the actual establishment
of computed paths, and because it might not be the unique element to
compute paths.
In addition, it can be argued that maintaining such a stateful
database is not a function of the PCE, but rather of a Network
Management System (NMS).
On the other hand, a stateless PCE does not typically keep track of
computed paths, and each set of request(s) is processed independently
of each other, typically using a local copy of the TED. Since a
stateless PCE typically operates on a graph with computation
constraints and without tracking the current state of paths,
independent requests will be processed on the same TED graph, until
the graph is updated.
With a stateless PCE, there is a 'potential window of TED
inaccuracy', where a stateless PCE may compute paths based on current
TED information, which could be out-of-sync with the actual or
potential network state changes given other recent PCE-computed
paths.
For example, some sources for this potential TED inaccuracy are:
o Control Plane link latencies may increase due to several factors
such as: a) the time required for a PCC to obtain the paths after
a successful computation, requiring several Round-Trip-Times (RTT)
as per TCP; b) the setup delay and c) the time it takes for the
PCE to update the local TED given IGP update times.
o The routing and topology dissemination protocol (i.e. OSPF-TE) ),
which may operate with timers for LSA updates, to avoid excessive
control plane overhead.
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o Concurrent requests that arrive during the time window, between a
response is sent and the LSP is setup and the topology changes
flooded. Even for very fast networks with low latency, there may
be 'batched' requests: several path computation requests within a
PCReq message or, in dynamic restoration without pre-planning,
several LSPs that need to be rerouted avoiding a failed link.
o Local PCE contention, where the PCE needs to concurrently serve
path computation requests and update the LSA (e.g. parsing OSPF-TE
LSA updates). A PCE implementation may need to find a trade-off,
when synchronizing access to the local TED: favor OSPF-TE parsing
which means that some path computations are slightly delayed to
allow an 'update' to be processed, or give strict priority to
computation requests.
In consequence, a stateless PCE may assign the same (or a subset of
the same) resources to several requests, which may result in
contention and degraded network performance. The effects are
detected late, typically during path signaling, causing path blocking
and excessive crank-backs and retries.
Note that, as per RFC 5440 [RFC5440], a PCC may include a set of
previously computed paths in A given request, in order to take them
into account, for instance, to avoid double bandwidth accounting or
to try to minimize changes (minimum perturbation problem).
Section 6.8 of RFC 4655 [RFC4655] suggests that a limited form of
statefulness might be applied within an otherwise stateless PCE. The
PCE may retain some context from paths it has recently computed so
that it avoids suggesting the use of the same resources for other TE
LSPs, using heuristics / statistic or forecasting for improved
resource (i.e. wavelength) allocation. In other words, a given PCE
implementation may decide to perform additional book-keeping and
management of resources, deploying policies that prevent sub-optimal
allocations. For instance a PCE may compute the mean time used to
update the TED based on the previous calculated TE-LSPs and TED
updates. Those kinds of mechanisms may reduce the TED inaccuracy but
in all cases they cannot infer the PCC use of the TE-path.
This document proposes a set of extensions to the PCEP protocol to
allow a PCC to request a PCE to block or reserve the resources
associated with a path computation for a given path request. By
reservation, it is implied that a set of resources which have been
associated to such computation are excluded for subsequent path
computations for a given time period. This time-based temporary
reservation PCE system would be a compromise between a full-blown
stateful PCE and a stateless PCE to achieve efficiency without
costing and excessive resource commitment associated with the
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maintenance and synchronization of a stateful PCE system. Due to the
fact that the PCC is explicitly indicating this reservation, the PCE
can get a more accurate view of the dynamic of the TED and thus
increase the accuracy of its routing. In addition having an explicit
input may simplify how a PCE take into account the fact that the TED
may be outdated.
In the cases where the resource is uniquely identified in the
topology update (such as receiving an OSPF-TE TE LSA with a bitmap
encoded wavelength availability reflecting a change in the link
status)), the reservation can still hold after a topology update, as
there is a correspondence between the resource in both reservation
and traffic engineering update, and the PCE can infer whether a given
reserved resource has actually been committed. Otherwise, when the
traffic engineering update reaches the PCE, there is no way to
distinguish the resource in the reservation among the resources shown
in the TE update. Thus, to assure a coherent behavior, the general
rule is that as soon as the PCE gets updated traffic engineering
information, all the reservations are deleted, save the the cases
where the resource is uniquely identified and the PCE can infer
whether a given reserved resource has actually been committed.
Examples of resources potentially subject to reservations are: the
bandwidth computed for the path in PSC or L2SC layers, a specific
time slot (SDH) or tributary slot (OTN ODU-k) in TDM networks or a
given wavelength or regenerator (WSON or OTN OCh).
This document also presents some illustrative use cases where the PCC
would want the PCE to retain some context or state, like multiple LSP
restoration, and counterexamples where the PCC does not have the
intention to immediately set up the LSP, i.e., multidomain cases
where the PCE is probing different paths to decide the sequence of
domains.
2. PCEP Requirements
This section provides a set of requirements, both for PCCs and PCEs,
to support context awareness.
When requesting a path computation (PCReq) to a PCE, a PCC should be
able to indicate:
o Whether the resources computed in the request should be made
unavailable for further requests.
o The amount of time the resources should be commited/reserved for
the current computation request so that keeps subsequent requests
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from taking.
o The type and granularity of the resources to be blocked in the
request. The type refers to the actual resources blocked such as
path bandwidth or timeslot, wavelength, fiber... The granularity
refers to the possibility of not only reserving the resource
computed for the path but whether the associated links/nodes/SRLGs
may need to be reserved too.
A PCE should be able to:
o Apply policies whether a reservation request can be applied or
not.
o Compute one or more paths according to the request parameters and,
based on the PCC indications, prevent (part of) the resources
commited in the computed route from being used for subsequent
computation requests for a given period.
o If the request is allowed, the given reservation period SHOULD be
no less than the requested period by the PCC (e.g. for the cases
where the PCE is only able to reserve for multiples of a given
value). This does not preclude the fact that, if configured by
policy, a PCE MAY limit the period to a lower period.
Alternatively, a PCE MAY be configured to reply with a PCEP_ERROR
stating the cause of the failed computation/reservation.
o The PCE MAY decide to apply a different granularity for the
reservation request (e.g. block a given Time Slot or wavelength
but not the TE links). In this case, the PCE MUST reply with the
actual reservation.
Note that, the means by which a PCE can perform the reservation/
commitment of the resources are out of the scope of the present
document but could include, for example, marking the resources as
'reserved', applying internal exclude objects etc.
A PCE should be able to respond (PCRep) to the PCC the following:
o If the resources have been effectively locked, and the effective
allocated reservation period (if different from the requested
one).
o The granularity of the reservation, which may be different from
the requested one.
o Provide a means to allow a PCC to request the cancellation of an
active reservation (for example an identification of the
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reservation to allow its cancellation).
The PCC should be able to request the cancellation of an active
resource reservation.
3. PCEP Extensions (Encoding)
3.1. Requesting a Reservation of Resources
EDITORS NOTE: OPTION WITH PCC-ID-REQ
A PCC that wants to indicate a PCE to temporarily reserve or block
resources does so by including a RESERVATION object along with a
client PCC_ID_REQ in a request within a PCReq message.
Analogously to [RFC5886] the PCC-ID-REQ object is used to specify the
IP address of the requesting PCC. The PCC-ID-REQ MUST be inserted
within a PCReq message to specify the IP address of the requesting
PCC. In [RFC5886] two PCC-ID-REQ objects (for IPv4 and IPv6) are
defined.
EDITORS NOTE: OPTION WITHOUT PCC-ID-REQ
A PCC that wants to indicate a PCE to temporarily reserve or block
resources does so by including a RESERVATION object in a request
within a PCReq message.
A PCE that processes a PCEP request with a RESERVATION object MUST
act according to the P-bit in the object header: if the P-bit is set,
the object MUST be treated as mandatory and the request must either
be processed using the contents of the object or rejected as defined
in [RFC5440]. If the P-bit is clear, the object MAY be used by the
PCE or MAY be ignored.
The RESERVATION object is optional in a PCEP request. Multiple
instances of the object MUST NOT be used on a single PCEP request and
if a PCE finds multiple instances of the object it MUST use the first
one and discard the rest (Editors note: alternatively, it could send
a PCErr, OR it could allow several RESERVATION objects, and let the
PCE choose which one will be used). The RESERVATION object may
appear either at an individual request level or within a SVEC. The
latter means that the RESERVATION object applies to all requests
involved in the SVEC object.
The PCReq ([RFC5440][RFC5541][RFC5557]) message is
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<PCReq Message> ::= <Common Header>
[svec_list]
<request-list>
where
<svec-list> ::= <SVEC>
[<OF>]
[<GC>]
[<XRO>]
[<metric-list>]
[<PCC-REQ-ID> <RESERVATION>]
[<svec-list>]
<metric-list> ::= <METRIC>
[<metric-list>]
<request-list>::= <request>
[<request-list>]
<request>::= <RP>
<END-POINTS>
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<OF>]
[<PCC_REQ_ID> <RESERVATION>]
[<RRO> [<BANDWIDTH>]]
[<IRO>]
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[<LOAD-BALANCING>]
3.2. Replying a reservation status
If the PCE that receives the request applies the reservation, it
indicates so using a RESERVATION_CONF object in the PCRep message.
EDITOR'S NOTE: Alternatively a RESERVATION object can be used in the
PCReq message
The PCRep message is extended with regard to the one defined in
[RFC5440] as follows:
<attribute-list>::=[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
[<RESERVATION_CONF>]
Note that the reservation applies at PATH level, and a
RESERVATION_CONF object is included within every path in a given PCEP
response. This means distinct reservations for each path, which can
be cancelled independently (Editor's Note: TDB, the PCC could
indicate whether to have a single reservation or multiple
reservation).
It is RECOMMENDED that the RESERVATION_CONF object appears the last
attribute for a Path (or as an optional object in the attribute-list
associated to a NO_PATH object.
3.3. Cancelling a Reservation
A PCC that wishes to cancel a reservation may send an unsolicited
notification to the PCE, including the identifier of the reservation.
The PCNtf message used for one or more cancellations has no RP
object. As with [RFC5440], the PCNtf message MUST carry at least one
NOTIFICATION object and MAY contain several NOTIFICATION objects
should the PCE or the PCC intend to notify of multiple events:
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<PCNtf Message>::=<Common Header>
<notify-list>
<notify-list>::=<notify> [<notify-list>]
<notify>::= <notification-list>
<notification-list>::=<NOTIFICATION>[<notification-list>]
NOTIFICATION objects used for the purposes of cancelling an active
reservation MUST include the RESERVATION_ID TLV. It is RECOMMENDED
to use dedicated PCNtf messages for the purposes of cancelling
reservations.
Both the Notification-type and Notification-value are TBD by IANA
The following Notification-type and Notification-value values are
currently defined:
o Notification-type=TBD: Pending Reservation cancelled
o Notification-value=TBD (sug 1): PCC cancels a set of reservation
requests.
3.4. RESERVATION object format
RESERVATION Object-Class is to be assigned by IANA.
RESERVATION Object-Type is to be assigned by IANA (recommended
value=1)
The RESERVATION object indicates the intention of the PCC to set up
the requested path and request the PCE to reserve the resources of
the computed path to avoid being used by other requests.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S N L| Resource Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional TLVs |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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o Timer is the value in ms of the time that the resources should be
blocked, encoded as a 32 bit unsigned integer.
o Resource Type indicates the type of resource to be reserved. A
value of 0 means the default resource type:
* Bandwidth (PSC, L2SC, ...)
* Time Slot (Sonet/SDH TDM)
* Tributary Slot (G709 OTN ODU-k TDM)
* Wavelength (G709 OTN OCh or WSON LSC)
o Bit L: if set, TE Links should be part of the reservation, and
excluded from subsequent request.
o Bit N: if set, Nodes should be part of the reservation.
o Bit S: if set, the set of SRLG (Shared Risk Link Group) deduced
from the associated resources (i.e., the union of SRLGs of the
links) should be part of the reservation.
Currently no TLVs are defined.
3.5. RESERVATION_CONF object format
The RESERVATION_CONF object is optional. The RESERVATION_CONF object
indicates that the PCE has reserved the resources of computed path to
avoid being used by other requests. The RESERVATION_CONF object is
sent in the PCRep.
The RESERVATION_CONF Object-Class is to be assigned by IANA.
The RESERVATION_CONF Object-Type is to be assigned by IANA
(recommended value=1)
The format of the RESERVATION_CONF object body is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reservation ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reservation timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S N L| Reservation Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Timer is the value in ms of the time that the resources are blocked.
The PCE May decide to apply a different value that the one requested
by the PCC.
A PCC MUST NOT send a RESERVE_RESPONSE object if the client has not
requested a RESERVATION in the PCReq message. A PCE MAY apply
reservations as a means of internal policy and/or operation.
3.6. RESERVATION_ID TLV
The TLV indicates the reservation ID (Type TBA 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reservation ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4. Procedures
A client that wishes to request a path computation with reservation
shall:
o Include a PCC_REQ_ID and RESERVATION objects in the involved
Request within the PCReq message.
o Specify what level of reservation to apply after the request.
Upon receiving a PCReq with a Resource Reservation object, the PCE
may:
o Perform the Path Computation using the local Traffic Engineering
Database which has been extended to account for resources that
have been marked reserved or blocked and which SHOULD not be used
while blocked. This includes both synchronized / dependent path
computations via SVEC or individual Path Computations requested in
the request_list.
o For the successful path computations, and for all paths
corresponding to a given Request, determine the type of resources
to be blocked (marked as reserved) with the granularity requested
by the client once mapped to PCE policies.
o It will start a local timer associated with this blocking action.
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o Send the Responses (successful or not) using PCRep message(s) and,
where appropriate, indicate the level of reservation and
associated period.
o For subsequent requests, perform path computation as detailed
above, updating the local TED with potential new reservations.
Whenever a timer expires, the PCE will:
o Remove the reservation status / blocking that affected the
reservation (e.g. add the previously substracted unreserved
bandwidth, mark the label, wavelength or time slot as available,
etc).
o Delete any data related with this blocking action.
Whenever a traffic engineering update reaches the PCE, the PCE will:
o If the reserved resource can be uniquely identified in the traffic
engineering update, keep the reservation
o If the reserved resource cannot be uniquely identified in the
traffic engineering update, delete the reservation
5. Use cases
This section aims to show the use cases of the proposed possibility
to activate the limited context awareness.
5.1. Multiple LSP restoration in a WSON network
One of the most challenging scenarios for a PCE-based architecture is
the one of PCE-based dynamic multiple LSP restoration in a WSON
network without pre-planning. In the event of a network failure
affecting a high number of LSPs (e.g. a fiber cut), a PCE could
potentially receive a significant amount of restoration requests in a
short period of time from different PCCs.
One of the various challenges in this scenario is the fact that the
PCE needs to sequentially perform multiple independent path
computations including routing and wavelength assignment. In this
scenario, a stateless PCE would rely on TED information, which could
potentially be up-to-date before the first incoming request (e.g. in
case the routing algorithm has disseminated the failure event), but
will definitely be outdated for subsequent requests.
It might be expected that the paths calculated for different
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connections would rely on the same nodes, TE links or even labels
(lambdas). It might occur at the signaling phase that multiple
connection requests are contending for the same resources. After the
eventual failure in the establishment of some of the connections,
subsequent requests to the PCE would be triggered. After a number of
loops, the PCE-based restoration would be eventually solved, but the
potential number of retries could be significantly high.
The main issue is that the stateless PCE relied on an outdated TED to
perform path computation. As the subsequent connection request is
expected to be computed immediately, there is either no time for the
routing algorithm to update the TED after a successful signaling or
for the signaling process to successfully finish.
In this context, the availability of a limited context aware PCE
could potentially solve the issue in a graceful fashion. Each of the
restoration path requests will have an associated Resource
Reservation object, which will state the kind of resources and the
amount of time they should be blocked.
The PCE will then temporarily 'mark' the resources as blocked, so as
not to consider them in subsequent connection requests, and thus
avoiding the contention at the signaling phase. The timer should be
in line with the LSP set up time and TED time to update.
This use case might be solved in the PCE by having a policy to
implicitly pre-reserve the resources for a given time, which can be
based on the mean time between a PCRep and a TED update indicating
that the labels are not available. The drawback of this implicit
reservation is that path establishment time may depend and a variety
of factor that may be strongly depend on the chosen path and
technology used (e.g. power equalization algorithms). In this case
the PCC have a better view on those aspects and can provide more
accurate view on when the TED will be updated.
5.2. Domain path selection
When selecting the set of domains of a multidomain path, a PCE may
request paths to several PCEs of different domains. Thus, the
intention of the request is not to establish a LSP, but to obtain a
hint on the domain path. Thus, in this case, no Reservation Object
would be sent.
Here implicit policies in PCE will be inaccurate as they cannot
determine if the PCC will setup the path or not.
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5.3. Multidomain path computation
Once the domain path is known, when computing the actual path, the
reservation object can be used. Note that multidomain paths may take
a long time to be established, as it involves several AS or domains
with different behavior and policies. Thus, it is a way to guarantee
the availability of resources.
6. Manageability Considerations
Standard PCEP [RFC5440] describes various manageability
considerations in PCEP, and most of the manageability requirements
are already covered there. Specific aspects are detailed in this
section.
6.1. Control of Function and Policy
In addition to PCE configuration parameters listed in [RFC5440], the
following additional parameters might be required:
o The ability to enable or disable reservations on the PCE.
o The ability to retrieve a list of reservations currently active in
the PCE.
o The ability to configure which PCCs are allowed to perform
reservations and the ability to configure limits on the timer
periods requested. This includes, for example, the configuration
of IP based access lists for PCCs.
o The ability to configure which PCCs are allowed to perform
reservations for single-domain and multi-domain scenarios,
typically according to pre-defined agreements.
o The ability to configure which reservation granularity a given PCC
group is able to request, and the associated action (error or
downgrade).
o TDB: Advertisements of capabilities via IGP and configurability
6.2. Information and Data Models
A number of MIB objects have been defined for general PCEP control
and monitoring of P2P computations in [PCEP-MIB]. For the time
being, no extra models are considered although it could be possible
that current means to retrieve information from the PCE be extended
to include eventual resource reservations.
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6.3. Liveness Detection and Monitoring
Other than the considerations expressed in [RFC5440], a PCE could
provide extensions to [MONITORING] to verify reservation status, and
to obtain statistics on the system.
6.4. Verifying Correct Operation
There are no additional requirements for verifying the correct
operation of the PCEP sessions. Future MIB objects could facilitate
verification of correct operation and reporting of reservations and
errors.
6.5. Requirements for Other Protocols and Functional Components
The method for the PCC to obtain information about a PCE capable of
reservation may include extensions to IGP protocols.
6.6. Impact on Network Operation
It is expected that the use of PCEP extensions specified in this
document will not significantly increase the level of operational
traffic. However, mis-configured, excessive reservation requests,
excessive reservation periods, or excessive granularity may increase
the number of failed requests or cause the PCE to provide sub-optimal
routes due to existing reservations. Coarse reservations may also
limit the resources that are available for a a PCE in order to serve
requests.
An excessive number of reservation requests and reservation
cancellations may degrade server performance. A PCE SHOULD provide a
means to control the rate of messages with reservation, extending the
proposed mechanism of [RFC5440].
7. Security Considerations
In the event of an unauthorized path computation request with
mandatory resource reservation, or in case of a (distributed) denial
of service attack, the subsequent state/context managed within the
PCE may be disruptive to the network, resulting in performance
degradation or sub-optimal computed routes. Implementations should
conform to the relevant security requirements of [RFC5440] that
specifically help to control unauthorized requests. These mechanisms
include securing the PCEP session requests and responses using TCP
security techniques, authenticating the PCEP requests and responses
to ensure the message is intact and sent from an authorized node,
providing policy control by explicitly defining which PCCs are
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allowed to perform resource reservations to the PCE and disallowing
reservation requests that may block an excessive amount of resources.
8. IANA Considerations
IANA maintains a registry of PCEP parameters. A number of IANA
considerations have been highlighted in previous sections of this
document.
8.1. RESERVATION object
8.2. RESERVATION_CONF object
8.3. RESERVATION_ID TLV
8.4. PCEP Errors
For the RESERVATION object, the default error procedures regarding
supported unknown objects defined in [RFC5440] apply
o Unsupported Reservation Option
o Reservation Forbidden by Policy
o Unknown Reservation Request
9. Contributing Authors
Telefonica I+D
Victor Lopez
Don Ramon de la Cruz
email: vlopez@tid.es
Francisco Javier Jimenez Chico
10. Acknowledgements
The authors thank Meral Sherazipur for the discussions and
suggestions in the topic.
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11. Normative References
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
Objective Functions in the Path Computation Element
Communication Protocol (PCEP)", RFC 5541, June 2009.
[RFC5557] Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path
Computation Element Communication Protocol (PCEP)
Requirements and Protocol Extensions in Support of Global
Concurrent Optimization", RFC 5557, July 2009.
[RFC5886] Vasseur, JP., Le Roux, JL., and Y. Ikejiri, "A Set of
Monitoring Tools for Path Computation Element (PCE)-Based
Architecture", RFC 5886, June 2010.
Authors' Addresses
Oscar Gonzalez de Dios (editor)
Telefonica I+D
Don Ramon de la Cruz
Madrid, 28006
Spain
Phone: +34 913328832
Email: ogondio@tid.es
Ramon Casellas
CTTC
Av. Carl Friedrich Gauss n7
Castelldefels, Barcelona 08860
Spain
Phone:
Email: ramon.casellas@cttc.es
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Cyril Margaria
Nokia Siemens Networks
St Martin Strasse 76
Munich, 81541
Germany
Phone: +49 89 5159 16934
Email: cyril.margaria@nsn.com
Young Lee
Huawei
1700 Alma Drive, Suite 100
Plano, TX 75075
U.S.
Phone: (972) 509-5599
Email: leeyoung@huawei.com
Fatai Zhang
Huawei
F3-5-B RD Center
Bantian, Longgang District, Shenzhen 518129
P.R.China
Phone:
Email: zhangfatai@huawei.com
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